Protoavis
Encyclopedia
Protoavis is a problematic
taxon
of archosaur
ian known from fragmentary remains from Late Triassic
Norian
stage deposits near Post, Texas
. Much controversy remains over the animal, and there are many different interpretations of what Protoavis actually is. When it was first described, the fossils were described as being from a primitive bird
which, if the identification is valid, would push back avian origins some 60-75 million years. The original describer of Protoavis texensis, Sankar Chatterjee
of Texas Tech University
, interpreted the type specimen to have come from a single animal, specifically a 35 cm tall bird that lived in what is now Texas
, USA
, around 210 million years ago. Though it existed far earlier than Archaeopteryx
, its skeletal structure is allegedly more bird-like. Protoavis has been reconstructed as a carnivorous bird that had teeth on the tip of its jaws and eyes located at the front of the skull, suggesting a nocturnal or crepuscular lifestyle. Reconstructions usually depict it with feathers, as Chatterjee originally interpreted structures on the arm to be quill knobs, the attachment point for flight feathers found in some modern birds and non-avian dinosaurs. However, re-evaluation of the fossil material by subsequent authors such as Lawrence Witmer
have been inconclusive regarding whether or not these structures are actual quill knobs.
However, this description of Protoavis assumes that Protoavis has been correctly interpreted as a bird. Almost all palaeontologists doubt that Protoavis is a bird, or that all remains assigned to it even come from a single species, because of the circumstances of its discovery and unconvincing avian synapomorphies
in its fragmentary material. When they were found at the Tecovas
and Bull Canyon Formations in the Texas panhandle in 1984, in a sedimentary strata of a Triassic river delta, the fossils were a jumbled cache of disarticulated bones that may reflect an incident of mass mortality following a flash flood
.
, similar to several poposaurids and rauisuchids that may have been partially or habitually bipedal and lived during roughly the same time as Protoavis. In a description published by Sankar Chatterjee
, structures were identified as quill knobs, although there has been debate as to whether these are actually quill knobs or not.
of Protoavis is similar in some respects to Troodon
, with an enlarged cerebellum that shifted the optic lobes ventrolaterally, and also has a large floccular lobe. The inner ear is also pretty similar and bird-like in both taxa. The canalicular systems and the cochlear process differ in both taxa, and the vestibular region is relatively small and located in a ventral position to most of the anterior and posterior semicircular canals. The anterior semicircular canal is significantly longer than the others, and the cochlear process is a relatively long, vertically oriented tube. However, Protoavis is also remarkedly non-bird like in that it possess only a single exit for the trigeminal. However, these characters are not robust enough to identify Protoavis as a bird.
The skull has an extremely narrow parietal
with block like dorsal aspect, very broad, T-shaped frontals that form the "lateral wings" that Chatterjee applies to the lack of postorbitals. There are short curved ulnae with olecranon processes, and a possible scapula with bent shaft, and the cervicals have profiles and aspects to their exterior that are very similar to the Megalancosaurus
cervical series. All the cervicals but the most posterior and axis/atlas have hypopophyses and those triangular neural spines; all characteristics that have been described in Megalancosaurus.Specifically, the type specimen has these features, and they are
corroborated in other specimens, including a complete, articulated neck with dorsal series, pectoral girdle, and
forelimb. This suggests that portions of Protoavis may be drepanosaurid in nature.
Chatterjee presents the skull of Protoavis as complete, although only the caudal aspect of the cranium is represented in the available fossils. Chatterjee argues that the temporal region displays a streptostylic quadrate
with orbital process for attachment of the M. protractor pterygoidei et quadrati
, with associated confluence of the orbits with the temporal fenestrae, thus facilitating prokinesis. He further asserts ornithurine synapomorphies for the braincase
of Protoavis including the structure of the otic capsule, the widespread pneumatization of the braincase elements, a full complement of tympanic recesses, and the presence of an epiotic.
Of this material, only the quadrate and orbital roof, in addition to limited portions of the braincase are preserved with enough fidelity to permit any definitive interpretation. The quadrates of TTU P 9200 and TTU P 9201 are not particularly alike; a fact not easily explained away if the material is conspecific, as Chatterjee insists. There does not appear to be an orbital process present on either bone, and the modifications of the proximal condyle permitting wide range of motion against the squamosal
, are not readily apparent. Furthermore, the quadratojugal
and jugal
appear far more robust in the Protoavis specimens themselves, than represented by Chatterjee. The size and development of the quadratojugal
seems to contradict Chatterjee's assertion that this bone contacted the quadrate via a highly mobile pin joint. These data render the assertion of prokinesis in the skull of Protoavis questionable at best, and it seems most parsimonious to conclude that the specimen displays a conventional opisthostylic quadrate.
The braincase is where Protoavis comes close to being as avian as Chatterjee has maintained. The otic capsule is allegedly organized in avian fashion, with three distinct foramina arranged as such: fenestra ovalis, fenestra pseudorotunda, and the caudal tympanic recess, with a bony metotic strut positioned between the fenestra pseudorotunda and caudal tympanic recess. The claim that the full complement of tympanic recesses seen in ornithurines, are similarly observed in Protoavis is questionable, as the preservation of the braincase is not adequate to permit concrete observations on the matter. Chatterjee omits in his 1987 account of the braincase, the presence of a substantial post-temporal fenestra, which in all Aves (including Archaeopteryx
), is reduced or absent altogether, and the lack of a pneumatic sinus on the paroccipital. Furthermore, the braincase possesses multiple characters symplesiomorphic of Coelurosauria
, including an expanded cerebellar auricular fossa, and a vagal canal opening into the occiput. These data suggest that in the braincase attributed to Protoavis is the earliest known record of a coelurosaurian theropod, as opposed to that of an ornithothoracine bird. What is preserved of the preorbital skull curiously lacks apomorphic characters to be expected in a specimen, which is allegedly more closely allied to Ornithurae
than is Archaeopteryx lithographica. Most telling is the complete absence of accessory fenestrae in the antorbital fossa, leading to maxillary sinuses.
Curiously, Gregory Paul has noted that the cervicals of Protoavis and drepanosaurs are astonishingly similar, such they are hardly distinguishable from one another. Considering the modification of the drepanosaur neck for the purposes of snap-action predation, it becomes more likely that superficial similarities in the cervicals of both taxa are in fact only convergent with Aves. Chatterjee does not identify the remaining vertebrae as particularly avian in their osteology.
in Protoavis, displaying synapomorphies of Ornithothoraces
, including the presence of a hypocleidium-bearing furcula
, and a hypertrophied, carinate
sternum
. Chatterjee's interpretation of the fossils identified as such in his reviews of the Protoavis material are open to question due to the preservation quality of the elements and as of this time, it is not clear whether either character was in fact present in Protoavis. The glenoid appears to be oriented dorsolaterally permitting a wide range of humeral movement. Chatterjee implies that this is a highly derived trait which allies Protoavis to Aves, but why this should be so is not clearly discussed in the descriptions of the animal. In and of itself, the orientation of the glenoid is not a sufficient basis for placing Protoavis within Aves. The scapular blade is far broader than illustrated by Chatterjee in his 1997 account, and not particularly avian in its gross form. The coracoid, identified by Chatterjee as strut-like and retroverted, is, like the supposed furcula and sternum, too poorly preserved to permit accurate identification. Moreover, the original spatial relationship of the alleged coracoid to the scapula is entirely unknown. Uncinate processes
and sternal ribs are missing.
, fusion of the ischium and ilium
, an antitrochanter, and the presence of a renal fossa. The pubis does appear to display opisthopuby, although this has yet to be verified. The alleged fusion of the ischium and ilium into an ilioischiadic plate is currently not substantiated by the fossils at hand, despite Chatterjee's auspicious illustration to the contrary in The Rise of Birds. At this time the pelvic girdle is not sufficiently well preserved to ascertain whether or not a renal fossa was present, although as no known avian from the Mesozoic
displays a renal fossa, it is not clear why Protoavis should, even if it is ornithothoracine. Similarly, it is unclear if the alleged antitrochanter has been correctly identified as such.
and carpus
are among the few areas of the Protoavis material, which are well preserved, and they are astonishingly non-avian. The distal carpals, while long, are in no way similar to those observed in the urvogel or other archaic birds. There is no semilunate element, and the structure of the radiale and ulnare would have limited the flexibility of the wrist joint. The manus is not tridactyl, and metacarpal V is present. In even the most basal avialian, Archaeopteryx, there is no vestige of the fifth metacarpal and its presence in Protoavis; seems incongruous with the claim that it is a bird, let alone one more derived than Archaeopteryx
.
Chatterjee claims that the humerus
of Protoavis is "remarkably avian", but as in all matters with the fossils referred to this taxon, accurate identification of the elaborate trochanters, ridges, etc., attributed to the humerus
by Chatterjee is impossible at this time. Interestingly, the expanded distal condyles, which appear to be present in the humerus
of Protoavis and enlarged deltopectoral crest (a ridge for the attachment of chest and shoulder muscles), are congruent with the morphology of ceratosaur humeri, as is the apparent presence of a distal brachial depression.
The femur
of Protoavis is astonishingly like that of a ceratosaur
. The proximal femur
displays a trochanteric shelf caudal to the lesser and greater trochanters, a feature synapomorphic of Ceratosauria
Further similarities between the proximal humerus
of Protoavis and that of ceratosaurs are found in the shared presence of an enlarged obturator ridge, whose morphology in Protoavis is again, uncannily like that observed in robust ceratosaurs, e.g., Syntarsus. The resemblance between the femur
of Protoavis and that of a ceratosaur becomes ever more pronounced at the distal end of the bone. Both share a crista tibiofibularis groove, a synapomorphy
of ceratosaurs separating the medial and lateral condyles.
The tibia
of Protoavis allegedly possesses both a lateral and cranial cnemial crest, though the validity of this claim is subject to question due to the preservation quality of the material. The fibula is continuous to the astragalocalcaneal unit. A tibiotarsus
is absent, unusual considering Chatterjee's claims for the ornithurine affinity of Protoavis, as is a tarsometatarsus
. The ascending process of the astragalus
is reduced, a character entirely incongruous with a highly derived status for Protoavis. Curiously, such abbreviation of the ascending process is found in ceratosaurs
, and in its general osteology, the Protoavis tarsus
and pes
, is quite similar to those of ceratosaurs. Chatterjee's restoration of the hallux
as reversed is nothing more than speculation, as the original spatial relationships of the pedal elements are impossible to ascertain at this time.
In his 1997 account, Chatterjee infers the presence of feather
s from alleged quill knobs on the badly smashed ulna
and metacarpals III and IV, and infers the presence of remiges from such structures (though he does caution that this is uncertain). As is the case with the alleged quill knobs on the ulna
, the metacarpal structures appear to be attributable to post-mortem damage. Moreover, the thumb, unlike the case in all birds, is not medially divergent. Considering how poorly preserved the ulna
is, it is entirely premature to make any definitive conclusions as to the presence of quill knobs until such time as more adequate material becomes available. Upon further examination of the material no structures were isolated that could be deemed as homologous
to remigial papillae.
of Protoavis is controversial, with several palaeornithologists considering it to be an early ancestor of modern birds, while most other in the palaeontological community
regard it as a chimaera
, a mixture of several specimens. American palaeontologist Gregory Paul suggested that Protoavis is a herrerasaur. In a paper by Phil Currie
and X.J. Zhao discussing a braincase
of a Troodon formosus
, they compare the bird-like characters of Troodon and Protoavis. In the paper, they make a number of corrections involving both Chatterjee's and Currie's own misinterpretations of parts of Troodon cranial anatomy before the particular braincase being describing was found. At least a couple of the corrections (the anterior tympanic recess, and the relatively kinetic quadrate-squamosal contact) make Troodon more bird-like then Chatterjee made out in his Protoavis paper, but overall these particular corrections seem to have little bearing on the avian features of Protoavis. Currie and Zhao do not explicitly state whether or not they consider Protoavis to be a theropod, however they suggest that although Protoavis has characters suggesting avian affinities, most of these are also found in theropod dinosaurs.
(notably Evgeny Kurochkin and Stefan Peters) have claimed that this material documents a Triassic origin of birds and the presence of a bird more advanced
than Archaeopteryx. Though it existed approximately 75 million years before the oldest known bird, its skeletal structure is allegedly more bird-like. Protoavis has been reconstructed as a carnivorous bird that had teeth on the tip of its jaws and eyes located at the front of the skull, suggesting a nocturnal or crepuscular lifestyle. The fossil bones are too badly preserved to allow an estimate of flying ability; although reconstructions usually show feathers, judging from thorough study of the fossil material there is no indication that these were present.
However, this description of Protoavis assumes that Protoavis has been correctly interpreted as a bird. Almost all palaeontologists doubt that Protoavis is a bird, or that all remains assigned to it even come from a single species, because of the circumstances of its discovery and unconvincing avian synapomorphies
in its fragmentary material. When they were found at a Dockum Group
quarry in the Texas panhandle in 1984, in a sedimentary strata of a Triassic river delta, the fossils were a jumbled cache of disarticulated bones that may reflect an incident of mass mortality following a flash flood.
Protoavis is a chimaera
Chatterjee was convinced that some of these crushed bones belonged to two individuals – one old, one young – of the same species. However, only a few parts were found, primarily a skull and some limb bones which moreover do not well agree in their proportions respective to each other, and this has led many to believe that the Protoavis fossil is chimaeric
, made up of more than one organism: the pieces of skull appear like those of a coelurosaur, while most parts of the limb skeleton suggest affinities to ceratosaurs and at least some vertebrae are most similar to those of Megalancosaurus
, an avicephala
n diapsid
:The characters which suggest that Protoavis is a chimera and not a valid taxon, include:
If it really is a single animal and not a chimera, Protoavis would raise interesting questions about when birds began to diverge from the dinosaurs, but until better evidence is produced, the animal's status currently remains uncertain. Furthermore, palaeobiogeography suggests that true birds did not colonize the Americas
until the Cretaceous
; the most primitive lineages of unequivocal birds found to date are all Eurasia
n. Certainly, the fossils are most parsimoniously attributed to primitive dinosaurian and other reptiles as outlined above. However, coelurosaurs and ceratosaurs are in any case not too distantly related to the ancestors of birds and in some aspects of the skeleton not unlike them, explaining how their fossils could be mistaken as avian. Palaeontologist Zhonghe Zhou stated:
Welman has argued that the quadrate
of Protoavis displays synapomorphies of Theropoda
. Paul has demonstrated the drepanosaur affinities of the cervical vertebrae. Gauthier & Rowe, and Dingus & Rowe have argued convincingly for identifying the hind limb of Protoavis as belonging to a ceratosaur. Feduccia has argued that Protoavis represents an arboreal "thecodont
". In a study of early ornithischia
n dinosaur
s, Sterling Nesbitt
and others determined some of the partial remains of Protoavis to be a non-tetanuran
theropod. The entire skull
and neck are considered to be most likely from a drepanosaurid because the skull and neck are too big compared to the dorsal vertebrate of Protoavis.Features present in the remains of Protoavis that indicate that it is not a bird or more derived than Archaeopteryx
include:
birds have only been discovered since then. Chatterjee himself has since used Protoavis to support a close relationship between dinosaurs and birds.
that a true bird from the Triassic
would bring about the collapse of the theropod "dogma".
It has been claimed that there are no suitably par-avian theropods known from the Upper Triassic, which might be allied to Protoavis and therefore it is difficult to conceive of a plausible scenario in which birds might have been derived from theropod ancestors.
The osteology
of early theropods, Ceratosauria
, differs from this statement. Outside of maniraptora
ns, there is no other dinosaur clade
as avian as Ceratosauria. The acquisition of avian apomorphies within Ceratosauria is astounding, and were it not for an even greater body of data to suggest the maniraptoran affinity of Aves, ceratosaurs would surely be linked with birds. A list of synapomorphies convergent with Ornithurae
observed in Ceratosauria includes such quintessential traits as: a) synsacrum present, b) pubis, ilium, ischium fused, c) astragalus
and calcaneum fused, and confluent with tibia
, d) tarsometatarsus
present. The earliest known ceratosaur date from the Carnian
horizon of the Triassic
, and are fairly derived, indicating an extensive evolutionary history throughout the Upper Triassic
and perhaps into the Lower Triassic. Combined with the osteological data, the temporal distribution of ceratosaurs arguably demonstrates that from the outset, Theropoda
displayed distinct avian attributes.
Of greater interest, is that such traits do not appear to be limited to Ceratosauria. The opisthopubic pubis of Herrerasaurus ischigualastensis
, either a basal
saurischian or basal theropod, is again a convergent trait with Aves present in an otherwise thoroughly plesiomorphic body plan.
If there are in fact theropods from the Triassic
, which display a suite of par-avian characters, the assertion that conferring taxonomic validity to Protoavis scuttles theropod origin, is found to be lacking in realism. If Protoavis is actually avian, it is plausible that birds share a common ancestry with Ceratosauria, or are nested within Ceratosauria. If Protoavis is a chimera, and only contains avian material within this hodgepodge, the situation is less clear. Such scenarios however remain speculative until such time as more compelling evidence for the avian affinity of any of the Protoavis material is brought forth.
discoveries are comparatively abundant in Texas, and have been recovered in some quantity since E. D. Cope
worked the redbeds of the panhandle over a century ago. The holotype
specimen of Protoavis (TTU P 9200), the paratype
(TTU P 9201), and all referred materials,Chatterjee (1995) describes these Protoavis specimens in addition to the description of the skeletons referred to TTU P 9200 and TTU P 9201. They are:
were discovered in the Dockum Group
, from the panhandle of Texas. The Dockum dates from the Carnian
through the early Norian
, in the terminal Triassic
and is composed of four units of decreasing age: the Santa Rose Formation, the Tecovas Formation
, the Trujillo Formation, and the Cooper Canyon Formation
, and the Bull Canyon Formation. Many skeletal elements and partial elements of Protoavis were collected from the Post (Miller) Quarry of the Bull Canyon Formation in the 1980s and other specimens referred to Protoavis were collected from the underlying Kirkpatrick Quarry of the Tecovas Formation. The specimens altogether consists of a partial skull
and postcranial remains belonging to possibly several large individuals. The bones were completely freed of the surrounding matrix, and some were heavily reconstructed and the identification of some of the elements have been questioned by other palaeornithologists
and palaeontologists
.
The type material was collected from mudstone deposits in June of 1973 and initially identified as a juvenile Coelophysis bauri
. The level of the Dockum group from which the Protoavis material was recovered, was most likely deposited in a deltaic river system. The bone bed excavated by Sankar Chatterjee
and his students of Texas Tech University, in which Protoavis was discovered, likely reflects an incident of mass mortality following a flash flood. Chatterjee, who first described Protavis, has assigned the binomial Protoavis texensis ("first bird from Texas") to the small cache of bones, allegedly conspecific. He interpreted the type specimen to have come from a single animal, specifically a 35 cm tall bird that lived in what is now Texas
, USA
, between 225 and 210 million years ago.
Due to the nature of the bones being jumbled into sandstone nodules, and completely disarticulated, it has been suggested that Protoavis was reworked from later sediments. However, a basic stratigraphic principle, the "principle of inclusions", is a special case of the principle of cross-cutting relationships. It states that rock has to exist before it can be included in other sedimentary rock
. Reworking is the process of weathering fossils or rock containing fossils out of rocks already present, transporting them, and redepositing them in sediments which are later lithified
as new sedimentary rocks. Since the Jurassic
rocks occurred after the Triassic sediments of the Dockum Group, they could not have been reworked into the Dockum sediments as inclusions.
of the Dockum Group
would have been subtropical and governed by a distinct dry/wet season pattern, with the latter marked by monsoonal rains. The botanical evidence indicates that the area was densely forested, and the abundance of both invertebrate
and vertebrate
material from the site suggests that the locale was in general richly populated by a wide variety of species. Dinosaur
s were still fairly rare in the Dockum group, and only some ceratosaurs
and other basal
forms are well documented. The principal carnivore
s of the locale would have been poposaurids
such as Postosuchus
, a species well represented in the Triassic redbeds of Texas. Other archaic archosaur
s, such as rhynchosaurs and aetosaurs, were also fairly common.
and paratype
were recovered from disparate locations, both disarticulated and unassociated. Consequently, spatial relationships are impossible to determine. No record of the original orientation of the material even as recovered, exists. Further material assigned to the taxon
has been recovered in isolation with no apparent spatial relationships to each other, and more or less has been referred to Protoavis spuriously. Thus, the presentation of the holotype and paratype as coherent skeletons by Chatterjee is fallacious. Such representations are ad hoc conglomerations of bone whose status as conspecific is not apparent from their taphonomy.
Not only were the remains recovered disarticulated and unassociated, there are glaring morphometric differences in the various components of the holotype
and paratype
. For instance, the scapulae and coracoids are so reduced, that the association with the axial skeleton is extremely difficult to support. Juvenile ontogeny
cannot be invoked credibly to explain this discrepancy. Furthermore, the degree of morphometric variation in the holotype and paratype seems incongruent with the component material representing a conspecific assemblage of bones.
The fossils themselves display significant postmortem damage, and are in some cases so badly crushed and distorted at the hand of geological processes, that accurate interpretation thereof is impossible. Consequently, the lucid analyses offered by Chatterjee are in many cases more artistic creativeness than an accurate description.
In his definitive analysis of the material, The Rise of Birds (1997), Chatterjee failed to illustrate the Protoavis fossils via pictures or sketches of the fossils proper, and instead offers the reader artistic reconstructions. For this, Chatterjee has been sharply criticized. Such an approach in science is entirely intolerable in that it idealizes the material at hand, and obscures the very fragmentary nature of the fossils, and their poor state of preservation.
Nomen dubium
In zoological nomenclature, a nomen dubium is a scientific name that is of unknown or doubtful application...
taxon
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
of archosaur
Archosaur
Archosaurs are a group of diapsid amniotes whose living representatives consist of modern birds and crocodilians. This group also includes all extinct non-avian dinosaurs, many extinct crocodilian relatives, and pterosaurs. Archosauria, the archosaur clade, is a crown group that includes the most...
ian known from fragmentary remains from Late Triassic
Late Triassic
The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age...
Norian
Norian
The Norian is a division of the Triassic geological period. It has the rank of an age or stage . The Norian lasted from 216.5 ± 2.0 to 203.6 ± 1.5 million years ago. It was preceded by the Carnian and succeeded by the Rhaetian.-Stratigraphic definitions:The Norian was named after the Noric Alps in...
stage deposits near Post, Texas
Post, Texas
Post is a city in and the county seat of Garza County, Texas, United States. The population was 3,708 at the 2000 census.There are many ranchers and civic boosters in Garza County, among them Giles McCrary, a former mayor who operates the OS Museum, a hybrid of exhibits from both the American West...
. Much controversy remains over the animal, and there are many different interpretations of what Protoavis actually is. When it was first described, the fossils were described as being from a primitive bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
which, if the identification is valid, would push back avian origins some 60-75 million years. The original describer of Protoavis texensis, Sankar Chatterjee
Sankar Chatterjee
Sankar Chatterjee is a paleontologist, and is the Paul W. Horn Professor of Geosciences at Texas Tech University and Curator of Paleontology at the Museum of Texas Tech University. He earned his Ph. D. from the University of Calcutta in 1970 and was a Post-doctoral Fellow at the Smithsonian...
of Texas Tech University
Texas Tech University
Texas Tech University, often referred to as Texas Tech or TTU, is a public research university in Lubbock, Texas, United States. Established on February 10, 1923, and originally known as Texas Technological College, it is the leading institution of the Texas Tech University System and has the...
, interpreted the type specimen to have come from a single animal, specifically a 35 cm tall bird that lived in what is now Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
, USA
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, around 210 million years ago. Though it existed far earlier than Archaeopteryx
Archaeopteryx
Archaeopteryx , sometimes referred to by its German name Urvogel , is a genus of theropod dinosaur that is closely related to birds. The name derives from the Ancient Greek meaning "ancient", and , meaning "feather" or "wing"...
, its skeletal structure is allegedly more bird-like. Protoavis has been reconstructed as a carnivorous bird that had teeth on the tip of its jaws and eyes located at the front of the skull, suggesting a nocturnal or crepuscular lifestyle. Reconstructions usually depict it with feathers, as Chatterjee originally interpreted structures on the arm to be quill knobs, the attachment point for flight feathers found in some modern birds and non-avian dinosaurs. However, re-evaluation of the fossil material by subsequent authors such as Lawrence Witmer
Lawrence Witmer
Lawrence Witmer is an American paleontologist. He is a Professor of Anatomy and a Chang Ying-Chien Professor of Paleontology at the Department of Biomedical Sciences at the College of Osteopathic Medicine in Ohio University. Witmer is considered to be one of the world's foremost Armchair...
have been inconclusive regarding whether or not these structures are actual quill knobs.
However, this description of Protoavis assumes that Protoavis has been correctly interpreted as a bird. Almost all palaeontologists doubt that Protoavis is a bird, or that all remains assigned to it even come from a single species, because of the circumstances of its discovery and unconvincing avian synapomorphies
Synapomorphy
In cladistics, a synapomorphy or synapomorphic character is a trait that is shared by two or more taxa and their most recent common ancestor, whose ancestor in turn does not possess the trait. A synapomorphy is thus an apomorphy visible in multiple taxa, where the trait in question originates in...
in its fragmentary material. When they were found at the Tecovas
Tecovas Formation
-Vertebrate fauna:...
and Bull Canyon Formations in the Texas panhandle in 1984, in a sedimentary strata of a Triassic river delta, the fossils were a jumbled cache of disarticulated bones that may reflect an incident of mass mortality following a flash flood
Flash flood
A flash flood is a rapid flooding of geomorphic low-lying areas—washes, rivers, dry lakes and basins. It may be caused by heavy rain associated with a storm, hurricane, or tropical storm or meltwater from ice or snow flowing over ice sheets or snowfields...
.
Description
Protoavis is usually depicted as being a bipedal archosaurArchosaur
Archosaurs are a group of diapsid amniotes whose living representatives consist of modern birds and crocodilians. This group also includes all extinct non-avian dinosaurs, many extinct crocodilian relatives, and pterosaurs. Archosauria, the archosaur clade, is a crown group that includes the most...
, similar to several poposaurids and rauisuchids that may have been partially or habitually bipedal and lived during roughly the same time as Protoavis. In a description published by Sankar Chatterjee
Sankar Chatterjee
Sankar Chatterjee is a paleontologist, and is the Paul W. Horn Professor of Geosciences at Texas Tech University and Curator of Paleontology at the Museum of Texas Tech University. He earned his Ph. D. from the University of Calcutta in 1970 and was a Post-doctoral Fellow at the Smithsonian...
, structures were identified as quill knobs, although there has been debate as to whether these are actually quill knobs or not.
Skull and braincase
The braincaseEndocast
An endocast is the internal cast of a hollow object, often specifically used for an endocasts of the cranial vault. Endocasts can be man-made for examining the properties of a hollow, inaccessible space, or occur naturally through fossilisation....
of Protoavis is similar in some respects to Troodon
Troodon
Troodon is a genus of relatively small, bird-like dinosaur from the Late Cretaceous period . Discovered in 1855, it was among the first dinosaurs found in North America...
, with an enlarged cerebellum that shifted the optic lobes ventrolaterally, and also has a large floccular lobe. The inner ear is also pretty similar and bird-like in both taxa. The canalicular systems and the cochlear process differ in both taxa, and the vestibular region is relatively small and located in a ventral position to most of the anterior and posterior semicircular canals. The anterior semicircular canal is significantly longer than the others, and the cochlear process is a relatively long, vertically oriented tube. However, Protoavis is also remarkedly non-bird like in that it possess only a single exit for the trigeminal. However, these characters are not robust enough to identify Protoavis as a bird.
The skull has an extremely narrow parietal
Parietal bone
The parietal bones are bones in the human skull which, when joined together, form the sides and roof of the cranium. Each bone is roughly quadrilateral in form, and has two surfaces, four borders, and four angles. It is named from the Latin pariet-, wall....
with block like dorsal aspect, very broad, T-shaped frontals that form the "lateral wings" that Chatterjee applies to the lack of postorbitals. There are short curved ulnae with olecranon processes, and a possible scapula with bent shaft, and the cervicals have profiles and aspects to their exterior that are very similar to the Megalancosaurus
Megalancosaurus
Megalancosaurus is a genus of extinct reptile from the Late Triassic period of Northern Italy, and one of the best known drepanosaurids. The type species is M. preonensis; a translation of the animal's scientific name would be "long armed reptile from the Preone Valley."-Anatomy:Megalancosaurus was...
cervical series. All the cervicals but the most posterior and axis/atlas have hypopophyses and those triangular neural spines; all characteristics that have been described in Megalancosaurus.Specifically, the type specimen has these features, and they are
corroborated in other specimens, including a complete, articulated neck with dorsal series, pectoral girdle, and
forelimb. This suggests that portions of Protoavis may be drepanosaurid in nature.
Chatterjee presents the skull of Protoavis as complete, although only the caudal aspect of the cranium is represented in the available fossils. Chatterjee argues that the temporal region displays a streptostylic quadrate
Quadrate bone
The quadrate bone is part of a skull in most tetrapods, including amphibians, sauropsids , and early synapsids. In these animals it connects to the quadratojugal and squamosal in the skull, and forms part of the jaw joint .- Evolutionary variation :In snakes, the quadrate bone has become elongated...
with orbital process for attachment of the M. protractor pterygoidei et quadrati
M. protractor pterygoidei et quadrati
The M. protractor pterygoidei et quadrati is a cranial muscle which pulls the streptostylic quadrate dorsorostrally in birds....
, with associated confluence of the orbits with the temporal fenestrae, thus facilitating prokinesis. He further asserts ornithurine synapomorphies for the braincase
Endocast
An endocast is the internal cast of a hollow object, often specifically used for an endocasts of the cranial vault. Endocasts can be man-made for examining the properties of a hollow, inaccessible space, or occur naturally through fossilisation....
of Protoavis including the structure of the otic capsule, the widespread pneumatization of the braincase elements, a full complement of tympanic recesses, and the presence of an epiotic.
Of this material, only the quadrate and orbital roof, in addition to limited portions of the braincase are preserved with enough fidelity to permit any definitive interpretation. The quadrates of TTU P 9200 and TTU P 9201 are not particularly alike; a fact not easily explained away if the material is conspecific, as Chatterjee insists. There does not appear to be an orbital process present on either bone, and the modifications of the proximal condyle permitting wide range of motion against the squamosal
Squamosal
The squamosal is a bone of the head of higher vertebrates. It is the principal component of the cheek region in the skull, lying below the temporal series and otic notch and bounded anteriorly by postorbital. Posteriorly, the squamosal articulates with the posterior elements of the palatal complex,...
, are not readily apparent. Furthermore, the quadratojugal
Quadratojugal
The quadratojugal is a small jaw bone that is present in most amphibians, reptiles, and birds, but has been lost in mammals. It is connected to the jugal as well as other bones, though these may vary with species....
and jugal
Jugal
The jugal is a skull bone found in most reptiles, amphibians, and birds. In mammals, the jugal is often called the malar or Zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species....
appear far more robust in the Protoavis specimens themselves, than represented by Chatterjee. The size and development of the quadratojugal
Quadratojugal
The quadratojugal is a small jaw bone that is present in most amphibians, reptiles, and birds, but has been lost in mammals. It is connected to the jugal as well as other bones, though these may vary with species....
seems to contradict Chatterjee's assertion that this bone contacted the quadrate via a highly mobile pin joint. These data render the assertion of prokinesis in the skull of Protoavis questionable at best, and it seems most parsimonious to conclude that the specimen displays a conventional opisthostylic quadrate.
The braincase is where Protoavis comes close to being as avian as Chatterjee has maintained. The otic capsule is allegedly organized in avian fashion, with three distinct foramina arranged as such: fenestra ovalis, fenestra pseudorotunda, and the caudal tympanic recess, with a bony metotic strut positioned between the fenestra pseudorotunda and caudal tympanic recess. The claim that the full complement of tympanic recesses seen in ornithurines, are similarly observed in Protoavis is questionable, as the preservation of the braincase is not adequate to permit concrete observations on the matter. Chatterjee omits in his 1987 account of the braincase, the presence of a substantial post-temporal fenestra, which in all Aves (including Archaeopteryx
Archaeopteryx
Archaeopteryx , sometimes referred to by its German name Urvogel , is a genus of theropod dinosaur that is closely related to birds. The name derives from the Ancient Greek meaning "ancient", and , meaning "feather" or "wing"...
), is reduced or absent altogether, and the lack of a pneumatic sinus on the paroccipital. Furthermore, the braincase possesses multiple characters symplesiomorphic of Coelurosauria
Coelurosauria
Coelurosauria is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs. In the past, it was used to refer to all small theropods, although this classification has been abolished...
, including an expanded cerebellar auricular fossa, and a vagal canal opening into the occiput. These data suggest that in the braincase attributed to Protoavis is the earliest known record of a coelurosaurian theropod, as opposed to that of an ornithothoracine bird. What is preserved of the preorbital skull curiously lacks apomorphic characters to be expected in a specimen, which is allegedly more closely allied to Ornithurae
Ornithurae
Ornithurae is the name of a natural group which includes all modern birds as well as their extinct relatives with plough-shaped pygostyles, a bone at the end of the tail which allows the tail feathers to fan and retract....
than is Archaeopteryx lithographica. Most telling is the complete absence of accessory fenestrae in the antorbital fossa, leading to maxillary sinuses.
Post-cranial anatomy
The post-cranial remains are as badly preserved, or worse, than the cranial elements, and their interpretation by Chatterjee are in many cases unsubstantiated or speculative. Of the postcranial skeleton, Chatterjee has isolated the axial skeleton as displaying a suite of avian characters, including heterocoelus centra, hypapophyses and reduction of the neural spines. First and foremost, the preservation quality of the vertebrae is poor. While the centra are modified, they do not appear to be truly heterocoelus. The presence of incipient hypapophyses in and of itself might be considered indicative of avian affinity, but their poor development and presence on vertebrae otherwise thoroughly non-avian, is most parsimoniously regarded as mild convergence until further material should be brought to light. The reduction of the neural spines is questionable.Curiously, Gregory Paul has noted that the cervicals of Protoavis and drepanosaurs are astonishingly similar, such they are hardly distinguishable from one another. Considering the modification of the drepanosaur neck for the purposes of snap-action predation, it becomes more likely that superficial similarities in the cervicals of both taxa are in fact only convergent with Aves. Chatterjee does not identify the remaining vertebrae as particularly avian in their osteology.
Pectoral girdle
The pectoral girdle is discussed by Chatterjee as being highly derivedDerived
In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...
in Protoavis, displaying synapomorphies of Ornithothoraces
Ornithothoraces
Ornithothoraces is a clade of birds which includes all enantiornithines and modern birds .The name Ornithothoraces means "bird thoraxes". This refers to a modern, highly derived, anatomy of the thorax which gave the ornithothoracines superior flight capability compared to more primitive birds...
, including the presence of a hypocleidium-bearing furcula
Furcula
The ' is a forked bone found in birds, formed by the fusion of the two clavicles. In birds, its function is the strengthening of the thoracic skeleton to withstand the rigors of flight....
, and a hypertrophied, carinate
Carinate
This article is about a topic in pottery design. For the article about birds, see Carinatae.Carinate is a shape in pottery, glassware and artistic design usually applied to amphora or vases...
sternum
Sternum
The sternum or breastbone is a long flat bony plate shaped like a capital "T" located anteriorly to the heart in the center of the thorax...
. Chatterjee's interpretation of the fossils identified as such in his reviews of the Protoavis material are open to question due to the preservation quality of the elements and as of this time, it is not clear whether either character was in fact present in Protoavis. The glenoid appears to be oriented dorsolaterally permitting a wide range of humeral movement. Chatterjee implies that this is a highly derived trait which allies Protoavis to Aves, but why this should be so is not clearly discussed in the descriptions of the animal. In and of itself, the orientation of the glenoid is not a sufficient basis for placing Protoavis within Aves. The scapular blade is far broader than illustrated by Chatterjee in his 1997 account, and not particularly avian in its gross form. The coracoid, identified by Chatterjee as strut-like and retroverted, is, like the supposed furcula and sternum, too poorly preserved to permit accurate identification. Moreover, the original spatial relationship of the alleged coracoid to the scapula is entirely unknown. Uncinate processes
Uncinate processes of ribs
The uncinate processes of the ribs are extensions of bone that in birds project caudally from the vertical segment of each rib. These processes help to strengthen the rib cage of birds by overlapping with the rib behind them...
and sternal ribs are missing.
Pelvic girdle
Chatterjee asserts that the pelvic girdle is apomorphic comparative to archaic birds and displays a retroverted pubisPubis (bone)
In vertebrates, the pubic bone is the ventral and anterior of the three principal bones composing either half of the pelvis.It is covered by a layer of fat, which is covered by the mons pubis....
, fusion of the ischium and ilium
Ilium (bone)
The ilium is the uppermost and largest bone of the pelvis, and appears in most vertebrates including mammals and birds, but not bony fish. All reptiles have an ilium except snakes, although some snake species have a tiny bone which is considered to be an ilium.The name comes from the Latin ,...
, an antitrochanter, and the presence of a renal fossa. The pubis does appear to display opisthopuby, although this has yet to be verified. The alleged fusion of the ischium and ilium into an ilioischiadic plate is currently not substantiated by the fossils at hand, despite Chatterjee's auspicious illustration to the contrary in The Rise of Birds. At this time the pelvic girdle is not sufficiently well preserved to ascertain whether or not a renal fossa was present, although as no known avian from the Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
displays a renal fossa, it is not clear why Protoavis should, even if it is ornithothoracine. Similarly, it is unclear if the alleged antitrochanter has been correctly identified as such.
Arms and legs
The manusManus (zoology)
The manus is the zoological term for the distal portion of the fore limb of an animal. In tetrapods, it is the part of the pentadactyl limb that includes the metacarpals and digits . During evolution, it has taken many forms and served a variety of functions...
and carpus
Carpus
In tetrapods, the carpus is the sole cluster of bones in the wrist between the radius and ulna and the metacarpus. The bones of the carpus do not belong to individual fingers , whereas those of the metacarpus do. The corresponding part of the foot is the tarsus...
are among the few areas of the Protoavis material, which are well preserved, and they are astonishingly non-avian. The distal carpals, while long, are in no way similar to those observed in the urvogel or other archaic birds. There is no semilunate element, and the structure of the radiale and ulnare would have limited the flexibility of the wrist joint. The manus is not tridactyl, and metacarpal V is present. In even the most basal avialian, Archaeopteryx, there is no vestige of the fifth metacarpal and its presence in Protoavis; seems incongruous with the claim that it is a bird, let alone one more derived than Archaeopteryx
Archaeopteryx
Archaeopteryx , sometimes referred to by its German name Urvogel , is a genus of theropod dinosaur that is closely related to birds. The name derives from the Ancient Greek meaning "ancient", and , meaning "feather" or "wing"...
.
Chatterjee claims that the humerus
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
of Protoavis is "remarkably avian", but as in all matters with the fossils referred to this taxon, accurate identification of the elaborate trochanters, ridges, etc., attributed to the humerus
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
by Chatterjee is impossible at this time. Interestingly, the expanded distal condyles, which appear to be present in the humerus
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
of Protoavis and enlarged deltopectoral crest (a ridge for the attachment of chest and shoulder muscles), are congruent with the morphology of ceratosaur humeri, as is the apparent presence of a distal brachial depression.
The femur
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
of Protoavis is astonishingly like that of a ceratosaur
Ceratosauria
Ceratosaurs are members of a group of theropod dinosaurs defined as all theropods sharing a more recent common ancestry with Ceratosaurus than with birds. There is presently no universally agreed upon listing of species or diagnostic characters of Ceratosauria, though they were less derived...
. The proximal femur
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
displays a trochanteric shelf caudal to the lesser and greater trochanters, a feature synapomorphic of Ceratosauria
Ceratosauria
Ceratosaurs are members of a group of theropod dinosaurs defined as all theropods sharing a more recent common ancestry with Ceratosaurus than with birds. There is presently no universally agreed upon listing of species or diagnostic characters of Ceratosauria, though they were less derived...
Further similarities between the proximal humerus
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
of Protoavis and that of ceratosaurs are found in the shared presence of an enlarged obturator ridge, whose morphology in Protoavis is again, uncannily like that observed in robust ceratosaurs, e.g., Syntarsus. The resemblance between the femur
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
of Protoavis and that of a ceratosaur becomes ever more pronounced at the distal end of the bone. Both share a crista tibiofibularis groove, a synapomorphy
Synapomorphy
In cladistics, a synapomorphy or synapomorphic character is a trait that is shared by two or more taxa and their most recent common ancestor, whose ancestor in turn does not possess the trait. A synapomorphy is thus an apomorphy visible in multiple taxa, where the trait in question originates in...
of ceratosaurs separating the medial and lateral condyles.
The tibia
Tibia
The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....
of Protoavis allegedly possesses both a lateral and cranial cnemial crest, though the validity of this claim is subject to question due to the preservation quality of the material. The fibula is continuous to the astragalocalcaneal unit. A tibiotarsus
Tibiotarsus
The tibiotarsus is the large bone between the femur and the tarsometatarsus in the leg of a bird. It is the fusion of the proximal part of the tarsus with the tibia.A similar structure also occurred in the Mesozoic Heterodontosauridae...
is absent, unusual considering Chatterjee's claims for the ornithurine affinity of Protoavis, as is a tarsometatarsus
Tarsometatarsus
The tarsometatarsus is a bone that is found in the lower leg of certain tetrapods, namely birds.It is formed from the fusion of several bones found in other types of animals, and homologous to the mammalian tarsal and metatarsal bones...
. The ascending process of the astragalus
Talus bone
-External links:* *...
is reduced, a character entirely incongruous with a highly derived status for Protoavis. Curiously, such abbreviation of the ascending process is found in ceratosaurs
Ceratosauria
Ceratosaurs are members of a group of theropod dinosaurs defined as all theropods sharing a more recent common ancestry with Ceratosaurus than with birds. There is presently no universally agreed upon listing of species or diagnostic characters of Ceratosauria, though they were less derived...
, and in its general osteology, the Protoavis tarsus
Tarsus (skeleton)
In tetrapods, the tarsus is a cluster of articulating bones in each foot situated between the lower end of tibia and fibula of the lower leg and the metatarsus. In the foot the tarsus articulates with the bones of the metatarsus, which in turn articulate with the bones of the individual toes...
and pes
Pes (zoology)
The pes is the zoological term for the distal portion of the hind limb of tetrapod animals. It is the part of the pentadactyl limb that includes the metatarsals and digits . During evolution, it has taken many forms and served a variety of functions...
, is quite similar to those of ceratosaurs. Chatterjee's restoration of the hallux
Hallux
In tetrapods, the hallux is the innermost toe of the foot. Despite its name it may not be the longest toe on the foot of some individuals...
as reversed is nothing more than speculation, as the original spatial relationships of the pedal elements are impossible to ascertain at this time.
Quill knobs
Reconstructions usually depict it with feathers, as Chatterjee originally interpreted structures on the arm to be quill knobs, the attachment point for flight feathers found in some modern birds and non-avian dinosaurs. However, re-evaluation of the fossil material by subsequent authors such as Lawrence Witmer have been inconclusive regarding whether or not these structures are actual quill knobs.In his 1997 account, Chatterjee infers the presence of feather
Feather
Feathers are one of the epidermal growths that form the distinctive outer covering, or plumage, on birds and some non-avian theropod dinosaurs. They are considered the most complex integumentary structures found in vertebrates, and indeed a premier example of a complex evolutionary novelty. They...
s from alleged quill knobs on the badly smashed ulna
Ulna
The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form and runs parallel to the radius, which is shorter and smaller. In anatomical position The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form...
and metacarpals III and IV, and infers the presence of remiges from such structures (though he does caution that this is uncertain). As is the case with the alleged quill knobs on the ulna
Ulna
The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form and runs parallel to the radius, which is shorter and smaller. In anatomical position The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form...
, the metacarpal structures appear to be attributable to post-mortem damage. Moreover, the thumb, unlike the case in all birds, is not medially divergent. Considering how poorly preserved the ulna
Ulna
The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form and runs parallel to the radius, which is shorter and smaller. In anatomical position The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form...
is, it is entirely premature to make any definitive conclusions as to the presence of quill knobs until such time as more adequate material becomes available. Upon further examination of the material no structures were isolated that could be deemed as homologous
Homology (biology)
Homology forms the basis of organization for comparative biology. In 1843, Richard Owen defined homology as "the same organ in different animals under every variety of form and function". Organs as different as a bat's wing, a seal's flipper, a cat's paw and a human hand have a common underlying...
to remigial papillae.
Classification and taxonomy
The taxonomyTaxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...
of Protoavis is controversial, with several palaeornithologists considering it to be an early ancestor of modern birds, while most other in the palaeontological community
Scientific community
The scientific community consists of the total body of scientists, its relationships and interactions. It is normally divided into "sub-communities" each working on a particular field within science. Objectivity is expected to be achieved by the scientific method...
regard it as a chimaera
Chimera (paleontology)
In paleontology, a chimera is a fossil which was reconstructed with elements coming from more than a single species of animal. A now classic example of chimera is Protoavis.-List of paleontological chimeras:*Brontosaurus*Lametasaurus...
, a mixture of several specimens. American palaeontologist Gregory Paul suggested that Protoavis is a herrerasaur. In a paper by Phil Currie
Phil Currie
Philip John Currie, AOE is a Canadian palaeontologist and museum curator who helped found the Royal Tyrrell Museum of Palaeontology in Drumheller, Alberta and is now a professor at the University of Alberta in Edmonton...
and X.J. Zhao discussing a braincase
Endocast
An endocast is the internal cast of a hollow object, often specifically used for an endocasts of the cranial vault. Endocasts can be man-made for examining the properties of a hollow, inaccessible space, or occur naturally through fossilisation....
of a Troodon formosus
Troodon
Troodon is a genus of relatively small, bird-like dinosaur from the Late Cretaceous period . Discovered in 1855, it was among the first dinosaurs found in North America...
, they compare the bird-like characters of Troodon and Protoavis. In the paper, they make a number of corrections involving both Chatterjee's and Currie's own misinterpretations of parts of Troodon cranial anatomy before the particular braincase being describing was found. At least a couple of the corrections (the anterior tympanic recess, and the relatively kinetic quadrate-squamosal contact) make Troodon more bird-like then Chatterjee made out in his Protoavis paper, but overall these particular corrections seem to have little bearing on the avian features of Protoavis. Currie and Zhao do not explicitly state whether or not they consider Protoavis to be a theropod, however they suggest that although Protoavis has characters suggesting avian affinities, most of these are also found in theropod dinosaurs.
Protoavis is a bird
Chatterjee, and a few other palaeornithologistsPaleornithology
Paleornithology also known as Avian Paleontology is the scientific study of bird evolution and fossil birds. It is a mix of ornithology and paleontology. Paleornithology began with the discovery of Archaeopteryx. The reptilian relationship of birds and their ancestors, the theropod dinosaurs, are...
(notably Evgeny Kurochkin and Stefan Peters) have claimed that this material documents a Triassic origin of birds and the presence of a bird more advanced
Derived
In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...
than Archaeopteryx. Though it existed approximately 75 million years before the oldest known bird, its skeletal structure is allegedly more bird-like. Protoavis has been reconstructed as a carnivorous bird that had teeth on the tip of its jaws and eyes located at the front of the skull, suggesting a nocturnal or crepuscular lifestyle. The fossil bones are too badly preserved to allow an estimate of flying ability; although reconstructions usually show feathers, judging from thorough study of the fossil material there is no indication that these were present.
However, this description of Protoavis assumes that Protoavis has been correctly interpreted as a bird. Almost all palaeontologists doubt that Protoavis is a bird, or that all remains assigned to it even come from a single species, because of the circumstances of its discovery and unconvincing avian synapomorphies
Synapomorphy
In cladistics, a synapomorphy or synapomorphic character is a trait that is shared by two or more taxa and their most recent common ancestor, whose ancestor in turn does not possess the trait. A synapomorphy is thus an apomorphy visible in multiple taxa, where the trait in question originates in...
in its fragmentary material. When they were found at a Dockum Group
Dockum Group
The Dockum is a Late Triassic geologic group found primarily on the Llano Estacado of western Texas and eastern New Mexico with minor exposures in southwestern Kansas, eastern Colorado, and Oklahoma panhandle. The Dockum reaches a maximum thickness of slightly over 650 m but is usually much...
quarry in the Texas panhandle in 1984, in a sedimentary strata of a Triassic river delta, the fossils were a jumbled cache of disarticulated bones that may reflect an incident of mass mortality following a flash flood.
Protoavis is a chimaeraChimera (paleontology)In paleontology, a chimera is a fossil which was reconstructed with elements coming from more than a single species of animal. A now classic example of chimera is Protoavis.-List of paleontological chimeras:*Brontosaurus*Lametasaurus...
Chatterjee was convinced that some of these crushed bones belonged to two individuals – one old, one young – of the same species. However, only a few parts were found, primarily a skull and some limb bones which moreover do not well agree in their proportions respective to each other, and this has led many to believe that the Protoavis fossil is chimaericChimera (paleontology)
In paleontology, a chimera is a fossil which was reconstructed with elements coming from more than a single species of animal. A now classic example of chimera is Protoavis.-List of paleontological chimeras:*Brontosaurus*Lametasaurus...
, made up of more than one organism: the pieces of skull appear like those of a coelurosaur, while most parts of the limb skeleton suggest affinities to ceratosaurs and at least some vertebrae are most similar to those of Megalancosaurus
Megalancosaurus
Megalancosaurus is a genus of extinct reptile from the Late Triassic period of Northern Italy, and one of the best known drepanosaurids. The type species is M. preonensis; a translation of the animal's scientific name would be "long armed reptile from the Preone Valley."-Anatomy:Megalancosaurus was...
, an avicephala
Avicephala
thumb|right|Artist's reconstruction of [[Coelurosauravus]]Avicephala is a possibly polyphyletic and therefore disused clade of diapsid reptiles that lived during the Late Permian and Triassic periods...
n diapsid
Diapsid
Diapsids are a group of reptiles that developed two holes in each side of their skulls, about 300 million years ago during the late Carboniferous period. Living diapsids are extremely diverse, and include all crocodiles, lizards, snakes, and tuatara...
:The characters which suggest that Protoavis is a chimera and not a valid taxon, include:
- Quadrates similar to those of TheropodaTheropodaTheropoda is both a suborder of bipedal saurischian dinosaurs, and a clade consisting of that suborder and its descendants . Dinosaurs belonging to the suborder theropoda were primarily carnivorous, although a number of theropod groups evolved herbivory, omnivory, and insectivory...
. - Cervicals of Protoavis closely resemble those of drepanosaurs.
- Significant morphometric discrepancy between the holotypeHolotypeA holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
(TTU P 9200) and the paratypeParatypeParatype is a technical term used in the scientific naming of species and other taxa of organisms. The exact meaning of the term paratype when it is used in zoology is not the same as the meaning when it is used in botany...
(TTU P 9201). - Material attributed to the taxon was recovered disarticulated and unassociated.
"Everywhere one turns; the very fossils ascribed thereto challenge the validity of Protoavis. The most parsimonious conclusion to be inferred from these data is that Chatterjee's contentious find is nothing more than a chimera, a morass of long-dead archosaurArchosaurArchosaurs are a group of diapsid amniotes whose living representatives consist of modern birds and crocodilians. This group also includes all extinct non-avian dinosaurs, many extinct crocodilian relatives, and pterosaurs. Archosauria, the archosaur clade, is a crown group that includes the most...
s."
If it really is a single animal and not a chimera, Protoavis would raise interesting questions about when birds began to diverge from the dinosaurs, but until better evidence is produced, the animal's status currently remains uncertain. Furthermore, palaeobiogeography suggests that true birds did not colonize the Americas
Americas
The Americas, or America , are lands in the Western hemisphere, also known as the New World. In English, the plural form the Americas is often used to refer to the landmasses of North America and South America with their associated islands and regions, while the singular form America is primarily...
until the Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
; the most primitive lineages of unequivocal birds found to date are all Eurasia
Eurasia
Eurasia is a continent or supercontinent comprising the traditional continents of Europe and Asia ; covering about 52,990,000 km2 or about 10.6% of the Earth's surface located primarily in the eastern and northern hemispheres...
n. Certainly, the fossils are most parsimoniously attributed to primitive dinosaurian and other reptiles as outlined above. However, coelurosaurs and ceratosaurs are in any case not too distantly related to the ancestors of birds and in some aspects of the skeleton not unlike them, explaining how their fossils could be mistaken as avian. Palaeontologist Zhonghe Zhou stated:
"[Protoavis] has neither been widely accepted nor seriously considered as a Triassic bird ... [Witmer], who has examined the material and is one of the few workers to have seriously considered Chatterjee’s proposal, argued that the avian status of P. texensis is probably not as clear as generally portrayed by Chatterjee, and further recommended minimization of the role that Protoavis plays in the discussion of avian ancestry."
Welman has argued that the quadrate
Quadrate bone
The quadrate bone is part of a skull in most tetrapods, including amphibians, sauropsids , and early synapsids. In these animals it connects to the quadratojugal and squamosal in the skull, and forms part of the jaw joint .- Evolutionary variation :In snakes, the quadrate bone has become elongated...
of Protoavis displays synapomorphies of Theropoda
Theropoda
Theropoda is both a suborder of bipedal saurischian dinosaurs, and a clade consisting of that suborder and its descendants . Dinosaurs belonging to the suborder theropoda were primarily carnivorous, although a number of theropod groups evolved herbivory, omnivory, and insectivory...
. Paul has demonstrated the drepanosaur affinities of the cervical vertebrae. Gauthier & Rowe, and Dingus & Rowe have argued convincingly for identifying the hind limb of Protoavis as belonging to a ceratosaur. Feduccia has argued that Protoavis represents an arboreal "thecodont
Thecodont
Thecodont , now considered an obsolete term, was formerly used to describe a diverse range of early archosaurs that first appeared in the Latest Permian and flourished until the end of the Triassic period...
". In a study of early ornithischia
Ornithischia
Ornithischia or Predentata is an extinct order of beaked, herbivorous dinosaurs. The name ornithischia is derived from the Greek ornitheos meaning 'of a bird' and ischion meaning 'hip joint'...
n dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
s, Sterling Nesbitt
Sterling Nesbitt
Sterling Nesbitt , is an American paleontologist.-Biography:Sterling Nesbitt received his B.A. in integrative biology with a minor in geology from University of California Berkeley in 2004. He received his Ph.D from Columbia University in 2009, completing the majority of his research at the...
and others determined some of the partial remains of Protoavis to be a non-tetanuran
Tetanurae
Tetanurae, or "stiff tails", is a clade that includes most theropod dinosaurs, as well as birds. Tetanurans first appear during the early or middle Jurassic Period.-Definition:...
theropod. The entire skull
Skull
The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...
and neck are considered to be most likely from a drepanosaurid because the skull and neck are too big compared to the dorsal vertebrate of Protoavis.Features present in the remains of Protoavis that indicate that it is not a bird or more derived than Archaeopteryx
Archaeopteryx
Archaeopteryx , sometimes referred to by its German name Urvogel , is a genus of theropod dinosaur that is closely related to birds. The name derives from the Ancient Greek meaning "ancient", and , meaning "feather" or "wing"...
include:
- The cranium appears to lack accessory fenestrae enclosed within the antorbital fossa, leading to auxiliary maxillary sinuses.
- The braincase displays a large post-temporal foramenForamenIn anatomy, a foramen is any opening. Foramina inside the body of humans and other animals typically allow muscles, nerves, arteries, veins, or other structures to connect one part of the body with another.-Skull:...
. - A pneumatopore leading to a pneumatic sinus is not present on the paroccipital process.
- The quadrate lacks an orbital process, doubled proximal condyle, and pin-joint with the quadratojugalQuadratojugalThe quadratojugal is a small jaw bone that is present in most amphibians, reptiles, and birds, but has been lost in mammals. It is connected to the jugal as well as other bones, though these may vary with species....
. - The vertebral centra are only mildly heterocoelus.
- Uncinate processes and sternal ribs absent.
- CarpusCarpusIn tetrapods, the carpus is the sole cluster of bones in the wrist between the radius and ulna and the metacarpus. The bones of the carpus do not belong to individual fingers , whereas those of the metacarpus do. The corresponding part of the foot is the tarsus...
lacks a semilunate element. - CarpometacarpusCarpometacarpusThe carpometacarpus is the fusion of the carpal and metacarpal bone, essentially a single fused bone between the wrist and the knuckles. It is a smallish bone in most birds, generally flattened and with a large hole in the middle. In flightless birds, however, its shape may be slightly different,...
absent. - Fifth metacarpal retained.
- Manus not tridactyl.
- Thumb is not medially divergent.
- TibiotarsusTibiotarsusThe tibiotarsus is the large bone between the femur and the tarsometatarsus in the leg of a bird. It is the fusion of the proximal part of the tarsus with the tibia.A similar structure also occurred in the Mesozoic Heterodontosauridae...
absent. - PygostylePygostylePygostyle refers to a number of the final few caudal vertebrae fused into a single ossification, supporting the tail feathers and musculature. In modern birds, the rectrices attach to these....
absent, tail elongate.
In discussions of evolution
Scientists such as Alan Feduccia have cited Protoavis in an attempt to refute the hypothesis that birds evolved from dinosaurs. However, some scientists has claimed the only consequence would be to push back the point of bird divergence further back in time. At the time when such claims were originally made, the affiliation of birds and maniraptoran theropods which today is well-supported and generally accepted by most ornithologists was much more contentious; most MesozoicMesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
birds have only been discovered since then. Chatterjee himself has since used Protoavis to support a close relationship between dinosaurs and birds.
"As there remains no compelling data to support the avian status of Protoavis or taxonomic validity thereof, it seems mystifying that the matter should be so contentious. The author very much agrees with Chiappe in arguing that at present, Protoavis is irrelevant to the phylogenetic reconstruction of Aves. While further material from the Dockum beds may vindicate this peculiar archosaur, for the time being, the case for Protoavis is non-existent."
Phylogenetic implications and ceratosaurs
It has been argued that if valid, Protoavis will represent the death knell to the theropod descent of birds. Palaeontologists counter that if valid, Protoavis in no way falsifies the theropod origin of birds. The very fact that Chatterjee used his putative bird to defend theropod origin seems to contradict the argument of Alan FeducciaAlan Feduccia
Alan Feduccia is a paleornithologist, specializing in the origins and phylogeny of birds. He is now Professor Emeritus at the University of North Carolina. Feduccia's principal authored works include two books, The Age of Birds and The Origin and Evolution of Birds, and numerous papers in various...
that a true bird from the Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
would bring about the collapse of the theropod "dogma".
It has been claimed that there are no suitably par-avian theropods known from the Upper Triassic, which might be allied to Protoavis and therefore it is difficult to conceive of a plausible scenario in which birds might have been derived from theropod ancestors.
The osteology
Osteology
Osteology is the scientific study of bones. A subdiscipline of anatomy, anthropology, and archeology, osteology is a detailed study of the structure of bones, skeletal elements, teeth, morphology, function, disease, pathology, the process of ossification , the resistance and hardness of bones , etc...
of early theropods, Ceratosauria
Ceratosauria
Ceratosaurs are members of a group of theropod dinosaurs defined as all theropods sharing a more recent common ancestry with Ceratosaurus than with birds. There is presently no universally agreed upon listing of species or diagnostic characters of Ceratosauria, though they were less derived...
, differs from this statement. Outside of maniraptora
Maniraptora
Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the dinosaurs that were more closely related to them than to Ornithomimus velox. It contains the major subgroups Avialae, Deinonychosauria, Oviraptorosauria and Therizinosauria. Ornitholestes and the Alvarezsauroidea...
ns, there is no other dinosaur clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
as avian as Ceratosauria. The acquisition of avian apomorphies within Ceratosauria is astounding, and were it not for an even greater body of data to suggest the maniraptoran affinity of Aves, ceratosaurs would surely be linked with birds. A list of synapomorphies convergent with Ornithurae
Ornithurae
Ornithurae is the name of a natural group which includes all modern birds as well as their extinct relatives with plough-shaped pygostyles, a bone at the end of the tail which allows the tail feathers to fan and retract....
observed in Ceratosauria includes such quintessential traits as: a) synsacrum present, b) pubis, ilium, ischium fused, c) astragalus
Astragalus
Astragalus is a large genus of about 3,000 species of herbs and small shrubs, belonging to the legume family Fabaceae, subfamily Faboideae. The genus is native to temperate regions of the Northern Hemisphere...
and calcaneum fused, and confluent with tibia
Tibia
The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....
, d) tarsometatarsus
Tarsometatarsus
The tarsometatarsus is a bone that is found in the lower leg of certain tetrapods, namely birds.It is formed from the fusion of several bones found in other types of animals, and homologous to the mammalian tarsal and metatarsal bones...
present. The earliest known ceratosaur date from the Carnian
Carnian
The Carnian is the lowermost stage of the Upper Triassic series . It lasted from about 228.7 till 216.5 million years ago . The Carnian is preceded by the Ladinian and is followed by the Norian...
horizon of the Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
, and are fairly derived, indicating an extensive evolutionary history throughout the Upper Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
and perhaps into the Lower Triassic. Combined with the osteological data, the temporal distribution of ceratosaurs arguably demonstrates that from the outset, Theropoda
Theropoda
Theropoda is both a suborder of bipedal saurischian dinosaurs, and a clade consisting of that suborder and its descendants . Dinosaurs belonging to the suborder theropoda were primarily carnivorous, although a number of theropod groups evolved herbivory, omnivory, and insectivory...
displayed distinct avian attributes.
Of greater interest, is that such traits do not appear to be limited to Ceratosauria. The opisthopubic pubis of Herrerasaurus ischigualastensis
Herrerasaurus
Herrerasaurus was one of the earliest dinosaurs. All known specimens of this carnivore have been discovered in rocks of late Ladinian age in northwestern Argentina...
, either a basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
saurischian or basal theropod, is again a convergent trait with Aves present in an otherwise thoroughly plesiomorphic body plan.
If there are in fact theropods from the Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
, which display a suite of par-avian characters, the assertion that conferring taxonomic validity to Protoavis scuttles theropod origin, is found to be lacking in realism. If Protoavis is actually avian, it is plausible that birds share a common ancestry with Ceratosauria, or are nested within Ceratosauria. If Protoavis is a chimera, and only contains avian material within this hodgepodge, the situation is less clear. Such scenarios however remain speculative until such time as more compelling evidence for the avian affinity of any of the Protoavis material is brought forth.
Discovery and history
ArchosaurArchosaur
Archosaurs are a group of diapsid amniotes whose living representatives consist of modern birds and crocodilians. This group also includes all extinct non-avian dinosaurs, many extinct crocodilian relatives, and pterosaurs. Archosauria, the archosaur clade, is a crown group that includes the most...
discoveries are comparatively abundant in Texas, and have been recovered in some quantity since E. D. Cope
Edward Drinker Cope
Edward Drinker Cope was an American paleontologist and comparative anatomist, as well as a noted herpetologist and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy interested in science; he published his first scientific paper at the age of nineteen...
worked the redbeds of the panhandle over a century ago. The holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
specimen of Protoavis (TTU P 9200), the paratype
Paratype
Paratype is a technical term used in the scientific naming of species and other taxa of organisms. The exact meaning of the term paratype when it is used in zoology is not the same as the meaning when it is used in botany...
(TTU P 9201), and all referred materials,Chatterjee (1995) describes these Protoavis specimens in addition to the description of the skeletons referred to TTU P 9200 and TTU P 9201. They are:
- (TTU P 9350-9355) six dorsal vertebrae (6-10 mm)
- (TTU P 9356-9359) four caudal vertebrae (8-9 mm)
- (TTU P 9360) coracoid(?) (14 mm)
- (TTU P 9361) sternum(?) (25 mm)
- (TTU P 9362) humerus (~80 mm)
- (TTU P 9263) humerus
- (TTU P 9364) partial mandible
- (TTU P 9365) humerus
- (TTU P 9370) femur (~58 mm)
- (TTU P 9372) femur
- (TTU P 9373) femur
- (TTU P 9374) tibia
- (TTU P 9375-9380) phalanges
were discovered in the Dockum Group
Dockum Group
The Dockum is a Late Triassic geologic group found primarily on the Llano Estacado of western Texas and eastern New Mexico with minor exposures in southwestern Kansas, eastern Colorado, and Oklahoma panhandle. The Dockum reaches a maximum thickness of slightly over 650 m but is usually much...
, from the panhandle of Texas. The Dockum dates from the Carnian
Carnian
The Carnian is the lowermost stage of the Upper Triassic series . It lasted from about 228.7 till 216.5 million years ago . The Carnian is preceded by the Ladinian and is followed by the Norian...
through the early Norian
Norian
The Norian is a division of the Triassic geological period. It has the rank of an age or stage . The Norian lasted from 216.5 ± 2.0 to 203.6 ± 1.5 million years ago. It was preceded by the Carnian and succeeded by the Rhaetian.-Stratigraphic definitions:The Norian was named after the Noric Alps in...
, in the terminal Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
and is composed of four units of decreasing age: the Santa Rose Formation, the Tecovas Formation
Tecovas Formation
-Vertebrate fauna:...
, the Trujillo Formation, and the Cooper Canyon Formation
Cooper Canyon Formation
-Vertebrate fauna:...
, and the Bull Canyon Formation. Many skeletal elements and partial elements of Protoavis were collected from the Post (Miller) Quarry of the Bull Canyon Formation in the 1980s and other specimens referred to Protoavis were collected from the underlying Kirkpatrick Quarry of the Tecovas Formation. The specimens altogether consists of a partial skull
Skull
The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...
and postcranial remains belonging to possibly several large individuals. The bones were completely freed of the surrounding matrix, and some were heavily reconstructed and the identification of some of the elements have been questioned by other palaeornithologists
Paleornithology
Paleornithology also known as Avian Paleontology is the scientific study of bird evolution and fossil birds. It is a mix of ornithology and paleontology. Paleornithology began with the discovery of Archaeopteryx. The reptilian relationship of birds and their ancestors, the theropod dinosaurs, are...
and palaeontologists
Paleontology
Paleontology "old, ancient", ὄν, ὀντ- "being, creature", and λόγος "speech, thought") is the study of prehistoric life. It includes the study of fossils to determine organisms' evolution and interactions with each other and their environments...
.
The type material was collected from mudstone deposits in June of 1973 and initially identified as a juvenile Coelophysis bauri
Coelophysis
Coelophysis , meaning "hollow form" in reference to its hollow bones , is one of the earliest known genera of dinosaur...
. The level of the Dockum group from which the Protoavis material was recovered, was most likely deposited in a deltaic river system. The bone bed excavated by Sankar Chatterjee
Sankar Chatterjee
Sankar Chatterjee is a paleontologist, and is the Paul W. Horn Professor of Geosciences at Texas Tech University and Curator of Paleontology at the Museum of Texas Tech University. He earned his Ph. D. from the University of Calcutta in 1970 and was a Post-doctoral Fellow at the Smithsonian...
and his students of Texas Tech University, in which Protoavis was discovered, likely reflects an incident of mass mortality following a flash flood. Chatterjee, who first described Protavis, has assigned the binomial Protoavis texensis ("first bird from Texas") to the small cache of bones, allegedly conspecific. He interpreted the type specimen to have come from a single animal, specifically a 35 cm tall bird that lived in what is now Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
, USA
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, between 225 and 210 million years ago.
Due to the nature of the bones being jumbled into sandstone nodules, and completely disarticulated, it has been suggested that Protoavis was reworked from later sediments. However, a basic stratigraphic principle, the "principle of inclusions", is a special case of the principle of cross-cutting relationships. It states that rock has to exist before it can be included in other sedimentary rock
Sedimentary rock
Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....
. Reworking is the process of weathering fossils or rock containing fossils out of rocks already present, transporting them, and redepositing them in sediments which are later lithified
Rock (geology)
In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...
as new sedimentary rocks. Since the Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
rocks occurred after the Triassic sediments of the Dockum Group, they could not have been reworked into the Dockum sediments as inclusions.
Palaeoenvironment
The inferred palaeoclimatePaleoclimatology
Paleoclimatology is the study of changes in climate taken on the scale of the entire history of Earth. It uses a variety of proxy methods from the Earth and life sciences to obtain data previously preserved within rocks, sediments, ice sheets, tree rings, corals, shells and microfossils; it then...
of the Dockum Group
Dockum Group
The Dockum is a Late Triassic geologic group found primarily on the Llano Estacado of western Texas and eastern New Mexico with minor exposures in southwestern Kansas, eastern Colorado, and Oklahoma panhandle. The Dockum reaches a maximum thickness of slightly over 650 m but is usually much...
would have been subtropical and governed by a distinct dry/wet season pattern, with the latter marked by monsoonal rains. The botanical evidence indicates that the area was densely forested, and the abundance of both invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
and vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
material from the site suggests that the locale was in general richly populated by a wide variety of species. Dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
s were still fairly rare in the Dockum group, and only some ceratosaurs
Ceratosauria
Ceratosaurs are members of a group of theropod dinosaurs defined as all theropods sharing a more recent common ancestry with Ceratosaurus than with birds. There is presently no universally agreed upon listing of species or diagnostic characters of Ceratosauria, though they were less derived...
and other basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
forms are well documented. The principal carnivore
Carnivore
A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...
s of the locale would have been poposaurids
Poposauridae
The Poposauridae are a family of large carnivorous archosaurs which lived alongside dinosaurs during the Late Triassic. They are known from fossil remains from North and South America...
such as Postosuchus
Postosuchus
Postosuchus, meaning "crocodile from Post ", was a basal archosaur that lived in what is now North America during the middle through to the late Triassic period...
, a species well represented in the Triassic redbeds of Texas. Other archaic archosaur
Archosaur
Archosaurs are a group of diapsid amniotes whose living representatives consist of modern birds and crocodilians. This group also includes all extinct non-avian dinosaurs, many extinct crocodilian relatives, and pterosaurs. Archosauria, the archosaur clade, is a crown group that includes the most...
s, such as rhynchosaurs and aetosaurs, were also fairly common.
Taphonomy
Both the holotypeHolotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
and paratype
Paratype
Paratype is a technical term used in the scientific naming of species and other taxa of organisms. The exact meaning of the term paratype when it is used in zoology is not the same as the meaning when it is used in botany...
were recovered from disparate locations, both disarticulated and unassociated. Consequently, spatial relationships are impossible to determine. No record of the original orientation of the material even as recovered, exists. Further material assigned to the taxon
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
has been recovered in isolation with no apparent spatial relationships to each other, and more or less has been referred to Protoavis spuriously. Thus, the presentation of the holotype and paratype as coherent skeletons by Chatterjee is fallacious. Such representations are ad hoc conglomerations of bone whose status as conspecific is not apparent from their taphonomy.
Not only were the remains recovered disarticulated and unassociated, there are glaring morphometric differences in the various components of the holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
and paratype
Paratype
Paratype is a technical term used in the scientific naming of species and other taxa of organisms. The exact meaning of the term paratype when it is used in zoology is not the same as the meaning when it is used in botany...
. For instance, the scapulae and coracoids are so reduced, that the association with the axial skeleton is extremely difficult to support. Juvenile ontogeny
Ontogeny
Ontogeny is the origin and the development of an organism – for example: from the fertilized egg to mature form. It covers in essence, the study of an organism's lifespan...
cannot be invoked credibly to explain this discrepancy. Furthermore, the degree of morphometric variation in the holotype and paratype seems incongruent with the component material representing a conspecific assemblage of bones.
The fossils themselves display significant postmortem damage, and are in some cases so badly crushed and distorted at the hand of geological processes, that accurate interpretation thereof is impossible. Consequently, the lucid analyses offered by Chatterjee are in many cases more artistic creativeness than an accurate description.
In his definitive analysis of the material, The Rise of Birds (1997), Chatterjee failed to illustrate the Protoavis fossils via pictures or sketches of the fossils proper, and instead offers the reader artistic reconstructions. For this, Chatterjee has been sharply criticized. Such an approach in science is entirely intolerable in that it idealizes the material at hand, and obscures the very fragmentary nature of the fossils, and their poor state of preservation.
See also
- Origin of birds
- Origin of avian flightOrigin of avian flightAround 350 BCE, Aristotle and other philosophers of the time were attempting to explain the aerodynamics of avian flight. Even after the discovery of the ancestral bird Archaeopteryx, over 150 years ago, debates still persist regarding the evolution of flight...
- Feathered dinosaursFeathered dinosaursThe realization that dinosaurs are closely related to birds raised the obvious possibility of feathered dinosaurs. Fossils of Archaeopteryx include well-preserved feathers, but it was not until the early 1990s that clearly non-avialan dinosaur fossils were discovered with preserved feathers...
- Birds Came First
- Temporal paradox (paleontology)Temporal paradox (paleontology)The temporal paradox, or time problem is a controversial issue in the evolutionary relationships of birds. It was described by paleornithologist Alan Feduccia.-Objection to consensus:The concept of a "temporal paradox" is based on the following facts...
External links
- Protoavis at the Fossil Wiki, upon which this article is adapted from.