Eogavialis
Encyclopedia
Eogavialis is an extinct gavialoid. It superficially resembles Tomistoma schlegelii, the extant false gharial
, and consequently material from the genus was originally referred to Tomistoma. Indeed, it was not until 1982 that the name Eogavialis was constructed after it was realised that the specimens were from a more basal form.
in 1901 when Andrews named a new species of Tomistoma, T. africanum, on the basis of a specimen found from an outcrop of the Qasr el-Sagha Formation in Egypt, about 20 miles northwest of Faiyum, dating back to the Priabonian
stage of the late Eocene
37.2 to 33.9 million years ago. Other specimens were later found from the Gebel Qatrani Formation, slightly younger than the Qasr el-Sagha dating back to the Rupelian
stage of the early Oligocene
33.9 to 28.4 million years ago, and near the locality where the original specimen of T. africanum was found in the Faiyum depression
. A new species was also found from this locality and named T. gavialoides by Andrews in 1905.
One of the first papers to identify the differences between these two species and others within Tomistoma was published in 1955 by J. A. Kälin. Other papers were written in the following decades that also questioned these species' relationships within Tomistominae. Eric Buffetaut proposed the genus name Eogavialis in 1982 and reassigned both T. africanum and T. gavialoides to it.
A third species was assigned to Eogavialis in 2003 from material found in the 1990s from the lower Nawata Formation of the Turkana basin
outcropping in Lothagam
, Kenya
. The strata from which the material was found dates back to the late Miocene
and early Pliocene
, around 11.61 to 2.59 million years ago. This extends the fossil range of the genus by approximately 17 million years. It was named E. andrewsi for Charles Williams Andrews. The holotype consists of a well preserved, nearly complete skull.
One reason why Eogavialis was initially placed within Tomistoma was due to the fact that the premaxilla
and nasal bone
s made contact with one another, a feature also seen in Tomistoma. However, this characteristic has since been shown to be present in other extinct gavialids, meaning that premaxilla and nasal contact is a plesiomorphic trait of all tomistomines, including basal
ones. Eogavialis also has a very similar cranial anatomy when compared to Tomistoma, having the same proportions, rostral
length, and tooth number, leading to the conclusion by some authors of papers published after 1982 that Eogavialis is synonymous
with Tomistoma.
s. However, molecular analyses of the false gharial, the only living tomistomine, suggest that the subfamily is actually within Gavialidae
(along with the modern gharial
of the subfamily Gavialinae) rather than Crocodylinae. The presence of a prominent crista
that runs along the postorbital
in Eogavialis testifies to its position as a gavialid. Other characteristics such as a rectangular skull table, subcircular orbits with everted orbital rims, and a constricted antorbital area are also shared with Eogavialis and other modern gavialids, as seen in a well preserved skull of E. africanum housed at Yale
(YPM 6263) and material from Kenya of E. andrewsi.
Eogavialis has often been proposed to be non-tomistomine due to its lack of supposedly crocodylid synapomorphies
needed in order for a taxon to be placed within Tomistominae. The genus lacks the exposure of the vomer
on the palate
that has been viewed as a characteristic of tomistomines. The trend for a long, narrow rostrum developing progressively over time as seen in Eogavialis has been used to suggest that the genus was a direct ancestor of Gavialis. Gryposuchus
was once seen as phylogenetically between Eogavialis and Gavialis.
deposits within the Lower Nawata member of the Nawata Formation in Kenya. A broad, shallow, meandering river is thought to have existed at the time of deposition, suitable for an aquatic gavialid such as Eogavialis. Evidence for a semideciduous tree savanna
that may have surrounded the river is present in the lower beds, and a general trend in increased aridity can be seen in overlying beds in the member, suggesting a dry thornbush savanna environment. Fossil
s present from the strata that material from E. andrewsi were found include those of numerous teleost
fish
such as osteoglossiformes
and perciformes
, many turtle
s, crocodile
s, and birds such as ostrich
es, possible elephant bird
s, anatids
, rails
, and owl
s,, as well as many mammal
s representing both living and extinct taxa common in Africa
.
The area of the Gebel Qatrani Formation in the Faiyum Depression where most of the well-preserved specimens of E. africanum and E. gavialoides were found was also deposited in a fluvial paleoenvironment
, although much older. Other fossils found from the formation include those of turtles, crocodiles, hyaenodontids
, proboscideans such as Phiomia
, Palaeomastodon
, and Moeritherium
, the Embrithopoda
n Arsinoitherium
, numerous species of hyrax
es, artiodactyls, as well as some of the earliest simian
primate
s such as Apidium
, Catopithecus
, Oligopithecus, and Aegyptopithecus
. Discoveries from this formation have added greatly to the understanding of mammalian evolution
in Africa. The presence of this type of fauna suggests a humid, tropical climate existed in Egypt during the Oligocene.
Much of the Gebel Qatrani consists of other deposits that represent both marine and non-marine sedimentary depositional environment
s. Some specimens of Eogavialis are known from these strata as well, suggesting that the genus may also have been adapted to a coastal marine habitat. This differs from the mostly freshwater habitats inhabited by extant crocodilia
ns.
False gharial
The false gharial , also known as the Malayan gharial, false gavial, or Tomistoma is a freshwater crocodile of the Crocodylidae family with a very thin and elongated snout...
, and consequently material from the genus was originally referred to Tomistoma. Indeed, it was not until 1982 that the name Eogavialis was constructed after it was realised that the specimens were from a more basal form.
Species
The genus was first described by Charles William AndrewsCharles William Andrews
Charles William Andrews F.R.S., was a British palaeontologist whose career as a vertebrate paleontologist, both as a curator and in the field, was spent in the services of the British Museum, Department of Geology.-Biography:...
in 1901 when Andrews named a new species of Tomistoma, T. africanum, on the basis of a specimen found from an outcrop of the Qasr el-Sagha Formation in Egypt, about 20 miles northwest of Faiyum, dating back to the Priabonian
Priabonian
The Priabonian is, in the ICS's geologic timescale, the latest age or the upper stage of the Eocene epoch or series. It spans the time between and...
stage of the late Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
37.2 to 33.9 million years ago. Other specimens were later found from the Gebel Qatrani Formation, slightly younger than the Qasr el-Sagha dating back to the Rupelian
Rupelian
The Rupelian is, in the geologic timescale, the older of two ages or the lower of two stages of the Oligocene epoch/series. It spans the time between and . It is preceded by the Priabonian stage and is followed by the Chattian stage....
stage of the early Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
33.9 to 28.4 million years ago, and near the locality where the original specimen of T. africanum was found in the Faiyum depression
Faiyum Oasis
The Faiyum Oasis is a depression or basin in the desert immediately to the west of the Nile south of Cairo. The extent of the basin area is estimated at between 490 mi² and 656 mi²...
. A new species was also found from this locality and named T. gavialoides by Andrews in 1905.
One of the first papers to identify the differences between these two species and others within Tomistoma was published in 1955 by J. A. Kälin. Other papers were written in the following decades that also questioned these species' relationships within Tomistominae. Eric Buffetaut proposed the genus name Eogavialis in 1982 and reassigned both T. africanum and T. gavialoides to it.
A third species was assigned to Eogavialis in 2003 from material found in the 1990s from the lower Nawata Formation of the Turkana basin
Lake Turkana
Lake Turkana , formerly known as Lake Rudolf, is a lake in the Great Rift Valley in Kenya, with its far northern end crossing into Ethiopia. It is the world's largest permanent desert lake and the world's largest alkaline lake...
outcropping in Lothagam
Lothagam
The Lothagam is a palaeontological formation located in Kenya. It dates to the Miocene-Pliocene period.It is located near the southwestern shores of Lake Turkana, 55 kilometres from Kanapoi...
, Kenya
Kenya
Kenya , officially known as the Republic of Kenya, is a country in East Africa that lies on the equator, with the Indian Ocean to its south-east...
. The strata from which the material was found dates back to the late Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
and early Pliocene
Pliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
, around 11.61 to 2.59 million years ago. This extends the fossil range of the genus by approximately 17 million years. It was named E. andrewsi for Charles Williams Andrews. The holotype consists of a well preserved, nearly complete skull.
One reason why Eogavialis was initially placed within Tomistoma was due to the fact that the premaxilla
Premaxilla
The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....
and nasal bone
Nasal bone
The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face, and form, by their junction, "the bridge" of the nose.Each has two surfaces and four borders....
s made contact with one another, a feature also seen in Tomistoma. However, this characteristic has since been shown to be present in other extinct gavialids, meaning that premaxilla and nasal contact is a plesiomorphic trait of all tomistomines, including 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:...
ones. Eogavialis also has a very similar cranial anatomy when compared to Tomistoma, having the same proportions, rostral
Rostrum (anatomy)
The term rostrum is used for a number of unrelated structures in different groups of animals:*In crustaceans, the rostrum is the forward extension of the carapace in front of the eyes....
length, and tooth number, leading to the conclusion by some authors of papers published after 1982 that Eogavialis is synonymous
Synonym (taxonomy)
In scientific nomenclature, a synonym is a scientific name that is or was used for a taxon of organisms that also goes by a different scientific name. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies...
with Tomistoma.
Phylogeny
Tomistomines have been traditionally classified as crocodileCrocodile
A crocodile is any species belonging to the family Crocodylidae . The term can also be used more loosely to include all extant members of the order Crocodilia: i.e...
s. However, molecular analyses of the false gharial, the only living tomistomine, suggest that the subfamily is actually within Gavialidae
Gavialidae
Gavialidae is a family of reptiles within the order Crocodilia. Gavialidae consists of only one surviving species, the gharial , which is native to India. Many extinct species are also known...
(along with the modern gharial
Gharial
The gharial , , also called Indian gavial or gavial, is the only surviving member of the once well-represented family Gavialidae, a long-established group of crocodilians with long, slender snouts...
of the subfamily Gavialinae) rather than Crocodylinae. The presence of a prominent crista
Crista
Cristae are the internal compartments formed by the inner membrane of a mitochondrion. They are studded with proteins, including ATP synthase and a variety of cytochromes. The maximum surface for chemical reactions to occur is within the mitochondria...
that runs along the postorbital
Postorbital
The postorbital is one of the bones in vertebrate skulls which forms a portion of the dermal skull roof and, sometimes, a ring about the orbit. Generally, it is located behind the postfrontal and posteriorly to the orbital fenestra. In some vertebrates, the postorbital is fused with the postfrontal...
in Eogavialis testifies to its position as a gavialid. Other characteristics such as a rectangular skull table, subcircular orbits with everted orbital rims, and a constricted antorbital area are also shared with Eogavialis and other modern gavialids, as seen in a well preserved skull of E. africanum housed at Yale
YALE
RapidMiner, formerly YALE , is an environment for machine learning, data mining, text mining, predictive analytics, and business analytics. It is used for research, education, training, rapid prototyping, application development, and industrial applications...
(YPM 6263) and material from Kenya of E. andrewsi.
Eogavialis has often been proposed to be non-tomistomine due to its lack of supposedly crocodylid 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...
needed in order for a taxon to be placed within Tomistominae. The genus lacks the exposure of the vomer
Vomer
The vomer is one of the unpaired facial bones of the skull. It is located in the midsagittal line, and articulates with the sphenoid, the ethmoid, the left and right palatine bones, and the left and right maxillary bones.-Biology:...
on the palate
Palate
The palate is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but, in most other tetrapods, the oral and nasal cavities are not truly separate. The palate is divided into two parts, the anterior...
that has been viewed as a characteristic of tomistomines. The trend for a long, narrow rostrum developing progressively over time as seen in Eogavialis has been used to suggest that the genus was a direct ancestor of Gavialis. Gryposuchus
Gryposuchus
Gryposuchus is an extinct genus of gavialoid crocodilian. It is the type genus of the subfamily Gryposuchinae. Fossils have been found from Argentina, Colombia, Venezuela, Brazil and the Peruvian Amazon. The genus existed during the early and middle Miocene epoch. One recently described species, G...
was once seen as phylogenetically between Eogavialis and Gavialis.
Paleoecology
E. andrewsi was found in fluvialFluvial
Fluvial is used in geography and Earth science to refer to the processes associated with rivers and streams and the deposits and landforms created by them...
deposits within the Lower Nawata member of the Nawata Formation in Kenya. A broad, shallow, meandering river is thought to have existed at the time of deposition, suitable for an aquatic gavialid such as Eogavialis. Evidence for a semideciduous tree savanna
Savanna
A savanna, or savannah, is a grassland ecosystem characterized by the trees being sufficiently small or widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach the ground to support an unbroken herbaceous layer consisting primarily of C4 grasses.Some...
that may have surrounded the river is present in the lower beds, and a general trend in increased aridity can be seen in overlying beds in the member, suggesting a dry thornbush savanna environment. Fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s present from the strata that material from E. andrewsi were found include those of numerous teleost
Teleostei
Teleostei is one of three infraclasses in class Actinopterygii, the ray-finned fishes. This diverse group, which arose in the Triassic period, includes 20,000 extant species in about 40 orders; most living fishes are members of this group...
fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
such as osteoglossiformes
Osteoglossiformes
Osteoglossiformes is a relatively primitive order of ray-finned fish that contains two sub-orders, the Osteoglossoidei and the Notopteroidei. All of the living species inhabit freshwater...
and perciformes
Perciformes
The Perciformes, also called the Percomorphi or Acanthopteri, is one of the largest orders of vertebrates, containing about 40% of all bony fish. Perciformes means perch-like. They belong to the class of ray-finned fish and comprise over 7,000 species found in almost all aquatic environments...
, many turtle
Turtle
Turtles are reptiles of the order Testudines , characterised by a special bony or cartilaginous shell developed from their ribs that acts as a shield...
s, crocodile
Crocodile
A crocodile is any species belonging to the family Crocodylidae . The term can also be used more loosely to include all extant members of the order Crocodilia: i.e...
s, and birds such as ostrich
Ostrich
The Ostrich is one or two species of large flightless birds native to Africa, the only living member of the genus Struthio. Some analyses indicate that the Somali Ostrich may be better considered a full species apart from the Common Ostrich, but most taxonomists consider it to be a...
es, possible elephant bird
Elephant bird
Elephant birds are an extinct family of flightless birds found only on the island of Madagascar and comprising the genera Aepyornis and Mullerornis.-Description:...
s, anatids
Anatidae
Anatidae is the biological family of birds that includes ducks, geese and swans. The family has a cosmopolitan distribution, occurring on all the world's continents except Antarctica and on most of the world's islands and island groups...
, rails
Rallidae
The rails, or Rallidae, are a large cosmopolitan family of small to medium-sized birds. The family exhibits considerable diversity and the family also includes the crakes, coots, and gallinules...
, and owl
Owl
Owls are a group of birds that belong to the order Strigiformes, constituting 200 bird of prey species. Most are solitary and nocturnal, with some exceptions . Owls hunt mostly small mammals, insects, and other birds, although a few species specialize in hunting fish...
s,, as well as many mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s representing both living and extinct taxa common in Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
.
The area of the Gebel Qatrani Formation in the Faiyum Depression where most of the well-preserved specimens of E. africanum and E. gavialoides were found was also deposited in a fluvial paleoenvironment
Paleoecology
Paleoecology uses data from fossils and subfossils to reconstruct the ecosystems of the past. It involves the study of fossil organisms and their associated remains, including their life cycle, living interactions, natural environment, and manner of death and burial to reconstruct the...
, although much older. Other fossils found from the formation include those of turtles, crocodiles, hyaenodontids
Hyaenodontidae
Hyaenodontidae is a family of the extinct order Creodonta, which contains several dozen genera.The Hyaenodontids were important mammalian predators that arose during the late Paleocene and persisted well into the Miocene...
, proboscideans such as Phiomia
Phiomia
Phiomia is an extinct genus of basal proboscid that lived in what is now Northern Africa during the Late Eocene to Early Oligocene some 36-35 million years ago. "Phiomia serridens" means "saw-toothed animal of Faiyum"....
, Palaeomastodon
Palaeomastodon
Palaeomastodon an extinct genus of Proboscidea. Palaeomastodon fossils have been found in Africa, lived some 36-35 million years ago. They are believed to be the ancestors of elephants or mastodons. This genus is related to Moeritherium....
, and Moeritherium
Moeritherium
Moeritherium is a genus consisting of several species. These prehistoric mammals are related to the elephant and, more distantly, the sea cow...
, the Embrithopoda
Embrithopoda
Embrithopoda is an extinct order of mammals which first appeared in the fossil record during the late Eocene and then died out during the Oligocene....
n Arsinoitherium
Arsinoitherium
Arsinoitherium is an extinct genus of paenungulate mammal related to elephants, sirenians, hyraxes and the extinct desmostylians, as well as to other extinct embrithopods...
, numerous species of hyrax
Hyrax
A hyrax is any of four species of fairly small, thickset, herbivorous mammals in the order Hyracoidea. The rock hyrax Procavia capensis, the yellow-spotted rock hyrax Heterohyrax brucei, the western tree hyrax Dendrohyrax dorsalis, and the southern tree hyrax, Dendrohyrax arboreus live in Africa...
es, artiodactyls, as well as some of the earliest simian
Simian
The simians are the "higher primates" familiar to most people: the Old World monkeys and apes, including humans, , and the New World monkeys or platyrrhines. Simians tend to be larger than the "lower primates" or prosimians.- Classification and evolution :The simians are split into three groups...
primate
Primate
A primate is a mammal of the order Primates , which contains prosimians and simians. Primates arose from ancestors that lived in the trees of tropical forests; many primate characteristics represent adaptations to life in this challenging three-dimensional environment...
s such as Apidium
Apidium
The genus Apidium is that of at least three extinct primates living in the early Oligocene, roughly 36 to 32 millions years ago. Apidium fossils are common in the Fayoum deposits of Egypt...
, Catopithecus
Catopithecus
Catopithecus is an early fossil catarrhine that post dates the platyrrhine – catarrhine divergence but predates the hominoid – cercopithecoid divergence...
, Oligopithecus, and Aegyptopithecus
Aegyptopithecus
Aegyptopithecus zeuxis means “linking Egyptian ape”. It was discovered by E. Simons in 1965. There is controversy over whether or not Aegyptopithecus should be a genus on its own or whether it should be moved into the genus Propliopithecus. If Aegyptopithecus is placed in its own genus, then there...
. Discoveries from this formation have added greatly to the understanding of mammalian evolution
Evolution of mammals
__FORCETOC__The evolution of mammals within the synapsid lineage was a gradual process that took approximately 70 million years, beginning in the mid-Permian. By the mid-Triassic, there were many species that looked like mammals, and the first true mammals appeared in the early Jurassic...
in Africa. The presence of this type of fauna suggests a humid, tropical climate existed in Egypt during the Oligocene.
Much of the Gebel Qatrani consists of other deposits that represent both marine and non-marine sedimentary depositional environment
Sedimentary depositional environment
In geology, sedimentary depositional environment describes the combination of physical, chemical and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will be formed after lithification, if the sediment is preserved in the rock...
s. Some specimens of Eogavialis are known from these strata as well, suggesting that the genus may also have been adapted to a coastal marine habitat. This differs from the mostly freshwater habitats inhabited by extant crocodilia
Crocodilia
Crocodilia is an order of large reptiles that appeared about 84 million years ago in the late Cretaceous Period . They are the closest living relatives of birds, as the two groups are the only known survivors of the Archosauria...
ns.
External links
- Eogavialis in the Paleobiology DatabasePaleobiology Database' is an online resource for information on the distribution and classification of fossil animals, plants, and microorganisms.-History:The Paleobiology Database was founded in 2000. It has been funded by the National Science Foundation and the Australian Research Council...