Hesperornis
Encyclopedia
Hesperornis is a genus
of flightless aquatic bird
s that spanned the first half of the Campanian
age of the Late Cretaceous
period (83.5–78 mya). One of the lesser-known discoveries of the paleontologist O. C. Marsh
in the late 19th century Bone Wars
, it was an important early find in the history of avian paleontology. Famous locations for Hesperornis fossils are the Late Cretaceous marine limestone
s from Kansas
and the marine shales from Canada
. Nine species are recognised, eight of which have been recovered from rocks in North America and one from Russia.
Hesperornis was a large bird, reaching up to 1.5 meters (5 feet) in length. It had virtually no wings, and swam with its powerful hind legs. Fossil evidence shows that the toes were probably lobed, as in today's grebe
s, rather than webbed as in those of loon
s.
Like many other Mesozoic
birds such as Ichthyornis
, Hesperornis had teeth as well as a beak
, which were used to hold prey. In the hesperornithiform lineage they were of a different arrangement than in any other known bird (or in non-avian theropod dinosaurs), with the teeth sitting in a longitudinal groove rather than in individual sockets, in a notable case of convergent evolution
with mosasaur
s. The teeth of Hesperornis were present along nearly the entire lower jaw (dentary) and the back of the upper jaw (maxilla
). The front portion of the upper jaw (premaxilla
) and tip of the lower jaw (predentary) lacked teeth and were probably covered in a beak. Studies of the bone surface show that at least the tips of the jaws supported a hard, keratin
ous beak similar to that found in modern birds. The palate (mouth roof) contained small pits that allowed the lower teeth to lock into place when the jaws were closed.
The first Hesperornis specimen was discovered in 1871 by Othniel Charles Marsh
. Marsh was undertaking his second western expedition, accompanied by ten students. The team headed to Kansas where Marsh had dug before. Aside from finding more bones belonging to the flying reptile Pteranodon
, Marsh discovered the skeleton of a "large fossil bird, at least five feet in height". The specimen was large, wingless, and had strong legs—Marsh considered it a diving species. Unfortunately, the specimen lacked a head. Marsh named the find Hesperornis regalis, or "regal western bird".
Marsh headed back west with a smaller party the following year, where he discovered another Hesperornis skeleton. This specimen had enough of its head intact that Marsh could see that the creature's jaws had been lined with teeth. Along Marsh saw important evolutionary implications of this find along with Benjamin Mudge's find of the toothed bird Ichthyornis
. In an 1873 paper Marsh declared that "the fortunate discovery of these interesting fossils does much to break down the old distinction between Birds and Reptiles". Meanwhile Marsh's relationship with his rival Edward Drinker Cope
soured further after Cope accidentally received boxes of fossils, including the toothed birds, that were meant for Marsh. Cope called the birds "simply delightful", but Marsh replied with accusations Cope had stolen the bones. By 1873 their friendship dissolved into open hostility, helping to spark the Bone Wars
. While Marsh would rarely go into the field after 1873, the collectors he paid continued to send him a stream of fossils. He eventually received parts of 50 specimens of Hesperornis, which allowed him to make a much stronger demonstration of an evolutionary link between reptiles and birds than had been possible before.
have been described in this genus, though some are known from very few bones or even a single bone and cannot be properly compared with the more plentiful (but also incomplete) remains of other similar-sized taxa. In many cases, species have been separated by provenance, having been found in strata of different ages or in different locations, or by differences in size.
The first species to be described, the type species
, is Hesperornis regalis. H. regalis is also the best known species, and dozens of specimens (from fragments to more complete skeletons) have been recovered, all from the Smoky Hill Chalk Member of the Niobrara Formation
(dating to the early Campanian
age, between 83.5-80.5 million years ago). It is the only species of Hesperornis for which a nearly complete skull is known.
Hesperornis crassipes was named in 1876 by Marsh, who initially classified it in a different genus as Lestornis crassipes. H. crassipes was larger than H. regalis, had five ribs as opposed to four in the first species, and differed in aspects of the bone sculpturing on the breastbone and lower leg. H. crassipes is known from the same time and place as H. regalis. One incomplete skeleton is known, including teeth and parts of the skull.
Marsh explicitly named his second species of Hesperornis in 1876 for an incomplete metatarsus
recovered from the same layers of the Niobrara chalk as H. regalis. He named this species H. gracilis, and it was subsequently involved in the rather confused taxonomy of a specimen which would eventually form the basis of the new genus and species Parahesperornis alexi. The type specimen of P. alexi was assumed to belong to the same specimen as that of H. gracilis, so when Lucas (1903) decided that the former specimen represented a distinct genus, he mistakenly used the later specimen to anchor it, creating the name Hargeria gracilis. This mistake was rectified by later authors, who sank Hargeria back into Hesperornis and re-named the more distinctive specimen Parahesperornis.
The first species recognized from outside the Niobrara chalk, Hesperornis altus, lived about 78 million years ago in Montana
, and is known from a partial lower leg from the base of the freshwater Judith River Formation
(or, possibly, the top of the underlying, marine Claggett Shale
formation). While initially placed in the new genus Coniornis by Marsh, this was due mostly to his belief that Hesperornis existed only in Kansas, so any species from Montana should be placed in a different genus. Most later researchers disagreed with this, and have placed Coniornis altus in the same genus as Hesperornis as H. altus. A second species from Montana has also been described from the Claggett Shale. H. montana was named by Shufeldt in 1915, and while its known material (a single dorsal vertebra
) cannot be directly compared to H. altus, Shufeldt and others have considered it distinct due to its apparently smaller size.
In 1993, the first Hesperornis remains from outside of North America were recognized as a new species by Nessov and Yarkov. They named Hesperornis rossicus for a fragmentary skeleton from the early Campanian of Russia
near Volgograd
. Several other specimens from contemporary deposits have since been referred to this species. At about 1.4 metres (4.6 ft) long, H. rossicus was the largest species of Hesperornis and among the largest hesperornithines, slightly smaller than the large Canadian genus Canadaga
. Aside from its large size and different geographic location, H. rossicus differs from other Hesperornis in several features of the lower leg and foot, including a highly flattened metatarsus.
In 2002, Martin and Lim formally recognized several new species for remains that had previously been unstudied or referred without consideration to previously named North American hesperornithines. These include the very small H. mengeli and H. macdonaldi, the slightly larger H. bairdi, and the very large H. chowi, all from the Sharon Springs member of the Pierre Shale
Formation in South Dakota and Alberta, 80.5 million years ago).
In addition, there are some unassigned remains, such as SGU
3442 Ve02 and LO
9067t and bones of an undetermined species from Tzimlyanskoe Reservoir near Rostov
. The former two bones are probably H. rossicus; some remains assigned to that species in turn seem to belong to the latter undetermined taxon. The small form, initially called H. gracilis, was later moved into a monotypic
genus Hargeria, and ultimately placed in Parahesperornis
.
, the Turgai Strait, and the prehistoric North Sea
, which then were subtropical to tropical waters, much warmer than today. However, some of the youngest known specimens of Hesperornis have been found in inland freshwater deposits of the Foremost Formation
, suggesting that some species of Hesperornis may have eventually moved, at least partially, away from a primarily marine habitat. Additionally, the species H. altus comes from the freshwater deposits at the base of the Judith River Formation
.
Traditionally, Hesperornis is depicted with a mode of locomotion similar to modern loon
s or grebe
s, and study of their limb proportions and hip structure has borne out this comparison. In terms of limb length, shape of the hip bones, and position of the hip socket, Hesperornis is particularly similar to the Great Northern Loon (Gavia immer), probably exhibiting a very similar manner of locomotion on land and in water. Like loons, Hesperornis were probably excellent foot-propelled divers, but somewhat ungainly on land.
Young Hesperornis grew fairly quickly and continuously to adulthood, as is the case in modern birds, but not Enantiornithes
.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of flightless aquatic 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...
s that spanned the first half of the Campanian
Campanian
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...
age of the Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
period (83.5–78 mya). One of the lesser-known discoveries of the paleontologist O. C. Marsh
Othniel Charles Marsh
Othniel Charles Marsh was an American paleontologist. Marsh was one of the preeminent scientists in the field; the discovery or description of dozens of news species and theories on the origins of birds are among his legacies.Born into a modest family, Marsh was able to afford higher education...
in the late 19th century Bone Wars
Bone Wars
The Bone Wars, also known as the "Great Dinosaur Rush", refers to a period of intense fossil speculation and discovery during the Gilded Age of American history, marked by a heated rivalry between Edward Drinker Cope and Othniel Charles Marsh...
, it was an important early find in the history of avian paleontology. Famous locations for Hesperornis fossils are the Late Cretaceous marine limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
s from Kansas
Kansas
Kansas is a US state located in the Midwestern United States. It is named after the Kansas River which flows through it, which in turn was named after the Kansa Native American tribe, which inhabited the area. The tribe's name is often said to mean "people of the wind" or "people of the south...
and the marine shales from Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
. Nine species are recognised, eight of which have been recovered from rocks in North America and one from Russia.
Description
Grebe
A grebe is a member of the Podicipediformes order, a widely distributed order of freshwater diving birds, some of which visit the sea when migrating and in winter...
s, rather than webbed as in those of loon
Loon
The loons or divers are a group of aquatic birds found in many parts of North America and northern Eurasia...
s.
Like many other 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...
birds such as Ichthyornis
Ichthyornis
Ichthyornis is a genus of toothed seabirds from the Late Cretaceous of North America. Its fossil remains are known from the chalks of Alberta, Alabama, Kansas, New Mexico, Saskatchewan, and Texas, in strata that were laid down in the Western Interior Seaway during the Turonian-Campanian ages,...
, Hesperornis had teeth as well as a beak
Beak
The beak, bill or rostrum is an external anatomical structure of birds which is used for eating and for grooming, manipulating objects, killing prey, fighting, probing for food, courtship and feeding young...
, which were used to hold prey. In the hesperornithiform lineage they were of a different arrangement than in any other known bird (or in non-avian theropod dinosaurs), with the teeth sitting in a longitudinal groove rather than in individual sockets, in a notable case of convergent evolution
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
with mosasaur
Mosasaur
Mosasaurs are large extinct marine lizards. The first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764...
s. The teeth of Hesperornis were present along nearly the entire lower jaw (dentary) and the back of the upper jaw (maxilla
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
). The front portion of the upper jaw (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 tip of the lower jaw (predentary) lacked teeth and were probably covered in a beak. Studies of the bone surface show that at least the tips of the jaws supported a hard, keratin
Keratin
Keratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...
ous beak similar to that found in modern birds. The palate (mouth roof) contained small pits that allowed the lower teeth to lock into place when the jaws were closed.
History
Othniel Charles Marsh
Othniel Charles Marsh was an American paleontologist. Marsh was one of the preeminent scientists in the field; the discovery or description of dozens of news species and theories on the origins of birds are among his legacies.Born into a modest family, Marsh was able to afford higher education...
. Marsh was undertaking his second western expedition, accompanied by ten students. The team headed to Kansas where Marsh had dug before. Aside from finding more bones belonging to the flying reptile Pteranodon
Pteranodon
Pteranodon , from the Late Cretaceous geological period of North America in present day Kansas, Alabama, Nebraska, Wyoming, and South Dakota, was one of the largest pterosaur genera and had a maximum wingspan of over...
, Marsh discovered the skeleton of a "large fossil bird, at least five feet in height". The specimen was large, wingless, and had strong legs—Marsh considered it a diving species. Unfortunately, the specimen lacked a head. Marsh named the find Hesperornis regalis, or "regal western bird".
Marsh headed back west with a smaller party the following year, where he discovered another Hesperornis skeleton. This specimen had enough of its head intact that Marsh could see that the creature's jaws had been lined with teeth. Along Marsh saw important evolutionary implications of this find along with Benjamin Mudge's find of the toothed bird Ichthyornis
Ichthyornis
Ichthyornis is a genus of toothed seabirds from the Late Cretaceous of North America. Its fossil remains are known from the chalks of Alberta, Alabama, Kansas, New Mexico, Saskatchewan, and Texas, in strata that were laid down in the Western Interior Seaway during the Turonian-Campanian ages,...
. In an 1873 paper Marsh declared that "the fortunate discovery of these interesting fossils does much to break down the old distinction between Birds and Reptiles". Meanwhile Marsh's relationship with his rival Edward Drinker 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...
soured further after Cope accidentally received boxes of fossils, including the toothed birds, that were meant for Marsh. Cope called the birds "simply delightful", but Marsh replied with accusations Cope had stolen the bones. By 1873 their friendship dissolved into open hostility, helping to spark the Bone Wars
Bone Wars
The Bone Wars, also known as the "Great Dinosaur Rush", refers to a period of intense fossil speculation and discovery during the Gilded Age of American history, marked by a heated rivalry between Edward Drinker Cope and Othniel Charles Marsh...
. While Marsh would rarely go into the field after 1873, the collectors he paid continued to send him a stream of fossils. He eventually received parts of 50 specimens of Hesperornis, which allowed him to make a much stronger demonstration of an evolutionary link between reptiles and birds than had been possible before.
Classification and species
Many speciesSpecies
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
have been described in this genus, though some are known from very few bones or even a single bone and cannot be properly compared with the more plentiful (but also incomplete) remains of other similar-sized taxa. In many cases, species have been separated by provenance, having been found in strata of different ages or in different locations, or by differences in size.
The first species to be described, the type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
, is Hesperornis regalis. H. regalis is also the best known species, and dozens of specimens (from fragments to more complete skeletons) have been recovered, all from the Smoky Hill Chalk Member of the Niobrara Formation
Niobrara Formation
The Niobrara Formation, also called the Niobrara Chalk , is a geologic formation in North America that was laid down between 87 and 82 million years ago during the Coniacian, Santonian, and Campanian ages of the Late Cretaceous. It is composed of two structural units, the Smoky Hill Chalk Member...
(dating to the early Campanian
Campanian
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...
age, between 83.5-80.5 million years ago). It is the only species of Hesperornis for which a nearly complete skull is known.
Hesperornis crassipes was named in 1876 by Marsh, who initially classified it in a different genus as Lestornis crassipes. H. crassipes was larger than H. regalis, had five ribs as opposed to four in the first species, and differed in aspects of the bone sculpturing on the breastbone and lower leg. H. crassipes is known from the same time and place as H. regalis. One incomplete skeleton is known, including teeth and parts of the skull.
Marsh explicitly named his second species of Hesperornis in 1876 for an incomplete metatarsus
Metatarsus
The metatarsus or metatarsal bones are a group of five long bones in the foot located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the medial side : the first, second, third, fourth, and fifth...
recovered from the same layers of the Niobrara chalk as H. regalis. He named this species H. gracilis, and it was subsequently involved in the rather confused taxonomy of a specimen which would eventually form the basis of the new genus and species Parahesperornis alexi. The type specimen of P. alexi was assumed to belong to the same specimen as that of H. gracilis, so when Lucas (1903) decided that the former specimen represented a distinct genus, he mistakenly used the later specimen to anchor it, creating the name Hargeria gracilis. This mistake was rectified by later authors, who sank Hargeria back into Hesperornis and re-named the more distinctive specimen Parahesperornis.
The first species recognized from outside the Niobrara chalk, Hesperornis altus, lived about 78 million years ago in Montana
Montana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...
, and is known from a partial lower leg from the base of the freshwater Judith River Formation
Judith River Formation
The Judith River Formation is a fossil-bearing geologic formation in Montana, and is part of the Judith River Group. It dates to the upper Cretaceous, between 80 and 75 million years ago, corresponding to the "Judithian" land vertebrate age...
(or, possibly, the top of the underlying, marine Claggett Shale
Claggett Shale
The Claggett Shale is a geological formation in Montana whose strata date back to the Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation.-Vertebrate paleofauna:...
formation). While initially placed in the new genus Coniornis by Marsh, this was due mostly to his belief that Hesperornis existed only in Kansas, so any species from Montana should be placed in a different genus. Most later researchers disagreed with this, and have placed Coniornis altus in the same genus as Hesperornis as H. altus. A second species from Montana has also been described from the Claggett Shale. H. montana was named by Shufeldt in 1915, and while its known material (a single dorsal vertebra
Vertebral column
In human anatomy, the vertebral column is a column usually consisting of 24 articulating vertebrae, and 9 fused vertebrae in the sacrum and the coccyx. It is situated in the dorsal aspect of the torso, separated by intervertebral discs...
) cannot be directly compared to H. altus, Shufeldt and others have considered it distinct due to its apparently smaller size.
In 1993, the first Hesperornis remains from outside of North America were recognized as a new species by Nessov and Yarkov. They named Hesperornis rossicus for a fragmentary skeleton from the early Campanian of Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
near Volgograd
Volgograd
Volgograd , formerly called Tsaritsyn and Stalingrad is an important industrial city and the administrative center of Volgograd Oblast, Russia. It is long, north to south, situated on the western bank of the Volga River...
. Several other specimens from contemporary deposits have since been referred to this species. At about 1.4 metres (4.6 ft) long, H. rossicus was the largest species of Hesperornis and among the largest hesperornithines, slightly smaller than the large Canadian genus Canadaga
Canadaga
Canadaga is a flightless bird genus from the Late Cretaceous. The single known species is Canadaga arctica. It lived in the shallow seas around what today is Bylot Island in Nunavut, Canada...
. Aside from its large size and different geographic location, H. rossicus differs from other Hesperornis in several features of the lower leg and foot, including a highly flattened metatarsus.
In 2002, Martin and Lim formally recognized several new species for remains that had previously been unstudied or referred without consideration to previously named North American hesperornithines. These include the very small H. mengeli and H. macdonaldi, the slightly larger H. bairdi, and the very large H. chowi, all from the Sharon Springs member of the Pierre Shale
Pierre Shale
The Pierre Shale is a geologic formation or series in the Upper Cretaceous which occurs east of the Rocky Mountains in the Great Plains, from North Dakota to New Mexico....
Formation in South Dakota and Alberta, 80.5 million years ago).
In addition, there are some unassigned remains, such as SGU
Geological Survey of Sweden
Geological Survey of Sweden is a Swedish government agency that was founded in 1858 dealing with questions about the nature of the geological and mineral management in Sweden....
3442 Ve02 and LO
Lund University
Lund University , located in the city of Lund in the province of Scania, Sweden, is one of northern Europe's most prestigious universities and one of Scandinavia's largest institutions for education and research, frequently ranked among the world's top 100 universities...
9067t and bones of an undetermined species from Tzimlyanskoe Reservoir near Rostov
Rostov
Rostov is a town in Yaroslavl Oblast, Russia, one of the oldest in the country and a tourist center of the Golden Ring. It is located on the shores of Lake Nero, northeast of Moscow. Population:...
. The former two bones are probably H. rossicus; some remains assigned to that species in turn seem to belong to the latter undetermined taxon. The small form, initially called H. gracilis, was later moved into a monotypic
Monotypic
In biology, a monotypic taxon is a taxonomic group with only one biological type. The term's usage differs slightly between botany and zoology. The term monotypic has a separate use in conservation biology, monotypic habitat, regarding species habitat conversion eliminating biodiversity and...
genus Hargeria, and ultimately placed in Parahesperornis
Parahesperornis
Parahesperornis is a prehistoric flightless bird genus from the Late Cretaceous. Its range in space and time may have been extensive, but its remains are rather few and far between, at least compared with its contemporary relatives in Hesperornis. Remains are known from central North America,...
.
Paleobiology
Hesperornis was primarily marine, and lived in the waters of such contemporary shallow shelf seas as the Western Interior SeawayWestern Interior Seaway
The Western Interior Seaway, also called the Cretaceous Seaway, the Niobraran Sea, and the North American Inland Sea, was a huge inland sea that split the continent of North America into two halves, Laramidia and Appalachia, during most of the mid- and late-Cretaceous Period...
, the Turgai Strait, and the prehistoric North Sea
North Sea
In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean. In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively...
, which then were subtropical to tropical waters, much warmer than today. However, some of the youngest known specimens of Hesperornis have been found in inland freshwater deposits of the Foremost Formation
Foremost Formation
The Foremost Formation is a geological formation in Alberta, Canada whose strata date back to the Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation.-Dinosaurs:...
, suggesting that some species of Hesperornis may have eventually moved, at least partially, away from a primarily marine habitat. Additionally, the species H. altus comes from the freshwater deposits at the base of the Judith River Formation
Judith River Formation
The Judith River Formation is a fossil-bearing geologic formation in Montana, and is part of the Judith River Group. It dates to the upper Cretaceous, between 80 and 75 million years ago, corresponding to the "Judithian" land vertebrate age...
.
Traditionally, Hesperornis is depicted with a mode of locomotion similar to modern loon
Loon
The loons or divers are a group of aquatic birds found in many parts of North America and northern Eurasia...
s or grebe
Grebe
A grebe is a member of the Podicipediformes order, a widely distributed order of freshwater diving birds, some of which visit the sea when migrating and in winter...
s, and study of their limb proportions and hip structure has borne out this comparison. In terms of limb length, shape of the hip bones, and position of the hip socket, Hesperornis is particularly similar to the Great Northern Loon (Gavia immer), probably exhibiting a very similar manner of locomotion on land and in water. Like loons, Hesperornis were probably excellent foot-propelled divers, but somewhat ungainly on land.
Young Hesperornis grew fairly quickly and continuously to adulthood, as is the case in modern birds, but not Enantiornithes
Enantiornithes
Enantiornithes is an extinct group of primitive birds. They were the most abundant and diverse avialans of the Mesozoic. Almost all retained teeth and clawed fingers on each wing, but otherwise looked much like modern birds externally. Over 50 species of Enantiornithines have been named, but some...
.
External links
- Eastern Kentucky UniversityEastern Kentucky UniversityEastern Kentucky University, commonly referred to as Eastern or by the acronym EKU by local residents, is an undergraduate and graduate teaching and research institution located in Richmond, Kentucky, U.S.A.. EKU is accredited by the Southern Association of Colleges and Schools...
: Closeup of Hesperornis skull. Retrieved 2007-NOV-04. - savageancientseas.com: Forward view of H. regalis skeleton in diving pose. Note relalistic position of legs and toe rotation. Retrieved 2007-NOV-04.
- UC Davis: Moveable 3D rendering of patella (kneecap) of Hesperornis sp.. Digitized from KUVP PU17193. Requires Java, IFC or 3DC plugin. Retrieved 2007-NOV-04.
