Champsosaurus
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''Champsosaurus'' is an
extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of crocodile-like choristodere reptile, known from the Late
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
and early
Paleogene The Paleogene Period ( ; also spelled Palaeogene or Palæogene) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period Ma (million years ago) to the beginning of the Neogene Period Ma. It is the fir ...
periods of North America and Europe (
Campanian The Campanian is the fifth of six ages of the Late Cretaceous epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campa ...
Paleocene The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...
). The name ''Champsosaurus'' is thought to come from , () said in an Ancient Greek source to be an Egyptian word for "crocodiles", and , () Greek for "lizard". The morphology of ''Champsosaurus'' resembles that of
gharial The gharial (''Gavialis gangeticus''), also known as gavial or fish-eating crocodile, is a crocodilian in the family (biology), family Gavialidae and among the longest of all living crocodilians. Mature females are long, and males . Adult males ...
s, with a long, elongated snout. It was native to freshwater environments where it likely preyed on fish, similar to living gharials.


History of research

''Champsosaurus'' was the first member of the
Choristodera Choristodera (from the Greek χωριστός ''chōristos'' + δέρη ''dérē'', 'separated neck') is an extinct order of semiaquatic diapsid reptiles that ranged from the Middle Jurassic, or possibly Triassic, to the Miocene (168 to 20 or p ...
to be described. ''Champsosaurus'' was named by
Edward Drinker Cope Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American zoologist, paleontology, paleontologist, comparative anatomy, comparative anatomist, herpetology, herpetologist, and ichthyology, ichthyologist. Born to a wealthy Quaker fam ...
in 1876, from isolated vertebrae found in Late Cretaceous strata of the Judith River Formation on the banks of the Judith River in Fergus County,
Montana Montana ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Idaho to the west, North Dakota to the east, South Dakota to the southeast, Wyoming to the south, an ...
. Cope designated ''C. annectens'' as the
type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...
rather than the first named ''C. profundus'' due to the larger number of vertebrae he attributed to the species. ''C. annectens'' was based on 9 isolated vertebral centra (AMNH FR 5696) that were not figured in the paper of which two are now lost. Cope named several other species between 1876 and 1882, also based on isolated vertebrae.
Barnum Brown Barnum Brown (February 12, 1873 – February 5, 1963), commonly referred to as Mr. Bones, was an American paleontologist. He discovered the first documented remains of ''Tyrannosaurus'' during a career that made him one of the most famous fossil ...
in 1905 described the first complete remains of ''Champsosaurus'', and noted that one of the species attributed to ''Champsosaurus'' by Cope in 1876, ''C. vaccinsulensis'' actually represented indeterminate
plesiosaur The Plesiosauria or plesiosaurs are an Order (biology), order or clade of extinct Mesozoic marine reptiles, belonging to the Sauropterygia. Plesiosaurs first appeared in the latest Triassic Period (geology), Period, possibly in the Rhaetian st ...
remains, and that the vertebrae that Cope used to diagnose his species of ''Champsosaurus'' were heavily eroded and the diagnostic features varied substantially along the spinal column, and were not diagnostic to species level, including the remains that Cope attributed to the type species ''C. annectens''.B. Brown. 1905
The osteology of Champsosaurus Cope
''American Museum of Natural History, Memoirs'' 9:1–264
The conclusion that ''C. annectens'' was undiagnostic was supported by William Parks in 1933.W. A. Parks. 1933. New species of Champsosaurus from the Belly River Formation of Alberta, Canada. ''Transactions of Royal Society of Canada'' 27:121–137 Brown in 1905 named two species of ''Champsosaurus.'' One was ''C. ambulator'', named from the specimen AMNH 983, a fragmentary skeleton with a partial skull found in the
Hell Creek Formation The Hell Creek Formation is an intensively studied division of mostly Upper Cretaceous and some lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana. The Formation (stratigraphy), formation s ...
of Montana. The other was ''C. laramiensis'', named from AMNH 982, a nearly complete skeleton and skull, also found in the Hell Creek Formation. Parks in 1927 named ''C. albertensis'' from ROM 806, a partial skeleton lacking the skull, found in the Horseshoe Canyon Formation in Alberta, Canada. Parks in 1933 named the species ''C. natator'' from an incomplete skeleton with a fragmentary skull (TMP 81.47.1) found in the Belly River Group in the
Red Deer River The Red Deer River is a river in Alberta and a small portion of Saskatchewan, Canada. It is a major tributary of the South Saskatchewan River and is part of the larger Saskatchewan / Nelson River, Nelson system that empties into Hudson Bay. T ...
valley in Alberta. In 1979,
Denise Sigogneau-Russell Denise Sigogneau-Russell (born ''c.'' 1941/42) is a French palaeontologist who specialises in mammals from the Mesozoic, particularly from France and the UK. She is currently based at the Muséum National d'Histoire Naturelle. Background Denise S ...
named the species ''C. dolloi'' from remains found in the Paleocene of Belgium. In 1972, Bruce Erickson named the species ''C. gigas'' from SMM P71.2.1, a partial skeleton and skull found in the Sentinel Butte Formation,
Golden Valley County Golden Valley County is the name of two counties in the United States: *Golden Valley County, Montana Golden Valley County is a County (United States), county located in the U.S. state of Montana. As of the 2020 United States census, 2020 cens ...
, North Dakota. Erickson subsequently in 1981 named the species ''C. tenuis'' from SMM P79.14.1, a partial skeleton and skull found in the Bullion Creek Formation, North Dakota. In 1998 K. Q. Gao and Richard Carr Fox described the species ''C. lindoei'' from UALVP 931, a nearly complete skeleton with skull and jaws from the
Dinosaur Park Formation The Dinosaur Park Formation is the uppermost member of the Belly River Group (also known as the Judith River Group), a major geologic unit in southern Alberta. It was deposited during the Campanian stage of the Late Cretaceous, between about 7 ...
in Alberta. The publication also thoroughly reviewed ''Champsosaurus'', rediagnosing most species except for ''C. ambulator'' and ''C. laramiensis''. Fossils of ''Champsosaurus'' have been found in
North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...
(
Alberta Alberta is a Provinces and territories of Canada, province in Canada. It is a part of Western Canada and is one of the three Canadian Prairies, prairie provinces. Alberta is bordered by British Columbia to its west, Saskatchewan to its east, t ...
,
Saskatchewan Saskatchewan is a Provinces and territories of Canada, province in Western Canada. It is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and to the south by the ...
, Montana,
New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...
,
Texas Texas ( , ; or ) is the most populous U.S. state, state in the South Central United States, South Central region of the United States. It borders Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the we ...
,
Colorado Colorado is a U.S. state, state in the Western United States. It is one of the Mountain states, sharing the Four Corners region with Arizona, New Mexico, and Utah. It is also bordered by Wyoming to the north, Nebraska to the northeast, Kansas ...
, and
Wyoming Wyoming ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States, Western United States. It borders Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho t ...
) and
Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...
(
Belgium Belgium, officially the Kingdom of Belgium, is a country in Northwestern Europe. Situated in a coastal lowland region known as the Low Countries, it is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southeas ...
and
France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...
), dating from the
Upper Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cret ...
to the late
Paleocene The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...
. Remains tentatively referred to ''Champsosaurus'' are known from the high
Canadian Arctic Northern Canada (), colloquially the North or the Territories, is the vast northernmost region of Canada, variously defined by geography and politics. Politically, the term refers to the three territories of Canada: Yukon, Northwest Territories a ...
, dating to the Coniacian
Turonian The Turonian is, in the International Commission on Stratigraphy, ICS' geologic timescale, the second age (geology), age in the Late Cretaceous epoch (geology), Epoch, or a stage (stratigraphy), stage in the Upper Cretaceous series (stratigraphy), ...
, a time of extreme warmth.


Taxonomy

Sixteen species of ''Champsosaurus'' have been named, of which seven are presently considered valid. The
type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...
''Champsosaurus annectens'' Cope, 1876 is considered to be dubious. The only named European species ''C. dolloi'' Sigogneau-Russell 1979 was considered to be too fragmentary to warrant a new species by Gao and Fox in 1998.


Description

Most species grew to about 1.50 m (5 ft) long,D.Lambert, D.Naish and E.Wyse 2001, "Encyclopedia of Dinosaurs and prehistoric life", p. 77, Dorling Kindersley Limited, London. though ''Champsosaurus gigas'', the largest species, reached 3–3.5 m (10–12 ft) in length.


Anatomy

The skull of ''Champsosaurus'' is dorsoventrally flattened, while the temporal arches are expanded posteriorly (towards the back of the skull) and laterally (away from the midline), giving the skull a heart shaped appearance when viewed from above. The snout is greatly elongated and
gharial The gharial (''Gavialis gangeticus''), also known as gavial or fish-eating crocodile, is a crocodilian in the family (biology), family Gavialidae and among the longest of all living crocodilians. Mature females are long, and males . Adult males ...
-like, making up around half the length of the skull, and at least four times as long as it is wide, with the opening of the nostrils at the end of the snout. The openings of the ears are located on the underside of the skull. The body is flat and streamlined, with heavy
gastralia Gastralia (: gastralium) are dermal bones found in the ventral body wall of modern crocodilians and tuatara, and many prehistoric tetrapods. They are found between the sternum and pelvis, and do not articulate with the vertebrae. In these reptil ...
(rib-like bones situated in the belly). Compared to other choristoderes, the
lacrimal bone The lacrimal bones are two small and fragile bones of the facial skeleton; they are roughly the size of the little fingernail and situated at the front part of the medial wall of the orbit. They each have two surfaces and four borders. Several bon ...
is reduced in size to a small triangle, the
postorbital bone 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 ...
does not form part of the orbit (eye socket), there is no contact between the
premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammals h ...
and the
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. The vomer forms ...
bones, an internarial bone is present, the
choana The choanae (: choana), posterior nasal apertures or internal nostrils are two openings found at the back of the nasal passage between the nasal cavity and the pharynx, in humans and other mammals (as well as crocodilians and most skinks). They ...
e are located posteriorly in correlation to the elongation of the vomer, the interpterygoid vacuity is small and completely enclosed by the
pterygoid bone The pterygoid is a paired bone forming part of the palate of many vertebrates, behind the palatine bone In anatomy, the palatine bones (; derived from the Latin ''palatum'') are two irregular bones of the facial skeleton in many animal specie ...
s and located near the posterior margin of the suborbital fenestra, the shape of the suborbital fenestra is shortened and kidney like, the articulation between the pterygoid and the
parasphenoid The parasphenoid is a bone which can be found in the cranium of many vertebrates. It is an unpaired dermal bone which lies at the midline of the roof of the mouth. In many reptiles (including birds), it fuses to the endochondral (cartilage-derived ...
is fused, the joint between the skull and the lower jaws is anterior to level of the
occipital condyles The occipital condyles are undersurface protuberances of the occipital bone in vertebrates, which function in articulation with the superior facets of the Atlas (anatomy), atlas vertebra. The condyles are oval or reniform (kidney-shaped) in shape ...
, the neomorphic bone forms most of the border of the posttemporal fenestra, the paroccipital process is strongly deflected downwards, the basal tubera of the basisphenoid are wing-like in shape and expanded backwards and downwards, the
mandibular symphysis In human anatomy, the facial skeleton of the skull the external surface of the mandible is marked in the median line by a faint ridge, indicating the mandibular symphysis (Latin: ''symphysis menti'') or line of junction where the two lateral ha ...
(connection of the two halves of the lower jaw) is elongated to over half the length of the tooth row, and the
splenial The splenial is a small bone in the lower jaw of reptile Reptiles, as commonly defined, are a group of tetrapods with an ectothermic metabolism and Amniotic egg, amniotic development. Living traditional reptiles comprise four Order (biology ...
bone strongly intervenes in the mandibular symphysis.


Internal cranial anatomy

The
braincase In human anatomy, the neurocranium, also known as the braincase, brainpan, brain-pan, or brainbox, is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calv ...
of ''Champsosaurus'' is poorly ossified at the front of the skull (anterior), but is well ossified in the rear (posterior) similar to other diapsids. The cranial endocast (space occupied by the brain in the
cranial vault The cranial vault is the space in the skull within the neurocranium, occupied by the brain. Development In humans, the cranial vault is imperfectly composed in newborns, to allow the large human head to pass through the birth canal. During bir ...
) is similar to that of basal archosauromorphs, being proportionally narrow in both dorsoventral and lateral axes, with an enlarged
pineal body The pineal gland (also known as the pineal body or epiphysis cerebri) is a small endocrine gland in the brain of most vertebrates. It produces melatonin, a serotonin-derived hormone, which modulates sleep patterns following the diurnal cycles. ...
and
olfactory bulb The olfactory bulb (Latin: ''bulbus olfactorius'') is a neural structure of the vertebrate forebrain involved in olfaction, the sense of smell. It sends olfactory information to be further processed in the amygdala, the orbitofrontal cortex (OF ...
s. The optic lobes and flocculi are small in size, indicating only average vision ability at best. The olfactory chambers of the nasal passages and olfactory stalks of the braincase are reasonably large, indicating that ''Champsosaurus'' probably had good
olfactory The sense of smell, or olfaction, is the special sense through which smells (or odors) are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste. In humans, it ...
capabilities (sense of smell). The nasal passages lack bony turbinates. The
semicircular canals The semicircular canals are three semicircular interconnected tubes located in the innermost part of each ear, the inner ear. The three canals are the lateral, anterior and posterior semicircular canals. They are the part of the bony labyrinth, ...
are most similar to those of other aquatic reptiles. The expansion of the sacculus indicates that ''Champsosaurus'' likely had an increased sensitivity to low frequency sounds and vibrations. The absence of an
otic notch Otic notches are invaginations in the posterior margin of the skull roof, one behind each orbit. Otic notches are one of the features lost in the evolution of amniotes from their tetrapod ancestors. The notches have been interpreted as part of an ...
indicates that ''Champsosaurus'' lacked a tympanum, and probably had a poor ability to detect airborne sounds.


Teeth

''Champsosaurus'', like many of its fellow neochoristoderes, features teeth with striated enamel of the tooth crown with enamel infolding at the base. Anterior teeth are typically sharper and more slender than posterior teeth. Like other choristoderes, ''Champsosaurus'' possessed palatal teeth (teeth present on the bones of the roof of the mouth), with longitudinal rows present on the pterygoid,
palatine A palatine or palatinus (Latin; : ''palatini''; cf. derivative spellings below) is a high-level official attached to imperial or royal courts in Europe since Roman Empire, Roman times.
and vomer, alongside a small row on the flange of the pterygoid. The palatine teeth of ''Champsosaurus'' are located on raised platforms of bone, though the wideness of the platforms, the sharpness and orientation of teeth vary between species. The orientation of the teeth varies in the jaw, with the posterior teeth being orientated backward. The palatal teeth, likely in combination with a fleshy tongue probably aided in gripping and swallowing prey.


Skin

Skin impressions of ''Champsosaurus'' have been reported. They consist of small (0.6-0.1 mm) pustulate and rhomboid scales, with the largest scales being located on the lateral sides of the body, decreasing in size dorsally, no
osteoderm Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, temnospondyls (extinct amph ...
s were present.


Classification

''Champsosaurus'' belongs to the Neochoristodera, a clade within Choristodera, the members of which are characterised by elongated snouts and expanded temporal arches. The group first appeared during the Early Cretaceous in Asia, and are suggested to have evolved in the regional absence of aquatic crocodyliformes. While Neochoristodera is a well supported grouping, the relationships of the members of the group to each other are uncertain, with the clade having been recovered as a polytomy in recent analyses. Phylogeny of Choristodera after Dong and colleagues (2020).


Paleobiology

''Champsosaurus'' is thought to have been highly specialised for aquatic life. Erickson 1985 suggested that the expanded temporal arches, which likely anchored powerful jaw muscles, and elongated snout allowed ''Champsosaurus'' to prey on fish akin to modern gharials, with these adaptions allowing rapid movement of the head and jaws for prey capture. A study in 2021 found that the middle and posterior neck vertebrae of ''Champsosaurus'' were adapted for lateral movement, and that ''Champsosaurus'' may have fed by laterally sweeping its head, using its slender jaws to grab individual fish from shoals, akin to how modern gharials feed. The mechanism of head movement is different from that of gharials, where the lateral movement occurs at the head-neck joint. It is unlikely that ''Champsosaurus'' fed by inertial feeding (where the prey is temporarily let go and the head moved forwards in order to force the prey deeper into the throat), but that the prey was moved down the throat by the tongue in combination with the palatal dentition. Erickson 1985 proposed that the position of the nostrils at the front of the snout allowed ''Champsosaurus'' to spend large amounts of time at the bottom of water bodies, with the head being angled upwards to allow the snout to act like a snorkel when the animal needed to breathe. However, later studies suggested that the neck vertebrae of ''Champsosaurus'' only had a limited ability to flex upwards. ''Champsosaurus'' co-existed with similarly sized aquatic
crocodilia Crocodilia () is an order of semiaquatic, predatory reptiles that are known as crocodilians. They first appeared during the Late Cretaceous and are the closest living relatives of birds. Crocodilians are a type of crocodylomorph pseudosuchia ...
ns and at some Paleocene localities with fellow neochoristodere '' Simoedosaurus'', though in assemblages where ''Champsosaurus'' occurs longirostrine (long snouted) gharial-like crocodilians are absent, suggesting that there was
niche differentiation In ecology, a niche is the match of a species to a specific environmental condition. Three variants of ecological niche are described by It describes how an organism or population responds to the distribution of resources and competitors (for e ...
. Previously, two species of ''Champsosaurus'' were identified from the Tullock Formation in
Montana Montana ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Idaho to the west, North Dakota to the east, South Dakota to the southeast, Wyoming to the south, an ...
. However, these differences are now thought to be
sexually dimorphic Sexual dimorphism is the condition where sexes of the same species exhibit different Morphology (biology), morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecy, di ...
, with presumed females possessing robust limb bones. Non-deformation related fusion of the sacral vertebrae is also observed in specimens with robust limb bones. These are hypothesised to be related to breeding behaviour, with the more robust limb bones and fused sacrals of the females allowing them to move themselves onto land to lay eggs.


See also

* Tullock Formation *
Hell Creek Formation The Hell Creek Formation is an intensively studied division of mostly Upper Cretaceous and some lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana. The Formation (stratigraphy), formation s ...
* Paleontology in Montana


References

{{Taxonbar, from=Q860015 Paleontology in Alberta Fossils of Canada Choristodera Prehistoric marine reptiles Prehistoric reptile genera Maastrichtian genera Campanian genus first appearances Late Cretaceous reptiles of Europe Paleocene reptiles of Europe Late Cretaceous reptiles of North America Paleocene reptiles of North America Taxa named by Edward Drinker Cope Fossil taxa described in 1877