Champsosaurus

Champsosaurus Temporal range:
C. natator skeleton
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	†Choristodera
Suborder:	†Neochoristodera
Genus:	†Champsosaurus Cope, 1877
Species
C. albertensis Parks, 1927 C. ambulator Brown, 1905 C. annectens Cope, 1876 (nomen dubium) (type) C. dolloi Sigogneau-Russell, 1979 C. gigas Erickson, 1972 C. laramiensis Brown, 1905 C. lindoei Gao & Fox, 1998 C. natator Parks, 1933 C. tenuis Erickson, 1981
Synonyms
C. australis Cope, 1881 [nomen vanum] C. brevicollis Cope, 1876 [nomen vanum] C. inelegans Parks, 1933 C. inflatus Parks, 1933 C. profundus Cope, 1876 [nomen vanum] C. puercensis Cope, 1882 [nomen vanum] C. saponensis Cope, 1882 [nomen vanum]

Champsosaurus is an extinct genus of diapsid reptiles belonging to the order Choristodera, that existed in the Late Cretaceous and Paleogene periods. It consists of seven species: C. albertensis, C. ambulator, C. gigas, C. laramiensis, C. lindoei, C. natator, and C. tenuis. The name Champsosaurus is thought to come from χαμψαι [champsai] (said in an Ancient Greek source to be an Egyptian word for "crocodiles"), and σαύρος [sauros] (Greek for "lizard"). The largest species, C. gigas, grew to 3–3.5 m (10–12 ft) in length.

Discovery

Its fossils have been found in North America (Alberta, Saskatchewan, Montana, New Mexico, Texas, Colorado, and Wyoming) and Europe (Belgium and France), dating from the Upper Cretaceous to the mid Eocene.

Champsosaurus remains have also been found in the Hell Creek Formation, although most of these remains consist of isolated, fragmented postcranial elements.

Neonate sized Champsosaurus have been documented in the scientific literature.

Description

Restoration of C. natator

C. laramiensis

It grew to about 1.50 m (5 ft) long, though C. gigas, the largest species, reached 3–3.5 m (10–12 ft) in length. Champsosaurus vaguely resembled a gharial and, like gharials, it was primarily aquatic, catching fish with its long, tooth-lined jaws. It probably swam with lateral body movements, pinning its limbs against its body to increase its streamline, just like crocodiles and the marine iguana. Behind the eyes, Champsosaurus's skull was very wide, where powerful jaw muscles were attached. Due to specializations in hip and limb anatomy, only females could come ashore to lay eggs, while males primarily lived in water.

Anatomy

A skeleton of Champsosaurus reveals a flattened skull in the dorsoventral region, implicating adaptions to aquatic life. The skeleton featured a well-developed, intact secondary palate. Additionally, Champsosaurus is thought to have had a relatively rigid ribcage given the presence of a complete post-cranial skeleton. Internal dermal bones (gastralia) function with this ribcage to regulate the volume of the pleural cavity, effectively controlling the animal's center of gravity for underwater motion.

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 segments.

Ear bones

Endocast studies on champsosaurus suggest that the ear bones were internal, and located near the base of the skull. They are functionally most comparable to those of turtles and other aquatic reptiles, and seem more similar to those of archosauromorphs.

Sexual dimorphism

Previously, two species of Champsosaurus were identified from the Tullock formation in Montana. Because of their nesting behavior on land, it is believed that female champsosaurs were better adapted to terrestrial life, and this is seen in limb morphology between males and females. Sacral fusion is featured in discovered specimens, with of without deformations alike. The existence of a non-deformational development of sacral fusion – coupled with the presence of more robust limb bones in some discovered individuals – is thought to be a result of variation between individuals within the species, with the sturdier limbs belonging to females.

Metabolism

Nasal conchae have in found in neochoristoderes, suggesting that to some extent, they were able to regulate their body temperature. This is particularly relevant given the presence on Champsosaurus in cold regions, such as the high Arctic. Champsosaurus species were able to withstand areas of low temperatures, and were shown to reach a latitudinal range even into the high Arctic region. Due to the Paleocene occurrence of Champsosaurus, paleontologists infer a decreased annual temperature, resulting in a southward shift of habitat over 10° in latitude. Presumably due to cold-tolerance, their species greatly surpassed local crocodilians, which became a distinguishing characteristic of both.

See also

• Tullock Formation
• Hell Creek Formation
• Paleontology in Montana