Captorhinus

''Captorhinus'' (from , 'to gulp down' and , 'nose') is an extinct genus of captorhinid reptiles that lived during the Permian period. Its remains are known from North America (Oklahoma, Texas) and possibly South America.

Description

While there are several forms of ''Captorhinus'', there are three main species that are the best known. The previously mentioned ''Captorhinus aguti'' is the type species of ''Captorhinus'', but there is also a fair amount of material collected on ''Captorhinus magnus'' and ''Captorhinus laticeps''.

The most distinguishable trait of ''Captorhinus'' is its namesake: the hooking of the snout from prominent ventral angulation of the premaxillary process. Other notable characteristics include the dorsally positioned alary process of the jugal on the medial surface and flushed with the orbital margin, the retroarticular process longer anteroposteriorly than broad, and the anteriormost dentary tooth strongly procumbent. The posterior teeth are either chisel-shaped or ogival. Until the late 1990s, ''Captorhinus'' was diagnosed by the presence of multiple rows of marginal teeth on the maxillary and dentary bones. However, single-rowed captorhinid elements have been discovered, proving this hypothesis incorrect.Kissel 2002

''Captorhinus aguti''

''C. aguti'' was a small captorhinid reptile that lived during the Permian Period 286 MYA to 245 MYA when the continents were still connected as Pangea. An abundance of fossils have been found in Oklahoma, and Texas, including a skull, hindlimb bones, spinal vertebra, ribs, and forelimb bones. The entire skeleton of ''C. aguti'' resembles a modern lizard.
Although a subfamily of Captorhinidae, Moradisaurinae, also possessed multiple-tooth-rows, the best-known type species ''Captorhinus aguti'' clearly acquired multiple-rowed-teeth independently. In contrast to the teeth rows in moradisaurines, the ''C. aguti'' rows are oriented obliquely to the margins, where each row is followed posterolaterally by the next one.Fox 1966 The toothed areas of the maxilla and dentary are broader in ''C. aguti'' than in single-tooth-rowed captorhinids. ''C. aguti'' likely practiced lateralized feeding, as enamel on the teeth of the upper and lower right jaws was more worn down than on the left side.

The vertebral structure in ''C. aguti'' is that commonly possessed by primitive reptiles. The centra are amphicoelous and notochordal, with swollen, relatively massive neural arches. The vertebral column is differentiated into presacral, sacral, and postsacral or caudal vertebrae.

Similarly to extant reptiles, ''C. aguti'' has a functional “mesotarsal” joint. It divides the tarsus into a proximal and distal unit, where the centrale is linked mechanically to the proximal (astragalus-calcaneum) unit. The increased flexibility due to this multiple-jointed arrangement allowed for the articulations between the centrale and first three distal tarsals on the medial side of the mesotarsal joint to have mechanical independence from the lateral articulation between the astragalus-calcaneum and the fourth and fifth distal tarsals. This is almost certainly closely correlated with the primitive sprawling step cycle. Due to the shape of the distal femoral articulation, ''Captorhinus aguti'' would have had little capacity to compensate for lateral movement of the femur.

Preserved skin is known from the neck of the species, which preserves corneous epidermal bands.

''Captorhinus magnus''

''Captorhinus magnus'' has thus far been identified from only the Richards Spur locality in Oklahoma, a site that also produced the remains of ''C. aguti''. Fossils of ''C. magnus'' are found predominately in the deeper regions of the fissure complex, whereas in the upper, younger sediments of the fillings, ''C. magnus'' remains are extremely rare. This suggests the ecological replacement of ''C. magnus'' by the smaller, multiple-rowed ''C. aguti'' during the Early Permian.

The skeletal elements of ''Captorhinus magnus'' possess a nearly identical morphology to those elements of ''Captorhinus aguti'', with the lone exception of the size difference. ''Captorhinus magnus'' averaged about twice as large as ''C. aguti.'' Another important difference between the two species is that the teeth are arranged in a single row. ''Captorhinus magnus'' possesses ogival check teeth, where the distal tips of the teeth exhibit a triangular shape when viewed in anterior view. Unlike ''C. aguti'', the femur of ''C. magnus'' possesses a concave proximal articular surface in both immature and mature individuals. This allows for distinction between similar-sized femora of ''C. aguti'' and ''C. magnus'', regardless of the ontogenetic stage of the individuals preserved. Without the presence of the femur or a tooth-bearing element, it would prove difficult to distinguish between ''C. magnus'' and ''C. aguti'', although the two can likely be differentiated with size as the sole criterion.

''Captorhinus laticeps''

''C. laticeps'' is distinguished from ''C. aguti'' by the lack of multiple tooth rows, but is very similar in all other aspects. ''Captorhinus laticeps'' is considerably smaller than ''C. magnus'', and possesses chisel-shaped teeth instead of ogival teeth on the posterior portion of the maxilla and dentary.

Other remains

Possible remains of ''Captorhinus'' have been reported from the Pedra de Fogo Formation, Piauí, Brazil, but they are fragmentary and cannot be assigned to the genus with confidence.

History of discovery

In 1882, Edward Cope described a fragmentary skull from the Lower Permian of Texas collected by W. F. Cummins at Coffee Creek as ''Ectocynodon aguti''. The name had then been revised several times by different paleontologists as more genera were discovered. In 1911, paleontologist Ermine Cowles Case

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