Thecachampsoides

''Eosuchus'' ("dawn crocodile") is an extinct genus of eusuchian crocodylomorph, traditionally regarded as a gavialoid crocodilian. It might have been among the most basal of all gavialoids, lying crownward of all other known members of the superfamily, including earlier putative members such as ''Thoracosaurus'' and ''Eothoracosaurus''. Fossils have been found from France as well as eastern North America in Maryland, Virginia, and New Jersey. The strata from which specimens have been found date back to the late Paleocene and early Eocene epochs.

Discovery

The name ''Eosuchus'' was first used in 1907 to describe a single specimen found from northern France near the Belgian border, assigned to the type species ''Eosuchus lerichei''.

A second species, ''Eosuchus minor'', was actually discovered earlier in 1870 by Othniel Charles Marsh, but was assigned to the genus ''Gavialis''. The ''Gavialis minor'' holotype specimen YPM 282 consisted of cranial fragments and isolated vertebrae found from the Manasquan Formation in Monmouth County, New Jersey, dating back to the Ypresian stage of the early Eocene. The species name ''minor'' refers to the relatively small estimated size of the animal, estimated at no more than 2 meters, when compared to other gavialoids such as the modern gharial, which can grow up to 5 meters in length. However, this species was later recognized as distinct from ''Gavialis'' on the basis of certain aspects of the known cranial material, in particular the large foramen aerum of the quadrate formed from the epithelial tube that connects the pneumatic chambers of the quadrate and articular. Another diagnostic feature thought to distinguish the species from ''Gavialis'' was the narrow interfenestral bar of the parietal bone that is relatively smooth and unsculptured when compared to other gavialoids such as ''Thoracosaurus''. The new generic name '' Thecachampsoides'' was proposed for the species ''G. minor'' in 1986. A close relationship between ''T. minor'' and ''Eosuchus lerichei'' was always evident, yet it was not until 2006 that the name ''Eosuchus'' was applied to the ''T. minor'' specimens, specifically on the basis of a fairly complete specimen called NJSM 15437 from the Vincetown Formation in New Jersey, of which there is a visibly exposed braincase which aids greatly in the taxonomic classification of the genus. The examination of specimens of ''Thecachampsoides minor'' with those of ''Eosuchus lerichei'' yielded many similarities between the two species, including the foramen aerum as well as other features such as a long nasal process between the premaxillae, dentary alveoli arranged in pairs, and a W-shaped basioccipital tuberosity. ''E. minor'' differs from ''E. lerichei'' on the basis of a noticeably wider nasal and