Cteniogenys

Cteniogenys is a genus of choristodere, a morphologically diverse group of aquatic reptiles. It had a wide distribution temporally and geographically, from the Middle Jurassic and Late Jurassic of western Europe, to the Late Jurassic-age Morrison Formation of western North America, to the Late Cretaceous of Alberta, Canada. The genus was named in 1928 by Charles W. Gilmore, from a lower jaw collected during the late 19th century by Othniel Charles Marsh's workers at Como Bluff. He tentatively described the genus as a lizard, noting that it could instead be a frog. New material from Europe permitted Susan Evans to reevaluate it as an early choristodere in 1989. To date it is only known from fragmentary specimens. Morrison Formation Cteniogenys were 25 to 50 centimetres (9.8 to 19.7 in) long, and probably weighed less than 500 grams (1.1 lb). The skull of this genus was long and slender, and the jaws had numerous conical teeth. Cteniogenys in the Morrison probably fed on insects and small fish. It is mostly known from freshwater sites (rivers and ponds), and is a rare find in the formation (only 60 specimens out of over 2,800 total vertebrate specimens known from the formation), mostly known from northern outcrops (particularly Wyoming); this may reflect a preservation bias against small animals in terrestrial settings, rather than an accurate reflection of Cteniogenys populations in the Morrison. The Late Cretaceous record of this genus consists of a handful of skull and jaw fragments from the Oldman Formation and Dinosaur Park Formation. Given the long gap in time, these may represent a different, as-yet undetermined genus.