Db_abstract

Vision characteristics of Coelophysis bauri based on sclerotic ring, orbit, and skull morphology

Documents the eye and skull structure of Coelophysis and concludes that the dinosaur was a visual hunter.

Item Details

Abstract

New Mexico Museum of Natural History specimen P-42200 is a gracile (probably female) morph of Coelophysis bauri from the Whitaker Quarry in the Apachean-age Rock Point Formation of the Chinle Group of north-central New Mexico. This specimen preserves the first documented complete sclerotic ring in C. bauri. The skull length is 123 mm, which places it in the large juvenile to small adult range.


We corrected the skull, orbit, and sclerotic ring for slight taphonomic distortion, reconstructed the ring, and allometrically projected the specimen to adult size. The ring and orbit morphology were analyzed and compared to extant lizard and bird outgroups as well as the ornithischian dinosaur, Hypsilophodon foxii and the basal bird, Archaeopteryx. The bird outgroup comprised 18 species representing 10 orders; the lizards, 9 species from 6 families. Relative importance of vision to all the study animals was estimated by plotting orbit size versus skull size. In this regard, Coelophysis ranks with most of the birds and well above most lizards. Eye morphology was assessed in two ways: ring area versus orbit area, and cross sectional shape of the ring (indicative of eye shape) were both compared to the outgroups. In both cases the eyes of Coelophysis are most similar to those of Falconiformes (hawks and eagles), in which eye shape is globose and accommodation power is very high. Night vision capability was assessed by comparing cornea size to orbit size. Coelophysis shows poor nocturnal capability, similar to most lizards and nonraptorial birds. Night vision in Hypsilophodon and Archaeopteryx rated approximately equal to the Falconiformes. We note that in Coelophysis poor night vision probably indicates a round, as opposed to slit pupil. Skull and orbit measurements indicated an overlap in the left and right visual fields of 26 (minimum) to 40 (maximum) degrees, depending on the shape of the cornea. We conclude that Coelophysis was a diurnal, visually oriented predator and that higher power of accommodation and good frontal binocular vision is extremely probable.