Acleistorhinidae is notable for being the oldest-known parareptilian clade. The family is diagnosed by the presence twosynapomorphies: (1) the largesttooth is located far anteriorly on themaxilla; and (2)cranial ornamentation consists of sparse and shallow circular dimples.[2]
Two specimens of acleistorhinids described from theRichards Spur fissure-fill locality inOklahoma have provided compelling evidence of the diet of acleistorhinids. One specimen,OMNH 73362, was later referred toDelorhynchus cifellii, a species named in 2014. The other specimen, OMNH 73364, has not been formally described. Fragments ofarthropodcuticles are present in between the manypalatal teeth of both skulls. The fragments in OMNH 73362 are thought to be the segments of anantenna, while the fragments in OMNH 73364 are thought to be part of acercus.[7]
In acleistorhinids, the marginal teeth, which are small and recurved, are suggestive of an insectivorous diet, as they probably were used for gripping and piercing arthropod cuticle. The denticulated palate, with three pairs of tooth fields and smaller teeth in between the fields, is seen as an adaptation for holding food in the oral cavity.[7]
The teeth, which possess cutting edges, may also have been suitable for a carnivorous diet in which vertebrate flesh may have been consumed.[8] It is possible that acleistorhinids would have preyed ontetrapods that were small enough to swallow whole.[7] It is likely that one acleistorhinid,Colobomycter pholeter, specialized either on invertebrates with hard cuticles or on small tetrapods.[9]
