Colobomycter pholeter from the Lower Permian of Oklahoma: a parareptile, not a protorothyridid

Abstract

ABSTRACT Reexamination of the holotype of Colobomycter pholeter and description of a new specimen, from a Lower Permian fissure fill near Richards Spur, Oklahoma, reveals that this small enigmatic reptile is not the youngest known protorothyridid, but instead is one of the earliest parareptiles. Parareptilian apomorphies that are present include an anterior lateral maxillary foramen, a transversely broad antorbital buttress formed by the prefrontal and lacrimai, and a single median posterior emargination of the skull roof. The last feature is recognized for the first time as a parareptilian synapomorphy. The anterior lateral maxillary foramen of parareptiles is confirmed to be the lateral egress of a canal that opens into the nasal chamber. Colobomycter is the sister taxon of the parareptile Acleistorhinus pteroticus, known from the Lower Permian South Grandfield locality of Oklahoma. Together these two taxa comprise Acleistorhinidae, the oldest known parareptilian clade. The group is diagnosed by two synapomorphies: (1) the largest tooth is positioned far anteriorly on the maxilla; and (2) cranial ornamentation comprises sparse, shallow circular dimples.