THE CRANIAL ANATOMY OF THE CAPTORHINID REPTILE LABIDOSAURKOS-MEACHAMIFROM THE LOWER PERMIAN OF OKLAHOMA

Study Of Labidosaurikos meachami, from the Lower Permian Hennessey For mation (Sumner Group) of north-central Oklahoma, reveals the presence of over thirty new cranial characters not present in single-tooth-rowe d captorhinids and Captorhinus aguti. However, it is uncertain if thes e new characters represent autapomorphies of L. meachami because the s kulls of all other large, multiple-rowed captorhinids are poorly known ; many of these characters may instead diagnose subclades of multiple- tooth-rowed taxa within Captorhinidae. A suite of skeletal features, i ncluding the presence of tooth plates, prominent tooth wear, and the m orphology of the skull roof, suggests strongly that L. meachami was he rbivorous. Propaliny was probably a significant component of the feedi ng mechanism. Phylogenetic analysis of the interrelationships of the w ell known North American captorhinids indicates that Labidosaurikos me achami is more closely related to the large, single-rowed Labidasaurus hamatus than it is to Captorhinus aguti. The sister-group relationshi p between Labinosaurikos meachami and Labidosaurus hamatus is supporte d by fifteen synapomorphies, and is the most robust clade within Capto rhinidae. This relationship supports the hypothesis that multiple rows of teeth evolved independently at least twice among captorhinids. Eoc aptorhinus laticeps, recently assigned to the genus Captorhinus as 'Ca ptorhinus sp.', is formally recognized as Captorhinus laticeps (new co mbination). The phylogenetic analysis indicates that C. laticeps and C . aguti form a clade, identified here as Captorhinus, that is the sist er group of the L. meachami-L. hamatus clade.