Abstract
The early Permian Richards Spur locality of Oklahoma has produced abundant material of numerous terrestrial fossil tetrapods, including various “microsaurs,” several of which are considered to belong to the clade Recumbirostra. We present a new partial skull of the recumbirostran “microsaur”Nannaroter mckinziei; through computed tomography (CT) analysis of both this new specimen and the holotype, we provide an updated description of the taxon. This new description provides novel information regarding several regions that could not be examined previously due to either being absent in the holotype or difficult to access. This includes missing and obscured aspects of the skull roof, braincase, lower jaw, and the palatal region. Furthermore, the new information obtained from this description was used to update phylogenetic character codings ofNannaroter, and a revised phylogenetic analysis was conducted. The results of this updated analysis are congruent with those of other recent phylogenetic analyses of recumbirostran “microsaurs.” This new information adds to the ever-growing body of early tetrapod CT data, which has been, and will continue to be, important in revealing details regarding early tetrapod anatomy, interrelationships, paleoecology, and evolution.
Highlights
“Microsauria” (Dawson, 1863) was considered to represent a diverse clade of small Palaeozoic terrestrial lepospondyl anamniotes found in North America and Europe, over the past few decades it has been proposed that the clade is not monophyletic but instead represents a polyphyletic assemblage (Anderson, 2001, 2007)
Ostodolepis, which forms the basis for the family-level name, was described from the Arroyo Formation of Texas by Williston (1913) on the basis of an articulated series of seven vertebrae, associated ribs, and scales that he ascribed to a new genus of reptile
Both the holotype and a new referred specimen were examined as part of this study, these specimens were obtained from the karst fissures that make up the cave system found at the early Permian (∼289–286 Ma) Richards Spur locality in Oklahoma, United States
Summary
“Microsauria” (Dawson, 1863) was considered to represent a diverse clade of small Palaeozoic terrestrial lepospondyl anamniotes found in North America and Europe, over the past few decades it has been proposed that the clade is not monophyletic but instead represents a polyphyletic assemblage (Anderson, 2001, 2007). Daly (1973) described a third taxon, Micraroter, from the South Grandfield locality in Oklahoma on the basis of a partial skull with an articulated jaw and an assortment of highly fragmentary cranial, mandibular, vertebral, and pectoral elements Another specimen (BPI 3839) from around the same area as the holotype of Ostodolepis was assigned to Micraroter by Carroll and Gaskill (1978) but demonstrates a few significant differences from the latter (e.g., fewer presacral vertebrae, stapedial foramen) as well as a number of more minor ones (e.g., prefrontal excluded from the narial opening) that cannot be excluded as the result of ontogeny. Another specimen (BPI 3839) from around the same area as the holotype of Ostodolepis was assigned to Micraroter by Carroll and Gaskill (1978) but demonstrates a few significant differences from the latter (e.g., fewer presacral vertebrae, stapedial foramen) as well as a number of more minor ones (e.g., prefrontal excluded from the narial opening) that cannot be excluded as the result of ontogeny. Schultze and Foreman (1981) maintained the taxonomic distinction of BPI 3839 from Micraroter, they did not formalize the former as a new taxon; their position has been maintained in recent publications concerning ostodolepids (e.g., Anderson et al, 2009; Henrici et al, 2011)
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