Abstract
The early Permian cave system in the Dolese Brothers Limestone Quarry near Richards Spur, Oklahoma represents a unique depositional environment that has been interpreted as preserving an upland biota. The quarry and the region around it represent Paleozoic cave systems that underwent periods of flooding not unlike present-day conditions that are commonly associated with monsoonal episodes. The Richards Spur locality is particularly rich in captorhinid eureptiles which represent one of the earliest reptilian clades to have evolved a specialized dentition. Although the multiple-tooth rowed Captorhinus aguti is the most abundant captorhinid at Richards Spur, at least one other species has been described (Captorhinus magnus) and assigned to the same genus, but five other captorhinid taxa have also been found. We describe a new member of the genus Captorhinus (Captorhinus kieranensis) and explore details of the dental anatomy against the two other members of the genus at Richards Spur, C. aguti and C. magnus, as well as with a member of the genus not presently known from Richards Spur (C. laticeps). Findings suggest that the nature of the ogival dentition described previously as a synapomorphy uniting C. aguti with C. magnus is not supported and we propose a more informative method for differentiating among dental characters within the clade. The discovery of a new species of Captorhinus provides additional evidence for captorhinid taxic diversity at Richards Spur and is supportive of niche partitioning, which is likely associated with reducing intra-specific competition within the clade. Finally, we argue that the captorhinid fossils at Richards Spur likely includes one additional, currently undescribed multiple-tooth rowed form, that renders the current practice of assigning disarticulated cranial remains, specifically dental fragments, to the species C. aguti problematic.
Highlights
The genus Captorhinus and the more inclusive Captorhinomorpha presents one of the most widely recognized Paleozoic amniote clades
We describe a new member of the genus Captorhinus (Captorhinus kierani) and explore details of the dental anatomy against the two other members of the genus at Richards Spur, C. aguti and C. magnus, as well as with a member of the genus not presently known from Richards Spur (Captorhinus laticeps)
Aside from the difference in the angle formed by the frontals, there are no other notable differences between Captorhinus aguti, Captorhinus magnus and Captorhinus kierani that can be associated with the skull table
Summary
The genus Captorhinus and the more inclusive Captorhinomorpha presents one of the most widely recognized Paleozoic amniote clades. Not presently known from Richards Spur, there is one other species that has been assigned to the genus Captorhinus, which is known from the geologically older McCann Quarry locality in Oklahoma and from the Mitchell Creek locality in Texas This additional Captorhinus material, as assigned by Heaton (1979), represents yet another single-tooth rowed species, which was part of Heaton’s (1979) systematic study of captorhinids from outside of the Richards Spur locality. Most of the other Permian localities, where captorhinomorph material is known, are restricted in their composition to encompassing either basal or advanced forms, the Richards Spur locality, and notably the fossiliferous pocket discovered in 2005, contains a mixed faunal assemblage, which is supportive of a taxonomically diverse locality The nature of this diversity, which is predominantly due to a heteromorphic dentition across the various taxa, has been speculated to be representative of resource partitioning among Permian captorhinomorphs at Richards Spur (Modesto et al, 2018). It is important to recognize that this diversity is most obviously manifested in the dental morphology, which contrasts with the rather conservative nature of the gross skull anatomy
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