The anatomy of the dermatocranium and mandible of Cacops aspidephorus Williston, 1910 (Temnospondyli: Dissorophidae), from the Lower Permian of Texas

ABSTRACT

For the first time, the cranial suture pattern for the type species of Cacops, C. aspidephorus, is described in detail. A majority of sutures, including the lower jaw, the skull roof, and the palate, are now known in detail, although details are still lacking for the posterior skull table. Notable new information about C. aspidephorus includes the presence of a lateral exposure of the palatine (LEP), a lateral exposure of the ectopterygoid (LEE) that fuses with the jugal with growth, and a subtympanic flange composed mostly of the supratemporal. Cacops aspidephorus is very similar to C. morrisi, but differences, including a fully closed otic notch in C. aspidephorus, are sufficient to maintain both as distinct species. Uniquely, C. aspidephorus shows palatal dentition of the same size as the marginal dentition, but it remains to be seen whether this is a widespread feature or ontogenetically transient. These new data will finally permit the inclusion of this iconic taxon, described over 100 years ago, into larger-scale phylogenies of dissorophoid and temnospondyl relationships.

ACKNOWLEDGMENTS

We thank G. Johnston, Western University of Health Sciences, for taking the radiograph; P. Gajda, University of Calgary, for photography and photogrammetry; and N. Ken-Wong, University of Toronto at Mississauga, for preparation and early drawing drafts. For access to specimens, we thank W. Simpson and the late J. Bolt (FMNH) and P. Gingerich, M. Friedman, and the late G. Gunnell (UMMP). We thank J.-S. Steyer and an anonymous reviewer for comments that improved the manuscript. This research was supported by Natural Sciences and Engineering Council of Canada (NSERC) Discovery Grants to R.R.R. and J.S.A.