DOI: 10.15468/m7ujdp
title: New information on the cranial and postcranial anatomy of the early synapsid Ianthodon schultzei (Sphenacomorpha: Sphenacodontia), and its evolutionary significance

description: This dataset contains the digitized treatments in Plazi based on the original journal article Spindler, F., Scott, D., Reisz, R. R. (2015): New information on the cranial and postcranial anatomy of the early synapsid Ianthodon schultzei (Sphenacomorpha: Sphenacodontia), and its evolutionary significance. Fossil Record 18 (1): 17-30, DOI: 10.5194/fr-18-17-2015, URL: http://dx.doi.org/10.5194/fr-18-17-2015Abstract. Newly identified material belonging to the holotype specimen of Ianthodon schultzei substantially increases our knowledge of this poorly known basal sphenacodont synapsid from the fossil site in Garnett, Kansas (Missourian, Late Pennsylvanian). The original description, based on a partial dermal skull roof, is augmented with information on the palate and braincase, together with data on the mandible and a few postcranial elements. The known skeletal morphology resembles that of Haptodus garnettensis, another synapsid taxon known from this locality, but with fewer marginal, distinctly recurved teeth and smaller teeth on the transverse flange of the pterygoid. Although recognizing that the holotype and only known specimen represents a juvenile individual, Ianthodon appears to reflect a more basal sphenacodontian condition than H. garnettensis. A restricted phylogenetic analysis based on previous work and newly scored characters for Ianthodon, Cutleria and Pantelosaurus supports this hypothesis. The Garnett locality appears to preserve an assemblage of synapsids (Haptodus, Ianthasaurus, Ianthodon) that are close to the base of the large clade that includes Edaphosauridae and Sphenacodontia, suggesting that an initial diversification of this clade occurred well within the Carboniferous Period.1 IntroductionThe Garnett locality in Kansas has produced one of the best known Missourian-age continental fossil assemblages, including plants and pollen, invertebrates, fishes, amphibians, and amniotes. Its geology and the vertebrate biota have been summarized by Reisz et al. (1982) and Kissel and Reisz (2004). The tetrapod assemblage is characterized by the presence of numerous skeletons of the oldest known diapsid reptile Petrolacosaurus (Reisz, 1977, 1981) and multiple skeletons of several synapsids, including an undescribed ophiacodontid, an undescribed sphenacodontian, the small edaphosaurid Ianthasaurus hardestiorum (Reisz and Berman, 1986; Modesto and Reisz, 1990; Mazierski and Reisz, 2010) and the basal sphenacodontian Haptodus garnettensis (Currie, 1977; Laurin, 1993). Although originally identified as a synapsid, the precise identity of Xyrospondylus ecordi, known only from the holotype dorsal vertebra (KUVP 9963, University of Kansas Museum of Natural History, Lawrence, KS), remains uncertain (Reisz, 1986). The diversity of synapsids at this site recently increased with the description of a single partial skull of Ianthodon schultzei (Kissel and Reisz, 2004). The synapsid assemblage at Garnett seems to document the earliest known stages of eupelycosaurian evolution, and the taxic diversity preserved at this locality suggests that a detailed reexamination of all known materials from this locality may provide new insights into patterns of diversification within this important clade. Ianthodon schultzei is a critical component of this reexamination.The holotype of Ianthodon schultzei (Kissel and Reisz, 2004) was originally separated from a block that apparently also contained the remains of both Petrolacosaurus and Haptodus. Reexamination and additional preparation of the slabs, including the skull described originally, has revealed more skeletal material that can be confidently attributed to Ianthodon. We identify the synapsid material on the entire block as a single disarticulated partial skeleton of I. schultzei, accompanied by a partial Petrolacosaurus skeleton, in contrast with the previous mistaken interpretation of certain elements as belonging to Haptodus garnettensis (Kissel and Reisz, 2004). This identification is based largely on a detailed reevaluation of the available anatomical information. However, our interpretation is also supported by the following evidence: (1) there is no duplication of any of the non- Petrolacosaurus elements; (2) there is no discrepancy in size or stage of ossification among the cranial or postcranial elements that are not attributed to Petrolacosaurus; (3) it is unlikely that two synapsid skeletons of the same size and ontogenetic stage would be present without any overlap between the preserved elements. The assignment of the dentary to Haptodus garnettensis is questionable on anatomical grounds. After additional preparation and study of all known specimens from the locality, the surface texture characteristics used to identify the elements on this block as Haptodus garnettensis, as suggested by Kissel and Reisz (2004, p. 412), are rejected. Here, we provide a comprehensive redescription of I. schultzei and discuss the phylogenetic implications of this new data for sphenacodont evolution.The following instituional codes are used in this paper: FO – University of Toronto Mississauga Fossil; KUVP – University of Kansas Museum of Natural History, Lawrence, KS; RM – Redpath Museum, Montreal; ROM – Royal Ontario Museum, Toronto; RS and SS – Sächsisches Landesamt für Umwelt, Landwirtschaft und Geologie, Freiberg (geological survey).