Gee et al.—New early Permian vertebrate locality 92(6):1092–1106


Williston (1909b, p. 129, pl. 4), who described much larger specimens. Scincosaurus is known only from the Carboniferous of Europe, lacks a dorsal exposure of the quadratojugal, and the posterior margin of the skull roof is squared-off, rather than markedly indented as in diplocaulines and in this specimen (Milner and Ruta, 2009). Diceratosaurus is known only from the Carboniferous of Ohio, features more equant postparietals, and lacks a dorsal exposure of the quadratojugal (Bossy and Milner, 1998). Three neural spines are exposed dorsally in articulation with the skull, but they are only partially exposed and are uninformative for improving the resolution of the taxonomic identification.


Family Diplocaulidae Cope, 1881 Subfamily Diplocaulinae Cope, 1881 Diplocaulinae gen. indet. sp. indet. Figure 4.2, 4.3


Description.—An indeterminate diplocauline is represented by a nearly complete skull with articulated mandible on which the small indeterminate tetrapod material is preserved (TMM 43628-8); this was collected from the D2 site. Major features such as the orbits are identifiable, as are the posterior and lateral skull margins; the anteriormost portion of the snout appears to have been lost. The specimen can be referred to the Diplocau- linae based on an unpaired frontal that forms the entirety of the interorbital region (Fig. 4.2), but further taxonomic resolution is not possible because the palate is obscured by the mandible, most of the cranial sutures are obscured due to weathering and the overlying small-bodied tetrapod, and there is damage to the characteristically elongated tabular horns.


Genus Diplocaulus Cope, 1877a


Type species.—Diplocaulus salamandroides Cope, 1877a from the Bond Formation of Illinois, by original designation.


cf. Diplocaulus sp. indet. Figure 6


Description.—A small skull with articulated mandible (TMM 43628-9) was collected from the D2 site. The skull is broken in several places, but the fragments remain in relative articulation, and much of the palate is well exposed from the exoccipitals to the left vomer (Fig. 6). The skull would have been subequal in length and width and does not appear to have had well- developed tabular horns with a strong posterolateral orientation. The posterior midline elements (parietal, postparietal) are pro- portionately short transversely relative to those of large-bodied individuals. The unpaired frontal (a diplocauline synapomor- phy) constitutes the entirety of the interorbital region. A left postorbital is tentatively identified, separating it from Per- onedon Olson, 1970 (Haglund, 1977). The proportions of the skull roof conform favorably with those of a small-bodied spe- cimen of Diplocaulus sp. that was briefly described by Chaney et al. (2005) and the early stages of a detailed ontogenetic series described by Olson (1951a). In palatal view (Fig. 6.3, 6.4), the broad basal plate of the parasphenoid and the rectangular cul- triform process are well preserved, as are several of the openings


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Figure 6. cf. Diplocaulus sp. indet., juvenile specimen (TMM 43628-9): (1) photograph in dorsal profile; (2) illustration of Figure 6.1; (3) photograph in ventral profile; (4) illustration of Figure 6.3. ang, angular; cp, cultriform process; eo, exoccipital; f, frontal; fm, foramen magnum; ipv, interpterygoid vacuity; j, jugal; p, parietal; pf, prefrontal; po, postorbital; pof, postfrontal; pp, postparietal; ppf, postpterygoid fossa; psp, parasphenoid; pt, pterygoid; qj, quadratojugal; sp, splenial; sq, squamosal; stf, subtemporal fenestra; v, vomer. Scale bar=1 cm.


on the palate (e.g., subtemporal fossa, interpterygoid vacuity). The mandibles remain mostly articulated, although sutures are not clearly defined. The specimen is not sufficiently preserved to confidently


separate the specimen from the closely related Diploceraspis Beerbower, 1963 (unknown from Texas) based either on phylogenetic characters (e.g., Germain, 2010) or on informal differentiation (e.g., Beerbower, 1963; May and Hall, 2016). The immaturity of this specimen further confounds efforts to identify the subtle distinctions between them, and the referral is based on the indistinguishable nature from juvenile Diplocaulus and the abundance of Diplocaulus in Texas compared to the absence of Diploceraspis.


Remarks.—Differences between the various, highly-conserved species of Diplocaulus are relatively minor and characterized only for large-bodied specimens. Furthermore, Olson (1952a, p. 166) distinguished the two species that are found in the Vale Formation, D. magnicornis Cope, 1882 (Arroyo Formation and lower Vale) and D. recurvatus Olson, 1952a (upper Vale), only by the “frequency of occurrence of the recurved horn,” which is not as developed in immature individuals and not well-preserved in these specimens, inhibiting further taxonomic resolution.


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