Bourque—Middle–Late Miocene Kinosternon
inguinal buttress (Appendix 1: ch. 12) and position of the inguinal musk duct pore (Appendix 1: ch. 15) were not scored in the phylogenetic analysis because the states cannot be discerned in the holotype. Marginal 9 is preserved only on the right side of the
carapace. It is moderately heightened and not as tall as M10, but slightly taller than M8. The shape of the scute is obtusely angled and differs from Kinosternon pojoaque and the extant flavescens group in that it is not wave-shaped, that is, curved towards the posterior on the anterior half of the scute. In these attributes, the M9 compares well to Kinosternon integrum and the Kinosternon scorpioides complex. The crest of the M9 sulcus and the distal PLR3–4 sulcus are situated on the P8–9 suture. This is atypical for kinosternids and as such was tentatively included in the species diagnosis; however, it shares this with some specimens of the K. scorpioides complex examined including Kinosternon cruentatum. The M9 crest is anterior to the P8–9suturein K. pojoaque and most Kinosternon. In FAM 13822, PLR4 broadly overlaps the suprapygal, similar to the holotype of Kinosternon pannekollops. By contrast, PLR4 does not overlap the suprapygal in Kinosternon skullridgescens, and only slightly contacts the suprapygal in the paratype of K. pojoaque,FAM 13013. The holotype ofK. pojoaque, FAM12744 has an atypical posterior scute configuration comprised of supernumerary sulci on the suprapygal; however, these do broadly overlap the suprapygal. It is currently unclear if the high degree of PLR4 overlap on the suprapygal seen in the holotypes of Kinosternon rincon and K. pannekollops is phylogenetically significant. Plastron: The plastron of FAM 13822 is comprised of
paired epiplastra, hyoplastra, hypoplastra, and xiphiplastra. It is 86.23mm long and 81% carapace length. The shape of the forelobe is similar to that of Kinosternon pojoaque in that it is moderately angled at the distal margin at the gular–anterior humeral sulcus. The plastral fore- and hindlobes were probably highly kinetic. In the forelobe, this is evident by a smooth and rounded over edge along the anterior suture of the hyoplastron, and step along the posterior suture of the epiplastron. Additionally, when the epiplastron and hyoplastron of FAM 13822 are articulated, there is a substantial transverse notch between the forelobe and the hyoplastron, just proximal to the axillary notch of the hyoplastron (Fig. 3:4). Conceivably this notch could be an artifact of distortion in the preservation of the fossil, but more likely housed connective tissue to facilitate kinesis. In the hindlobe, a slightly depressed area between the posterior humeral–femoral sulcus and the hypo–xiphiplastral suture probably housed connective tissue as well to facilitate kinesis. The posterior humeral–femoral sulcus is situated just anterior and parallel to the hypo–xiphiplastral suture and the sutural teeth between the hypoplastron and xiphiplastron are shallow, typical of Kinosternon with hindlobe mobility.
827 The shape of the hyoplastron of Kinosternon rincon is more
similar to that of Kinosternon skullridgescens than to the type specimens of Kinosternon pojoaque. The hyoplastron is much wider than long and more transversely straight along its anterior margin than in K.
pojoaque.In K. pojoaque, the hyoplastron is relatively longer with deeper axillary notches. The length of the plastral bridge of FAM 13822 is 19.94mm long, ~19% carapace length. The plastral buttresses are flat like those of K. pojoaque, and lack an inguinal groove on the hypoplastron. A distinct anal notch is present on the hindlobe, which differs from K. pojoaque and Kinosternon wakeeniense. The type specimens of the latter two species possess a more lobate hindlobe with no anal notch. It is unclear at this time if this character is sexually dimorphic for middle and late Miocene Kinosternon as it is sexually dimorphic (males possessing and females lacking an anal notch) with extant members of the flavescens group. Plastral scutes on FAM 13822 comprise an intergular, and
paired gulars, anterior humerals, posterior humerals, femorals, anals, and axillary and inguinal inframarginals (sensu Hutchison and Bramble, 1981). The intergular length is 13.71mm, 13% carapace length, and the intergular width is 15.42mm, 15% carapace length. The gulars are much longer than the anterior humerals at the midline, which is typical of other Kinosternon (the anterior humerals are much longer in Sternotherus by contrast). The femorals are long, 14.21mm at the midline, 13% carapace length, and broadly overlap the hindlobe. The hindlobe is 30.93mm long and the femorals comprise 40% of the hindlobe length, similar to Kinosternon arizonense and Kinosternon wakeeniense, as well as Kinosternon pannekollops and Kinosternon sonoriense longifemorale in which the femorals comprise ~37%–38% of the hindlobe length. In contrast, the femoral overlap on the hindlobes of Kinosternon pojoaque and Kinosternon skullridgescens is distinctly less. In FAM 13822, the anals are relatively short at the midline (15.91mm) and 15% carapace length. The M5–6 sulcus contacts the inguinal inframarginal scute on the hyoplastron in FAM 13822, whereas in K. pojoaque and K. skullridgescens, the M5–6 sulcus contacts the axillary scute. Skull: The skull of FAM 13822 (Figs. 2 and 3) is poorly
preserved and as such, little will be described at this time. It is missing the anterior-dorsal and posterior-most portions. The mandible is well preserved in ventral view and looks almost identical to the holotype of Kinosternon pojoaque in size and shape. The triturating surfaces are obscured in part, but appear to be relatively slender and not overly expanded as in primarily durophagous taxa. The anteromedial boundary of the fossa temporalis superior lacks an overhanging ridge on the parietals. Instead only a weak ridge is present, typical of Kinosternon (Bourque, 2012b).
Figure 3.
Illustrations of Kinosternon rincon n. sp., holotype, FAM 13822. Partial skull and shell in (1) dorsal; and (2) ventral aspects. Shaded areas indicate
surrounding sediments. (3, 4) Reconstructions of K. rincon based on FAM 13822: (3) dorsal carapace with bone sutures and scute sulci drawn on the right side and scute sulci only on the left side of the shell, and (4) ventral plastron. Scale bar equals 1 cm. Abbreviations: abt, terminus of the axillary bridge buttress; ag, axillary musk duct groove; ahm, anterior humeral scute; an, anal scute; at, axillary musk duct terminus; ax, axillary scute; C1–8, costals 1–8; cb, cornu branchiale of the hyoid; cdv, caudal vertebrae; ch, corpus hyoideus; cor, coronoid process; cp, costiform process; crv, cervical vertebrae; dnt, dentary; epi, epiplastron; fem, femoral scute; gul, gular scute; hyo, hyoplastron; hyp, hypoplastron; igl, intergular scute; ing, inguinal scute; N1–5, neurals 1–5; nuc, nuchal; P1–10, peripherals 1–10; pa, parietal; pes, phalanges of the pes; pf, prefrontal; po, postorbital; pyg, pygal; spg, suprapygal; xip, xiphiplastron.
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