824
Journal of Paleontology 89(5):821–844
(2012b) and include the following. (Kinosternon) subrubrum group: Kinosternon subrubrum (Lacépède, 1788), Kinosternon hippocrepis (Gray, 1856), Kinosternon baurii (Garman, 1891), and
Kinosternon steindachneri (Siebenrock, 1906);
(Kinosternon) flavescens group: Kinosternon flavescens (Agassiz, 1857), Kinosternon arizonense (Gilmore, 1922), Kinosternon durangoense (Iverson, 1979). The generic names Platythyra Agassiz, 1857, and Thyrosternum Agassiz, 1857, are available for the flavescens and subrubrum groups respectively. These are used here minimally under subgeneric classifications as suggested by Iverson et al. (2013) regarding Thyrosternum pending more comprehensive analyses. Based on phylogenetic results of Iverson (1998) and those presented here (below) the taxon K. hippocrepis is discussed at the species level. Sternotherus peltifer is likewise referred to at the species level based on previous phylogenetic results (Iverson et al., 2013; Bourque and Schubert, 2015) and results presented below. Spinks et al. (2014) recently proposed that Kinosternon steindachneri be classified as a subspecies of K. subrubrum, but did not include K. steindachneri in their own analysis and as such had little basis for their nomenclatural recommendation. Currently there are no phylogenetic results (using genetic and/or morphological datasets) that support a subspecific classification of K. steindachneri under K. subrubrum (Iverson, 1998; Bourque, 2012a, 2012b; Iverson et al., 2013; Bourque and Schubert, 2015; results presented below).
Order Testudines Linnaeus, 1758 Suborder Cryptodira Cope, 1868 Family Kinosternidae Hay, 1892 Subfamily Kinosterninae Hay, 1892 Genus Kinosternon Spix, 1824
Diagnosis.—Plastral lobes moderately to very broad; plastron 75%–90%of carapace length; anterior and posterior plastral lobe kinesis; epiplastron without cusp; caudal notch between xiphi- plastra well developed to absent (as in some species with broad plastra); carapace tricarinate, unicarinate, or acarinate; perimeter length of nuchal longer to shorter than longest peripheral; weak or no cusp at posterolateral margin of femoral scute; posterior buttress terminates in posterior two-thirds of P7 (Hutchison, 1991); posterior humeral–femoral sulcus situated posteriorly on the hypoplastron running either parallel with, nearly parallel with, or along the hypo-xiphiplastral suture (Bramble et al., 1984; Bourque, 2012a); two or three sets of Rathke’s gland termini (axillary, inguinal, and caudal); anteromedial boundary of the fossa temporalis superior on the parietal reduced to a weakly developed ridge (Bourque, 2012b); anterior humeral scutes medially shorter than gular scutes (Ernst and Lovich, 2009).
Kinosternon rincon new species Figures 2 and 3
Holotype.—FAM 13822, nearly complete carapace, plastron, and partial skull of a young adult. The specimen is missing much of the left side of the carapace and plastron.
Diagnosis.—Lateral sulci of V1 do not extend onto P1 (shared with Kinosternon wakeeniense [described below], some of the subrubrum group such as Kinosternon steindachneri, and extant Sternotherus); costiform processes moderately developed; axillary buttress contacts posterior P3; M9 moderately heigh- tened (although not as tall as M10) and obtusely angled in shape (shared with Kinosternon integrum [LeConte, 1854] and Kinosternon scorpioides [Linnaeus, 1766] complex; not as tall or wave-shaped as Kinosternon pojoaque and the extant flavescens group); crest of M9 sulcus intersects P8–9 suture (shared with the K. scorpioides complex; M9 crest is anterior to the P8–9 suture in K. pojoaque and the extant flavescens group); femoral scute broadly overlaps ~40% of the hindlobe (shared with Kinosternon arizonense and K. wakeeniense); anal scute short, ~15% carapace length (shared with Kinosternon angustipons Legler, 1965, Kinosternon dunni Schmidt, 1947, Kinosternon herrerai Stejneger, 1925, and Kinosternon sonoriense longifemorale Iverson, 1981).
Occurrence.—Type locality: Rincon Quarry, northern Albuquerque Basin, Sandoval County, New Mexico. Age and formation: Middle Miocene, late Barstovian NALMA (Ba 2), 14.5–12.5 Ma, Cerro Conejo Formation (Tedford, 1981; Tedford et al., 2004; Connell et al., 2007) (also referred to as the Cerro Conejo Member of the Zia Formation sensu Connell [2001] and Morgan and Lucas [2001]).
Description.—Carapace: The carapace of FAM 13822 is ~106.09mm long and comprised of a nuchal, five neurals, one suprapygal, a pygal, eight paired costals, and ten paired per- ipherals (Fig. 3). The costals, peripherals, and suprapygal are best preserved on the right side of the shell. There are five ver- tebral scutes, a single cervical scute, four pairs of pleural scutes, and 11 pairs of marginal scutes. V1 is narrow (17.88mm wide, 17% carapace length) and the anterior sulci are wholly con- tained on the nuchal with no V1 overlap onto P1. This condition is atypical for Kinosternon (although it can be a variant) and shared with Kinosternon wakeeniense and many Kinosternon steindachneri. Extant Sternotherus possess a similarly narrow V1 that does not overlap P1; however, the oldest Sternotherus, Sternotherus palaeodorus Bourque and Schubert, 2015, possesses a wider V1 that does overlap P1. As such, in extant Sternotherus a narrow V1 without P1 overlap is likely inde- pendently derived. There is contact between the nuchal and N1 in FAM 13822, but this contact is narrow and not as broad as observed in the other middle Miocene taxa Kinosternon skullridgescens and Kinosternon pojoaque. The costiform pro- cesses are moderately developed and extend across the visceral face of P1 and contact the anterior of P2. The carapace is overall smooth and acarinate. However, on
N5 just anterior to the V3–4 sulcus and on the pygal, the faint trace of a posterior-medial keel is discernible. This is interpreted as an ontogenetically diminishing keel of which the keel is present in neonates, and lost in adults (which is typical of extant kinosternids that are acarinate as adults). As FAM 13822 appears to represent a young adult, the likelihood is high that it would possess some residual trace of neonatal carination. This keel was not significant enough to score as being present in the character analysis presented below. The posterior margin of the
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