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Bourque—Middle–Late Miocene Kinosternon


Kinosternon sonoriense sonoriense. The V2 sulcus indicates that V2 more significantly overlapped the C3 than the V3, similar to that seen for Kinosternon pannekollops. As such, Kinosternon notolophus may have possessed long and narrow vertebral scutes like those of K. pannekollops. The ratio of V2 and V3 overlap onto C3 appears to be more equal in extant Kinosternon with wider vertebral scutes. Similar to UF 150029, the proximal portion of a right C4, UF 225682 (Fig. 8.3) from the Suwannee River Mine of northern Florida possesses a faint keel just distal to the V3 sulci. This specimen belonged to a larger individual than UF 150029. The P8, UF 150032 (Fig. 8.6 and 8.8), is small with


bulbous marginal scutes and a rounded over (rather than sharp) distal edge. The transition from the ventral marginal to the visceral face forms an abrupt step at an angle of approximately 90 degrees. In these ways, it most closely resembles Kinosternon pannekollops, Kinosternon sonoriense sonoriense, Kinosternon angustipons, and the subrubrum group. Apit at the P7–8 suture in UF 150032 indicates that the inguinal bridge buttress was posteriorly extensive (Bourque, 2013). The inguinal buttress in Kinosternon notolophus probably termi- nated posteriorly on P7 or the anterior-most P8, which is shared with some K. sonoriense examined.


Etymology.—Species name is the combination of the Greek words ‘notos’ for ‘back’ and ‘lophos’ for ‘ridge.’ Thus, the colloquial name is the ‘ridgeback mud turtle,’ in reference to the thick pronounced dorsomedial keel on at least the anterior carapace.


Referred material.—UF 150029, proximal portion of left C3; UF 150030, proximal left costal fragment; UF 150031, right P1; UF 150032, right P8. Referred material: UF 287349, water- worn right P4; and UF 287350, proximal portion of a left C2 or C4 of a neonate; both from the Love Bone Bed. The proximal portion of a right C4, UF 225682, exhibits a weak lateral carina similar to that of K. notolophus and may represent it or perhaps a closely related species.Aleft P2,UCMP194406, from the Love Bone Bed may represent K. notolophus, but was unavailable for examination during this study.


Remarks.—This is the only tricarinate Kinosternon from the Miocene of the United States; however, Bourque (2012b) reported a laterally keeled kinosternid from the late Miocene (6.6–9 Ma) Gracias Formation of Honduras that was possibly related to the Kinosternon scorpioides species complex. The kinosternid taxon from Honduras has a much more pronounced lateral keel than that of Kinosternon notolophus. The degree of carination in K. notolophus is similar to Kinosternon sonoriense sonoriense, which too has a distinct medial keel and lesser costal carinae and also possesses a thickened posterior marginal rim similar to K. notolophus, Kinosternon pannekollops, and members of the subrubrum group. It shares the possession of slight contact between the hypoplastral buttress and P8 with some K. s. sonoriense (e.g., UF/H 153871). The type specimens of Kinosternon notolophus were


previously described in some detail (Bourque, 2013). Only isolated carapacial bones have been collected and no plastral elements are currently known. The type and referred specimens


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of this species are not clearly associated with one another and it is therefore presumed that these specimens represent multiple individuals. Therefore, much of the description of this species is a composite based on isolated bones believed by the author to represent a single taxon. The referred specimen UF 225682 may represent the oldest record of K. notolophus or a closely related species.


Phylogenetic analysis


A phylogenetic analysis was performed using the matrix of Bourque and Schubert (2015) with the addition of 19 characters and the taxa Kinosternon rincon n. sp., Kinosternon pannekollops n. sp., and Kinosternon hippocrepis (Appendix 1). Additionally, both subspecies of Kinosternon sonoriense (Kinosternon sonoriense sonoriense and Kinosternon sonoriense longifemorale) were analyzed. Kinosternon wakeeniense n. sp. and Kinosternon notolophus n. sp. were excluded from the analysis due to a lack of more complete fossil material at this time. The program Mesquite 2.5 (Maddison and Maddison, 2008) was used to develop the character-taxon matrix (Appendix 2), which comprised 57 morphological char- acters and 35 fossil and extant kinosternid ingroup taxa. The extinct taxon Xenochelys Hay, 1906, was used as the outgroup. A parsimony analysis was conducted using 1000 heuristic search replicates with random addition sequence and tree- bisection-reconnection branch swapping in the programPAUP* 4.0 b10 (Swofford, 2003). The maximum number of trees was set to 100,000. Character states were unordered and equally weighted, and multistate characters were interpreted as poly- morphisms. To assess support for these topologies, 1,000 bootstrap replicates were performed for each of three heuristic searches. The analysis was conducted using the High Performance Computing Center at the University of Florida.


Results.—Fifteen equally most-parsimonious trees were recovered (tree length = 255; consistency index = 0.4902; homoplasy index = 0.6902; retention index = 0.7240; rescaled consistency index = 0.3549). The strict consensus and 50% majority rule consensus cladograms are presented in Figure 9. Kinosternon is recovered as a monophyletic assemblage. The Kinosternon flavescens group (Platythyra Agassiz, 1857) and Kinosternon subrubrum group (Thyrosternum Agassiz, 1857) represent distinct monophyletic clades nested within Kinosternon, but with low bootstrap support. Kinosternon rincon is nested between the clade that comprises Kinosternon pojoaque and the flavescens group, the subrubrum group, and more derived Kinosternon including the clade comprised of Kinosternon angustipons and Kinosternon dunni. Kinosternon pannekollops is recovered as a stem taxon of the subrubrum group with Kinosternon hippocrepis as the most basal living member of that clade. Kinosternon herrerai is recovered as the most basal Kinosternon, which is similar to results of Iverson (1991) using combined allozyme and morphological data. The early Barstovian Kinosternon skullridgescens is the sister taxon to K. herrerai and likewise recovered as a basal Kinosternon. The position of the clade composed of K. angustipons and K. dunni differs from results of previous analyses, which have suggested these taxa have closer affinities with K. herrerai and


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