Data from: New mud turtles (Kinosternidae, Kinosternon) from the Middle-Late Miocene of the United States

Kinosternon Spix, 1824, was widespread in xeric to savanna associated paleowetlands across North America during the middle–late Miocene and steadily diversified following its first occurrences in the Hemingfordian. In the middle Miocene, Kinosternon rincon, n. sp. occurred in the late Barstovian Cerro Conejo Formation of north central New Mexico, perhaps concurrently with Kinosternon pojoaque Bourque 2012a from the Tesuque Formation. Subsequent late Miocene kinosternine fossils indicate that at least three potentially contemporaneous species existed throughout the Clarendonian. These are Kinosternon pannekollops, n. sp., from the Ogallala Formation of northern Texas; Kinosternon wakeeniense, n. sp., from the Ogallala Formation of north-western Kansas and Ash Hollow Formation of south-central Nebraska; and Kinosternon notolophus, n. sp., from the Alachua and Statenville formations of northern Florida. Kinosternon rincon is phylogenetically nested between the Kinosternon flavescens (Agassiz, 1857) group (=Platythyra Agassiz, 1857) and more derived Kinosternon including the Kinosternon subrubrum (Lacépède, 1788) group (=Thyrosternum Agassiz, 1857). Kinosternon pannekollops is recovered on the stem of the K. subrubrum group and is the oldest and largest member of that lineage. Kinosternon notolophus is readily differentiated from other Miocene Kinosternon in possessing a distinct dorsomedial keel on the nuchal and faint dorsolateral costal carination. The K. subrubrum group probably originated in the late Miocene savannas of the Great Plains and dispersed eastward via the Gulf Coastal Plain. An unnamed kinosternine taxon existed in the coastal plains of the eastern and southeastern United States during the Middle Miocene Climatic Optimum (with fossils from ~18–15 Ma), and disappeared from the region coincident with the end of that megathermal event.动胸龟属（Kinosternon）由斯皮克斯于1824年确立，在中新世中晚期，该属广泛分布于北美洲与稀树草原相关的古湿地及干旱生境中，且自赫明福德期首次出现后持续稳步分化。中新世中期，林孔动胸龟（Kinosternon rincon n. sp.）发现于新墨西哥州中北部巴尔斯托维安期晚期的塞罗科内霍组（Cerro Conejo Formation），其生存时代可能与产自特苏克组（Tesuque Formation）的波霍阿克动胸龟（Kinosternon pojoaque Bourque, 2012a）同期。后续发现的晚中新世动胸龟亚科（Kinosterninae）化石显示，克拉伦多尼安期至少存在三种可能同期的物种：分别是产自得克萨斯州北部奥加拉拉组（Ogallala Formation）的潘尼科洛普斯动胸龟（Kinosternon pannekollops n. sp.）；产自堪萨斯州西北部奥加拉拉组及内布拉斯加州中南部阿什霍洛组（Ash Hollow Formation）的韦基恩动胸龟（Kinosternon wakeeniense n. sp.）；以及产自佛罗里达州北部阿拉楚阿组（Alachua Formation）与斯塔滕维尔组（Statenville Formation）的背脊动胸龟（Kinosternon notolophus n. sp.）。林孔动胸龟的系统发育位置嵌套于黄动胸龟群（Kinosternon flavescens (Agassiz, 1857)，即扁盾动胸龟亚属Platythyra Agassiz, 1857）与更衍化的动胸龟类群之间，后者包括锦动胸龟群（Kinosternon subrubrum (Lacépède, 1788)，即喉盾动胸龟亚属Thyrosternum Agassiz, 1857）。潘尼科洛普斯动胸龟被复原为锦动胸龟群的基干类群，是该支系中最古老且体型最大的成员。背脊动胸龟可通过颈盾上明显的背中脊以及肋盾上微弱的背侧肋脊线，与其他中新世动胸龟物种清晰区分。锦动胸龟群可能起源于大平原地区的晚中新世稀树草原，并通过墨西哥湾沿岸平原向东扩散。在中新世中期气候适宜期（约18–15 Ma），美国东部及东南部沿海平原存在一种未命名的动胸龟亚科类群，该类群随该巨型热事件的结束而从该区域消失。