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Journal of Paleontology, 89(5), 2015, p. 821–844 Copyright © 2016, The Paleontological Society 0022-3360/16/0088-0906 doi: 10.1017/jpa.2015.63


New mud turtles (Kinosternidae, Kinosternon) from the middle–late Miocene of the United States


Jason R. Bourque


Division of Vertebrate Paleontology, Florida Museum of Natural History, University of Florida, Gainesville, Florida 32611, USA ⟨jbourque@flmnh.ufl.edu


Abstract.—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 northwestern 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 to 15 Ma), and disappeared from the region coincident with the end of that megathermal event.


Introduction


The mud turtle genus Kinosternon Spix, 1824, is a diverse taxon that comprises at least 34 currently recognized extant and fossil taxa (Iverson, 1991; Bourque, 2012b). Some molecular studies have suggested that the genus is paraphyletic relative to its sister taxon Sternotherus Gray, 1825 (Seidel et al., 1986; Iverson et al., 2007, 2013; Reid et al., 2011), whereas others have recovered a monophyletic group (Iverson, 1991, 1998; Iverson et al., 2007; Spinks et al., 2014). All published morphology- based analyses have recovered a monophyletic assemblage (Hutchison and Bramble, 1981; Hutchison, 1991; Iverson, 1991; Bourque, 2012a, 2012b; Bourque and Schubert, 2015; results below). The oldest reports of Kinosternon are from the Hemingfordian NorthAmerican Land Mammal Age (NALMA) between 18 and 16 million years old (Holman, 1998; Hutchison, 1991; Bourque, 2013; Weems and George, 2013), but those voucher specimens are fragmentary and it is uncertain if they are stem representatives or referable to the crown group. The vouchers reported as the oldest record of Kinosternon (sensu Holman, 1998; Weems and George, 2013) may in fact represent a new genus yet to be diagnosed, perhaps directly ancestral to Kinosternon and Sternotherus (Bourque and Schubert, 2015; see Discussion below). The most complete previously described fossils that represent the Kinosternon crown group are the types


of Kinosternon skullridgescens Bourque, 2012b, and Kinosternon pojoaque Bourque, 2012a, from the middle Mio- cene (Barstovian NALMA) Tesuque Formation (16–13 Ma) of the Española Basin, New Mexico. Little has been published about kinosternines from the late Miocene, particularly from the Clarendonian NALMA, and what has been reported from this interval is based on scant and fragmentary material (Wilson, 1968; Bourque, 2011; Bourque, 2013). Here I will describe a new species of mud turtle from the late Barstovian of the northern Albuquerque Basin of New Mexico, and discuss its relationships with other middle–late Miocene Kinosternon. Additionally, I will describe three extinct species of Kinosternon from the Clarendonian of Texas, Kansas, Nebraska, and Florida and present an updated morphology- based phylogenetic hypothesis for the Kinosternidae that incorporates extant and more completely preserved extinct taxa.


Geological settings and background


Rincon Quarry, Sandoval County, New Mexico.—Two pre- viously undescribed partial kinosternine specimens are part of the Frick Collection housed at the AMNH in New York. The specimens, FAM 13822 and FAM 13014, were collected by John Blick and Ted Galusha from the Rincon Quarry locality at Arroyo Ojito, in the northern Albuquerque Basin of Sandoval


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