Journal
PALAEONTOLOGISCHE ZEITSCHRIFT
Volume 85, Issue 2, Pages 125-142Publisher
SPRINGER HEIDELBERG
DOI: 10.1007/s12542-010-0081-x
Keywords
Hell Creek Formation; North Dakota; Maastrichtian; Late Cretaceous; Kinosternoidea; Hoplochelys clark n. sp.; Dermatemys mawii
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Funding
- Doris O. and Samuel P. Welles Research Fund (UCMP)
- University of Iowa Department of Geoscience
- National Science Foundation Graduate
- University of Tubingen
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A nearly complete turtle shell from the Late Cretaceous (Maastrichtian) Hell Creek Formation of Slope County, North Dakota, represents the most complete remains to date of a Mesozoic kinosternoid turtle and a new species, Hoplochelys clark nov. sp. The new taxon is diagnosable from other representatives of Hoplochelys by the plesiomorphic placement of the humeral/femoral sulcus behind the hyo/hypoplastral suture and the autapomorphic development of an interrupted median (neural) keel. All six previously named Paleocene (Puercan and Torrejonian) representatives of Hoplochelys lack diagnostic characters and are synonymized as Hoplochelys crassa. A phylogenetic analysis reveals that Hoplochelys spp. and Agomphus pectoralis are most parsimoniously placed within Kinosternoidea along the phylogenetic stem of the extant Mesoamerican River Turtle Dermatemys mawii, extending that taxon's stem lineage from the early Eocene to the late Maastrichtian. The two primary crown lineages of Kinosternoidea are thus known from the Mesozoic and split prior to the late Campanian. The presence of a thickened cruciform plastron, true costiform processes, only three inframarginals, and the reduction of the medial contact of the abdominals are synapomorphies of Chelydroidea, the clade formed by Chelydridae and Kinosternoidae.
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