A new kinosternoid from the Late Cretaceous Hell Creek Formation of North Dakota and Montana and the origin of the Dermatemys mawii lineage

Abstract

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.Keywords Hell Creek Formation Á North Dakota Á Maastrichtian Á Late Cretaceous Á Kinosternoidea Á Hoplochelys clark n. sp. Á Dermatemys mawii Kurzfassung Eine fast komplette Schildkrötenschale, die in der spätkretazischen (Maastrichtium) Hell Creek Formation in Slope County, Norddakota, gefunden wurde, stellt den bisher vollständigsten mesozoischen Rest einer kinosternoideen Schildkröte dar und wird hier als neue Art Hoplochelys clark beschrieben. Anhand der plesiomorphen Lage des humero/femoralen Sulcus hinter der hyo/hypoplastralen Sutur und des autapomorphisch unterbrochenen medianen Kiels kann die neue Schildkröte von anderen Hoplochelys Arten unterschieden werden. Allen sechs bisher bekannten Arten aus dem Paläozän (Puercium und Torrejonium) fehlen diagnostische Merkmale. Daher werden sie als Hoplochelys crassa synonymisiert. Die phylogenetische Analyse ergibt, dass es am sparsamsten ist, Hoplochelys spp. und Agomphus pectoralis entlang der

Allaeochelys libyca, a New Carettochelyine Turtle from the Middle Miocene (Langhian) of Libya

“…Several interesting trends are apparent through time from the Early Cretaceous to the Holocene: (1) increase in overall body size; (2) increase in the relative size of the plastron; (3) reduction of the plastral and carapacial scutes; (4) reduction of the antrum postoticum; and (5) expansion of the fossa at the base of the processus articularis. These clear trends are certainly an artifact of the low diversity of the group and are therefore only mirrored by similar trends apparent among the lineage leading to Dermatemys mawii (Knauss et al 2011). …”

Turtles and Tortoises of the World During the Rise and Global Spread of Humanity: First Checklist and Review of Extinct Pleistocene and Holocene Chelonians.

“…Hesperotestudo turgida (Cope 1892a Kuhn (1964) and Auffenberg (1974) mistakenly cited Emys turgidus Cope 1870b as the original name for this tortoise, but that name described a Cretaceous dermatemyid turtle from New Jersey, now synonymized under Agomphus (Hutchison and Weems 1998;Knauss et al 2011).…”

A Review of the Fossil Record of Turtles of the CladePan-Chelydridae

“…A series of increasingly well-sampled analyses that utilize molecular data (e.g., Shaffer et al 1997;Krenz et al 2005;Parham et al 2006;Barley et al 2010;Crawford et al 2015), however, have more recently revived the sister group relationship between chelydrids and kinosternoids to the exclusion of P. megacephalum. This resulting "superfamilial" clade is named Chelydroidea following Baur (1893), who was the first to recognize this exact arrangement (Knauss et al 2011). Although current morphological studies still fail to retrieve a monophyletic Chelydroidea (e.g., Joyce 2007;Anquetin 2012;Sterli et al 2013;Rabi et al 2014), some compelling character evidence is nevertheless available that supports the monophyly of this clade (Knauss et al 2011).…”

“…This resulting "superfamilial" clade is named Chelydroidea following Baur (1893), who was the first to recognize this exact arrangement (Knauss et al 2011). Although current morphological studies still fail to retrieve a monophyletic Chelydroidea (e.g., Joyce 2007;Anquetin 2012;Sterli et al 2013;Rabi et al 2014), some compelling character evidence is nevertheless available that supports the monophyly of this clade (Knauss et al 2011).…”

“…from North America should be considered to be pan-chelydrids based on the presence of a cruciform plastron and the absence of a midline contact of the abdominal scutes, but Hutchison and Bramble (1981) later highlighted the affinities of Hoplochelys spp. with pan-kinosternoids, a conclusion supported by more recent analyses (e.g., Knauss et al 2011). Similarly, the Late Cretaceous (Maastrichtian) Emarginachelys cretacea Whetstone, 1978 was originally described as a pan-chelydrid (Whetstone 1978b) but was later reinterpreted to be a pan-kinosternoid, although an explicit rationale was not provided for this assessment (e.g., Meylan and Gaffney 1989;Holroyd and Hutchison 2002;Holroyd et al 2014).…”