A New Species of Neurankylus from the Milk River Formation (Cretaceous: Santonian) of Alberta, Canada, and a Revision of the Type Species N. eximius

Abstract

A new species of Neurankylus (N. lithographicus sp. nov.) is described on the basis of skull and shell material from the Santonian-aged Milk River Formation, Alberta, Canada. The genus Neurankylus is also rediagnosed on the basis of the Milk River material and on new material pertaining to the type species N. eximius. N. eximius previously was considered to be a long-lived and cosmopolitan taxon. New Neurankylus material provides insights into the range of morphological variation present in the genus and indicates that many specimens previously referred to N. eximius may belong to different species. The congeners recognized in this chapter have a more restricted geographical and temporal range than has been suggested previously. A new phylogenetic analysis of all known baenid taxa, including all described species of Neurankylus and several basal paracryptodiran taxa of uncertain affinities, yields two important results: a monophyletic Neurankylus is recovered as a basal radiation within Baenidae and parallel evolution is identified among many features previously regarded as synapomorphies for Baenidae. In light of this study and other recent work on turtle systematics, it is now apparent the biogeography and biostratigraphy of Cretaceous turtles may have been more complex than previously appreciated.

A Review of the Fossil Record of Turtles of the CladeBaenidae

“…The influential classification of was centered on the same set of Late Cretaceous to Eocene turtles, similar to previous authors, but Baenidae was expanded to include Trinitichelys hiatti from the Early Cretaceous (Aptian-Albian) of Texas and the idiosyncratic Compsemys victa Leidy, 1856 from the Late Cretaceous to Paleocene of the American West . All recent global (e.g., Joyce 2007;Anquetin 2012;Sterli et al 2013) and local phylogenetic analyses (e.g., Lyson and Joyce 2009aLarson et al 2013) have reproduced the overall grouping of , with the exception of Compsemys victa, which is retrieved outside of Baenidae .…”

“…The following, alphabetically organized list summarizes the available literature: Baena arenosa (Baena clara, Baena emiliae and Baena sima of ; the specimen figured in Gaffney 1972 is "Baena" affinis); "Baena" affinis (Leidy 1871a; Baena riparia of ; Baena inflata of Gilmore, 1916c; Baena arenosa of ; "Baena" escavada ; Boremys grandis Sullivan et al 2013); Boremys pulchra , material from Judith River Group/Formation only; Brinkman and Nicholls 1991); Cedrobaena brinkman (Case 1939;Lyson and Joyce 2009b); Chisternon undatum ; Denazinemys nodosa Wiman 1933;Sullivan et al 2013); Eubaena hatcheri (Hay, 1901) (Hay 1901; Neurankylus baueri Wiman 1933;Sullivan et al 2013); Neurankylus eximius (Lambe 1902;Larson et al 2013); Neurankylus lithographicus (Larson et al 2013); Neurankylus torrejonensis (Lyson et al, in press); Palatobaena cohen (Lyson and Joyce 2009a); Plesiobaena antiqua ; Protobaena wyomingensis (Gilmore, 1920) (Gilmore 1920); Scabremys ornata Sullivan et al 2013); "Baena" hayi (Gilmore 1916a); Thescelus insiliens figure in Gaffney 1972 is a chimera); Thescelus rapiens ; and Trinitichelys hiatti .…”

“…Although it appears likely that the shell taxon "G. caelatus" will eventually be shown to belong to the skull taxon A. dardeni, we agree with Lipka et al (2006) that it is currently not possible to synonymize these taxa, as this material was not found in direct association. Phylogenies universally retrieve A. dardeni as a basal baenid (e.g., Lipka et al 2006;Larson et al 2013). …”

“…Taxonomic history. Neurankylus baueri (new species); Neurankylus eximius ϭ Baena fluviatilis ϭ Charitemys captans ϭ Neurankylus baueri Gaffney, 1972 (junior synonym); Neurankylus eximius ϭ Baena fluviatilis ϭ Charitemys captans ϭ Neurankylus baueri ϭ Neurankylus wyomingensis Brinkman and Nicholls, 1993 (junior synonym); Neurankylus baueri Larson et al, 2013 andSullivan et al, 2013 (nomen validum).…”

“…The following, alphabetically organized list summarizes the available literature: Arundelemys dardeni Lipka et al, 2006; Baena arenosa , including skull of "Baena sima"; note that the skulls figured by are chimeras); "Baena" affinis , including skull of "Baena riparia"); Boremys pulchra (Lambe, 1906a) (Brinkman and Nicholls 1991); Cedrobaena brinkman Joyce, 2009b (Case 1939;Lyson and Joyce 2009b); Ce. putorius Lyson and Joyce 2009b); Chisternon undatum (Gaffney , 1982b; Eubaena cephalica (Hay, 1904b) (Hay 1904bGaffney , 1982aGaffney , 1982b; Gamerabaena sonsalla ; Goleremys mckennai ; Hayemys latifrons ; Neurankylus eximius Lambe, 1902 (Brinkman andNicholls 1993); Neurankylus lithographicus Larson et al, 2013; Neurankylus torrejonensis Lyson et al, in press (Lyson et al, in press); Palatobaena bairdi , 1982a [late Paleocene material only]); Palatobaena cohen Lyson and Joyce, 2009a Gaffney 1982aGaffney , 1982b [Maastrichtian and early Paleocene material]); Palatobaena gaffneyi ; Plesiobaena antiqua (Lambe, 1902) (Gaffney 1982b;; Stygiochelys estesi Gaffney , 1982b; and Trinitichelys hiatti (Gaffney , 1982a.…”