Donald B. Brinkman (1) (2), Caelan Libke (3) (4), Ryan C. McKellar (3) (4), Sergei Gasilov (5), Christopher M. Somers (4)
The Anatomical Record. Volume 306, Issue 6, pages Pages 1481-1500 (3 June 2022). DOI: https://doi.org/10.1002/ar.24952

Keywords

Kinosternidae, frenchman formation, late cretaceous

Abstract

Previously, only a single member of Pan-Kinosternidae (Yelmochelys rosarioae) had been documented from the Late Cretaceous epoch. In this report we describe a new pan-kinosternid genus and species, herein named Leiochelys tokaryki, based on a nearly complete, articulated skeleton from the Late Cretaceous (Maastrichtian) Frenchman Formation of Saskatchewan, Canada. L. tokaryki differs most notably from the previously described Y. rosarioae in having triangular plastral lobes, and in that the suture between the hyo- and hypoplastron is in line with the suture between the fifth and sixth peripherals. A maximum parsimony analysis suggests that L. tokaryki is intermediate between Y. rosarioae and crown-group kinosternids. Kinosternid features present in L. tokaryki include the presence of a reduced plastral bridge that extends from the posterior tip of peripheral 4 to the anterior tip of peripheral 7, two inframarginals that contact one another, a smooth triturating surface, and participation of the palatine in the triturating surface. An unexpected feature of the skull is the presence of a large stapedial canal, suggesting that the decrease in size of the stapedial canal and increase in the canalis caroticus cerebralis occurred independently in Dermatemydidae and Kinosternidae. The character-states of the skull and skeleton of L. tokaryki indicate that morphological changes occurring during the diversification of Kinosternoidea were more complex than expected based on data from derived members of the group.

How Our Software Was Used

The body and skull were also segmented utilizing thresholding functions to select regions containing bone, and manually segmenting areas where density contrast was insufficient for threshold-based segmentation. Results were rendered with Dragonfly.

Author Affiliation

(1) Department of Preservation and Research, Royal Tyrrell Museum of Palaeontology, Drumheller, Alberta, Canada
(2) Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada
(3) Department of Palaeontology, Royal Saskatchewan Museum, Regina, Saskatchewan, Canada
(4) Department of Biology, University of Regina, Regina, Saskatchewan, Canada
(5) Biological and Life Sciences Department, Canadian Light Source, Saskatoon, Saskatchewan, Canada