Tamaki Sato

Tim T. Tokaryk

Academic paper

Journal of Vertebrate Paleontology

Abstracts

21

3

97A

Short-necked polycotyltd plesiosaurs are common components of marine vertebrate faunas of the Late Cretaceous Western Interior Seaway and their remains are known from Texas to the Canadian Arctic, Most of Canadian specimens, however, are poorly preserved and inadequate for detailed morphological examination. Here we report the occurrence and anatomy of well-preserved specimen, RSMP2310.1 (Royal Saskatchewan Museum) from the Bearpaw Formation of Herschel, southwestern Saskatchewan.
RSMP2310.1 is from a sandy unit of the formation. Based on palynological evidence it is Late Campanian in age, making it the youngest occurrence of a polycotylid in North America. Although the specimen was disarticulated, there has been little deformation or gypsum damage, and the specimen is remarkably well preserved. It is composed of the skul! and mandible, numerous vertebrae, ribs, and pectoral and pelvic girdles. A severely weathered propodial bone found nearby may belong to the same individual. The skull is three dimensionally preserved, allowing detailed observation of the braincase, palate, occipital region, skull roof, and mandibles.
Morphological features such as vertical suspensorium, gracile teeth, straight ilium and position of chevron facets indicate thai the Saskatchewan polycotylid is closely related to Dolichorhynchops (Trinacromerum) osborni. This individual is comparable to juveniles of that species in skull size, but palate elements are completely fused without leaving sutures, indicating advanced ossification. The anterorbital region is relatively short in comparison with other individuals of D. osborni of comparable size. There is a sharp rise in front of the parietal crest thai has never been reported from D. osborni.

English