Thescelosaurus assiniboiensis, Brown & Boyd & Russell, 2011

Brown, Caleb Marshall, Boyd, Clint A. & Russell, Anthony P., 2011, A new basal ornithopod dinosaur (Frenchman Formation, Saskatchewan, Canada), and implications for late Maastrichtian ornithischian diversity in North America, Zoological Journal of the Linnean Society 163 (4), pp. 1157-1198 : 1162-1163

THESCELOSAURUS ASSINIBOIENSIS SP. NOV.

1989 Thescelosaurus neglectus Galton : pl. 4, figs 1–8; Galton 1995: fig. 4; Galton 1997: figs 3, 4, 10, pl. 1–2. Diagnosis: Dorsal and posterior margins of the squamosal convex; supraoccipital bearing a distinct median foramen running from the roof of the myelencephalon through to the dorsal surface of the element. Differentiated from T. garbanii by the calcaneum not being reduced and thus participating in the mesotarsal joint.

Specific etymology: Named for the District of Assiniboia, a regional administrative unit of the North- West Territories, Canada, from 1882 to 1905 (located between 49° and 51.97°N, and ~101.5 and ~ 111.5°W). The majority of this district became the southern portion of the modern province of Saskatchewan, with the westernmost area becoming the easternmost portion of the province of Alberta. It encloses the exposures of the Frenchman Formation. This district was named after the Assiniboine First Nations People .

Holotype: RSM P 1225.1 , a small, relatively complete skeleton, preserving a partial skull (including a nearly complete braincase), dorsal, sacral, and caudal vertebral series, dorsal ribs, pelvic girdles, and hindlimbs. Based on the 1968 quarry map, the skeleton was found in articulated condition, with the anterior part of the animal extending into the hill, but with the tail exposed.

Locality: Specimen RSM P 1225.1 was discovered on 19 June 1968 and collected by Albert E. Swanston of the Royal Saskatchewan Museum (then the Saskatchewan Museum of Natural History) on 17 July 1968. The original location, stated as ‘northwest of Clarks Ranch , from NW 1/4 Sec 35, T 4 , R 19 , west of the 3 rd Meridian , Frenchman River Valley , Saskatchewan’ , is incorrect. Tim Tokaryk ( RSM) relocated the original site in the late 1980s (with the relocation being confirmed by the matching of a rib fragment collected at the site with a rib of the specimen, and residual plaster persisting at the site; T. T. Tokaryk , pers. comm., 2007). Located in LSD 11, Sec 2, T 5 , R 19 , west of the 3 rd Meridian in southwestern Saskatchewan ( Fig. 3 ). The quarry is located on the north side of the Frenchman River Valley on the north-west facing side of a butte extending from the valley wall. Exact locality information is available from the RSM upon request .

Distribution: Frenchman Formation, Saskatchewan – Maastrichtian (65.5–65.0 Mya) ( Lerbekmo & Coulter, 1985; Braman & Sweet, 1999; Lerbekmo, 1999) ( Fig. 2 ).

Remarks: Although RSM P 1225.1 is a relatively small specimen that may not be skeletally mature, its recognition as representing a distinct species rests upon two major observations. Firstly, it is only 13% is more deeply concave in immature specimens of T. neglectus than it is in adults, which is opposite to the trend that would be required for RSM P 1225.1 to be an immature specimen of T. neglectus .

smaller (based on femur length) than the holotype of T. neglectus ( USNM 7757), and is less than 9% smaller than both CMN 8537 and LACM 33543. Neither of the latter two specimens, nor the similarly sized paratype of T. neglectus ( USNM 7758), display the autapomorphies evident in RSM P 1225.1. Secondly, the autapomorphies cited above (presence of the supraoccipital foramen and the shape of the posterior margin of the squamosal) are unlikely to be ontogenetically variable or to vary allometrically by size. In fact, the posterior margin of the squamosal

DESCRIPTION

Figures

Figure 2. Chronostratigraphy of the Late Cretaceous of Alberta, Saskatchewan, and Montana, Wyoming, and North and South Dakota, showing approximate time equivalence. Numbers on the left are in millions of years before present. Formations in white are terrestrial, and those in grey are marine; DMT, Drumheller Marine Tongue. Complied from Eberth, 2004; Brinkman DB. 2003; Koppelhus EB, Braman DR. 2010; Hamblin and Abrahamson, 1996; McIver 2002.

Figure 3. The geographic location of the RSM P 1225.1 quarry. A, the location of the Province of Saskatchewan in Canada, highlighting the area of south-western Saskatchewan illustrated in (B). B, regional map of southwestern Saskatchewan with star indicating the location of the quarry on the north side of the Frenchman River Valley near Cambery Coulee.