NMC 2280, links, en NMC 2245 in hun oorspronkelijke opstelling met veel te sterk gespreide voorpoten
English: Title: The Canadian field-naturalist Identifier: canadianfieldnat120otta (find matches) Year: 1919 (1910s) Authors: Ottawa Field-Naturalists' Club Subjects: Natural history; Sciences naturelles Publisher: Ottawa, Ottawa Field-Naturalists' Club Contributing Library: Harvard University, Museum of Comparative Zoology, Ernst Mayr Library Digitizing Sponsor: Harvard University, Museum of Comparative Zoology, Ernst Mayr Library View Book Page: Book Viewer About This Book: Catalog Entry View All Images: All Images From Book Click here to view book online to see this illustration in context in a browseable online version of this book. Text Appearing Before Image: 404 The Canadian Field-Naturalist Vol. 120 Text Appearing After Image: Figure 2. CMN 2280 (left) and CMN 2245 (right) on display at the National Museum of Canada (circa 1926). (Courtesy of the Canadian Museum of Nature). As restored, the skeletons measured "approximately the same length but the bones of one... are much Ughter in construction than those of the other" (Sternberg 1927: 67). According to Sternberg, the total length of the 'gracile' skeleton measured 4.93 m, while that of the "robust" skeleton measured 4.95 m. Unfortunately, their supports have since been disassembled and these original measurements cannot be verified. Sternberg attributed the difference in robustness between the two specimens to sexual dimorphism, stating, "it is thought that they represent male and female as it is common, among reptiles, for the female to be larger than the male" (Sternberg 1927: 67). This assumption has gone largely unchallenged in the literature (e.g.. Lull 1933; Carpenter and Carrie 1990; Dodson 1996), except for an implication by Godfrey and Holmes (1995) that the reported differences between the specimens do not reflect sexual dimorphism because they pertain to two separate species of Chasmosaurus. The recognition of sexual dimorphism in a fossil species must begin with the establishment that the vari- ation observed within that species does represent dimor- phism. With only two reasonably complete skeletons of Chasmosaurus belli at his disposal, Sternberg could not have established this with certainty, and indeed, he neither quantified nor qualified the differences he observed between the specimens. It is also important to note that many of the bones were highly reconstruct- ed with plaster and subsequently painted over so that the reconstructed portions cannot be easily identified. As chronicled by C. H. Sternberg (C. M. Sternberg's father) regarding the restoration of one of the skulls: "we had colored our plaster to resemble the fossil bone - no small task, by the way, as we had to learn to mix colors as well as do the work of a sculptor - with wax" (Sternberg 1917: 83). As such, the possibility remains that the difference in robustness between the two specimens might in part be attributable to the extensive restoration of certain elements. With these concerns in mind, we set out to identify and describe the variation noted between the skeletons, and con- ducted a reevaluation of Sternberg's original attribu- tion of sexual dimorphism to C. belli. Materials The two Chasmosaurus belli skeletons (Figure 3) described by Sternberg (1927) reside in the collec- tions of the Canadian Museum of Nature in Aylmer, Quebec. The "gracile" specimen was designated CMN 2245: the "robust," CMN 2280. CMN 2245 was col- lected from quarry Q037, and CMN 2280 from QOlO, of the Dinosaur Park Formation (upper Campanian, -75 Ma) in Dinosaur Provincial Park, Alberta (origi- nally referred to by Sternberg (1927: 67) as the "Belly River series"). CMN 2245 (Figure 3A) is represented by the pos- terior half of a skull and mandibles (missing only the predentary), complete presacral series, synsacrum com- plete to the sixth sacral vertebra, twenty-four caudal vertebrae, most cervical and thoracic ribs, pectoral gir- Note About Images Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original work.