CONIASAURUS OWEN, 1850 (REPTILIA: SQUAMATA), FROM THE UPPER CRETACEOUS NIOBRARA CHALK OF WESTERN KANSAS

Journal of Paleontology, May 2006 by Shimada, Kenshu, Bell, Gorden L Jr

Caldwell and Cooper (1999, p. 447) noted that all known specimens of Coniasaurus (and Dolichosaurus) occurred in deposits that accumulated in "relatively shallow marine environments along the coastlines of land masses" (see also Jacobs et al., 2005b). On the basis of Cenomanian materials, Caldwell (2000, p. 732) described dolichosaurids as "predators feeding in crevices and narrow spaces such as might exist in coral reefs and on rocky shores." The occurrence of Coniasaurus in the Smoky Hill Chalk in western Kansas is paleoecologically intriguing, because the rock unit represents an offshore deposit (Hattin, 1982). where the nearest coastline was likely a few hundred kilometers away during the Middle Sunloniun (Fig. 2). The water was possibly 150-300 m deep, and the ocean floor was muddy. Hat. dark, and monotonous, with sparsely distributed epifaunal invertebrates, such as inoccrumids and rudists (Hattin, 1982).

There arc several possibilities that may explain the apparent discrepancy concerning the paleoenvironment of Coniasaurus. They include: 1) a misinterpretation of the proposed position of paleocoastlines (e.g., see Fig. 2); 2) the presence of one or more unrecogni/.ed islands in the vicinity inhabited by Coniasaurus: 3) that Coniasaurus constitutes a true marine inhabitant that lived in both nearshore and offshore environments; 4) Coniasaurus' ability as a nearshore resident to explore offshore environments: 5) a shift in the preferred habitat of Coniasaurus over geologic time; 6) that the Coniasaurus individual was accidentally carried to the offshore environment (e.g., living individual transported by a drifting log); 7) that the Coniasaurus vertebra represents a skeletal element transported from a coastline (e.g., submarine transport by oceanic current, or representing part of a fioat-and-bloat carcass); and 8) that the vertebra represents a part of the gastric residue or coprolitic remains of another animal that ingested the Coniiisanrus individual in a nearshore environment. The exact reason cannot be determined only from the described Coniasaurns vertebra, and it may be a combination of two or more of these reasons. However, it should be noted that the seventh and eighth possibilities appear unlikely, because the bone surface of the specimen shows no sign of damage that could have resulted from erosion through long transportation or acid etching through digestion.

Prospecting vertebrate fossils in the Smoky Hill Chalk has been conducted chiefly by walking (i.e., visually searching for remains from a standing position). Thus, Hamm and Shimada (2002) pointed out that collecting biases towards large vertebrate specimens may be present in the fossil record of the Smoky Hill Chalk of Kansas. Such biases, if indeed present, reduce the accuracy of paleoecological inferences. FHSM VP-2219 is a small, incomplete specimen. Nevertheless, it is important because the record adds a new ecological component to the Niobrara fauna during the Middle Santonian (Table 1).