Meeting Abstract
The Late Cretaceous (LK) Lance Formation (Maastrichtian) is a well-sampled division from which a variety of vertebrates are known, especially avian and non-avian dinosaur species. A recent expedition by the Missouri Institute of Natural Science (MINS) recovered an incomplete postcranial skeleton (MINS V1036) of an especially large chasmosaurine ceratopsian from Weston County Locality in the Lance Formation of Wyoming. The specimen is represented by cervical, dorsal and caudal vertebrae, a scapulocoracoid, and elements of the pelvic girdle and hind limb. Lack of a skull precludes species alloccation. The remains show morphology consistent with Triceratops, but no postcranial characters distinguish Eotriceratops, Torosaurus, and Triceratops spp. Moreover, the specimen’s extremely large size offers the possibility that it represents a new taxon. Recent studies have reported femur lengths of 1020 mm, 1033.5 mm, and 1104 mm respectively for the LK chasmosaurines Pentaceratops aquilonius (OMNH 10165), Triceratops horridus (AMNH FR 5033), and Triceratops prorsus (USNM PAL 4842). Recent mass estimates suggest that the most robust of these animals, Triceratops horridus, reached 14 tonnes. The preserved part of the femur (lacking its proximal end) in MINS V1036 is approximately 1070 mm long and may be conservatively restored to a length of 1140 mm, which conforms to the expected length based on the complete 1143 mm scapula. The femur is similar in robustness to that of AMNH FR 5033. Based on these proportions, we estimate the mass of MINS V1036 to have been more than 18 tonnes. This would make MINS V1036 the largest known ornithischian, exceeding Shantungosaurus (with a published estimate of 17 tonnes). Although the Lance Formation is a well-studied paleoenvironment, this discovery demonstrates that further exploration offers the opportunity to expand our understanding of the system.
