James Alexander Campbell, Michael P.J. Ryan & Jason Anderson (2019)
A taphonomic analysis of a multi-taxic bonebed from the St. Mary River Formation (uppermost Campanian to lowermost Maastrichtian) of Alberta, dominated by cf. Edmontosaurus regalis (Ornithischia: Hadrosauridae), with significant remains of Pachyrhinosaurus canadensis (Ornithischia: Ceratopsidae).
Canadian Journal of Earth Sciences (advance online publication)
doi:
https://doi.org/10.1139/cjes-2019-0089https://www.nrcresearchpress.com/doi/abs/10.1139/cjes-2019-0089#.XaCkz1VKjX4Scabby Butte is an isolated exposure of Upper Cretaceous (uppermost Campanian to lowermost Maastrichtian) strata of the St. Mary River Formation. These rocks have produced a diverse assemblage of both terrestrial and aquatic vertebrates, although hadrosaurid and ceratopsid dinosaurs represent the largest component by volume. Almost all of these dinosaur remains were collected from a single bonebed (Site 2) at Scabby Butte and have been referred to the hadrosaurid Edmontosaurus regalis and the ceratopsid Pachyrhinosaurus canadensis. This study presents a quantitative taphonomic reanalysis of the originally published data, providing new information previously overlooked and important information about the age class structure of the dinosaur fauna preserved at the site. Site 2 is a lag deposit with a minimum number of individuals = 11 (two ceratopsid, nine hadrosaurid), with three quarters of the material being adult-sized based on size class analysis. Most elements have undergone moderate to severe breakage and abrasion, and are completely disarticulated, suggesting that they were transported from where they died; post-mortem scavenging is also a possibility, as evidenced by the presence of toothmarks and trample marks on several elements. Burial took place soon after scavenging, as there is little evidence of subaerial weathering.
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David A. Eberth & Sandra L. Kamo (2019)
High-precision U-Pb CA-ID-TIMS dating and chronostratigraphy of the dinosaur-rich Horseshoe Canyon Formation (Upper Cretaceous, CampanianâMaastrichtian), Red Deer River valley, Alberta, Canada.
Canadian Journal of Earth Sciences (advance online publication)
doi:
https://doi.org/10.1139/cjes-2019-0019https://www.nrcresearchpress.com/doi/abs/10.1139/cjes-2019-0019#.XaClZ1VKjX4The non-marine Horseshoe Canyon Formation (HCFm, southern Alberta) yields taxonomically diverse, late Campanian to middle Maastrichtian dinosaur assemblages that play a central role in documenting dinosaur evolution, paleoecology, and paleobiogeography leading up to the end-Cretaceous extinction. Here, we present high-precision U-Pb CA-ID-TIMS ages and the first calibrated chronostratigraphy for the HCFm using zircon grains from (1) four HCFm bentonites distributed through 129 m of section, (2) one bentonite from the underlying Bearpaw Formation, and (3) a bentonite from the overlying Battle Formation that we dated previously. In its type area, the HCFm ranges in age from 73.1â68.0 Ma. Significant paleoenvironmental and climatic changes are recorded in the formation, including (1) a transition from a warm-and-wet deltaic setting to a cooler, seasonally wet-dry coastal plain at 71.5 Ma, (2) maximum transgression of the Drumheller Marine Tongue at 70.896 Â 0.048 Ma, and (3) transition to a warm-wet alluvial plain at 69.6 Ma. The HCFmâs three mega-herbivore dinosaur assemblage zones track these changes and are calibrated as follows: Edmontosaurus regalis-Pachyrhinosaurus canadensis zone, 73.1â71.5 Ma; Hypacrosaurus altispinus-Saurolophus osborni zone, 71.5â69.6 Ma; and Eotriceratops xerinsularis zone, 69.6â68.2 Ma. The Albertosaurus bonebedâa monodominant assemblage of tyrannosaurids in the Tolman Memberâis assessed an age of 70.1 Ma. The unusual triceratopsin, Eotriceratops xerinsularis, from the Carbon Member, is assessed an age of 68.8 Ma. This chronostratigraphy is useful for refining correlations with dinosaur-bearing upper Campanian-middle Maastrichtian units in Alberta, and elsewhere in North America.