Gradual Dinosaur Extinction and Simultaneous Ungulate Radiation in the Hell Creek Formation

Abstract

Dinosaur extinction in Montana, Alberta, and Wyoming was a gradual process that began 7 million years before the end of the Cretaceous and accelerated rapidly in the final 0.3 million years of the Cretaceous, during the interval of apparent competition from rapidly evolving immigrating ungulates. This interval involves rapid reduction in both diversity and population density of dinosaurs. The last dinosaurs known are from a channel that contains teeth of Mantuan mammals, seven species of dinosaurs, and Paleocene pollen. The top of this channel is 1.3 meters above the likely position of the iridium anomaly, the Cretaceous/Tertiary boundary.

Dinosaur morphological diversity and the end-Cretaceous extinction

“…The prime example is hadrosauroids, which underwent a significant late Campanian-Maastrichtian disparity decrease in North America but a possible increase in Asia (which, although insignificant, is consistently found when all four metrics are subject to rarefaction). Almost all work on Late Cretaceous dinosaur diversity and abundance has focused either on pooled global datasets or the North American record, which is understandable given the relatively limited number of quality Campanian-Maastrichtian dinosaur fossils from other continents and the detailed stratigraphic understanding of the well-sampled Hell Creek Formation [4][5][6][7][8] . It may be, however, that the North American record represents a local anomaly.…”

“…Despite 30 years of intensive research, a fundamental question remains: were dinosaurs undergoing a long-term decline before intensive volcanism and the Chicxulub bolide impact in the latest Cretaceous, or did these contingencies of Earth history strike down dinosaurs during or near their prime (at a time when their global biodiversity was stable or even increasing) [3][4][5][6][7][8][9][10][11][12][13][14][15] ?…”

“…Finally, understanding the global picture of Late Cretaceous dinosaur evolution may be complicated by a traditional focus on the North American record 22 , particularly the abundance and distribution of dinosaurs within a single formation (Hell Creek Formation). This is understandable, as the Hell Creek is one of the few units that globally preserves a dinosaurdominated ecosystem and a precisely located Cretaceous-Palaeogene boundary [4][5][6][7][8] , but may be only partially informative, if there were region-specific trends in biodiversity. It also cannot reveal patterns that occurred over longer timescales (for example, the last 12 million years of the Cretaceous).…”

Dinosaurs and the Cretaceous Terrestrial Revolution

“…According to a long-standing hypothesis (Sloan et al 1986;Sarjeant & Currie 2001;Sullivan 2006), the group was in decline long before its extinction at the end of the Cretaceous Period, 65 Myr ago. However, new evidence (Fastovsky et al 2004;Taylor 2006;Wang & Dodson 2006) suggests a major increase in diversification during the Campanian and Maastrichtian, spanning approximately the last 18 Myr of the Cretaceous, a finding that emphasizes the dramatic nature of the apparently sudden extinction of dinosaurs at the end of the Cretaceous.…”

Analytical chemists and dinosaurs

“…It is always possible to find some support in favour of negation of any well-tried theory. For example, dinosaur bones have been reported from Hell Creek, Montana, in a stratum some 1.3 m above the putative K-T boundary (30). This has been advanced as proof that dinosaurs outlived the terminal Cretaceous.…”