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Major extinctions of land-dwelling vertebrates at the Cretaceous-Tertiary boundary, eastern Montana

Authors:
  • University of Wisconsin - Milwaukee Geosciences

Abstract

A large database recording species of terrestrial vertebrates present in formations above and below the Cretaceous-Tertiary (K-T) boundary in eastern Montana was assembled by J. D. Archibald and L. J. Bryant. Division of the species in this database into freshwater and land-dwelling vertebrate assemblages reveals that the K-T vertebrate extinction was concentrated in land- dwelling forms. In data corrected for the effects of rare taxa, 90% of the species in the freshwater assemblage survived into the Tertiary, but only 12% of the land-dwelling forms survived. The pattern of differential extinction of terrestrial vertebrates in eastern Montana may be in large part the result of the dependence of land-based communities on primary productivity. This is in contrast to the riverine communities, which may derive much of their organic carbon from detritus. The pattern of extinction and survival is compatible with the hypothesis of an asteroid impact after which there was a temporary cessation of primary, photosynthetic productivity.
Geology
doi: 10.1130/0091-7613(1992)020<0556:MEOLDV>2.3.CO;2
1992;20;556-560Geology
Peter M. Sheehan and David E. Fastovsky
eastern Montana
Major extinctions of land-dwelling vertebrates at the Cretaceous-Tertiary boundary,
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... As the Hell Creek Formation is one of the few well-sampled examples of a late Maastrichtian assemblage globally, our understanding of its diversity and paleoecology is paramount to our interpretations of mass extinction dynamics at the end of the Cretaceous (e.g., Sheehan and Fastovsky 1992 have discussed the possibility that the end-Cretaceous dinosaur mass extinction was size dependent (Bakker 1977;Russell 1977;Buffetaut 1990;Benson et al. 2014), with a disproportionate effect on larger taxa. If, however, our understanding of the dinosaur size distribution within this formation is taphonomically biased against small taxa, as we revealed here, then a size-independent extinction of all non-avian dinosaurs will appear to be size selective against large-bodied taxa. ...
... The strongest extinction selectivity has been proposed for body sizes >25 kg for the terrestrial and freshwater realms (Bakker 1977;Russell 1977;Sheehan and Fastovsky 1992;Buffetaut 2006). Virtually no species above this body-mass threshold survived the K/Pg extinction event. ...
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The end-Cretaceous (K/Pg) mass extinction event is the most recent and well-understood of the “big five” and triggered establishment of modern terrestrial ecosystem structure. Despite the depth of research into this event, our knowledge of upper Maastrichtian terrestrial deposits globally relies primarily on assemblage-level data limited to a few well-sampled formations in North America, the Hell Creek and Lance Formations. These assemblages disproportionally affect our interpretations of this important interval. Multiple investigations have quantified diversity patterns within these assemblages, but the potential effect of formation-level size-dependent taphonomic biases and their implications on extinction dynamics remains unexplored. Here, the relationship between taphonomy and body size of the Hell Creek Formation and Lance Formation dinosaurs and mammals are quantitatively analyzed. Small-bodied dinosaur taxa (<70 kg) are consistently less complete, unlikely to be articulated, and delayed in their description relative to their large-bodied counterparts. Family-level abundance (particularly skeletons) is strongly tied to body mass, and the relative abundance of juveniles of large-bodied taxa similarly is underrepresented. Mammals show similar but nonsignificant trends. The results are remarkably similar to those from the Campanian-aged Dinosaur Park Formation, suggesting a widespread strong taphonomic bias against the preservation of small taxa, which will result in their seemingly depauperate diversity within the assemblage. This taphonomically skewed view of diversity and abundance of small-bodied taxa amid our best late Maastrichtian samples has significant implications for understanding speciation and extinction dynamics (e.g., size-dependent extinction selectivity) across the K/Pg boundary.
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Article
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... Furthermore, no dinosaur bones have been found in any indisputable Cenozoic or Tertiary assemblages. The sites where researchers have claimed dinosaur bones in Cenozoic contexts, such as the Hell Creek site in Montana, are fiercely disputed (Sheehan et al., 1991;Archibald and Bryant, 1990;Sheehan and Fastovsky, 1992;Hurlbert and Archibald, 1995). The lack of dinosaurs in Cenozoic contexts contrasts the prevalence of at least 310 mammal genera in Mesozoic contexts (Luo, 2007). ...
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Mass extinctions have repeatedly shaped global biodiversity. The Cretaceous-Paleogene (K-Pg) mass extinction caused the demise of numerous vertebrate groups, and its aftermath saw the rapid diversification of surviving mammals, birds, frogs, and teleost fishes. However, the effects of the K-Pg extinction on the evolution of snakes—a major clade of predators comprising over 3,700 living species—remains poorly understood. Here, we combine an extensive molecular dataset with phylogenetically and stratigraphically constrained fossil calibrations to infer an evolutionary timescale for Serpentes. We reveal a potential diversification among crown snakes associated with the K-Pg mass extinction, led by the successful colonisation of Asia by the major extant clade Afrophidia. Vertebral morphometrics suggest increasing morphological specialisation among marine snakes through the Paleogene. The dispersal patterns of snakes following the K-Pg underscore the importance of this mass extinction event in shaping Earth’s extant vertebrate faunas.
... This paleoenvironmental segregation could also contribute to explain the tethysuchian survivorship, while mosasaurs and plesiosaurs became extinct during the K-Pg crisis. The fresh-water environments suffered less from the K-Pg crisis than marine realm (Bakker, 1977;Van Valen and Sloan, 1977;Sheehan and Fastovsky, 1992;Cavin, 2002), and this constrained fresh-water life, as a flexibility in their environment of life probably helped tethysuchians to survive to the K-Pg crisis. ...
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