Size-driven preservational and macroecological biases in the latest Maastrichtian terrestrial vertebrate assemblages of North America

Abstract

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.

Shifts in food webs and niche stability shaped survivorship and extinction at the end-Cretaceous

“…S8), providing further support for the robustness of our interpretations. These results are also compatible with an undersampling of small-sized taxa in both Campanian ( 53 ) and Maastrichtian ( 54 ) faunas.…”

The appendicular myology of Stegoceras validum (Ornithischia: Pachycephalosauridae) and implications for the head-butting hypothesis

“…Our proposed muscle reconstruction is largely limited by a lack of available study material, reflective of the strong preservational bias against the preservation of small skeletons in the fossil record [ 6 , 122 , 123 ]. UAVLP 2 is among the most complete known pachycephalosaur skeletons, although it is missing significant portions of the axial column and distal limb elements.…”

Interelemental osteohistological variation in Massospondylus carinatus and its implications for locomotion

“…This is consistent with the conclusions of Myhrvold (2013) , who noted that very immature and very mature individuals are underrepresented in a wide variety of dinosaur clades. This could be due to preservation bias ( Brown et al, 2013 ; Brown et al, 2021 ), errors in age estimation methods, or to high mortality rates in mature individuals (due to competition, disease, predation) ( Erickson, 2005 ; Erickson et al, 2006 ; Hone & Rauhut, 2010 ).…”