Shape of Mesozoic dinosaur richness

Abstract

Figure 1. Dinosaur generic richness through Mesozoic by epoch. Each epoch has two metrics: left tabulation is absolute generic richness and consists of summation of different genera found during that time interval; right tabulation in each epoch is total sample counts, tallied from different geographic localities represented in that time interval. E.-Early; M.-Middle; L.-Late.TABLE 1. DINOSAUR GENERIC RICHNESS THROUGH THE MESOZOIC BY CONTINENT Epoch

Dinosaurs and the Cretaceous Terrestrial Revolution

“…As we show, and as noted before (Fastovsky et al 2004), much or all of the Campanian and Maastrichtian boost in diversity in the last phases of the Mesozoic is probably an artefact of abundant preservation and intense sampling. Our diversification shift tests indicate that only two significant diversifications happened in the Late Cretaceous, corresponding to the initial diversifications of the euhadrosaurs and the ceratopsids.…”

“…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. This Late Cretaceous diversification has been seen as evidence that dinosaurs were part of the Cretaceous explosion of terrestrial life (Fastovsky et al 2004;Weishampel et al 2004) characterized by, among others, the rise of flowering plants, social insects and butterflies, as well as modern groups of lizards, mammals and possibly birds (Hedges et al 1996;Grimaldi 1999;Dilcher 2000;Fountaine et al 2005;Bininda-Emonds et al 2007).…”

Dinosaur morphological diversity and the end-Cretaceous extinction

“…Others, however, including carnivorous dinosaurs, mid-sized herbivores, and some Asian taxa evidently did not. It must be remembered that our coarse time bins, which are necessary because of the imprecise ages of most fossils included in our study 12 , only examine changes between two or three subintervals of the latest Cretaceous, and results will likely be refined as the temporal ages of fossils become better constrained 10 . It should also be remembered that, whatever the cause and tempo of the dinosaur extinction, by the beginning of the Paleocene non-avian dinosaur disparity was zero, indicating that the focal point of the extinction was within or at the end of the Maastrichtian, the final bin in our analysis.…”

“…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] ?…”

“…Diversity counts, however, are problematic because of the emerging realizations that observed taxonomic richness is heavily biased by uneven sampling of the fossil record 16,17 and that many supposed Late Cretaceous dinosaur species are likely juveniles or sexual morphs of other known taxa [18][19][20] . Attempts to 'correct' terminal Cretaceous diversity counts for such biases have produced conflicting results [10][11][12][13][14][15] . Similarly, abundance measures are also potentially distorted by taphonomic and palaeoenvironmental heterogeneity over time 21 .…”