Dinosaur diversification rates were not in decline prior to the K-Pg boundary

Abstract

Determining the tempo and mode of non-avian dinosaur extinction is one of the most contentious issues in palaeobiology. Extensive disagreements remain over whether their extinction was catastrophic and geologically instantaneous or the culmination of long-term evolutionary trends. These conflicts have arisen due to numerous hierarchical sampling biases in the fossil record and differences in analytical methodology, with some studies identifying long-term declines in dinosaur richness prior to the Cretaceous–Palaeogene (K-Pg) boundary and others proposing continued diversification. Here, we use Bayesian phylogenetic generalized linear mixed models to assess the fit of 12 dinosaur phylogenies to three speciation models (null, slowdown to asymptote, downturn). We do not find strong support for the downturn model in our analyses, which suggests that dinosaur speciation rates were not in terminal decline prior to the K-Pg boundary and that the clade was still capable of generating new taxa. Nevertheless, we advocate caution in interpreting the results of such models, as they may not accurately reflect the complexities of the underlying data. Indeed, current phylogenetic methods may not provide the best test for hypotheses of dinosaur extinction; the collection of more dinosaur occurrence data will be essential to test these ideas further.

Dinosaur biodiversity declined well before the asteroid impact, influenced by ecological and environmental pressures

“…Overall, our results indicate that the diversity dynamics of Late Cretaceous dinosaurs support the hypothesis of a diversity decline 10 million years before the K/Pg event, which is in agreement with a recent phylogeny-based analysis 10 . This result, however, contrasts with other fossil-based estimates showing no decline prior to the K/Pg 3 , 30 , 32 .…”

“…The latest thorough analyses of fossil data found no evidence for a decline of non-avian dinosaurs before their extinction 3 , 30 , and little evidence of any decline in dinosaur species richness or ecological diversity during the last million years of the Cretaceous. However, a phylogenetic study using dinosaur timetrees 10 challenged the idea of a sudden extinction, but instead supported a diversity decline with extinction rates exceeding speciation rates well before the K/Pg event, which has been disputed recently 32 . Thus, there is no consensus on whether dinosaurs were in decline or not prior to their extinction.…”

Strong support for a heterogeneous speciation decline model in Dinosauria: a response to claims made by Bonsor et al . (2020)

“…Recently, Bonsor et al [1] criticized our selection of a model of diversification in dinosaurs that supported a long-term decline in the rate at which speciation events accumulated across the dinosaur tree of life through time (time-quadratic model) [2]. Core to their criticism, Bonsor et al [1] applied our analytical approach to nine additional trees that were published subsequently to our 2016 paper [2], claiming that the timequadratic model is not as well supported as we originally reported. They go on to list several criticisms of our choices in selecting the time-quadratic model as the preferred model of diversification.…”

“…1 from [2] but also reproduced as fig. 1 in [1]), we compared three models, each differing in how the temporal effects were modelled as the predictor variables: Model A, the time-linear (null) model, N Nodes = Time; Model B, the time-square root model, N Nodes = √Time; and Model C, the time-quadratic model, N Nodes = Time + Time 2 .…”

“…We found that Model C-5G had the lowest DIC score and we thus selected this model as the preferred model. Now that we have covered our model fitting and comparisons, we can proceed to address the criticisms made by Bonsor et al [1].…”