The spatiotemporal distribution of Mesozoic dinosaur diversity

Abstract

Much of our view on Mesozoic dinosaur diversity is obscured by biases in the fossil record. In particular, spatiotemporal sampling heterogeneity affects identification of the timing and geographical location of radiations, the recognition of the latitudinal diversity gradient, as well as interpretation of purported extinctions, faunal turnovers and their drivers, including the Early Jurassic Jenkyns Event and across the Jurassic/Cretaceous boundary. The current distribution of sampling means it is impossible to robustly determine whether these 'events' were globally synchronous and geologically instantaneous or spatiotemporally staggered. Accounting for sampling heterogeneity is also paramount to reconciling notable differences in results based on sampling-standardized dinosaur species richness versus reconstructions of diversification rates, particularly with regards to the lead-up to the Cretaceous/Paleogene mass extinction. Incorporation of a greater proportion of stratigraphically well-resolved dinosaurs into analyses is also imperative and must include the substantial Mesozoic radiation of birds. Given the relative rarity of temporally successive, well-sampled spatial windows, it remains possible that dinosaur species richness and diversification rate showed little change after the clade's initial radiation until the Cretaceous/Paleogene boundary. However, better understanding of underlying sampling, combined with a holistic approach to reconstructing dinosaur diversity and diversification, is an important step in testing this hypothesis.

Keywords: Dinosauria; Mesozoic; common cause hypothesis; diversity; extinction; latitudinal diversity gradient.

Figure 1.

The spatiotemporal distribution of Mesozoic dinosaurs, including birds. (a) Spatial distribution of Late Triassic occurrences. (b) Spatial distribution of Jurassic occurrences. (c) Spatial distribution of Cretaceous occurrences. (d) Observed dinosaur species richness through the Mesozoic, showing contributions from each palaeocontinental region. Data in (a–c) plotted on a present-day Mollweide map projection using The Paleobiology Database navigator (https://paleobiodb.org/navigator/). Data in (d) plotted at the midpoint of each stratigraphic stage based on data in The Paleobiology Database as of 31 July 2024.

Figure 2.

Impact of sampling on dinosaur diversity. (a) Schematic of the spatial sampling filter that affects consistency of sampling effort, with differing sampling coverage (i.e. size, location and environment) dictating observed diversity. (b) Taphonomic filter that affects preservation and recognition of species and their inclusion in analyses of dinosaur diversity. (c) Terrestrial common cause scenarios that affect both genuine and observed species richness.

Figure 3.

Palaeogeographic reconstructions of Mesozoic intervals showing spatial distribution of well-sampled dinosaur body fossil-bearing deposits. (a) Carnian (purple circles; plate reconstruction = 232 Ma); (b) latest Triassic (purple circles) to earliest Jurassic (dark blue circles; plate reconstruction = 200 Ma); (c) Toarcian (dark blue circles) to early Middle Jurassic (light blue circles; plate reconstruction = 179 Ma); (d) Kimmeridgian–Tithonian (light blue circles) to earliest Cretaceous (green circles; plate reconstruction = 147 Ma).