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Comparative Study
. 2008 Nov 7;275(1650):2483-90.
doi: 10.1098/rspb.2008.0715.

Dinosaurs and the Cretaceous Terrestrial Revolution

Graeme T Lloyd  1 , Katie E Davis, Davide Pisani, James E Tarver, Marcello Ruta, Manabu Sakamoto, David W E Hone, Rachel Jennings, Michael J Benton
Affiliations
Comparative Study

Dinosaurs and the Cretaceous Terrestrial Revolution

Graeme T Lloyd et al. Proc Biol Sci. .

Abstract

The observed diversity of dinosaurs reached its highest peak during the mid- and Late Cretaceous, the 50 Myr that preceded their extinction, and yet this explosion of dinosaur diversity may be explained largely by sampling bias. It has long been debated whether dinosaurs were part of the Cretaceous Terrestrial Revolution (KTR), from 125-80 Myr ago, when flowering plants, herbivorous and social insects, squamates, birds and mammals all underwent a rapid expansion. Although an apparent explosion of dinosaur diversity occurred in the mid-Cretaceous, coinciding with the emergence of new groups (e.g. neoceratopsians, ankylosaurid ankylosaurs, hadrosaurids and pachycephalosaurs), results from the first quantitative study of diversification applied to a new supertree of dinosaurs show that this apparent burst in dinosaurian diversity in the last 18 Myr of the Cretaceous is a sampling artefact. Indeed, major diversification shifts occurred largely in the first one-third of the group's history. Despite the appearance of new clades of medium to large herbivores and carnivores later in dinosaur history, these new originations do not correspond to significant diversification shifts. Instead, the overall geometry of the Cretaceous part of the dinosaur tree does not depart from the null hypothesis of an equal rates model of lineage branching. Furthermore, we conclude that dinosaurs did not experience a progressive decline at the end of the Cretaceous, nor was their evolution driven directly by the KTR.

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Figures

Figure 1
Figure 1
The year of publication of source trees shows a strong skew among included trees towards more recent analyses. Excluded trees include those that were uncorroborated; solid grey line (lacked an accompanying matrix and character list) or redundant; dashed grey line (trees that have been superseded by a later, more comprehensive study). Included trees are either independent; solid black line (are characterized by a unique combination of characters and taxa) or dependent; dashed black line (trees derived from a shared character list, but have differing and non-redundant taxon sets). The latter were down-weighted in the supertree searches so that their summed contribution was equal to that of one independent tree. The three major peaks (1990, 1999 and 2004) correspond to the publication of The Dinosauria first edition (Weishampel et al. 1990), a Science review paper (Sereno 1999) and The Dinosauria second edition (Weishampel et al. 2004), respectively.
Figure 2
Figure 2
Results of different analyses of dinosaur diversification. (a) A summary version of the supertree used here; the 11 statistically significant diversification shifts present in both the entire tree and at least one time slice are marked with white arrows denoting the branch leading to the more speciose clade. Taxa in bold represent the collapsing of a larger clade, the size of which is indicated in parentheses. An ‘*’ indicates the collapsing of a paraphyletic group and a ‘†’ that of an extant clade (i.e. birds). (b) Diversification rates based on the raw record (solid line), the raw record plus additional ghost ranges (dashed line) and subsampled data (dotted lines; see text). (c) Mean values of Δ2 shift statistic through time (see text).
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