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Re: How archosauromorphs beat out therapsids

From: Ben Creisler

Here's the official citation:

Roland B. Sookias, Richard J. Butler and Roger B. J. Benson (2012)
Rise of dinosaurs reveals major body-size transitions are driven by
passive processes of trait evolution.
Proceedings of the Royal Society B (advance online publication)
doi: 10.1098/rspb.2011.2441

The pdf of the data supplement is free:

A major macroevolutionary question concerns how long-term patterns of
body-size evolution are underpinned by smaller scale processes along
lineages. One outstanding long-term transition is the replacement of
basal therapsids (stem-group mammals) by archosauromorphs, including
dinosaurs, as the dominant large-bodied terrestrial fauna during the
Triassic (approx. 252–201 million years ago). This landmark event
preceded more than 150 million years of archosauromorph dominance. We
analyse a new body-size dataset of more than 400 therapsid and
archosauromorph species spanning the Late Permian–Middle Jurassic.
Maximum-likelihood analyses indicate that Cope's rule (an active
within-lineage trend of body-size increase) is extremely rare, despite
conspicuous patterns of body-size turnover, and contrary to proposals
that Cope's rule is central to vertebrate evolution. Instead, passive
processes predominate in taxonomically and ecomorphologically more
inclusive clades, with stasis common in less inclusive clades.
Body-size limits are clade-dependent, suggesting intrinsic, biological
factors are more important than the external environment. This
clade-dependence is exemplified by maximum size of Middle–early Late
Triassic archosauromorph predators exceeding that of contemporary
herbivores, breaking a widely-accepted ‘rule’ that herbivore maximum
size greatly exceeds carnivore maximum size. Archosauromorph and
dinosaur dominance occurred via opportunistic replacement of
therapsids following extinction, but were facilitated by higher
archosauromorph growth rates.


Two news story links about a new study of how archosauromorphs beat
out therapsids and reached huge size.
The official article has not been posted yet on the Proceedings of the
Royal Society B site: