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Re: How archosauromorphs beat out therapsids

Didn't notice this when it first came up, found out about it through a
search. Unfortunately my campus has a 1 year rolling embargo on all
Pr.Roy.Soc.B sources. (this is where the frowny face goes). Nice the
the SOM is free.

My understanding is that they built a supertree using a group of
datasets and applied parsimony analysis to them. Then I think they
tacked on their size data (femur & skull length) and used that to
reconstruct ancestral states (assuming this is done through the
parsimony analyzer).

What I'm a little unclear about is where the Maximum Likelihood comes
in, the SOM only really mentions that they used AIC, but it doesn't
say what models they're comparing (must be in the actual paper). Their
big conclusion is that Cope's Rule doesn't apply, so I have to assume
that they're comparing Cope's Rule to a null hypothesis as two models.

Interesting stuff.

On Wed, Feb 1, 2012 at 11:48 AM, Ben Creisler <bcreisler@gmail.com> wrote:
> From: Ben Creisler
> bcreisler@gmail.com
> 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
> http://rspb.royalsocietypublishing.org/content/early/2012/01/31/rspb.2011.2441.abstract
> The pdf of the data supplement is free:
> http://rspb.royalsocietypublishing.org/content/suppl/2012/01/31/rspb.2011.2441.DC1/rspb20112441supp2.pdf
> 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:
> http://news.discovery.com/animals/how-dinosaurs-got-so-big-120131.html
> http://news.sciencemag.org/sciencenow/2012/01/the-secret-of-dinos-success.html?ref=hp

Robert J. Schenck
Kingsborough Community College
Physical Sciences Department
Follow Me on Twitter: @Schenck