Thursday, May 3, 2007

Bininda-Emonds et al. 2007

Bininda-Emonds, O.R.P., M. Cardillo, K.E. Jones, R.D.E. MacPhee, R.M.D. Beck, R. Grenyer, S.A. Price, R.A. Vos, J.L. Gittleman and A. Purvis. 2007. The delayed rise of present-day mammals. Nature. 446:; 507-512.

This paper uses a species-level phylogeny of extant Mammalia to answer the question of did the end-Cretaceous mass extinction event trigger the evolutionary radiation of present day mammals. They conclude that no, it did not.

The phrase that caught my eye while reading this paper was "phylogenetic fuses". The authors define phylogenetic fuses as: where lineages persist at low diversity for some time after their initial origins before undergoing evolutionary radiations (explosions).

Long fuse model= a long time period between the Cretaceous origins of the orders and the first split among their living representatives (crown groups) immediately after the KT boundary.
Short fuse model= diversity occured before the KT boundary

The long- and short fuse models are two competing hypotheses for when mammalian crown groups evolved.

Their hypothesis: there was a significant increase in the net per-lineage rate of extant mammalian diversification, r (the difference between the per-lineage speciation and extinction rates), immediately after the K/T mass extinction.

Methods: -only used extant mammals (this is probably a big problem in their study)
-2, 500 partial estimates (whatever that means)
-66 gene alignment w/ 30 calibration points

Results: They found low rates of extant mammalian diversification during the Cenozoic and little evidence for the long fuse model, indicating that the extinction of dinosaurs and other taxa had a major effect on mammalian diversification. However I noticed that their supertree is only 46.7% resolved. I wouldn't trust that tree.


David Marjanović said...

Some of their calibration points are bogus because they confused the origin of a crown-group with the origin of its total group.

One calibration point simply hangs in the air: it consists of two isolated Palaeocene teeth called Monotrematum ("the tooth, the whole tooth, and nothing but the tooth"). Bininda-Emonds et al. assume that they belong to a platypus and use it to calibrate the platypus-echidna divergence. But no known echidna has any trace of teeth, and their fossil record starts in the Pleistocene, IIRC. When you find isolated monotreme teeth of Palaeocene age, you have no way of telling whether they belong to a platypus, an echidna, or neither.

Tonya said...

"the tooth, the whole tooth, and nothing but the tooth".

Yeah, it must be difficult sometimes to work with fossils that are missing their entire body. But still, you can't just assume what it is and use it to calibrate. Thanks for the info on that.

David Marjanović said...

Sorry -- there is a jaw fragment of Monotrematum, and the echidna fossil record goes all the way back to the Miocene. My last sentence, however, unfortunately stands.