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Re: Platypuses may be older than we think...


You don't think so? What if Rowe &c are correct? As it says in the SVP abstract, which you kindly posted (http://dml.cmnh.org/2007Oct/msg00309.html)...

"New evidence from high-resolution X-ray computed tomography indicates that *Teinolophos*, an Early Cretaceous fossil from Australia's Flat Rocks locality (121-112.5 Ma), lies within the crown clade Monotremata, as a basal platypus. Divergence of the two monotreme clades therefore had occurred in or before the Early Cretaceous."

I interpret this to mean that the tomography shows the presence of a nerve that ended in a bill with electrosensory organs. If this nerve is secondarily reduced in the echidnas (which have a bill and an apparently reduced electro-sense), we can't tell where on the monotreme tree *Teinolophos* lies.

I know this contradicts Bininda-Emonds et al. (2007; Nature 446: 507-512), who provide a molecular-clock-based divergence at around the end-K extinction for the echidna and platypus lineages.

Worse. They used the latest possible date of this divergence to _calibrate_ their tree.

Still worse: they got that minimal age by means of assuming that the Palaeocene *Monotrematum* was a platypodan. Problem is, *M.* is only known from two teeth, and not a single tachyglossan tooth is known, so we can say absolutely nothing about its phylogenetic position with respect to Tachyglossa.

Thus, if Bininda-Emonds &c are correct on the divergence times of the major placental groups

There are several more mistakes in their calibration points; several times they used the appearance of total groups as the appearance of crown-groups.

Advice to peer-reviewers: Read the whole supplementary information, tables included.