National Geographic has an interesting story on the Platypus. The article talks about recent high-resolution scans of the Teinolophos jawbone. The find dates to 112.5-120 MYA and was considered to be an ancestor to both the platypus and the echidna. The osteological details revealed by the scan was quite interesting:
The scientists found that the Teinolophos had already developed features thought to be unique to modern platypuses, including an electro-sensitive “bill” for finding aquatic prey.
The research discussed in the National Geographic article has been published in PNAS. The features mentioned in the quote above include:
The ornithorhynchid mandibular canal transmits the mandibular artery and hypertrophied mandibular branch of the trigeminal nerve, in support of the electroreceptive bill that gives the duckbilled platypus its common name…
The paper goes on to argue that:
Both have comparatively narrow mandibular canals, reflecting the plesiomorphic condition that is
found in Morganucodon and all therians sampled (Fig. 4). Electroreception therefore appears to be an apomorphic characteristic of Monotremata, whereas the evolution of a specialized
duckbill for high-resolution aquatic electroreception is unique to the platypus clade. Teinolophos preserves the oldest evidence of a duckbill in its hypertrophied mandibular canal.
Additionally, a fossil known as Steropodon is also reclassified as a platypus. The paper then argues, based on a phylogenetic analysis using a data set published by Luo and Wible, for an evolutionary rate slowdown in the monotremes.
I haven’t had time to read the entire paper, much less think over the implications so I don’t want to say much more about it.
Filed under: Paleontology | Tagged: Ornithorhynchus anatinus |
Afarensis: Anthropology, Evolution, and Science 
What is the current ID theoretical prediction about the probable age of the oldest Ornytorynx fossil likely to be found ?
I saw this one, too, but I haven’t been able to get the paper yet. It looks pretty interesting, but I’m going to wait to say anything until I’ve read it (especially since I don’t know how much of the jaw they’ve recovered).
Arthur asked
IIRC, it was about 2 years 4 months old, a mother, and was nailed by a pterosaur as it crawled from river to waterhole and its remains were scattered. 🙂
C’mon: ID makes no predictions. Hell, ID won’t even commit to an age of the earth, say nothing of some old fossil.
However old it eventually gets to be dated to, it certainly is an unusual creature. I have heard it referred to as an animal constructed by a committee!
Dave Briggs :~)
Dave Briggs,
That’s, “A platypus is an animal designed by a committee meeting in a bar.”
(I posted a version of this on the DML yesterday):
Looking at the Rowe et al. paper including the supplementary info (but without re-running their analysis), I am not convinced at all. There are no support values shown on their cladogram (suggesting they were nothing to shout about), and the only characters mentioned in the text as supporting a position of tachyglossids outside the (Teinolophos, Ornithorhynchus) clade are the hypertrophy of the mandibular canal and presence of the medial tubercle at its posterior opening (derived in platypuses), which are presumably not independent (can or would a tubercle be recognizable without the large canal?).
It is known that tachyglossids have electroreceptive organs homologous to those of Ornithorhynchus, but with a much lower number of receptors; contrary to the assumption in Rowe et al., it is certainly plausible that this condition is vestigial (partial reversal) rather than an ‘incipient’ stage that has been retained for over 100 Ma! The tachyglossid mandible is edentulous and reduced overall, so reduction of one of its constituents (mand. canal) is arguably of no weight at all.
And given what we know about survival of other amniote lineages at the K/T (K/Pg, whatever), the prior expectation would be that one monotreme lineage survival is rather more likely than two.
So, to argue that tachyglossids split from a common ancestor of Teinolophos and Ornithorhynchus, one would need to perform a statistical test: with what level of confidence does the evidence reject the hypothesis that tachyglossids are nested somewhere within ‘platypuses’? There is no such test presented, and only one (or ‘two’) dubious characters mentioned to support the conclusion.
The mandibular character(s) seem to me to be outweighed by: complete loss of adult dentition, and more or less complete fusion of cranial sutures in adults. These fairly uncommon and logically independent apomorphies unite Tachyglossidae and Ornithorhynchus to the exclusion of Obdurodon (and other known monotremes for the tooth character, skulls being unknown). Oligo-Miocene Obdurodon is clearly a ‘platypus’, so I inferred a couple of decades ago that ‘platypuses’ were ancestral to Miocene-to-Recent echidnas.
How would I know if I’m wrong? Somebody finding Cretaceous ‘echidnas’ would do it, but I accept that the data set analysed by Rowe et al. could also. The published text, however, does not.