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Re: Obdurodon (was Re: Coronosaurus, new ceratopsid genus for Centrosaurus brinkmani)



"Another hypothesis is that _Obdurodon_ is referrable to the Ornithorhynchidae (the platypus family), but that _Monotrematum_ is a stem-monotreme. This is the hypothesis advanced by Phillips et al. (2009; doi: 10.1073/pnas.0904649106 ). This still means that the terrestrial, ant-eating echidnas likely evolved from amphibious ancestors, given how similar the teeth and femora of _Monotrematum_ are to ornithorhynchids. So the platypus-like characters of _Monotrematum_ would be primitive for the crown Monotremata; but _Monotrematum_ would *not* be referrable to _Obdurodon_."


I was thinking along the lines of secondarily terrestrial echidnas, in my own utterly unqualified, amateurish way, for a different reason a few years ago, and that was spurred on by a paper proposing platypus-credentials for /Teinolophus/ from the Lower Cretaceous; that is the proposed placement of Teino in the family of Ornithorhyncidae. That was at least in part based upon jaw similarities with a platy.

It left me wondering how on Earth echidnas ended up with electro-receptors in the beak, albeit not all that many of them. These aren't an obvious blessing for terrestrial mammals, although they could presumably be of some help in the moist soils of humid mountain forests. They could, I mused on the basis of nothing in particular, be a hang-over from semi-aquatic ancestors.


On 10.11.2012 05:51, Tim Williams wrote:
David Marjanovic <david.marjanovic@gmx.at> wrote:


_Monotrematum_ is now often  considered a junior synonym of
_Obdurodon_.
Really? *M.* is two isolated teeth from the Paleocene of South America; *O.*
is good material (at least one skull, IIRC) from the Miocene of Australia.

_Obdurodon_ was originally described from two isolated teeth, named
_O. insignis_.  The superb skull is from the referred species, _O.
dicksoni_.  Both _Obdurodon_ species are from Australia.  The teeth
from Patagonia named _Monotrematum sudamericum_ are very similar to
those of _Obdurodon_, although substantially larger.  Hence the
proposed synonymy.  However...


Another hypothesis is that _Obdurodon_ is referrable to the
Ornithorhynchidae (the platypus family), but that _Monotrematum_ is a
stem-monotreme.  This is the hypothesis advanced by Phillips et al.
(2009; doi: 10.1073/pnas.0904649106 ).  This still means that the
terrestrial, ant-eating echidnas likely evolved from amphibious
ancestors, given how similar the teeth and femora of _Monotrematum_
are to ornithorhynchids.  So the platypus-like characters of
_Monotrematum_ would be primitive for the crown Monotremata; but
_Monotrematum_ would *not* be referrable to _Obdurodon_.





Cheers

Tim






Cheers

Tim