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Platypus niche (was Re: The birds vs. the pterosaurs)

David Marjanovic wrote:

- the platypus niche (occupied by platypuses since the Early Cretaceous).

This is not to refute David's informative post, but I would be very careful about transposing modern-day ecological niches back in time. As one listmember put it, niches are the way by which organisms divide up the available resources in a given habitat. A niche is not so much a "socket" waiting to be filled by a "peg" in the form of a species. It is more like a piece of a jigsaw puzzle, in which the size and shape and location of each piece is determined by the size and shape and location of each neighboring piece in the puzzle. Together, the puzzle pieces combine to "fill out" a complete picture. Individually, each piece is almost meaningless.

As for the "platypus niche" existing since the Early Cretaceous... This is based on the identification of the Australian monotreme _Steropodon_ as an ornithorhynchid (the platypus family). I don't think this is still regarded as correct; _Steropodon_ is a monotreme, but not an ornithorhynchid.

A second Early Cretaceous monotreme from Australia, _Kollikodon_, is certainly not an ornithorhynchid. Interestingly, based on _Kollikodon_'s dentition, this mammal may have been a shellfish-eater and hence aquatic.

But since _Steropodon_ and _Kollikodon_ are both known only from jaw material, I think it's fair to say we have very little idea how similar the ecologies of these Early Cretaceous monotremes were to that of the modern platypus (_Ornithorhynchus_). (This is even more true of a possible ornithorhynchid from the Paleocene, named _Monotrematum_, which is known only from a tooth.) The earliest monotreme which is known to have at least looked like the modern platypus is the Miocene genus _Obdurodon_, known from a beautiful skull (among other material)found in the Rivesleigh site in Queensland, northern Australia.

I strongly suspect there are people Out There who know more about >Mesozoic mammals...

Alas, I'm not one of them... :-(



Timothy J. Williams

USDA/ARS Researcher
Agronomy Hall
Iowa State University
Ames IA 50014

Phone: 515 294 9233
Fax:   515 294 3163

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