monotremes and multituberculates (was reply to reply...Cynodont)

[Pieter.Depuydt@rug.ac.be]

Ron Dass asked:
 > >  Incidently, are any fossil monotremes known that are generalist "normal"
 > >  herbivores and carnivores or are they all highly specialized wierdos
 > >  like the platypus and echidna. 
Nick Pharris answered:
> Unfortunately, the fossil record of monotremes is almost nonexistent apart
> from a jaw from South America, nearly identical to a modern platypus apart
> from its teeth (it had them).
I wrote:
> The platypus does have some teeth as a juvenile, but it quickly loses 
> them. The fossil record of monotremes is very very poor indeed; as far 
> as I know off my head, there are only some Miocene teeth and three 
> genera from the Cretaceous of Australia (Steropodon, Kallimodon and a 
> third one) all based on isolated teeth. However at least one of these 
> Cretaceous genera reached the size of a cat, which was respectable 
> for a mammal in those times. They probably occupied more habitats 
> than nowadays, the platypus and the echidnas being relicts that 
> survived by specialisation towards a very peculiar niche.

Phiew. A Major Lapsus escaped the otherwise very attentive and 
critical leadership of the list subscribers. 'Kallimodon' should of 
course be 'Kollikodon', accurately mentioned by Adam Yates. Kallimodon 
has nothing to do with monotremes, it's a Jurassic Sphenodontian...
The Miocene teeth or jaw fragments I spoke of are from the 
ornithorynchid Obdurodon. The third Australian monotreme has probably 
appeared in my dreams. Have to learn to resist to the temptation of 
quickly answering interesting questions without checking 
references...
So to summarize things, there are currently four Monotreme 'families' 
known: the platypi (Ornithorynchidae), represented by the extant 
Ornithorynchus, and some fossil relatives, one of these from the 
Palaeocene of Patagonia, South America (the ONLY monotreme from 
outside Australia AFAIK); the echidnas (Tachyglossidae), and
the Steropodontidae and the Kollikodontidae of the 
Cretaceous of Australia, the latter having aberrant crushing teeth 
but perhaps a sort of ornithorynchid beak (the mandibular fragment 
shows a very large mandibular canal). By the way, if I am informed 
correctly, the Steropodon jaw should be one of those famous opalized 
fossils.

<for example, were multituberculates monotremes or monotreme-like?

The question about the relationships of Multituberculata is as yet 
unsolved. Based on the ear ossicle morphology of a well preserved 
Chinese multi. (Lambdopsalis), Meng and Wyss suggested monotreme 
affinities; in the same Nature volume Sereno and McKenna stated 
multis were quite advanced in their front limb position, having a 
fully erect forelimb stance, and thus closer related to Therians than 
to monotremes and morganucodontids.
Of course in the light of the new molecular data, Monotremata and 
Marsupialia are sister groups, so Meng's and Sereno's conclusions are 
not mutually exclusive, aren't they?

Pieter Depuydt