MESOZOIC MONOTREMES

[darren.naish@port.ac.uk]

Ronald Orenstein wrote..

> Actually, I am not sure why it is any more of a problem than (say) 
> the absence (as far as I am aware) of undoubted monotreme fossils 
> from the Mesozoic 

To my knowledge, there are undoubted monotreme fossils from the 
Mesozoic. _Steropodon_ and _Kollikodon_ are monotremes, yes?

And on the subject of monotremes.. this just in.

FOX, R.C. and MENG, J. 1997. An X-radiographic and SEM study of the 
osseous inner ear of multituberculates and monotremes (Mammalia): 
implications for mammalian phylogeny and evolution of hearing. _Zool. 
J. Linn. Soc._ 121: 249-291.

In quick summary.. (1) at some MTB cochlea have a legena (previously 
known only from monotremes), (2) different MTB lineages convergently 
evolved an enlarged vestibule, so it is not an MTB synapomorphy as 
previously proposed, (3) MTB ears are poorly adapted for reception of 
high-frequency airborne sounds as their cochlear canals lack osseous 
laminae to support short, wide basilar membranes, (4) 
bone-conducted hearing may have been important to some MTBs. 

Some of this is perhaps supportive of subterranean, fossorial habits 
for certain MTBs.

"Don't EVER ask me about Paris again!"

DARREN NAISH
darren.naish@port.ac.uk









is for the view that these creatures represent an 
earlier offshoot of the mammal stock than marsupials and placentals.  
For one thing, how good is the fossil record generally for the upper 
Triassic / lower Jurassic when protobirds presumably existed?  
Compare (for example) the preservation of Protavis (whatever that is) 
with that of Archaeopteryx or the new Chinese finds.  Are there any 
comparable beds to the Solnhofen in terms of preservational quality 
for these critical periods?  If not, this could be a reason why bird 
ancestors have yet to be found.--
Ronald I. Orenstein                           Phone: (905) 820-7886
International Wildlife Coalition              Fax/Modem: (905) 569-0116
1825 Shady Creek Court                 
Mississauga, Ontario, Canada L5L 3W2          mailto:ornstn@inforamp.net