RE: Mesozoic mammals

["Williams, Tim" <TiJaWi@agron.iastate.edu>]

Dino Rampage wrote:

> Is there fossil evidence that the Chiroptera were already in existence 
> before the K-T? 

There's no evidence at all.  The first bats, AFAIK, come from Eocene
deposits (Green River Fm; Messel) and show clear evidence of wings.  Scrappy
remains (teeth and jaws) of Paleocene age may belong to bats (or close
relatives of the Chiroptera), but without the forelimb skeleton we cannot
know if they were capable of flight (or any type of aerial locomotion).

It's my understanding that NO placental order (as currently defined) is
currently known from Cretaceous deposits.

> What about the colugos (or flying lemurs)? 

Nope.  Unless you (1) regard the plesiadapiforms as belonging to the
Dermoptera and (2) believe that plesiadapiforms (such as _Purgatorius_)
lived at the end of the Cretaceous.  A LK tooth referred to _Purgatorius_
may actually be of early Paleocene age (when most _Purgatorius_ material is
known from).  The Plesiadapiformes are archaic primate- and dermopteran-like
placentals that most workers are reluctant to refer to either order.  

> And is there a  possibility that the Mesozoic mammals evolved gliding 
> just like sugar gliders, anomalures or flying squirrels?

No direct evidence either way.  Actually, ascribing a gliding lifestyle to
extinct vertebrates is often more difficult than you might think.  Certain
plesiadapiforms (paromomyids) have been restored as gliding mammals, like
modern colugos, based on the similar structure of their hands which in
colugos supports (and is enclosed by) the gliding membrane (patagium).
However, more recent fossils indicate that the evidence for gliding behavior
in paromomyids is weak.  

Usually, we need direct evidence of a patagium to establish whether an
animal was capable of gliding - as we have with the extinct eomyids
(rodents).  Nobody thought eomyids were gliding mammals until a
well-preserved fossil specimen was discovered with a skin membrane between
the front and back limbs.  So far, no Mesozoic mammal specimens have turned
up which show a patagium, nor any skeletal structures that might indicate
gliding behavior (such as the complex wrist anatomy seen in modern flying
squirrels).




Tim



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Timothy J. Williams, Ph.D. 

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

Phone: 515 294 9233 
Fax:   515 294 9359