[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]


In a message dated 95-12-01 12:10:39 EST, martz@holly.ColoState.EDU (Jeffrey
Martz) writes:

>Not knowing much about Cenozoic bird evolution, are you saying that 
>the first flightless (were they always flightless?) ratites evolved in a 
>predator free environment?  I understand there is a current theory that 
>ratites are a monophyletic group descended from a single flightless 
>ancestor widely distributed across Gondwana during the early Paleocene, 
>In which case they must have been living around predators.  What about 
>Diatryma or the Phorusrhacids?  I realize all these birds 
>(except for the isolated kiwi) are humungous birds, some of which were 
>predatory themselves, but is there any evidence that thier ancestors were 
>small, flightless, and evolved in environs where they may have been 
>subject to predation?

I'm not sure I like the dangling participle that you begin your message

Predator-scarce might be the best description. As far as I know, ratites were
secondarily flightless (a theory disputed by a few ornithologists). The
impression I get from examining the fossil record of large, flightless birds
is that they appear rather suddenly without obvious ancestral forms, hang
around for a while, then become extinct; and that the various groups of
fossil forms are not particularly closely related to one another above the
family level. To me this indicates sporadic, rapid-fire evolution in isolated
environments. The absence of ancestral forms is evidence that they were small
and not easily fossilized. As Greg Paul pointed out, this idea extrapolates
nicely back into the Mesozoic to the theropods.