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Brooding (was Re: Arms into wings)



At 01:10 PM 3/5/99 -0800, Randy King wrote:

>>    It's not the photo that does it. It's the identified behavior in a wide
>>range of species. Perhaps this can never "establish" the trait as basal, but
>>it can make it extremely uncomfortable for anyone arguing that modern birds
>>developed wing feather brooding recently and independently. As we pile on
>more
>>examples, such critics will have to say that convergent evolution happened
>>separately in the great majority of modern species.
>
>By a similar argument, a counterexample would disprove it?
>The cowbird does not brood, being somewhat parasitic.  
>

To which Tom Hopp replied:
>
>Yeah, okay. And here's another. Ostriches don't fly. Therefore birds don't
>fly.
>

Gentlemen, gentlemen, gentleman.

Might I suggest that you actually employ the appropriate test for this?
That is, map this trait on a bird phylogeny (or multiple bird phylogenies)
and find out its distribution? That way you can find out if it is basal for
Neornithes, at least.

Ignoring the specimens I'm about to mention, that only gets you to the base
of Neornithes, though.  Characters found in all *modern* birds are not
necessarily found in basal birds as well: toothlessness, pubic apices not in
contact, a pygostyle, and a carpometacarpus are four good examples.

However, as troodontids and oviraptorosaurs seem to have been found in the
brooding position over eggs, we can hypothesize that this condition is basal
for at least Maniraptora (or possibly Maniraptoriformes if troodontids are
closer to ornithomimosaurs than to birds).

However, as far as fossilized behavior goes, that is as far down the tree
that we can take it right now.  Below that point we enter the realm of mere
speculation (and to get to that point we have to accept that what the
"brooding" oviraptorosaurs and troodontids were doing was homologous to what
birds do).

Playing the "my scenario is better than your scenario" game doesn't get
people anywhere without some sort of method to chose (provisionally) between
scenarios.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:tholtz@geol.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661