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What is a "Bird"? (was Re: Moasaurus)

On Tue, 13 Feb 2001 ELurio@aol.com wrote:

> In a message dated 2/13/01 3:48:45 PM, tmk@dinosauricon.com writes:
> << OOC, what is your definition of "bird"? >>
> Anything with feathers. In other words, anything that looks like a bird. An
> Ovaraptor is probably a bird.

This definition works well for extant animals, which are pretty obviously
either feathered or not. But among fossil animals, there is more of a grey
area. Are _Sinosauropteryx_'s integumentary structures feathers? What
about those of _Beipiaosaurus_, _Sinornithosaurus_, _Microraptor_, etc.?

Furthermore, integument is generally not known among fossil animals. Out
of nearly 800 genera of Mesozoic Ornithodira, non-bony integumentary
structures are reliably known from about a couple dozen genera.

I don't really have any argument with people who want "bird" to mean
"feathered animal". They should just realize that A) it is not a binary
condition, that is, yes, some things will definitely be birds and some
things will definitely not be birds, but a number of animals will be
"semi-birds" (e.g. _Sinosauropteryx_), and B) the vast majority of the
time, you simply can't tell from the fossil record whether something is
feathered or not.

I (and many others) prefer to use "bird" as a more vernacular form of
"avian", with Aves defined as Clade(_Archaeopteryx_ + _Passer_) (or some
equivalent). This is a binary condition, and, even though people sometimes
disagree as to what exactly belongs, you don't need remains of integument
to tell -- you just need a phylogenetic hypothesis.

Of course, "bird" is a vernacular term and can really be used however one
wants. In discussions like these, I think it's far preferable to use terms
like "avian" and "feathered animal", given the differing usages of the
word "bird". People may argue about what is and isn't an avian, or what is
and isn't feathered, but it's clearer what's being discussed.

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