Re: another dumb question: Terror Birds are not dinosaurs?

[Roberto Takata <rmtakata@gmail.com>]

Anything that is derived from the most recent common ancestor of
_Archaeopteryx lithographica_ and _Passer domesticus_ is regarded as a
bird (Aves). (There are few other definitions too...)

If it is derived from the most recent common ancestor of _Triceratops
horridus_ and _Megalosaurus bucklandii_ it is classified as a dinosaur
(so any bird is a dinosaur too - from the fact that they are derived
from that ancestor).

If a critter is derived from the most recent common ancestor of _T.
horridus_ and _M. bucklandii_ but not from the most recent common
ancestor of _A. lithographica_ and _P. domesticus_ than it is
informally called a non-avian dinosaur, that is commonly called simply
as a dinosaur.

How do we know that an organism if derived from such common ancestor?
By an analysis of characters called philogenetic analysis or
cladistics - it group together organisms that share some exclusive
derived characters.

[]s,

Roberto Takata

On 6/29/07, Paula Goodman <paulawilder@mac.com> wrote:
> With all this talk about birds-are-dinosaurs, I'm curious to know what,
> if anything, distinguishes the bird status of Phorusrhacidae from that
> of the recently discovered Gigantoraptor, for example. Why do we call
> one a big bird fossil, and the other a dinosaur fossil?
>
> Paula Goodman
> bemused lay-person
> Berkeley