Re: Dino Birds (was Re: Dinosaur = extinct animal)

["T. Mike Keesey" <tkeese1@gl.umbc.edu>]

On Sun, 11 Jul 1999, Carl Ramm wrote:

> If we are going to classify birds as dinosaurs because of their descent, then
> would we classify mammals as reptiles, reptiles as amphibians, amphibians as
> fish, etc.?  If not, what is the difference in the case of dinosaurs and
> birds?  If the idea is that the birds never "left" the dinosauria, then how do
> you ever "leave"?   If in fact we should consider mammals as a form of reptile
> (and thereby also a type of amphibian, fish, etc.) haven't we stretched the
> meaning of the terminology past the breaking point?  Wouldn't it be better to
> come up with a new terminology?

An effort has been made to adapt the old terminology to the new system. In
some cases, names are thrown out, in others, applied to clades.

Many of these re-definitions have been based on extant taxa. Reptilia, for
example, was defined as the most recent common ancestor of chelonians
(turtles), lepidosaurs (tuataras, lizards, & snakes), and crocodylians,
plus all of its descendants. By the most widely accepted phylogenies,
Synapsida (mammals and their ancestors) falls outside of this, while
Dinosauria (including Aves) is included. Were it discovered that Mammalia
did fall inside, Reptilia would become synonymous with Amniota and
probably be dropped.

Amphibia was defined as all animals sharing more recent ancestry with
modern-day amphibians (frogs, salamanders, and blindworms) than with
Amniota. Thus, many forms once called amphibians are now not amphibians,
but simply basal tetrapods.

Pisces has not been used as a taxon for decades. "Fish" remains an
informal term. All bony vertebrates do belong to Osteichthyes, however
(the node containing Actinopterygii and Sarcopterygii).

I have a discussion on the definition of Dinosauria at
http://dinosaur.umbc.edu/taxa/dinosaur.htm

For more, see the Tree of Life. I forget the URL, but have a link at
http://dinosaur.umbc.edu/links.htm

--T. Michael Keesey
tkeese1@gl.umbc.edu | THE DINOSAURICON: http://dinosaur.umbc.edu/
AOL IM:   RicBlayze | WORLDS:    http://www.gl.umbc.edu/~tkeese1/