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From: evs@duke.UUCP (Ed Simpson)
Newsgroups: sci.bio
Subject: Re: evolution, parthogenesis, ad nauseum.
Message-ID: <9014@duke.duke.UUCP>
Date: Tue, 30-Dec-86 22:10:43 EST
Article-I.D.: duke.9014
Posted: Tue Dec 30 22:10:43 1986
Date-Received: Wed, 31-Dec-86 04:01:17 EST
References: <7436@utzoo.UUCP> <531@cdx39.UUCP>
Reply-To: evs@duke.UUCP (Ed Simpson)
Organization: Duke University Medical Center, Durham, NC
Lines: 61

In article <531@cdx39.UUCP> jc@cdx39.UUCP (John Chambers) writes:
>Hmmm...I thought that birds had been classified as a suborder  of
>the dinosaurs, not a class.  Anyone out there know what the official 
>taxonomy really is these days?  Like, draw me a cladogram, perhaps,
>and label the 'class' and 'order' levels.

In the most commonly accepted classificatory schemes Dinosuars belong to
the class Reptilia and birds comprise their own class, Aves.  The phylogeny
is as follows:  Phylum Chordata -> Subphylum Vertebrata -> Class Aves.
Birds arose from the group of dinosuars called saurischians (meaning "lizard-
hipped",  which is kind of strange since the other major group of dinosaurs
were ornithiscians, meaning "bird-hipped").

Birds are so different from living reptiles that it warrants placing
them in a class separate from reptiles.  I think the dispute is
whether dinosaurs should be placed in the class Reptilia.  Both birds
and mammals have a four chambered heart and are endothermic (traits
arrived at independently) and there is some evidence that dinosaurs
were also endothermic.  Does anybody know anything about the structure
of the dinosaur heart?  Dinosaurs may have been sufficiently different
from living reptiles to justify placing them in their own class,
perhaps including birds in this separate dinosaur class.  However
their are some people who think birds should be placed in the class
Reptilia as surviving dinosaurs.

A common phylogenetic tree for reptiles and their descendents is as follows:


         Turtles  Tuatara  Lizards  Snakes  Crocs         Birds        Mammals
              |       |    |          |       |             |               |
              |       |    |__________|       |             |               |
              |       |    |    ______________|             |               |
              |       |    |   |                            |               |
              |       |    |   |                            |               |
Plesiosaurs   |       |    |   |    Pterosaurs              |               |
     |        |       |    |   |     |                      |               |
     |        |       |    |   |     |                      |               |
     |        |       |    |   |     |   Ornithiscian    Saurischian        |
     |        |       |    |   \     |   Dinosaurs       Dinosaurs          |
     |        |       |     \   \    |          |        /                  |
     |        |       -------\   \   \          |       /                   |
     |        |               \   \   \         |      /     Ichthyosaurs   |
     |        |                \   \   \        |     /        /            |
     |        |______________   \   \   \____   |    /        /             |
     |                       \   \   \       |  |   |        /              |
     |                        \   \   ------Thecodonts      /               |
     |______________________   \   \            /          /                |
                            \   \   \          /          /          Therapsids
                             \   \   \    ____/          /                /
                              \   \   |  |              /                /
                               \   |  |  |   __________/                /
                                |  |  |  |  |                          /
                                Stem Reptiles-------------------------/


-------------------------------------------------------------------------------
{decvax, seismo}!mcnc!duke!evs
Ed Simpson, P.O.Box 3140, Duke Univ. Medical Center, Durham, NC 27710
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{decvax, seismo}!mcnc!duke!evs
Ed Simpson, P.O.Box 3140, Duke Univ. Medical Center, Durham, NC 27710