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Re: Are dinosaurs really reptiles?



The only thing I'd add to Roberto's excellent summary is that there are several researchers that think the term "Reptilia" should be dropped altogether. The arguement (which I sympathize with) is that the original definition of reptile (non-mammalian synapsids and diapsids excluding avian theropods) is so different from the current definition that there is no continuity to justify contined use of the name. The reason I sympathize with the view point is because a) Names should not be infinitely plastic (especially traditional names that were not defined phylogeneticall), and b) the term "reptile" is overly laden with misleading implications. To school kids still learning that reptiles are "scaly, cold-blooded animals that usually lay eggs" they are wholly unprepaired mentally to grasp that birds are reptiles while basal synapsids are not. Worse, the question (which I get a lot at our museum) "But...aren't dinosaurs reptiles?" is almost always a mental roadblock to them understanding the information they've just been given (fuzzy warm-blooded pterosaurs, feathered theropods, rapid growth in sauropods and otehr dinosaurs, parentla care, etc).

Since "Reptilia" cannot possibly contain the groups it was originally intended for (and to be used at is must include groups it was explicitly NOT supposed to contain) and is manifestly detrimental pedagologically, I frankly would rather it just be dropped all together.

At one point there was a decent amount of support for this idea, but I believe neontological herpitologists have reallly spear-headed the change to the new "crocodiles, turtles, lizzards, snakes, tuataras their most recent common ancestor and all its descendants" definition, since that has minimal impact on their work (except having to include birds).

Sigh...

Scott Hartman
Science Director
Wyoming Dinosaur Center
110 Carter Ranch Rd.
Thermopolis, WY 82443
(800) 455-3466 ext. 230
Cell: (307) 921-8333

www.skeletaldrawing.com


-----Original Message----- From: Roberto Takata <rmtakata@gmail.com> To: trex_kid@hotmail.com Cc: dinosaur@usc.edu Sent: Fri, 25 Apr 2008 4:18 am Subject: Re: Are dinosaurs really reptiles?



Well, it is an issue more or less well settled down.

In a phylogenetic systematics (a classification system that takes into
account only derived - evolutionarily novel - characteristics) there
is no such thing as class, order or so on. Just monophyletic groups (a
group that is formed by an ancestral form and all of its descendants).
And a monophyletic group could and must be nested within a broader
(more inclusive) monophyletic group: just in the same way that Primate
is within Mammalia and Mammalia within Synapsida and Synapsida within
Amniota and so on. (Only the group that include all life forms will
not be included in any other group.)

Most researches agree that Reptilia is a group that include
crocodiles, turtles, lizzards, snakes, tuataras their most recent
common ancestor and all its descendants. So, birds and dinosaurs are
included within Reptilia - they share a exclusive ancestor with
crocodyles. But mammals and their extinct relatives are not.

If we exclude dinosaurs from Reptilia, it won't be a monophyletic group anymore.

Alternatively we could expand Reptilia to include Mammalia and their
relatives - but in doing so it will be the same as Amniota.

(Robert T Bakker once argued to elect a class to dinosaurs - including
birds - but he was not using the phylogenetic way of thought.)

[]s,

Roberto Takata

[]s,

Roberto Takata

On Fri, Apr 25, 2008 at 6:57 AM, Brandon Pilcher <trex_kid@hotmail.com> wrote:
"Traditionally, dinosaurs have been considered reptiles, and it's true
that many share some physical characteristics with reptiles (scaly
skin). However, I know that there are paleontologists who think
dinosaurs are distinct enough from traditional reptiles to justify
getting their own taxonomic class. I am inclined towards this view.
The very fact that birds, traditionally considered to be non-reptiles,
are the closest living relatives of dinosaurs, not any extant
reptiles, convinces me to consider the Dinosauria as separate from
Reptilia. There's no good reason to classify a group of animals inside
one class when those animals are more closely related to members of
another class (birds) than to those within the class they've been
assigned."