Were dinosaurs reptiles? Are birds reptiles?

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Another thread led to the question of whether dinosaurs were reptiles. I didn't think so because I have come to believe that some dinosaurs were warm blooded, which I *thought* made them a non-reptile. And of course I assumed birds were not reptiles for the same reason. Then I found this, on a reputable site:

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Reptilia, presented as a Class in our classification, includes turtles (Testudines), snakes and lizards (Lepidosauria), crocodiles and their relatives (Crocodilia), and birds (Aves), as well as a number of extinct groups. Reptiles (including birds!) are amniotes; that is, their eggs are protected from dessication and other environmental problems by an extra membrane, the amnion, not found in the first terrestrial vertebrates (amphibians). Mammals (Mammalia) are also amniotes, but they differ from reptiles in the structure of their skulls (especially the regions associated with chewing and hearing). Mammals also have hair and feed their young with milk produced by modified skin glands (mammary glands).

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Are dinosaurs and birds still considered to be reptiles (by virtue of skull structure), even though they are warm blooded?

I thought dinosaurs and mammals and reptiles all had common ancestors, but I didn't know that all dinosaurs evolved from reptiles.

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I'm surprised, too. Searched for "are dinosaurs reptiles?" and got:

Quote:

> Are dinosaurs reptiles?
> Yes one of those simple questions that I have a hard time answering without
> boring the heck out of everyone. So, I thought I'd leave it up to the
> experts, who have probably answered this question to droves of school children
> in simple language. The kind of simple language that would be good for a TV
> special aimed at a very general audience. Sometimes knowing a lot about a
> subject makes the simplest question difficult. And I thought I'd never need
> that "Handy Answers" book...shame,shame,shame.

Answer: yes

Old System of Classification (Linnaean): Reptilia includes all
land-dwelling vertebrates which lay eggs with shells except for birds
(Aves) and mammals (Mammalia).

New System (cladistic/phylogenetic): Reptilia includes the most recent
common ancestor of turtles, crocodiles, snakes, lizards, and tuataras,
plus all of that ancestor's descendants. Dinosauria is a subset of this
(and Aves a subset of Dinosauria -- hence Aves is part of Reptilia, too).

I think Bakker's Linnaean classification might be the only one that
excluded Dinosauria from Reptilia.

http://dml.cmnh.org/2000Apr/msg00382.html

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sozobe wrote:

I'm surprised, too. Searched for "are dinosaurs reptiles?" and got:

I know. I did the same search, got the same link. I also got a few links which said, "no". So I started searching some of the .edu sites (like the one above), and found that most consider dino's reptiles, and also BIRDS to be reptiles.

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Dinosaurs evolved from reptiles. The predator-type dinosaurs needing speed to catch their prey became warm-blooded. A biped dinosaurs evolved into birds. Birds are dinosaurs. Chickens can be turned into dinosaurs. The DNA in their beaks contains teeth-forming genes. Scientists can alter the beak DNA to develop teeth in their beaks.

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Here is a website on Dinosaurs:
Everything you want to know about Dinosaurs.

Dinosaurs

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talk wrote:

The DNA in their beaks contains teeth-forming genes. Scientists can alter the beak DNA to develop teeth in their beaks.

Hens teeth. Heard they were rare Laughing

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All birds are oviparous--egg laying. Many reptiles are viviparous--live bearing. But some reptiles, including the shingle-backed skink--Trachydosaurus rugosa --and the red-sided garter snake--Thamnophis sirtalis ssp--have to shown to have primitave placentas. There may be many placental reptiles, and only future research will prove it.

I know that at least some dinosaurs were egg laying. Were any viviparous? Some arguments suggest that dinosaurs were warm blooded. So it seems that birds are descended from dinosaurs and not reptiles.

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i did quite a bit of web browsing on this topic. mammals are synapsids, reptiles are anapsids or diapsids--there's one other type of reptile that included icthyosaurs, i think, but they're all extinct. dinosaurs, birds, snakes, and lizards are diapsids, but turtles are anapsids.

dimetrodon is maybe the best-known fossil synapsid. they were once described as "mammal-like reptiles" but now they're just non-reptile amniotes, i guess.

http://www.ccsf.cc.ca.us/Departments/History_of_Time_and_Life/images/FoyerDisplayA.jpg

the fossil records for both reptiles & synapsids go back to about 310 or 320 million years, at the Joggins area of Nova Scotia. either they had a common ancestor, in which case they're all reptiles, or they evolved separately from amphibians. if i learn anything more, i'll post, but it's a lot of data to wade thru.

[update] i've come across a candidate for the earliest amniote, and hence ancestor to mammals, reptiles, or both--casineria--which preceded synapsids & anapsids by 20 million years. here's a tiny image of a hand, with five digits, only one of which is complete:

http://www.sciencenews.org/pages/sn_arc99/5_22_99/bob1b.jpg

and here's a link to an article about it. since the fossil lacks a skull, it could have been synapsid, diapsid, or neither:

http://www.sciencenews.org/pages/sn_arc99/5_22_99/bob1.htm