Archosauria?

Andrew J. · Post by **Andrew J.** » 2005-05-19 08:45pm

How long has Archosauria been its own class, and why was it changed? I'm going along, thinking it's a classification somewhere below class Reptilia like i'ts been for decades, and then I go and found out that dinosaurs (and pterosaurs, and plesiosaurs) aren't even reptiles anymore! I'm mildly annoyed.

SirNitram · Post by **SirNitram** » 2005-05-19 08:49pm

Andrew J. wrote:How long has Archosauria been its own class, and why was it changed? I'm going along, thinking it's a classification somewhere below class Reptilia like i'ts been for decades, and then I go and found out that dinosaurs (and pterosaurs, and plesiosaurs) aren't even reptiles anymore! I'm mildly annoyed.

Given that dinosaurs look less and less like reptiles all the time, it's not exactly surprising.

Hell, when I was growing up they were on about feathered ones and ones giving live birth...

Shroom Man 777 · Post by **Shroom Man 777** » 2005-05-19 08:49pm

Wha? They ARE Reptiles, Archosaurs ARE reptiles. Where the hell did you get this?

Mayabird · Post by **Mayabird** » 2005-05-19 08:57pm

SirNitram wrote:
Andrew J. wrote:How long has Archosauria been its own class, and why was it changed? I'm going along, thinking it's a classification somewhere below class Reptilia like i'ts been for decades, and then I go and found out that dinosaurs (and pterosaurs, and plesiosaurs) aren't even reptiles anymore! I'm mildly annoyed.
Given that dinosaurs look less and less like reptiles all the time, it's not exactly surprising. Hell, when I was growing up they were on about feathered ones and ones giving live birth...

Live birth? I haven't heard that one before. Linkies, please? (If you know of any, of course.)

"When I was growing up." Pfft. You're only a couple years older than me!

Shroom Man 777 · Post by **Shroom Man 777** » 2005-05-19 09:05pm

Pachysephalusaurus (sp?), the bigheaded headbutting one, the one that trashed the Landrover in Jurassic Park 2, was said to give birth to its kiddies since it had unusually wide hips or something.

Its not like reptiles giving birth is that unusual. Lots of snakes do it *shrugs*

The Original Nex · Post by **The Original Nex** » 2005-05-19 09:53pm

Well, from todays strandpoint, Dinosaurs share extremely few characteristics with reptiles as we know them today. If they truly have upgraded Archsauria from sub-class to a full class I wouldn't be at all suprised.

If this truly is the case, has the class Aves subsequently been downgraded to a sub-class under Archosauria?

Shroom Man 777 · Post by **Shroom Man 777** » 2005-05-19 10:45pm

But how are plesiosaurs different from your standard reptile? Sure, they looked funky, but they weren't as un-reptilian as the dinosaurs. By that logic, whales wouldn't belong to mammalia!

Darth Raptor · Post by **Darth Raptor** » 2005-05-20 02:29am

Plesiosaurs and ichthyosaurs are NOT archosaurs. As for the Archosauria itself being a class, that depends largely on who you talk to.

Paleontological phylogeny is fragmented, convoluted and horribly inconsistent. Bear in mind that the original, simplistic classes like "Mammalia" and "Aves" that are fine for modern life, don't quite cut it for in-betweeners like Archaeopteryx and Cynognathus.

Andrew J. · Post by **Andrew J.** » 2005-05-20 02:00pm

Shroom Man 777 wrote:Wha? They ARE Reptiles, Archosaurs ARE reptiles.

Try telling that to InnerBrat.

wolveraptor · Post by **wolveraptor** » 2005-05-20 07:36pm

In which case, mammals and birds are reptiles too. They just have modified scales, four-chambered hearts, erect limbs (most of them) and endothermy.

Mayabird · Post by **Mayabird** » 2005-05-20 07:51pm

Shroom Man 777 wrote:Pachysephalusaurus (sp?), the bigheaded headbutting one, the one that trashed the Landrover in Jurassic Park 2, was said to give birth to its kiddies since it had unusually wide hips or something.

Its not like reptiles giving birth is that unusual. Lots of snakes do it *shrugs*

Yes, but when snakes do that, they have eggs that hatch inside the body and then little wigglers pour out. I was thinking more along the lines of mammalian (non-monotreme) live birth, which I'd never heard of in dinosaurs before.

Andrew J. · Post by **Andrew J.** » 2005-05-21 07:56am

Darth Raptor wrote:Plesiosaurs and ichthyosaurs are NOT archosaurs.

Okay, I was thinking of the "old" Archosauria, which included dinosaurs, plesiosaurs, pterosaurs, and crocodilians. What animals are included in the "new" one?

Majin Gojira · Post by **Majin Gojira** » 2005-05-21 08:35am

Dinosaurs, Thecodonts and Crocodilians IIRC.

I'm not sure on Pterrosaurs, but I think they're included as well.

Elasmasaurs and Icthyosaurs are way different--they're not eve Diapsids!

Darth Raptor · Post by **Darth Raptor** » 2005-05-21 12:36pm

You're right, MG. Dinosaurs, pterosaurs, thecodonts, crocodilians and arguably, birds are all members of the Archosauria.

Marine reptiles like plesiosaurs, pliosaurs and ichthyosuars were never part of the Archosauria. They're euryapsid reptiles to be precise. While mosasaurs are diapsids, they're basically aquatic monitor lizards.

wolveraptor · Post by **wolveraptor** » 2005-05-21 05:43pm

Aren't the major clades of reptillia mostly determined by the number of holes in the animals' heads? Anapsids have no holes, Diapsids have...something, and Archosaurs have antiorbital fenestrae.

Darth Raptor · Post by **Darth Raptor** » 2005-05-21 08:15pm

I'm running completely off of memory here, but reptiles are classified acording to the number of fenestrae (holes, essentially) they have in their skull aside from the orbit (eye socket) and naris (nostril).

Anapsids have no extra holes. This includes the most primitive reptiles including turtles and the therapsid protomammals that were ultimately our own ancestors.

Diapsids have two antorbital fenestrae. This broad group includes lizards, snakes and crocodilians. Since crocodiles are already a part of this group, it's no real stretch to have it include the rest of the archosaurs.

Euryapsids are marine reptiles, and are completely extinct. I'm pretty sure this group almost exclusively refers to placodonts, nothosaurs and their direct descendents: the plesiosaurs and icthyosaurs. I don't remember how their skull differ from the other two clades, but they're not closly related to the archosaurs at all, really.

RedImperator · Post by **RedImperator** » 2005-05-21 11:06pm

So where do birds fall in all this? I've seen them classified as an independent class (Aves), and as a subclass of Reptillia. If you're going to put the dinosaurs and crocodiles in their own class, shouldn't the birds be included there (I hope so, since I was never really comfortable with birds and reptiles in the same order).

Darth Raptor · Post by **Darth Raptor** » 2005-05-21 11:22pm

RedImperator wrote:So where do birds fall in all this? I've seen them classified as an independent class (Aves), and as a subclass of Reptillia. If you're going to put the dinosaurs and crocodiles in their own class, shouldn't the birds be included there (I hope so, since I was never really comfortable with birds and reptiles in the same order).

Yes. Virtually every modern definition of Archosauria as a class includes avian dinosaurs. Modern zoology is really the only discipline in which Aves are considered an independent class, and understandably so.

wolveraptor · Post by **wolveraptor** » 2005-05-22 11:32am

I've heard theories that Archaeopteryx, which actually had a retractable second-toe claw like dromaeosaurids, gave rise to them. This would imply that they're birds. I'm not sure how other maniraptorans fall into this, though. Are troodontids included in Aves too?

Darth Raptor · Post by **Darth Raptor** » 2005-05-23 01:04am

Here is the complete cladogram of the non-avian Dinosauria as of 1999. It's still pretty much current, as far as I know. Archaeopteryx is considered a bona-fide bird by all rights. Irrelevant if you (like me) just consider the Aves to be a highly specialized branch of the Theropoda.

Post by **Alyrium Denryle** » 2005-05-23 01:12am

you know, with phylocode, we could fix all these classification issues

wolveraptor · Post by **wolveraptor** » 2005-05-24 07:36pm

Darth Raptor wrote:Here is the complete cladogram of the non-avian Dinosauria as of 1999. It's still pretty much current, as far as I know. Archaeopteryx is considered a bona-fide bird by all rights. Irrelevant if you (like me) just consider the Aves to be a highly specialized branch of the Theropoda.

Well, I found this theory in a fifteen year old book; this is current enough.

Anyways, I notice that they don't include a sister-group of the tyrannosaurs, whose name completely escapes me. It starts with an au-. Is that no longer current?

Darth Raptor · Post by **Darth Raptor** » 2005-05-25 01:46am

wolveraptor wrote:Anyways, I notice that they don't include a sister-group of the tyrannosaurs, whose name completely escapes me. It starts with an au-. Is that no longer current?

Aublysodon? It's pretty tough to base an entire sub-family on some teeth. Last I heard, A. mirandus is considered a tyrannosaurid.

wolveraptor · Post by **wolveraptor** » 2005-05-25 02:53pm

Oh yeah. I was switching the l and the y. I thought they still might exist because of the discovery of Jane. Of course, five min with Google told me that Jane was either a juvenile t. rex of a Nanotyrannus

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