Talk:Ornithodira

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[edit] Cladisitc analysis of Dinosauriformes

A cladistic analysis by Ezcurra (2006) places Pseudolagosuchus one step above Marasuchus, and recovers Eucoelophysis and Silesaurus as the closest relatives of the clade Dinosauria. For this reason, update the section "Phylogeny" for Ornithodira.

(After Ezcurra, 2006)

Dinosauromorpha

     |--Lagerpeton
     `--Dinosauriformes
          |--Marasuchus
          `--+--Pseudolagosuchus
             `--+--Silesaurus
                `--+--Eucoelophysis
                   `-- Dinosauria
                        |--Saurischia
                        |   |--Herrerasauridae
                        |   |   |--Herrerasaurus
                        |   |   `--Staurikosaurus
                        |   `--Eusaurischia                  
                        |       |--Theropoda
                        |       `--Sauropodomorpha
                        `--Ornithischia

The reason why Lagosuchus, Lewisuchus, and Saltopus were not inlcuded in this cladistic analysis, even if Lagosuchus was erected to stabilize the validity of Lagosuchidae, is because these three dinosauromorphs are based on poor fossil remains.

Ezcurra, M.D. (2006). "A review of the systematic position of the dinosauriform archosaur Eucoelophysis baldwini Sullivan & Lucas, 1999 from the Upper Triassic of New Mexico, USA." Geodiversitas, 28(4):649-684.

[edit] Scleromochlus

See said article, where the Pterosaur ancestry is flatly contradicted. We should present all theories that are part of current scientific debate, whatever our own opinions, and not exclude one theory at the expense of another. I will put the same comment in the Discussion page for Scleromochlus. Jayen466 20:02, 3 October 2007 (UTC)

Since pterosaurs are widely accepted as ornithodiran right now, should not the scleromochlus-origin be by far the most dominant theory? --Draco ignoramus sophomoricus (talk) 12:13, 9 May 2008 (UTC)

I don't think there's enough evidence to tie Scleromochlus in particular to pterosaurs, just based on their position, their ancestors may have been something vaguely like it. Trying to figure out pterosaur origins would be like trying to figure out bird origins if the most primitive bird known was Ichthyornis. That is, nearly impossible, excpt for very broad, general statements. Dinoguy2 (talk) 12:32, 9 May 2008 (UTC)

Scleromochlus now says, "A lightly-built cursorial animal, it is an early representative of the Ornithodira, a group that later gave rise to the Dinosauromorpha and Pterosauromorpha." Last October, when I wrote the above, it said "[Scleromochlus] ... was a gracile cursorial animal that in the past was hypothesised to be an ancestor of the pterosaurs." That made it sound a bit too much as though people now thought there was no relationship at all between Scleromochlus and the Pterosaurs, hence my comment. Current consensus is that there is some relationship – even if, like Dinoguy says, it's just not possible to pin it down to this particular species. Also see User_talk:Jayen466#Scleromochlus_.2F_Ornithodira. Jayen466 12:36, 9 May 2008 (UTC)

Let me express my unedjucated opinion as a non-professional observer. I do see that you have a very strong point but if we skip the strict scientific method using common sense it is obvious with a quick sight of the particular depiction that Scleromochlus has elongated arms, very gracile structure and a head that resembles basal "rhamphorynchids" (though that last one might be artistic liberty). Those traits does not seem to be synapomorphies for other basal ornithodirans or any possible ancestor of ornithodirans or its near relatives (correct me, please, if I am wrong) while they seem quite serving as primitive apomorphies for the pterosaur clade. Off course I do not suggest that any changes in favour of the Schleromochlus origin should be done (and I strongly agree with your view that there is not enough strong evidence in favour of that), I just want to mention that as I see it Scleromochlus seems to be the most propable ancestor to pterosaurs but not dinosauromorpha than any other (though this might be higlhy inaccurate since I formed my opinion over a single artistic depiction of an unmentioned authority). --Draco ignoramus sophomoricus (talk) 00:43, 29 May 2008 (UTC)

There are several points of confusion here:

1. The Pterosauria are by definition part of the Ornithodira.
2. There is consensus that the hypothesis that Dinosauromorpha and Pterosauromorpha are closely related is now the best supported of all alternatives. However, there is no consensus that it is more likely than the sum of all other alternatives. So it is the best supported — yet still not very likely to be true, because too poorly supported.
3. Ornithodira is a node clade and there are, by definition no "basal ornithodirans" that are not also either basal Dinosauromorpha or basal Pterosauromorpha. The relevant stem clade is Avemetatarsalia.
4. Your description <<elongated arms, very gracile structure and a head that resembles basal "rhamphorynchids">> applies, without further qualification, to basal Dinosauromorpha as well — and these characters could all be symplesiomorphies.--MWAK (talk) 07:37, 8 June 2008 (UTC)

That was more than enlighting. Thank you MWAK. --Draco ignoramus sophomoricus (talk) 09:52, 13 June 2008 (UTC)