Dinogeorge@aol.com wrote:
> What prompted me to exclude segnosaurs from being derived prosauropods was that they
> would have had to evolve a furcula independently. Furculae plus other maniraptoran features
> together would have "overwhelmed" the hypothesis of prosauropod ancestry for segnosaurs.
The furcula is just one character. The segnosaur skeleton is chock-full of maniraptoran characters. The basal segnosaur _Falcarius_ documents the transition from a light-bodied carnivore/omnivore (basal maniraptoran bauplan) to a heavy-bodied herbivore (derived segnosaur bauplan). How does your segnosaurs-are-prosauropods argument take into account _Falcarius_?
> But now that we have furculae in prosauropods, too, we're practically back to square one.
> Segnosaur forelimbs alone, without considering the furculae, are significantly different from
> those of other maniraptorans and suggest convergence as a possibility rather than common
> descent.
Are you kidding? The segnosaur forelimb is loaded with maniraptoran features. Segnosaurs even have that wondrous semilunate carpal joint in the wrist that is diagnostic for the Maniraptora!!!
> Eshanosaurus is transitional in both time and morphology between prosauropods and
> segnosaurs
Don't be too sure. _Eshanosaurus_ is known only from a partial lower jaw, and could equally be some other form of theropod (like an ornitholestid) rather than a segnosaur. Many paleontologists remain skeptical that _Eshanosaurus_ is a segnosaur at all.
> Once the errors in the description of the skull of Erlikosaurus are corrected,
What errors? Are you referring to the numerous features (especially in the braincase) that link _Erlikosaurus_ to other maniraptorans. If so, then you're using circular reasoning to label these features "errors in the description". Clark, Perle, and Norell carried out an extensive examination of the skull of _Erlikosaurus_ in an issue of American Museum Novitates. I'd be intrigued to know how Clark et al. were in "error", and that they were actually studying a prosauropod skull without knowing it.
> The evidence for putting segnosaurs into Theropoda is not overwhelming, it's merely
> equivocal.
No, it's overwhelming. The segnosaurs-are-prosauropods argument never had much support (Greg Paul, maybe a few others), and went out of fashion around 15 years ago, along with the Rubik's cube and A Flock of Seagulls.
Cheers
Tim
Dinogeorge@aol.com wrote:
In a message dated 7/26/2005 1:44:16 PM Pacific Standard Time, tijawi@yahoo.com writes:
Theropods also have furculae, so this does not advance your argument one iota. All this demonstrates is that furculae are primitive for the Saurischia. The evidence putting segnosaurs in the Theropoda is overwhelming.
What prompted me to exclude segnosaurs from being derived prosauropods was that they would have had to evolve a furcula independently. Furculae plus other maniraptoran features together would have "overwhelmed" the hypothesis of prosauropod ancestry for segnosaurs. But now that we have furculae in prosauropods, too, we're practically back to square one. Segnosaur forelimbs alone, without considering the furculae, are significantly different from those of other maniraptorans and suggest convergence as a possibility rather than common descent. Eshanosaurus is transitional in both time and morphology between prosauropods and segnosaurs; too bad there's not more of it. Once the errors in the description of the skull of Erlikosaurus are corrected, the skull becomes quite prosauropod-like as well.
The evidence for putting segnosaurs into Theropoda is not overwhelming, it's merely equivocal.
Start your day with Yahoo! - make it your home page