tag:blogger.com,1999:blog-5519292617097628087.post2753728109352910315..comments2024-01-02T16:09:12.886-07:00Comments on Chinleana: Upcoming Paper on the Basal Ornithischian Dinosaurs Lesothosaurus and StormbergiaBill Parkerhttp://www.blogger.com/profile/05941940882532354219noreply@blogger.comBlogger7125tag:blogger.com,1999:blog-5519292617097628087.post-91298811537145843442009-04-21T21:26:00.000-07:002009-04-21T21:26:00.000-07:00Randy,
Good points, but obviously your ideas rega...Randy,<br /><br />Good points, but obviously your ideas regarding Pisanosaurus have changed a bit since our 2007 paper in which we stated:<br /><br />"we tentatively consider Pisanosaurus an ornithischian dinosaur"<br /><br />"the hypothesis that Pisanosaurus is a basal dinosauriform with jaw morphology convergent upon<br />ornithischians cannot be eliminated"<br /><br />I guess that I have not kept up.Bill Parkerhttps://www.blogger.com/profile/05941940882532354219noreply@blogger.comtag:blogger.com,1999:blog-5519292617097628087.post-59498973476848071412009-04-21T20:44:00.000-07:002009-04-21T20:44:00.000-07:00Bill - I think you miss the point. Of course scie...Bill - I think you miss the point. Of course science is conditional on present knowledge. Some new discovery could totally overturn what we know about the early evolutionary history of ornithischians. Nonetheless, right now, our best information suggests that ornithischians should have a Triassic record (you'd really have to change their phylogenetic position alot to get rid of that Triassic ghost lineage), and that <I>Pisanosaurus</I> is part of that lineage.<br /><br />To be honest, I think you're not giving <I>Pisanosaurus</I> enough credit. And no, I don't think its quite the same as the <I>Revueltosaurus</I> situation. The lower jaw isn't just *similar* to other ornithischians - its nearly identical in every way. And the teeth are a similar situation. Plus, the post-crania is exactly what one would expect in a very basal ornithischian dinosaur. In contrast, <I>Revueltosaurus</I> and other alleged Triassic ornithischian teeth were always *similar* to true ornithischians, but in a very general way. For example, none of the teeth were ever considered a spot-on imitation of <I>Lesothosaurus</I> or <I>Heterodontosaurus</I>. The phylogenetic mismatch between the crania and postcrania of <I>Pisanosaurus</I> was only a problem when heterodontosaurids were considered ornithopods. It now makes total sense with heterodontosaurids as the basal most clade of Ornithischia. Of course this could all change with the discovery of a complete <I>Pisanosaurus</I> skeleton that shows the taxon is a basal turtle, but thats just fantasy right now. We're scientists - we have to go with the best conclusions on the available evidence.<br /><br />Zach - that would require that there is good character evidence for placing <I>Silesaurus</I> and friends as ornithischians. Which, as of right now, there isn't.220myahttps://www.blogger.com/profile/06403919493457640549noreply@blogger.comtag:blogger.com,1999:blog-5519292617097628087.post-14201709413263786842009-04-21T19:43:00.000-07:002009-04-21T19:43:00.000-07:00Wouldn't this problem go away (sort of) if silesau...Wouldn't this problem go away (sort of) if silesaurids turn out to be basal ornithischians?Zachhttps://www.blogger.com/profile/08692080707969333711noreply@blogger.comtag:blogger.com,1999:blog-5519292617097628087.post-54216691799952183142009-04-20T22:44:00.000-07:002009-04-20T22:44:00.000-07:00Let me switch the emphasis on one of your sentence...Let me switch the emphasis on one of your sentences, "because even if you discount the known Triassic ornithischian fossils, ornithischians must have been present IF we have their phylogenetic position correct, as their sister-groups are all Late Triassic in age".<br /><br />I agree that all of the evidence for this positioning is extremely strong, except for one thing, the lack of good Triassic age ornithischian fossils. Because of this lack of specimens we are stuck with some sizeable ghost lineages and being forced to explain this paucity with statements such as they don't fossilize well, or maybe they were endemic to Gondwana, or...<br /><br />I'm just saying that I am still dubious despite the phylogentic analyses. Sure Pisanosaurus has a coranoid process and an ornithischian-like dentition but hasn't this just gotten us into trouble in the past? I'd just like to see more and better specimens. Right now we have evidence of Triassic ornithischians because of phylogenetic hypotheses and two scrappy specimens; however, would it really be that shocking if Pisanosaurus turned out to be a non-ornithischian dinosauriform with a couple of convergences? As I said, I'm tentatively believing it is an ornithischian for now, but don't bet the farm just yet until better specimens are found.<br /><br />Because of some unpublished proposed phylogenies we are going to have to start looking for lots of things in much older rocks. Some have started to show up, others have not. I suppose that we just need to keep at it, but the phylogeny is only a predictor of fossils, not the actual fossils on which presence or absence is based. We can only hope that in the future these predictions are confirmed.Bill Parkerhttps://www.blogger.com/profile/05941940882532354219noreply@blogger.comtag:blogger.com,1999:blog-5519292617097628087.post-48554641867406357532009-04-20T21:54:00.000-07:002009-04-20T21:54:00.000-07:00So you think that ornithischians are misplaced in ...So you think that ornithischians are misplaced in current phylogenies? Because even if you discount the known Triassic ornithischian fossils, ornithischians MUST have been present if we have their phylogenetic position correct, as their sister-groups are all Late Triassic in age.<br /><br />In any case, why don't you buy <I>Pisanosaurus</I>? Its not just the teeth that place it as an ornithischian - the lower jaw is spot on for an ornithischian in every way, and particularly similar to heterodontosaurid lower jaws.220myahttps://www.blogger.com/profile/06403919493457640549noreply@blogger.comtag:blogger.com,1999:blog-5519292617097628087.post-58532820704618627592009-04-20T20:11:00.000-07:002009-04-20T20:11:00.000-07:00Almost non-existant. One very scrapy, poorly diagn...Almost non-existant. One very scrapy, poorly diagnostic specimen of Pisanosaurus; one fragment of a possible heterodontosaurid, and then Eocursor. That's all. Three specimens, two very badly preserved and barely diagnostic, and the other right at the end of the Triassic if not in the early Jurassic.<br /><br />I'm still not buying the presence of Triassic ornithischians 100%; however, Lesothosaurus and Stormbergia are Jurassic.Bill Parkerhttps://www.blogger.com/profile/05941940882532354219noreply@blogger.comtag:blogger.com,1999:blog-5519292617097628087.post-78640979071863600902009-04-20T18:25:00.000-07:002009-04-20T18:25:00.000-07:00So the bottom line is that ornithischians were rid...So the bottom line is that ornithischians were ridiculously rare in the Late Triassic?Zachary Millerhttps://www.blogger.com/profile/05035947146927565746noreply@blogger.com