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DrScottHartman — A mouth full of different teeth
Published: 2013-04-03 20:38:07 +0000 UTC; Views: 9168; Favourites: 153; Downloads: 0
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Heterodontosaurus is a funny little ornithischian. On the one hand it seems primitive as all get-out, but on the other hand there are people who persistently link them to marginocephalians (horned dinosaurs and dome-heads), and later taxa like Tianyulong really aren't clearing it up to anyone's satisfaction. I will say this, Heterodontosaurus has a bigger head and somewhat smaller abdomen than I was expecting.Related content
Comments: 40
would you happen to know if your skeletals of this, Eocursor, and Lesothosaurus need any updates?
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Not that I'm aware of.
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Why did you put different color(black/white) with teeth in the front and teeth in the back?
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If I'd made the cheek teeth black they'd have been awfully difficult to see.
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It's cute!
By the way, do you think he could have had lips or sort of hardened skin covering the premaxilla rather than a beak as usually restored?
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i did try that idea out with the lips.
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It doesn't look like lips to me, but in the new skull the bone texture I usually associate with beaks does seem to be restricted to the very far front, so it's possible some other sort of extra-oral tissue was involved. I still think the predentary had to have supported a regular beak though.
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Interesting; is there any other ornitischian known with this mix of textures in the mouth area?
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I don't actually know - I don't spend as much time looking at premaxillary bone texture in ornithischians as I ought to.
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Oh well, there's always time to do it, am i rite?
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With the last two skeletals being Megalosaurus and Heterodontosaurus: Is this a project for the NHM in London?
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No, they're for a book on British dinosaurs.
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That's it, it's a dino monkey. Although... the claws don't seem really curved like you'd expect in a climber. What long arms you have.
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More like a digger if anything.
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Fascinating; just like in All Yesterdays.
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I've never seen this dinosaur before but this hands are looked like uses for digging like all yesterdays or use for grooming.
And perhaps it legs were all standing on two and not four, right?
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My thoughts exactly.
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Whoah, it's the first depiction of Heterodontosaurus I've ever seen that shows how big its big hands and forelimbs in general seem to be.
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Ich habs mir auch immer anders vorgestellt
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Wouldn't you say some features here are more derived than in marginocephalians? For instance, the reduced first metatarsal and fifth metacarpal? Would these features preclude heterodontosaurs from being close to an ancestral group for marginocephalians, or are these variations immaterial? Don't have a clue, myself.
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It would take a bit of a reversal, but nothing like what coelurosaurs did with their feet on the way to therizinosaurs, so I don't find that hard to envision.
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Except for the opposable ring and pinky fingers on Heterodontosaurus.
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It seems your "trunk length" is dependant almost entirely on the position of the shoulder girdle. How exactly do you constrain the position of the shoulder?
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It's dependent on a couple things - yes, the placement of the pectoral girdle, but it generally sits right around the transition between the cervicals and the dorsals, and in this case is also right where it's preserved in the fossil. It should be noted though that my scap/coracoid is in almost the identical position (fore to aft) as Greg Paul's (I had to check because they seem to be very different proportions); what make's Greg's version so much bigger torsoed is actually the depth created by restoring the sternum at a strong downward angle (and also by having the sternum extend up anterior to the coracoids, a very unlikely condition).
The other factor is the length of the ischia - everyone seems to have followed Santa Luca's restoration of the pelvic proportions, but the "restored pelvis" image in the paper is significantly longer than what the actual fossil seems to show. Unfortunately no measurement was given of the shaft in the text, but I feel more comfortable going with the photo than the line drawing.
It's possible that the pectoral girdle could be moved forward a half vertebrae(ish), but it's still going to end up being shorter in the torso than other contemporary reconstructions.
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My concern here is the issue of how you're constraining the position. The old standby, where the coracoid marks roughly the position of the first dorsal, doesn't coincide with an argument for why this is so. Rather, it is asserted. We "accept" this because it is common. For example, why are we not calibrating the shoulder with muscle reconstructions, using the one to moderate the other, and vice versa? We position our scapcor, then muscle it, and call it a day. Why?
I do not agree with Greg's reconstruction, largely because he did his largely to be ornamental, but also nor with the preserved fossil, as there are taphonomic elements at play that may pull the scapcor out of alignment. Not accounting for this, assuming rather that it is so, is like arguing that the Sinosauropteryx/Scipionyx scapcors, which are distended and certainly also out of alignment, are in fact correct. If they are not, why is Het's suddenly so?
You may notice that here: [link] I approximate several of your arguments, don't have the manus on the ground, rotate the thumb out, etc. -- all art -- but also that the scapcor is possitioned roughly at the first dorsal, but this is still a question I am curious about. I also estimate the scape of the ischium, but give mine a bit of a longer tail than yours. I am thinking on the tail length bit that given proportions of the vertebrae, assuming an abrupt shortening may not be very likely. If basal ornithopods like Leaellynasaura and basal thyreophorans like Scutellosaurus are exceptionally long-tailed, then so too should Het. I also did this skeletal for Darren Naish sometime back in 2006-7 or so, assuming at the time the basal ornithopod position for Het and kin.
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Ah - the developmental reason why the pectoral girdle is tied there are twofold: one has to do with basic genetic patterning - the overall patterning genes of vertebrae seem to be tied to torso development, and perhaps more mechanistically the nervous system of vertebrates seems to always have the brachial nerves exiting at that juncture, thus constraining the limb to not moving beyond it (note of course that individual vertebral condensates can move ahead or behind, just that the patterning genes keep the pectoral girdle and attendant nerves tied to the transition).
Again, I fully admit you have a +/- most of a vertebrae, but there doesn't appear to be more wiggle room than that.
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Scott, I hope you don't think I'm not intelligent enough to understand your answer. I am asking for some data on constraint of the shoulder girdle in these animals; I can accept references. Without the use of reference internal organs, the curvature of ribs, angle of deflection from the midline, curavture of the scapulocoracoid, and width at the sternum/interclavicle system -- even presuming the difference of merely one vertebral position in either direction -- how can we assume the position of these elements? We have very, very few 3D preserved small ornithischians and virtually NO studies on their shoulder positions, much less a good, detailed analysis like Mallison's work on Plateosaurus. What you render is in two-dimensions, though obviously you do work in three as well, but for this specimen in particular, there's only the two. The specimen is partially flattened, the shoulder displaced as mandated by the effect of crushing a curved object, and the two halves not one directly on top of the other; there's the issue of scapular rotation, and which position reflects the "forward" one, and the far forward extreme of the "natural" position.
It is these things that I am looking for insight on, also hopefully additional input into what has been argued about in the past. Theropods have it easy, the cervicodorsal transition has unique muscular/ligament attachment points that may connect to soft-tissue that is objectively positioned and which the shoulder can be objectively placed in relation to; mammals we can observe, and in odd cases like giraffes we have explanations for why; but not so giant quadrupeds with distinct shoulder anatomy from quadrupeds, longer or shorter trunks, or fossae on ribs where scapulae might "lie" whlist still allowing rotation. These things are of interest to me, and I am trying to see if there is any other objective way to place the shoulder than what you've argued.
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Hi Jaimie,
I hardly think a lack of intelligence has anything to do with it. You raise some good points, and I must confess that part of this is stemming from work I've been doing on pectoral girdle placement ever since I worked on Brachylophosaurus about a decade ago (and which I started to expand when I was mounting skeletons at the WDC). Without tipping my hand too far, I'll say that in other (more three dimensionally preserved) specimens there actually aren't very many options for where you can mount the pectoral girdle and still have the coracoids come together (or at least nearly so, depending on one's preference) while still being in line with how articulated specimens consistently show them. Restoring the muscles that run from the pectoral girdle to the body and head also provides limits to the orientation that will actually work - for example in your linked version of Heterodontosaurus the m. levator scapulae could only operate at an awkward angle relative to its insertion point; dinosaurs that actually have horizontal scapulae have adaptations to allow these muscles to still work properly.
I apologize for being sort of fuzzy here - if you want I could share more via PM or email without tossing out the whole thing publicly. You are correct that in some taxa (including saurischians in general) it is much easier to pinpoint where the transition is from the cervicals to the dorsals than in small ornithopods, but despite that I don't think there's actually much disagreement about the cervical count in them, despite the increased morphological ambiguity. Most of the actual variation in pectoral girdle placement outside of orientation stems (as near as I can tell) not from a disagreement about vertebral count, but from people being forced to alter the position because they don't articulate the rib cage correctly.
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I am perfectly happy to discuss this in more private venues, if it allows me to better understand your position.
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