Scott Hartman's Dinosaur Anatomy

A tumblr blog based on work from my website.

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It’s been a while, but here’s the next update to the Keep Your Mouth Shut dinosaur line: Heterodontosaurus tucki managing to not run around like a drooling moron.

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Hello , Scott! I'm really curious about something. If a dinosaur has fallen on his hip, then how would it get up? Its wings aren't helpful in this case, are they.

Presumably the same way that this emu does at the 0:22 mark:

https://www.youtube.com/watch?v=05BaRz8d438&ab_channel=MattYellen

Except for perhaps turtles, very few animals are helpless on their sides or backs, and it’s likely that non-avian dinosaurs could get back upright at least as easily as living dinosaurs do today (especially since living dinosaurs have fewer back vertebrae and more fused pelvic vertebrae).

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I'm wondering how flexible the arms/wings on dromaeosaurs are (generally speaking I guess). Could for example a Velociraptor or Dakotaraptor neatly tuck their wings close to the body just like modern birds, or flap the arms the same dynamic way an eagle or a hawk do?

Great question! There seems to be some variability in the range of motion at the shoulder (especially) and the elbow and wrist even among dromaeosaurs, but it looks like microraptorians and Bambiraptor, at least, could get a decent range of extension above holding the arm horizontally. They don’t have as much extension as in living birds, and they certainly couldn’t exert as much power into their prot-flaps (i.e. they weren’t powered fliers).

As for tucking their arms up next to their bodies, the shoulder joint should let them do so, but neither the elbow nor the wrist could fold up as tightly as in living birds. As a result, while dromaeosaurs almost certainly would have tucked their wings up to their bodies as much as possible, they could not have done so as tightly as in living birds.

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In most paleoart I've seen, the theropod hallux is reconstructed with the claw curving backwards, more or less parallel to the animal's spine, but in modern birds without a weight-bearing hallux (e.g. kiwis, seriemas), the claw always projects from the metatarsus at an angle and then curves back towards it, following the splay of the other toes. Do we actually know exactly how the hallux of non-avian theropods was positioned? Is there a reason it's always reconstructed the way that it is?

Great question! Starting with roughly Confuciusornis the hallux started to rotate backwards. This happens when the developmental pathways of the first metatarsal actually twist during development, allowing the otherwise normal muscles to control the toe with the proper tendons (that themselves now twist along the axis). In Confuciusornis this is just splayed out to the side, rather than facing the same way as the other metatarsals (as it does in Archaeopteryx and other more primitive theropods). Further up the avian stem the fully reversed hallux evolved (possibly because that’s the first time they were actually arboreal, but that’s controversial), but it evolved well before crown group Aves appeared. With the fully reversed hallux being the primitive condition for living birds, clades with a unreversed hallux are actually a derived condition, and they often don’t turn it back all the way around like it was in Archaeopteryx and further down the family tree.

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When can we expect to see a Concavenator skeletal either here or on your other blg?

Not in the near future I’m afraid. Which is a shame, because it’s a beautiful specimen.

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Do you have a bigger image of your Brontosaurus than the one you have on your website? I can barely make out the details of its head as it is, and downloading it to increase its size just makes it pixellated.

I do those skeletals at very high resolutions, but I don’t post those to the web.

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The basal oviraptorosaur Caudipteryx with its mouth closed, looking very birdy.

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I thank you sir. I thank you for all the skeletals you've done and the many more you will do.

You are most certainly welcome!

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The utterly bizarre giant ornithomimid Deinocheirus, closing its oversized jaw.

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A theropod limb moving without violating its anatomy. Notice the knee never straightens, and the ankle doesn't flex past 90 degrees on the recovery. Perhaps most importantly for animators, notice that the toes are really important for driving the animal forward in the last 1/3 of the stride as they push off - the reason most made-for-TV dinosaur specials have dinosaurs that look like they lack mass (or worse, are floating along the ground) is because riggers and animators want to skip the toes to save time, which basically means they are cutting off a third of the propulsive stroke (and often break other joints in the process).

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I've noticed that some of my favorite paleoartists (Eg. Emily Willoughby, even David Krentz) are dabbing more and more into non-visible dino over bites in their art. As someone who knows the degree of dino over bites, what is your opinion?

Almost all of the dinosaur skulls I've examined have overbites that let them close their mouths and largely or completely hide the lower teeth. There is also some reasons to suspect they had lips as well, though that issue is still contentious with some workers.

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The spinosaurid Baryonyx walkeri saunters around, possibly looking for fish, but not snarling its head off like a movie monster in the process.

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There's something fishy about the new Spinosaurus

Today, after weeks of rampant internet speculation the new-look  Spinosaurus was revealed. And it certainly didn't disappoint: the paper by Ibrahim et al. musters a range of evidence from bone density, bone isotope data, facial innervation, osteology, etc., to suggest that Spinosaurus not only was a fish-eater (i.e. piscivorous) but was adaptive to that lifestyle to a greater degree than other known spinosaurids. Not only do they claim that Spinosaurus spent most of its life swimming in the water with adaptations that would rival early whales, but Ibrahim et al. specifically claim that the altered limb proportions would require Spinosaurus to have been an obligate quadruped on land, a first for a theropod. Unfortunately, there seems to be something fishy with those new proportions...

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I'm on the record claiming that Guanlong's crest turns this basal tyrannosauroid up to 11, but does closing its mouth dial it back down to 9?

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Hey, what's the deal with all this stuff about new Spinosaurus material? I can't find any concrete information about it, and it conflicts with the material you've previously mentioned.

Since this is like the 3 question I've gotten on the issue (apologies to theload and osteobones) my answer for now is simple: we have to wait for the paper.

It's been an open secret for a while that there was new material (there's actually more than just what is incorporated into the upcoming Nat Geo announcement), but since I haven't seen any of the specimens in person I have not incorporated them into my reconstructions until such time as they get published. Remember, if it isn't published in a peer-reviewed journal, it isn't science yet. 

Since Nat Geo has scheduled a press event for later in September, I have to assume that the paper will be published soon (like in the coming few weeks). Then we can evaluate whether the new specimen(s) are a composite, or if Spinosaurus is simply weirder than we had previously realized. The scalloped dorsal spines would not themselves be a huge surprise, but some of the other proportions would be. Either way it's certainly exciting, but we can't know how exciting until the facts become part of the scientific body of data, and so far they are not. 

But hopefully soon. /fingers crossed

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Majungasaurus doesn't need any special treatment to look bizarre, but in the post-snarl calm you can just sit and gaze at how strange this beast really was.

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Getting the armor placed correctly on Scelidosaurus made this skeletal my second-hardest reconstruction of all time (with the first being freakin' Majungasaurus, which perhaps will be the next in the series). And of course it's mouth is closed, even though it didn't really open that wide in the first place.

Bonus fact: Plant-eaters have to spend much more of their day eating than do meat-eaters, so you are probably an order of magnitude more likely to see one of these guys with their mouth open than a theropod, but then these guys don't have totally awesome sharp teeth. Amirite?