Tag Archives: dinosaur

Shaking dinosaur hips and messing with their heads

by Piter Kehoma Boll

This week brought astonishing news regarding the phylogeny of dinosaurus, as you perhaps have heard or read. New anatomical evidences have completely rebuilt the basis of the dinosaur family tree and I’m here to explain a little bit of what happened.

As we all know, Dinosaurs include a great variety of beasts, from the meat-eating theropods to the long-necked sauropods and from the horned ceratopsians to the armored ankylosaurs, among many others.

largestdinosaursbysuborder_scale

Silhouette of a human compared to the largest known dinosaurs of each major group. Picture by Matt Martyniuk.*

For more than a century now, dinosaurus have been divided into two groups, called Ornithischia and Saurischia. Ornithischia (“bird-hipped”) includes dinosaurus whose pelvic bones are more similar to what is found in birds, with a pubis directed backward. Saurischia (“lizard-hipped”), on the other hand, have a pubis directed forward, as in reptiles in general. This grouped the theropods and the sauropods in the same group as Saurischia while other dinosaurus were grouped as Ornithischia. But birds are actually theropods, thus being lizard-hipped dinosaurus and not bird-hipped dinosaurus! Confusing, isn’t it? So let’s take a look at their hips:

Pelvic_bones

Comparison of the hips of a crocodile (Crocodylus), a sauropod (Diplodocus), a non-avian theropod (Tyrannosaurus), a bird (Apteryx), a thyreophoran (Stegosaurus), and an ornithopod (Iguanodon). Red = pubis; Blue = ischium; Yellow = ilium. Picture by myself, Piter K. Boll.**

As you can see, the primitive state, found in crocodiles, sauropods and early theropods, is a pubis pointing forward. A backward-pointing pubis evolved at least twice independently, both in more advanced theropods (such as birds) and the ornithischian dinosaurus. But could we be so certain that Tyrannosaurus and Diplodocus are more closely related to each other (forming a clade Saurischia) just because of their hips? Afterall, this is a primitive hip, so it is very unlikely to be a synapomorphy (a shared derived character). Nevertheless, it continued to be used as a character uniting sauropods and theropods.

A new paper published by Nature this week, however, showed new evidences that point to a different relationship of the groups. After a detailed analysis of the bone anatomy, Matthew G. Baron, David B. Norman and Paul M. Barrett have found 20 characters that unite theropods with ornithischians and not with sauropods. Among those we can mention the presence of a foramen (a hole) at the anterior region of the premaxillary bone that is inside the narial fossa (the depression of the bone that surrounds the nostril’s opening) and a sharp longitudinal ridge along the maxilla.

skulls

The skulls of both ornithischians and theropods (above) show an anterior premaxillary foramen in the narial fossa (shown in yellow) and and a sharp ridge on the maxilla (shown in green), as well as other characters that are not present in sauropodomorphs and herrerasaurids (below). Composition using original pictures by Carol Abraczinskas and Paul C. Sereno (Heterodontosaurus), Wikimedia user Ghedoghedo (Eoraptor and Herrerasaurus), and flickr user philosophygeek (Plateosaurus).**

In his blog Tetrapod Zoology, Dr. Darren Naish comments the new classification and points out some problems that arise with this new view. One of them is the fact that both theropods and sauropodomorphs have pneumatic (hollow) bones, while ornithischians do not. If the new phylogeny is closer to the truth, that means that pneumacity evolved twice independently or evolved once and was lost in ornithischians.

He also mentions that both ornithischians and theropods had hair-like or quill-like structures on their skin. In theropods this eventually led to feathers. Could this be another synapomorphy uniting these groups? Maybe… but when we think that pterosaurs also had “hairs”, one could also conclude that a “hairy” integumentary structure was already presented in the common ancestor of dinosaurus. In this case, perhaps, we only had not found it yet on sauropods. Now imagine a giant Argentinosaurus covered with feathers!

One concern that appeared with this new organization is whether sauropodomorphs would still be considered dinosaurs. The term “dinosaur” was coined by Richard Owen in 1842 to refer to the remains of the three genera known at the time, Iguanodon, Hylaeosaurus and Megalosaurus, the first two being ornithischians and the latter a theropod. As a consequence, the original definition of dinosaur did not include sauropods. Similarly, the modern phylogenetic definition of dinosaur was “the least inclusive clade containing Passer domesticus (the house sparrow) and Triceratops horridus“. In order to allow Brachiosaurus and his friends to continue sitting  with the dinosaurs, Baron et al. suggested to expand the definition to include Diplodocus carnegii. So, dinosaurus would be the least inclusive clade containing P. domesticusT. horridus and D. carnegii.

In this new family tree, the name Saurischia would still be used, but to refer only to the sauropodomorphs and some primitive carnivores, the herrerasaurids. The new clade formed by uniting theropods and ornithischians was proposed to be called Ornithoscelida (“bird-legged”), a name coined in 1870 to refer to the bird-like hindlimbs of both theropods and ornithopods (the subgroup of ornithischians that includes dinosaurs such as Iguanodon and the duck-billed dinosaurs).

What can we conclude with all that? Nothing will change if you are just a dinosaur enthusiast and do not care about what’s an ornithischian and a saurischian. Now if you are a phylogeny fan, as I am, you are used to sudden changes in the branches. Most fossils of basal dinosaurs are incomplete, thus increasing the problem to know how they are related to each other. Perhaps this new view will last, perhaps new evidence will change all over again the next week.

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ResearchBlogging.orgReferences and further reading:

Baron, M., Norman, D., & Barrett, P. (2017). A new hypothesis of dinosaur relationships and early dinosaur evolution Nature, 543 (7646), 501-506 DOI: 10.1038/nature21700

Naish, D. (2017). Ornithoscelida Rises: A New Family Tree for DinosaursTetrapod Zoology.

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*Creative Commons License
This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.

**Creative Commons License
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

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Filed under Evolution, Extinction, Paleontology, Systematics

Horrible Dinosaur Expos: Via Brasil

By Carlos Augusto Chamarelli

Hey everybody, once again things are a little slow on my side because I couldn’t decide what my next article would be, because what I was going to talk about proved to be rather polemical within EN, so until then here’s a little something to general amusement and despair.

As you can guess from the title, this post is about a dinosaur expo, a terrible one at that. See unlike other countries paleontology as a whole in Brazil is rather lacking, so dinosaur expos are hard to come by. Good dinosaur expos are even harder.

I do remember one exceptional expo that took place when Jurassic Park was first released in Brazil, but it’s possible I thought because I was 4 at the time and dinosaurs were awesome no matter what, but I don’t have many memories of it. Specially because the huge, roaring animatronic beasts terrified me. To this day I’m not entirely sure if it was Dinamation’s exhibit, and I’m still unable to find the photos we took there (where I remember always appearing with a cringe of sheer terror mixed with marvel).

So after that everything went downhill because every dinosaur expo I came across ranged from “kind of bad” to “crap”. And no, I’m not being harsh, “crap” is the perfect analogy for some of them. Really.

That being said, let’s take a look of one which I actually bothered taking pictures of. This one took place in Shopping Via Brasil (which seemingly sprung out of nowhere) in Irajá, Rio de Janeiro, in 2011 I believe.

Not picture because I just took photos inside the thing: the ugliest Velociraptor right at the mall’s entrance, the huge and hideous Tyrannosaurus skull with an actual picture of a Tyrannosaurus skull right behind it (how come nobody looked at it and said “hey, they don’t look like each other”), the entrance ticket with Jurassic Park’s logo and a mini-cinema exhibiting Disney’s Dinosaur…. Yeah

How come they couldn’t afford a second one so they could bash heads? What a letdown.

Apart from the deformed and slightly human-like arms, this Stegoceras is not that bad since they actually tried to make the skull have mostly the right shape. Also the atrocity is lessened by what was right next to him: the disembodied neck of a “Camarasaurus” (with the head of a Diplodocus) that stood in the back of what looked like a circus arena….

I like JP style Raptors when it comes to entertainment, but that’s too much.

This is what the Velociraptor at the mall entrance looked like. What can I say? The lack of feathers is the last of the concerns here. How can these even be called “raptors” if they didn’t even bothered to give them the trademark feet claws? I swear I thought they were Herrarasaurus, which would make everything a bit less shameful.

“AAAAAAAAAAAHHH!!!”

This one got me by surprise, I would never expect to see Therizinosaurus in such low-end expo. It’s also interesting because unlike the Velociraptors they did used feathers to coat the model. Very badly, but feathered nonetheless. Maybe he has such aghast expression because he know they stole the zebra-therizinosaurus idea from either Luis Rey or that CGI model from Dorling Kindersley. I’m guessing the latter.

If they had another and made it hairy they could pass it as Coelodonta.

I’ll never understand why they put an rhinoceros in the exhibit… Wait, that’s Styracosaurus? Yipes, moving on…

Mammoth: the Tenontosaurus of the Pleistocene.

What you mean Ice Age beasts aren’t dinosaurs? At least compared to the dinosaurs, these are quite tolerable. The mammoth is as good as one can make a mammoth look good when covering it with hair, but the static Smilodon will always remind me of another appalling expo that seemingly consisted entirely of Smilodons scattered in dark rooms lit by pulsating lights and walls covered by palm tree leaves made of fabric.

And you were thinking I was being harsh when I said some were crap.

And there was a crocodile-like Dimetrodon next to them for no good reason.

Can we go back to man-in-suit theropods after that?

No, that’s not the perspective being wonky, this is what this mockery of a Tyrannosaurus looked like in profile. I have nothing to add to this other that the most infuriating part was that…

For a change, there’s nothing dead laying before him.

… There was a much bigger and impressive (and slightly less inaccurate) animatronic Tyrannosaurus right next. This was the last thing in the expo, and with good reason it seems. Even with the huge feet and sounds stolen directly from Jurassic Park, this one was life-sized, which made it best than most I’ve seen…. And look, there’s the hideous skull behind him.

As with other exhibits, this one wasn’t the longest, but thankfully it wasn’t the most expensive, and I could learn a lesson out of it: research about the expo before you go.

I have hopes one day Brazil will once again see a decent dinosaur exhibit like the one I barely remember, but until then the average brazilian is stuck with sucky depictions while us dinomaniacs can only laugh and facepalm.

Stay tuned for my next article. See ya!

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