Abelisaurid Evolution Proposal

futurepaleontologist1

MemberCompsognathusJune 24, 20131379 Views12 Replies

For a while now, I've been wondering a lot about the Abelisaurs and how and why they evolved the way they did. I believe I have constructed a viable theory on their evolution. Based off of thiervarm structure, and number of digits on their hands, I believe they can be linked to early crocodillian archosaurs. The best example of this that I can concieve is Postosuchus. Looking at Postosuchus, I can see that the forearms are slightly smaller than the rear limbs. What does this tell me? It tells me that Postosuchus was slowly losing his arms. By the late Cretaceous period, they would probably be very small. Of course things like the toe digits and hip joints would have to evolve differently over time. The fossil record is full of holes, so this is very possible. What do you guys think? Questions? Comments? Tell me!

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June 24, 2013

The abelisaurs were an offshoot of the earlier ceratosaurs. Many large theropod dinosaur groups seem to be slowly losing their arms and trading them for their heads. The tyrannosaurs are the most notorious for this. You have Guan long at one end of the spectrum and Tyrannosaurus at the other. As far as the abelisaurs go, you got Ceratosaurus with a nasty head and teeth to match, but still long arms. Then you get to Tarascosaurus and the head is stronger and the arms smaller. The allosaurs/carcharodontosaurs did it too. Allosaurus had long arms and claws. Then carnivores like Giganotosaurus showed up and their arms were pretty short and their heads were large. The only group that did not do this were the spinosaurs. That's my thought.

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futurepaleontologist1
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June 24, 2013

Right, that explains why, but the Abelisaurids had an extra digit on their hands that no other therapod species had at the time. And there isn't a very large link between abelisaurs and Ceratosaurs. The link between abelisaurs and early crocodilian archosaurs may be missing in the fossil record

Pity is for the living. Envy is for the dead. -Mark Twain

Makaveli7
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June 24, 2013

I was going to argue that spinosaurs did and use Suchomimus and Baryonyx as examples, but then i remembered that both specimens found were subadults and thus had proportionately larger heads that probably stayed the same until adulthood but still small by cretaceous theropod standards. I think Giga's skull is the longest found to date.

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June 25, 2013

I think the abelisaurs had more in common with the ceratosaurs then you realize. Both groups are known for having strange crest/horn structures on their heads. And both groups had 4 fingers. The reason the abelisaurs had them even though it was much later in the reign of the dinosaurs is because, not only were the size of their arms left behind, but they never dropped that extra digit. That's my theory at least. Early archosaurs are too distant in both familial connection and time.

"Men like me don't start the wars. We just die in them. We've always died in them, and we always will. We don't expect any praise for it, no parades. No one knows our names." ―Alpha-98

futurepaleontologist1
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June 25, 2013

Okay, but even so, what can we link Ceratosaurs to? Not saying I disagree with you, but I don't entirely agree either

Pity is for the living. Envy is for the dead. -Mark Twain

Deltadromeus
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June 25, 2013

Not all Ceratosaurus had four fingers, but most of the early dinosaurs did. Although, I think, and this is just a five second thought up theory, but maybe the Tyrannosaurs and Abelisaurs evolved from the same ancestor, and I'm not talking about the first dinosaurs. Or the Abelisaurs evolved from the Jurassic three clawed tyrannosaurs. Just my thoughts.

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June 25, 2013

We can link the Ceratosaurus to the Herrerasaurs, the early dinosaur, they had four to five fingers.

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June 25, 2013

Which ceratosaur had more less than 4 fingers? I'm not being rude, just wondering if I forgot one. Personally, I exclude Deltadromeus because, in my opinion, it's exact placement is too sketchy. Seems very allosaurian to me. The abelisaurs/ceratosaurs were outside both the Carnosaur and Coelourosaur groups. The tyrannosaurs were pretty advanced coelourosaurs so the abelisaurs could not have descended from early tyrannosaurs.

"Men like me don't start the wars. We just die in them. We've always died in them, and we always will. We don't expect any praise for it, no parades. No one knows our names." ―Alpha-98

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June 25, 2013

[img]http://blog.everythingdinosaur.co.uk/wp-content/uploads/2012/11/Phylogeny-Sauroniops1.jpg[/img] Seems pretty accurate to me. Notice the abelisaurs relationship with the ceratosaurs

"Men like me don't start the wars. We just die in them. We've always died in them, and we always will. We don't expect any praise for it, no parades. No one knows our names." ―Alpha-98

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June 25, 2013

Sorry, ignore that orange arrow, haha

"Men like me don't start the wars. We just die in them. We've always died in them, and we always will. We don't expect any praise for it, no parades. No one knows our names." ―Alpha-98

futurepaleontologist1
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June 27, 2013

But what if Herrerasaurus has a distant archosaur relative? IDK I just thought the Archosaurs went somewhere else than crocodiles

Pity is for the living. Envy is for the dead. -Mark Twain

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June 27, 2013

They are related to the archosaurs. Crocodilians and dinosaurs are the only living archosaurs(dinosaurs=birds). But the archosaurs that may have given rise to the dinosaurs were too old and distant to have any lasting effects on them. That includes the ceratosaurs and abelisaurs.

"Men like me don't start the wars. We just die in them. We've always died in them, and we always will. We don't expect any praise for it, no parades. No one knows our names." ―Alpha-98

Abelisaurid Evolution Proposal

futurepaleontologist1

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