|
|
Post by lionclaws on Oct 2, 2023 5:21:12 GMT 5
Most of the Neotheropoda had their share of giants (10+ meter or 4+ tonne animals). Coelurosaurs had T-rex. Allosauroids had Saurophaganax, Epanterias, and the various giant Carcharodontosaurs. The Megalosaurs had Torvosaurus gurneyi and the larger Spinosaurs.
But the Ceratosaurs don't seem to have hit the 10 meter/4 tonne mark. They had opportunity - once the Carcharodontosaurs went extinct, the Coelurosaurs started getting big. The Abelisaurs started big, but they never got bigger than 9 meters.
Why did T-rex reach 10 tonnes while the Abelisaurs seem to have maxed out around 3 tonnes?
|
|
|
|
Post by Infinity Blade on Oct 2, 2023 6:40:29 GMT 5
It may be worth waiting to see how large this currently unnamed Maastrichtian Kenyan abelisaurid turns out to be. The one thing that everyone claims about it is that it is truly gigantic, but of course, only time will tell, so take this for what you will.  Image source->But for now, let's (mostly) ignore that. My guess off the top of my head is that some abelisaurid-inhabited landmasses, even after allosauroids became extinct, just weren't quite big enough to support abelisaurids in the 4+ tonne mark. Majungasaurus lived in Madagascar, which was already an island at the end of the Cretaceous. Rajasaurus lived in India, which was still an island and had yet to collide with Asia. Things like Arcovenator lived in Europe, which during the Maastrichtian was a series of small islands. So I wonder if it could be that abelisaurids living on smaller landmasses couldn't get to T. rex-level sizes for that reason alone. This idea of mine, however, isn't perfect, considering abelisaurids also lived in continental South America and Africa. The latter may have had a truly gigantic abelisaurid (as I alluded to above). As for South America, the largest abelisaurid from that time and continent (and seemingly our biggest abelisaurid on record, at least until this Kenyan abelisaurid gets described, perhaps), Pycnonemosaurus gets close to the 4 tonne mark, and I could personally envision some individuals growing larger, hitting the 4 tonne threshold and perhaps a big bigger. But if that's not satisfactory to you, we should probably also consider that post-allosauroid South America was still home to megaraptorans. Judging from this post-> by theropod, the largest megaraptorans could get scary huge, easily 5-ish tonnes (so maybe it was still relatively difficult to reach the size threshold we're talking about here when megaraptorans were already doing it). |
|
|
|
Post by lionclaws on Oct 2, 2023 7:01:18 GMT 5
Ah, megaraptorans. Instead of confusing us by being weird, they confuse us by being annoyingly fragmentary and hard to classify. They certainly got big in South America, and I can believe it if they were the reason that abelisaurids stayed small, at least pending further evidence.
But even then, 5 tonnes is on the small side compared to, say, 9 tonnes for the Giganotosaurus holotype. I mean, titanosaurs were still around. Why was nobody getting big to eat Alamosaurus (or its Gondwanan counterparts)?
|
|
|
|
Post by theropod on Oct 2, 2023 14:19:32 GMT 5
Ah, megaraptorans. Instead of confusing us by being weird, they confuse us by being annoyingly fragmentary and hard to classify. They certainly got big in South America, and I can believe it if they were the reason that abelisaurids stayed small, at least pending further evidence. But even then, 5 tonnes is on the small side compared to, say, 9 tonnes for the Giganotosaurus holotype. I mean, titanosaurs were still around. Why was nobody getting big to eat Alamosaurus (or its Gondwanan counterparts)? 5 tons is well within adult T. rex territory.  This is the mass distribution for the T. rex specimens in Paul et al. 2022 based on Campione et al. 2014’s regression for femur circumference. While yes, the Maip holotype is smaller than the average adult T. rex or Giganotosaurus, and, based on that, it is likely that the taxon was not quite as big as those two, it alone is by no means conclusive proof of that. If that scenario seems to throw up implausibilities, then besides looking for an explanation resolving said implausibilities, we need to consider the possibility that the scenario itself might not be correct based on how solid the evidence for it even is (based on a single specimen→not very solid). Perhaps there were larger latest-cretaceous megaraptorans around, which equalled the size of the largest mid-cretaceous carcharodontosaurs, perhaps the Maip macrothorax holotype was a small individual and its species overall grew as large as other giant theropods and we just haven’t happened to find a big one, or perhaps (most likely) it was a typical-sized individual, and this taxon simply stayed a little bit smaller than the very largest theropods, while still growing gigantic. Now I personally wouldn’t tie myself in knots over this, assuming (which is the most probable scenario when looking at the size distributions) Maip was on average 1 or 1.5 tons smaller than T. rex, that would still make it a gigantic theropod. I wouldn’t see something particularly suspicious about that. Apex predators on different continents today aren’t all exactly the same size either, and neither were apex predators throughout earth’s history. Not every apex-predatory theropod in every era on every continent necessarily has to have grown to exactly the same size (the others aren’t all exactly the same size either). |
|
|
|
Post by theropod on Oct 2, 2023 19:04:17 GMT 5
On the subject of Pycnonemosaurus: Here’s a gdi based on randomdinos reconstruction→ and a dorsal view adapted from Greg Paul’s Carnotaurus:  I think 4 t is pushing it. Seeing how Paul’s skeletal is probably too conservative on the body width, I’m willing to assume the real volume was greater than the 2.5 m³ you’d get for the base-model, but I think the +40% model is probably plenty liberal enough, with the real volume likely somewhere in between. So a body mass at most around 3 t or maybe slightly above seems more reasonable. That’s not unimpressive, but still more Allosaurus- or albertosaurine-sized than truly giant theropod territory imo. Admittedly the specimen is apparently not fully mature yet though (although I always wonder a bit as to how much when it comes to statements like this; still somewhat actively growing, ok, but does that make it a subadult, or a young adult? That comes down to terminology more than to biological reality), and there are indications of larger Abelisaurs out there that might be adults of the same species, or similar, but larger taxa. And of course the Kenyan abelisaur, that I don’t know a lot about except that according to an old SVP abstract from 2013 it’s supposed to be 11-12 m +. Unfortunately such estimates have been made for large abelisaurids in past, such as Ekrixinatosaurus, estimated at 10-11 m as recently as 2011, and have turned out to be totally incorrect, so I really hope this gets substantiated by a paper and actually holds up to scrutiny. Whenever the only published record of a major discovery like this is a conference abstract that still hasn’t been followed up on by a paper a decade later, I tend to get a bit suspicious. That the largest abelisaurs (these two guys and Carnotaurus) would seemingly come from Africa and South America would fit in well with Infinity Blade ’s hypothesis as to why Indian, Malagasy and European Abelisaurs never seem to have grown gigantic (though I will note that India was a pretty damn big island, apparently big enough for blue-whale-sized sauropods, so I wouldn’t be surprised if a gigantic theropod existed there as well). If it turns out that the giant Kenyan Abelisaur is legit, that also might indicate some sort of faunal differentiation between Africa and South America in the terminal Cretaceous, with Megaraptorans being important apex predators on one, but not the other continent. So we shouldn’t count them out based on the frustratingly little evidence for gigantic Abelisaurids that we have so far, even if in the past such hopes have so far turned out to be in vain, but I think we also don’t have much to work with right now. --- Juárez Valieri, R.D., Porfiri, J.D. and Calvo, J.O. Forthcoming. New Information on Ekrixinatosaurus novasi Calvo et al 2004, a giant and massively-constructed Abelisauroid from the “Middle Cretaceous” of Patagonia. . |
|
|
|
Post by Infinity Blade on Oct 2, 2023 19:55:51 GMT 5
(though I will note that India was a pretty damn big island, apparently big enough for blue-whale-sized sauropods, so I wouldn’t be surprised if a gigantic theropod existed there as well) I can't fully tell if this is a diss on that Bruhathkayosaurus paper or if it's a sincere citation of it lol (I say that since most people I've seen talk about the paper just seem to dismiss it). On a serious note, I don't have a problem with the idea of sauropods being that large, but yeah, even ignoring Bruhathkayosaurus completely, Isisaurus was still a roughly Paraceratherium-sized beast on the island. |
|
|
|
Post by theropod on Oct 2, 2023 20:03:42 GMT 5
(though I will note that India was a pretty damn big island, apparently big enough for blue-whale-sized sauropods, so I wouldn’t be surprised if a gigantic theropod existed there as well) I can't tell if this is a diss on that Bruhathkayosaurus paper or if it's a sincere citation of it lol A bit of both, really. My past advocacy for blue whale-sized sauropods is well known, I won’t deny it, nor that I see nothing in particular wrong with this one. That doesn’t mean it’s definitely true, or that Bruhathkayosaurus isn’t sort of a funny animal though. But even if it was half the size it was estimated at, it would still rank among the largest sauropods, so that would still suggest that India could support gigantic, resource-intensive animals. |
|
