Largest dinosaurs of the Triassic?

[theropod]

dracovenator.wordpress.com/2011/03/10/the-largest-prosauropods-part-3/

[Derdadort]

Sept 25, 2014 19:42:47 GMT 5 blaze said:

Maybe is a sampling issue? What could there be to hunt them? rauisuchians were already gone by the latest Triassic

Were the other known herrerasaurids as large as Herrerasaurus? I also think a sampling bias is more likely so far, furthermore rauisuchids seem to exist at least until the Rhaetian or even to the Early Jurassic
1) R. E. Kirby. 1991. A vertebrate fauna from the Upper Triassic Owl Rock Member of the Chinle Formation in Northern Arizona, Northern Arizona University. 1-476
2) D. Munyikwa. 1997. Faunal analysis of Karoo-aged sediments in the northern Limpopo Valley, Zimbabwe. Arnoldia Zimbabwe 10(13):129-14

[blaze]

Not that I'm aware off.

The early Jurassic remains are said by Nesbitt et al. (2013) to possibly be crocodylomorph in origin and the only possible Rhaetian (it might as well be late Norian) record is CM 73372, previously referred to as Postosuchus sp. but Nesbitt (2011) hypothesized it could be a crocodylomorph too and that gained support as it came out as a crocodylomorph in Zanno et al. (2015) phylogenetic analysis of Carnufex, so we can't say with confidence any rauisuchian made it pass the Norian.

While writing this I had the idea that maybe we were ignoring some early crocodylomorphs but I forgot that while they (Carnufex and Redondavenator) had skull size similar to adult Herrarasaurus, their heads would be proportionally bigger to their bodies will only be 3-4m long.

[Derdadort]

Regarding the Rhaetian one I was talking about MNA V5604, a fragmentary tibia also assigned to Postosuchus sp. by Spielmann et al. (2007) from the Owl Rock Member, which is after PBDB Rhaetian in age, however there are also older studies which say it's Norian. IMHO different more admittedly uncertain specimens are still holding up the possibility of post-Norian rauisuchids. In the end the exact age of the Norian-Rhaetian boundary isn't generally determined so far. For the ominous unknown Late Triassic predator I will keep myself away from "Could X take down a Y" speculations, but some unknown theropods (early averostra) or your mentioned crocodylomorphs could be possible candidates.

Back to the original topic, there are probably Late Triassic remains of thyreophorans, in Martill et al. (1997) named as Scelidosaurus sp., however I have no idea about the size of the fossils. The name suggests a small to medium sized animal at least.

[theropod]

We seem to have been ignoring Isanosaurus attavipachi. 
There is a 104cm humerus referred to it, comparable to both Camarasaurus and Diplodocus. Based on Shunosaurus, which is probably the best of the analogues offered by the paper, this would suggest an animal over 15m long. And we have to keep in mind that’s a relatively robust, short-necked bauplan for a sauropod, so likely quite a massive animal. However, there is some doubt as to whether its horizon is really upper Triassic in age.

Buffetaut, E., V. Suteethorn, J. Le Loeuff, G. Cuny, H. Tong, and S. Khansubha. 2002: The first giant dinosaurs: a large sauropod from the Late Triassic of Thailand. Comptes Rendus Palevol 1:103–109.
www.sciencedirect.com/science/article/pii/S1631068302000192

[theropod]

And Ingentia and Lessemsaurus are also candidates:
www.nature.com/articles/s41559-018-0599-y
Apaldetti, C., R. N. Martínez, I. A. Cerda, D. Pol, and O. Alcober. 2018: An early trend towards gigantism in Triassic sauropodomorph dinosaurs. Nature Ecology & Evolution:1.

[Infinity Blade]

Are we so sure Eubrontes was made by a theropod?

I've come across an interpretation that questioned this idea back when I was researching theropod foot claw sharpness (I'm sure a few users here will remember that).

See Late Triassic Footprint Fauna from the Culpeper Basin, Northern Virginia (U. S. ) (hyperlinked)

At any rate, there seem to have been big, even enormous dinosaurs in the Triassic. Interesting to find that just as how mammals were not all mouse-sized and unspecialized during the Mesozoic, nor were all dinosaurs in the Triassic kept down in size (though, unlike Triassic dinosaurs, no Mesozoic mammal could be deemed "large", i.e. megafauna).

[theropod]

^Probably not all Eubrontes, no, but some are probably from theropods, including some big ones (e.g. the Silva et al. prints).
The source you cite itself refers theropod footprints to Eubrontes right after arguing why some Eubrontes tracks are probably plateosaurian in origin.

However, some of the arguments, especially about apparent gregariousness and being the largest animal in the ecosystem, seem rather weak to me, with the probable existence of basal sauropodomorphs the size of large elephants in the Upper Triassic.
Plateosaurus also definitely does have trenchant pedal unguals, their lack in some footprints seems more likely related to preservation than taphonomy.

Digit I in the pes of Plateosaurus is shortened and may not have been in contact with the ground, but seems more massive than in theropods, so where hallux prints are present, I’d expect them to be pretty large.

But indeed distinguishing plateosaurid-grade sauropodomorph footprints from theropod footprints is pretty difficult.

[theropod]

I think Liliensternus/Gojirasaurus/Zupaysaurus are back in the race for biggest triassic theropod. 

Firstly because of the increasing doubts about Herrerasaurids being theropods.
Secondly I think those coelophysoids might be quite a bit bigger (by mass) than previously estimated (by Greg Paul and on this thread), especially considering the known specimens of the former two are immature. I think the known specimens are more likely around the 200 kg mark, with the possibility of adults being considerably larger.
That’s still not very impressive for the largest theropods of any time period though, and downright tiny when compared to the sizes reached by both contemporaneous sauropodomorphs and earlier pseudosuchian predators.

Ben Pabst has hypothesized that bear-like omnivory by intermediate grade Sauropodomorphs such as Plateosaurus might have blocked the apex-predator niche later filled by truly large theropods (and filled by pseudosuchians and herrerasaurs during the Carnian). This would make a lot of sense to me, although from what I’ve read the dentition of Plateosaurus isn’t very suitable for carnivory, even if it could have used its claws a lot in scavenging and potential prey-acquisition, similar to extant bears. In that scenario Plateosaurus/Liliensternus would be sort of analogous to brown bear/siberian tiger, and the sizes actually sort of fit as long as we are speaking of a typical-sized Plateosaurus.
Although of course the largest Plateosaurs got to 10m and 3-4t, which is more like elephant territory and in a completely different ballpark from bears, while the theropods really do seem to be similar to, or slightly larger than, big extant pantherines. Maybe with all that ontogenetic and morphological plasticity going on, there was also ecological variation between different sizes.

[creature386]

The teeth of prosauropods have often been compared to those of herbivorous iguanines (See: The Dinosauria 2004) which are to an extent omnivorous, but not as much as bears, so I think bear-like omnivory is a stretch.

[theropod]

Yes, I know, tooth morphology doesn’t really support carnivory at all, this has been noted previously (e.g. Galton 1985). The question is if its possible it did something we don’t see its teeth being well adapted for (bear molars, or ours for that matter, really aren’t adapted for carnivory either).

[creature386]

I don't doubt that it occasionally ate meat (after all, iguanas also occasionally eat meat), I just thought if it did so as much as bears do*, it would have developed adaptations. The bear dentition has a whole shows clear adaptations towards carnivory.

*For distinction, iguana-like omnivory only involves scavenging and killing much smaller animals. Bear-liek omnivory is this with the addition of occasionally going after large-bodied prey. This distinction is important if we want to look at if Plateosaurus competed with Liliensternus.

[theropod]

But pretty much the only common thing in Plateosaurus’ ecosystem that would qualify as large-bodied next to an adult Plateosaurus would be other basal sauropodomorphs, mainly Plateosaurus itself. At least that’s the case in Europe, though ecosystems on the southern continents seem a little more varied.

Obviously active predation on its own species is unsustainable in the long term anyway, but scavenging would be a viable option (especially in the context of the bonebeds we have, this would make sense, and also explain the general rarity of large-bodied theropods and other predators on these localities), so in effect, it would compete for the same food source with theropods. What I mean is that a large-bodied theropod (for the time) might not be able to compete with plateosaurids (which were at least twice the size of the largest contemporaneous theropods that we know, and could grow much larger than that) over carcasses, and could not realistically prey upon living individuals either, so perhaps the lack of an exploitable food source would have prevented theropods from attaining larger sizes.

However I’ve been ignoring that there are in fact still large-bodied rauisuchians around at the time. Teratosaurus is from the Löwenstein Fm., though I’m not sure about its actual size, and Fasolasuchus is from the upper Los Colorados Fm., i.e. even younger. The latter is definitely in a different league than any known Triassic coelophysoid if blaze’s reconstruction of the skull is anything to go by. I’d mistakenly thought Fasolasuchus was Carnian, like Saurosuchus. So yeah, we probably still have "rauisuchian" apex predators up until the triassic/jurassic boundary, which might have been what was keeping theropods so small.

[blaze]

But they seem to be extinct by the late Norian, that leaves a good 10 million years for theropods to grow until the boundary. Fasolasuchus is from 217-215mya, Vivaron is 212mya. Any new discovery recently?

[theropod]

Nice to see you posting, I’ve missed your input!
None that I’m aware of, no. Well, Smok is uppermost Norian or Rhaetian, phylogenetically indeterminate, but could be rauisuchian. There’s Effigia from the Rhaetian of the US, but it’s small and doesn’t really count. The same quarry apparently yielded a specimen "referred to Postosuchus", but which Nesbitt et al. 2011 think might rather be a crocodylomorph (however "rauisuchians" as a whole being basically stem crocs too, I don’t think the distinction really matters if it is ecologically similar).

The Norian-Rhaetian boundary isn’t well-resolved in many important localities, so it’s difficult to really tell.

At least Rauisuchians did still coexist with Plateosaurus and were probably the top predators at that point.