Large prey predation in non-avian theropods

[Infinity Blade]

Jul 7, 2024 6:16:41 GMT 5 Supercommunist said:

Jul 7, 2024 5:24:30 GMT 5 Infinity Blade said:

Also, there's a basal sauropodomorph tail where the distal third appears to have been shorn off at the 25th caudal vertebra. This injury healed and wasn't immediately fatal (although, the authors didn't rule out the possibility that it may have eventually contributed to its death). The sauropodomorph is referred to as cf. Massospondylus, and if it is indeed Massospondylus, it would be the largest specimen known; it was estimated to be 6 meters long in total based on the size of its tail elements (Butler et al., 2013).



The authors think that the injury was most likely caused by a predator bite, probably from something like Dracovenator. To put this into perspective, Dracovenator was estimated to be ~6 m long and ~250 kg in GSP's Princeton field guide. His estimate for Massospondylus was ~4.3 meters long and ~200 kg (which is already 80% of the Dracovenator body mass estimate). If we assume these numbers are correct and scale the Massospondylus size estimate up to 6 meters, we'd get an animal weighing ~543 kg.

That's pretty strong evidence that macropredatory theropod bites are vastly more lethal than extant carnivoran bites. Can't remember the last time I heard a carnivora sever a large living animals limbs. Of course, in fairness the prey modern day mammals hunt typically hunt don't usually have substantial tails. Then again. I can't recall any accounts of otters/pinnipeds biting off similar sized fish tails and Dracovenator was hardly the most powerfully built theropod.

I will admit to having a strong theropod bias but at this point I think it does appear that theropods had better macropredatory capabilities than modern carnivores.

We have fossil evidence of theropods attacking much larger sauropods and stegosaurs, and the Montana dueling dinosaur indicates that even juvenile tyrannosaurids might have hunted adult ceratopsians.

In contrast, we don't seem to have much direct evidence that smilodon, American lions, giant bears, ecetra hunting giant prehistoric fauna despite presumably having more fossil material. In addition, many large theropods were further handicapped by square cubic law, yet we know allosaurus still at least attempted to hunt adult large stegosaurus.

Apparently the T. rex specimen Wyrex getting its tail bitten off while it was alive is indeed legit too, which further solidifies just how damaging theropod bites were.

x.com/deak_michael/status/1756747506828866046

[Supercommunist]

Oh yeah, I forgot about Wyrex. Still this account in a way is more interesting since tyrannosaurus was an outlier and had an unusually powerful jaw compared to other theropods. I know Dracovenator is poorly preserved but most reconstructions seem to assume it had a dilophosaurus-like build, and I would argue that would make it a middle tier theropod fighter.

Given that many species of herbivorous dinosaurs appear to have objectively better armaments than modern day herbivores, I suppose it really shouldn't be surprising that theropod bites where on another level.


Something else we should consider is that predator is that it's pretty rare for experienced adult predators to get killed by their prey, especially against animals outside their weight class. For instance, although everyone here would agree that an adult hippo or rhino is usually beyond a lion, there are a lot more incidents of lions killing rhinos and hippos because the predators are usually the ones that dictates whether a fight happens or not and can escape if things go pear-shaped. Because of this its actually more common for predators to get killed by a regular prey item, rather than one that could obviously destroy them in a fair fight.

Therefore if we have evidence of adult theropod being killed by a herbivore, I think that is good evidence that the predators hunted that prey item with some degree of regularity.



However, according to a guy that works with black footed ferrets, it not uncommon for young ferrets to be wounded or even killed in the training pens so we would have to be more cautious of making predator-prey relationship conclusions if we find fossils of young theropods getting killed by a large herbivore it is possible that the young animal overestimated its abilities and paid the price.

[Infinity Blade]

So I was looking at the supplementary material of Therrien et al. (2023). They have equations to calculate the minimum and maximum body mass of prey taken for a mammalian or reptilian predator of a given body mass.

The phylogenetically-corrected generalized least-squares regression for maximum prey body mass for mammalian predators is log max prey mass = a log predator mass + b, where a equals 1.165 and b equals -0.233.

This study looked at Gorgosaurus, and estimated an adult specimen to weigh ~2,626 kg. To estimate its maximum prey size, this would mean a formula as follows:

log max prey mass = 1.165*log(2626) – 0.233

log max prey mass = 3.750

max prey mass = 5,623.4 kg


So if we take this equation at face value, an adult Gorgosaurus weighing ~2.6 tonnes could prey on an animal as massive as an average adult bull African bush elephant (5.2-6.9 tonnes on average). Contemporary megaherbivorous dinosaurs like Styracosaurus (~4,370 kg) and Corythosaurus (3,620 kg) are within this prey size range.


The juvenile Gorgosaurus specimen that had small Citipes in its gut contents was estimated to weigh 334.4 kg by the authors. If we put its body mass into this equation, we get a maximum prey mass of ~509.33 kg.

The bivariate plot (Figure 5 in main text) demonstrates that ceratopsids (e.g., Styracosaurus albertensis, 4370 kg, (107)) and hadrosaurids (e.g., Corythosaurus casuarius, 3620 kg, (107)), the documented diet of adult Gorgosaurus (17), are consistent with maximum prey size for mammalian predators with a body mass of an adult Gorgosaurus but surpass the predicted maximum prey size for similar-sized reptilian predators. However, actual maximum prey size for some extant, large crocodylians plot along the mammalian regression and near ceratopsids and hadrosaurids, revealing that large reptilian predators are capable of capturing very large prey relative to their body size. In comparison, both yearling and adult Citipes fall in the lower prey size range for mammalian predators with a body mass of an adult Gorgosaurus and in the upper prey size range for reptilian predators of the size of an adult Gorgosaurus. In the context of a juvenile Gorgosaurus individual, the bivariate plot shows that juvenile and adult Citipes plot in the mid-size prey range for mammalian predators with a body mass of a juvenile Gorgosaurus and in the upper range for similar-sized reptilian predators. Dinosaurian megaherbivores plot far above the maximum prey size for either mammalian or reptilian predators of this body mass. These results suggest that Citipes could have been a common prey choice for juvenile Gorgosaurus individuals but more rarely selected by adult individuals due to its small size, whereas dinosaurian megaherbivores (i.e., hadrosaurids and ceratopsids) could have been preyed upon by adult Gorgosaurus individuals but not juvenile individuals.

HOWEVER...

I question the accuracy of at least some of the maximum prey mass figures for extant predators they use. For example, the lion's maximum prey body mass in log(kg) is 2.740, which translates to animals weighing 549.54 kg (the lion's body mass in log(kg) is reported as 2.312, which is 205.12 kg). And how accurate is that? Well...

Jun 5, 2024 9:01:31 GMT 5 Infinity Blade said:

Adult bull giraffe killed by a single adult male lion.

web.archive.org/web/20081212195202/http://www.desertlion.info/news08a.html

Clearly even a single lion is capable of taking down animals far larger than about half a metric ton. By contrast, the tiger (reported at 111.94 kg) has a reported maximum prey body mass of 2,722.7 kg. Needless to say, no matter how much of a tiger fan you may be, I think anyone should see the absurdity of a tiger being able to take prey 24 times its own body mass, while a lion nearly twice said tiger's body mass is limited to taking prey only ~2.7 times its own body mass.

As the excerpt from the supplementary material above alludes to, some of their data input for reptilian predator maximum prey body mass is also not quite accurate, namely underestimating the maximum prey mass of some large crocodilians. Similarly, what do they report the Komodo dragon's (reported body mass 47 kg) maximum prey mass as? 1.717, which translates to 52.119 kg (said prey claimed to be a Rusa deer)...

Lol

One Komodo dragon actually killed a water buffalo by ripping a hole in its abdomen, effectively eviscerating the buffalo.

www.google.com/books/edition/Komodo_Dragons/MqFfBgAAQBAJ?hl=en&gbpv=1&dq=komodo%20dragon%20predation%20water%20buffalo%20auffenberg&pg=PT9&printsec=frontcover


Now, to be fair, I'm not a reptile expert, and I can't speak for the vast majority of the species listed in their supplementary info. However, it's clear that some of the info could use a bit of work. I guess the takeaway here is that, while this equation can be very useful, and maybe it gives some idea as to how big of a prey item a certain predator can take (I don't doubt an adult Gorgosaurus could take an animal weighing 5.6 tonnes, or a juvenile weighing 334 kg could take an animal weighing half a tonne), maybe it should be refined with more accurate information on extant predator maximum prey size. Maybe some extinct predators will have their maximum prey size underestimated (although, I can't think of many prey items in Gorgosaurus' ecosystem that were several times its body mass). Maybe some overestimated (especially if it lacks macropredatory adaptations)?

Just some food for thought.

[Supercommunist]

Yeah I don't think you can make up an equation for maximum prey size. The topic is complex and understudied. To this day we don't really have super reliable equations for topics that are a lot more relevant to government interests. For instance, I think militaries still struggle to come up with equations that allow them to accurately predict ballistic penetration.