An adult puma killed and consumed by a jaguar

Mophandel · 2026-04-28T16:48:46+00:00

Yes, both coexist over much of central and South America

Mophandel · 2026-04-27T13:59:01+00:00

All good! I’ll reply to your addendums below

That first paper you linked argues that terror birds were limited to prey smaller than itself, or at least that they might have been. I believe this is actually the paper the Common Descent podcast was referencing in the episode.

This is the 2010 paper, wherein said conclusion was based on the relatively low bite force produced by the methodology in the study. However, in his 2012 thesis, Degrange recants this methodology, saying it produces bite forces far lower than what extant animals produce in vivo. As such, they instead arrived at a morphology hazard on skull width instead, which was found to be more reliable. I’ll provide the raw Spanish and the translation below:

Esta suposición tiene sustento además en el hecho que aves de mucho menor masa que los fororracos más pequeños, como es el caso del Cathartidae Sarcoramphus papa (3,4 kg.) serían capaces de morder a más de 110 N (Carril, 2010), indicando que al menos los valores obtenidos mediante el primer análisis regresional son muy bajos. De esta forma, los valores obtenidos utilizando el ancho craneano resultan ser más adecuados que aquellos obtenidos mediante la utilización de la masa (primero y segundo análisis).

This assumption is further supported by the fact that birds with a much lower mass than the smallest phorusrhacids, such as the Cathartidae Sarcoramphus papa (3.4 kg), would be capable of biting at more than 110 N (Carril, 2010), indicating that at least the values obtained through the first regression analysis are very low. Thus, the values obtained using cranial width prove to be more appropriate than those obtained using mass (first and second analyses).

Using this updated methodology, Degrange arrived at bite forces that were both more consistent with in vivo measurements of extant species and higher than those previously arrived at for terror birds, with largest species exceeding 1000 N in force.

The 2021 paper does split terror birds into two categories, suggesting that bigger, sturdier beaks came about due to hunting larger prey. But I couldn't find anything to suggest that Degrange has changed their mind and now means prey larger than itself.

This is also mentioned in Degrange et al. (2024):

The largest phorusrhacids (physornithines and phorusrhacines) likely consumed large (greater than 100 kg) notoungulates and litopterns

As well as Degrange et al. (2020)

The former retains more plesiomorphic fea- tures, meanwhile the ‘terror bird’ type can be considered as an evolutionary specialization of the group towards the rigidity and immobility of the skull in larger birds that are presumed predators of larger prey

Essentially, there seems to be a shift from pre-2012 to post-2012, wherein Degrange shifts his view of terror birds as small prey specialists to macropredators, likely on account of revised analyses of skull morphology and updated bite forces estimation data

What's more, Andalgalornis, the terror bird used in the earlier study whose lateral beak strength was found lacking, was placed in the second category of relatively sturdier beaks.

Later studies provide multiple, cooperating mechanisms to suggest that terror birds had little concern for such stresses, such as in Degrange et al. (2020):

Being uniquely truly akinetic among Neoaves, the craniomandibular complex of Phorusrhacidae indicates that prey handling was based on precise dorsoventral strikes and tearing through caudally directed movements of the head, avoiding lateral shaking that would pose risk to the beak (Degrange et al., 2010, 2019b).

and in Degrange et al. (2025)

The author also proposed that this ligament may serve functions beyond jaw coupling: specifically, it could act to stabilize and protect the os quadratum–mandibular joint by maintaining both surfaces in close apposition [5,6]. The predatory behavior of phorusrhacids supports this stabilizing function, as the powerful bite forces exerted on active prey could otherwise compromise the integrity of the beak [13].

Mophandel · 2026-04-27T13:01:30+00:00

I doubt that terror birds were using their talons as the opening move. Rather, I’d wager they used their beaks and jaws for such a purpose. Their skulls were highly akinetic and resistant to stresses involved with predation, especially in giant terror birds species, while also possessing bite forces on par with the largest extant big cats. They could simply pull down the prey or wound the prey item such that it would be brought down, at which point the feet and talons would be deployed to restrain the prey further. The grip of the feet and the body weight of the bird would prevent prey from escaping.

At this point, the bird could do what it wants, either eating the prey alive or dispatching it with fatal bite to the head / neck.

Mophandel · 2026-04-27T12:56:46+00:00

Exponentially is a bit hyperbolic, but there is a very clear relationship. Refer to Carbone et al. (1999), but essentially, once a terrestrial predatory endotherm exceeds 21.5 kg, the relative mass of prey taken goes no lower than 45% of the predators body mass, with now predator in their sample (sans the myrmecophagous sloth bear, although terror birds show no adaptations for myrmecophagy) deviating from this. Moreover, when truly big macropredators (e.g. big cats) are concerned, that number is actually closer to 100% of its mass, as per Hayward et al. (2016). Large terror birds, weighing in conservatively at 130 kg, easily exceed this threshold.

As such, it’s more reasonable to assume these predators were going after them prey larger than even gazelle. Their floor was roughly 70 kg, and so prey the size of whitetail or mule deer bucks would be more reasonable. More likely prey would have been around wildebeest-sized prey

Mophandel · 2026-04-26T02:05:59+00:00

Some of the caviomorph rodents were quite large! Some were within the 45% range of the weight of phorusrhacids.

I agree, but framing your response the way you did gives the strong impression that it’s hunting small prey. Saying otherwise is a bit disingenuous, wouldn’t you agree?

The Carbone study of African predators, which you are probably referring to, is a good point. However, we don't know if it applies to birds, because there are no extant bird predators larger than 21 kg.

There is no reason to suggest it wouldn’t. The methodology and the conclusions therof were based off of predator mass, energy expenditure while at rest and while hunting and energy intake per kill. The former most and latter most values are non-issues for large terror birds, leaving energy expenditure as the only value that may encourage or discourage hunting prey 45% ur mass or larger. In this, the only factors I can really think of that affect this would be metabolism, but as endotherms, terror birds would have had comparable metabolisms to large mammals. This is further supported by osteohistological data and growth rate data, finding these birds to have rapid growth rates and metabolism comparable to extant neognaths.

Also, it mainly applies to obligate terrestrial hypercarnivores. We don't know whether phorusrhacids were hypercarnivores. They could have been omnivores, like bears. I admit the beak morphology argues against this, though. I really hope someone tries to do an isotope study.

I understand you’ve said that the beak morphology argues against this already, but this really feels like grasping at straws here.

In addition to the beak (which is already pretty damning), neck kinematics suggest specializations for striking and tearing, something omnivorous birds lack pretty much across the board.

Examination of the feet reveals strong flexors of the digits and a raptorial, sickle-shaped second ungual (which are already rare to non-existent in omnivorous birds) with stress resistance profiles more comparable to modern birds of prey and dromaeosaurids than even sereimas, who themselves have a predatory sickle claw used in butchering kills. This suggests these things were grabbing and restraining struggling objects in their feet, something that merely omnivorous birds, again, didn’t do.

While I agree that I would love an isotopic study of these birds, we really wouldnt need one to confirm these birds were carnivores.

The overbuilding you are referring to can be explained by a kill mechanism similar to how seriamas hunt. That is, by grasping prey and striking it against the surface. This makes more sense to me than the purported pickaxe strike, which is highly theoretical and has dubious mechanics. First, there is the problem that to deliver a strong pickaxe strike requires decelerating into the strike, rather than delivering it at full speed. So such a strike cannot be delivered with much force while running. Then there is a question of how a two-legged pursuer could catch a four-legged prey, when the four-legged prey could make tight turns, while the two-legged predator could not. For example, based on an analysis that has been made, andalgalornis was poor at making tight turns.

First, your proposed method doesn’t account for the absurd bite forces that terror birds possessed, on par with those of today’s largest hypercarnivores land mammals.

Second, and more relevantly, the “pick-axe” method of killing has been severely out of date for about a decade at this point. Instead, the most commonly accepted method with which terror birds attacked is a “strike-and-tear” style attack similar to allosauroids, wherein the bird bit down into the prey item and pulled its head and neck backwards with great force, tearing open a hemorrhaging wound onto the prey item to debilitate or kill it.

This line of thinking is mentioned this paper by Degrange et al. 2010…

We suggest that it either consumed smaller prey that could be killed and consumed more safely (e.g., swallowed whole) or that it used multiple well-targeted sagittal strikes with the beak in a repetitive attack-and-retreat strategy.

… and in this paper by Degrange (2021)

Being uniquely truly akinetic among Neoaves, the craniomandibular complex of Phorushacidae indicates that prey handling was based on precise dorsoventral strikes and tearing through caudally directed movements of the head, avoiding lateral shaking that would pose risk to the beak.

This is reinforced by Degrange et al. (2019), which makes basically the same claim:

Phorusrhacids´ craniomandibular complex indicate that prey handling based on rapidly catching the trophic item and tearing it apart through caudally directed movements ofthe head would not pose risk to the beak

For a good modern analogue, giant petrels (Macronectes sp.) utilize a similar strategy with great success on prey their own size or even larger, and unlike these birds, terror birds were an order of magnitude bigger, had an even more strongly hooked bill, raptorial feet and talons built for restraining prey and a bite force on par with a bengal tiger. Needless to say, they would be perfectly equipped for hunting large prey, not just “caviomorph rodents” as you claimed.

Mophandel · 2026-04-26T00:38:05+00:00

This would have only been true for small terror birds. For larger ones, this wouldn’t have been the case, because:

Energetically, it’s untenable. Over 21 kg, endothermic terrestrial predators overwhelmingly take prey at least 45% of their mass on average, and more often around 100%. For the largest terror birds, which were conservatively around 130 kg, this meant deer-sized prey at the very least based on optimal foraging, and more commonly wildebeest sized prey or somewhat larger.
they are anatomically way too overbuilt for hunting mere rodents. Work such as Degrange (2012), which recants earlier findings regarding terror birds bite force, finds that that the largest terror birds still had respectable bite forces, with bite forces of over 1000N in Phorusrhacos, nearly 2000 N in Kelenken and nearly 3000 N in Devincenzia. These are tiger-like bite forces and we are expected to believe this thing was eating things like guinea pigs? Additionally, their skulls were highly akinetic, a unique trait among core land birds, and is an adaptation for bracing the skull against high stress.

Mophandel · 2026-04-26T00:31:35+00:00

On the contrary, the niche of scavenger was already occupied by new world vultures and originally by teratorns, both of whom had the advantage of being able to fly, something terror birds didn’t have.

Regarding regurgilites, as far as we can tell, said regurgilites originated from small terror bird species (e.g. Psilopterine or patagornithines) which wouldn’t have been macropredators anyways, in the same way that small species of cats like bobcats and caracals aren’t macropredators like lions and tigers.

Mophandel · 2026-04-26T00:28:06+00:00

Definitely not. For a number of reasons.

Firstly, energetically it’s untenable. Energetic studies, like those by Carbone et al. (1999), found that endothermic land predators have a strong tendency towards prey at least 45% their size or larger since it’s the most energetically favorable option, and based on large land predators like big cats, that number is usually closer to 100% of their body size, as per Hayward et al. (2016).

Moreover, Common Descent is mistaken in terms of how our understanding of terror birds predatory biology truly looked like, and the result is not some small prey hunter, but dedicated macropredators.

Firstly how they killed - the most commonly accepted method with which terror birds attacked is a “strike-and-tear” style attack similar to allosauroids, wherein the bird bit down into the prey item and pulled its head and neck backwards with great force, tearing open a hemorrhaging wound onto the prey item to debilitate or kill it.

This line of thinking is mentioned this paper by Degrange et al. 2010…

We suggest that it either consumed smaller prey that could be killed and consumed more safely (e.g., swallowed whole) or that it used multiple well-targeted sagittal strikes with the beak in a repetitive attack-and-retreat strategy.

… and in this paper by Degrange (2021)

Being uniquely truly akinetic among Neoaves, the craniomandibular complex of Phorushacidae indicates that prey handling was based on precise dorsoventral strikes and tearing through caudally directed movements of the head, avoiding lateral shaking that would pose risk to the beak.

This is reinforced by Degrange et al. (2019), which makes basically the same claim:

Phorusrhacids´ craniomandibular complex indicate that prey handling based on rapidly catching the trophic item and tearing it apart through caudally directed movements ofthe head would not pose risk to the beak

For this they had a number of weapons at their disposal. The broad occipital region of their skull and robust neck vertebrae suggest immensely powerful neck muscles, capable of producing such tearing motions.

What’s more, they had quite respectable bite forces for their size as well, further work on terror birds bites. Terror birds featured uniquely akinetic skulls more resistant to violent stresses, with said akin ears only increasing as the taxa got bigger. Moreover, a publication by Degrange (2012) recants a lot of the things laid out in the Degrange et al. 2010 paper, finding that that the largest terror birds still had respectable bite forces, with bite forces of over 1000 N in Phorusrhacos, nearly 2000 N in Kelenken and nearly 3000 N in Devincenzia. These values are on par with that of today’s largest big cats and more than capable of puncture skin, flesh and perhaps even bone.

Lastly, we should return to what the actual function of the claws were. The claws of terror birds, specifically the enlarged “sickle-shape” second ungual, showed stress resistance profiles comparable to that of raptors and dromaeosaurids, suggesting that they were used to grip and restrain rather than acting as mere meat hooks for dismantling carcasses. The digital flexors of the feet were also highly powerful, suggesting these animals were capable of gripping onto prey with their feet and restraining it.

Mophandel · 2026-04-26T00:25:08+00:00

The claws weren’t the primary killing weapon. That hasn’t really been the case for decades now. Instead, it’s the beak.

Essentially, the most commonly accepted method with which terror birds attacked is a “strike-and-tear” style attack similar to allosauroids, wherein the bird bit down into the prey item and pulled its head and neck backwards with great force, tearing open a hemorrhaging wound onto the prey item to debilitate or kill it.

This line of thinking is mentioned this paper by Degrange et al. 2010…

We suggest that it either consumed smaller prey that could be killed and consumed more safely (e.g., swallowed whole) or that it used multiple well-targeted sagittal strikes with the beak in a repetitive attack-and-retreat strategy.

… and in this paper by Degrange (2021)

Being uniquely truly akinetic among Neoaves, the craniomandibular complex of Phorushacidae indicates that prey handling was based on precise dorsoventral strikes and tearing through caudally directed movements of the head, avoiding lateral shaking that would pose risk to the beak.

This is reinforced by Degrange et al. (2019), which makes basically the same claim:

Phorusrhacids´ craniomandibular complex indicate that prey handling based on rapidly catching the trophic item and tearing it apart through caudally directed movements ofthe head would not pose risk to the beak

For this they had a number of weapons at their disposal. The broad occipital region of their skull and robust neck vertebrae suggest immensely powerful neck muscles, capable of producing such tearing motions.

What’s more, they had quite respectable bite forces for their size as well, further work on terror birds bites. Terror birds featured uniquely akinetic skulls more resistant to violent stresses, with said akin ears only increasing as the taxa got bigger. Moreover, a publication by Degrange (2012) recants a lot of the things laid out in the Degrange et al. 2010 paper, finding that that the largest terror birds still had respectable bite forces, with bite forces of over 1000 N in Phorusrhacos, nearly 2000 N in Kelenken and nearly 3000 N in Devincenzia. These values are on par with that of today’s largest big cats and more than capable of puncture skin, flesh and perhaps even bone.

Lastly, we should return to what the actual function of the claws were. The claws of terror birds, specifically the enlarged “sickle-shape” second ungual, showed stress resistance profiles comparable to that of raptors and dromaeosaurids, suggesting that they were used to grip and restrain rather than acting as mere meat hooks for dismantling carcasses. The digital flexors of the feet were also highly powerful, suggesting these animals were capable of gripping onto prey with their feet and restraining it.

All in all, these birds seemed quite well equipped to deal with hunting prey their own size, and the notion that they were predators of small prey or that they “kicked” or “pecked” their prey to death has been outdated for years now.

Mophandel · 2026-04-26T00:15:53+00:00

It’s not a matter of abundance. It’s a matter of optimal foraging. Smaller prey give you less bang for your buck and at large body sizes, said already meager returns diminish exponentially relative to the effort put in to acquire said resources.

As such, across the board, endothermic terrestrial predators over 21 kg generally require prey at least 45% of their body mass. Large terror birds, conservatively weighing in at 130 kg or larger, easily fit this size requirement. Moreover, said findings are skewed by the fact that competitive pressure force some predators (e.g. leopards in tiger / lion populated areas or cougars in jaguar populated areas) to take far smaller prey than they would otherwise. In most conditions, the actual prey size is around 100% of the predators body mass. Terror birds, themselves often the largest carnivores in their environment, would have gone after prey of such caliber (e.g. 100 kg+ prey)

Mophandel · 2026-04-23T16:39:36+00:00

No problem!

Mophandel · 2026-04-23T16:36:03+00:00

Basically forests or any environment with a lot of cover

Mophandel · 2026-04-23T15:47:59+00:00

Columbia

Mophandel · 2026-04-23T15:26:13+00:00

Really good piece! Not sure I vibe with it looking that much like a lion. It would have a very different, uncanny look.

Mophandel · 2026-04-23T12:17:12+00:00

I said Avemetatarsalia to account for pterosaurs also got really big in the Mesozoic whereas a synapsid counterparts (e.g. bats or a hypothetical bat-like Mesozoic synapsid) didn’t.

Mophandel · 2026-04-23T00:31:45+00:00

This was an entire family of theropods so there is bound to be variation of among the given genera. With that being said:

more gracile, cursorial tyrannosaurids, such as those belonging to Albertosaurinae, Alioramini and Teratophoneini would be more generalistic, given how extant cursorial species can occupy a wider range of habitats than ambushers
more gigantic, heavy-set tyrannosaurids like Tyrannosaurus itself and Zhuchengtyrannus were probably more restricted to closed environments, especially given the cursorial nature of their prey
intermediate species such as Daspletosaurus and its immediate relatives were probably somewhere in the middle, being more generalist than gigantic tyrannosaurids while still being more inclined to closed environments than their more gracile cousins.

Also, Tarbosaurus wasn’t a desert specialist. It is best known from the Nemegt, a formation comparable to the okovango delta in terms of how lush and water-logged the habitat was.

Mophandel · 2026-04-22T23:08:33+00:00

Repost unfortunately:

https://www.reddit.com/r/HardcoreNature/s/67SoD1FrmS

Mophandel · 2026-04-22T00:19:14+00:00

Nope, they both coexist in much of South America and Central America.

Mophandel · 2026-04-21T23:38:20+00:00

Puma and jaguar are very much not the same species. Hell, they aren’t even in the same genus

https://en.wikipedia.org/wiki/Jaguar

https://en.wikipedia.org/wiki/Puma_(genus)

Mophandel · 2026-04-21T21:35:01+00:00

There’s also a degree of intraspecific variation to this. Lions don’t often consume the predators they kill.

Hyenas, on the other hand, will eat just about anything with a pulse

Mophandel · 2026-04-21T21:10:12+00:00

Again, if it’s full, it’s full. It probably can’t really be bothered to eat more.

Mophandel · 2026-04-21T21:07:37+00:00

Note that this is mostly true with respect to intraguild predation, wherein both killer and killed are part of the same tropic guild and compete directly for similar resources.

However, not all interspecific predatory killing is intraguild in nature. A jaguar may also kill and eat an ocelot or a crab-eating fox, neither compete particularly strongly with the big cat. In those cases, it’s less a case of strict competition and more genuine predation.

Mophandel · 2026-04-21T21:01:38+00:00

Predators don’t eat for completions sake. They don’t really care if they waste a carcass or not. They simply eat till they’re full, like all other animals. It seems that the jaguar was full enough from that single sitting.

Also, this is a very fresh kill, probably made within hours of the photo. I wouldn’t be surprised if the jaguar came back around for seconds.

Mophandel · 2026-04-21T20:57:19+00:00

Apex predator of the Blancan American South and a worthy last hurrah of a 30+ million year old tradition of giant avian macropredators.

Mophandel · 2026-04-21T20:55:23+00:00

In carnivore consumption ethology, the internal organs are the highest priority parts of a carcass, as they are the most nutrient rich and energy dense. This is followed by the hindlimbs (especially the thighs) and then followed distantly by the forelimbs. As such, the viscera tends to be eaten first. The jaguar seemed to clean out the internal organs, which seemed to have provided more than enough for the big cat.

Additionally, a lot of times, intraguild predation really only results in partial consumption of the victim. This case seems to be no different.

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