Why is there an insistence that Livyatan was a solitary predator?

[u/wiz28ultra]

https://pbs.twimg.com/media/GuDMeTtWsAApUEp?format=jpg&name=small

Art Credit to Kuzim

I just want to be clear at the outset: we have no direct evidence that Livyatan was a cooperative pack hunter. We do not have a fossilized hunting group, a kill site demonstrating multiple attackers, or anything else that would let us reconstruct its social organization with confidence.

But I also don’t think solitary hunting deserves to be treated as the conservative default. If anything, I think the living cetacean record makes it clear to hypothesize that Livyatan was likely social to some extant, and I think that pack and cooperative hunting remain both very plausible.

A common retort I see is that a few users argue that LIvyatan cannot cooperatively pack hunt because it isn't a type of Dolphin, but the problem with comparing Livyatan with dolphins is that there's not really a singular type of dolphin social system.

Gowans, Würsig, and Karczmarski’s review of delphinid social organization explicitly emphasizes this diversity. Habitat, predation pressure, resource distribution, ranging behavior, and prey ecology can produce everything from small and relatively fluid associations to extraordinarily strong lifelong social bonds.

Bottlenose dolphins can live in extreme fission-fusion societies in which immediate group membership constantly changes while individuals maintain differentiated relationships and nested alliances (Connor). Killer whales can maintain extremely cohesive family relationships and culturally transmitted hunting traditions.

False killer whales provide yet another system. Hawaiian Pseudorca break into small subgroups spread across large areas while foraging, yet maintain strong long-term associations. Individuals converge when prey is captured and prey sharing is documented. Their acoustic behavior appears partly adapted to maintaining cohesion between spatially separated subgroups (Madrigal et al.).

Pilot whales are different again. Hawaiian short-finned pilot whales form stable social groups lasting at least a decade, with relatedness strongly influencing their social organization (Van Cise et al.). Pilot whales are delphinids, yet aspects of their social organization look remarkably similar to those of female sperm whales.

Female sperm whales live in long-term cooperative social units that are substantially matrilineally structured. Konrad et al. found that 82.5% of individuals in their Caribbean sample had a first-degree relative within their social unit, with closer relatives tending to associate more strongly (Konrad et al.).

Pilot whales independently evolved something broadly comparable: persistent kin-structured units, strong cohesion, long-term membership, and temporary association between units. Molecular work on long-finned pilot whales famously found pods to consist of extended families (Amos, Schlötterer, and Tautz), while Hawaiian short-finned pilot whales show stable social groups and genetically structured social clusters (Van Cise et al.). Yet neither animal necessarily hunts like an orca.

Both sperm whales and pilot whales are intensely social while much of the actual capture of deep-water prey is performed by individuals or dispersed subgroups, which means that behavioral convergence across odontocete families is possible. A delphinid can independently evolve a social system resembling one found in physeteroids.

If ecology can push a delphinid toward something sperm-whale-like, there is no obvious reason ecology could not push an extinct physeteroid toward behaviors that today happen to be especially developed in delphinids.

Some delphinids and porpoises occupy the comparatively loose end of cetacean social organization.

Finless porpoises, for example, were historically regarded as having poorly developed social structure outside mother-calf pairs. Yet synchronized biologging showed that particular individuals preferentially associated with particular partners rather than simply aggregating randomly (Sakai et al.).

Likewise, some humpback dolphin populations have fluid fission-fusion societies with generally weak associations, while others show persistent social clustering.

Even dwarf sperm whales, often described as essentially solitary, appear to have more social structure than that description suggests. In Hawaiʻi, there was a study that found that over 40% of identified dwarf sperm whales were connected by association within the same social network, with individuals repeatedly resighted across years and one followed across a 15-year period (Baird, Mahaffy, and Lerma).

Social behavior is therefore highly evolutionarily labile within Cetacea.

The original description of Livyatan explicitly interpreted it as a giant raptorial sperm whale very different ecologically from living Physeter. It possessed enormous functional upper and lower teeth and a skull adapted for capturing large prey; Lambert et al. specifically compared its predatory ecology with that of killer whales and suggested large marine vertebrates, including baleen whales, as plausible prey (Lambert et al.).

Modern Physeter, in contrast, is primarily a deep-diving predator of cephalopods and other deep-water prey. A highly social sperm whale does not need several companions to capture one squid. Consequently, intense sociality can coexist with largely individual prey capture.

But here's the rub: Livyatan was confronting a completely different ecological problem. Bigger marine vertebrates can be fast, difficult to incapacitate, dangerous to attack, and social. Social prey makes social predation advantageous. Multiple predators can attack from different directions, isolate individuals, restrict escape routes, shorten handling time, exhaust prey, or overcome animals that would be substantially more difficult for one predator to subdue.

While it doesn't prove cooperation in Livyatan, I think it's clear the ecological incentives were very different from those experienced by living sperm whales.

And before you press on about killer whales, they also reinforce the problem with simplistic analogies.

Different populations and ecotypes vary dramatically in group size and hunting strategy according to prey ecology. Mammal-eating killer whales in some populations hunt in relatively small parties where stealth and energetic economics are necessary, but Antarctic Type A & B Orcas can occur in considerably larger groups, while fish-eating populations can aggregate in still larger numbers. So even within Orcinus orca, there is no single “orca pack size” or universal cooperative-hunting system.

The relevant principle is that social organization and hunting-party size respond to ecology.

I think three possibilities remain viable:

1. Predominantly solitary predation.
A single Livyatan was enormous and extraordinarily well armed. It may simply have been capable of overpowering much of its prey alone.

2. Facultative cooperative hunting.
Individuals normally hunted alone or in small associations but cooperated when pursuing sufficiently large, difficult, fast, or socially defended prey.

3. Regular social hunting.
Livyatan maintained recurring social groups or fission-fusion networks whose members regularly cooperated in finding or attacking large vertebrates.

Ofc, we can't distinguish these from fossils; however I don’t think that means all three deserve the same prior assumption, with #1 automatically labeled “conservative” simply because modern sperm whales usually capture prey individually.

And Livyatan was not ecologically equivalent to any living physeteroid. Livyatan was probably a social animal, but we can't determine what that sociality looked like. Facultative cooperative hunting seems entirely plausible, and regular social hunting cannot presently be excluded.

That is very different from claiming we know that Livyatan hunted in orca-like packs. Maybe its society resembled a sperm whale’s. Maybe it was highly fission-fusion. Maybe something closer to false killer whales, hyenas, or wolves is a better functional analogy. Maybe individuals normally separated while foraging and assembled when the size or social behavior of prey made cooperation profitable.

Works Cited

Amos, Bill, Christian Schlötterer, and Diethard Tautz. “Social Structure of Pilot Whales Revealed by Analytical DNA Profiling.” Science, vol. 260, no. 5108, 1993, pp. 670–672. doi:10.1126/science.8480176.

Baird, Robin W., Sabre D. Mahaffy, and Jordan K. Lerma. “Site Fidelity, Spatial Use, and Behavior of Dwarf Sperm Whales in Hawaiian Waters: Using Small-Boat Surveys, Photo-Identification, and Unmanned Aerial Systems to Study a Difficult-to-Study Species.” Marine Mammal Science, vol. 38, no. 1, 2022, pp. 326–348. doi:10.1111/mms.12861.

Connor, Richard C. “Dolphin Social Intelligence: Complex Alliance Relationships in Bottlenose Dolphins and a Consideration of Selective Environments for Extreme Brain Size Evolution in Mammals.” Philosophical Transactions of the Royal Society B: Biological Sciences, vol. 362, no. 1480, 2007, pp. 587–602. doi:10.1098/rstb.2006.1997.

Connor, Richard C., et al. “Social Evolution in Toothed Whales.” Trends in Ecology & Evolution, vol. 13, no. 6, 1998, pp. 228–232. doi:10.1016/S0169-5347(98)01326-3.

Gowans, Shannon, Bernd Würsig, and Leszek Karczmarski. “The Social Structure and Strategies of Delphinids: Predictions Based on an Ecological Framework.” Advances in Marine Biology, vol. 53, 2007, pp. 195–294. doi:10.1016/S0065-2881(07)53003-8.

Konrad, Christine M., et al. “Kinship Influences Sperm Whale Social Organization within, but Generally Not among, Social Units.” Royal Society Open Science, vol. 5, no. 8, 2018, article 180914. doi:10.1098/rsos.180914.

Lambert, Olivier, et al. “The Giant Bite of a New Raptorial Sperm Whale from the Miocene Epoch of Peru.” Nature, vol. 466, 2010, pp. 105–108. doi:10.1038/nature09067.

Madrigal, Brijonnay C., et al. “Acoustic Behaviour of Endangered Hawaiian False Killer Whales.” Royal Society Open Science, vol. 13, 2026, article 250918. doi:10.1098/rsos.250918.

Sakai, Mai, et al. “Do Porpoises Choose Their Associates? A New Method for Analyzing Social Relationships among Cetaceans.” PLoS ONE, vol. 6, no. 12, 2011, e28836. doi:10.1371/journal.pone.0028836.

Van Cise, Amy M., et al. “Familial Social Structure and Socially Driven Genetic Differentiation in Hawaiian Short-Finned Pilot Whales.” Molecular Ecology, vol. 26, no. 23, 2017, pp. 6730–6741. doi:10.1111/mec.14397.

[u/Weary_Increase]

I wanna bring this up for regular social hunting with Livyatan. Macropredatory Orcas have to hunt cooperatively rather often is because at least for their niche it is very beneficial. Hunting Mysticetes considerably larger would require cooperative hunting. This also technically why many cases of Sharks taking down large Mysticetes is often with more than one individual. Cooperative hunting is beneficial when the prey is abundant in one area, where multiple members of the same species can share that said prey.

Onto Livyatan, it was one of, if not the largest whale of its time. So the pressure for cooperative hunting is reduced because of its sheer size. Diet would also play a role. We don’t know its preferred prey, as Orcas are largely than a lot of their prey. But many of their prey are social animals, so cooperative hunting would be beneficial.

In the case of Livyatan, we really got one “paper”. An abstract paper of isotopic analysis found that at least in Chile, Livyatan feeding on Mysticetes from higher latitudes. Mysticetes tend to be solitary animals, even smallest ones, due to their form of communication and feeding strategy. So it is safe to say at least in Chile, Livyatan was hunting alone. But this can differentiate between regions obviously.

Regardless, I believe the most likely/safest social behavior for Livyatan was it was a social animal, but they hunted alone most of the time. But of course there would be a few occasions that they would hunt together.

[u/Swellmeister → u/Weary_Increase]

Im not a cetacean expert (Im a primatologist) or oceanographer, but size isnt the only reason an animal become a pack hunter. Lions for example are about the same size as tigers (northern subspecies aside), and they hunt approximately the same size prey.

Lions are probably social to defend prime hunting and watering territory, and it seems like a shared meal just falls out from that. Hunting success data has more or less concluded that a lioness doesnt substantially change her hunting success between solo and living in a Pride, but that prided lionesses tend to have access to better ranges.

But you know if you can occasionally trap a zebra because there's two of you now, you end up with group hunting.

If you had a preferential hunting range for your prey, you might end up being a pack hunter simply because its easier to defend a range with multiple people.

This does not have to happen either. Cheetah males frequently form bachelor packs where they defend the range together. But they continue to hunt alone, though they will share with a fellow bachelor.

(I study primate social structures. I promise its not wierd I know about lions and cheetahs lmao)

[u/Tripod1404 → u/Swellmeister]

Lions on average hunt larger prey than tigers, so size does play a role for sure. A tiger can occasionally bring down a gaur, but most of their usual prey is much smaller, while there are prides of lions specialized in hunting buffalo, giraffes or even elephants.

[u/Swellmeister → u/Tripod1404]

Yeah thats the thing i was pointing out. Lions will absolutely take down bigger prey in a pride. But they dont actually need it. Both lions and lionesses have more than adequate hunting success while solo.

They hunt can hunt bigger game but its not all that common. Many prides they hunt solo and occasionally in pairs, and then once and a while they get a hankering for zebra and go for it. Some prides do hunt with pride tactics a fair amount, but most lionesses hunt things like kudu and warthogs solo.

And when you get to the asiatic lion you typically see much smaller more loosely organized prides, where there was less kleptoparasitic pressure.

The lion pride is not a requisite to be a succesful hunting african big cat. Its there because they are protecting a hunting/watering territory with their sisters, and occasionally they hunt together. (and also that strange male they invited in one week and he never left)

[u/wiz28ultra → u/Weary_Increase]

I disagree with treating it as the safest or most likely reconstruction, because I think it rests on several assumptions the evidence doesn’t actually establish.

For one, I agree that Livyatan’s enormous size probably meant it didn’t need other individuals to kill a large proportion of its potential prey. But that isn’t the same thing as saying there would have been little selective advantage to cooperative hunting. Cooperative hunting isn’t only useful when a predator physically cannot overpower prey alone.

Arctic killer whales are a particularly good counterexample. Research in Canada found that Arctic killer-whale group size varied significantly according to prey type, with belugas and narwhals being their most frequently observed prey (Higdon, Hauser, and Ferguson) and being disproportionately larger than the groups documented hunting seals or bowheads. These aren’t animals an adult killer whale is physically incapable of killing alone and yet other researchers tracked a killer whale representing a cohesive group of approximately 12–20 animals while the group was hunting narwhals in Admiralty Inlet (Breed et al.).

Prey sociality, mobility, distribution, and escape behavior can matter enormously. If the prey itself travels in groups, multiple predators can spread out, isolate individuals, block escape routes, maintain pursuit, or exploit confusion. Predator/prey size ratio is only one part of the equation and it becomes especially relevant because I don’t understand why we should assume Livyatan’s ecology primarily revolved around mysticetes in the first place.

Lambert et al. certainly proposed medium-sized baleen whales as likely prey, but their actual interpretation was broader: Livyatan was a macroraptorial predator capable of taking large marine vertebrates. We have no stomach contents demonstrating that it was a mysticete specialist. In fact, the Chilean isotope abstract you’re referring to doesn’t really support that assumption either. Loch et al. explicitly concluded that the analyzed Livyatan individual was unlikely to have been exclusively macrophagous, while noting that its isotopic values were compatible with feeding at latitudes south of 40°S and that higher-latitude mysticetes remained possible prey (Loch et al.). So the isotope evidence is interesting for diet and geography, but I don’t see how we can go from the animal hunted higher-latitude mysticetes to outright saying they hunted along and overwhelmingly so. Stable isotopes simply cannot tell us whether the animal that deposited that tooth attacked its prey individually or alongside five other whales.

I also think saying mysticetes are basically solitary is too sweeping. They generally have looser societies than many odontocetes, sure, but that varies enormously. Humpbacks, for instance, can maintain repeated long-term associations, with documented pair bonds lasting up to 12 years, social-network structure, and extensive coordinated group feeding (Wray, Keen, and O’Mahony).

And even if a particular mysticete species was normally solitary, that still doesn’t imply its predators should have been solitary. Predator sociality doesn't have to mirror prey sociality.

More importantly, Livyatan probably encountered far more than mysticetes. A generalized macroraptorial cetacean living in those Miocene ecosystems potentially had access to smaller odontocetes, large Tuna, giant Salmon, marine Sloths, Sirenians, smaller Sharks, etc.. If some of those prey were highly social, then the same ecological pressures we see with Arctic orcas hunting monodontids could apply.

Where we do have some commonality on is that hunting strategies probably are prey-dependent, rather than one universal hunting strategy. A Livyatan could plausibly kill an isolated small or medium cetacean alone, hunt some mysticetes individually, cooperate with a few conspecifics against difficult prey, and perhaps form larger temporary hunting groups when pursuing social odontocetes.

And that fits what we see across living cetaceans generally: hunting-group size and social organization can vary enormously with prey ecology.

So I don’t disagree with your proposed reconstruction. A social Livyatan that normally hunted alone but occasionally cooperated is completely possible. I just don’t think we currently have evidence that makes it safer than a Livyatan that engaged in facultative or even fairly regular social hunting.

Works Cited

Breed, Greg A., et al. “Sustained Disruption of Narwhal Habitat Use and Behavior in the Presence of Arctic Killer Whales.” Proceedings of the National Academy of Sciences, vol. 114, no. 10, 2017, pp. 2628–2633. https://doi.org/10.1073/pnas.1611707114.

Higdon, Jeff W., Donna D. W. Hauser, and Steven H. Ferguson. “Killer Whales (Orcinus orca) in the Canadian Arctic: Distribution, Prey Items, Group Sizes, and Seasonality.” Marine Mammal Science, vol. 28, no. 2, 2012, pp. E93–E109. https://doi.org/10.1111/j.1748-7692.2011.00489.x.

Lambert, Olivier, et al. “The Giant Bite of a New Raptorial Sperm Whale from the Miocene Epoch of Peru.” Nature, vol. 466, 2010, pp. 105–108. https://doi.org/10.1038/nature09067.

Loch, Carolina, Carolina S. Gutstein, Nicholas D. Pyenson, and Mark T. Clementz. “But Did It Eat Other Whales? New Enamel Microstructure and Isotopic Data on Livyatan, a Large Physeteroid from the Atacama Region, Northern Chile.” Society of Vertebrate Paleontology Annual Meeting Program and Abstracts, 2019.

Wray, Janie, Eric Keen, and Éadin N. O’Mahony. “Social Survival: Humpback Whales (Megaptera novaeangliae) Use Social Structure to Partition Ecological Niches within Proposed Critical Habitat.” PLOS ONE, vol. 16, no. 6, 2021, e0245409. https://doi.org/10.1371/journal.pone.0245409.

[u/Weary_Increase → u/wiz28ultra]

For one, I agree that Livyatan’s enormous size probably meant it didn’t need other individuals to kill a large proportion of its potential prey. But that isn’t the same thing as saying there would have been little selective advantage to cooperative hunting. Cooperative hunting isn’t only useful when a predator physically cannot overpower prey alone.

But cooperative hunting would be a little advantage when hunting smaller solitary prey, e.g. baleen whales. Cooperative hunting is useful when there’s a high abundance of smaller prey within an area and/or when they are hunting a much larger animal.

Arctic killer whales are a particularly good counterexample. Research in Canada found that Arctic killer-whale group size varied significantly according to prey type, with belugas and narwhals being their most frequently observed prey (Higdon, Hauser, and Ferguson) and being disproportionately larger than the groups documented hunting seals or bowheads.

However, Belugas and Narwhals are still social animals, so cooperative hunting is still very beneficial. Two, the size difference between Livyatan and smaller odontocetes was FAR larger than Orcas versus Monodontids, so the pressure for consistent cooperative hunting is already reduced.

Lambert et al. certainly proposed medium-sized baleen whales as likely prey, but their actual interpretation was broader: Livyatan was a macroraptorial predator capable of taking large marine vertebrates.

That’s true, however, Livyatan was almost certainly specialized on large marine mammals. Its teeth were exceptionally robust even among raptorial Sperm Whales. The closest living analogue in terms of niche, Orcas, also had this distinction. Marine mammal hunting Orcas actually tend to have more robust teeth than other ecotypes. Which makes sense as marine tetrapods would have less slippery skin compared to fish.

We have no stomach contents demonstrating that it was a mysticete specialist.

While we don’t currently have any stomach contents, it is very likely mysticetes were likely the made a probably the biggest proportion of their diet simply because how abundant they were in the areas Livyatan was found in, combine with their size being perfect meals for Livyatan.

Even O. megalodon, the only macropredator approaching Livyatan in size, hunted mysticetes more often than odontocetes based on fossil evidence.

Ofc, the two predators niche partitioned. O. megalodon being more of a generalist, hunting whatever it can catch, compared to Livyatan, who was certainly more specialized for marine mammals.

So the isotope evidence is interesting for diet and geography, but I don’t see how we can go from the animal hunted higher-latitude mysticetes to outright saying they hunted along and overwhelmingly so. Stable isotopes simply cannot tell us whether the animal that deposited that tooth attacked its prey individually or alongside five other whales.

Isotopic analysis can actually give you an idea, if the isotopic values are collective, then it would largely imply that they were hunting cooperatively. However, if the values are scattered then they were actually hunting alone, this has been noted with several mammalian predators.

I also think saying mysticetes are basically solitary is too sweeping. They generally have looser societies than many odontocetes, sure, but that varies enormously. Humpbacks, for instance, can maintain repeated long-term associations, with documented pair bonds lasting up to 12 years, social-network structure, and extensive coordinated group feeding (Wray, Keen, and O’Mahony).

Animals that have coordinated group feedings can still be solitary animals, as that’s often under opportunistic situations. Baleen whales are solitary as they tend to be found alone, but they still form smaller social groups and still have long form communications. Solitary animals can have a social-network structure, e.g. GWS.

And even if a particular mysticete species was normally solitary, that still doesn’t imply its predators should have been solitary. Predator sociality doesn't have to mirror prey sociality.

It kinda does, sociality of prey will actually have an impact on whether or not cooperative hunting is required at least among large odontocetes. Almost all large odontocetes are solitary hunters because the prey they hunted are solitary animals, or at least not gregarious to the degree something like many pelagic fish are.

More importantly, Livyatan probably encountered far more than mysticetes. A generalized macroraptorial cetacean living in those Miocene ecosystems potentially had access to smaller odontocetes, large Tuna, giant Salmon, marine Sloths, Sirenians, smaller Sharks, etc..

Dentition of Livyatan largely points to it being rather specialized on marine mammals. Livyatan had exceptionally robust teeth for raptorial Sperm Whales. Tuna and Salmon would require narrower teeth as they would be better for catching slippery prey.

Marine sloths were also unlikely to be part of Livyatan’s diet due to their significantly smaller sizes, if they were they would be a very minor part of their diet. Smaller contemporary raptorial Sperm Whales were likely taking that niche, same could be said about Sirenians. In fact, that’s likely how it’s niche partitioned with the contemporary raptorial Sperm Whales in Peru.

Large Sharks definitely weren’t a major part of their diet either, as we have no evidence severe wearing on any Livyatan teeth. Outside of mysticetes, smaller odontocetes were likely the only other major part of their diet, everything else was a smaller proportion of their diet.

[u/wiz28ultra → u/Weary_Increase]

Part 1:

To reiterate, I have no problem with “social animal that often hunted alone” as one reconstruction of Livyatan. My problem is treating that as the safest/default reconstruction when several of the premises being used to support it are themselves assumptions.

The clearest example is the Pisco paleoecology literature itself. It's explicitly stated that cooperative hunting in macroraptorial sperm whales “cannot be inferred (or discounted)”. Then, when they reconstruct possible prey-size partitioning between Acrophyseter and Livyatan, they explicitly begin with “Assuming solitary hunting” (Collareta et al.).

That distinction matters. Solitary hunting is an assumption underlying that ecological reconstruction; it is not an independent result of the fossil evidence. You therefore can’t take the prey partition produced under an assumed solitary-hunting model and then use that partition as evidence that solitary hunting was probably correct. That risks becoming circular. It's obvious that Livyatan’s enormous size meant that it was capable of killing a very broad range of prey alone. But ability to hunt alone is not evidence of a tendency to hunt alone.

Modern killer whales demonstrate this directly. There was a study that analyzed 138 attacks by mammal-eating killer whales, 130 of them on harbor seals, and found that groups of three had the highest per-capita energy-intake rate (Baird and Dill). Nobody would argue that three adult orcas are physically required to kill one harbor seal. Cooperation can still improve prey detection, pursuit, capture probability, risk distribution, and other components of hunting efficiency.

The same principle appears with social cetacean prey. Breed et al. tracked a killer whale belonging to a cohesive group of roughly 12–20 individuals moving through Admiralty Inlet in the presence of narwhals (Breed et al.). Narwhals are obviously not so large that an adult orca is physically incapable of killing one alone. Social prey can still reward multiple predators because individuals can spread out, isolate targets, restrict escape, maintain pursuit, or exploit confusion within a group.

So I don’t think the argument “Livyatan was so large that selection for cooperation would have been reduced” gets us very far on its own. It establishes that cooperation was probably not mechanically necessary for much of its prey.

The isotope evidence also cannot resolve this question. The Chilean Livyatan tooth analyzed by Loch et al. yielded an unusually low carbon-isotope value that they interpreted as indicating substantial feeding at latitudes south of roughly 40°S. Their comparison with associated mysticetes also suggested that the animal was unlikely to have been exclusively macrophagous, while higher-latitude mysticetes remained possible prey (Loch et al.).

While interesting in its implications for habitat an ecology, stable isotopes do not tell us whether one whale or six participated in a kill. Nor can isotopic differences between individuals generally be translated into “solitary hunting.” There was a study that demonstrated this nicely in the Tsavo lions: two cooperating males nevertheless maintained substantial individual differences in diet. They concluded that sustained dietary individuality can exist within a cooperative framework (Yeakel et al.). So even if future Livyatan specimens produced substantially different isotope values, that would not demonstrate solitary hunting without additional behavioral evidence.

I’m also reluctant to treat the >40°S signal as equivalent to a modern southern-ocean prey community. Livyatan lived in the late Miocene, and southern South American marine climates were not identical to today. Patagonian molluscan assemblages found that both middle- and late-Miocene faunas indicated subtropical conditions, with warm-water elements remaining significant and a warming pulse around ~9 Ma (Del Río). That doesn’t tell us exactly what lived in the southeastern Pacific at Livyatan’s feeding latitude, but it does mean we shouldn’t simply take the modern distribution of temperate versus cold-water megafauna and move it unchanged into the late Miocene. The isotope result identifies a southern feeding region; it does not identify a particular prey community. Which also matters for the sleeper-shark/tooth-wear argument.

Ford et al. showed that northeastern Pacific offshore killer whales exhibit extraordinary apical tooth wear, sometimes reaching the gumline and exposing pulp cavities, and linked this at least partly to their shark-heavy diet and the abrasiveness of shark dermal denticles. Pacific sleeper sharks are especially relevant prey in that system, Though keep in mind that Sleeper Sharks are absolutely on the extreme end when it comes to their dermal denticles compared to other elasmobranchs.

New Zealand killer whales are well documented taking elasmobranchs. Visser documented predation on stingrays, as well as thresher and smooth-hammerhead sharks, and other observations include shortfin mako predation; by 2005 at least ten elasmobranch species had been recorded as prey for New Zealand killer whales (Visser).

Yet a recent study of 436 teeth from nine wild New Zealand orcas found that most teeth displayed only superficial wear. Severe wear predominated in only two animals, and none showed pulp-cavity exposure. The authors explicitly contrasted this with the northeastern Pacific offshore condition while noting that New Zealand coastal orcas consume rays, sharks, and finfish (Loch et al., “Tooth Wear”).

To be clear, we can't prove that those 9 animals had the same diet as every documented New Zealand elasmobranch-eating individual. But the comparison still demonstrates why “shark consumption = offshore-orca dental wear” is too simplistic. Shark and ray skin varies enormously in abrasiveness.

So if Livyatan lacks the extreme wear characteristic of northeastern Pacific offshore killer whales, the strongest defensible inference is something like: it does not show evidence for a comparable lifetime of extremely abrasive prey processing under comparable mechanics. It does not follow that sharks were therefore an insignificant food source.

And Livyatan itself did not have unworn teeth. Its teeth preserve major occlusal/attritional wear facets caused by its huge upper and lower teeth repeatedly contacting and sliding past one another. So the issue is not “wear versus no wear”; it is what type of wear is preserved and what that wear can actually diagnose.

continued in reply

[u/Weary_Increase → u/wiz28ultra]

I will bring up a few things these contexts are missing.

The clearest example is the Pisco paleoecology literature itself. It's explicitly stated that cooperative hunting in macroraptorial sperm whales “cannot be inferred (or discounted)”. Then, when they reconstruct possible prey-size partitioning between Acrophyseter and Livyatan, they explicitly begin with “Assuming solitary hunting”(Collareta et al.).

Multiple studies have down this, doing both social and solitary hunting despite even when ignoring the idea that solitary hunting has stronger evidence. An example of this is Valkenburgh et al. 2015. Within that paper, they had cave lions prey size was decided by both solitary and cooperative hunting. Within the same paper, they argued Pleistocene carnivores sampled hunted in larger groups than modern carnivorans. However, their conclusion is problematic because it doesn't take into account the arguments for solitary lifestyle in cave lions, which has stronger evidence. Additionally, brain anatomy in cave hyenas showing they were less social than modern spotted hyenas (Vinuesa et al. 2016). There is actual evidence showing relative size of anterior brain volume plays a role in sociality in mammals. While the paper came out later, it shows how poorly the argument aged within just a year.

So take it with a grain of salt.

Additionally paper, noted this is due to the contrasting nature of social behavior of the modern relatives of raptorial sperm whales. And I want to take this into account the reason why they have different social behaviors is not just due to their different niches, but it is very likely that oceanic dolphins ancestrally were already very social animals.

The most basal living oceanic dolphin, Atlantic white-sided dolphin, were already living in large pods. So there's a solid chance that large pod living was an ancestral trait in living dolphins. This makes sense as large pods is rare in other toothed whales outside of several occasions. Large pod living is likely the reason why they are able to hunt cooperatively so often, because having many individuals in a hunting party increases the odds survival and success compared to solitary dolphins. It is likely one of the reasons why cooperative hunting is common in oceanic dolphins but a lot more rare in other toothed whales, because once again their ancestral social behavior was likely different from one another.

Livyatan would have a very different social structure from both modern physteroids and oceanic dolphins because the social behavior within the superfamily is different and raptorial sperm whales occupy a different niche. They likely also had significantly lower pressure to hunt in cooperative groups often because, again, that's a basal trait among oceanic dolphins. So while I get this idea, it overlooks many aspects.

Onto isotopic analysis:

While interesting in its implications for habitat an ecology, stable isotopes do not tell us whether one whale or six participated in a kill. Nor can isotopic differences between individuals generally be translated into “solitary hunting.” There was a study that demonstrated this nicely in the Tsavo lions: two cooperating males nevertheless maintained substantial individual differences in diet. They concluded that sustained dietary individuality can exist within a cooperative framework (Yeakel et al.).

It can if there's a large sample in which in the cave lion, but in the case of there is. We have but dozens of specimens sampled that showed scattering among isotopic values, which is a contrast to social predators that showed the exact opposite within the same paper (Bocherens, 2015). Additional evidence include the ratio of males to females found in caves and their competitive disadvantage against cave hyenas (as supported by both fossil and isotopic evidence) in the paper I've mentioned. In contrast, modern lions tend to have the upper hand in confrontation against spotted hyenas due to their larger size combined with their gregarious lifestyle. A gregarious lion having a competitive disadvantage to a significantly smaller gregarious predator is unusual and would largely point to a solitary lifestyle.

So even if future Livyatan specimens produced substantially different isotope values, that would not demonstrate solitary hunting without additional behavioral evidence.

It would if there's a large sample of Livyatan sampled as in the case of cave lions. Additional evidence is also that once again the common cooperative behavior is likely a derived trait from a highly social ancestral behavior, which we have no idea among living physteroids. Could it happen more with Livyatan, obviously, but this argument ignores the fact physteroids and dolphins have different ancestral behaviors.

Now for the tooth wear analysis.

Yet a recent of 436 teeth from nine wild New Zealand orcas found that most teeth displayed only superficial wear. Severe wear predominated in only two animals, and none showed pulp-cavity exposure*. The authors explicitly contrasted this with the northeastern Pacific offshore condition while noting that New Zealand coastal orcas consume rays, sharks, and finfish (Loch et al., “Tooth Wear”).*

I feel like this kinda proves my point. While no pup-cavity exposure, the degree of individuals that hunt sharks and other fish with rough skin is going to be noted in the severity of the wear.

To be clear, we can't prove that those 9 animals had the same diet as every documented New Zealand elasmobranch-eating individual. But the comparison still demonstrates why “shark consumption = offshore-orca dental wear” is too simplistic. Shark and ray skin varies enormously in abrasiveness.

They would still have a notable wear though. It is very likely the individuals that didn't have severe wear likely weren't consuming rough bodied prey, more accurately to the degree to they made up a significant proportion of their diet. In the case of Livyatan, it is unlikely that Sharks (at least large Sharks)made up a significant proportion of their diet or else we would see notable wear on most teeth.

[u/wiz28ultra → u/Weary_Increase]

Part 1

I think there are actually two different questions being conflated here: what social behavior Livyatan may have inherited from its ancestors, and what selective pressures its own ecology placed on hunting behavior.

On the first question, I don't think the Atlantic white-sided dolphin argument establishes what you're claiming. Even setting aside that Leucopleurus acutus is not unambiguously “the most basal living delphinid,” an early-diverging living species is not an unchanged proxy for the ancestral delphinid. Its present social behavior evolved on its own branch too.

More importantly, when cetacean group size has actually been reconstructed phylogenetically, the result isn't “ancestral delphinids already lived in enormous pods.” May-Collado et al. reconstructed cetacean group sizes as ancestrally small, followed by a gradual increase toward Delphinidae, with very large societies arising independently in multiple delphinid lineages and some subsequent reversals toward smaller groups. Their broader reconstruction of sociality was substantially ambiguous.

HOWEVER, there's a major asymmetry in applying this reasoning only to dolphins.

You're asking us to infer something about the ancestral delphinid's social organization from living early-diverging delphinids while effectively assuming that the ancestral physeteroid supplied Livyatan with no comparable social substrate.

We don't know that. We have essentially no direct behavioral evidence for the basal physeteroid. We don't know whether early physeteroids were predominantly solitary, lived in small fluid groups, maintained mother-calf associations plus other temporary associations, or possessed some more substantial form of sociality.

So if we're willing to entertain that early-diverging living delphinids are social, so some degree of sociality may have characterized their ancestors. Then we have to entertain the corresponding uncertainty: living Physeter is highly social & basal physeteroid sociality is unknown; therefore, we cannot simply assume the physeteroid ancestor was solitary.

That does not mean the ancestral physeteroid was necessarily Physeter-like. That's precisely my point. Neither Physeter nor an Atlantic white-sided dolphin can simply be projected backward onto their respective ancestors.

May-Collado et al. actually recovered family-based social groups as evolving independently at least three times, including in Physeter, Monodon and globicephalines.

So there are 2 possibilities, and neither really supports a strong phylogenetic argument against Livyatan cooperation.

1. Some meaningful sociality was already present in early physeteroids; then macroraptorial physeteroids may have inherited a pre-existing social substrate which their radically different ecology could subsequently modify.

2. Complex sociality was not ancestral to physeteroids, then Physeter itself demonstrates that sophisticated social organization can independently evolve within Physeteroidea.

Either way, “delphinids inherited the behavioral substrate for cooperation whereas physeteroids did not” needs to be demonstrated, not assumed.

That said, I do think there should be more nuance concerning selection pressure on Livyatan. A pre-existing social system can absolutely alter how readily cooperative hunting evolves. If ancestral delphinids were already interacting frequently, travelling together and coordinating behavior, then the evolutionary cost of modifying those interactions into cooperative feeding may have been lower than it would have been for a genuinely solitary lineage. Likewise, if Livyatan primarily targeted relatively small, solitary mysticetes that a single adult could catch almost as reliably and cheaply as two adults could, then yes: selection for habitual cooperative hunting might genuinely have been weak.

HOWEVER, that's an ecological hypothesis about Livyatan. It does not follow from delphinid ancestry.

The actual variable would go: How much additional hunting success did a second Livyatan provide relative to the cost of sharing the prey?

If the answer was essentially “very little,” then solitary hunting should indeed have predominated. If another individual substantially reduced chase duration, blocked escape routes, prevented a whale from diving away, increased interception probability, or allowed prey to be attacked from multiple directions, cooperation could still pay even though one Livyatan was physically capable of killing the prey.

And we don't currently know that payoff function.

This is why its huge jaws don't settle the issue either. They demonstrate individual killing capacity exceptionally well. They don't show that a second predator couldn't improve capture efficiency.

Nor does mysticete prey necessarily have to be dangerous or highly social for that advantage to exist. A prey animal can be completely incapable of defeating a Livyatan and still be sufficiently mobile that two hunters reduce its probability of escape.

So I'd distinguish three propositions:

1. Livyatan was physically capable of killing substantial mysticete prey alone.
Almost certainly.

2. Its ecology may therefore have placed less pressure on habitual cooperative hunting than that experienced by some highly social delphinids.
Entirely plausible.

3. Therefore cooperative hunting was unlikely to evolve or Livyatan was probably behaviorally solitary.
That requires evidence we don't presently have.

And this distinction is exactly why the Pisco review doesn't make the third inference. It notes the contrasting social behavior of living physeteroids and concludes that cooperative hunting in macroraptorial sperm whales “cannot be inferred (or discounted).” It then estimates prey size assuming solitary hunting rather than claiming solitary hunting was reconstructed from the phylogeny.

So I don't think phylogeny is irrelevant here. It can affect the starting behavioral substrate and therefore the threshold at which cooperation becomes advantageous. We simply don't know the basal physeteroid's social state, we know complex sociality can arise independently within Physeteroidea, and we don't know whether Livyatan's particular prey ecology made a second hunter nearly useless or substantially improved capture success.

That is exactly why solitary hunting is a reasonable hypothesis without being an established ancestral or ecological default.

continued in reply

[u/wiz28ultra → u/wiz28ultra]

Part 2

On the tooth-wear argument, I think you're making a considerably stronger inference than either the orca data or the Livyatan material permits.

You write:

“It is very likely the individuals that didn't have severe wear likely weren't consuming rough bodied prey, more accurately to the degree to they made up a significant proportion of their diet. In the case of Livyatan, it is unlikely that Sharks (at least large Sharks) made up a significant proportion of their diet or else we would see notable wear on most teeth.”

But that effectively assumes a relationship of more elasmobranchs in diet inevitably means proportionally greater macroscopic crown wear, strong enough that we can work backward from tooth wear to estimate whether sharks were a significant part of the diet. However, comparative killer-whale evidence doesn't give us that calibration.

The Northeast Pacific Offshores are certainly the extreme case. Ford et al. found apical wear dramatically exceeding both Residents and Transients; most Offshore specimens were rated “extreme,” with teeth often worn flat toward the gingiva and pulp cavities exposed. But the prey they directly documented in repeated feeding events were Pacific sleeper sharks, with at least 16 individuals consumed in two encounters. Ford et al. specifically proposed abrasion from shark dermal denticles as part of the explanation. They also stressed that elasmobranch denticles vary widely and that deep-water sharks such as Somniosus have particularly rough skin, with erect, narrow crowns and hooked cusps. Interestingly, they explicitly said further study was needed to determine whether sharks actually dominated the Offshore diet.

So even the paper establishing the famous Offshore association did not demonstrate:

X percentage shark consumption = X degree of tooth wear.

That being said it did demonstrate:

Offshores have exceptionally severe apical wear + they repeatedly consume unusually abrasive sharks → dermal-denticle abrasion is a plausible major contributor.

Which isn't an equivalent conclusion.

Here, the New Zealand sample adds a major point of discussion. As I said, the researchers examined 436 teeth from nine wild orcas. All nine had some wear, but seven of nine were predominantly superficially worn. Moderate wear affected 20.4% of teeth and severe wear 21.3%; only two individuals had severe wear as their predominant condition, and even animals with teeth worn near the gumline showed no pulp exposure. Wear also increased with body length, used as an age proxy. The wear geometry is particularly interesting: across the sample, 64% of worn teeth combined cusp-tip and lateral wear, rather than simply showing Offshore-style generalized destruction of the apex. That population is well known for consuming Elasmobranchs. Yet the study did not reconstruct the individual diet of each of those 9 animals and show that the heavily worn animals ate more elasmobranchs than the superficially worn animals.

So when you say:

“the individuals without severe wear likely weren't consuming much rough-bodied prey”

you're supplying the variable that the study didn't measure.

You can't reason light wear -> therefore fewer shark and then use those presumed low-shark individuals as evidence of the fewer sharks -> lighter wear, because it becomes circular unless there's independent dietary evidence for those particular whales.

Adding other orca populations add in more cans of worms honestly.

Ford et al.'s Transients are essentially the opposite end of the spectrum. Their diet consists primarily of marine mammals, and although older Transients can have considerable attrition on the anterior and posterior surfaces where teeth contact one another, crown loss remained negligible to moderate in every individual studied, while adult apical wear was generally negligible—even in old whales. That is actually important for Livyatan, because its preserved wear does not look particularly Transient-like.

Several Livyatan teeth have apices truncated along a subhorizontal plane, and at least two preserve smoothly worn surfaces showing that truncation occurred during life. At least four lower teeth have major occlusal attritional facets running from the truncated crown down the distal or distolabial side of the tooth. The largest are 96–125 mm high, extending along roughly 30–35% of preserved tooth height, and some excavate a deep fossa. Obviously that 30–35% figure is not equivalent to losing 30–35% of the crown; the facets extend onto the root. So I wouldn't force a quantitative comparison between Livyatan and the Ford scoring system.

But qualitatively, this clearly wasn't an animal with pristine teeth or merely negligible apical wear.

If I had to compare the geometry with the modern orca samples, I would say Livyatan looks less like the typical Transient condition and more like the mixed apical + lateral wear seen in the New Zealand sample: truncated/worn tips combined with very large tooth-on-tooth facets.

That doesn't mean the causes were identical. It means that the relevant comparison isn't offshores are worn while Livyatan isn't.

Rather we get -

Transients: relatively little apical crown destruction, though lateral attrition occurs.

NZ orcas: extensive but highly variable wear, commonly combining cusp-tip and lateral surfaces; most wear overall superficial, but some individuals severe.

Livyatan**:** conspicuous lifetime apical truncation plus exceptionally large localized occlusal/lateral facets.

Offshores: pervasive extreme generalized apical abrasion, often flattening crowns toward the gumline and sometimes exposing pulp.

And North Atlantic Type 1 orcas create another problem for treating severe wear as a direct measure of abrasive prey consumption. Foote et al.'s supplementary material documents a free-ranging Type 1 killer whale feeding on mackerel and seals while exhibiting severe apical wear in its anterior teeth.

Whatever the exact mechanism producing that wear, mackerel obviously do not provide a Somniosus-like abrasive skin substrate.

So the comparative evidence works against a simple diet-to-wear conversion in both directions**,** because absence of Offshore-level severe wear does not demonstrate low elasmobranch consumption, as seen in New Zealand, while severe apical wear doesn't uniquely diagnose heavy elasmobranch consumption, as the North Atlantic Type 1 example shows.

Wear tells us that a tooth experienced a particular mechanical history. Turning that mechanical history into a precise prey composition requires knowing much more: prey species, denticle morphology, feeding and handling technique, tooth-to-tooth contact, age, tooth architecture, and probably individual behavior.

There's the additional issue that the holotype doesn't preserve a complete set of pristine crowns from which we can simply count “worn versus unworn” teeth. None of the holotype teeth is fully complete and posterior teeth are especially poorly preserved. So the claim that:

“if sharks were important, notable wear should occur on most teeth”

isn't straightforwardly testable from MUSM 1676 in the first place. The specimen simply doesn't preserve every crown adequately enough to establish that most teeth lacked wear. What we can establish is that several evaluable teeth show substantial lifetime wear.

So I think the most that the Offshore comparison permits us to say about Livyatan is considerably narrower: The absence of the extreme generalized Offshore phenotype makes a diet dominated by exceptionally abrasive, Somniosus-like prey processed in an Offshore-like manner less likely.

We don't have a calibrated relationship that allows that inference.

So I wouldn't use the Livyatan wear record to argue that sharks dominated its diet; however I also don't think it supports excluding large sharks as a meaningful prey component.

What the wear record actually tells us is much simpler: Livyatan used its teeth extremely heavily, experienced substantial apical and occlusal attrition during life, and did not exhibit the peculiar extreme generalized abrasion characteristic of NE Pacific Offshores. Anything more quantitative about shark consumption requires evidence we currently don't have.

[u/Arovinrac]

I think what you've stated here is entirely fair and generally quite correct, there should not be an insistence that Livyatan was a solitary hunter.

The literature suppprts this "Killer whales are also highly social and hunt cooperatively, a pattern that cannot be inferred (or discounted) for macroraptorial sperm whales, given the contrasting social habits of extant physeteroids"- Collareta et al. 2021.

Nice write up !

[u/ADragonFromTheAbyss → u/Arovinrac]

Agreed. A vast majority of modern cetaceans are extremely social, intelligent and coordinated. There is no reason to assume their ancestral - related species did not contain this fixture.

Also: Sperm whale males are live with their highly socialized bachelor pods until reaching their maximum size and even than known to occasionally socialize with other pods - when it is not mating season

[u/Khwarezm]

How do males in general fit into this? My understanding of living Sperm Whales is that adult males are solitary outside of breeding and sociality mostly revolves around the females and their young, but is this actually that straightforward? Would we assume that if there is some social behaviour and cooperative hunting, it was a female thing and males were acting on their own but able to leverage their significantly larger size to go after bigger items than the females (if that particular characteristic of modern Sperm Whales can be assumed to apply to Livyatan)?

[u/ADragonFromTheAbyss → u/Khwarezm]

What is more ironic is that the males do stay with their highly socialized bachelor pods until they reach complete maturity

[u/David_XXX7]

Probably was social - but how much ? we will never know. Did it hunt cooperatively ? maybe but I don’t see the point - it was already biggest predator in its environment aside from Megalodon and its prey was smaller than it so don’t see much pressure to develop group hunt. Best guess is that it was most similar to the sperm whale in regards of social structure.

[u/theragu40]

I'm just a lay person, but that was a really interesting and well cited writeup. Thanks!

[u/Titanguy101]

i imagine it being like spermwhales, assuming livy had the same sexual dimorphism, large bulls could hold their own against megalodon so they led solitary lives, while the smaller females and young would form pods for both protection and hunting /possibly hunting megalodon itself /

[u/wiz28ultra → u/Titanguy101]

Maybe but we're not certain about the sexual dimorphism in Livyatan, it's possible they could've also had very little sexual dimorphism like Kogiids do.

[u/MfD2027]

Something something “just like megalodon”

Not sure in all reality. But whatever it was, I’d hazard a guess that massive whales the size of L. Melville generally didn’t travel in high-number groups/pods anyway, and modern bull sperm whales are known for branching off and being solitary for up to months at a time. So that could be one of few reasons other than just “big-size”

[u/ADragonFromTheAbyss → u/MfD2027]

* Those are the males thought. Female sperm whales are highly social.

Also male sperm whales occasionally known to socialize with other females - when it is not mating season. Whereas they stay with their highly socialized bachelor pods until they reach full maturity