Yet another terrifying predatory mosasaur from Morocco

Khinjaria acutus, from the Maastrichtian of Morocco, is a freakish new species of mosasaur, with a demon’s face and teeth like knives. Why were there so many species of apex predator at the end of the Cretaceous?

Mosasaurs aren’t exactly pretty creatures, but some of them are uglier than others, and Khinjaria acuta may well take first in the ugly contest. Its eyes are small and beady, the face is short and massive, the back of the skull is weirdly stretched out. The jaws were powerful, with the teeth in the front of the jaws being long, straight, and flattened side to side, like a set of daggers, giving it a wicked smile.

It’s pretty freakish-looking; a cruel and nightmarish-looking animal. Looking at the skull and teeth, I can’t help but think of the series Chainsaw Man.

This mosasasur is positively demonic. I actually had an idea for a genus name that would allude to this otherworldly appearance. The Arabic word for “devil” is shaytan, which suggested to me the name Shaytania, so I figured Shaytania pandaemonium would sound appropriately evil, and just… really, really metal.

Unfortunately, my co-authors and collaborators also felt it sounded, well, pretty evil.

The word shaytan is actually a cognate of the word satan, but it has a slightly different meaning in Arabic- it doesn’t necessarily refer to the Devil himself (think “devil” and not “Devil”), and the Devil doesn’t play the same role in Islam as he does in certain Christian traditions. Still, the consensus was that naming a mosasaur after a race of evil demon wouldn’t go over fantastically well in a religious country like Morocco. 

Ah well.

Instead, we went with the name Khinjaria acuta, the word khinjar being an Arabic word for “dagger”, and acuta being Latin for “sharp”, so literally, “sharp dagger” or “sharp knife”. 

So what is this animal doing? Well, it’s probably some kind of apex predator, simply because of the size.

Khinjaria acuta with a human for scale. Nick Longrich, 2024.

Khinjaria is a fairly big animal— the skull was a bit under a meter in length, and the whole animal may have been seven or eight meters long, about 25 feet, extrapolating from related plioplatecarpines like Platecarpus ictericus. That’s pretty big for the Plioplatecarpinae, the mosasaur subfamily that Khinjaria was part of.

By comparison, the largest known great white sharks are about 6 meters, or 20 feet long. This is an animal that’s longer than a great white, and comparable to a killer whale in terms of either length, or skull length— although, given the massive body of a killer whale, it was probably not as heavy as an orca. Still a sizeable animal. In general, big animals take big prey, so whatever Khinjaria was feeding on was likely large as well. Big fish like Enchodus, saurocephalids, and Stratodus, sharks like Cretoxyrhina, and juvenile mosasaurs would have been potential prey.

The jaws are also specialized to produce a large bite force. The elongation of the posterior of the skull creates an enormous area for jaw-closing muscles to attach. Meanwhile, Khinjaria’s shortened face improves the leverage of the jaws, just as the short face of a bulldog or a lion give them a stronger bite. Together these adaptations made for a powerful bite, allowing Khinjaria to strike, subdue, and kill large prey.

The teeth are also sizeable. Big teeth, in general, correlate with big prey. Great white sharks, which feed on marine mammals, have huge teeth, the related megamouth sharks, which filter feed on tiny plankton, have tiny teeth. Likewise, dolphins have small teeth to eat small fish, while orcas have big teeth, so they can eat big prey, like dolphins.

Khinjaria’s daggerlike tooth shape is similar to that of mako sharks, rather than great whites, so it’s probably primarily feeding on very large fish, as opposed to other marine tetrapods, but like makos, it probably took larger prey from time to time.

What’s surprising here is that we already have a high diversity of large apex predators from the phosphates. These include large mosasaurs like the mosasaurines Mosasaurus beaugei, Thalassotitan atrox, Prognathodon currii, and the tylosaurine Hainosaurus. The seas off of Morocco would seem far too crowded to allow for still another big predator. And yet we keep finding more species.

The top predator Thalassotitan atrox hunting another mosasaur, Halisaurus arambourgi. By Andrey Atuchin.

So Khinjaria was yet another top predator. But whatever Khinjaria was doing, it seems to be very different from what the other mosasaurs did.

The teeth of Khinjaria are flattened side-to-side into blades. Rather than being recurved, they’re straight, dagger-like. Again, mako sharks seem the closest modern analogue, suggesting it ate a mix of fish, squid, and marine tetrapods, like makos do. However, the teeth are a lot larger than those of makos, and the animal was much larger than a mako, so the prey probably were correspondingly bigger. The phosphates were full of big fish though- Enchodus libycus got about 1.5 meters / 5 feet long.

Khinjaria may also have hunted in an unusual way- the eyes seem reduced, so it probably relied on other senses- hearing, or tasting the water with its forked, snakelike tongue- to find prey.

The other big mosasaurs seem to be hunting big prey in other ways. Mosasaurus beaugei had long teeth that were probably effective in stabbing and holding prey. Thalassotitan’s massive, conical tooth crowns looked like those of an orca, and probably functioned in the same way, being used to seize and tear apart big animals, like sea turtles, plesiosaurs, and other mosasaurs.

The orca-like tooth of Thalassotitan atrox.

The tylosaur Hainosaurus had teeth that were laterally compressed and recurved, like those of a shark; these teeth were probably used for cutting: it may have fed like a giant barracuda, sawing its prey apart.

Prognathodon currii had straight teeth with blunt tips that were probably used to crush bone.

And fossils from Morocco hint that still other large, predatory species may have inhabited these seas as well… but this will need further study.

All these mosasaurs are apex predators, but they’re apex predators in different ways- feeding on different prey, perhaps hunting in different ways. This explains how so many predators could coexist, they’re engaged in niche partitioning, a sort of ecological division of labor, with each species specializing on different prey and perhaps different hunting styles. But it raises a question- why don’t other marine faunas look like this? Why the plethora of predators?

Today’s oceans have relatively few apex predators- orcas, false killer whales, leopard seals, great white sharks- compared to the seas of the Late Cretaceous. There are a lot of cetacean species- around 100 in total- but with the conspicuous exception of orcas, modern whales feed fairly low on the food chain. Dolphins have lots of tiny teeth to eat little fish and squid, baleen whales filter feed on tiny animals like krill and herring, beaked whales don’t have any teeth at all, they’re suction feeders, using their long snouts to suck up small fish.

Mosasaurs, with relatively few, large teeth are clearly sitting a lot higher up the food chain than most cetaceans. Mosasaurs never evolved filter-feeding; and even animals like Halisaurus and Pluridens, which had relatively small teeth and high tooth counts, didn’t evolve the tiny teeth seen in modern dolphins and porpoises, suggesting they’re feeding on larger prey, neither do they ever evolve suction feeding as far as we can tell.

So the predator fauna just looks very different.

Why is that?

It could be that there was something fundamentally different about Late Cretaceous seas. Different species inhabited the ocean, for one. The fish groups that dominated, fish like enchodids, dercetids, and saurodontids, are different from the ones found today, which include tuna, billfish, and barracuda.

The little ammonite Hoploscaphites from the Late Maastrichtian of Poland. N. Longrich.

There were also different kinds of invertebrates- belemnites, a kind of archaic squid whose bullet-like internal shells are common as fossils, would have been a major prey item. Ammonites, shelled relatives of modern cephalopods, were extremely diverse, and are so different from any living creature, they probably occupied niches that don’t even exist today. The existence of ammonites, for example, opens up a niche- ammonite eating predators- which doesn’t exist anymore.

The plankton were different too. Diatoms are a major part of the plankton in the seas today, but that’s a fairly recent phenomenon; other plankton dominated in the Cretaceous. So the lower part of the food chain was different, naturally we might expect the predators and the trophic web at higher levels to look different in response.

It was also warmer in the Cretaceous, which is likely to have affected the primary productivity and ecosystem structure. Maybe warmer seas could support more predators? 

And then sea levels were higher, pushing the seas up onto the continents and creating more continental shelf environments. Continental shelves tend to support more life than the open ocean. That too would mean more food for more predators, and perhaps more kinds of predators.

High rates of volcanic eruption drove the sea levels up in the Cretaceous, flooding the margins and interiors of the continents, and creating lots of habitat for fish- and mosasaurs

The opportunities were simply different. Maybe mosasaurs are just responding to different opportunities, to a wider range of opportunities, and so evolved in a different direction than modern faunas.

Maybe.

The other possibility is that there’s something fundamentally different about the mosasaurs themselves, something that made them uniquely suited to producing a high diversity of large predators. Maybe they’re just sort of made for these apex predator niches in a way that whales aren’t.

This seems a bit speculative, but a recent paper has argued that snakes exhibit fundamentally different dynamics than other lizards. Snakes are unusual in their high diversity, rapid speciation, and they tend to have a lot of specialist species. Exactly what makes snakes this way is unclear- is it their elongate, serpentine bodies, their flexible jaws which can gape to accommodate large prey, or their venom, which lets them rapidly subdue prey- or all of these things combined together?

Whatever the reason (or reasons), snakes seem to be able to evolve predators in a way no other group of animals ever has before. It’s possible that mosasaurs, in the same way as snakes, hit on a design that was uniquely flexible and adaptible, and this let them to specialize on a huge range of prey the way no other group has before or since. Other groups may have gotten larger- pliosaurs, ichthyosaurs and whales all got bigger than mosasaurs ever did- but I’m unsure if any other group of marine animals produced the sheer diversity of predators we see in the Maastrichtian seas.

This raises some interesting questions about evolution. Is evolution predictable- was the diversity of the mosasaurs a predictable outcome of the environment, of the warm climates, sea levels, and diverse prey of the Cretaceous?

Or was it unpredictable? Was something different about mosasaurs that led evolution to create a very different sort of fauna than the mammal-dominated faunas we have today? Do different starting points lead to different endpoints?

It’s tempting to think of mosasaurs as whale analogues, but maybe they’re not. Mosasaurs are like whales insofar as they’re tetrapods that returned to the sea. They occupy broadly similar niches, insofar as mosasaurs ate fish and squid and other marine tetrapods.

A humpback photo surfaces off the coast in Kodiak, Alaska

But mosasaurs aren’t whales.

Unlike whales, mosasaurs don’t have sonar. However, they did have snakelike tongues to scent prey underwater.

Mosasaurs had smaller brains than whales. On the other hand, mosasaurs had flexible skulls and jaws to swallow huge prey, which whales lack. 

Mosasaurs had live birth, like whales… but no milk, and they probably had no parental care either.

Because mosasaur evolved from lizards, mosasaur physiology was unlike that of mammals. Still, mosasaurs may have had a degree of endothermy, although being overgrown lizards, they may not have been warm-blooded to the same degree as modern whales.

Since mosasaurs are not whales, an ecosystem with mosasaurs at the top of the ecological pyramid might just look very different than a world where whales came to dominate the seas.

So maybe this ecosystem structure was contingent on the unique set of adaptations these giant sea lizards evolved in the Late Cretaceous. Maybe some feature or particular combination of features, made them especially formidable as predators. And maybe that led to the evolution of the uniquely dangerous seas of the latest Cretaceous— and if mosasaurs hadn’t entered the seas 100 million years ago, and if those mutations hadn’t appeared in that particular sequence, the entire structure of the marine ecosystem would have looked very, very different.

Maybe there are many different ways to build an ecosystem, many stable equilibria, and what you end up with depends a bit on luck, and a lot on what species you start out with. And if you start out with something like a big, fierce mosasaur, the ecosystem you end up with is full of terrifying predators, and, for lack of a better word, it’s just very, very metal.

Other readings

Thalassotitan, the Killer Mosasaur

Pluridens and the insane, incredible, neverending diversity of Moroccan mosasaurs

A strange new mosasaur with screwdriver teeth from the Maastrichtian of Morocco.

References

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