66 million years ago, sea monsters really existed. They were mosasaurs, huge sea lizards that lived at the same time as the last dinosaurs. Growing up to 12 meters in length, the mosasaurs resembled a Komodo dragon with shark-like fins and tail. They were also extremely diverse, evolving dozens of species that filled different niches. Some ate fish and squid, others shellfish or ammonites.
We’ve now found a new mosasaur that feeds on large sea animals, including other mosasaurs.
The new species Atrox thalassotitaniumwas unearthed in the Oulad Abdoun basin of Khouribga province, one hour from Casablanca in Morocco.
At the end of the Cretaceous, sea levels were high, flooding much of Africa. Ocean currents, driven by trade winds, have drawn nutrient-rich bottom waters to the surface, creating a thriving marine ecosystem. The seas were full of fish, attracting predators – mosasaurs. They brought their own predators, the giant Thalassotitanium. Nine meters long and with a massive head 1.3 meters long, it was the deadliest animal in the sea.
Most mosasaurs had long jaws and small teeth for catching fish. But Thalassotitanium was built very differently. It had a short, broad snout and strong, killer whale-like jaws. The back of the skull was wide to attach large jaw muscles, giving it a powerful bite. Anatomy tells us that this mosasaur was adapted to attack and tear apart large animals.
The massive, conical teeth resemble the teeth of killer whales. And the tips of those teeth are chipped and broken and ground. This heavy wear – not found in fish-eating mosasaurs – suggests Thalassotitanium damaged its teeth biting into the bones of marine reptiles like plesiosaurs, sea turtles and other mosasaurs.
At the same site, we found what looks like the fossilized remains of his victims. The rocks producing Thalassotitanium the skulls and skeletons are full of partially digested bones of mosasaurs and plesiosaurs. The teeth of these animals, including those of the half-meter skull of a long-necked plesiosaur, were partially eaten away by acid. This suggests they were killed, eaten, and digested by a large predator, which then spat out the bones. We can’t prove Thalassotitanium ate them, but that fits the profile of the killer, and nothing else does, making him the prime suspect.
Thalassotitaniumsitting at the top of the food chain also says a lot about ancient marine food chains and their evolution in the Cretaceous.
Evolution of a killer
The discovery of Thalassotitanium tells us about marine ecosystems just before the asteroid hit 66 million years ago, ending the age of the dinosaurs.
Thalassotitanium was just one of twelve species of mosasaurs living in the waters off Morocco. Mosasaurs were a fraction of the thousands of species living in the oceans, but the fact that predators are so diverse implies that lower levels of the food chain were also diverse, so the oceans could feed them all. This means that the marine ecosystem was not in decline before the asteroid impact.
Instead, mosasaurs and other animals – plesiosaurs, giant sea turtles, ammonites, countless species of fish, molluscs, sea urchins, crustaceans – thrived, then suddenly died out when the 10-year-old asteroid Chicxulub miles wide slammed into the earth, kicking up dust and soot. in the air and blocking the sun. The extinction of mosasaurs was not the predictable result of gradual environmental changes. It was the unpredictable result of a sudden catastrophe. Like a thunderbolt in a clear blue sky, their end was quick, final, unpredictable.
But the evolution of mosasaurs may also have started with a disaster. Curiously, the evolution of the giant carnivorous mosasaurs resembles that of another family of predators – the Tyrannosauridae. The giant T. rex evolved on land around the same time that mosasaurs became the top predators of the seas. Is it a coincidence? Maybe not.
Mosasaurs and tyrannosaurs begin to diversify and grow in size at the same time, around 90 million years ago, in the Turonian stage of the Cretaceous. This follows major extinctions on land and in the sea around 94 million years ago, at the Cenomanian-Turonian boundary.
These extinctions are associated with extreme global warming – a “super greenhouse effect” climate – driven by volcanoes releasing C02 into the atmosphere. In the aftermath, giant predatory plesiosaurs disappeared from the seas and giant predatory allosaurids were wiped out on land. As predator niches were left vacant, mosasaurs and tyrannosaurs moved to the upper predator niche. Although they were wiped out by a mass extinction, Thalassotitanium and T. rex evolved in the first place only because of a mass extinction.
The bigger they are, the harder they fall
Large predators are fascinating because they are large, dangerous animals. But their size and position at the top of the food chain also make them vulnerable. You have fewer animals as you move up the food chain. It takes a lot of small fish to feed a big fish, a lot of big fish to feed a small mosasaur, and a lot of small mosasaurs to feed a giant mosasaur. This means that large predators are rare. And large predators need a lot of food, so they have problems if the food supply is interrupted.
If the environment deteriorates, dangerous predators can quickly become endangered species.
It is this sensitivity to environmental changes that makes predators like Thalassotitanium so interesting for studying extinction. They suggest that being a top predator is a risky evolutionary strategy. On short timescales, evolution drives the evolution of larger and larger predators. Their size means they can compete and take down prey. But over long periods of time, specialization for the top predator niche increases vulnerability to disasters. Eventually, a mass extinction wipes out the top predators and the cycle begins again.
Nicholas R. Longrich, Lecturer in Paleontology and Evolutionary Biology, University of Bath
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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