Paleontologists have discovered a huge new mosasaur from Morocco, named Thalassotitan atrox, which filled the top of the carnivores. With massive killer whale-like jaws and teeth, Thalassotitan hunted other marine reptiles – plesiosaurs, sea turtles and other mosasaurs. Sea monsters really existed at the end of the Cretaceous period, 66 million years ago. While dinosaurs flourished on land, huge marine reptiles called mosasaurs dominated the seas. Mosasaurs were not actually dinosaurs, but huge marine lizards that reached 12 meters (40 feet) in length. They were distant relatives of modern iguanas and monitor lizards. Mosasaurs resembled Komodo dragons, except for flippers instead of legs and a shark-like tail fin. Mosasaurs became larger and more specialized in the last 25 million years of the Cretaceous period, taking niches once filled by other marine reptiles such as plesiosaurs and ichthyosaurs. Some evolved to eat small prey such as fish and squid. Others crush ammonites and clams. The new mosasaur, named Thalassotitan atrox, evolved to prey on all other marine reptiles. The remains of the new species were discovered at a dig in Morocco, about an hour outside of Casablanca. Here, near the end of the Cretaceous, the Atlantic flooded northern Africa. Nutrient-rich waters rising from the depths feed plankton blooms. Those that fed small fish, fed larger fish, which fed mosasaurs and plesiosaurs — and so on, with these marine reptiles becoming food for the giant, carnivorous Thalassiaurus. Nick Longrich with the mosasaur fossil. Credit: Nick Longrich Thalassotitan had a massive skull 1.4 meters (5 ft) long and grew to nearly 9 meters (30 ft) long, the size of a killer whale. Most mosasaurs had long jaws and thin teeth for catching fish, but Thalassotitan had a short, broad snout and massive, conical teeth like those of an orca. These allow it to grab and tear apart huge prey. These anatomical adaptations suggest that Thalassotitan was an apex predator, sitting at the top of the food chain. Essentially, the giant mosasaur occupied the same ecological niche as today’s killer whales and great white sharks. Thalassotitan’s teeth are often worn and broken. Eating fish would not have caused this kind of tooth wear. Instead, this suggests that the giant mosasaur attacked other marine reptiles, crushing, grinding and breaking its teeth as it bit into their bones and tore them apart. Some teeth are so badly damaged that they are almost ground down to the root.
Fossilized remains of prey
Notably, the remains of possible victims of Thalassotitan have also been discovered. Fossils from the same beds show acid damage, with teeth and bones eaten away. Fossils with this strange damage include large predatory fish, a sea turtle, a half-meter-long (1.6-foot-long) plesiosaur head, and the jaws and skulls of at least three different species of mosasaur. They would have digested in the Thalassotitan’s stomach before it spat out their bones. “It’s circumstantial evidence,” said Dr. Nick Longrich, lead author of the study, published today (August 24, 2022) in Cretaceous Research. Longrich is a Senior Lecturer at the Milner Center for Evolution at the University of Bath. Thalassotitan atrox size comparison. Credit: Nick Longrich “We can’t say for sure what kind of animal ate all those other mosasaurs. But we have the bones of marine reptiles that were killed and eaten by a large predator. “And in the same location, we find Thalassotitan, a species that fits the killer profile – it’s a mosasaur that specializes in preying on other marine reptiles. This is probably not a coincidence.” Thalassotitan was a threat to everything in the oceans – including other Thalassotitan. The massive mosasaurs bear wounds sustained in violent combat with other mosasaurs, with injuries to their faces and jaws sustained in combat. Other mosasaurs show similar injuries, but in Thalassotitan these injuries were extremely common, indicating frequent, intense battles for food or mates. “Thalassotitan was an amazing, terrifying animal,” said Dr Nick Longrich, who led the study. “Imagine a Komodo Dragon crossed with a great white shark crossed with a T. Rex crossed with a killer whale.” Sea titan distribution map. Credit: Nick Longrich The new mosasaur lived in the last million years of the Age of Dinosaurs, a contemporary of animals like T. rex and Triceratops. Together with the recent discoveries of mosasaurs from Morocco, it suggests that mosasaurs were not in decline before the asteroid impact that led to the Cretaceous mass extinction. Instead, they thrived. Professor Nour-Eddine Jalil, co-author of the paper from the Natural History Museum in Paris, said: “The phosphate fossils of Morocco offer an unparalleled window into palaeobiodiversity at the end of the Cretaceous. “They tell us how life was rich and varied just before the end of the ‘age of the dinosaurs’, when animals had to specialize to have a place in their ecosystems. Thalassotitan completes the picture by assuming the role of megapredator at the top of the food chain.” “There’s still a lot to do,” Longrich said. “Morocco has one of the richest and most diverse marine faunas known from the Cretaceous. We are just beginning to understand the diversity and biology of mosasaurs.” Dr. Longrich has blogged about the research here: https://www.nicklongrich.com/blog/thalassotitan-the-killer-mosasaur Reference: “Thalassotitan atrox, a giant predatory mosasaurite (Squamata) from the Upper Maastrichtian phosphates of Morocco” by Nicholas R. Longrich, Nour-Eddine Jalil, Fatima Khaldoune, Oussama Khadiri Yazami, Xabier Peredetau, and S. Cretaceous Research .DOI:10.1016/j.crests.2022.105315
