Forgotten Museum Fossil Reveals Britain's First Megaraptoran, a Clawed Predator Named Invictibellatrix amberina

In 2020, palaeontologist Paul Barrett was working through the fossil collections of the Natural History Museum in London when he picked out a small chunk of bone and recognised it as the braincase, an important part of a dinosaur's skull. It had been sitting in storage for more than a century.

The museum is nearly 150 years old and holds over 30 million specimens, so an odd fossil or rock can easily slip out of mind. That is almost certainly what happened here. Barrett went through the museum's records and learned that the braincase had been found on a beach near Sudmoor Point on the Isle of Wight, the island off England's south coast known for its dinosaur fossils.

Knowing the origin, Barrett brought in Cassius Morrison, then a PhD student specialising in dinosaur braincases, to study the bone and work out which animal it belonged to. Their analysis showed that the roughly 120-million-year-old fossil was unlike anything previously found on the island. It belonged to a new species in the Megaraptora, a poorly understood family of meat-eating dinosaurs. They named it Invictibellatrix amberina.

Megaraptorans are recognised by slender skulls, lightly built skeletons and enormous hand claws, with some larger species carrying claws over a foot long. They are known worldwide, though most species come from South America, particularly Argentina. The British animal was small by comparison: about 5 metres from head to tail and as heavy as a large tiger, making it the smallest megaraptoran known.

The team compared the fossil directly with the skulls of other carnivores, a kind of scientific spot-the-difference. They also used computed tomography scanning, which combines X-rays and computer processing, to look inside the braincase and study what they could of the brain. They then fed their findings into a computer algorithm to place the species on the family tree, a step meant to limit bias in their interpretation. The results suggest Invictibellatrix belonged to the early phase of megaraptoran evolution, showing what these animals looked like before they grew large, as their relatives the tyrannosaurs also did.

The placement matters for the geography. Before this find, megaraptorans were known from the early Cretaceous (130 to 120 million years ago) of Thailand and Japan, plus several larger species from the late Cretaceous (85 to 66 million years ago) of Australia and Argentina. Animals this large could not have swum the oceans separating those continents, so the group must have been more widespread than its fossils show. As the first European megaraptoran, Invictibellatrix is strong evidence that they travelled from Asia to the southern continents via Europe and Africa, then spread across South America and Australia during or possibly before the early Cretaceous.

On the Isle of Wight, it probably shared its world with Neovenator, a relative of Allosaurus; Ceratosuchops, a relative of Spinosaurus; and Eotyrannus, an early relative of Tyrannosaurus rex. The four likely hunted different prey. The spinosaur specialised in fish, while the others took land animals. Invictibellatrix probably fed on small dinosaurs, mammals, lizards and even crocodiles.

The researchers see in this a familiar pattern: a small opportunist living in the shadow of larger animals, later becoming the dominant predator in a few ecosystems until the end of the age of dinosaurs. The name honours the megaraptorans' later role as apex predators in the late Cretaceous of South America, and translates as "unconquered female warrior of the amber."

The fossil does not settle everything. Scientists still do not know when megaraptorans first evolved, though this specimen offers clues. It also implies that other megaraptorans may be waiting to be found in Africa and even Antarctica, and that more discoveries may be sitting in museum drawers, waiting for someone to look closely.