Stunning fossil shows small mammals once hunted big dinosaurs

It’s a bad day for a dinosaur when it gets entombed in a mudslide. Even worse if moments before that it was being attacked – by a furry animal half its size.

However, that was the fate of a beak-nosed dinosaur, Psittacosaurus lujiatunensis, found stuck in a fossilised fight to the death with a meat-eating Repenomamus for 125 million years.

Palaeontologists unearthed the incredible scene in northeastern China, prompting a major rethink of dinosaurs as prey.

‘The two animals are locked in mortal combat – intimately intertwined,’ said co-author Dr Jordan Mallon, of the Canadian Museum of Nature, Ottawa, Ontario.

‘It’s among the first evidence to show actual predatory behaviour by a mammal on a dinosaur.’

Close examination shows the dinosaur is lying prone with its hindlimbs folded on either side of its body. Psittacosaurus was about the size of a large dog.

Badger-like Repenomamus, the largest mammal of the Cretaceous period, coils to the right and sits atop – gripping the jaw of its prey.

It is also biting into some of the ribs, while the back foot is holding onto Psittacosaurus’s hind leg.

‘The weight of the evidence suggests that an active attack was underway,’ said Dr Mallon.

The international team ruled out scavenging, as the bones of the dinosaur have no tooth marks. It is also unlikely the two would have become so entangled if the dinosaur was not alive.

The elevated position of Repenomamus also suggests it was the aggressor.

In the modern world, lone wolves are known to hunt larger animals, including caribou and domestic sheep, in the modern world. On the African savanna, wild dogs, jackals and hyenas will attack prey that are still alive, with the target collapsing, often in a state of shock.

‘This might be the case of what is depicted in the fossil, with the Repenomamus actually eating the Psittacosaurus while it was still alive – before both were killed in the roily aftermath,’ said Dr Mallom.

The discovery was made at a prehistoric animal graveyard in Liaoning dubbed ‘China’s Dinosaur Pompeii’.

There are also small mammals, lizards and amphibians buried suddenly en masse by mudslides and debris following volcanic eruptions.

The stunning find contradicts the idea dinosaurs had few threats from mammal contemporaries. Both skeletons are nearly complete.

Repenomamus was known to have preyed on Psittacosaurus because of fossilised baby bones of the herbivore found in the mammal’s stomach.

‘What’s new to science through this amazing fossil is the predatory behaviour it shows,’ said Dr Mallon.

Deposits from the Lujiatun beds will continue to yield new evidence of interactions among species – otherwise unknown from the rest of the fossil record, added the researchers.

The study is published in the journal Scientific Reports.

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