Caught in the act: Mammal found with teeth sunk in a much larger dinosaur

A brand new fossil described this week captures two intertwined animals caught in a life-or-death wrestle proper earlier than each have been entombed in a volcanic occasion. Published in Scientific Reports this Tuesday, the fossil doesn’t seize one dinosaur attacking one other—moderately, the predator in this case is a smaller mammal referred to as Repenomamus robustus, and it died with its teeth clamped upon the herbivorous Psittacosaurus lujiatunensis, a dinosaur 3 times its dimension.

Gut contents from a Repenomamus fossil described in 2005 show this identical mammalian species ate very younger and significantly smaller Psittacosaurus. But the exceptional fossil revealed right this moment is the first proof of any Cretaceous mammal attacking a larger dinosaur. It’s an astounding snapshot of historical conduct, difficult earlier assumptions of predator/prey dynamics tens of millions of years in the past.

A last wrestle

These two species in the fossil couldn’t be extra completely different. Psittacosaurus is a sort of bipedal ceratopsian dinosaur—an early relative of dinosaurs akin to Triceratops—with a massive beak-like snout and spiky tail bristles. This was a herd animal, and it is the mostly found fossil in the Lujiatun Member of the Lower Cretaceous Yixian Formation of China. This specific Psittacosaurus was roughly 6.5–10 years outdated when it died.

Repenomamus robustus was an early mammal roughly the dimension and weight of a Virginia opossum. Its left paw is seen grabbing the dislocated decrease jaw of the dinosaur, and the two animal’s hindlimbs are tangled. Because Repenomamus died whereas biting the dinosaur, the authors couldn’t use its teeth to find out its age. However, they concluded that it was nearly an grownup based mostly on its fused lengthy bones. This voracious little mammal was a mere 1.42–3.43 kg (roughly three to seven lbs.), Yet its prey was 6–10.6 kg (13–23 lbs).

Two of Repenomamus’ ribs could also be damaged, however whether or not this occurred in its wrestle with the dinosaur or via the fossilization course of is unknown.

This extraordinary fossil was found in the aforementioned Lujiatun Member of the Lower Cretaceous Yixian Formation of China in 2012 by a native farmer. It’s an space referred to as the “Chinese Pompeii,” a nod to the Italian archaeological web site, for its degree of beautiful fossil natural world that have been preserved as a consequence of volcanic exercise.

The authors suggest that the dinosaur and mammal have been rapidly overcome by a lahar—a “volcanic debris flow, which occurs after an eruption, via hydraulic reworking of the deposited ash,” co-author Jordan Mallon defined in an e mail to Ars.

But wouldn’t such a particles movement not solely influence the positioning of the animals but additionally transport them from the place they died? At the very least, wouldn’t the animals have seen one thing that enormous and harmful racing towards them? Not in keeping with a 2007 paper describing a cluster of younger Psittacosauruses preserved in the identical method and from the identical rock formation in China.

“These kinds of flows still happen today and can bury entire villages quite rapidly,” Mallon provided. “We know of other dinosaurs from the Lujiatun beds, including the sleeping Mei long, which indicates that such animals were not [awakened] by the debris flow(s). In the case of the fossil we describe, I would argue that the animals were otherwise [too] occupied to notice the incoming mudflow.”