Around 145 million years ago, the beach in what is today Dorset, England, was covered in a freshwater lagoon. It was teeming with dinosaurs, pterosaurs, crocodiles and turtles. Making its way among all these beasts was a small puff of fur with excruciatingly sharp teeth.
Scientists last month described the prehistoric mammal in The Proceedings of the Geologists’ Association. They named it Novaculadon mirabilis, from novacula, the Latin word for razor.
“The premolars form quite a sharp cutting edge,” said Steven Sweetman, a paleontologist at the University of Portsmouth in England and an author of the paper. The species was probably omnivorous, with teeth designed for processing vegetation but also possibly meat.
Novaculadon, about the size of a mouse, came from an order of mammals called multituberculates. They are named for the round “tubercles,” or outgrowths on their teeth. They were among the most successful groups of ancient mammals yet discovered, living alongside dinosaurs during the Mesozoic Era. Though unrelated to mice and rats, they most likely filled a similar role as an easy food source for larger predators while also dispersing seeds and controlling insects, all the while avoiding the weighty footfalls of roaming sauropods.
The Novaculadon specimen was discovered in a rock on the Dorset beach. Its full jawbone was found with the majority of its teeth intact, including a robust incisor and premolars, though it lacked the molars. Scientists used X-ray computed tomography to digitally isolate the teeth without the risk of damaging the delicate fossil.
The fossil was so complete that researchers knew almost immediately they had found something new. The jawbone was part of a skeleton of an animal that most likely died nearby and hadn’t been damaged in transport by rivers or other bodies of water.
This is the first substantially complete multituberculate jaw found since the 1850s, when Samuel Beckles, a lawyer and aspiring dinosaur hunter, undertook a large-scale excavation, exposing a bed in a limestone formation now known as the Purbeck Group. It resulted in the discovery of several mammal species as well as turtles, crocodiles and herbivorous dinosaurs. The newly discovered fossil came from a layer above Beckles’s findings, which showed that it was younger than those found over 170 years ago.
“It didn’t resemble any of these forms that had been found back in Victorian times,” Dr. Sweetman said.
The possibly nocturnal Novaculadon was probably doing things similar to the activities of the modern brown rat, commonly found in England today. The finding demonstrates how these tiny mammals forged an ecological niche that allowed for their survival well past the end of the dinosaur age.
“This wasn’t some meek, pathetic creature — it was an animal that was well adapted to its particular lifestyle,” said Steve Brusatte, a vertebrate paleontologist at the University of Edinburgh, who was not involved in the study. “Mammals of this time were very good at living underground.”
This furtive lifestyle, burrowing beneath the surface and through plant undergrowth, allowed this line of mammals to survive the Cretaceous-Paleogene (K-Pg) extinction 66 million years ago, when three-quarters of all species on Earth, including non-avian dinosaurs, went extinct.
The fossil record shows over 200 species of multituberculates, living on nearly every continent and ranging from the size of a mouse to Taeniolabidoidea, which evolved to be the size of a beaver. It’s a bit of an enigma how they carved out their survival until around 30 million years ago, only to go extinct as other mammals were thriving.
Previous research has speculated that a changing environment led to the decline of the animals, which were outcompeted by rodent rivals. Ornella Bertrand, a mammalian paleontologist at the Miquel Crusafont Catalan Institute of Paleontology in Spain who was not involved in the study, contends that it could be that other lines of mammals were better equipped to protect their young.
Still, it’s a question that scientists have yet to answer. In surviving the dinosaur extinction, these rodent-like creatures “achieved something that very few mammals did,” Dr. Bertrand said. “So it’s just very weird that we don’t have multituberculates today.”
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