New prehistoric “Hobbit” from the dawn of the Age of Mammals

Researchers from the University of Colorado have described three previously unknown mammal species that lived not long after the extinction of the dinosaurs – and one is named after a hobbit.

Their findings, described in a new study in the Journal of Systematic Palaeontology, suggest that mammal evolution was far more rapid in the wake of the extinction than once thought.

The mass extinction event that wiped out the bulk of the dinosaurs 66 million years ago is often seen as the genesis of the “Age of Mammals”, because the opportunistic little creatures were able to thrive, dominate and diversify in the ecological vacuum the dinosaurs left behind. This cataclysmic event was bad for the dinosaurs but serendipitous for us: without the mammalian bloom it precipitated, humans would likely never have evolved.

“When the dinosaurs went extinct, access to different foods and environments enabled mammals to flourish and diversify rapidly in their tooth anatomy, and evolve larger body size,” says lead author Madelaine Attebury, from the University of Colorado’s Geological Sciences Department. “They clearly took advantage of this opportunity, as we can see from the radiation of new mammal species that took place in a relatively short amount of time following the mass extinction.”

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The three newly described species roamed North America during the earliest Palaeocene Epoch, within just a few hundred thousand years of the mass extinction. They were found in the Great Divide Basin in the Red Desert of Wyoming, an arid and rugged region today populated by sand dunes, shrubs and feral horses.

The new creatures are known respectively as Miniconus jeanninae, Conacodon hettingeri, and Beornus honeyi. They belonged to a diverse collection of mammals known as archaic ungulates (or condylarths), and they are the ancestors of today’s hoofed animals, including horses, elephants, cows and hippopotami. They are all part of the family Periptychidae, distinguished from other archaic ungulates by their swollen premolars and vertical enamel ridges.

The largest of the three, Beornus honeyi, would have rivalled the modern house cat in size, which is significantly larger than the rat-sized mammals that lived alongside the dinosaurs. B. honeyi in particular also shows unique dental features, including the inflated molars that gave rise to its name, an homage to The Hobbit character Beorn.

“Previous studies suggest that in the first few hundred thousand years after the dinosaur extinction (what is known in North America as the early Puercan) there was relatively low mammal species diversity across the Western Interior of North America, but the discovery of three new species in the Great Divide Basin suggests rapid diversification following the extinction,” says Atteberry.

“These new periptychid ‘condylarths’ make up just a small percentage of the more than 420 mammalian fossils uncovered at this site. We haven’t yet fully captured the extent of mammalian diversity in the earliest Paleocene, and predict that several more new species will be described.”

“Instead of an initial recovery of perhaps hundreds of thousands of years after the dinosaur extinction, the mammals appear to be quite diverse soon after the extinction,” says Thomas Rich, senior curator of vertebrate palaeontology at Museums Victoria, who was not involved in the study. “[That’s] a most thought provoking difference implying that further study of the topic of the recovery rate of the mammalian fauna after the extinction of the dinosaurs is a topic far from settled.”