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A restoration of Repenomamus snacking on a young Psittacosaurus. Image by Nobu Tamura, from Wikipedia.

What dinosaurs ate, and how they ate it, is an endless source of fascination. Whether it’s the predatory habits of Tyrannosaurus rex or how sauropods managed to horf down enough food to fuel their bulky bodies, the details of dinosaurs’ paleo diets fuel scientific study and dinosaur restorations alike. If basic cable documentaries have taught me anything, it’s that dinosaurs were all about eating.

But dinosaurs were not invulnerable consumers. Even the biggest and fiercest dinosaurs were food sources for other organisms—from giant crocodylians to parasites and bone-boring beetles that took up residence in dinosaur carcasses. Even mammals sometimes dined on dinosaur.

The most famous case is Repenomamus. Hardly a household name, this critter is the exception to everything I heard about mammals in the Age of Dinosaurs. The classic story is that mammals were so stifled by the dinosaurian reign that our furry ancestors and cousins remained small and hid among the shadows. There is some truth to the notion. Mammalian evolution was influenced by dinosaur evolution, and as Mesozoic mammals diversified, most stayed small and became adapted to burrowing, swimming, gliding and other modes of life in the shadow of the dinosaurs.

Repenomamus, on the other hand, was huge for a mammal of its time. This roughly 130-million-year-old carnivore, found in the rich fossil beds of northeastern China, was a badger-like creature a little over three feet long—bigger than some of the feathery dinosaurs that lived at that same time. Repenomamus was big enough to eat dinosaurs, and we know that the mammal definitely did. In 2005, paleontologist Yaoming Hu and co-authors described a Repenomamus skeleton with the remains of a juvenile Psittacosaurus, an archaic ceratopsian dinosaur, in its gut contents. Based on the way the little dinosaur bones were broken up, the researchers said, “the juvenile Psittacosaurus was dismembered and swallowed as chunks.”

We don’t know whether Repenomamus caught the young dinosaur or scavenged it. Those details aren’t recorded in the fossils. Either scenario is possible—Repenomamus was certainly large enough to catch and kill a juvenile Psittacosaurus, but there’s no reason to think that such a large carnivorous mammal would have passed up a dinosaur carcass. While many Mesozoic mammals might have qualified as dinosaur prey, Repenomamus reminds us that the classic narrative of total dinosaur dominance gives the prehistoric archosaurs too much credit.

Of course, mammals didn’t have to be burly carnivores to eat dinosaurs. Dead dinosaurs were rich food resources on the prehistoric landscape, and mammals took advantage of these bonanzas. In a study I wrote about two years ago, paleontologists Nicholas Longrich and Michael Ryan documented several fossils—including dinosaur limb and rib fragments—that displayed toothmarks made by small mammals called multituberculates. These mammals, often restored in opossum-like garb, had large, pointed incisors that helped them gnaw on tough plant foods but that could also be repurposed to scrape at dinosaur carcasses. Given the chance, mammals made the most of dead dinosaurs.

References:

Longrich, N., & Ryan, M. (2010). Mammalian tooth marks on the bones of dinosaurs and other Late Cretaceous vertebrates Palaeontology DOI: 10.1111/j.1475-4983.2010.00957.x

Yaoming Hu, Jin Meng, Yuanqing Wang, Chuankui Li (2005). Large Mesozoic mammals fed on young dinosaurs Nature, 433, 149-152 DOI: 10.1038/nature03102