Archaeologists have recently found a fossil of a 150-million-year-old mammal
known as Repenornamus robustus (R. robustus). Interestingly, the mammal's
stomach contained the remains of a psittacosaur dinosaur. Some researchers have
therefore suggested that R. robustus was an active hunter of dinosaurs. However,
a closer analysis has made the hypothesis that R. robustus was an active hunter
unlikely. It was probably Just a scavenger that sometimes fed on dinosaur eggs
containing unhatched dinosaurs.
First, R. robustus, like most mammals living 150 million years ago, was small—
only about the size of a domestic cat. It was much smaller than psittacosaurs,
which were almost two meters tall when full grown. Given this size difference, it is
unlikely that R. robustus would have been able to successfully hunt psittacosaurs
or similar dinosaurs.
Second, the legs of R. robustus appear much more suited for scavenging
than hunting: they were short and positioned somewhat to the side rather than
directly underneath the animal. These features suggest that R. robustus did not
chase after prey. Psittacosaurs—the type of dinosaur found in the stomach of
R. robustus—were fast moving. It is unlikely that they would have been caught by
such short-legged animals.
Third, the dinosaur bones inside the stomach of the R. robustus provide no
evidence to support the idea that the dinosaur had been actively hunted. When
an animal has been hunted and eaten by another animal, there are usually teeth
marks on the bones of the animal that was eaten. But the bones of the psittacosaur
inside the R. robustus stomach do not have teeth marks. This suggests that
R. robustus found an unguarded dinosaur nest with eggs and simply swallowed an
egg with the small psittacosaur still inside the eggshell.
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