First evidence found of a dinosaur eating a mammal

First evidence found of a dinosaur eating a mammal
Holotype specimen of Microraptor zhaoianus (IVPP V 12330) with mammal foot gut contents. A, entire specimen. Box inset indicates the location of B and C. B, close-up view of mammal foot. C, illustration of visible bones: dark gray elements are Microraptor ribs, yellow bones are the articulated mammalian foot and light gray are unidentified bones. Note the juxtaposition of the foot over the inside of the left ribs and the overlap of the right ribs over the foot, particularly over digits II and III. Abbreviations: ast, astragalus; cal, calcaneum; mtI, metatarsal 1; nav, navicular; lr, left rib; rr, right rib. Scale bar in A equals 100 mm and in B and C equals 5 mm. Credit: Journal of Vertebrate Paleontology (2022). DOI: 10.1080/02724634.2022.2144337

An international team of researchers has found the first evidence of a dinosaur eating a mammal. In their paper published in Journal of Vertebrate Paleontology, the group describes their reexamination of a fossil found more than 20 years ago.

The work builds on the findings of a prior team who studied the fossil, Microraptor zhaoianus, back in 2000. It was found in the Jiufotang Formation in a western part of China. Back then, the research team dated it to approximately 120 million years ago, and noted that the fossil was missing most of its middle part but its rib cage was still intact.

Microraptors were three-toed dinosaurs that, like their larger cousins, were carnivores. They lived in and were quite small compared to other dinosaurs—about the size of a modern house cat. Some species of microraptors sported , which might have been used for gliding down from perches in trees.

In this new effort, the researchers found evidence of another fossil inside of the microraptor that once belonged to a tiny . A small fossil mammal foot was found just behind the ribs, proof that the larger creature had feasted on a mouse-size mammal.

The researchers note that prior research has shown that other small creatures have been eaten by dinosaurs, such as snakes, squamates and birds—but never a mammal. The researchers suggest the lack of mammal remains inside the stomachs of dinosaurs is likely due to the rarity of finding any remains of other creatures inside of , and not an indication that eating mammals was rare.

First evidence found of a dinosaur eating a mammal
Life reconstruction of Microraptor eating a small mammal. Credit: Artwork (c) Hans Larsson

The researchers have also been studying the foot of the remains inside of the microraptor, but thus far, have been unable to identify which kind of mammal they belonged to. They note it had thin toes, similar to modern possums, but were shorter. The researchers are also looking into the possibility of whether the dinosaur actively chased down and ate the mammal or if was merely scavenging. They note that if it had glider-type wings, that would have allowed it to swoop down and catch a small creature such as the one found in its gut.

More information: David W. E. Hone et al, Generalist diet of Microraptor zhaoianus included mammals, Journal of Vertebrate Paleontology (2022). DOI: 10.1080/02724634.2022.2144337

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