Scientists Find a Mammal's Foot Inside a Dinosaur, a Fossil First

Isaac Schultz
Wed, December 21, 2022 

An illustration of Microraptor chowing down on a mammal foot.

Paleontologists taking a second look at a species of small, four-winged dinosaur have found a fossilized mammalian foot in the predator’s stomach.

It’s the first concrete evidence of dinosaurs eating mammals, the researchers say. Specimens of the dinosaur, Microraptor zhaoinus, have been discovered containing ancient birds, fish, and lizards, so the mammalian find is just the latest known source of protein for this spunky hunter. The team who re-scrutinized the Microraptor fossil published their findings today in the Journal of Vertebrate Paleontology.
“It really demonstrates the generalist diet in this small feathered dinosaur,” said Hans Larsson, a paleontologist at McGill University and the study’s lead author, in an email to Gizmodo. “Adding mammals to the menu shows just how un-specialized this dinosaur was.”

The tree-dwelling Microraptor lived during the early Cretaceous, and specimens have been found across what is now northeast China. The fossil-rich region is called the Jehol Biota, and its well-preserved treasures are a great resource for understanding nuances of dinosaur anatomy, as well as details about different animals’ ecological niches.

Microraptor is thought to have lived in trees, gliding around the Cretaceous forests looking for morsels on branches as well as on the ground. The recently studied specimen is the holotype, meaning it was first of its species to be found and named. It’s only recently been revisited after its discovery back in 2000. The new analysis revealed the mammalian foot—a seemingly unprecedented find.

The mammal foot (center) within the Microraptor fossil.

The researchers couldn’t identify the particular mammal species, but the foot’s preservation within Microraptor allowed them to understand its ecological niche and, obviously, its predators.

“Gut contents are amazing snapshots into the diet of fossil animals, but they are so rare that it can be difficult to figure out whether the preserved ‘last meal’ represents the animal’s normal diet or a weird, one-off event that lucked into getting fossilized,” said Stephanie Drumheller-Horton, a paleontologist at the University of Tennessee, Knoxville, who was not affiliated with the recent paper, in an email to Gizmodo.

“Microraptor is shaping up to be a very interesting exception to that rule, with multiple, beautifully fossilized specimens preserving different ‘last meals,’” Drumheller-Horton added. “Taken together, the authors make a compelling case that this little theropod wasn’t a particularly picky eater, eating all sorts of small-bodied animals in its environment.”

Another illustration of Microraptor with its prey.

The mammal foot apparently did not belong to a distant human ancestor; the team said it had similarities to the morphologies of Sinodelphys, Yanoconodon, and Eomaia, all ancient species of early mammals that looked roughly like opossums or rodents.

The foot belonged to an animal about the size of a mouse. The team’s analysis found the critter wouldn’t have been a good climber—an indicator that Microraptor may have occasionally swooped down to the forest floor for feeding.

“The foot seems completely intact, and thus was swallowed whole. How much of the mammal was swallowed is unknown,” Larsson said. “However, there were several other unidentified bones around the foot in the rib cage, so I suspect that more of that mammal was consumed.”

The researchers could not determine whether the animal was hunted and killed or if the feathered dinosaur had scavenged its body.

Given the luck paleontologists have had with the Jehol Biota so far, it may just be a matter of time before another meal-laden specimen offers more insights about the Cretaceous food scene.

More: A Shark, Eating a Squid, Eating a Lobster, in One Fossil

Feathered dinosaur the size of a cat is 'first proven to have eaten a mammal'

Telegraph reporters
Tue, December 20, 2022

A feathered flying dinosaur the size of a cat is the first that has been proven to eat mammals by scientists.

Palaeontologists in the UK have analysed fossil remains from around 120 million years ago, showing a small, feathered dinosaur - known as Microraptor - with the foot of an animal inside its ribcage.

The experts said their findings, published in the Journal of Vertebrate Paleontology, is “the first record of a dinosaur eating a mammal”.

Dr David Hone, from Queen Mary University of London, who is first author on the study, said: “It’s so rare to find examples of food inside dinosaurs, so every example is really important as it gives direct evidence of what they were eating.

Fossil remains showing a mammal foot in the ribcage of a Microraptor - PA

“While this mammal would absolutely not have been a human ancestor, we can look back at some of our ancient relatives being a meal for hungry dinosaurs.

“This study paints a picture of a fascinating moment in time - the first record of a dinosaur eating a mammal - even if it isn’t quite as frightening as anything in Jurassic Park.”

Microraptors lived in the ancient forests of what is now China, somewhere between 125 and 113 million years ago.

While it moved on its two legs, experts believe some species may have been capable of guided flight.

About the size of a crow or a small cat, Microraptors would have been gliding from tree to tree to prey on small animals.

Although the specimen was first described in 2000, the researchers said the previous team had failed to see the remains of another animal inside the dinosaur.

Further analysis suggests the prey was a mammal about the size of a mouse, which likely lived on the ground and was not a good climber.

A mammal foot in the ribcage of a Microraptor may be first known incident of a mammal being eaten by a dinosaur - PA

Previous research has shown other Microraptor specimens with preserved food in their stomachs, such as a bird, a lizard and a fish.

However, the team added that it is not certain if these dinosaurs had directly preyed on these animals or found them already dead and had scavenged them.

Dr Alex Dececchi, from Mount Marty College in South Dakota, US, and one of the study authors, said: “The great thing is that - like your housecat, which was about the same size - Microraptor would have been an easy animal to live with but a terror if it got out, as it would hunt everything from the birds at your feeder to the mice in your hedge or the fish in your pond.”