Dinosaurs often leave modern humans with the impression they were overwhelmingly dominant during their rule, but a recent study suggests they may have fallen prey to mammal predators, despite being much larger in size.
The study, entitled "An Extraordinary Fossil Captures the Struggle for Existence during the Mesozoic", was conducted by Chinese and Canadian paleontologists and their findings were published on Tuesday in the journal Scientific Reports.
By examining a Cretaceous Period fossil, which is 125 million years old, scientists came to the conclusion a badger-like mammal preyed on a herbivorous dinosaur three times its body weight. But before they could finish the do-or-die battle, they were suddenly engulfed by volcanic debris, eternally locked in mortal conflict.
The fossil was collected in Lujiatun of Beipiao, Liaoning province, in May 2012 by Han Gang, a professor at the Hainan Vocational University of Science and Technology. It is now part of the collection at Weihai Ziguang Shi Yan School Museum in Weihai, Shandong province. Dubbed "Chinese Pompeii" by scientists, the Lujiatun location has an abundance of ancient vertebrate fossils.
The fossil preserved skeletons of a pair of larger and smaller animals. Paleontologists said the larger one, the size of a present-day dog, was identified as a Psittacosaurus, a plant-eating dinosaur. The smaller one, a Repenomamus robustus, was a mammal similar to a present-day badger. One of the largest mammals at the time, it still weighs in at just a third of the Psittacosaurus.
Previously, scientists determined the badgerlike mammal was a carnivore, but they couldn't decide whether it was attacking other live animals or was just a scavenger.
By studying the posture of their skeletons as well as body mass distribution, scientists came to the conclusion the mammal was actually the aggressor.
"The Repenomamus robustus was atop the Psittacosaurus' back, grasping its jaw, biting its ribs and its hind foot was wrapped tightly around the lower hindlimb of the dinosaur," said Wu Xiaochun, a paleontologist in the Canadian Museum of Nature who participated in the study, as quoted by Science and Technology Daily.
The authors agreed if the mammal were feeding from an animal carcass, there would be plenty of bite marks. The lack of these marks and the animals' posture all suggest the mammal was the aggressor.
Wu said it's not that difficult for a mammal to attack a larger dinosaur despite its size, as weasels and hyenas do in the present day.
After analysis of the volcanic debris that formed the fossil found by mineralogist Aaron Lussier, who also participated in the study, Wu said the Repenomamus robustus was trying to eat the Psittacosauruswhen it was still alive, but they were both entombed by a sudden volcanic eruption.
"The new fossil thus challenges the common assumption that Mesozoic mammals were merely fodder for the ruling dinosaurs," the scientists said.