Scientists have identified a remarkably preserved fossil from the Middle Jurassic period that offers some of the oldest evidence of distinctly mammalian behaviors, including chewing, swallowing, and suckling. The specimen, named Megacauda sungei, dates back approximately 165 million years and was discovered in the Inner Mongolia region of China.
Led by Zhe-Xi Luo, a paleontologist at the University of Chicago, the research team described the findings in the journal Nature. The fossil, housed at the Paleontological Museum of Liaoning, is significant because early mammalian remains from this era are exceedingly rare. According to Luo, the integrity of the specimen allowed researchers to determine that the animal possessed the ability to chew food, swallow it in boluses, and nurse its young—traits that define modern mammals.
The animal was roughly the size of a chihuahua. Initial visual examination was challenging due to the dark coloration of both the bones and the surrounding shale slab. To overcome this, collaborator Chang-Fu Zhou of Shandong University of Science and Technology utilized X-ray fluorescence spectroscopy, which rendered the skeleton in bright yellow and highlighted its unique anatomical features.
The posterior section of the fossil, including the pelvis, hind limbs, and tail, closely resembles that of a modern platypus, suggesting a semi-aquatic lifestyle adapted for swimming. However, the head differed significantly; the sharp teeth and jaw structure indicate a predatory diet. Inside the fossil, researchers found small salamander bones, leading them to conclude that M. sungei hunted and consumed prey by cutting and shearing it with its teeth.
Crucially, the fossil preserved delicate hyoid bones and a series of bone hooks and ridges on the underside of the skull, revealed through CT scanning. This allowed the team to reconstruct the muscular and skeletal machinery responsible for swallowing. Unlike other vertebrates that typically bite and gulp, mammals chew their food thoroughly before swallowing it whole. Additionally, the anatomical features suggest the animal was capable of suckling milk, a fundamental trait linked to mammary glands.
Jessica Theodor, a paleontologist at the University of Calgary who was not involved in the study, described the specimen as fascinating and noted that its anatomy aligns closely with modern mammals. She emphasized the importance of the find in tracing the evolution of lactation, describing it as a complex biological interaction between mother and offspring that began far back in the Mesozoic era.
Luo stated that the fossil illustrates how diverse feeding strategies helped early mammals and their predecessors survive and diversify during the age of dinosaurs. Despite not being dominant predators, these small creatures occupied various ecological niches—including gliders, swimmers, diggers, and tree-dwellers—united by their shared mammalian characteristics.
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