In the Inner Mongolia region of China, a slab of shale recovered about a decade ago has yielded a remarkably complete fossil of a tiny Jurassic mammal. The specimen, dated to roughly 165 million years ago, was identified as a new species, Megacauda sungei, and described in the journal Nature. Researchers say the find provides the oldest clear evidence that early mammals could both chew food before swallowing and suckle their young—behaviors that define the mammalian lineage.
Discovery and preservation
University of Chicago paleontologist Zhe‑Xi Luo and his colleague Thomas Martin of the University of Bonn visit the Paleontological Museum of Liaoning each year to examine new material from the region, which Luo describes as “more than a hotspot” for fossils ranging from feathered dinosaurs to flying reptiles. The slab that captured their attention contained dark, blackened bones and soft‑tissue impressions of an animal about the size of a chihuahua. Because the bone material is unusually dark, conventional photography struggled to reveal details.
To overcome this, Chang‑Fu Zhou of Shandong University of Science and Technology applied X‑ray fluorescence spectroscopy, producing a vivid image in which the skeleton appears bright yellow. The enhanced view highlighted a combination of features: a pelvis, hind limbs and a broad tail reminiscent of a modern platypus, suggesting a semi‑aquatic lifestyle, and a predatory head with sharp teeth. Small salamander bones were found within the abdominal cavity, indicating the animal likely captured and sliced prey before swallowing.
Implications for mammalian evolution
Among the most striking aspects of the fossil are the tiny hyoid bones near the throat, structures that in humans support the tongue. A CT scan of the skull’s underside revealed a delicate roof of the mouth and a series of bone hooks and ridges. With these rare elements preserved, Luo’s team could reconstruct the entire muscular‑skeletal system with confidence.
The reconstruction demonstrates two capabilities that are unique to mammals. First, the animal appears to have chewed food before swallowing, a process that contrasts with most vertebrates, which bite and gulp. Luo explains that mammals break down food with teeth and then move a single bolus down the esophagus. Second, the presence of hyoid and related structures suggests the ability to suckle, a behavior tied to the production of milk and the origin of the term “mammal.” These findings push the emergence of chewing and suckling back to at least the middle Jurassic, extending the timeline for key mammalian innovations.
Expert commentary
Jessica Theodor, a paleontologist at the University of Calgary who was not involved in the study, called the specimen “fascinating” and noted that its overall anatomy resembles that of modern mammals. She emphasized that the fossil offers a window into the early evolution of lactation, describing it as a “dietary and hormonal conversation” between mother and offspring that began far back in the Mesozoic era.
Luo added that, although mammals were never dominant during the age of dinosaurs, they diversified into a range of ecological niches—gliders, swimmers, terrestrial and arboreal dwellers, and diggers—by the Jurassic. The new evidence of chewing, swallowing and suckling suggests that novel feeding strategies helped these early mammals survive and evolve alongside the dominant reptiles.
The discovery of Megacauda sungei thus provides a rare glimpse into the functional anatomy of one of the earliest mammals, confirming that the fundamental traits of modern mammalian biology were already in place more than 160 million years ago.
Norman Pearlstine is the Executive Editor and Co-Founder at News Raise. With over two decades of experience across financial journalism, corporate governance, and market analysis, Norman leads the editorial direction and ensures strict adherence to journalistic accuracy and ethics.
