Researchers say a small fossil from the middle Jurassic provides some of the oldest evidence of chewing and swallowing as well as suckling, which are distinctly mammalian traits. Over the years, the Inner Mongolia region of China has yielded remarkable fossils, ranging from feathered dinosaurs to flying reptiles. Many of these specimens wind up at the Paleontological Museum of Liaoning, where paleontologist Zhe-Xi Luo and his colleague Thomas Martin of the University of Bonn visit each year to examine new finds. A decade ago, a specimen in a thick slab of shale caught their eye. It preserved the fossilized bones and soft tissue impressions of an ancient mammal that lived some 165 million years ago. Early fossil mammals are exceedingly rare. The team named the animal Megacauda sungei and described it in the journal Nature. The remains were intact enough to determine that it was likely capable of chewing food and then swallowing it, as well as suckling. Luo and his colleagues concluded that these evolutionary innovations extend deep into the past to at least the middle Jurassic. The fossil was about the size of a chihuahua. Because the fossil bones and the rock slab were both very dark, collaborator Chang-Fu Zhou of Shandong University of Science and Technology used X-ray fluorescence spectroscopy to make the skeleton pop out in bright yellow. The imaging showcased a curious combination of characteristics, with a back end resembling a modern-day platypus that suggested the animal was semi-aquatic and foraged in the water. However, its teeth and jaw were very different from a platypus, indicating the head of a predator. The researchers found a smattering of small salamander bones inside the fossil that the animal likely ate by shearing with its sharp teeth. Luo also noticed tiny hyoid bones. After CT scanning the fossil, the team exposed a delicate roof of the mouth and a series of bone hooks and ridges. This reconstruction revealed that the animal was likely capable of chewing food and then swallowing it, rather than simply biting and gulping like other vertebrates. The fossil also appeared capable of suckling, representing some of the oldest fossil evidence of an animal with both key mammalian abilities. Jessica Theodor, a paleontologist at the University of Calgary who was not involved in the research, noted that the specimen tracks the evolution of lactation far back into the Mesozoic. Luo explained that new ways of feeding helped mammals and their predecessors diversify during the age of dinosaurs.
Source: npr.org
