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Headline: Jurassic China was an 'Otterpus's garden' thanks to one of our bizarre newly discovered ancestors
Caption: **VIDEO AVAILABLE: CONTACT INFO@COVERMG.COM TO RECEIVE** BY MARK WORGAN The rivers of Jurassic China were terrorised by a bizarre mammal ancestor that looked like a cross between an otter and a platypus, scientists have found. While dinosaurs ruled most of the Earth, Megacauda sungei was one of the oldest known mammaliaforms adapted for swimming and hunting in water. The discovery comes from a remarkably well-preserved 165-million-year-old fossil found in Inner Mongolia that also contains the earliest evidence yet of bony structures in the throat known as hyoids. These structures allowed the mammal predecessor to feed and swallow in a way similar to modern mammals – an evolutionary development that helped pave the way for mammals to diversify and exploit a wide range of diets. “This is an incredibly important evolutionary innovation. After mammals chew their food, be it plants or meat, they all swallow it in the same efficient and effortless way,” said Zhe-Xi Luo, Mila Pierce-Rhoads Professor of Organismal Biology and Anatomy at the University of Chicago and senior author of a study describing the fossil in Nature. “Once early mammals had this apparatus, each group could develop specialized teeth and diversify into a tremendous range of food resources. They could be carnivores, insectivores, herbivores, omnivores, or anywhere in between.” All modern mammals, including humans, have hyoid bones connecting the mouth and throat to the oesophagus and larynx. The bones form a U-shaped structure suspended from the skull by a chain of smaller bony segments. This arrangement allows mammals to use muscles in the throat to swallow chewed food in manageable portions, rather than gulping down large pieces or whole prey, as alligators do. The structures also allow young mammals to suckle milk from their mothers. Megacauda belonged to an extinct group known as docodonts, which were close relatives of mammals living during the Mesozoic Era. In 2019, Luo and colleagues discovered a much smaller docodont from roughly the same period, Microdocodon gracilis, which also possessed mammal-like hyoid bones. Megacauda, however, was considerably larger, measuring about 40 to 50cm in length and weighing between 1kg and 2kg. Its fossil is also unusually well preserved, including delicate bony structures beneath the skull that supported muscles involved in movement of the palate and throat. The anatomy is comparable to the throat muscles of the modern opossum, according to co-author Peishu Li, who recently completed a PhD in integrative biology at the University of Chicago and is now a member of the faculty at Ohio University. Study co-author Chang-Fu Zhou, of Shandong University of Science and Technology, took the specimen to several research laboratories around China for CT scanning and X-ray fluorescence imaging. The large slab containing the fossil had to be broken into smaller pieces for scanning. The resulting images allowed April Neander, a scientific artist and CT imaging specialist at the University of Chicago, to reconstruct its anatomy in fine detail. As well as its intricate hyoid and throat structures, the fossil preserves the pelvis, hind limbs and tail, providing evidence that Megacauda was a powerful swimmer. Its hind feet had long outer digits resembling those of a platypus, while its tail contained broad, H-shaped vertebrae and had a wide overall shape that could have helped propel the animal through water. The skull contained robust canine teeth and shearing cheek teeth, suggesting it could cut and chew meat in a way distinct from modern carnivorous mammals. Luo's team previously discovered another swimming docodont, Castorocauda, in 2006. “The new fossil is particularly interesting because it’s older than Castorocauda. Although both docodonts occupied the same niche in the water, the new fossil is more complete,” Neander said. “In addition to the exciting features of the skull and the hyoid bones, we have this fantastic pelvis, which is more complete than all other specimens from this time.” The researchers believe Megacauda lived a semi-aquatic lifestyle, entering the water to hunt millions of years before the emergence of modern swimming mammals such as platypuses, otters and minks. The fossil even contains tiny fragments of vertebrate bones in its stomach, suggesting the animal may have preyed on small creatures such as salamanders, which were abundant in the same fossil beds. Docodonts were an exceptionally diverse group, occupying a variety of environments during the Mesozoic Era. They included tree-dwelling species such as Microdocodon and aquatic animals such as Megacauda. The nearly complete fossil is helping scientists understand how these early mammaliaforms fitted into ecosystems dominated by dinosaurs, long before modern mammals underwent their later evolutionary diversification. “Docodonts are the most speciose group of the stem mammals across North America, Europe, and China, and this is probably one of the two most complete specimens for the group,” Luo said. “This fossil shows that the intricate structures of the throat are starting to come together, long before modern mammals split off from their predecessors, and they are very important to the evolutionary innovation that underlies later adaptive radiation.” The study, A Jurassic Mammaliaform Swimmer and Transformation of the Mammalian Pharynx, was supported by the US National Science Foundation, the Taishan Scholar Program of Shandong, China, the German Research Foundation and Ohio University. Additional authors were Yikun Li and Honggang Zhang of Shenyang Normal University in China, and Thomas Martin of the University of Bonn in Germany.
Keywords: feature,photo,fossil,science,palaeontology
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