A fossil discovered in Inner Mongolia has given paleontologists a look at an early step in mammalian evolution. The species, named Megacauda sungei, lived about 165 million years ago and measured roughly 20 inches long. It was a predator that swam in Jurassic waterways, using teeth with backward-curving cusps to hold slippery prey.
The researchers, from institutions in Shenyang, Chicago, and Bonn, used CT scans to reconstruct the animal's anatomy. They found evidence of a soft palate that separated the mouth from the pharynx. That structure allows mammals to breathe while swallowing, something many other vertebrates cannot do. The team says this would have made it possible for early mammals to nurse milk safely, without liquid entering the nasal passages.
According to the study, published in Nature, this swallowing adaptation is directly linked to mammalian evolution and, eventually, brain development. The researchers describe Megacauda sungei as the largest known mammaliaform from the Jurassic, weighing about two kilograms. Its broad, flattened tail and paddle-like limbs suggest it was the earliest known aquatic mammal relative.