Two brand-new species of early mammals from the Jurassic period have been discovered, revealing the secrets of how we got our ears...
These new species are hoped to give paleontologists insight into how the mammalian middle ear evolved from the joints of the jaw, millions of years ago.
One of the new species is a type of ancient mammal called a shuotheriid, discovered in a Middle Jurassic fossil site in Mongolia, and has been named Feredocodon chowi. The other new species, Dianoconodon youngi, was found in the Early Jurassic Lufeng Biota in China and is more similar to a type of ancient mammal called Morganucodon. Both of these new species had special characteristics in their jaws and ears that indicate that they were waypoints in evolution as the jaw joint was slowly evolving towards being specialized for use in hearing. The Middle Jurassic spanned around 174 to 163.5 million years ago, while the Early Jurassic was even longer, between 174 million years ago and about 201 million years ago.
"The significance of this discovery is that both species have mandibular middle ears (MdME), and the morganucodontan-like species have new postdentary bone structures," study author Patricia Vickers-Rich from the Monash University School of Earth, Atmosphere and Environment, said in a statement. "This species is losing the load-bearing function of its articular-quadrate joint, whereas the shuotheriid species is showing characteristics suited for purely auditory function."
The Dianoconodon youngi fossil's jaw joints appear to have lost their load-bearing ability, while its mandibular inner ear seems to be better adapted for hearing. The bones of the Feredocodon chowi specimen—which lived later on—appear even more specialized for hearing. "Studying transitional stages in evolutionary history is crucial," said Vickers-Rich. "The fossils show incremental modifications that demonstrate the complex process of adaptation that resulted in the advanced hearing systems found in modern animals."
The Feredocodon chowi fossil also sheds light on the mysteries of the teeth of ancient shuotheriids, helping paleontologists figure out the ancient mammal family tree. These animals had a special basin-like structure in their molars not seen in modern mammals, leading them to be classified evolutionarily with a group of animals named australosphenidans, which includes modern monotremes like echidnas and platypuses.
However, this classification has long been contested by paleontologists.
"This unique tooth pattern has hindered our comprehension of shuotheriid relationships and the first steps in the evolution of mammaliaform species," Vickers-Rich said. Full article: https://www.newsweek.com/new-mammal-fossils-ears-teeth-1886471
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