Our ancestors in the age of dinosaurs

Published by Adrien - Tuesday, April 16, 2024 - Other Languages: FR, DE, ES, PT
Source: Nature & Nature

Fossil discoveries from the Jurassic period in China shed light on the evolution of mammals, especially regarding teeth, jaws, and ears.

New research revealing significant Jurassic-era fossils, offering new insights into mammalian evolution and the development of the middle ear in mammals. Reconstruction of Feredocodon chowi (right) and Dianoconodon youngi (left).
Credit: Chuang Zhao

An international team of paleontologists, led by the American Museum of Natural History and the Chinese Academy of Sciences, has unearthed Jurassic fossils providing insights into the early evolution of mammals. Published in the journal Nature, these findings could change how scientists view the early branches of the mammalian evolutionary tree.

The research highlights the shuotheriids, mouse-sized mammals with unique molars. These have been a subject of long debate and seem to be related to the australosphenidans, including present-day monotremes like the platypus. Two shuotheriid fossils, discovered well-preserved in Inner Mongolia and dating back 168 to 164 million years, exhibit molars similar to those of another extinct group, the docodontans. These specimens have been classified into a new genus and species, named Feredocodon chowi.

Reconstruction of the newly described species Feredocodon chowi.
Credit: Chuang Zhao

The second study focuses on the evolution of the middle ear in mammals, through fossilized skulls of Feredocodon chowi and a second newly identified species, Dianoconodon youngi, which lived between 201 to 184 million years ago. The middle ear of modern mammals, converting air vibrations into fluid undulations in the inner ear, is distinguished by its three bones, a characteristic unique to mammals.

The analysis of the older fossil (Dianoconodon youngi) reveals that one of its reptilian joints was beginning to lose its ability to handle chewing forces. The more recent specimen (Feredocodon chowi) already possessed a middle ear formed and adapted exclusively for hearing, illustrating a key stage in this transition.

Reconstruction of the newly described species Dianoconodon youngi.
Credit: Chuang Zhao

These findings provide compelling fossil evidence of the transition to the mammalian middle ear, enriching our understanding of the gradual evolution of this distinctive feature.
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