New Jurassic fossils document evolutionary changes from the jaw joint to the middle ear of mammals | Trending Viral hub

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Two new species from the Jurassic: those similar to morganucodontans Dianoconodon youngi and the pseudotribosphenic shuotheriid Feredocodon chowi — offer key information about the evolutionary change from the bones of the jaw joint to those of the middle ear in early mammals.

Dianoconodon youngi.  Image credit: Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences.

Dianoconodon youngi. Image credit: Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences.

Both Dianoconodon youngi and Feredocodon chowi He lived in China more than 150 million years ago (Jurassic period).

The type specimens Feredocodon chowi They were found in the town of Dauhugou in the Ningchen Basin in Inner Mongolia.

He Dianoconodon youngi Fossils were discovered at the Heiguopeng locality of the Lufeng Formation in Yunnan province.

The specimens display notable physical characteristics, suggesting a gradual shift in jaw joint function toward specialization in hearing.

“The importance of this discovery is that both species have mandibular middle ears, and the morganucodontan-like species have new postdentary bone structures,” said Professor Patricia Vickers-Rich, a researcher at Monash University and Museums Victoria.

Dianoconodon youngi is losing the load-bearing function of his quadrate-articular joint, while Feredocodon chowi shows characteristics suitable for purely auditory function.”

Fossils provide important evidence of transitional phases in the evolution of the mammalian middle ear.

A progressive decrease in the load-bearing capacity of the main jaw joint is causing the separation of the postdentary bones from the dentary.

The findings revise previous ideas about the original state of the mammalian middle ear.

They improve the understanding of mammalian development by resolving questions related to the evolution of the middle ear in close relatives of mammals.

“Studying transitional stages in evolutionary history is crucial,” said Professor Vickers-Rich.

“The fossils show incremental modifications that demonstrate the complex adaptive process that resulted in the advanced auditory systems found in modern animals.”

The results also provide information about how tissues such as ossified Meckel’s cartilage It helped in the change from jaw movement to hearing ability.

Paleontologists can follow the constant evolution of the middle ear ossicles by studying features such as the medial displacement of the quadrate relative to the articular.

“The newly recognized well-preserved fossils from the Jurassic of China significantly clarify how one of the most remarkable transitions in vertebrate history occurred,” said Dr Thomas Rich, also from Monash University and Museums Victoria.

“That is, the transformation of many of the multiple bones in the lower jaw of reptiles became tiny bones in the middle ear of mammals.”

He study appears today in the magazine Nature.

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F. Mao et al. Fossils document evolutionary changes from the jaw joint to the middle ear of mammals. Nature, published online April 3, 2024; doi:10.1038/s41586-024-07235-0

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