Discovery of Jurassic fossils leads to new theory of mammals

Two new species of early mammals from the Jurassic period have been discovered, revealing the secrets of how we got our ears.

two New leaves In the magazine nature It indicates that the two fossilized specimens resemble a modern weasel and are ancient mammalian species.

It is hoped that these new species will give paleontologists an insight into how the mammalian middle ear evolved from the jaw joints, millions of years ago.

One of the new species is a type of ancient mammal called the Shuthrid, which was discovered at a Middle Jurassic fossil site in Mongolia, and has been named Viridocodon choy. And other new types Dyanoconodon jungiIt was found in the Early Jurassic Lufeng Biota in China and closely resembles a species of ancient mammal called Morganocodon.

Both of these new species had special characteristics in their jaws and ears suggesting that they served as waypoints in evolution as the jaw joint was slowly evolving toward becoming specialized for use in hearing. The Middle Jurassic extended from about 174 to 163.5 million years ago, while the Early Jurassic was longer, between 174 million years ago and about 201 million years ago.

Study author Patricia Vickers-Rich, from Monash University's School of Earth, Atmosphere and Environment, said: “The importance of this discovery is that both species have mandibular mesial ears (MdME), and the Morganocodontan-like species have new skeletons after growth.” In the current situation. “This species loses the carrying function of its square articular joint, whereas shuotheriid species show characteristics suitable for a purely auditory function.”

the Dyanoconodon jungi The fossil's jaw joints appear to have lost their ability to bear loads, while its maxillary inner ear appears to be better adapted for hearing. bones Viridocodon choy Later living specimens appear to be more specialized in hearing.

Thus, this new species represents the intermediate period between the jaw joint used for eating and hearing, allowing paleontologists to better understand how our ears got to where they are today.

“Studying transitions in evolutionary history is crucial,” Vickers-Rich said. “The fossils show gradual modifications that illustrate the complex process of adaptation that gave rise to the advanced hearing systems found in modern animals.”

the Viridocodon choy The fossil also sheds light on the secrets of ancient Chauthyrids' teeth, helping paleontologists uncover the ancient mammalian family tree. These animals had a special pelvis-like structure in their molars not seen in modern mammals, which led to them being classified phylogenetically with a group of animals called Australosphenidans, which includes modern monotremes such as echidnas and platypuses.

However, paleontologists have long disputed this classification.

“This unique tooth pattern has hampered our understanding of the chowdial relationships and the first steps in the evolution of mammalian species,” Vickers-Rich said.

Now, the new species of Chauthrididae, Viridocodon choyIt reveals that these animals have teeth that are most similar to the molar pattern of a group of different animals – the docodontids.

“Our study questions current theories and provides a new perspective on the evolutionary history of mammalian forms,” Vickers-Rich said. “We provide vital insights into the evolutionary relationships and evolutionary trajectories of chowthyridids, which were unknown until recent discoveries in China, by explaining their complex tooth shapes and occlusal patterns.”

Therefore, chautheridids are evolutionarily separate from ausktribosphenids and should be grouped more closely to docodontans.

“The study confirms the presence of a large variety of tooth morphology in early mammalian forms, suggesting unique environmental adaptations throughout evolutionary development within mammals,” Vickers-Rich said.

“Dental modifications such as transverse enlargement of posterior teeth, rearrangement of cusps, and even rotation indicate several ecological niches inhabited by early mammals.”

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