Scientists trace the earliest evolution of human teeth to ancient species of reptiles

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The discovery of a 300 million year old extinct reptile has provided insight into the evolution of the predatory nature of mammals.

A study conducted by researchers at the University of Bristol and published in the Royal Society Open Science found that the teeth of the now-known extinct species known as Shashajaia laid the foundation for the incisors, canines and molars. that all mammals, including humans, now have. .

Dr Suresh A. Singh, postdoctoral research associate in the Department of Earth Sciences at the University of Bristol and co-author of the study, said News week that Shashajaia is at or near the base of the therapsid evolutionary tree “and therefore belongs to our own evolutionary lineage as we descend from the therapsids”.

An extinct species of reptile 300 million years ago has offered insight into the evolution of mammalian teeth. This graphic gives an overview of history, including the work of Dr. David Berman over a 50-year period.
Dr Suresh A. Singh

“Shashajaia seems to show that his branch of synapsids had evolved dental differentiation [heterodonty]“It was passed down to their descendants and subsequent species have built on these basic adaptations, which ultimately resulted in the incisors, canines and molars that we have in the mouth,” Singh said.

According to Singh, the study began thanks to his colleague, Dr Adam Huttenlocker, who discovered the fossil during fieldwork in the summer of 2019. He is described as an “expert” on synapsids, or mammals and their extinct relatives.

“Adam came to see me in the summer of 2020 as I was finishing my PhD because my specialty is studying the major evolutionary and ecologic patterns of several different animal groups over time,” said Singh. “I studied the biomechanics of the synapsid jaw and Adam knew I had the larger data and analytical knowledge he needed to better understand and highlight the importance of new species in the larger context of the ‘evolution of synapsids. “

Huttenlocker, assistant professor of integrative clinical anatomical sciences at the University of Southern California and lead author of the study, could see from the anatomy that Shashajaia had a clearly defined canine-like tooth, distinct from other teeth in before.

This is typical of the more advanced synapsids known as therapsids, or “mammalian-like reptiles,” Singh said, although this has never been seen before in a non-therapsid synapsid. When the fossil was fully excavated, it was revealed that the teeth on the back of the jaw were stockier as well.

“Canine-like teeth in small sphenacodontids like Shashajaia could have facilitated a rapid raptor bite in riparian habitats where a mixture of terrestrial and semi-aquatic prey could be found in abundance,” Huttenlocker said.

Singh said paleontologists have long believed that therapsids evolved and separated from the evolutionary tree of other synapsids around 300 million years ago, based on the evolution of their closest relatives, the sphenacodontids. , animals like the famous sailing Dimetrodon.

However, he said, the oldest therapsid fossils date from around 270 million years ago “so there is a big void in the fossil record.”

Shashajaia was discovered in the summer of 2019 at a fossil site in the valley of
the Gods, Utah — a site discovered in 1989 by Dr. David Berman, known for his work with the Carnegie Museum of Natural History.

The full name of the new species is Shashajaia bermani, meaning “Berman’s Bear Heart” in honor of Berman and the local Navajo people at the discovery site.

“Dr. Berman has led numerous excavations in the Bears Ears area of ​​southern Utah, which is why we decided to name the new species and its extraordinary 51-year career studying these early land animals, ”Singh said. “This area has generated a lot of interest over the years from paleontologists, especially those working on early tetrapods, as the rocks here archive the later stages of the Upper Paleozoic Ice Age. Can drastically alter ecosystems. in distant time, as well as in the present. “

It is not unusual for humans to share a common ancestry with reptiles due to millions of years of evolutionary traits that become advantageous or disadvantageous, ”Singh said. was remarkable. “

“For me, the most important discovery is that we are now filling the void in our evolutionary tree,” he said. “We now know that we evolved from something that probably looked a lot like Shashajaia. The comparative analytical part of the study tells us more about our origins; our first ancestors were eking [out] a life as a small predator and one of the hallmarks of mammals, heterodont teeth, likely evolved as a way to improve prey capture for these small carnivores. “


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