Extinct reptile fossil reveals the prehistoric origins of human teeth

BRISTOL, United Kingdom — An extinct reptile discovered by scientists may reveal the origins of specialized teeth in early humans, a new study explains. Researchers at the University of Bristol say this reptile species would later evolve into a mammal and laid the foundation for modern-day incisors, canines, and molars — which humans still possess today.

The team calls this “new” species Shashajaia. It’s one of the most primitive members of the Sphenacodontoidea reptile group, which includes mammal-like reptiles called therapsids. This is important because therapsids eventually evolved into mammals as well.

The study finds Shashajaia possessed an incredibly unique set of teeth for that time period, roughly 300 million years ago! These teeth set the animal apart from other synapsids, or the long lineage of animals that mammals belong to.

“The teeth show clear differentiation in shape between the front and back of the jaw, organized into distinct regions. This is the basic precursor of what mammals have today – incisors and canines up front, with molars in the back. This is the oldest record of such teeth in our evolutionary tree,” says Dr. Suresh Singh from the School of Earth Sciences in a university release.

Prehistoric teeth changed with the menu

reptile teeth evolution
(CREDIT: Dr. Suresh Singh)

Study authors say the unique arrangement of teeth in the Shashajaia fossil points to synapsids in the Late Carboniferous period already having canine-like teeth that modern mammals have now. During this period, scientists believe there were giant insects and more swampy rainforests around the globe.

However, as the climate on Earth changed, researchers say predators had to adapt as well. Around 300 million years ago, more arid and seasonal environments replaced Carboniferous wetlands. This also changed the types of prey living here, leading to the evolution of our synapsid ancestors — who developed more specialized teeth to catch and eat these animals.

“Canine-like teeth in small sphenacodonts like Shashajaia might have facilitated a fast, raptorial bite in riparian habitats where a mix of terrestrial and semi-aquatic prey could be found in abundance,” says lead author Dr. Adam Huttenlocker from the University of Southern California.

Valley of the Gods reveals more evolutionary clues

Study authors believe the new reptile is one of the oldest synapsids in history. Its official name, Shashajaia bermani, translates to “Berman’s bear heart.” The name honors paleontologist Dr. David Berman of the Carnegie Museum of Natural History and the local Navajo people of the fossil’s discovery site at the Bears Ears National Monument in Utah.

“The study is a testament to Dr. Berman who originally discovered the fossil site in 1989, and his decades of work on synapsids and other early tetrapods from the Bears Ears region of Utah which helped to justify the Bears Ears National Monument in 2016,” Dr. Singh explains.

Researchers note that this area, known as the Valley of the Gods, has been a gold mine for ancient fossils. Bears Ears National Monument is home to many fossils from the final stages of the Late Paleozoic Ice Ages.

“Understanding changes in its fossil assemblages through time will shed light on how climate change can drastically alter ecosystems in deep time, as well as in the present,” Dr. Huttenlocker adds.

The findings are published in the journal Royal Society Open Science.

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