Extinct reptile discovery reveals earliest origins of human teeth, study
finds

Date:
December 21, 2021
Source:
University of Bristol
Summary:
A new extinct reptile species has shed light on how our earliest
ancestors became top predators by modifying their teeth in response
to environmental instability around 300 million years ago.



FULL STORY ==========================================================================
A new extinct reptile species has shed light on how our earliest ancestors became top predators by modifying their teeth in response to environmental instability around 300 million years ago.


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In findings published in Royal Society Open Science, researchers at the University of Bristol have discovered that this evolutionary adaptation
laid the foundations for the incisor, canine and molar teeth that all
mammals - - including humans -- possess today.

Shashajaia is one of the most primitive members of a group called the Sphenacodontoidea, which includes the famous sail-backed Dimetrodon,
and mammal-like reptiles known as therapsids, which eventually evolved
into mammals. It is remarkable for its age and anatomy, possessing
a very unique set of teeth that set it apart from other synapsids --
meaning the animal lineage that mammals belong to -- of the time.

Dr Suresh Singh of the School of Earth Sciences explained: "The teeth
show clear differentiation in shape between the front and back of the
jaw, organised 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." The novel dentition of Shashajaiademonstratesthat
large, canine-like differentiated teeth were present in synapsids by
the Late Carboniferous period -- a time famous for giant insects and
the global swampy rainforests that produced much of our coal deposits.

By analytically comparing the tooth variation observed in Shashajaiawith
other synapsids, the study suggests that distinctive, specialised teeth
likely emerged in our synapsid ancestors as a predatory adaptation to
help them catch prey at a time when global climate change approximately
300 million years ago saw once-prevalent Carboniferous wetlands replaced
by more arid, seasonal environments. These new, more changeable conditions brought a change in the availability and diversity of prey.

Lead author Dr Adam Huttenlocker of the University of Southern California
said: "Canine-like teeth in small sphenacodonts like Shashajaiamight
have facilitated a fast, raptorial bite in riparian habitats where a
mix of terrestrial and semi-aquatic prey could be found in abundance."
The new reptile is one of the oldest synapsids. It was named "Shashajaia bermani," which translates as Berman's bear heart, to honour the 51-year
career of veteran palaeontologist, Dr David Berman of the Carnegie Museum
of Natural History, as well as the local Navajo people of the discovery
site within the Bears Ears National Monument, Utah.

Dr Singh said: "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." The site
is located within an area known as the Valley of the Gods and is of huge importance to palaeontologists.

"The Monument archives the final stages of the Late Paleozoic Ice Ages,
so 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," added Dr Huttenlocker.

========================================================================== Story Source: Materials provided by University_of_Bristol. Note: Content
may be edited for style and length.


========================================================================== Related Multimedia:
* Shashajaia_jaw_and_infographic_showing_differentiated_teeth ========================================================================== Journal Reference:
1. Adam K. Huttenlocker, Suresh A. Singh, Amy C. Henrici, Stuart
S. Sumida.

A Carboniferous synapsid with caniniform teeth and a reappraisal of
mandibular size-shape heterodonty in the origin of mammals. Royal
Society Open Science, 2021; 8 (12) DOI: 10.1098/rsos.211237 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211221102729.htm

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