World's oldest mammal ancestor ever discovered had 'saber teeth'

The narrative of life on Earth has been built upon billions of years of existence, with therapsids playing a crucial role in this evolutionary story.

These ancient creatures are the direct predecessors of one remarkable group: the mammals.

Mammals, relatively recent additions to the evolutionary timeline, trace their inception to nearly 200 million years ago, amidst the prolific era of dinosaurs.

However, even mammals have antecedents, all categorized under the collective term “therapsids.”

Understanding therapsids — the basics

Therapsids thrived during the Permian period, which was over 250 million years ago. They came in all shapes and sizes, from small, nimble hunters to larger, plant-eating giants.

What made therapsids special was their mix of reptile-like and mammal-like features, such as differentiated teeth and more advanced jaw structures, which set the stage for the evolution of true mammals later on.

For instance, therapsids had openings on the sides of their skulls to anchor jaw muscles, as well as structures in their jawbones that eventually evolved into the distinct middle ear bones found in mammals.

As time went on, therapsids started to dominate the land, filling niches that today’s mammals occupy.

Some therapsids even showed early signs of having warm-blooded metabolisms and better ways to regulate their body temperatures, which are key traits of mammals.

Unfortunately, most therapsids didn’t make it past the Permian-Triassic extinction event, the biggest mass extinction in Earth’s history.

However, a few lineages survived and eventually evolved into the diverse mammals we see today.

Gorgonopsians and saber teeth

In a recently published paper, scientists are buzzing about the find of a lifetime — an ancient therapsid fossil, potentially the most ancient of its kind, that hails from an era perhaps far older than any therapsid discovery thus far.

This fossil belongs to a group known as the “gorgonopsians,” and its features suggest something akin to a saber-toothed predator with a slightly canine touch.

The newly found fossil, yet to receive a species name, introduces an exciting anomaly into the therapsid fold.

Gorgonopsians, according to Ken Angielczyk, MacArthur Curator of Paleomammalogy at the Field Museum’s Negaunee Integrative Research Center, are closer relatives to mammals than any other living species we are aware of.

“They don’t have any modern descendants and, while they’re not our direct ancestors, they’re related to species that were our direct ancestors.”

Breaking age records

Prior to this discovery, the record for the oldest known gorgonopsian was set at approximately 265 million years.

The new fossil, however, has potentially pushed this benchmark back even further, dating back to somewhere between 270 and 280 million years ago.

“It is most likely the oldest gorgonopsian on the planet,” proclaims Josep Fortuny, a senior author of the study and head of the Computational Biomechanics and Evolution of Life History group at Spain’s Institut Català de Paleontologia Miquel Crusafont (ICP).

Surprising amount of bones

The surprising find was unearthed on the Mediterranean island of Mallorca, which is part of modern-day Spain.

During the age of the gorgonopsians, however, Mallorca was a strip of land nestled within the supercontinent of Pangea.

“The large number of bone remains is surprising. We have found everything from fragments of skull, vertebrae, and ribs to a very well-preserved femur,” explains Rafel Matamales, curator of the Museu Balear de Ciències Naturals (MUCBO | MBCN), research associate at the ICP, and first author of the study.

“In fact, when we started this excavation, we never thought we would find so many remains of an animal of this type in Mallorca.”

A glimpse into the past

These skeletal remnants have allowed scientists to piece together what this ancient beast might have looked like.

“If you saw this animal walking down the street, it would look a little bit like a medium-sized dog, maybe about the size of a husky, but it wouldn’t be quite right,” detailed Angielczyk.

“It didn’t have any fur, and it wouldn’t have had dog-like ears,” “But it’s the oldest animal scientists have ever found with long, blade-like canine teeth.”

The elongated, blade-like canine teeth were a distinct feature, suggesting it was likely a top predator in its ecosystem.

Therapsids and mammal evolution

The existence of this ancient gorgonopsian that predates its closest relatives by tens of millions of years, redefines when scientists believe therapsids first evolved.

This significant milestone also alters our understanding of the eventual emergence of mammals, shedding light on our own evolutionary history.

“Before the time of dinosaurs, there was an age of ancient mammal relatives. Most of those ancient mammal relatives looked really different from what we think of mammals looking like today,” acknowledges Angielczyk.

“But they were really diverse and played lots of different ecological roles. The discovery of this new fossil is another piece of the puzzle for how mammals evolved.”

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The full study was published in the journal Nature Communications.

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