Kimbetopsalis simmonsae: Newly discovered mammal species survived dinosaur extinction

reconstruction of Kimbetopsalis simmonsae

Kimbetopsalis simmonsae discovered

Paleontologists recently found a species of mammal that survived the extinction of the dinosaurs and named it Kimbetopsalis simmonsae, meaning “Simmon’s cutting shears of Kimbeto Wash,” in honor of the scientist who found the fossils, the place where they were found, and the snipping front teeth of the beast.

The deadly asteroid almost six miles across struck the earth at several tens of thousands of miles per hour, producing a greater explosive force than a billion Hiroshima bombs and creating worldwide earthquakes and tsunamis. About the same time, huge lava flows in and around India (maybe also caused by the impact) filled the atmosphere with suffocating and poison gasses. Fires started by the impact and its ejecta and by the lava spread around the planet, filling the air with particulates and more gasses. Particles blocked the sun, cooling the world and cutting off photosynthesis for years. Over half of all life on Earth was wiped out.

Plants that were not destroyed in the initial cataclysm died from cold and lack of sunshine. Animal herbivores starved without plants to feed upon. Carnivores starved without herbivores to feed upon. Within probably a year, most life on earth had died. Before it was over, all non-avian dinosaurs and three quarters of earth’s other species were extinct.

It was not a good time to be alive, and most species made a swift exit from the global stage: Vegetation withered. Ocean life gasped for air and energy, then collapsed. Gone were the fearsome Tyrannosaurus, the winged Pterosaurs, the massive Triceratops with its three horns and bony neck frill. The dinosaurs’ 100 million-year reign had ended. And when the smoke cleared, a new hero had taken over.

Washington Post

That new “hero” was the mammal.

Kimbetopsalis simmonsae, the newly discovered species, was a plant-eating mammal that resembled a beaver. More specifically, it was a multituberculate, a superficially rodent-like order of extinct mammals named for the numerous cusps, or tubercles, found on their teeth. They lived another 30 million years after the extinction.

Those teeth may have been their secret of success in the wake of the mass-extinction. The anatomy of their jaws gave them “a grinding-focused chewing stroke,” according to the report. Together with their snipping incisor teeth, these allowed them to eat a large variety of whatever vegetation was available.

This particular species lived about 64.5 million years ago in what is now the San Juan Basin of northern New Mexico. Estimated at around three feet long and over 22 pounds. That’s quite large when one considers that most mammals living in the age of dinosaurs were about the size of a mouse.

The world had been wrecked. An asteroid impact in Mexico compounded by colossal volcanism in India 66 million years ago had killed about three-quarters of Earth’s species including the dinosaurs.

But relatively soon afterward, a plucky critter that looked like a beaver was thriving, exemplifying the resilience of the mammals that would arise from the margins of the animal kingdom to become Earth’s dominant land creatures.

Scientists on Monday announced the discovery in northwestern New Mexico’s badlands of the fossil remains of Kimbetopsalis simmonsae, a plant-eating, rodent-like mammal boasting buck-toothed incisors like a beaver that lived just a few hundred thousand years after the mass extinction, a blink of the eye in geological time.

Kimbetopsalis, estimated at 1 metre, would have been covered in fur and possessed large molar teeth with rows of cusps used to grind down plants.

Asked what someone’s impression of Kimbetopsalis might be, New Mexico Museum of Natural History and Science curator of paleontology Thomas Williamson said, “They would probably think something like, ‘Hey, look at that little beaver! Why doesn’t it have a flat tail?”

Dr Stephen Brusatte from the University of Edinburgh told how Carissa Raymond, a student on his team, found the fossils of Kimbetopsalis simmonsae while prospecting at a site in New Mexico. The Zoological Journal of the Linnean Society published it.

While Earth’s ecosystems struggled to recover from the catastrophe, New Mexico became a lush area of forests, rivers, streams and lakes. Kimbetopsalis grew from the size of a mouse to the size of a very large beaver over the course of just 500,000 years — a mere blink of an eye in evolutionary terms. It had a beaver’s broad face and chunky frame, but probably no paddle-like tail. It is known from a partial skull and parts of the upper jaws, including teeth still in their sockets.

Mammals originated from early dinosaurs.

 jaws of Kimbetopsalis simmonsae

Mammals had originated about the same time as the dinosaurs got their start; but nearly all of them remained very small until the dinosaurs were superseded by rodents. With the “terrible lizard” predators gone, they were finally free to grow larger without being eaten.

Multituberculates were one of evolution’s greatest success stories. That may seem odd to say now, being that they’ve been extinct for over 30 million years, but that’s why a Deep Time perspective is essential to comprehending Life. As New Mexico Museum of Natural History and Science paleontologist Thomas Williamson and colleagues write at the top of their latest paper on the beasts, multituberculates originated and thrived while the dinosaurs still gripped the world in their claws, survived the mass extinction at the end of the Cretaceous, and again proliferated during the “Age of Mammals” for tens of millions of years before finally expiring. And thanks to some pieces of skull found in northern New Mexico, Williamson and colleagues have identified one of the pioneering “multis” that evolved soon after the dinosaurs had global dominance wrested from them.

National Geographic (Phenomena:Laelaps)

The mass extinction not only killed all the dinosaurs except for the specific lineage that was already evolving into birds; it also devastated the world’s biodiversity. But it gave mammals an opportunity to quickly fill the niches left by the reptiles, and for a particular group of them to evolve into you and me.


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