Mini T-rex Struck Fear Into Hearts of Jurassic Proto-rabbits Everywhere

The Suskityrannus probably weighed no more than a fat Labrador, and could have easily fit inside the skull of a true T-rex

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This March 28, 2019 photo provided by Virginia Tech shows the fossilized bones of Suskityrannus hazelae.
This March 28, 2019 photo provided by Virginia Tech shows the fossilized bones of Suskityrannus hazelae.Credit: Erin Williams/Virginia Tech via AP
Ruth Schuster
Ruth Schuster
Ruth Schuster
Ruth Schuster

Its three-toed feet made the ground shake and its breath was, presumably, foul enough to kill you on the spot, if you were a primordial rabbit. Otherwise the Jurassic set was probably not too impressed with Suskityrannus hazelae, a pint-sized relative of the dread Tyrannosaurus rex that lived in what is today western North America 92 million years ago.

Its discovery was announced Monday in Nature Ecology & Evolution.

Suskityrannus is the second species of teacup tyrannosaur to be found this year, the first being the wee Moros intrepidus, the “harbinger of doom” – to early mammals and small lizards, maybe. It was slightly earlier, living about 96 million years ago, in Utah.

Artist's impression of SuskityrannusCredit: Virginia Tech, Andrey Atuchin

Paleontologists, on the other hand, are exhilarated with the discovery of the two mini-rexes, which fall roughly in the middle of tyrannosaurian evolution and shed light on how these giants of the prehistoric scene arose.

Sterling Nesbitt and fossil remains of Suskityrannus hazelaeCredit: Photo by Erin Williams / Virgini

The earliest known tyrannosaurian (which doesn’t mean it was necessarily the ancestor of any of the ensuing ones) is the Jurassic predator Proceratosaurus, which was discovered lying on a shelf in the Natural History Museum in London in 2010. It was about the same size as Suskityrannus and lived 165 million years ago.

Now we have small rexes discovered from about 96 and 92 million years ago, predating the giants that ruled North America from 80 million years ago until their near-total extinction 66 million years ago.

Standing three feet in height, at the hip, and nine feet in length, Suskityrannus is estimated to have weighed no more than a fat Labrador, somewhere from 45 to 90 pounds.

Credit: Photo by Erin Williams / Virgini

A true T-rex weighed about 18,000 pounds, give or take, which is about nine tons. The even earlier mini-rex, Moros intrepidus, also measured about three or four feet tall.

To drive home the point of their size, either of the bantamweight rexes could have fit inside the skull of a true T-rex. Yet the Suskityrannus bones that were found were not of a baby, though it may still have been a juvenile. The researchers found remains from two skeletons, and at least one was at least three years old when it passed on from this vale of tears, based on its bone rings, which are akin to tree rings.

Actually the researchers found two specimens of Suskityrannuses. How big the adult would have been is a matter for speculation and the paleontologists don’t go there, but believe it was on the small end of the tyrannosaurus scale.

Suskityrannus was also clearly a predator, like its bigger and later cousin. No herbivore has fangs and powerful jaws like that.

An artistic rendering of Moros intrepidus may have looked. Or not.Credit: Jorge Gonzalez

Regarding the clade’s dining habits, in 2013 an assiduous team of paleontologists noted the lack of solid evidence for exactly how the T-rex fed, and went to find some. Did it scavenge? Did it hunt? It hunted, concluded the team, based on their discovery of a T-rex tooth crown embedded in a hadrosaurian vertebrae, surrounded by healed bone growth. Ergo, the hadrosaur got bitten in the back but survived for enough time afterward to heal. The T-rex is very unlikely to think it was scavenging a dead hadrosaur if it was kicking and screaming.

That doesn’t prove that the Suskityrannus and its cousin in miniature rexdom, the Moros, also hunted rather than scavenged, but it is indicative. Potential prey could have included the small nocturnal mammals that existed during the dinosaurian age, a family that only came into their own when the reign of the “terrible lizards” had all but ended.

An artist's rendering of how Suskityrannus hazelae may have looked, inside.Credit: Virginia Tech

The name Suskityrannus hazelae is based on suski, the Zuni Native American tribe’s word for coyote, the Latin word tyrannus, meaning king, and the “hazelae” is for Hazel Wolfe, who funded much fossil exploration in the Zuni Basin.

Classification of a new species of any kind, let alone one dead for tens of millions of years, is a hairy issue. Taxonomy is somewhere between a science and a war zone, and the classifier has to defend the thesis that the animal was truly unknown, and can be distinguished from all other near species.

In this case, the paper, by Sterling Nesbitt of Virginia Tech et al, argues that Suskityrannus differs in the shape of its teeth, the front part of its upper palate, the features of its vertebrae and more. Like its cousins, the scientists believe it would have had a long, low snout when seen in profile.

Tickle it purple

Precious few fossils can be found for the period from about 100 to 80 million years ago: The present paper speculates that it may have been a time of intense climate change, leading to extreme sea-level rise. Animals living by the coasts would not have been preserved for the fossil record.

Yet it was during this black hole in the paleontological record that the herbivores grew into giants, and tyrannosaurs morphed from small, gracile hunters in the Jurassic into monster apex predators in the Cretaceous and in Hollywood.

Suskityrannus has a much more slender skull and foot than its later and larger cousins, the great and mighty Tyrannosaurus rex, the researchers say. But carrying on from the Proceratosaurus, they all shared roughly the same body plan – under the skin, at least.

Two questions have to remain open for now. One is whether the Suskityrannus had oddly short arms like its later relative. They do not purport to know. They didn’t find its arms. Maybe it did, maybe it didn’t, but partial hand claws were found, and they were indeed small relative to the rest of the beast. So probably yes, it also had small arms, the researchers think.

Fossil remains of Suskityrannus hazelaeCredit: Photo by Erin Williams / Virgini

The other is what it looked like. Regarding its appearance, one has to wonder. When researchers reported finding a “teacup T-rex” in Utah this February, some artists depicted it with a purple mohawk of feathers that would slay in Tel Aviv, where that hairdo seems to be undying in popularity.

Paleontologists are starting to think that being feathered was the baseline dinosaurian condition and that the giants lost their feathers (though they may have been downy as infants) or retained a ring of feathers around their ankles.

There had even been some pretty wild speculation over whether the great and dreadful T-rex itself sported a coat of feathers and what color or colors they might have been. One proposal looks positively Trumpian.

However, findings of fossil skin indicate: The T-rex was not feathered, at least not on much of its body. Sorry. None of the giant tyrannosaur species (Albertosaurus, Daspletosaurus, Gorgosaurus and Tarbosaurus) were feathered, at least not extensively. Their skin was lizard-like, other scientists reported in 2017 in Biology Letters.

They further speculated that the loss of body covering wasn’t a matter of the paleoclimate, but of gigantism: It can be hard to cool enormous body mass and body covering, whether hair or feathers, doesn’t help.

Which brings us back to the wee one reported this week, which by all the above criteria could well have been feathered. But might it have had a violet crest?

Fascinating work has been done on deducing color in fossil feathers from a being that died millions, tens of millions or hundreds of millions of years ago based on fossil melanosomes that look like contemporary melanosomes. Also, therapods, of which the T-rex was one, evolved into birds, some of which definitely sport flamboyantly colored crests and other feathers.

Further to their avian future, a new theory published in PLOS Computational Biology just this week even suggested that dinosaurs evolved the ability to fly rather passively – as a result of its early wings flapping as it raced along the ground. That study was based on another very small dinosaur, Caudipteryx, which couldn’t lift off the ground but could, it seems, zip along up to eight meters a second, claim Jing-Shan Zhao of Tsinghua University, Beijing, and his colleagues. That’s not bad for a beast the size of a turkey.



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