America’s Most Complete Armored Dinosaur, Soft Tissues Intact, Found in Montana

The fossil of an armored dinosaur unearthed in Montana is the most complete ever found in North America, paleontologists say, and it’s the first anywhere to be found with a complete skull and tail.

The animal belonged to a group of extinct dinosaurs known as ankylosaurs — stout, stocky herbivores that cast a distinctive silhouette, with spiky skulls, backs cladded with armor-like scales, and tails tipped with bony growths that could be wielded like clubs.

These dinosaurs are known for their variety of strange and amazing physical features, but never have so many been seen in a single specimen until now.

Finding a complete skull and tail intact, along with a host of well-preserved soft tissues, may illuminate the physiology and evolution of these unusual animals, said Drs. Victoria Arbour and David Evans of the Royal Ontario Museum, who reported the find.

“The new specimen … is the most complete ankylosaurid ever found in North America, making it a key reference skeleton for interpreting more fragmentary specimens,” the researchers write, in the new issue of Royal Society Open Science.

“Notably, it preserves both a complete skull and tail club, two of the most taxonomically informative parts of the ankylosaurine skeleton, yet which are rarely preserved in the same skeleton.”

Skull of Zuul crurivastator, the newly identified species of ankylosaur discovered in Montana. (Photo by Brian Boyle © Royal Ontario Museum)

The dinosaur was discovered accidentally in 2014 by a for-profit fossil hunting company near the town of Havre, in north-central Montana.

The site is near the heart of the Judith River Formation, the bone-rich remains of a boggy swampland where an interior seaway once crept into the Northern Plains.

(See last year’s dinosaur find from the Judith: “‘Audacious’ New Species of Horned Dinosaur Discovered in Montana“)

The firm was excavating the scattered remains of a tyrannosaur in a dense bed of bones dating back some 75 million years, when an earth-moving machine uncovered the tail club of the ankylosaur.

Researchers quickly recognized how complete and exceptionally well preserved the fossil was, and in time determined that the specimen represented an entirely new species to science.

Owing to its fearsome appearance, the researchers named the new genus Zuul, after the monster in 1984’s Ghostbusters (technically, the Gatekeeper of Gozer, for you fans).

In addition to its completeness, the specimen is remarkable because of its fossilized soft tissues — that is, the networks of tissues that surround and support major organ systems, like muscles, tendons, ligaments, and connective tissue.

In the case of Zuul, tendons are clearly visible along the length of its tail — which, at 206 centimeters, or 6.75 feet, long, is the longest ankylosaur tail ever found.

The tail also revealed several patches of skin impressions, casts of the dinosaur’s skin left in the surrounding sandy rock.

And along the torso the researchers found fossilized osteoderms, bony growths in the skin that formed its spiky back.

Several of these features were covered in a dark film that the experts believe is keratin, the same protein that forms the scutes on a crocodile as well as your hair and nails.

The keratin sheaths on some of the spikes were found to occur in layers, creating a texture much like those found in cows’ horns, they note.

The knob of bone forming the club-like tip of the tail in Zuul crurivastator. (Photo by Brian Boyle © Royal Ontario Museum)

“These features make the holotype of [Zuul] a critical specimen for interpreting other … ankylosaurine remains, given that osteoderms typically dissociate from the rest of the skeleton after death, and will be important for understanding the evolution of dermal and epidermal structures in these unusual armoured vertebrates,” the pair writes.

In fact, Zuul’s state of preservation has allowed the researchers to estimate the animal’s evolutionary relationships to other armored dinos.

For instance, the scaly features around its nose and eyes are six-sided, like those found on Euoplocephalus, an ankylosaur found in Canada, and on Ziapelta, a genus that Arbour and her colleagues recently unearthed in New Mexico.

(Read about Ziapelta’s discovery: “Spiky, Scaly New Species of Ankylosaur Discovered in New Mexico“)

But other features, like the horns on the top and back of its skull, grew in different directions or had different shapes than those other animals.

Likewise, the bony knobs on its tail, and the flattened shape of its club, are distinctive.

The new ankylosaur Zuul crurivastator compared to an African elephant for scale. (Graphic by Danielle Dufault © Royal Ontario Museum)

But many of Zuul’s cousins appear close together, both geographically and chronologically, the researchers note, so it may be that the ankylosuars of the American West evolved rapidly and diverged from each other quickly.

“The occurrence of [Zuul] from the upper Judith River Formation fills a gap in the ankylosaurine stratigraphic and geographical record in North America, and further highlights that Campanian ankylosaurines were undergoing rapid evolution,” Arbour and Davis write.

And, they add, Zuul is surely not the only fantastic beast that’s been waiting to be found in northern Montana.

“The excellent preservation of ROM 75860 [the specimen] and the abundant diversity represented elsewhere in the same quarry highlight the potential for significant new fossil discoveries in the upper Judith River Formation and emphasize the need for continued work in this historically significant geological unit,” they write.

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