ZUUL

Fossils from Montana's Judith River Formation were first noted by Lewis and Clark during their "Corps of Discovery" expedition in the early 1800s, and the first dinosaurian remains were found there by F. V. Hayden during a mapping mission for the U.S. Geological Survey in 1855. But despite being prospected almost continuously since then, relatively complete dinosaur discoveries in this area have been few and far between. That changed unexpectedly on May 16th, 2014.

While removing overburden from a potential Gorgosaurus specimen near Havre, Montana, a skid-steer loader operated by Theropoda Expeditions LLC struck an unexpected find: not the bones of a tyrannosaurid, but the tail club of an ankylosaurid. What emerged—encased within two enormous blocks, one tipping the scales at over 15 tons—was a stunningly complete skeleton, preserved upside down yet virtually untouched by erosion, including a fully articulated tail, an intact skull, rare traces of soft tissue such as skin impressions, and armour capped in keratin—the same tough protein found in human fingernails and hair.

The specimen, nicknamed "Sherman", was initially misidentified as a new species of Euoplocephalus, a familiar ankylosaurid from the Late Cretaceous of North America. However, detailed preparation revealed a suite of distinctive features: overlapping skull tiles (imbricated caputegulae) and pyramid-shaped ornamentation, long rear-pointing horns (elongated squamosals), and a previously unseen tail design. These traits set it apart from known taxa, prompting palaeontologists Victoria Arbour and David Evans to name a new genus and species in 2017—Zuul crurivastator, meaning "Zuul, destroyer of shins": the most complete ankylosaurid ever found in North America, and the first ankylosaurine specimen from anywhere with a complete skull and a tail club.

Measuring around six meters long and weighing over 2.5 tons, Zuul was a low-slung, heavily armored herbivore. Its tail club—stiffened by fused vertebrae and flanked by scooped spikes—was biomechanically capable of delivering powerful lateral blows. While no predator fossils from the Judith River Formation show confirmed shin injuries caused by ankylosaurid strikes, at least three Daspletosaurus specimens from other formations have been found with fractured fibulae. Though the cause remains uncertain, the location and nature of these injuries are consistent with the kind of trauma an ankylosaur tail could inflict—not just to shins, but to calves as well. More compelling evidence of tail use comes from Zuul itself: healed damage to its flank armour, especially near the hips, points to tail strikes from another ankylosaurid—likely during social contests over territory or mating rights.