Description and Classification

Zuul was a heavily armored dinosaur, measuring about 6 meters (20 feet) in length and weighing around 2.5 metric tons (2.75 short tons). Like other ankylosaurids, its body was covered in bony plates called osteoderms, which acted like a suit of armor. Some of these osteoderms had prominent keels or ridges.

The head of Zuul was short, wide, and triangular when viewed from above, and it was also heavily armored. The most striking features on its skull were the large, horn-like squamosal bones that projected backwards from the corners of its skull, and smaller quadratojugal horns below them. These are the features that reminded scientists of the “Ghostbusters” character. The top of its snout and skull were covered with many small, flat or slightly bumpy bony plates called caputegulae. Its tail was long and stiffened towards the end, ending in a massive, bony club, which was likely used as a defensive weapon.

Zuul belongs to the family Ankylosauridae, a group of “armored dinosaurs” within the larger group Ornithischia. Ankylosaurids are known for their extensive body armor and powerful tail clubs. Within Ankylosauridae, Zuul is classified in the subfamily Ankylosaurinae. It is considered to be closely related to other North American ankylosaurids such as Ankylosaurus and Euoplocephalus, sharing many features with them but also possessing unique characteristics.

Distinguishing Features

Zuul can be identified by several unique characteristics:

• Large, pointed squamosal horns that extend backward and slightly outward from the rear corners of the skull.
• A covering of numerous, mostly flat or gently domed caputegulae (bony head tiles) on the snout and the top of the skull, unlike the more pyramid-shaped ones seen in some other ankylosaurs.
• An exceptionally well-preserved tail club, including the bony knob and the “handle” (the stiffened part of the tail leading to the club). Pointed, blade-like osteoderms ran along the sides of the tail leading up to the club.
• The species name crurivastator highlights its “destroyer of shins” nickname, suggesting its tail club was effectively used to strike the legs of attacking predators like Gorgosaurus.
• Its fossil is one of the most complete ankylosaur skeletons ever found in North America, remarkably including preserved impressions of skin scales and the keratinous sheaths that covered its bony spikes and plates.

Paleoenvironment and Diet

Zuul lived in what is now Montana during the Campanian age of the Late Cretaceous. The environment of the Judith River Formation at that time was a coastal plain with rivers, swamps, and forests, similar to parts of modern-day Louisiana. The climate was warm and seasonal, with both wet and dry periods. This lush environment supported a rich diversity of life.

Zuul shared its habitat with many other dinosaurs. These included duck-billed hadrosaurs like Brachylophosaurus, horned ceratopsians such as Judiceratops and Spiclypeus, and large predatory tyrannosaurids like Daspletosaurus and Gorgosaurus, which would have been a threat to Zuul. Other creatures like smaller theropods, different types of ankylosaurs, crocodiles, turtles, and fish also lived in this ecosystem.

As an ankylosaurid, Zuul was a herbivore. Its broad snout and small, leaf-shaped teeth suggest it was a low-browser, feeding on ferns, cycads, and other low-growing plants. It likely wasn’t very selective, consuming a variety of vegetation close to the ground.

Significance and Ongoing Research

The discovery of Zuul is highly significant because its fossil specimen is incredibly complete. This allows scientists to learn much more about the anatomy and appearance of ankylosaurid dinosaurs. The preservation of soft tissues, such as skin impressions and the keratinous (fingernail-like material) coverings of its osteoderms, is especially rare and valuable. These findings provide direct evidence of how these armored dinosaurs looked in life.

Zuul also helps paleontologists better understand the diversity of ankylosaurs that lived in North America during the Late Cretaceous. Its unique features help distinguish it from relatives like Ankylosaurus. The popular culture reference in its name also helped capture public imagination and interest in paleontology.

Ongoing research on Zuul continues to yield new information. Scientists are further studying the preserved soft tissues to understand their structure and function. Detailed analysis of its skeleton, particularly its formidable tail club, is helping to understand how it moved and defended itself. Researchers are also working to clarify its exact relationships with other ankylosaurids. The specimen even shows signs of injuries on its tail, possibly from battles, which offers insights into its behavior and interactions with predators. The study of Zuul provides a fantastic window into the world of these amazing armored dinosaurs.