Rare, 8.6" Fossil Dinosaur (Ankylosaurus) Side Spike - Montana

Ankylosaurus was the namesake of the Ankylosaurid family of dinosaurs to which it belonged, and one of the last ones to live before the Cretaceous-Paleogene extinction event 65 million years ago. Residing in western North America, Ankylosaurus was an herbivorous dinosaur with a low, squat body, a short neck with a square head, and a long tail ending with a large, bony club which it likely used for self-defense against predators like T.rex. Perhaps most notably, Ankylosaurus was one of the most heavily armored dinosaurs of all time. Ankylosaurs were known for their heavy bone armor all over the top half of their bodies, as well as bony knobs protruding all over their backs and face. Even their eyelids were protected against potential attack.

At adult size, these impenetrable behemoths measured about 25-30 feet and 4 to 8 tons. At that size, even an adult Tyrannosaurus would have had difficulty getting close enough to try and flip it to get at Ankylosaurus's less armored underbelly. Dinosaurs like Ankylosaurus prove indubitably that herbivores were just as impressive and dangerous as their carnivorous counterparts.

The Hell Creek Formation

Renowned for both its age and rich sedimentary layers, the Hell Creek Formation is one of the most intensively studied fossil-bearing regions on Earth. To date, scientists have documented 158 genera of animals and 64 genera of plants from its rocks, with new finds emerging regularly. Beyond iconic dinosaurs such as tyrannosaurs, ceratopsians, and hadrosaurs, the formation has produced an extraordinary array of life, including amphibians, reptiles, lizards, snakes, turtles, fish, sharks, birds, and early mammals. Together, these fossils provide the most complete picture of the ecosystems that thrived just before the Cretaceous–Paleogene extinction event.