This specimen is a half tail club fossil from an Ankylosaurus recovered on private land in the Hell Creek Formation. It is estimated to be 67,000,000 years old.

Pictured here is the posterior or front of the tail club with the cutting blade on the right edge. It is an example of one of the greatest defense mechanisms of all time—a powerful biological "sledgehammer" that could deter tyrannosaurs, raptors, or even rival ankylosaurs.

The cutting blade edge of the fossil also contains sections of fossilized skin. Underneath the fossil is the sutured side which was connected by muscle tendons to the other tail club.

This specimen ships with a black metal stand for display, though it is removable if you would like to study the item in hand. An individual certificate of authenticity will also accompany the specimen.

The Ankylosaurus is an iconic dinosaur and we are excited to offer such a complete section of its tail! This fossil is a magnificent, one-of-a-kind display piece that any collector would be proud to have.

"The armor are bones that form within the skin, just like crocodiles." ~ Ken Carpenter, Director USU Eastern Prehistoric Museum

Ankylosaurus was a dinosaur evolved for offense and defense, its body protected by thick osteoderm armor and its tail adorned with a club for attack.

The plates of an Ankylosaurus were not part of the skeleton, but rather formed within the skin. This type of growth is called an osteoderm. Osteoderms usually begin with small nodules of cartilage around which more dense material forms.

Osteoderms are found in many different and unrelated species from reptiles and amphibians to mammals, fish, and of course dinosaurs. They sometimes form fantastic structures such as the shells of the armadillo and glyptodon, or the tall, dorsal plates and tail spikes of Stegosaurus.

The dinosaurs' clubs could cripple a theropod, allowing the lumbering Ankylosaurus to escape, though a 2022 study suggests that these tails initially evolved for fighting other Ankylosaurs in competition over mates.

This study was based on an examination of the Zuul holotype, an ankylosaurid genus named for the demon from Ghostbusters. Injuries to the specimen are in line with damage from a tail club, not predation or disease, with blows falling on the dinosaur’s flanks, where an Ankylosaur's attack would likely land. These tails boasted tightly interlocked vertebrae on their insides and enlarged osteoderms on their outside, packing a powerful punch.

These conspecific duels would have likely been used as ritualized displays, the ankylosaurus vying over a mate. A similar case is found in the mammalian Glyptodonts, who also used their tails in such conspecific duels.

Evidence is not conclusive for this hypothesis but importantly other ankylosaurids did not evolve this feature, despite living alongside predators. With ankylosaurus, one sees that evolutionary adaptations often come from within a genus itself, not from outside pressures.

Another interesting aspect of Ankylosaurus's evolution is a progressive widening of the "hindgut" over time. The hindgut is broadly referred to as the lower part of the digestive system. In certain animals, this feature is highly developed, allowing for the extraction of nutrients from cellulose via microbial fermentation.

An increase in the size of this feature over time might speak specifically to competitive pressure between different herbivorous dinosaur species such as the ceratopsids and hadrosaurids.