11.1" Fossil Juvenile Ankylosaur (Ankylosaurus) Fibula - Montana

This is a fibula (lower lateral leg) bone of Ankylosaurus magniventris, a species of ankylosaurid that thrived during Late Cretaceous of North America. It was collected from the Hell Creek Formation on a private lease in Dawson County, Montana and likely comes from a juvenile ankylosaur. Much of the bone is in good condition, though the diaphysis is compressed which resulted in some fragmentation.

The bone measures about 11.1" long, 2.4" wide (proximal end), and 2.4" wide (distal end).

There is touchup and gap fill restoration through the diaphysis of the bone where it required some stabilization due to the fragmenting of the bone, as a result of geologic compression. The proximal and distal ends, while weathered, are still overall intact.

An artists reconstruction of an Ankylosaur.  Image Public Domain by Mariana Ruiz
An artists reconstruction of an Ankylosaur. Image Public Domain by Mariana Ruiz

Ankylosaurs were herbivorous dinosaurs that lived during the Cretaceous (65 - 68 million years ago). As the evolution of Ankylosaurus progressed, they developed bony armor that covered their bodies in the form of plates, scutes and spikes, with some even developing armor on their eyelids. While their armor and bone shattering tail club are thought to have been used for defensive purposes against predators such as Tyrannosaurus, it's possible that some of the armor on their head may have been used for display. Adult Ankylosaurs are believed to have reached up to 25 feet in length and a weight of 3.3 tons!
Ankylosaurus magniventris
Dawson County, Montana
Hell Creek Formation
11.1" long
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