Early Giant Tyrannosaur Fossil Found in New Mexico

A fossilized shinbone unearthed in northwestern New Mexico decades ago belongs to a massive tyrannosaur that lived about 74 million years ago, researchers reported in a study published Thursday. The bone, from a predator potentially related to Tyrannosaurus rex, suggests that giant members of the tyrannosaur family evolved several million years earlier than previously thought.

The tibia, or shinbone, measures about 3.2 feet long and 5 inches wide. Discovered in the 1970s by students from the University of New Mexico in the remote Bisti/De-Na-Zin Wilderness within the Kirtland Formation's Hunter Wash layer, it remained largely unexamined until a recent analysis by an international team of paleontologists. Lead author Nick Longrich of the University of Bath in England, along with co-authors Anthony Fiorillo and Spencer Lucas from the New Mexico Museum of Natural History and Science, determined its age through isotopic analysis of nearby volcanic ash, confirming it dates to the Late Campanian stage of the Late Cretaceous period.

Based on comparisons to the tibia of Sue, the largest and most complete T. rex specimen at Chicago's Field Museum, the New Mexico bone is roughly 84...