Thespesius is an interesting dinosaur, but it’s considered dubious, meaning there is uncertainty about its classification. It lived during the Late Cretaceous period, around 66 million years ago.
The name Thespesius means “wondrous one.” It was first described by a paleontologist named Joseph Leidy in 1856, based on a few bones that were sent to him by another geologist named Ferdinand Vandeveer Hayden. The fossils came from what we now call the Lance Formation in South Dakota. The specific species identified is called Thespesius occidentalis, which means “western” in Latin.
The original fossils included two tail vertebrae and a toe bone. The size of these bones was impressive, which is why they were named “wondrous.”
For many years, the classification of Thespesius has been complicated. At one point, it was used to refer to various hadrosaurid dinosaurs that lived in North America during the same time period. Some scientists even thought Thespesius was just another name for a different dinosaur called Claosaurus.
As time went on, many researchers felt the original fossils of Thespesius were too incomplete to draw strong conclusions. They suggested that it might not be a valid dinosaur name anymore, leading to it being labeled a “nomen dubium,” which means an unclear name.
Thespesius also had a related species named Thespesius saskatchewanensis, but further studies showed that it was the same as another dinosaur called Edmontosaurus annectens. Another name associated with Thespesius is Thespesius edmontoni, which is now believed to be a synonym of Edmontosaurus regalis.
In summary, Thespesius is a fascinating dinosaur, but because of incomplete fossils and naming confusion, we can’t say much about it with certainty.