Stygiomurus

Stygiomurus is a genus of pachycephalosaurid dinosaur that lived during the Late Cretaceous period. The name Stygiomurus means "Styx tail" in reference to the spikes on its tail and the mythological river Styx. This dinosaur is known from fossil remains found in the Hell Creek Formation of Montana, USA. It is characterized by a distinctive cranial dome and a series of spikes projecting from the back of its skull and along its tail.

Stygiomurus is estimated to have been a medium-sized dinosaur, with adults reaching lengths of around 4 to 5 meters. Like other pachycephalosaurs, it is believed to have been herbivorous, likely feeding on low-lying vegetation. The prominent cranial dome and tail spikes have led to various hypotheses regarding their function. They may have been used for defense against predators, for display, or in intraspecific combat, similar to how modern-day bighorn sheep use their horns.

The genus Stygiomurus was first described in 2002 based on a partial skeleton. For a long time, it was considered a valid genus, distinct from other pachycephalosaurs. However, more recent research has questioned its distinctiveness. Some paleontologists now consider Stygiomurus to be a junior synonym of Pachycephalosaurus, suggesting that the features attributed to Stygiomurus might represent variations within the Pachycephalosaurus genus or possibly an immature individual. Further fossil discoveries and detailed analyses are needed to definitively resolve the taxonomic status of Stygiomurus.