Stygimoloch’s tough, bony skull was thought to have protected its brain during its amazing headbutting fights. This hypothesis has been disputed in recent years.
Stygimoloch lived in herds and grazed in woodland areas. It had short front legs, but far longer back legs. It also had a lengthy tail which it held level with its body when running. On its head were prominent horns. These were originally thought to have functioned solely for show and not used as weapons.
The name of this pachycephalosaur derives from its frightful appearance. Moloch was a horned devil in Hebrew mythology, and in Greek legends the river Styx was the river that the dead had to cross to reach the underworld. The fossils were found in the Hell Creek formation in Montana, and this was a further inspiration for the name. The first Stygimoloch horn core was found in 1896 and regarded as part of a Triceratops skull. In the 1940s, when pachycephalosaurs were recognized, it was classed as a species of Pachycephalosaurus.
Name: Stygimoloch, meaning ‘horned devil from the river of death’
Size: 3m long
Lived: about 70 million years ago during the Cretaceous Period in North America
The most obvious feature of Stygimoloch is the array of horns projecting from the rim of the dome. The head is quite long and the dome is high, narrow and thin. From the front, this presents a startling apparition of ornamentation, with long horns surrounded by clusters of more stubby spikes, that would evidently have been very effective as a threat or defence display, very much like those of some of the horned ceratopsians.
Unlike other pachycephalosaurs, the domed skull is relatively small, slightly flattened from side to side, and pear-shaped; even when isolated this unusual dome can easily be distinguished from the broader, larger domes of Pachycephalosaurus. While the dome is reduced in size, the ornamentation over the skull is more elaborate than in any other pachycephalosaur. Short, conical hornlets covered the nose, and the back corners of the skull bore an enormous pair of massive, backward-pointing spikes, up to 5cm in diameter and 15 cm long; these are surrounded by two or three smaller spikes. The function of this unusual ornamentation is unknown. Even if other pachycephalosaurs did butt heads (which is a subject of continuing debate), the small dome of Stygimoloch suggests that this behaviour was not as important. Instead, the skull ornament might have functioned for display, may have been used for self-defence, or perhaps were locked together and used in shoving matches, like the horns of deer. More likely, however, is that the squamosal horns were used to inflict pain during flank-butting.
Stygimoloch is known mostly from the skull. There have been five partial skulls found, but there have been other parts of the skeleton found in remains from North and South Dakota, USA.