Stygimoloch

Chapter • Meet the dinosaur

Overview

Stygimoloch was a small, bipedal plant-eater with one of the most extravagant heads of any dinosaur. Its skull carried a narrow, raised bony dome, and from the rear margin projected a crown of thick bony horns, the longest reaching around 15 centimetres. Rows of smaller knobs and spikes studded the snout. The body was compact, with short arms, a stiffened tail held horizontally as a counterbalance, and long, powerful hind limbs. The animal walked with its back level and its tail clear of the ground, never dragging. Skin is not preserved for this genus, but relatives among the ornithischians show both scaly skin and simple filament-like structures, so a fully scaled reconstruction remains the most cautious reading of the evidence. The long shins and short, muscular trunk suggest Stygimoloch was a quick, agile runner that could sprint away from predators across open ground. For decades pachycephalosaurs were pictured slamming head-on into each other like bighorn sheep, but CT scanning and microscopic study of the bone tissue point instead to flank-butting or shoving contests. The horn crown was probably above all a visual badge — a way of advertising species, age and status at a distance. Even so, healed injuries on the skulls of close relatives show that the head really was used in physical contact. The teeth were small, leaf-shaped and coarsely serrated, well suited to cropping soft leaves, fruit, seeds and young shoots. Sharper, more pointed teeth at the front of the jaw have led some researchers to suggest an omnivorous diet that included insects and other small animal food when available. Standing roughly a metre tall at the hip, Stygimoloch browsed low vegetation in the undergrowth along rivers and at forest edges. Stygimoloch spinifer was described in 1983 by Peter Galton and Hans-Dieter Sues from skull material collected in the Hell Creek Formation of Montana, USA. The name means roughly "horned demon from the river Styx", nodding both to Hell Creek and to the demon Moloch. Since 2009 several researchers, notably Jack Horner and Mark Goodwin, have argued that Stygimoloch is not a separate genus at all but a subadult Pachycephalosaurus wyomingensis, whose horns were resorbed as the dome expanded with age. Others hold that the differences are too great to be explained by growth alone. The debate is unresolved, and you will still meet the animal both as its own genus and as a teenage Pachycephalosaurus in books and museums.

Chapter • Where it lived

Habitat

Stygimoloch lived at the very end of the Cretaceous, in the Maastrichtian stage roughly 68–66 million years ago, in what is now western North America. Fossils come mainly from the Hell Creek Formation of Montana and South Dakota, the Lance Formation of Wyoming and the Ferris Formation of Wyoming. The landscape was a warm, humid coastal lowland of broad floodplains, meandering rivers, swampy backwaters and forests of conifers, ginkgoes, palm-like plants and early flowering plants. Here Stygimoloch shared its world with Triceratops, Edmontosaurus, Ankylosaurus, Thescelosaurus and Tyrannosaurus rex. The dense riverside undergrowth offered both food and cover for a small, fleet-footed animal like this.

Chapter • Wild behavior

Behavior & Ecology

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Chapter • Scientific place

Taxonomy