Stygimoloch

Taxobox
name = "Stygimoloch"

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image_width = 275px
image_caption = "Stygimoloch spinifer" skull (Museum für Naturkunde, Berlin)
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Ornithischia
subordo = Marginocephalia
infraordo = Pachycephalosauria
familia = Pachycephalosauridae
genus = "Stygimoloch"
genus_authority = Galton & Sues, 1983
subdivision_ranks = Species
subdivision =
*"S. spinifer" Galton & Sues, 1983 (type)

"Stygimoloch" (meaning "horned devil from the river of death") is a genus of pachycephalosaurid dinosaur from the end of the Cretaceous period, roughly 65 million years ago. It is currently known from the Hell Creek Formation and Lance Formation of the Western Interior (United States), where it lived alongside "Tyrannosaurus" and "Triceratops".

The type species, "S. spinifer", was described by British vertebrate paleontologist Peter Galton and German paleontologist Hans-Dieter Sues of the National Museum of Natural History in 1983.

It is a relatively large pachycephalosaur, with the skull being about 46 centimeters long (18 in). Among North American pachycephalosaurs, only "Pachycephalosaurus" is larger. 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 5 centimeters in diameter (2 in) and 15 centimeters long (6 in); 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 behavior was not as important. Instead, the skull ornament might have functioned for display, may have been used for self-defense, 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.cite journal |last=Carpenter |first=Kenneth |authorlink=Kenneth Carpenter |year=1997 |title=Agonistic behavior in pachycephalosaurs (Ornithischia:Dinosauria): a new look at head-butting behavior |journal=Contributions to Geology |volume=32 |issue=1 |pages= 19–25 |url=https://scientists.dmns.org/sites/kencarpenter/PDFs%20of%20publications/pachy%20head%20butting.pdf |format=pdf]

The pachycephalosaur "Dracorex" may actually be an individual of "Stygimoloch" or "Pachycephalosaurus" in which the dome and horns are not well-developed, either because the animal was a juvenile or a female. This consideration was supported at the 2007 annual meeting of the Society of Vertebrate Paleontology. Jack Horner of Montana State University presented evidence, from analysis of the skull of the single existing "Dracorex" specimen, that this dinosaur may well be a juvenile form of "Stygimoloch". In addition, he presented data that indicates that both "Stygimoloch" and "Dracorex" may be juvenile forms of "Pachycephalosaurus". [Erik Stokstad,"SOCIETY OF VERTEBRATE PALEONTOLOGY MEETING: Did Horny Young Dinosaurs Cause Illusion of Separate Species?", "Science" Vol. 18, 23 Nov. 2007, p. 1236; http://www.sciencemag.org/cgi/content/full/318/5854/1236]

References