Stygivenator

Stygivenator, also known as the "Jordan theropod" is a dubious genus of tyrannosauroid dinosaur from the Hell Creek Formation, containing the type and only species Stygivenator molnari. Originally considered a species of Aublysodon, another dubious genus, and then a juvenile of Tyrannosaurus, its specific identity can not presently be determined due to its poor preservation making it impossible to rule out an identity as either a specimen of Tyrannosaurus or Nanotyrannus.

Stygivenator Temporal range: Late Cretaceous, 66 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Holotype specimen of S. molnari, LACM 28471
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Dinosauria
Clade:	Saurischia
Clade:	Theropoda
Superfamily:	†Tyrannosauroidea
Clade:	†Eutyrannosauria
Genus:	†Stygivenator Olshevsky, 1995
Type species
†Stygivenator molnari Paul, 1988a
Synonyms
Aublysodon molnaris Paul, 1988a Aublysodon molnari Paul, 1988a emend Paul, 1989

Discovery and naming

LACM 28471 on display at the Natural History Museum of Los Angeles County

Skull material of a theropod dinosaur was discovered by Harley Garbani in 1966 near Jordan, Montana, Garfield County, Montana, Montana. Found alongside the skull of a Triceratops, it is from rock layers of the Hell Creek Formation. The specimen was returned to Garbani's institution, the Natural History Museum of Los Angeles County in California and given the specimen number LACM 28471. It's a portion of the snout consisting of both maxillae, teeth, nasals, frontals, a parietal, and portions of the surangular and dentaries.^[1] Though originally considered to include one tooth from the unpreserved premaxilla, later studies have reinterpretted this element as a maxillary tooth.^[2][3]

In 1978 it was scientifically described by Ralph E. Molnar, who noted similarities to both tyrannosaurids and dromaeosaurids but considered it most likely to represent a large dromaeosaur. Considering the material too lacking to give it a name, he simply referred to it as the "Jordan theropod".^[3][4] Gregory S. Paul, in the 1988 book Predatory Dinosaurs of the World, instead identified as a tyrannosaurid belonging to the genus Aublysodon due to the anatomy of its supposed premaxillary tooth. He considered it a new species, and named it Aublysodon molnaris after Molnar.^[5] This was later corrected by Paul to the correctly formed Aublysodon molnari.^[6][7] Independently, Molnar returned to the specimen alongside Kenneth Carpenter in a 1989 study, independently concluding it was similar to Aublysodon based on the "premaxillary" tooth. However, they assignined it to the type species of that genus, Aublysodon mirandus, rather than a distinct species.^[1][8]

In modern research, Aublysodon is considered to be a dubious genus, as the features of its teeth are common amongst tyrannosaurs.^[2][3] Due to the doubtful nature of Aublysodon, George Olshevsky gave it a distinct genus Stygivenator in a 1995 publication. This name was derived from the Underworld river Styx of Greek mythology, referring to the Hell Creek formation, as well as -venator, the Latin word for hunter. Together, it formed the intended meaning "Hell Creek hunter". The name came from Molnar, who would have used it in his original 1978 were he more certain of its identity at the time.^[6][7]