[D] Glishades ericksoni [sG] [T]
Cretaceous Late Campanian
Ornithischia Ornithopoda Hadrosauridae [Hadrosauroidae]
Two Medicine Formation, South Milk River, 30 miles west of Sweetgrass, Glacier County, Montana, US
A new genus and species of hadrosauroid dinosaur, Glishades ericksoni, is described based on paired partial premaxillae collected from the Upper Cretaceous Two Medicine Formation of Montana, in the Western Interior of the United States of America. This taxon is diagnosed on the basis of a unique combination of characters: absence of everted oral margin, arcuate oral margin with wide and straight, obliquely oriented, and undeflected anterolateral corner, grooved transversal thickening on ventral surface of premaxilla posterior to denticulate oral margin, and foramina on anteromedial surface above oral edge and adjacent to proximal end of narial bar.
Maximum parsimony analysis positioned G. ericksoni as a derived hadrosauroid. Exclusion of G. ericksoni from Hadrosauridae was unambiguously supported by the lack in AMNH 27414 of a dorsomedially reflected premaxillary oral margin. Furthermore, the maximum agreement subtree positioned G. ericksoni as the sister taxon to Bactrosaurus johnsoni. This position was unambiguously supported by posteroventral thickening on the ventral surface of the premaxilla (independently derived in saurolophid hadrosaurids and Ouranosaurus nigeriensis) and having foramina on each premaxilla on the anterior surface, adjacent to the parasagittal plane of the rostrum (reconstructed as independently derived in Brachylophosaurus canadensis, Maiasaura peeblesorum, and Edmontosaurus annectens).
AMNH 27414, partial left and right premaxillae.
“Glis” is the Latin for “mud” and “hades” means “unseen” in Greek; thus, the generic name may be translated as “concealed in mud”, in reference to its being found in sedimentary strata. Also, “Hades” was the dark lord of the underworld in Greek mythology, here metaphorically referring to the “world” beneath the surface where fossils occur. - The specific name honors Dr. Gregory M. Erickson, for his important contributions to the knowledge of archosaur paleobiology.
Type locality and horizon
The specimen was collected by Brown, Kaiser, and Johnson ca. 1915 in South Milk River, 30 miles west of Sweetgrass, Glacier County, Montana (United States of America), from strata corresponding to the Two Medicine Formation (Campanian, Upper Cretaceous).
Hadrosauroid dinosaur with the following unique combination of premaxillary characters: absence of recurvature (“reflection”) of oral margin; arcuate oral margin with wide and straight, obliquely oriented, and undeflected anterolateral corner; foramina on anteromedial surface above oral edge and adjacent to proximal end of narial bar; and grooved transversal thickening on ventral surface of premaxilla posterior to denticulate oral margin.