In 1915, the
American Museum of Natural History obtained the nearly complete, articulated front half of an armoured dinosaur, found the same year by
Barnum Brown in
Alberta, Canada. In 1922,
William Diller Matthew referred this specimen, AMNH 5381, to
Palaeoscincus in a popular-science article, not indicating any particular species. It had been intended to name a new
Palaeoscincus species in cooperation with Brown but their article was never published. This species was based on
type specimen USNM 11868, a skeleton found by
George Fryer Sternberg in June 1928. The
specific name is derived from
Latin rugosus, "rough", and
dens, "tooth". In 1940,
Loris Shano Russell referred all three specimens to
Edmontonia, as an
Edmontonia rugosidens. Meanwhile, the
type species of
Edmontonia,
Edmontonia longiceps, had been named by
Charles Mortram Sternberg in 1928. The generic name
Edmontonia refers to
Edmonton or the Edmonton Formation. The specific name
longiceps means "long-headed" in Latin. Its
holotype is specimen
NMC 8531, consisting of a skull, right lower jaw and much of the postcranial skeleton, including the armour. It was discovered near
Morrin in 1924 by George Paterson, the teamster of the expedition led by C.M. Sternberg.
Edmontonia species include: •
E. longiceps, the
type, known from a complete skull, is known from the middle
Horseshoe Canyon Formation (Unit 2) which used to be dated to 71.5-71 million years ago. This unit, which straddles the
Campanian-
Maastrichtian boundary, has since been recalibrated to an age of about 72 million years. Isolated bones and shed teeth from
E. longiceps are also known from the upper Judith River Formation in Montana. •
E. rugosidens. This species has been given its own genus,
Chassternbergia, first coined as a
subgenus by Dr.
Robert Thomas Bakker in 1988, as
Edmontonia (Chassternbergia) rugosidens and is based on differences in skull proportion from
E. longiceps and its earlier time period. It was given its full generic name in 1991 by
George Olshevsky. The name
Chassternbergia honours Charles, "Chas", M. Sternberg. This subgenus or genus name is rarely applied.
E. rugosidens is found in the
Campanian lower
Dinosaur Park Formation, dating from about 76.5-75 million years ago. RTMP 98.98.01, a skull and right lower jaw; and RTMP 2001.12.158, a skull. This
taxon was erected by Bakker in 1988 for a skull from the
Late Maastrichtian Upper Cretaceous lower
Hell Creek Formation of
South Dakota, specimen DMNH 468 which was first described as
Edmontonia sp. by Carpenter and Breithaupt (1986). This
type specimen of
Denversaurus is in the collections of the Denver Museum of Natural History (now the
Denver Museum of Nature and Science), Denver,
Colorado for which the genus was named. The specific name honours Lee E. Schlessman, whose Schlessman Family Foundation sponsored the museum. Bakker described the skull as being much wider at the rear than
Edmontonia specimens. and considered the taxon a
junior synonym of
Edmontonia longiceps. Recent phylogenetic analyses included
Denversaurus as a valid genus closely related to
Edmontonia.
Edmontonia australis was named by Tracy Lee Ford in 2000 on the basis of cervical scutes, the holotype NMMNH P-25063, a pair of medial keeled neck osteoderms from the Maastrichtian
Kirtland Formation of
New Mexico and the
paratype NMMNH P-27450, a right middle neck plate. The naming history was further complicated in 1971, when
Walter Preston Coombs Jr renamed both
Edmontonia species, into
Panoplosaurus longiceps and
Panoplosaurus rugosidens respectively. The latter species, which due to its much more complete material has determined the image of
Edmontonia, until 1940 thus appeared under the name of
Palaeoscincus, and during the 1970s and 1980s was shown as "Panoplosaurus" until newer research revived the name
Edmontonia. In 2010, G.S. Paul suggested that
E. rugosidens was the direct ancestor of
Edmontonia longiceps and the latter was again the direct ancestor of
E. schlessmani. ==Phylogeny==