In 1986, the paleontologists
Kenneth Carpenter and
Brent Breithaupt described
DMNH 468 which was a specimen of a late
Maastrichtian nodosaurid, tentatively assigned to
Edmontonia sp., discovered from the lower
Hell Creek Formation of
South Dakota. In 1988,
Robert Thomas Bakker decided to split the genus
Edmontonia. The species
Edmontonia rugosidens was made into a separate genus named
Chassternbergia and DMNH 468 was designated as a holotype of a new genus and species. The
type species of this genus was
Denversaurus schlessmani. The generic name referred to the Denver Museum of Natural History at
Denver, Colorado. The
specific name honoured Lee E. Schlessman, a major benefactor of the museum and the founder of the Schlessman Family Foundation. The holotype consists of a skull without the lower jaws and a number of
osteoderms of the body armour. It is part of the collection of the Denver Museum of Nature and Science after which the genus was named. Bakker referred a second fossil to the species, specimen AMNH 3076, a skull found by Brown and
American Museum of Natural History paleontologist
Roland T. Bird at the Tornillo Creek in
Brewster County, Texas, in a layer of the poorly dated
Upper Cretaceous Aguja Formation, possibly from the Maastrichtian too. The validity of
Denversaurus was disputed in a 1990 paper on ankylosaurian systematics by
Kenneth Carpenter, who noted that Bakker's diagnosis of
Denversaurus was based primarily on Bakker's artistic restoration of the holotype in an uncrushed state. Since DMNH 468 was found crushed, Carpenter assigned
Denversaurus back to
Edmontonia sp., even though he noted its similarity to
Edmontonia rugosidens. A number of workers treated
Denversaurus as synonymous with either
E. rugosidens or
E. longiceps, or alternatively as a valid species of
Edmontonia:
E. schlessmani. In 1988, fossil hunters found a partial nodosaurid skeleton consisting of the fragmentary skull, parts of postcranial skeleton and seventy-five osteoderms from the
Lance Formation of
Niobrara County, Wyoming, nicknamed "Tank", which has been tentatively assigned to as
Edmontonia sp. in 1994. It was part of the collection of the
Rocky Mountain Dinosaur Resource Center under inventory number
BHI 127327, referred to as
Edmontonia schlessmani by Carpenter et al. (2013), and is now under the inventory number FPDM-V9673. In the 2015 thesis, Michael Burns revisited the systematics of latest Cretaceous nodosaurids from the Western Interior. According to Burns,
Denversaurus is likely a valid taxon based on its
phylogenetic position. Recent phylogenetic analyses included
Denversaurus as a valid genus closely related to
Edmontonia. ==Description==