E. annectens has a complicated
taxonomic history, with various specimens having been classified in a variety of genera. Its history involves
Anatosaurus,
Anatotitan,
Claosaurus,
Diclonius,
Hadrosaurus,
Thespesius, and
Trachodon, as well as
Edmontosaurus. References predating the 1980s typically use
Anatosaurus,
Claosaurus,
Diclonius,
Thespesius, or
Trachodon for
E. annectens fossils, depending on the author and date.
Cope's Diclonius mirabilis in 1908 The history of
E. annectens predates the naming of both the genus
Edmontosaurus and the species
annectens. The first quality specimen, the former
holotype of
Anatosaurus copei (
Anatotitan), was a complete skull and most of a skeleton collected in 1882 by Dr. J. L. Wortman and R. S. Hill came from northeast of the
Black Hills of
South Dakota, and originally had extensive skin impressions. It was missing most of its pelvis and part of its torso due to a stream cutting through it. The bill had impressions of a horn-like sheath with a tooth-like series of interlocking points on the upper and lower jaws. His reasoning was that the teeth of the lower jaw were weakly connected to the bone, and liable to break off if used to eat terrestrial food; he described the beak as weak, too. by chance, the lower jaws were missing the walls supporting the teeth from the inside, and the teeth were actually very well-supported. Cope intended to describe the skeleton and skull, but his promised paper never appeared. and it is cataloged as
YPM 616. As noted by Lull and Wright, this long, slender partial jaw shares with Cope's specimen a prominent ridge running on its side. However, it is much larger: Cope's specimen had a
dentary that is long, whereas Marsh's dentary is estimated at long. This species has some historical footnotes attached, as it is among the first dinosaurs to receive a skeletal restoration, and is the first hadrosaurid so restored. YPM 2182 and UNSM 2414 are, respectively, the first and second essentially complete mounted dinosaur skeletons in the United States. The Sternbergs recovered a second similar specimen from the same area in 1910. It was not as well-preserved, but also found with skin impressions. They sold this specimen, SM 4036, to the
Senckenberg Museum in
Germany. The Horseshoe Canyon Formation is older than the rocks in which
Claosaurus annectens was found. now the
Frenchman Formation. A multiplicity of names resumed, with the AMNH duckbills being known as
Diclonius mirabilis,
Trachodon mirabilis,
Trachodon annectens,
Claosaurus, or
Thespesius. Lull and Wright decided to remove the AMNH specimens from
Diclonius (or
Trachodon), because they found no convincing reason to assign the specimens to either. Because this left the skeletons without a species name, Lull and Wright gave them their own species:
Anatosaurus copei, in honor of Cope. Cope's original specimen, AMNH 5730, was made the
holotype of the species, with Brown's AMNH 5886 as the
plesiotype. This state of affairs persisted for several decades until
Michael K. Brett-Surman reexamined the pertinent material for his graduate studies in the 1970s and 1980s. The name
Edmontosaurus annectens was first coined some time in the 1980s. He concluded that the type species of
Anatosaurus,
A. annectens, was actually a species of
Edmontosaurus, and that
A. copei was different enough to warrant its own genus. Although theses and
dissertations are not regarded as official publications by the
International Commission on Zoological Nomenclature, which regulates the naming of organisms, his conclusions were known to other paleontologists, and were adopted by several popular works of the time. His replacement name,
Anatotitan (the
Latin word
anas ("duck"), and the
Greek word
Titan, meaning large), was known and published as such in the popular literature by 1990. Formal publication of the name
Anatotitan copei took place the same year in an article co-written by Brett-Surman with
Ralph Chapman (although the name is sometimes credited as Brett-Surman
vide Chapman and Brett-Surman, because it came out of Brett-Surman's work). and
A. longiceps went to
Anatotitan, as either a second species or as a synonym of
A. copei. The conception of
Edmontosaurus that emerged included three valid species: the type species
E. regalis;
E. annectens (including
Anatosaurus edmontoni, emended to
edmontonensis); and
E. saskatchewanensis. In a 2011 study by Nicolás Campione and David Evans, the authors conducted the first-ever
morphometric analysis of the various specimens assigned to
Edmontosaurus. They concluded that only two species are valid:
E. regalis, from the late Campanian; and
E. annectens, from the late Maastrichtian. Their study provided further evidence that
Anatotitan copei is a synonym of
E. annectens (specifically, that the long, low skull of
A. copei is the result of ontogenetic change, and represents mature
E. annectens individuals).
E. saskatechwanensis represents young
E. annectens, and
Anatosaurus edmontoni specimens belong to
E. regalis—not
E. annectens. The reassessment of
Edmontosaurus assigns twenty skulls to
E. annectens. Adult skulls of
E. annectens can be distinguished from skulls of
E. regalis by the elongate snout and other details of skull anatomy, such as the small comb on top of the latter's skull. ==Description==