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''Edmontosaurus annectens'' (meaning "connected lizard from
Edmonton Edmonton ( ) is the capital city of the Canadian province of Alberta. Edmonton is situated on the North Saskatchewan River and is the centre of the Edmonton Metropolitan Region, which is surrounded by Alberta's central region. The city ancho ...
") is a
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
of flat-headed and duck-billed (
hadrosaurid Hadrosaurids (), or duck-billed dinosaurs, are members of the ornithischian family Hadrosauridae. This group is known as the duck-billed dinosaurs for the flat duck-bill appearance of the bones in their snouts. The ornithopod family, which inclu ...
)
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
from the very end of the
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
Period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...
, in what is now North America. Remains of ''E. annectens'' have been preserved in the
Frenchman The French people (french: Français) are an ethnic group and nation primarily located in Western Europe that share a common French culture, history, and language, identified with the country of France. The French people, especially th ...
,
Hell Creek The Hell Creek Formation is an intensively studied division of mostly Upper Cretaceous and some lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana. The formation stretches over portions of ...
, and
Lance Formation The Lance (Creek) Formation is a division of Late Cretaceous (dating to about 69 - 66 Ma) rocks in the western United States. Named after Lance Creek, Wyoming, the microvertebrate fossils and dinosaurs represent important components of the late ...
s. All of these formations are dated to the late
Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval from ...
stage of the
Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...
Period, representing the last three million years before the
extinction of the dinosaurs Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
(between 68 and 66 
million years ago The abbreviation Myr, "million years", is a unit of a quantity of (i.e. ) years, or 31.556926 teraseconds. Usage Myr (million years) is in common use in fields such as Earth science and cosmology. Myr is also used with Mya (million years ago). ...
Holtz, Thomas R. Jr. (2012) ''Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages,'
Winter 2011 Appendix.
/ref>). ''E. annectens'' is also found in the
Laramie Formation The Laramie Formation is a geologic formation of Late Cretaceous (Maastrichtian) age, named by Clarence King in 1876 for exposures in northeastern Colorado, in the United States.King, C. 1876. Report of the Geological Exploration of the Fortieth P ...
, and
magnetostratigraphy Magnetostratigraphy is a geophysical correlation technique used to date sedimentary and volcanic sequences. The method works by collecting oriented samples at measured intervals throughout the section. The samples are analyzed to determine their '' ...
suggests an age of 69-68 Ma for the Laramie Formation.*Hicks, J.F., Johnson, K.R., Obradovich, J. D., Miggins, D.P., and Tauxe, L. 2003. Magnetostratigraphyof Upper Cretaceous (Maastrichtian) to lower Eocene strata of the Denver Basin, Colorado. In K.R. Johnson, R.G. Raynolds and M.L. Reynolds (eds), Paleontology and Stratigraphy of Laramide Strata in the Denver Basin, Pt. II., Rocky Mountain Geology 38: 1-27. ''Edmontosaurus annectens'' is known from numerous specimens, including at least twenty partial to complete skulls, discovered in the U.S. states of
Montana Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columbi ...
,
South Dakota South Dakota (; Sioux language, Sioux: , ) is a U.S. state in the West North Central states, North Central region of the United States. It is also part of the Great Plains. South Dakota is named after the Lakota people, Lakota and Dakota peo ...
,
North Dakota North Dakota () is a U.S. state in the Upper Midwest, named after the Native Americans in the United States, indigenous Dakota people, Dakota Sioux. North Dakota is bordered by the Canadian provinces of Saskatchewan and Manitoba to the north a ...
,
Wyoming Wyoming () is a U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the south ...
and
Colorado Colorado (, other variants) is a state in the Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the western edge of t ...
and the
Canadian Canadians (french: Canadiens) are people identified with the country of Canada. This connection may be residential, legal, historical or cultural. For most Canadians, many (or all) of these connections exist and are collectively the source of ...
province of
Saskatchewan Saskatchewan ( ; ) is a Provinces and territories of Canada, province in Western Canada, western Canada, bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and on t ...
. It had an extremely long and low
skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...
and was a large animal, up to approximately in length and in average asymptotic body mass, and may have been even larger. ''E. annectens'' exhibits one of the most striking examples of the "duckbill" snout common to hadrosaurs. It has a long taxonomic history, and specimens have at times been classified in the genera ''
Diclonius ''Diclonius'' (meaning "double sprout") is a genus of dinosaur from the Late Cretaceous. It was a hadrosaur based solely on teeth. Its fossils were found in the Judith River Formation of Montana, northern US. The name is in reference to the met ...
'', ''
Trachodon ''Trachodon'' (meaning "rough tooth") is a dubious genus of hadrosaurid dinosaur based on teeth from the Campanian-age Upper Cretaceous Judith River Formation of Montana, U.S.Leidy, J. (1856). "Notice of remains of extinct reptiles and fishes, d ...
'', ''
Hadrosaurus ''Hadrosaurus'' (; ) is a genus of hadrosaurid ornithopod dinosaurs that lived in North America during the Late Cretaceous Period in what is now the Woodbury Formation about 80 million to 78 million years ago. The holotype specimen was found in f ...
'', ''
Claosaurus ''Claosaurus'' ( ; Greek κλάω, ''klao'' meaning 'broken' and , ''sauros'' meaning 'lizard'; "broken lizard", referring to the odd position of the fossils when discovered) is a genus of hadrosauroid dinosaur that lived during the Late Cretac ...
'', '' Thespesius'', ''Anatosaurus'' and ''Anatotitan'', before being grouped together in ''
Edmontosaurus ''Edmontosaurus'' ( ) (meaning "lizard from Edmonton") is a genus of hadrosaurid (duck-billed) dinosaur. It contains two known species: ''Edmontosaurus regalis'' and ''Edmontosaurus annectens''. Fossils of ''E. regalis'' have been found in rocks ...
''.


Discovery and history

''E. annectens'' has a complicated
taxonomic Taxonomy is the practice and science of categorization or classification. A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. ...
history, with various specimens having been classified in a variety of genera. Its history involves ''Anatosaurus'', ''Anatotitan'', ''
Claosaurus ''Claosaurus'' ( ; Greek κλάω, ''klao'' meaning 'broken' and , ''sauros'' meaning 'lizard'; "broken lizard", referring to the odd position of the fossils when discovered) is a genus of hadrosauroid dinosaur that lived during the Late Cretac ...
'', ''
Diclonius ''Diclonius'' (meaning "double sprout") is a genus of dinosaur from the Late Cretaceous. It was a hadrosaur based solely on teeth. Its fossils were found in the Judith River Formation of Montana, northern US. The name is in reference to the met ...
'', ''
Hadrosaurus ''Hadrosaurus'' (; ) is a genus of hadrosaurid ornithopod dinosaurs that lived in North America during the Late Cretaceous Period in what is now the Woodbury Formation about 80 million to 78 million years ago. The holotype specimen was found in f ...
'', '' Thespesius'', and ''
Trachodon ''Trachodon'' (meaning "rough tooth") is a dubious genus of hadrosaurid dinosaur based on teeth from the Campanian-age Upper Cretaceous Judith River Formation of Montana, U.S.Leidy, J. (1856). "Notice of remains of extinct reptiles and fishes, d ...
'', as well as ''
Edmontosaurus ''Edmontosaurus'' ( ) (meaning "lizard from Edmonton") is a genus of hadrosaurid (duck-billed) dinosaur. It contains two known species: ''Edmontosaurus regalis'' and ''Edmontosaurus annectens''. Fossils of ''E. regalis'' have been found in rocks ...
''. References predating the 1980s typically use ''Anatosaurus'', ''Claosaurus'', ''Diclonius'', ''Thespesius'', or ''Trachodon'' for ''E. annectens'' fossils, depending on author and date.


Cope's ''Diclonius mirabilis''

The history of ''E. annectens'' predates both ''Edmontosaurus'' and ''annectens''. The first good specimen, the former
holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...
(specimen on which a taxonomic name is based) 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 for American
paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...
Edward Drinker Cope Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American zoologist, paleontologist, comparative anatomist, herpetologist, and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy interested ...
. This specimen, found in
Hell Creek Formation The Hell Creek Formation is an intensively studied division of mostly Upper Cretaceous and some lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana. The formation stretches over portions of ...
rocks, came from northeast of the
Black Hills The Black Hills ( lkt, Ȟe Sápa; chy, Moʼȯhta-voʼhonáaeva; hid, awaxaawi shiibisha) is an isolated mountain range rising from the Great Plains of North America in western South Dakota and extending into Wyoming, United States. Black Elk P ...
of
South Dakota South Dakota (; Sioux language, Sioux: , ) is a U.S. state in the West North Central states, North Central region of the United States. It is also part of the Great Plains. South Dakota is named after the Lakota people, Lakota and Dakota peo ...
and originally had extensive skin impressions. It was missing most of the pelvis and part of the torso due to a stream cutting through it. The bill had impressions of a horny sheath with a tooth-like series of interlocking points on the upper and lower jaws. When describing this specimen
AMNH The American Museum of Natural History (abbreviated as AMNH) is a natural history museum on the Upper West Side of Manhattan in New York City. In Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 26 inter ...
 5730, Cope assigned it to the species '' Diclonius mirabilis''. This species name was created by combining ''
Diclonius ''Diclonius'' (meaning "double sprout") is a genus of dinosaur from the Late Cretaceous. It was a hadrosaur based solely on teeth. Its fossils were found in the Judith River Formation of Montana, northern US. The name is in reference to the met ...
'', a hadrosaurid genus Cope had named earlier from teeth, with ''
Trachodon mirabilis ''Trachodon'' (meaning "rough tooth") is a dubious genus of hadrosaurid dinosaur based on teeth from the Campanian-age Upper Cretaceous Judith River Formation of Montana, U.S.Leidy, J. (1856). "Notice of remains of extinct reptiles and fishes, ...
'', an older name based on teeth and published by
Joseph Leidy Joseph Mellick Leidy (September 9, 1823 – April 30, 1891) was an American paleontologist, parasitologist and anatomist. Leidy was professor of anatomy at the University of Pennsylvania, later was a professor of natural history at Swarthmore ...
. Cope believed that Leidy had failed to properly characterize the genus ''Trachodon'' and later abandoned its use, so he assigned the old species to his newer genus. Leidy had come to recognize that his ''Trachodon'' was based on the remains of multiple kinds of dinosaurs, and though he had made some attempts to revise the genus, he had not yet made any formal declaration of his intentions. Cope's description promoted hadrosaurids as amphibious, contributing to this long-time image. His reasoning was that the teeth of the lower jaw were weakly connected to the bone and liable to break off if used to consume terrestrial food, and he described the beak as weak as well. However, aside from misidentifying several of the skull bones, by chance the lower jaws were missing the walls supporting the teeth from the inside; the teeth were actually well-supported.Lull and Wright, ''Hadrosaurian Dinosaurs of North America'', pp. 43. Cope intended to describe the skeleton as well as the skull, but his promised paper never appeared. It was purchased for the American Museum of Natural History in 1899, where it acquired its present designation AMNH 5730. Several years after Cope's description, his rival
Othniel Charles Marsh Othniel Charles Marsh (October 29, 1831 – March 18, 1899) was an American professor of Paleontology in Yale College and President of the National Academy of Sciences. He was one of the preeminent scientists in the field of paleontology. Among h ...
published on a sizable lower jaw recovered by John Bell Hatcher in 1889 from
Lance Formation The Lance (Creek) Formation is a division of Late Cretaceous (dating to about 69 - 66 Ma) rocks in the western United States. Named after Lance Creek, Wyoming, the microvertebrate fossils and dinosaurs represent important components of the late ...
rocks in
Niobrara County, Wyoming Niobrara County is a county in the U.S. state of Wyoming. As of the 2020 United States Census, the population was 2,467, making it the least populous county in Wyoming. Its county seat is Lusk. Its eastern boundary abuts the west lines of the s ...
. Marsh named this partial jaw ''Trachodon longiceps''. 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 In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...
, or tooth-bearing bone of the lower jaw, that is long, whereas Marsh's dentary is estimated at long. A second mostly complete skeleton (AMNH 5886) was found in 1904 in Hell Creek Formation rocks at Crooked Creek in central
Montana Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columbi ...
by Oscar Hunter, a rancher. Upon finding the partially exposed specimen, he and a companion argued about whether or not the remains were recent or fossil. Hunter demonstrated that they were brittle and thus stone by kicking the tops off the vertebrae, an act later lamented by the eventual collector
Barnum Brown Barnum Brown (February 12, 1873 – February 5, 1963), commonly referred to as Mr. Bones, was an American paleontologist. Named after the circus showman P. T. Barnum, he discovered the first documented remains of ''Tyrannosaurus'' during a career ...
. Another cowboy, Alfred Sensiba, bought the specimen from Hunter for a
pistol A pistol is a handgun, more specifically one with the chamber integral to its gun barrel, though in common usage the two terms are often used interchangeably. The English word was introduced in , when early handguns were produced in Europe, an ...
, and later sold it to Brown, who excavated it for the American Museum of Natural History in 1906. This specimen had a nearly complete
vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...
l column, permitting the restoration of Cope's specimen. In 1908, these two specimens were mounted side by side in the American Museum of Natural History, under the name ''Trachodon mirabilis''. Cope's specimen is positioned on all fours with its head down, as if feeding, because it has the better skull, while Brown's specimen, with a less perfect skull, is posed bipedally with the head less accessible.
Henry Fairfield Osborn Henry Fairfield Osborn, Sr. (August 8, 1857 – November 6, 1935) was an American paleontologist, geologist and eugenics advocate. He was the president of the American Museum of Natural History for 25 years and a cofounder of the American Euge ...
described the tableau as representing the two animals feeding along a
marsh A marsh is a wetland that is dominated by herbaceous rather than woody plant species.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p Marshes can often be found at ...
, the standing individual having been startled by the approach of a ''
Tyrannosaurus ''Tyrannosaurus'' is a genus of large theropoda, theropod dinosaur. The species ''Tyrannosaurus rex'' (''rex'' meaning "king" in Latin), often called ''T. rex'' or colloquially ''T-Rex'', is one of the best represented theropods. ''Tyrannosa ...
''. Impressions of appropriate plant remains and shells based on associated fossils were included on the base of the group, including
ginkgo ''Ginkgo'' is a genus of non-flowering seed plants. The scientific name is also used as the English name. The order to which it belongs, Ginkgoales, first appeared in the Permian, 270 million years ago, and is now the only living genus within ...
leaves, '' Sequoia'' cones, and
horsetail ''Equisetum'' (; horsetail, snake grass, puzzlegrass) is the only living genus in Equisetaceae, a family of ferns, which reproduce by spores rather than seeds. ''Equisetum'' is a "living fossil", the only living genus of the entire subclass Eq ...
rushes.


Marsh's ''Claosaurus annectens''

The species now known as ''Edmontosaurus annectens'' was named in 1892 as ''Claosaurus annectens'' by
Othniel Charles Marsh Othniel Charles Marsh (October 29, 1831 – March 18, 1899) was an American professor of Paleontology in Yale College and President of the National Academy of Sciences. He was one of the preeminent scientists in the field of paleontology. Among h ...
. This species is based on USNM 2414, a partial skull-roof and skeleton, with a second skull and skeleton, YPM 2182, designated the
paratype In zoology and botany, a paratype is a specimen of an organism that helps define what the scientific name of a species and other taxon actually represents, but it is not the holotype (and in botany is also neither an isotype nor a syntype). Of ...
. Both were collected in 1891 by
John Bell Hatcher John Bell Hatcher (October 11, 1861 – July 3, 1904) was an American paleontologist and fossil hunter known as the "king of collectors" and best known for discovering ''Torosaurus'' and ''Triceratops'', two genera of dinosaurs described by Ot ...
from the late Maastrichtian-age Upper Cretaceous
Lance Formation The Lance (Creek) Formation is a division of Late Cretaceous (dating to about 69 - 66 Ma) rocks in the western United States. Named after Lance Creek, Wyoming, the microvertebrate fossils and dinosaurs represent important components of the late ...
of Niobrara County (then part of Converse County),
Wyoming Wyoming () is a U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the south ...
. This species has some historical footnotes attached: it is among the first dinosaurs to receive a skeletal restoration, and is the first hadrosaurid so restored; and YPM 2182 and UNSM 2414 are, respectively, the first and second essentially complete mounted dinosaur skeletons in the United States. YPM 2182 was put on display in 1901, and USNM 2414 in 1904. In the first decade of the twentieth century, two additional important specimens of ''C. annectens'' were recovered. The first, the " Trachodon mummy" (AMNH 5060), was discovered in 1908 by
Charles Hazelius Sternberg Charles Hazelius Sternberg (June 15, 1850 – July 20, 1943) was an American fossil collector and paleontologist. He was active in both fields from 1876 to 1928, and collected fossils for Edward Drinker Cope and Othniel C. Marsh, and for the ...
and his sons in Lance Formation rocks near Lusk, Wyoming. Sternberg was working for the
British Museum of Natural History The Natural History Museum in London is a museum that exhibits a vast range of specimens from various segments of natural history. It is one of three major museums on Exhibition Road in South Kensington, the others being the Science Museum an ...
, but
Henry Fairfield Osborn Henry Fairfield Osborn, Sr. (August 8, 1857 – November 6, 1935) was an American paleontologist, geologist and eugenics advocate. He was the president of the American Museum of Natural History for 25 years and a cofounder of the American Euge ...
of the American Museum of Natural History was able to purchase the specimen for $2,000. The Sternbergs recovered a second similar specimen from the same area in 1910, not as well-preserved but also found with skin impressions. They sold this specimen (SM 4036) to the
Senckenberg Museum The Naturmuseum Senckenberg is a museum of natural history, located in Frankfurt am Main. It is the second-largest of its type in Germany. The museum contains a large and diverse collection of birds with 90,000 bird skins, 5,050 egg sets, 17,0 ...
in Germany.


Canadian discoveries

''Edmontosaurus'' itself was coined in 1917 by
Lawrence Lambe Lawrence Morris Lambe (August 27, 1863 – March 12, 1919) was a Canadian geologist, palaeontologist, and ecologist from the Geological Survey of Canada (GSC). His published work, describing the diverse and plentiful dinosaur discoveries from th ...
for two partial skeletons found in the
Horseshoe Canyon Formation The Horseshoe Canyon Formation is a stratigraphic unit of the Western Canada Sedimentary Basin in southwestern Alberta. It takes its name from Horseshoe Canyon, an area of badlands near Drumheller. The Horseshoe Canyon Formation is part of the ...
(formerly the lower Edmonton Formation) along the
Red Deer River The Red Deer River is a river in Alberta and a small portion of Saskatchewan, Canada. It is a major tributary of the South Saskatchewan River and is part of the larger Saskatchewan-Nelson system that empties into Hudson Bay. Red Deer River ...
of southern Alberta, Canada. The Horseshoe Canyon Formation is older than the rocks in which ''Claosaurus annectens'' was found. Lambe found that his new dinosaur compared best to Cope's ''Diclonius mirabilis''. In 1926,
Charles Mortram Sternberg Charles Mortram Sternberg (1885–1981) was an American-Canadian fossil collector and paleontologist, son of Charles Hazelius Sternberg. Late in his career, he collected and described ''Pachyrhinosaurus'', ''Brachylophosaurus'', ''Parksosaurus ...
named ''Thespesius saskatchewanensis'' for NMC 8509, a skull and partial skeleton from the Wood Mountain plateau of southern
Saskatchewan Saskatchewan ( ; ) is a Provinces and territories of Canada, province in Western Canada, western Canada, bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and on t ...
. He had collected this specimen in 1921, from rocks that were assigned to the Lance Formation, now the
Frenchman Formation The Frenchman Formation is stratigraphic unit of Late Cretaceous (late Maastrichtian) age in the Western Canada Sedimentary Basin. It is present in southern Saskatchewan and the Cypress Hills of southeastern Alberta. The formation was defined by ...
. NMC 8509 included an almost complete skull, numerous vertebrae, partial shoulder and hip girdles, and partial hind limbs, representing the first substantial dinosaur specimen recovered from Saskatchewan. Sternberg opted to assign it to ''Thespesius'' because that was the only hadrosaurid genus known from the Lance Formation at the time. At the time, ''T. saskatchewanensis'' was unusual because of its small size, estimated at in length.


Early classifications

Because of the incomplete understanding of hadrosaurids at the time, following Marsh's death in 1899 ''Claosaurus annectens'' was variously classified as a species of ''Claosaurus'', ''Thespesius'' or ''Trachodon''. Opinions varied greatly; textbooks and encyclopedias drew a distinction between the "''
Iguanodon ''Iguanodon'' ( ; meaning 'iguana-tooth'), named in 1825, is a genus of iguanodontian dinosaur. While many species have been classified in the genus ''Iguanodon'', dating from the late Jurassic Period to the early Cretaceous Period of Asia, Eu ...
''-like" ''Claosaurus annectens'' and the "duck-billed" ''Hadrosaurus'' (based on Cope's ''Diclonius mirabilis''), while Hatcher explicitly identified ''C. annectens'' as synonymous with the hadrosaurid represented by those same duck-billed skulls, the two differentiated only by individual variation or distortion from pressure. Hatcher's revision, published in 1902, was sweeping: he considered almost all hadrosaurid genera then known as synonyms of ''Trachodon''. This included ''
Cionodon ''Cionodon'' (meaning 'column tooth') is a dubious genus of hadrosauridJ. R. Horner, D. B. Weishampel, and C. A. Forster. 2004. Hadrosauridae. In D. B. Weishampel, H. Osmolska, and P. Dodson (eds.), ''The Dinosauria'' (2nd edition). ''Universi ...
'', ''Diclonius'', ''Hadrosaurus'', ''
Ornithotarsus ''Ornithotarsus'' () is a genus of hadrosaurid ornithopod dinosaurs that lived in North America during the Late Cretaceous Period in what is now the Merchantville Formation The Merchantville Formation is a geological Formation (geology), forma ...
'', '' Pteropelyx'', and ''Thespesius'', as well as ''
Claorhynchus ''Claorhynchus'' (meaning "broken beak", as it is based on broken bones from the snout region) is a dubious genus of cerapodan dinosaur with a confusing history behind it. It has been considered to be both a hadrosaurid and a ceratopsid, someti ...
'' and ''
Polyonax ''Polyonax'' (meaning "master over many") was a genus of ceratopsid dinosaur from the late Maastrichtian-age Upper Cretaceous Denver Formation of Colorado, United States. Founded upon poor remains, it is today regarded as a dubious name. Hi ...
'', fragmentary genera now thought to be horned dinosaurs. Hatcher's work led to a brief consensus until about 1910, when new material from Canada and Montana showed a greater diversity of hadrosaurids than previously suspected.
Charles W. Gilmore Charles Whitney Gilmore (March 11, 1874 – September 27, 1945) was an American paleontologist who gained renown in the early 20th century for his work on vertebrate fossils during his career at the United States National Museum (now the N ...
in 1915 reassessed hadrosaurids and recommended that ''Thespesius'' be reintroduced for hadrosaurids from the Lance Formation and rock units of equivalent age, and that ''Trachodon'', based on inadequate material, should be restricted to a hadrosaurid from the older
Judith River Formation The Judith River Formation is a fossil-bearing geologic formation in Montana, and is part of the Judith River Group. It dates to the Late Cretaceous, between 79 and 75.3 million years ago, corresponding to the "Judithian" land vertebrate age. It ...
and its equivalents. In regards to ''Claosaurus annectens'', he recommended that it be considered the same as ''Thespesius occidentalis''. A multiplicity of names resumed, with the American Museum duckbills being known as ''Diclonius mirabilis'', ''Trachodon mirabilis'', ''Trachodon annectens'', ''Claosaurus'', or ''Thespesius''.


''Anatosaurus'' to the present

This confusing situation was temporarily resolved in 1942 by
Richard Swann Lull Richard Swann Lull (November 6, 1867 – April 22, 1957) was an American paleontologist and Sterling Professor at Yale University who is largely remembered now for championing a non-Darwinian view of evolution, whereby mutation(s) could unl ...
and
Nelda Wright Nelda is a given name. Notable people with the name include: * Nelda Garrone ( 1880–?), Italian mezzo-soprano *Nelda Martinez (born 1961), American real estate agent and politician *Nelda Speaks (born 1943), American politician See also *Zelda ...
. In their
monograph A monograph is a specialist work of writing (in contrast to reference works) or exhibition on a single subject or an aspect of a subject, often by a single author or artist, and usually on a scholarly subject. In library cataloging, ''monograph ...
on hadrosaurian dinosaurs of North America, they opted to settle the questions revolving around the American Museum duckbills, Marsh's ''Claosaurus annectens'', and several other species by creating a new generic name. They created the new genus ''
Anatosaurus ''Edmontosaurus annectens'' (meaning "connected lizard from Edmonton") is a species of flat-headed and duck-billed ( hadrosaurid) dinosaur from the very end of the Cretaceous Period, in what is now North America. Remains of ''E. annectens'' have ...
'' ("duck lizard", because of its wide, duck-like beak;
Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
''anas'' = duck +
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
''sauros'' = lizard) and made Marsh's species the
type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...
, calling it ''Anatosaurus annectens''. To this genus, they also assigned Marsh's ''Trachodon longiceps'', a pair of species that had been assigned to ''Thespesius'' under Gilmore's "Lance Formation hadrosaurid" conception (''T. edmontoni'' from Gilmore in 1924 and ''T. saskatchewanensis''), and Cope's ''Diclonius mirabilis''.Lull and Wright, ''Hadrosaurian Dinosaurs of North America'', pp. 154–164. Lull and Wright decided to remove the American Museum 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 A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...
of the species, with Brown's (AMNH 5886) as the plesiotype. ''Anatosaurus'' would come to be called the "classic duck-billed dinosaur." 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 The International Commission on Zoological Nomenclature (ICZN) is an organization dedicated to "achieving stability and sense in the scientific naming of animals". Founded in 1895, it currently comprises 26 commissioners from 20 countries. Orga ...
, 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'' (
Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
''anas'' ("duck") and the
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
'' 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 Ralph D. "Slouie" Chapman (May 8, 1892 – August 1969) was an American football player. He was the son of P. T. Chapman, a wealthy banker in Vienna, Illinois. He played at the guard position for Robert Zuppke's University of Illinois footb ...
(although the name is sometimes credited as Brett-Surman ''vide'' Chapman and Brett-Surman because it came out of Brett-Surman's work). Because the type species of ''Anatosaurus'' (''A. annectens'') was sunk into ''Edmontosaurus'', the name ''Anatosaurus'' is abandoned as a
junior synonym The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently. * In botanical nomenclature, a synonym is a scientific name that applies to a taxon that (now) goes by a different scientific name. For example, Linna ...
of ''Edmontosaurus''. Of the remaining species of ''Anatosaurus'', ''A. saskatchewanensis'' and ''A. edmontoni'' were assigned to ''Edmontosaurus'' as well, and ''A. longiceps'' went to ''Anatotitan'', as either a second species or as a synonym of ''A. copei''. ''A. longiceps'' may be a synonym of ''E. annectens'', though it has also been treated as a ''nomen dubium'' by some.Lund, E. & Gates, T. (2006). "A historical and biogeographical examination of hadrosaurian dinosaurs." Pp. 263-276 in Lucas, S.G. and Sullivan, R.M. (eds.), ''Late Cretaceous vertebrates from the Western Interior''. New Mexico Museum of Natural History and Science Bulletin 35. The conception of ''Edmontosaurus'' that emerged included three valid species: the type ''E. regalis'', ''E. annectens'' (including ''Anatosaurus edmontoni'', emended to ''edmontonensis''), and ''E. saskatchewanensis''. The debate about the proper taxonomy of the ''A. copei'' specimens continues to the present: returning to Hatcher's argument of 1902, Jack Horner,
David B. Weishampel Professor David Bruce Weishampel (born November 16, 1952) is an American palaeontologist in the Center for Functional Anatomy and Evolution at Johns Hopkins University School of Medicine. Weishampel received his Ph.D. in Geology from the Universi ...
, and Catherine Forster regarded ''Anatotitan copei'' as representing specimens of ''Edmontosaurus annectens'' with crushed skulls. In 2007 another "mummy" was announced; nicknamed "
Dakota Dakota may refer to: * Dakota people, a sub-tribe of the Sioux ** Dakota language, their language Dakota may also refer to: Places United States * Dakota, Georgia, an unincorporated community * Dakota, Illinois, a town * Dakota, Minnesota, a ...
", it was discovered in 1999 by Tyler Lyson, and came from the
Hell Creek Formation The Hell Creek Formation is an intensively studied division of mostly Upper Cretaceous and some lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana. The formation stretches over portions of ...
of
North Dakota North Dakota () is a U.S. state in the Upper Midwest, named after the Native Americans in the United States, indigenous Dakota people, Dakota Sioux. North Dakota is bordered by the Canadian provinces of Saskatchewan and Manitoba to the north a ...
. In a 2011 study by Nicolás Campione and David Evans, the authors conducted the first-ever
morphometric Morphometrics (from Greek μορϕή ''morphe'', "shape, form", and -μετρία ''metria'', "measurement") or morphometry refers to the quantitative analysis of ''form'', a concept that encompasses size and shape. Morphometric analyses are co ...
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 can be distinguished from skulls of ''E. regalis'' by the elongate snout and other details of skull anatomy.


Description

The skull and skeleton of ''E. annectens'' are well-known.
Edward Drinker Cope Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American zoologist, paleontologist, comparative anatomist, herpetologist, and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy interested ...
estimated the length of one specimen as about long, with a skull long. This body length estimate was later revised down to a length of , although to be fair to Cope a dozen
vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...
e, the
hips In vertebrate anatomy, hip (or "coxa"Latin ''coxa'' was used by Celsus in the sense "hip", but by Pliny the Elder in the sense "hip bone" (Diab, p 77) in medical terminology) refers to either an anatomical region or a joint. The hip region is ...
, and thigh bones had been carried away by a stream cutting through the skeleton, and the tip of the tail was incomplete. A second skeleton currently exhibited next to Cope's specimen, but in a standing posture, is estimated at long, with its head above the ground. The hip height of this specimen is estimated as approximately . Other sources have estimated the length of ''E. annectens'' as approximately . Most specimens are somewhat shorter, representing individuals that are not fully grown. Two well-known mounted skeletons, USNM 2414 and YPM 2182, measure long and long, respectively. ''E. annectens'' may have weighed about 6.6 
metric ton The tonne ( or ; symbol: t) is a unit of mass equal to 1000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton (United States c ...
s (7.3  tons) when fully grown. Recently-found specimens that are still under study at the
Museum of the Rockies Museum of the Rockies is a museum in Bozeman, Montana. Originally affiliated with Montana State University in Bozeman, and now also, the Smithsonian Institution, the museum is largely known for its paleontological collections. The Museum houses ...
, namely MOR 1142 ("X-rex") and MOR 1609 ("Becky's Giant"), suggest that ''E. annectens'' may have reached lengths of nearly and weighed , potentially making it one of the largest hadrosaurids; however, Horner and his colleagues suggested that such large individuals would have been extremely rare. The 2022 study on the osteohistology and growth of ''E. annectens'' suggested that previous estimates might have underestimated or overestimated the size of this dinosaur and argued that a fully grown adult ''E. annectens'' would have measured up to in length and in average asymptotic body mass, while the largest individuals measured more than , even up to , based on the comparison between various specimens of different sizes from the Ruth Mason Dinosaur Quarry and other specimens from different localities. The skull of ''E. annectens'' is known for its long, wide muzzle. Cope compared this feature to that of a
goose A goose ( : geese) is a bird of any of several waterfowl species in the family Anatidae. This group comprises the genera ''Anser'' (the grey geese and white geese) and '' Branta'' (the black geese). Some other birds, mostly related to the ...
in side view, and to a short-billed spoonbill in top view. The skull was longer and lower proportionally than in any other known hadrosaurid. The toothless portion of the
anterior Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...
was relatively longer than in any hadrosaur. The extreme length and breadth did not appear until an individual reached maturity, so many specimens lack the distinctive shape. The bones surrounding the large openings for the
nostril A nostril (or naris , plural ''nares'' ) is either of the two orifices of the nose. They enable the entry and exit of air and other gasses through the nasal cavities. In birds and mammals, they contain branched bones or cartilages called turbi ...
s formed deep pockets around the openings. The
eye sockets In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents. In the adult human, the volume of the orbit is , o ...
were rectangular and longer front to back than top to bottom, although this may have been exaggerated by postmortem crushing. The skull roof was flat and lacked a bony crest, and the
quadrate bone The quadrate bone is a skull bone in most tetrapods, including amphibians, sauropsids (reptiles, birds), and early synapsids. In most tetrapods, the quadrate bone connects to the quadratojugal and squamosal bones in the skull, and forms upper ...
that formed the articulation with the lower jaw was distinctly curved. The lower jaw was long and straight, lacking the downward curve seen in other hadrosaurids, and possessing a heavy ridge running its length. The
predentary Ornithischia () is an extinct order of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek st ...
was wide and shovel-like.Lull and Wright, ''Hadrosaurian Dinosaurs of North America'', pp. 157-159. The ridge on the lower jaw may have reinforced the long, slender structure.Lull and Wright, ''Hadrosaurian Dinosaurs of North America'', pp. 163-164. As mounted, the vertebral column of ''E. annectens'' includes twelve neck, twelve back, nine
sacral Sacral may refer to: *Sacred Sacred describes something that is dedicated or set apart for the service or worship of a deity; is considered worthy of spiritual respect or devotion; or inspires awe or reverence among believers. The property ...
, and at least thirty tail vertebrae. The limb bones were longer and more lightly built than those of other hadrosaurids of comparable size. ''E. annectens'' had a distinctive pelvis, based on the proportions and form of the pubis bone. ''E. annectens'', like other hadrosaurids, could move both on two legs and on four legs. It probably preferred to forage for food on four legs, but ran on two.
Henry Fairfield Osborn Henry Fairfield Osborn, Sr. (August 8, 1857 – November 6, 1935) was an American paleontologist, geologist and eugenics advocate. He was the president of the American Museum of Natural History for 25 years and a cofounder of the American Euge ...
used the skeletons in the
American Museum of Natural History The American Museum of Natural History (abbreviated as AMNH) is a natural history museum on the Upper West Side of Manhattan in New York City. In Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 26 inter ...
to portray both quadrupedal and bipedal stances for ''E. annectens''.


Classification

''E. annectens'' was a
saurolophine Saurolophinae is a subfamily (biology), subfamily of hadrosaurid dinosaurs. It has since the mid-20th century generally been called the Hadrosaurinae, a group of largely non-crested hadrosaurs related to the crested sub-family Lambeosaurinae. How ...
or "flat-headed"
hadrosaurid Hadrosaurids (), or duck-billed dinosaurs, are members of the ornithischian family Hadrosauridae. This group is known as the duck-billed dinosaurs for the flat duck-bill appearance of the bones in their snouts. The ornithopod family, which inclu ...
; this group was historically known as Hadrosaurinae. Species now considered to be synonyms of ''Edmontosaurus annectens'' were long recognized as closely related to both the genus and the species. However, the skull of the sub-adult type specimen of ''E. annectens'' differs noticeably from fully mature remains, so many researchers had classified the two growth stages as different species or even genera. On the other side of the issue, other authors, from
John Bell Hatcher John Bell Hatcher (October 11, 1861 – July 3, 1904) was an American paleontologist and fossil hunter known as the "king of collectors" and best known for discovering ''Torosaurus'' and ''Triceratops'', two genera of dinosaurs described by Ot ...
in 1902, to Jack Horner,
David B. Weishampel Professor David Bruce Weishampel (born November 16, 1952) is an American palaeontologist in the Center for Functional Anatomy and Evolution at Johns Hopkins University School of Medicine. Weishampel received his Ph.D. in Geology from the Universi ...
, and
Catherine Forster Catherine Ann Forster is an American paleontologist, taxonomist and expert in ornithopod evolution and ''Triceratops ''Triceratops'' ( ; ) is a genus of herbivorous chasmosaurine ceratopsid dinosaur that first appeared during the late ...
in 2004, and most recently Nicolás Campione and David Evans, have proposed that the large, flat-headed specimens most recently classified as ''Anatotitan copei'' belong to ''E. annectens''. ''E. annectens'' was also historically classified in an independent genus, ''Anatosaurus'', following the influential 1942 revision of Hadrosauridae by
Richard Swann Lull Richard Swann Lull (November 6, 1867 – April 22, 1957) was an American paleontologist and Sterling Professor at Yale University who is largely remembered now for championing a non-Darwinian view of evolution, whereby mutation(s) could unl ...
and
Nelda Wright Nelda is a given name. Notable people with the name include: * Nelda Garrone ( 1880–?), Italian mezzo-soprano *Nelda Martinez (born 1961), American real estate agent and politician *Nelda Speaks (born 1943), American politician See also *Zelda ...
, until it was reclassified as a species of ''Edmontosaurus'' by Michael K. Brett-Surman. With the discovery that ''A. copei'' and ''E. annectens'' likely represent the same species, some paleontologists have proposed using ''Anatosaurus'' as a valid genus name for ''E. annectens''. The
cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to d ...
below follows Godefroit ''et al.'' (2012) analysis.


Paleobiology

As hadrosaurids, individuals of ''Edmontosaurus annectens'' would have been large
herbivore A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...
s, eating plants with a sophisticated skull that permitted a grinding motion analogous to
chewing Chewing or mastication is the process by which food is crushed and ground by teeth. It is the first step of digestion, and it increases the surface area of foods to allow a more efficient break down by enzymes. During the mastication process, th ...
. Their
teeth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...
were continually replaced and packed into dental batteries that contained hundreds of teeth, only a relative handful of which were in use at any time. Plant material would have been cropped by the broad beak, and held in the jaws by a
cheek The cheeks ( la, buccae) constitute the area of the face below the eyes and between the nose and the left or right ear. "Buccal" means relating to the cheek. In humans, the region is innervated by the buccal nerve. The area between the inside ...
-like structure. Feeding would have been from the ground up to around 4 meters (13 ft) above. Like other hadrosaurs, they could have moved both
bipedally Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning 'two feet' (from Latin ''bis'' 'double' a ...
and
quadruped Quadrupedalism is a form of locomotion where four limbs are used to bear weight and move around. An animal or machine that usually maintains a four-legged posture and moves using all four limbs is said to be a quadruped (from Latin ''quattuor' ...
ally. The extensive depressions surrounding its nasal openings may have hosted nasal diverticula. These postulated
diverticula In medicine or biology, a diverticulum is an outpouching of a hollow (or a fluid-filled) structure in the body. Depending upon which layers of the structure are involved, diverticula are described as being either true or false. In medicine, t ...
would have taken the form of inflatable soft-tissue sacs. Such sacs could be used for both visual and auditory signals. A preserved
rhamphotheca The beak, bill, or rostrum is an external anatomical structure found mostly in birds, but also in turtles, non-avian dinosaurs and a few mammals. A beak is used for eating, preening, manipulating objects, killing prey, fighting, probing for food, ...
present in specimen LACM 23502, housed in the Los Angeles County Museum, also indicates the beak of ''Edmontosaurus'' was more hook-shaped and extensive than many illustrations in scientific and public media have previously depicted.


Growth

In a 2011 study, Campione and Evans recorded data from all known "edmontosaur" skulls from the Campanian and Maastrichtian and used it to plot a morphometric' graph, comparing variable features of the skull with skull size. Their results showed that within both recognized ''Edmontosaurus'' species, many features previously used to classify additional species or genera were directly correlated with skull size. Campione and Evans interpreted these results as strongly suggesting that the shape of ''Edmontosaurus'' skulls changed dramatically as they grew. This has led to several apparent mistakes in classification in the past. The three previously recognized Maastrichtian edmontosaur species likely represent growth stages of a single species, with ''E. saskatchewanensis'' representing juveniles, ''E. annectens'' subadults, and ''Anatotitan copei'' fully mature adults. The skulls became longer and flatter as the animals grew. In a 2022 study, Wosik and Evans proposed that ''E. annectens'' reached maturity in 9 years of age based on their analysis for various specimens from different loaclities. They found the result to be similar to that of other hadrosaurs.


Paleoecology

True ''E. annectens'' remains are known only from latest
Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval from ...
-age rocks of the
Hell Creek The Hell Creek Formation is an intensively studied division of mostly Upper Cretaceous and some lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana. The formation stretches over portions of ...
and
Lance Formation The Lance (Creek) Formation is a division of Late Cretaceous (dating to about 69 - 66 Ma) rocks in the western United States. Named after Lance Creek, Wyoming, the microvertebrate fossils and dinosaurs represent important components of the late ...
s from South Dakota, Montana, and Wyoming, USA and the
Frenchman Formation The Frenchman Formation is stratigraphic unit of Late Cretaceous (late Maastrichtian) age in the Western Canada Sedimentary Basin. It is present in southern Saskatchewan and the Cypress Hills of southeastern Alberta. The formation was defined by ...
of Saskatchewan, Canada. The Lancian time interval was the last interval before the
Cretaceous–Paleogene extinction event The Cretaceous–Paleogene (K–Pg) extinction event (also known as the Cretaceous–Tertiary extinction) was a sudden mass extinction of three-quarters of the plant and animal species on Earth, approximately 66 million years ago. With the ...
that eliminated non-
avian Avian may refer to: *Birds or Aves, winged animals *Avian (given name) (russian: Авиа́н, link=no), a male forename Aviation *Avro Avian, a series of light aircraft made by Avro in the 1920s and 1930s *Avian Limited, a hang glider manufacture ...
dinosaurs. ''Edmontosaurus'' was one of the more common dinosaurs of the interval. Robert Bakker reports that it made up one-seventh of the large dinosaur sample, with most of the rest (five-sixths) made up of the horned dinosaur ''
Triceratops ''Triceratops'' ( ; ) is a genus of herbivore, herbivorous Chasmosaurinae, chasmosaurine Ceratopsidae, ceratopsid dinosaur that first appeared during the late Maastrichtian stage of the Late Cretaceous Period (geology), period, about 68 m ...
''.Bakker, Robert T. (1986). ''
The Dinosaur Heresies ''The Dinosaur Heresies: New Theories Unlocking the Mystery of the Dinosaurs and Their Extinction'' is a 1986 book written by Robert T. Bakker. The book sums up the extant evidence that indicates that dinosaurs, rather than being Ectotherm, cold ...
''. p. 438.
The
coastal plain A coastal plain is flat, low-lying land adjacent to a sea coast. A fall line commonly marks the border between a coastal plain and a piedmont area. Some of the largest coastal plains are in Alaska and the southeastern United States. The Gulf Coa ...
''Triceratops''–''Edmontosaurus'' association, dominated by ''Triceratops'', extended from Colorado to Saskatchewan. Typical dinosaur faunas of the Lancian formations where ''Edmontosaurus annectens'' has been found also included the hypsilophodont ''
Thescelosaurus ''Thescelosaurus'' ( ; ancient Greek - (''-'') meaning "godlike", "marvellous", or "wondrous" and (') "lizard") was a genus of small neornithischian dinosaur that appeared at the very end of the Late Cretaceous period in North America. It was a ...
'', the rare ceratopsid ''
Torosaurus ''Torosaurus'' ("perforated lizard", in reference to the large openings in its frill) is a genus of herbivorous ceratopsid dinosaur that lived during the late Maastrichtian stage of the Cretaceous period, between 68 and 66 million years ago, th ...
'', the pachycephalosaurid ''
Pachycephalosaurus ''Pachycephalosaurus'' (; meaning "thick-headed lizard", from Greek ''pachys-/'' "thick", ''kephale/'' "head" and ''sauros/'' "lizard") is a genus of pachycephalosaurid dinosaurs. The type species, ''P. wyomingensis'', is the only known species, ...
'', the ankylosaurid ''
Ankylosaurus ''Ankylosaurus'' is a genus of armored dinosaur. Its fossils have been found in geological formations dating to the very end of the Cretaceous Period, about 68–66 million years ago, in western North America, making it among the last of the n ...
'', and the theropods ''
Ornithomimus ''Ornithomimus'' (; "bird mimic") is a genus of ornithomimid dinosaurs from the Late Cretaceous Period of what is now North America. ''Ornithomimus'' was a swift bipedal theropod which fossil evidence indicates was covered in feathers, equipped w ...
'', ''
Pectinodon ''Pectinodon'' is a genus of troodontid dinosaurs from the Late Cretaceous period (66  mya). It currently contains a single valid species, ''Pectinodon bakkeri'' (sometimes classified as ''Troodon bakkeri''), known only from teeth. In 1982, ...
'', ''
Acheroraptor ''Acheroraptor'' is an extinct genus of dromaeosaurid theropod dinosaur known from the latest Maastrichtian Hell Creek Formation of Montana, United States. It contains a single species, ''Acheroraptor temertyorum''. ''A. temertyorum'' is ...
'', ''
Dakotaraptor ''Dakotaraptor'' (meaning “thief from Dakota”) is a potentially chimaeric genus of large dromaeosaurid theropod dinosaur that lived in North America during the Late Cretaceous period. The remains have been found in the Maastrichtian stage of ...
'', and ''
Tyrannosaurus ''Tyrannosaurus'' is a genus of large theropoda, theropod dinosaur. The species ''Tyrannosaurus rex'' (''rex'' meaning "king" in Latin), often called ''T. rex'' or colloquially ''T-Rex'', is one of the best represented theropods. ''Tyrannosa ...
''. The Hell Creek Formation, as typified by exposures in the
Fort Peck Fort Peck is a town in Valley County, Montana, United States. The population was 239 at the 2020 census. History The name Fort Peck is associated with Col. Campbell K. Peck, the partner of Elias H. Durfee in the Leavenworth, Kansas trading firm ...
area of Montana, has been interpreted as a flat forested floodplain, with a relatively dry
subtropical The subtropical zones or subtropics are geographical zone, geographical and Köppen climate classification, climate zones to the Northern Hemisphere, north and Southern Hemisphere, south of the tropics. Geographically part of the Geographical z ...
climate that supported a variety of plants ranging from
angiosperm Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...
trees, to conifers such as bald cypress, to
fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes except t ...
s and
ginkgo ''Ginkgo'' is a genus of non-flowering seed plants. The scientific name is also used as the English name. The order to which it belongs, Ginkgoales, first appeared in the Permian, 270 million years ago, and is now the only living genus within ...
s. The coastline was hundreds of kilometers or miles to the east. Stream-dwelling turtles and tree-dwelling
multituberculate Multituberculata (commonly known as multituberculates, named for the multiple tubercles of their teeth) is an extinct order of rodent-like mammals with a fossil record spanning over 130 million years. They first appeared in the Middle Jurassic, a ...
mammals were diverse, and
monitor lizard Monitor lizards are lizards in the genus ''Varanus,'' the only extant genus in the family Varanidae. They are native to Africa, Asia, and Oceania, and one species is also found in the Americas as an invasive species. About 80 species are recogn ...
s as large as the modern
Komodo dragon The Komodo dragon (''Varanus komodoensis''), also known as the Komodo monitor, is a member of the monitor lizard family Varanidae that is endemic to the Indonesian islands of Komodo, Rinca, Flores, and Gili Motang. It is the largest extant ...
hunted on the ground. ''Triceratops'' was the most abundant large dinosaur, and ''Thescelosaurus'' the most abundant small herbivorous dinosaur. Edmontosaur remains have been collected here from stream channel sands, and include fossils from individuals as young as a meter- or yard-long infant. The edmontosaur fossils probably represent accumulations from groups on the move.Russell, Dale A. (1989). ''An Odyssey in Time: Dinosaurs of North America''. pp. 175–180. The Lance Formation, as typified by exposures approximately north of
Fort Laramie Fort Laramie (founded as Fort William and known for a while as Fort John) was a significant 19th-century trading-post, diplomatic site, and military installation located at the confluence of the Laramie and the North Platte rivers. They joined ...
in eastern Wyoming, has been interpreted as a
bayou In usage in the Southern United States, a bayou () is a body of water typically found in a flat, low-lying area. It may refer to an extremely slow-moving stream, river (often with a poorly defined shoreline), marshy lake, wetland, or creek. They ...
setting similar to the
Louisiana Louisiana , group=pronunciation (French: ''La Louisiane'') is a state in the Deep South and South Central regions of the United States. It is the 20th-smallest by area and the 25th most populous of the 50 U.S. states. Louisiana is borde ...
coastal plain. It was closer to a large delta than the Hell Creek Formation depositional setting to the north and received much more sediment. Tropical araucarian
conifers Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single extant class, Pinopsida. All extan ...
and arecaceae, palm trees dotted the hardwood forests, differentiating the flora from the northern coastal plain.Russell, Dale A. (1989). ''An Odyssey in Time: Dinosaurs of North America''. pp. 180–181. The climate was humid and subtropical, with conifers, sabal, palmettos, and ferns in the swamps, and conifers, Fraxinus, ash, live oak, and shrubs in the forests. Freshwater fish, salamanders, turtles, diverse lizards, snakes, shorebirds, and small mammals lived alongside the dinosaurs. Small dinosaurs are not known in as great of abundance here as in the Hell Creek rocks, but ''Thescelosaurus'' once again seems to have been relatively common. ''Triceratops'' is known from many skulls, which tend to be somewhat smaller than those of more northern individuals. The Lance Formation is the setting of two edmontosaur "mummies".


See also

* Timeline of hadrosaur research


Notes

Many of the original references deal with specimens or species that were not assigned to ''E. annectens'' until later. This is particularly true with the specimens long known, chronologically, as ''Diclonius mirabilis'', ''Anatosaurus copei'', and ''Anatotitan copei''. This toothless section is also known as a ''diastema''.


References

{{Taxonbar, from=Q15063746 Late Cretaceous dinosaurs of North America Saurolophines Lance fauna Maastrichtian life Hell Creek fauna Scollard fauna Paleontology in Montana Paleontology in South Dakota Paleontology in North Dakota Paleontology in Wyoming Paleontology in Colorado Paleontology in Saskatchewan Maastrichtian species Taxa named by Othniel Charles Marsh Fossil taxa described in 1892