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Edmontosaurus annectens

Edmontosaurus annectens (meaning "connected lizard from Edmonton"), often colloquially and historically known as the Anatosaurus (meaning "duck lizard"), is a species of flat-headed saurolophine hadrosaurid dinosaur from the late Maastrichtian age at the very end of the Cretaceous period, in what is now western North America. Remains of E. annectens have been preserved in the Frenchman, Hell Creek, and Lance Formations. All of these formations are dated to the late Maastrichtian age of the Late Cretaceous period, which represents the last three million years before the extinction of the dinosaurs (between 68 and 66 million years ago[1]).[2] E. annectens is also found in the Laramie Formation, and magnetostratigraphy suggests an age of 69–68 Ma for the Laramie Formation.[3] Edmontosaurus annectens is known from numerous specimens, including at least twenty partial to complete skulls, discovered in the U.S. states of Montana, South Dakota, North Dakota, Wyoming, and Colorado, as well as the Canadian province of Saskatchewan. It had an extremely long and low skull, and was quite a large animal, growing up to approximately 12 metres (39 ft) in length and 5.6 metric tons (6.2 short tons) in average asymptotic body mass, although it could have been even larger.[4][5][6][7] E. annectens exhibits one of the most striking examples of the "duckbill" snout that is common to hadrosaurs. It has a long taxonomic history, and specimens have at times been classified as Diclonius, Trachodon, Hadrosaurus, Claosaurus, Thespesius, Anatosaurus, and Anatotitan before all being grouped together in Edmontosaurus

Edmontosaurus annectens
Temporal range: Late Cretaceous (Maastrichtian),[1] 68–66 Ma
Mounted cast of a fossil E. annectens skeleton, Oxford University Museum of Natural History
Scientific classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Ornithischia
Clade: Ornithopoda
Family: Hadrosauridae
Subfamily: Saurolophinae
Genus: Edmontosaurus
Species:
E. annectens
Binomial name
Edmontosaurus annectens
(Marsh, 1892)
Synonyms
  • Trachodon longiceps
    Marsh, 1890
  • Hadrosaurus longiceps
    (Marsh, 1890) Nopcsa, 1900
  • Claosaurus annectens
    Marsh, 1892
  • Trachodon annectens
    (Marsh, 1892) Hay, 1902
  • Thespesius annectens
    (Marsh, 1892) Sternberg, 1925
  • Thespesius saskatchewanensis
    Sternberg, 1926
  • Trachodon saskatchewanensis
    (Sternberg, 1926) Kuhn, 1936
  • Thespesius longiceps
    (Marsh, 1890) Russell, 1930
  • Anatosaurus annectens
    (Marsh, 1892) Lull & Wright, 1942
  • Anatosaurus longiceps
    (Marsh, 1890) Lull & Wright, 1942
  • Anatosaurus saskatchewanensis
    (Sternberg, 1926) Lull & Wright, 1942
  • Anatosaurus copei
    Lull & Wright, 1942
  • Edmontosaurus copei
    (Lull & Wright, 1942) Brett-Surman, 1975
  • Anatotitan copei
    (Lull & Wright, 1942) Brett-Surman vide Chapman & Brett-Surman, 1990
  • Anatotitan longiceps
    (Marsh, 1890) Olshevsky, 1991
  • Edmontosaurus saskatchewanensis
    (Sternberg, 1926) Horner, Weishampel & Forster, 2004

Discovery and history edit

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.[8][9] 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 edit

 
Skeletons (AMNH 5730, left, and AMNH 5886, right), first mounted in the American Museum of Natural History in 1908.[10]

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[11] for American paleontologist Edward Drinker Cope. This specimen, found in Hell Creek Formation rocks,[12] 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.[13] When describing this specimen, AMNH 5730, Cope assigned it to the species Diclonius mirabilis. This species name was created by combining Diclonius, a hadrosaurid genus Cope had named earlier from teeth, with Trachodon mirabilis, an older name based on teeth that was published by Joseph Leidy. 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.[14] Leidy had come to recognize that his Trachodon was based on the remains of multiple kinds of dinosaurs, and although he had made some attempts to revise the genus, he had not yet made any formal declaration of his intentions.[9]

Cope's description promoted hadrosaurids as amphibious animals, contributing to this long-time image.[15] 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.[14] However, aside from misidentifying several of the skull bones,[16] by chance, the lower jaws were missing the walls supporting the teeth from the inside, and the teeth were actually very well-supported.[15][17] Cope intended to describe the skeleton and skull, but his promised paper never appeared.[9] It was purchased for the American Museum of Natural History in 1899, where it acquired its present designation: AMNH 5730.[18]

 
Outdated 1909 life restoration of Trachodon by Charles R. Knight, based on the two specimens (now classified as E. annectens) mounted in 1908 at the AMNH, New York.[10]

Several years after Cope's description, his arch-rival, Othniel Charles Marsh, published a paper on a sizable lower jaw recovered by John Bell Hatcher in 1889 from the Lance Formation rocks in Niobrara County, Wyoming.[19] Marsh named this partial jaw Trachodon longiceps,[20] 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 92.0 centimetres (36.2 in) long, whereas Marsh's dentary is estimated at 110.0 centimetres (43.3 in) long.[19]

A second mostly complete skeleton, AMNH 5886, was found in 1904 in the Hell Creek Formation rocks at Crooked Creek in central Montana by a local rancher named Oscar Hunter. 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. Another cowboy, Alfred Sensiba, bought the specimen from Hunter for a pistol and later sold it to Brown, who excavated it for the American Museum of Natural History in 1906.[12] This specimen had a nearly complete vertebral 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.[10] 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 described the tableau as representing the two animals feeding alongside a marsh, the standing individual having been startled by the approach of a Tyrannosaurus. Impressions of appropriate plant remains and shells based on associated fossils were included on the base of the group, including ginkgo leaves, Sequoia cones, and horsetail rushes.[13]

Marsh's Claosaurus annectens edit

 
Skeletal restoration of the E. annectens (then Claosaurus) holotype, by Othniel Charles Marsh.
 
E. annectens paratype YPM 2182 at the Yale University Museum, the first nearly complete dinosaur skeleton mounted in the United States.[21]

The species now known as Edmontosaurus annectens was named in 1892 as Claosaurus annectens by Othniel Charles Marsh. This species is based on USNM 2414, a partial skull-roof and skeleton, with a second skull and skeleton, YPM 2182, being designated as the paratype. Both were collected in 1891 by John Bell Hatcher, from the late Maastrichtian-age Upper Cretaceous Lance Formation of Niobrara County (then part of Converse County), Wyoming.[22] 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.[9][23] YPM 2182 and UNSM 2414 are, respectively, the first and second essentially complete mounted dinosaur skeletons in the United States.[21] YPM 2182 was put on display in 1901,[9] and USNM 2414 was put on display in 1904.[21]

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 and his sons in the Lance Formation rocks near Lusk, Wyoming. Sternberg was working for the British Museum of Natural History, but Henry Fairfield Osborn of the American Museum of Natural History was able to purchase the specimen for $2,000.[24] The Sternbergs recovered a second similar specimen from the same area in 1910.[25] It was not as well-preserved, but also found with skin impressions. They sold this specimen, SM 4036, to the Senckenberg Museum in Germany.[24]

Canadian discoveries edit

Edmontosaurus itself was coined in 1917 by Lawrence Lambe for two partial skeletons found in the Horseshoe Canyon Formation (formerly the lower Edmonton Formation), along the Red Deer River of southern Alberta.[26] The Horseshoe Canyon Formation is older than the rocks in which Claosaurus annectens was found.[27] Lambe found that his new dinosaur compared best to Cope's Diclonius mirabilis.[26]

In 1926, Charles Mortram Sternberg named Thespesius saskatchewanensis for NMC 8509, a skull and partial skeleton from the Wood Mountain plateau of southern Saskatchewan. He had collected this specimen in 1921 from rocks that were assigned to the Lance Formation,[28] now the Frenchman Formation.[8] NMC 8509 included an almost complete skull, numerous vertebrae, partial shoulder and hip girdles, and partial back legs, 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.[28] At the time, T. saskatchewanensis was unusual because of its small size, estimated at 7 to 7.3 meters (23 to 24 ft) in length.[29]

Early classifications edit

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, with textbooks and encyclopedias drawing a distinction between the "Iguanodon-like" Claosaurus annectens and the "duck-billed" Hadrosaurus (based on Cope's Diclonius mirabilis); conversely, Hatcher explicitly identified C. annectens as synonymous with the hadrosaurid represented by those same duck-billed skulls,[9] the two differentiated only by individual variation or distortion from pressure.[30] Hatcher's revision, published in 1902, was sweeping, as he considered almost all hadrosaurid genera then known as synonyms of Trachodon. This included Cionodon, Diclonius, Hadrosaurus, Ornithotarsus, Pteropelyx, and Thespesius, as well as Claorhynchus and Polyonax,[30] fragmentary genera now thought to be ceratopsians. 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.[9] In 1915, Charles W. Gilmore reassessed hadrosaurids, and recommended that Thespesius should 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 and its equivalents. In regards to Claosaurus annectens, he recommended that it be considered the same as Thespesius occidentalis.[31] A multiplicity of names resumed, with the AMNH duckbills being known as Diclonius mirabilis, Trachodon mirabilis, Trachodon annectens, Claosaurus, or Thespesius.[9]

Anatosaurus to the present edit

 
AMNH 5060: a well-preserved specimen of E. annectens.

This confusing situation was temporarily resolved in 1942 by Richard Swann Lull and Nelda Wright. In their monograph on hadrosaurian dinosaurs of North America, they opted to settle the questions revolving around the AMNH duckbills, Marsh's Claosaurus annectens, and several other species, by creating a new generic name. They created the new genus Anatosaurus (meaning "duck lizard", because of its wide, duck-like beak; Latin anas = duck + Greek sauros = lizard), and made Marsh's species the type species, calling it Anatosaurus annectens. They also assigned Marsh's Trachodon longiceps to this genus, 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.[32] 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.[18] Anatosaurus would come to be called the "classic duck-billed dinosaur".[33]

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.[34][35][36] 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.[37][38] 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.[39] 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).[40] Because the type species of Anatosaurus (A. annectens) was sunk into Edmontosaurus, the name Anatosaurus is abandoned as a junior synonym of Edmontosaurus.

 
A well-preserved skin impression of the specimen nicknamed "Dakota," which was found in 1999.

Of the remaining species of Anatosaurus, A. saskatchewanensis and A. edmontoni were assigned to Edmontosaurus as well,[41] and A. longiceps went to Anatotitan, as either a second species[42] or as a synonym of A. copei.[41] A. longiceps may be a synonym of E. annectens,[8] though it has also been treated as a nomen dubium by some.[43]

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.[41] The debate about the proper taxonomy of the A. copei specimens continues to the present day. Returning to Hatcher's argument of 1902, Jack Horner, David B. Weishampel, and Catherine Forster regarded Anatotitan copei as representing specimens of Edmontosaurus annectens with crushed skulls.[8] In 2007, another "mummy" was announced. Nicknamed "Dakota," it was discovered in 1999 by Tyler Lyson, and came from the Hell Creek Formation of North Dakota.[44][45]

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.[27]

Description edit

 
Scale diagram comparing large adult specimens of E. regalis (gray) and E. annectens (green) to a human.

The skull and skeleton of E. annectens are very well-known. Edward Drinker Cope estimated the length of one specimen as about 38 feet (12 m) long, with a skull 3.87 feet (1.18 m) long.[14]* This body length estimate was later revised down to a length of 29 feet (8.8m).[29] To be fair to Cope, a dozen vertebrae, the hips, and thigh bones had been carried away by a stream cutting through the skeleton, and the tip of the tail was incomplete.[13] A second skeleton currently exhibited next to Cope's specimen, but in a standing posture, is estimated at 30 feet (9.1 m) long, with its head 17 feet (5.2 m) above the ground.[13] The hip height of this specimen is estimated as approximately 6.9 feet (2.1 m).[11] Other sources have estimated the length of E. annectens as approximately 39 feet (12 m).[46][47] Most specimens are somewhat shorter, representing individuals that are not fully grown.[27] Two well-known mounted skeletons, USNM 2414 and YPM 2182, measure 26.25 feet (8.00 m) long and 29.3 feet (8.9 m) long, respectively.[29][21] E. annectens may have weighed about 7.3 tons (6.6 metric tons) when fully grown.[11]

 
Artist illustration depicting a life restoration.

Recently-found specimens that are still under study at the Museum of the Rockies, namely MOR 1142 ("X-rex") and MOR 1609 ("Becky's Giant"), suggest that E. annectens may have reached lengths of nearly 49 feet (15 m) and weighed 11 short tons (10.0 t), potentially making it one of the largest hadrosaurids ever. However, Jack Horner and his colleagues suggested that such large individuals would have been extremely rare.[5][6][7] 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 36–39 feet (11–12 m) in length and 5.6 metric tons (6.2 short tons) in average asymptotic body mass, while the largest individuals measured more than 6 metric tons (6.6 short tons) and even up to 6.6–7 metric tons (7.3–7.7 short tons), based on the comparison between various specimens of different sizes from the Ruth Mason Dinosaur Quarry and other specimens from different localities.[4]

 
Tail vertebrae

The skull of E. annectens is known for its long, wide muzzle. Cope compared this feature to that of a goose in side view, and to a short-billed spoonbill in top view.[14] The skull was proportionally longer and lower than in any other known hadrosaurid. The toothless portion of the anterior mandible* was also relatively longer than in any hadrosaur.[40] The extreme length and breadth did not appear until an individual reached maturity, so many specimens lack the distinctive shape.[27] The bones surrounding the large openings for the nostrils formed deep pockets around the openings. The eye sockets were rectangular and longer front to back than they were top to bottom, although this may have been exaggerated by postmortem crushing. The skull roof was flat and lacked a bony crest like that of E. regalis. The quadrate bone that formed the articulation with the lower jaw was distinctly curved. The lower jaw was long, straight, and lacking the downward curve seen in other hadrosaurids, as well as possessing a heavy ridge running its length. The predentary was wide and shovel-like.[18] The ridge on the lower jaw may have reinforced the long, slender structure.[19]

As mounted, the vertebral column of E. annectens includes twelve neck, twelve back, nine sacral, and at least thirty tail vertebrae.[18] 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.[40] 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.[8] Henry Fairfield Osborn used the skeletons in the American Museum of Natural History to portray both quadrupedal and bipedal stances for E. annectens.[13]

Classification edit

 
E. annectens holotype, Smithsonian National Museum of Natural History
 
Most known complete Edmontosaurus skulls (E. annectens from lower middle to right).

E. annectens was a saurolophine, or "flat-headed", hadrosaurid. This group was historically known as Hadrosaurinae.[48] Species now considered to be synonymous with Edmontosaurus annectens were long recognized as closely related to both the genus[49] and the species.[30] 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 different genera. On the other side of the issue, other authors, from John Bell Hatcher in 1902,[30] to Jack Horner, David B. Weishampel, and Catherine Forster in 2004,[8] and most recently Nicolás Campione and David Evans,[27] 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 and Nelda Wright, until it was reclassified as a species of Edmontosaurus by Michael K. Brett-Surman.[40] With the discovery that A. copei and E. annectens most likely represent the same species, some paleontologists have proposed using Anatosaurus as a valid genus name for E. annectens.[1]

The cladogram below follows Godefroit et al. (2012) analysis.[50]

Paleobiology edit

 
Close-up of teeth.

As a hadrosaurid, Edmontosaurus annectens was a fairly large herbivore, eating plants with a sophisticated skull that permitted a grinding motion analogous to chewing. Their teeth were continually replaced and packed into dental batteries that contained hundreds of teeth, but only a relative handful of them were in use at any time. Plant material would have been cropped by the broad beak, and held in the jaws by a cheek-like structure. Feeding would have been from the ground up to around 13 feet (4 meters) above the ground. Like other hadrosaurs, they could have moved both bipedally and quadrupedally.[8]

The extensive depressions surrounding its nasal openings may have hosted nasal diverticula. These postulated diverticula would have taken the form of inflatable soft-tissue sacs. Such sacs could be used for both visual and auditory signals.[51]

A preserved rhamphotheca 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.[52][53]

Growth edit

 
Mounted skeletons of a juvenile and adult E. annectens at the Houston Museum of Natural Science, nicknamed Diana and Leon.

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 skulls with skull size. Their results showed that, in both recognized Edmontosaurus species, many features previously used to classify additional species or genera were directly correlated to skull size. Campione and Evans interpreted these results as strongly suggesting that the shape of Edmontosaurus skulls changed dramatically as they grew and matured. This has led to several apparent mistakes in past classification. 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 being fully mature adults. The skulls became longer and flatter as the animals grew.[27] In a 2022 study, Wosik and Evans proposed that E. annectens reached maturity in 9 years, based on their analysis for various specimens from different localities. They found the result to be similar to that of other hadrosaurs.[4]

Paleoecology edit

 
The damage to the tail vertebrae of this E. annectens skeleton (on display at the Denver Museum of Nature and Science) indicates that it may have been bitten by a Tyrannosaurus.

True E. annectens remains are known only from latest Maastrichtian rocks of the Hell Creek and Lance Formations of South Dakota, Montana, and Wyoming, alongside the Frenchman Formation of Saskatchewan.[27]

The Lancian time interval was the last interval before the Cretaceous–Paleogene extinction event that killed off the non-avian dinosaurs. Edmontosaurus was one of the most common dinosaurs of the interval. Robert Bakker reports that it made up one-seventh of the large dinosaur sample, with most of the remaining five-sixths made up of Triceratops.[54] The coastal plain TriceratopsEdmontosaurus association, dominated by Triceratops, extended from Colorado to Saskatchewan.[55] Typical dinosaur faunas of the Lancian formations where Edmontosaurus annectens has been found also included: the hypsilophodont Thescelosaurus; the rare ceratopsid Torosaurus; the pachycephalosaurid Pachycephalosaurus; the ankylosaurid Ankylosaurus; and the theropods Ornithomimus, Pectinodon, Acheroraptor, Dakotaraptor, and Tyrannosaurus.[56][57]

 
The Hell Creek Formation is well exposed in the badlands in the vicinity of Fort Peck Reservoir.

The Hell Creek Formation, as typified by exposures in the Fort Peck area of Montana, has been interpreted as a flat forested floodplain, with a relatively dry subtropical climate supporting a variety of plants that ranged from angiosperm trees to conifers, such as bald cypress, as well as ferns and ginkgos. The coastline was hundreds of kilometers or miles to the east. Stream-dwelling turtles and tree-dwelling multituberculate mammals were diverse, and monitor lizards as large as the modern Komodo dragon 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/yard-long infant. The edmontosaur fossils potentially represented accumulations from groups on the move.[58]

The Lance Formation, as typified by exposures approximately 62 miles (100 km) north of Fort Laramie in eastern Wyoming, has been interpreted as a bayou setting similar to the Louisiana coastal plain. It was closer to a large delta than the Hell Creek Formation depositional setting to the north, and consequently received much more sediment. Tropical araucarian conifers and palm trees dotted the hardwood forests, differentiating the flora from the northern coastal plain.[59] The climate was humid and subtropical, with conifers, palmettos, and ferns in the swamps, and conifers, ash, live oak, and shrubs in the forests.[60] Freshwater fish, salamanders, turtles, 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 in this formation 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".[59]

See also edit

Notes edit

* 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 edit

  1. ^ a b c Holtz, Thomas R. Jr. (2012) Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages, Winter 2011 Appendix.
  2. ^ Rohrer, Willis L.; Konizeski, Richard L. (1 May 1960). "On the Occurrence of Edmontosaurus in the Hell Creek Formation of Montana". Journal of Paleontology. 34 (3): 464–466. JSTOR 1300943. Retrieved 16 October 2020.
  3. ^ *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.
  4. ^ a b c Wosik, M.; Evans, D.C. (2022). "Osteohistological and taphonomic life-history assessment of Edmontosaurus annectens (Ornithischia: Hadrosauridae) from the Late Cretaceous (Maastrichtian) Ruth Mason dinosaur quarry, South Dakota, United States, with implication for ontogenetic segregation between juvenile and adult hadrosaurids". Journal of Anatomy. 241 (2): 272–296. doi:10.1111/joa.13679. PMC 9296034. PMID 35801524. S2CID 250357069.
  5. ^ a b Horner, J.R.; Goodwin, M.B.; Myhrvold, N. (2011). "Dinosaur Census Reveals Abundant Tyrannosaurus and Rare Ontogenetic Stages in the Upper Cretaceous Hell Creek Formation (Maastrichtian), Montana, USA". PLOS ONE. 6 (2): e16574. Bibcode:2011PLoSO...616574H. doi:10.1371/journal.pone.0016574. PMC 3036655. PMID 21347420.
  6. ^ a b Prieto-Márquez, A. (2014). "A juvenile Edmontosaurus from the late Maastrichtian (Cretaceous) of North America: Implications for ontogeny and phylogenetic inference in saurolophine dinosaurs". Cretaceous Research. 50: 282–303. doi:10.1016/j.cretres.2014.05.003.
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edmontosaurus, annectens, meaning, connected, lizard, from, edmonton, often, colloquially, historically, known, anatosaurus, meaning, duck, lizard, species, flat, headed, saurolophine, hadrosaurid, dinosaur, from, late, maastrichtian, very, cretaceous, period,. Edmontosaurus annectens meaning connected lizard from Edmonton often colloquially and historically known as the Anatosaurus meaning duck lizard is a species of flat headed saurolophine hadrosaurid dinosaur from the late Maastrichtian age at the very end of the Cretaceous period in what is now western North America Remains of E annectens have been preserved in the Frenchman Hell Creek and Lance Formations All of these formations are dated to the late Maastrichtian age of the Late Cretaceous period which represents the last three million years before the extinction of the dinosaurs between 68 and 66 million years ago 1 2 E annectens is also found in the Laramie Formation and magnetostratigraphy suggests an age of 69 68 Ma for the Laramie Formation 3 Edmontosaurus annectens is known from numerous specimens including at least twenty partial to complete skulls discovered in the U S states of Montana South Dakota North Dakota Wyoming and Colorado as well as the Canadian province of Saskatchewan It had an extremely long and low skull and was quite a large animal growing up to approximately 12 metres 39 ft in length and 5 6 metric tons 6 2 short tons in average asymptotic body mass although it could have been even larger 4 5 6 7 E annectens exhibits one of the most striking examples of the duckbill snout that is common to hadrosaurs It has a long taxonomic history and specimens have at times been classified as Diclonius Trachodon Hadrosaurus Claosaurus Thespesius Anatosaurus and Anatotitan before all being grouped together in EdmontosaurusEdmontosaurus annectensTemporal range Late Cretaceous Maastrichtian 1 68 66 Ma PreꞒ Ꞓ O S D C P T J K Pg N Mounted cast of a fossil E annectens skeleton Oxford University Museum of Natural HistoryScientific classificationDomain EukaryotaKingdom AnimaliaPhylum ChordataClade DinosauriaClade OrnithischiaClade OrnithopodaFamily HadrosauridaeSubfamily SaurolophinaeGenus EdmontosaurusSpecies E annectensBinomial name Edmontosaurus annectens Marsh 1892 SynonymsTrachodon longiceps Marsh 1890 Hadrosaurus longiceps Marsh 1890 Nopcsa 1900 Claosaurus annectens Marsh 1892 Trachodon annectens Marsh 1892 Hay 1902 Thespesius annectens Marsh 1892 Sternberg 1925 Thespesius saskatchewanensis Sternberg 1926 Trachodon saskatchewanensis Sternberg 1926 Kuhn 1936 Thespesius longiceps Marsh 1890 Russell 1930 Anatosaurus annectens Marsh 1892 Lull amp Wright 1942 Anatosaurus longiceps Marsh 1890 Lull amp Wright 1942 Anatosaurus saskatchewanensis Sternberg 1926 Lull amp Wright 1942 Anatosaurus copei Lull amp Wright 1942 Edmontosaurus copei Lull amp Wright 1942 Brett Surman 1975 Anatotitan copei Lull amp Wright 1942 Brett Surman vide Chapman amp Brett Surman 1990 Anatotitan longiceps Marsh 1890 Olshevsky 1991 Edmontosaurus saskatchewanensis Sternberg 1926 Horner Weishampel amp Forster 2004 Contents 1 Discovery and history 1 1 Cope s Diclonius mirabilis 1 2 Marsh s Claosaurus annectens 1 3 Canadian discoveries 1 4 Early classifications 1 5 Anatosaurus to the present 2 Description 3 Classification 4 Paleobiology 4 1 Growth 5 Paleoecology 6 See also 7 Notes 8 ReferencesDiscovery and history editE 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 8 9 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 edit nbsp Skeletons AMNH 5730 left and AMNH 5886 right first mounted in the American Museum of Natural History in 1908 10 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 11 for American paleontologist Edward Drinker Cope This specimen found in Hell Creek Formation rocks 12 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 13 When describing this specimen AMNH 5730 Cope assigned it to the species Diclonius mirabilis This species name was created by combining Diclonius a hadrosaurid genus Cope had named earlier from teeth with Trachodon mirabilis an older name based on teeth that was published by Joseph Leidy 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 14 Leidy had come to recognize that his Trachodon was based on the remains of multiple kinds of dinosaurs and although he had made some attempts to revise the genus he had not yet made any formal declaration of his intentions 9 Cope s description promoted hadrosaurids as amphibious animals contributing to this long time image 15 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 14 However aside from misidentifying several of the skull bones 16 by chance the lower jaws were missing the walls supporting the teeth from the inside and the teeth were actually very well supported 15 17 Cope intended to describe the skeleton and skull but his promised paper never appeared 9 It was purchased for the American Museum of Natural History in 1899 where it acquired its present designation AMNH 5730 18 nbsp Outdated 1909 life restoration of Trachodon by Charles R Knight based on the two specimens now classified as E annectens mounted in 1908 at the AMNH New York 10 Several years after Cope s description his arch rival Othniel Charles Marsh published a paper on a sizable lower jaw recovered by John Bell Hatcher in 1889 from the Lance Formation rocks in Niobrara County Wyoming 19 Marsh named this partial jaw Trachodon longiceps 20 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 92 0 centimetres 36 2 in long whereas Marsh s dentary is estimated at 110 0 centimetres 43 3 in long 19 A second mostly complete skeleton AMNH 5886 was found in 1904 in the Hell Creek Formation rocks at Crooked Creek in central Montana by a local rancher named Oscar Hunter 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 Another cowboy Alfred Sensiba bought the specimen from Hunter for a pistol and later sold it to Brown who excavated it for the American Museum of Natural History in 1906 12 This specimen had a nearly complete vertebral 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 10 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 described the tableau as representing the two animals feeding alongside a marsh the standing individual having been startled by the approach of a Tyrannosaurus Impressions of appropriate plant remains and shells based on associated fossils were included on the base of the group including ginkgo leaves Sequoia cones and horsetail rushes 13 Marsh s Claosaurus annectens edit nbsp Skeletal restoration of the E annectens then Claosaurus holotype by Othniel Charles Marsh nbsp E annectens paratype YPM 2182 at the Yale University Museum the first nearly complete dinosaur skeleton mounted in the United States 21 The species now known as Edmontosaurus annectens was named in 1892 as Claosaurus annectens by Othniel Charles Marsh This species is based on USNM 2414 a partial skull roof and skeleton with a second skull and skeleton YPM 2182 being designated as the paratype Both were collected in 1891 by John Bell Hatcher from the late Maastrichtian age Upper Cretaceous Lance Formation of Niobrara County then part of Converse County Wyoming 22 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 9 23 YPM 2182 and UNSM 2414 are respectively the first and second essentially complete mounted dinosaur skeletons in the United States 21 YPM 2182 was put on display in 1901 9 and USNM 2414 was put on display in 1904 21 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 and his sons in the Lance Formation rocks near Lusk Wyoming Sternberg was working for the British Museum of Natural History but Henry Fairfield Osborn of the American Museum of Natural History was able to purchase the specimen for 2 000 24 The Sternbergs recovered a second similar specimen from the same area in 1910 25 It was not as well preserved but also found with skin impressions They sold this specimen SM 4036 to the Senckenberg Museum in Germany 24 Canadian discoveries edit Edmontosaurus itself was coined in 1917 by Lawrence Lambe for two partial skeletons found in the Horseshoe Canyon Formation formerly the lower Edmonton Formation along the Red Deer River of southern Alberta 26 The Horseshoe Canyon Formation is older than the rocks in which Claosaurus annectens was found 27 Lambe found that his new dinosaur compared best to Cope s Diclonius mirabilis 26 In 1926 Charles Mortram Sternberg named Thespesius saskatchewanensis for NMC 8509 a skull and partial skeleton from the Wood Mountain plateau of southern Saskatchewan He had collected this specimen in 1921 from rocks that were assigned to the Lance Formation 28 now the Frenchman Formation 8 NMC 8509 included an almost complete skull numerous vertebrae partial shoulder and hip girdles and partial back legs 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 28 At the time T saskatchewanensis was unusual because of its small size estimated at 7 to 7 3 meters 23 to 24 ft in length 29 Early classifications edit 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 with textbooks and encyclopedias drawing a distinction between the Iguanodon like Claosaurus annectens and the duck billed Hadrosaurus based on Cope s Diclonius mirabilis conversely Hatcher explicitly identified C annectens as synonymous with the hadrosaurid represented by those same duck billed skulls 9 the two differentiated only by individual variation or distortion from pressure 30 Hatcher s revision published in 1902 was sweeping as he considered almost all hadrosaurid genera then known as synonyms of Trachodon This included Cionodon Diclonius Hadrosaurus Ornithotarsus Pteropelyx and Thespesius as well as Claorhynchus and Polyonax 30 fragmentary genera now thought to be ceratopsians 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 9 In 1915 Charles W Gilmore reassessed hadrosaurids and recommended that Thespesius should 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 and its equivalents In regards to Claosaurus annectens he recommended that it be considered the same as Thespesius occidentalis 31 A multiplicity of names resumed with the AMNH duckbills being known as Diclonius mirabilis Trachodon mirabilis Trachodon annectens Claosaurus or Thespesius 9 Anatosaurus to the present edit nbsp AMNH 5060 a well preserved specimen of E annectens This confusing situation was temporarily resolved in 1942 by Richard Swann Lull and Nelda Wright In their monograph on hadrosaurian dinosaurs of North America they opted to settle the questions revolving around the AMNH duckbills Marsh s Claosaurus annectens and several other species by creating a new generic name They created the new genus Anatosaurus meaning duck lizard because of its wide duck like beak Latin anas duck Greek sauros lizard and made Marsh s species the type species calling it Anatosaurus annectens They also assigned Marsh s Trachodon longiceps to this genus 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 32 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 18 Anatosaurus would come to be called the classic duck billed dinosaur 33 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 34 35 36 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 37 38 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 39 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 40 Because the type species of Anatosaurus A annectens was sunk into Edmontosaurus the name Anatosaurus is abandoned as a junior synonym of Edmontosaurus nbsp A well preserved skin impression of the specimen nicknamed Dakota which was found in 1999 Of the remaining species of Anatosaurus A saskatchewanensis and A edmontoni were assigned to Edmontosaurus as well 41 and A longiceps went to Anatotitan as either a second species 42 or as a synonym of A copei 41 A longiceps may be a synonym of E annectens 8 though it has also been treated as a nomen dubium by some 43 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 41 The debate about the proper taxonomy of the A copei specimens continues to the present day Returning to Hatcher s argument of 1902 Jack Horner David B Weishampel and Catherine Forster regarded Anatotitan copei as representing specimens of Edmontosaurus annectens with crushed skulls 8 In 2007 another mummy was announced Nicknamed Dakota it was discovered in 1999 by Tyler Lyson and came from the Hell Creek Formation of North Dakota 44 45 In a 2011 study by Nicolas 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 27 Description edit nbsp Scale diagram comparing large adult specimens of E regalis gray and E annectens green to a human The skull and skeleton of E annectens are very well known Edward Drinker Cope estimated the length of one specimen as about 38 feet 12 m long with a skull 3 87 feet 1 18 m long 14 This body length estimate was later revised down to a length of 29 feet 8 8m 29 To be fair to Cope a dozen vertebrae the hips and thigh bones had been carried away by a stream cutting through the skeleton and the tip of the tail was incomplete 13 A second skeleton currently exhibited next to Cope s specimen but in a standing posture is estimated at 30 feet 9 1 m long with its head 17 feet 5 2 m above the ground 13 The hip height of this specimen is estimated as approximately 6 9 feet 2 1 m 11 Other sources have estimated the length of E annectens as approximately 39 feet 12 m 46 47 Most specimens are somewhat shorter representing individuals that are not fully grown 27 Two well known mounted skeletons USNM 2414 and YPM 2182 measure 26 25 feet 8 00 m long and 29 3 feet 8 9 m long respectively 29 21 E annectens may have weighed about 7 3 tons 6 6 metric tons when fully grown 11 nbsp Artist illustration depicting a life restoration Recently found specimens that are still under study at the Museum of the Rockies namely MOR 1142 X rex and MOR 1609 Becky s Giant suggest that E annectens may have reached lengths of nearly 49 feet 15 m and weighed 11 short tons 10 0 t potentially making it one of the largest hadrosaurids ever However Jack Horner and his colleagues suggested that such large individuals would have been extremely rare 5 6 7 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 36 39 feet 11 12 m in length and 5 6 metric tons 6 2 short tons in average asymptotic body mass while the largest individuals measured more than 6 metric tons 6 6 short tons and even up to 6 6 7 metric tons 7 3 7 7 short tons based on the comparison between various specimens of different sizes from the Ruth Mason Dinosaur Quarry and other specimens from different localities 4 nbsp Tail vertebraeThe skull of E annectens is known for its long wide muzzle Cope compared this feature to that of a goose in side view and to a short billed spoonbill in top view 14 The skull was proportionally longer and lower than in any other known hadrosaurid The toothless portion of the anterior mandible was also relatively longer than in any hadrosaur 40 The extreme length and breadth did not appear until an individual reached maturity so many specimens lack the distinctive shape 27 The bones surrounding the large openings for the nostrils formed deep pockets around the openings The eye sockets were rectangular and longer front to back than they were top to bottom although this may have been exaggerated by postmortem crushing The skull roof was flat and lacked a bony crest like that of E regalis The quadrate bone that formed the articulation with the lower jaw was distinctly curved The lower jaw was long straight and lacking the downward curve seen in other hadrosaurids as well as possessing a heavy ridge running its length The predentary was wide and shovel like 18 The ridge on the lower jaw may have reinforced the long slender structure 19 As mounted the vertebral column of E annectens includes twelve neck twelve back nine sacral and at least thirty tail vertebrae 18 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 40 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 8 Henry Fairfield Osborn used the skeletons in the American Museum of Natural History to portray both quadrupedal and bipedal stances for E annectens 13 Classification edit nbsp E annectens holotype Smithsonian National Museum of Natural History nbsp Most known complete Edmontosaurus skulls E annectens from lower middle to right E annectens was a saurolophine or flat headed hadrosaurid This group was historically known as Hadrosaurinae 48 Species now considered to be synonymous with Edmontosaurus annectens were long recognized as closely related to both the genus 49 and the species 30 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 different genera On the other side of the issue other authors from John Bell Hatcher in 1902 30 to Jack Horner David B Weishampel and Catherine Forster in 2004 8 and most recently Nicolas Campione and David Evans 27 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 and Nelda Wright until it was reclassified as a species of Edmontosaurus by Michael K Brett Surman 40 With the discovery that A copei and E annectens most likely represent the same species some paleontologists have proposed using Anatosaurus as a valid genus name for E annectens 1 The cladogram below follows Godefroit et al 2012 analysis 50 Bactrosaurus Hadrosauridae Hadrosaurinae HadrosaurusLophorhothon Saurolophidae Lambeosaurinae Saurolophinae Wulagasaurus Brachylophosaurini AcristavusMaiasauraBrachylophosaurusKritosaurusGryposaurus latidensGryposaurus notabilisGryposaurus monumentensis Saurolophini ProsaurolophusSaurolophus angustirostrisSaurolophus osborni Edmontosaurini KerberosaurusKundurosaurusEdmontosaurus annectensEdmontosaurus regalisPaleobiology edit nbsp Close up of teeth As a hadrosaurid Edmontosaurus annectens was a fairly large herbivore eating plants with a sophisticated skull that permitted a grinding motion analogous to chewing Their teeth were continually replaced and packed into dental batteries that contained hundreds of teeth but only a relative handful of them were in use at any time Plant material would have been cropped by the broad beak and held in the jaws by a cheek like structure Feeding would have been from the ground up to around 13 feet 4 meters above the ground Like other hadrosaurs they could have moved both bipedally and quadrupedally 8 The extensive depressions surrounding its nasal openings may have hosted nasal diverticula These postulated diverticula would have taken the form of inflatable soft tissue sacs Such sacs could be used for both visual and auditory signals 51 A preserved rhamphotheca 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 52 53 Growth edit nbsp Mounted skeletons of a juvenile and adult E annectens at the Houston Museum of Natural Science nicknamed Diana and Leon 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 skulls with skull size Their results showed that in both recognized Edmontosaurus species many features previously used to classify additional species or genera were directly correlated to skull size Campione and Evans interpreted these results as strongly suggesting that the shape of Edmontosaurus skulls changed dramatically as they grew and matured This has led to several apparent mistakes in past classification 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 being fully mature adults The skulls became longer and flatter as the animals grew 27 In a 2022 study Wosik and Evans proposed that E annectens reached maturity in 9 years based on their analysis for various specimens from different localities They found the result to be similar to that of other hadrosaurs 4 Paleoecology edit nbsp The damage to the tail vertebrae of this E annectens skeleton on display at the Denver Museum of Nature and Science indicates that it may have been bitten by a Tyrannosaurus True E annectens remains are known only from latest Maastrichtian rocks of the Hell Creek and Lance Formations of South Dakota Montana and Wyoming alongside the Frenchman Formation of Saskatchewan 27 The Lancian time interval was the last interval before the Cretaceous Paleogene extinction event that killed off the non avian dinosaurs Edmontosaurus was one of the most common dinosaurs of the interval Robert Bakker reports that it made up one seventh of the large dinosaur sample with most of the remaining five sixths made up of Triceratops 54 The coastal plain Triceratops Edmontosaurus association dominated by Triceratops extended from Colorado to Saskatchewan 55 Typical dinosaur faunas of the Lancian formations where Edmontosaurus annectens has been found also included the hypsilophodont Thescelosaurus the rare ceratopsid Torosaurus the pachycephalosaurid Pachycephalosaurus the ankylosaurid Ankylosaurus and the theropods Ornithomimus Pectinodon Acheroraptor Dakotaraptor and Tyrannosaurus 56 57 nbsp The Hell Creek Formation is well exposed in the badlands in the vicinity of Fort Peck Reservoir The Hell Creek Formation as typified by exposures in the Fort Peck area of Montana has been interpreted as a flat forested floodplain with a relatively dry subtropical climate supporting a variety of plants that ranged from angiosperm trees to conifers such as bald cypress as well as ferns and ginkgos The coastline was hundreds of kilometers or miles to the east Stream dwelling turtles and tree dwelling multituberculate mammals were diverse and monitor lizards as large as the modern Komodo dragon 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 yard long infant The edmontosaur fossils potentially represented accumulations from groups on the move 58 The Lance Formation as typified by exposures approximately 62 miles 100 km north of Fort Laramie in eastern Wyoming has been interpreted as a bayou setting similar to the Louisiana coastal plain It was closer to a large delta than the Hell Creek Formation depositional setting to the north and consequently received much more sediment Tropical araucarian conifers and palm trees dotted the hardwood forests differentiating the flora from the northern coastal plain 59 The climate was humid and subtropical with conifers palmettos and ferns in the swamps and conifers ash live oak and shrubs in the forests 60 Freshwater fish salamanders turtles 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 in this formation 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 59 See also edit nbsp Dinosaurs portalTimeline of hadrosaur researchNotes edit 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 edit a b c Holtz Thomas R Jr 2012 Dinosaurs The Most Complete Up to Date Encyclopedia for Dinosaur Lovers of All Ages Winter 2011 Appendix Rohrer Willis L Konizeski Richard L 1 May 1960 On the Occurrence of Edmontosaurus in the Hell Creek Formation of Montana Journal of Paleontology 34 3 464 466 JSTOR 1300943 Retrieved 16 October 2020 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 a b c Wosik M Evans D C 2022 Osteohistological and taphonomic life history assessment of Edmontosaurus annectens Ornithischia Hadrosauridae from the Late Cretaceous Maastrichtian Ruth Mason dinosaur quarry South Dakota United States with implication for ontogenetic segregation between juvenile and adult hadrosaurids Journal of Anatomy 241 2 272 296 doi 10 1111 joa 13679 PMC 9296034 PMID 35801524 S2CID 250357069 a b Horner J R Goodwin M B Myhrvold N 2011 Dinosaur Census Reveals Abundant Tyrannosaurus and Rare Ontogenetic Stages in the Upper Cretaceous Hell Creek Formation Maastrichtian Montana USA PLOS ONE 6 2 e16574 Bibcode 2011PLoSO 616574H doi 10 1371 journal pone 0016574 PMC 3036655 PMID 21347420 a b Prieto Marquez A 2014 A juvenile Edmontosaurus from the late Maastrichtian Cretaceous of North America Implications for ontogeny and phylogenetic inference in saurolophine dinosaurs Cretaceous Research 50 282 303 doi 10 1016 j cretres 2014 05 003 a b Henderson D 2012 Engineering a Dinosaur In Brett Surman M K Holtz T R Farlow J O eds The Complete Dinosaur Life of the Past Indiana University Press p 647 ISBN 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