Edmontosaurus annectens

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Edmontosaurus annectens
Temporal range: Late Cretaceous (Maastrichtian), [1] 68–66  Ma
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Oxford Edmontosaurus.jpg
Mounted cast of a fossil E. annectens skeleton, Oxford University Museum of Natural History
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade:† Ornithischia
Clade:† Neornithischia
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

Edmontosaurus annectens (meaning "connected lizard from Edmonton"), often colloquially and historically known as 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 non-avian 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 .

Contents

Discovery and history

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

Skeletons (AMNH 5730, left, and AMNH 5886, right), first mounted in the American Museum of Natural History in 1908 Anatotitan copei.jpg
Skeletons (AMNH 5730, left, and AMNH 5886, right), first mounted in the American Museum of Natural History in 1908

The history of E. annectens predates the naming of both the genus Edmontosaurus and the species annectens. The first quality specimen, the former holotype of Anatosaurus copei (Anatotitan), was a complete skull and most of a skeleton collected in 1882 by Dr. J. L. Wortman and R. S. Hill [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. Edmontosaurus annectens, by Charles R. Knight.jpg
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.

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

Skeletal restoration of the E. annectens (then Claosaurus) holotype, by Othniel Charles Marsh. Large marsh claosaurus.jpg
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. Transactions of the Connecticut Academy of Arts and Sciences (1901) (14783568452).jpg
E. annectens paratype YPM 2182 at the Yale University Museum, the first nearly complete dinosaur skeleton mounted in the United States.

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

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

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

AMNH 5060: a well-preserved specimen of E. annectens Edmontosaurusmummy.jpg
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 Dakota skin impression.jpg
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

Scale diagram comparing large adult specimens of E. regalis (gray) and E. annectens (green) to a human Edmontosaurus scale.png
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 (8.8 m). [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 tonnes (7.3  t ) when fully grown. [11]

Artist illustration depicting a life restoration Anatotitan BW.jpg
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 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 EdmontosaurCMNTail.jpg
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

E. annectens holotype, Smithsonian National Museum of Natural History Edmontosaurus annectens USNM 2414.jpg
E. annectens holotype, Smithsonian National Museum of Natural History
Most known complete Edmontosaurus skulls (E. annectens from lower middle to right). Edmontosaurus skulls.png
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

Close-up of teeth Edmontosaurus jaw.jpg
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 m) 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

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

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. DMNS Edmontosaurus.png
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]

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

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.

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Trachodon is a dubious genus of hadrosaurid dinosaur based on teeth from the Campanian-age Upper Cretaceous Judith River Formation of Montana, U.S. It is a historically important genus with a convoluted taxonomy that has been all but abandoned by modern dinosaur paleontologists.

<span class="mw-page-title-main">Hadrosauridae</span> Extinct family of dinosaurs

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 includes genera such as Edmontosaurus and Parasaurolophus, was a common group of herbivores during the Late Cretaceous Period. Hadrosaurids are descendants of the Late Jurassic/Early Cretaceous iguanodontian dinosaurs and had a similar body layout. Hadrosaurs were among the most dominant herbivores during the Late Cretaceous in Asia and North America, and during the close of the Cretaceous several lineages dispersed into Europe, Africa, and South America.

<i>Edmontosaurus</i> Hadrosaurid dinosaur genus from Late Cretaceous US and Canada

Edmontosaurus, with the second species often colloquially and historically known as Anatosaurus or Anatotitan, 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 of western North America that date from the late Campanian age of the Cretaceous period 73 million years ago, while those of E. annectens were found in the same geographic region from rocks dated to the end of the Maastrichtian age, 66 million years ago. Edmontosaurus was one of the last non-avian dinosaurs to ever exist, and lived alongside dinosaurs like Triceratops, Tyrannosaurus, Ankylosaurus, and Pachycephalosaurus shortly before the Cretaceous–Paleogene extinction event.

<i>Claosaurus</i> Extinct genus of dinosaurs

Claosaurus is a genus of hadrosauroid dinosaur that lived during the Late Cretaceous Period (Santonian-Campanian).

<i>Saurolophus</i> Hadrosaurid dinosaur genus from the Late Cretaceous period

Saurolophus is a genus of large hadrosaurid dinosaur from the Late Cretaceous period of Asia and North America, that lived in what is now the Horseshoe Canyon and Nemegt formations about 70 million to 66 million years ago. It is one of the few genera of dinosaurs known from multiple continents. The type species, S. osborni, was described by Barnum Brown in 1912 from Canadian fossils. A second valid species, S. angustirostris, is represented by numerous specimens from Mongolia, and was described by Anatoly Konstantinovich Rozhdestvensky.

<i>Gryposaurus</i> Extinct genus of reptiles

Gryposaurus was a genus of duckbilled dinosaur that lived about 80 to 75 million years ago, in the Late Cretaceous of North America. Named species of Gryposaurus are known from the Dinosaur Park Formation in Alberta, Canada, and two formations in the United States: the Lower Two Medicine Formation in Montana and the Kaiparowits Formation of Utah. A possible additional species from the Javelina Formation in Texas may extend the temporal range of the genus to 66 million years ago.

<i>Kritosaurus</i> Extinct genus of dinosaurs

Kritosaurus is an incompletely known genus of hadrosaurid (duck-billed) dinosaur. It lived about 74.5-66 million years ago, in the Late Cretaceous of North America. The name means "separated lizard", but is often mistranslated as "noble lizard" in reference to the presumed "Roman nose".

<i>Agathaumas</i> Extinct genus of dinosaurs

Agathaumas is a dubious genus of a large ceratopsid dinosaur that lived in Wyoming during the Late Cretaceous. The name comes from Ancient Greek: αγαν - 'much' and θαυμα - 'wonder'. It is estimated to have been 15 metres (49 ft) long and weighed 17.5 tonnes, and was seen as the largest land animal known at the time of its discovery.

Claorhynchus 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, sometimes the same as Triceratops, with two different assignments as to discovery formation and location, and what bones make up its type remains.

<i>Thespesius</i> Dubious extinct genus of dinosaurs

Thespesius is a dubious genus of hadrosaurid dinosaur from the late Maastrichtian-age Upper Cretaceous Lance Formation of South Dakota.

<i>Mandschurosaurus</i> Extinct genus of dinosaurs

Mandschurosaurus is an extinct genus of hadrosaurids based on material from the Late Cretaceous of China and possibly also the Early Cretaceous of Laos. It was the first dinosaur genus named from China.

<i>Prosaurolophus</i> Extinct genus of dinosaurs

Prosaurolophus is a genus of hadrosaurid dinosaur from the Late Cretaceous of North America. It is known from the remains of at least 25 individuals belonging to two species, including skulls and skeletons, but it remains obscure. Its fossils have been found in the late Campanian-age Upper Cretaceous Dinosaur Park Formation in Alberta, and the roughly contemporaneous Two Medicine Formation in Montana, dating to around 75.5-74.0 million years ago. Its most recognizable feature is a small solid crest formed by the nasal bones, sticking up in front of the eyes.

Diclonius 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 method of tooth replacement, in which newly erupting replacement teeth could be in functional use at the same time as older, more worn teeth. Thus, the number of "sprouting" teeth was doubled in comparison to Monoclonius, which used only one set of teeth at a time and which Cope named in the same paper.

<i>Naashoibitosaurus</i> Extinct genus of dinosaurs

Naashoibitosaurus is a genus of hadrosaurid dinosaur that lived about 73 million years ago, in the Late Cretaceous, and was found in the Kirtland Formation of the San Juan Basin in New Mexico, United States. Only a partial skeleton has been found to date. It was first described as a specimen of Kritosaurus by Jack Horner, and has been intertwined with Kritosaurus since its description.

<i>Edmontosaurus</i> mummy AMNH 5060 Exceptionally well-preserved fossil in the American Museum of Natural History

The Edmontosaurus mummy AMNH 5060 is an exceptionally well-preserved fossil of a dinosaur in the collection of the American Museum of Natural History (AMNH). Discovered in 1908 in the United States near Lusk, Wyoming, it was the first dinosaur specimen found to include a skeleton encased in skin impressions from large parts of the body. It is ascribed to the species Edmontosaurus annectens, a hadrosaurid. The mummy was found by fossil hunter Charles Hazelius Sternberg and his three sons in the Lance Formation. Although Sternberg was working under contract to the British Museum of Natural History, Henry Fairfield Osborn of the AMNH managed to secure the mummy. Osborn described the fossil in detail in 1912, coining the name "dinosaur mummy" for it—several dinosaur mummies of similar preservation have been discovered since then. This specimen has considerably influenced the scientific conception of hadrosaurids. Skin impressions found in between the fingers were once interpreted as interdigital webbing, bolstering the now-rejected perception of hadrosaurids as aquatic animals, a hypothesis that remained unchallenged until 1964. Today, the mummy is considered one of the most important fossils of the AMNH.

<i>Edmontosaurus regalis</i> Extinct species of dinosaur

Edmontosaurus regalis is a species of comb-crested hadrosaurid dinosaur. Fossils of E. regalis have been found in rocks of western North America that date from the late Campanian age of the Cretaceous Period 73 million years ago, but it may have possibly lived into the early Maastrichtian.

<span class="mw-page-title-main">Hadrosaur diet</span>

Hadrosaurids, also commonly referred to as duck-billed dinosaurs or hadrosaurs, were large terrestrial herbivores. The diet of hadrosaurid dinosaurs remains a subject of debate among paleontologists, especially regarding whether hadrosaurids were grazers who fed on vegetation close to the ground, or browsers who ate higher-growing leaves and twigs. Preserved stomach content findings have indicated they may have been browsers, whereas other studies into jaw movements indicate they may have been grazers.

<span class="mw-page-title-main">Ankylopollexia</span> Extinct clade of dinosaurs

Ankylopollexia is an extinct clade of ornithischian dinosaurs that lived from the Late Jurassic to the Late Cretaceous. It is a derived clade of iguanodontian ornithopods and contains the subgroup Styracosterna. The name stems from the Greek word, “ankylos”, mistakenly taken to mean stiff, fused, and the Latin word, “pollex”, meaning thumb. Originally described in 1986 by Sereno, a most likely synapomorphic feature of a conical thumb spine defines the clade.

<span class="mw-page-title-main">Timeline of hadrosaur research</span>

This timeline of hadrosaur research is a chronological listing of events in the history of paleontology focused on the hadrosauroids, a group of herbivorous ornithopod dinosaurs popularly known as the duck-billed dinosaurs. Scientific research on hadrosaurs began in the 1850s, when Joseph Leidy described the genera Thespesius and Trachodon based on scrappy fossils discovered in the western United States. Just two years later he published a description of the much better-preserved remains of an animal from New Jersey that he named Hadrosaurus.

<i>Edmontosaurus</i> mummy SMF R 4036 Dinosaur fossil in Naturmuseum Senckenberg

The Edmontosaurus mummy SMF R 4036 is an exceptionally well-preserved dinosaur fossil in the collection of the Naturmuseum Senckenberg (SM) in Frankfurt am Main, Germany. Found in 1910 in Wyoming, United States, it is ascribed to the species Edmontosaurus annectens, a member of the Hadrosauridae. The fossil comprises a nearly complete skeleton that was found wrapped in impressions of its skin, a rare case of exceptional preservation for which the term "dinosaur mummy" has been used. Notably, the horny beak is preserved with this specimen. Plant remains found within the thorax cavity had been interpreted as stomach contents, although later research questioned this identification. The mummy's hands are wrapped in skin impression, which was interpreted as evidence for interdigital webbing and an aquatic lifestyle in hadrosaurids; this hypothesis, although universally accepted once, is now widely refused. SMF R 4036 is one of the four best preserved hadrosaurid mummies, and was the second to be discovered. The find was made by fossil hunter Charles Hazelius Sternberg and his sons, who sold their numerous finds to various museums in North America and Europe. Only two years earlier the Sternbergs had discovered the Edmontosaurus mummy AMNH 5060 in the same region, which is now on display at the American Museum of Natural History (AMNH) in New York City.

References

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