Edmontosaurus

*Edmontosaurus regalis*

***Edmontosaurus*** (Greek for "lizard from Edmonton") is an extinct genus of large Hadrosaur ornithopod from the Late Cretaceous of North America 73- 66 mya (Campanian to Maastrichtian). It contains the 2 known species: E. regalis and E. annectens. Fossils of *E. regalis* have been found in rocks of western North America that date from the Late Campanian stage of the Cretaceous Period 73 million years ago, while those of *E. annectens* were found in the same geographic region but in rocks dated to the end of the Maastrichtian stage of the Cretaceous, 66 million years ago.

*Edmontosaurus* was some of the largest Hadrosaur genera, being up to 14 m (46 ft) long and weighing about 15 tonnes (16.5 short tons). Evidence does exist in the form of two fossilized specimens in the Museum of the Rockies for an even greater maximum size of 17 m (49 ft) and weighing 17 metric tons (19.00 short tons) *Edmontosaurus* annectens. A few well-preserved specimens are known that include not only bones, but in some cases extensive skin impressions and possible gut contents. It is classified as a genus of saurolophine (or hadrosaurine) hadrosaurid, a member of the group of hadrosaurids which lacked large, hollow crests, instead having smaller solid crests or fleshy combs.

The first fossils named *Edmontosaurus* were discovered in southern Alberta (named after Edmonton, the capital city), in the Horseshoe Canyon Formation (formerly called the lower Edmonton Formation). The type species, *E. regalis*, was named by Lawrence Lambe in 1917, although several other species that are now classified in *Edmontosaurus* were named earlier. The best known of these is *E. annectens*, named by Othniel Charles Marsh in 1892; originally as a species of *Claosaurus*, known for many years as a species of *Trachodon*, and later as *Anatosaurus annectens*. ***Anatosaurus,*** ***Anatotitan*** and ***Ugrunaaluk*** are now generally regarded as synonyms of *Edmontosaurus*.

*Edmontosaurus* was widely distributed across western North America. The distribution of *Edmontosaurus* fossils suggests that it preferred coasts and coastal plains. It was a herbivore that could move on both two legs and four. Because it is known from several bone beds, *Edmontosaurus* is thought to have lived in groups, and may have been migratory as well. The wealth of fossils has allowed researchers to study its paleobiology in detail, including its brain, how it may have fed, and its injuries and pathologies, such as evidence for tyrannosaur attacks on a few edmontosaur specimens.

## Discovery and history

*Edmontosaurus* has had a long and complicated history in paleontology, having spent decades with various species classified in other genera. Its taxonomic history intertwines at various points with the genera *Agathaumas*, *Anatosaurus*, *Anatotitan*, *Claosaurus*, *Hadrosaurus*, *Thespesius*, and *Trachodon*, and references predating the 1980s typically use *Anatosaurus*, *Claosaurus*, *Thespesius*, or *Trachodon* for edmontosaur fossils (excluding those assigned to *E. regalis*), depending on author and date. Although *Edmontosaurus* was only named in 1917, its oldest well-supported species (*E. annectens*) was named in 1892 as a species of *Claosaurus*.

## Description

*Edmontosaurus* has been described in detail from numerous specimens. Like other hadrosaurids, it was a bulky animal with a long, laterally flattened tail and a head with an expanded, duck-like beak. The fore legs were not as heavily built as the hind legs, but were long enough to be used in standing or movement. *Edmontosaurus* was among the largest hadrosaurids: depending on the species, a fully grown adult could have been 9 metres (30 ft) long, and some of the larger specimens reached the range of 13 metres (43 ft) to 14 metres (47 ft) long. Its weight was on the order of 15.0 metric tons (16.5short tons). Traditionally, *E. regalis* has been regarded as the largest species, though this was challenged by the hypothesis that the larger hadrosaurid *Anatotitan copei* is a synonym of *Edmontosaurus annectens*, as put forward by Jack Horner and colleagues in 2004, and supported in studies by Campione and Evens in 2009 and 2011.

The type specimen of *E. regalis*, NMC 2288, is estimated as 9 to 12 metres (30 to 39 ft) long. *E. annectens* is often seen as smaller. Two mounted skeletons, USNM 2414 and YPM 2182, measure 8.00 metres (26.25 ft) long and 8.92 metres (29.3 ft) long, respectively. However, these are probably subadult individuals, and there is at least one report of a much larger potential *E. annectens* specimen, almost 13.5 metres (45ft) long. Two specimens still under study in the collection of the Museum of the Rockies - a 7.6 m (25 ft) tail labelled as MOR 1142 and another labelled as MOR 1609 - indicate that *Edmontosaurus annectens* could have grown to larger sizes, possibly rivaling *Shantungosaurus* in size. The specimens of these individuals indicate a length of up to 17 m (57 ft), according to paleontologists. Such large individuals of *Edmontosaurus* would likely have been very rare due to such factors as environmental stress, disease, and predation.

## Classification

*Edmontosaurus* was a hadrosaurid (a duck-billed dinosaur), a member of a family of dinosaurs which to date are known only from the Late Cretaceous. It is classified within the Saurolophinae (alternately Hadrosaurinae), a clade of hadrosaurids which lacked hollow crests. Other members of the group include *Brachylophosaurus*, *Gryposaurus*, *Lophorhothon*, *Maiasaura*, *Naashoibitosaurus*, *Prosaurolophus*, and *Saurolophus*. It was either closely related to or includes the species *Anatosaurus annectens* (alternately *Edmontosaurus annectens*), a large hadrosaurid from various latest Cretaceous formations of western North America. The giant Chinese hadrosaurine *Shantungosaurus giganteus* is also anatomically similar to *Edmontosaurus*; M. K. Brett-Surman found the two to differ only in details related to the greater size of *Shantungosaurus*, based on what had been described of the latter genus.

While the status of *Edmontosaurus* as a saurolophine has not been challenged, its exact placement within the clade is uncertain. Early phylogenies, such as that presented in R. S. Lull and Nelda Wright's influential 1942 monograph, had *Edmontosaurus* and various species of *Anatosaurus* (most of which would be later considered as additional species or specimens of *Edmontosaurus*) as one lineage among several lineages of "flat-headed" hadrosaurs. One of the first analyses using cladistic methods found it to be linked with *Anatosaurus* (=*Anatotitan*) and *Shantungosaurus* in an informal "edmontosaur" clade, which was paired with the spike-crested "saurolophs" and more distantly related to the "brachylophosaurs" and arch-snouted "gryposaurs". A 2007 study by Terry Gates and Scott Sampson found broadly similar results, in that *Edmontosaurus* remained close to *Saurolophus* and *Prosaurolophus* and distant from *Gryposaurus*, *Brachylophosaurus*, and *Maiasaura*. However, the most recent review of Hadrosauridae, by Jack Horner and colleagues (2004), came to a noticeably different result: *Edmontosaurus* was nested between *Gryposaurus* and the "brachylophosaurs", and distant from *Saurolophus*.

## Paleobiology

In a 2011 study, Campione and Evans recorded data from all known "edmontosaur" skulls from the Campanian and Maastrichtian and used it to plot a *morphometric* graph, comparing variable features of the skull with skull size. Their results showed that within both recognized *Edmontosaurus* species, many features previously used to classify additional species or genera were directly correlated with skull size. Campione and Evans interpreted these results as strongly suggesting that the shape of *Edmontosaurus* skulls changed dramatically as they grew. This has led to several apparent mistakes in classification in the past. The Campanian species *Thespesius edmontoni*, previously considered a synonym of *E. annectens* due to its small size and skull shape, is more likely a subadult specimen of the contemporary *E. regalis*.

Similarly, the three previously recognized Maastrichtian edmontosaur species likely represent growth stages of a single species, with *E. saskatchewanensis* representing juveniles, *E. annectens* subadults, and *Anatotitan copei* fully mature adults. The skulls became longer and flatter as the animals grew.

## Paleoecology

*Edmontosaurus* was a wide-ranging genus in both time and space. The rock units from which it is known can be divided into two groups by age: the older Horseshoe Canyon and St. Mary River formations, and the younger Frenchman, Hell Creek, and Lance formations. The time span covered by the Horseshoe Canyon Formation and equivalents is also known as Edmontonian, and the time span covered by the younger units is also known as Lancian. The Edmontonian and Lancian time intervals had distinct dinosaur faunas.

The Edmontonian land vertebrate age is defined by the first appearance of *Edmontosaurus regalis* in the fossil record. Although sometimes reported as of exclusively early Maastrichtian age, the Horseshoe Canyon Formation was of somewhat longer duration. Deposition began approximately 73 million years ago, in the late Campanian, and ended between 68.0 and 67.6 million years ago. *Edmontosaurus regalis* is known from the lowest of five units within the Horseshoe Canyon Formation, but is absent from at least the second to the top. As many as three quarters of the dinosaur specimens from badlands near Drumheller, Alberta may pertain to *Edmontosaurus*.

## JPInstitute.com Description

Edmontosaurus was possibly the largest of the duck-billed hadrosaurs. It was a little bigger than a T. rex and was probably a food source for the large meat-eater. It walked on all four legs much of the time, but it could also stand easily on its hind legs, as they were much larger than its front legs. Edmontosaurus had on average over 500 teeth and some had over 1,000! These were all jammed together in what is called a dental battery. This dinosaur could really chew up the tough plants on which it fed.

Edmontosaurus was originally described as Anatosaurus; for many years the species annectens was attributed to the genus Anatosaurus. Now both Anatosaurus and Claosaurus are known as Edmontosaurus. Hadrosaurs were among the most common herbivores of the late Cretaceous. Like other hadrosaurs, it had a beak that was covered with a horny sheath. Excellent mummified specimens of these dinosaurs have been found, adding a great deal to the knowledge of dinosaur skin and musculature.

When first discovered, many researchers thought these dinosaurs would have lived in the water due to the shape of their heads and the fact that one mummified specimen seemed to have webbing on its front feet. Later research has shown, however, that these creatures lived primarily on coastal plains, floodplains and river deltas. Their dental structure also supports a more terrestrial lifestyle, as was perfectly suited for plants that were found in forests near water, and not those that were found in the water. Another interesting Edmontosaurus feature is that the skin seemed to consist, at least partly, of horny plates - good defense against glancing bites and blows from predators.

## Links

http://web.archive.org/web/20040207175643fw\_/http://www.jpinstitute.com/dinopedia/dinocards/dc\_edmon.html
https://web.archive.org/web/20080517182549/http://kids.yahoo.com/dinosaurs/19--Edmontosaurus

## References

* https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5383305/

* https://www.cell.com/current-biology/fulltext/S0960-9822(13)01394-8?\_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0960982213013948%3Fshowall%3Dtrue

* https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3036655/
* https://archive.org/details/TheGenusAndSpeciesOfTheTrachodontidaehadrosauridaeClaosauridae
* https://archive.org/details/discoveringdinos00nore\_0
* https://web.archive.org/web/20071113101737/https://www.cspg.org/conventions/abstracts/2002abstracts/extended/227S0125.pdf
* https://pubs.geoscienceworld.org/gsa/books/book/547/chapter/3802049/Hadrosaurian-Dinosaurs-of-North-America