Edmontosaurus (Edmonton lizard)
Edmontosaurus (Edmonton lizard)
Named By : Lawrence Lambe - 1917
Diet : Herbivore
Size : Estimated 13 meters long
Type of Dinosaur : Euornithopod
Type Species : regalis (type)
Found in : Canada
When it Lived : Late Cretaceous, 76-65 million years ago
Edmontosaurus (/ed.mant@’so:r@s/ed-MON–t@–SAWR-@s/) is a genus that includes hadrosaurids (duck-billed dinosaurs). There are two species known to be in the genus: Edmontosaurus royalis and Edmontosaurus aninectens. E. regalis fossils have been found in rocks in western North America dating from the late Campanian Stage of the Cretaceous Period, 73 million years back. While E. annectens fossils were found in the same geographical region, but in rocks that are dated to the end the Maastrichtian Stage of the Cretaceous (66 million years) Edmontosaurus was one the last non-avian dinosaurs to survive. It lived with dinosaurs such as Tyrannosaurus and Triceratops shortly before the Cretaceous–Paleogene extinction.
Edmontosaurus was one of the most massive hadrosaurid species. It measured up to 12 m (39 ft) in length and weighed around 4.0 metric tonnes (4.4 short tons). Two fossilized specimens, which are housed at the Museum of the Rockies, provide evidence for an even larger Edmontosaurus annectens maximum size of 15.m (49ft). They weigh 9.07 metric tonnes (10.00 short tons). There are a number of well-preserved specimens that have bones and, in some cases, extensive skin impressions. It is classified as a hadrosaurine (or genus of saurolophine) hadrosaurid. This group includes hadrosaurids that lack large hollow crests and instead have smaller, solid crests or fleshy hairs.
Othniel C. Marsh, Public domain, via Wikimedia Commons
In southern Alberta, in the Horseshoe Canyon Formation (formerly known as the lower Edmonton Formation), the first fossils called Edmontosaurus were found. Although E. regalis was the first species to be named in Edmontosaurus, several species are still being classified there. E. annectens is the most well-known of these species. It was first named by Othniel Marsh in 1892 as E. regalis. However, it has been known for many years as E. annectens and then as Anatosaurus anectens. Anatosaurus and Anatotitan are considered synonyms for Edmontosaurus.
Peabody Museum, Yale, Public domain, via Wikimedia Commons
Edmontosaurus was widespread in western North America. It is evident that Edmontosaurus preferred coastal plains and the coasts, as evidenced by its fossil distribution. It could walk on either two or four legs. Edmontosaurus, which is found in several bone beds, is believed to have lived in groups and could have been migratory. Researchers have been able to examine its paleobiology, including its brain and how it might have eaten, as well as its injuries and pathologies. For example, evidence of tyrannosaur attacks against a few edmontosaur remains.
Numerous specimens have been used to describe Edmontosaurus in detail. It was similar to other hadrosaurids. It was large with a broad, flattened tail, and a duck-like head. Although the forelegs were not as strong as the hind, they were still long enough to allow movement and standing. Edmontosaurus was one of the largest hadrosaurids. A fully grown adult could measure 9m (30ft), while others may have measured between 12m (39ft) and 13m (43ft). It weighed in at 4.0 metric tons (4.4 small tons). E. regalis was traditionally considered the largest species. However, this assumption was challenged by Jack Horner and his colleagues in 2004. They also supported the idea that Anatotitan copei, a larger hadrosaurid, is a synonym for Edmontosaurus nectens. These findings were confirmed in Campione’s 2009 and 2011 studies. NMC 2288 is the type specimen of E. royalis. It measures 9-12 metres (30-39 ft) in length. E. annectens can be seen smaller. Two mounted skeletons USNM 2414 (26.25 ft.) and YPM 281 (29.3ft.) measure 8.00 metres respectively. These are likely subadults and at least one report has a specimen of E. annectens measuring almost 12 metres (39 feet) in length. Two specimens are still being studied in the Museum of the Rockies. One tail measuring 7.6m (25ft) and the other MOR 1609 indicate that Edmontosaurus thenectens may have reached larger sizes than Shantungosaurus. According to paleontologists, these specimens indicate that they measured up to 15m (49ft) in length. Due to environmental stress, disease and predation, Edmontosaurus may have been rare.
Edmontosaurus is a complex species that has spent many decades in paleontology with other species. Its taxonomic story intertwines with various genera such as Anatosaurus and Anatotitan and Claosaurus. References predating 1980s often use Anatosaurus or Claosaurus for edmontosaur fossils, but not those assigned to E. royalis, depending on the date and author. Even though Edmontosaurus was not named until 1917, the oldest known species (E.annectens), was identified in 1892 and is a Claosaurus species.
Claosaurus annectens was the first species of Edmontosaurus to be named by Othniel Charles Marsh in 1892. This species is based upon USNM 2414. It has a partial skull-roof, skeleton and skull. YPM 2182 is the paratype. John Bell Hatcher, a Wyoming geologist, collected both from the Maastrichtian-age Upper Cretaceous Lance Formation in Niobrara County (then a part of Converse County). Some historical footnotes are attached to this species: It is one of the first dinosaurs that has had a skeletal restoration and the first hadrosaurid to have its bones so restored; YPM 2182 is the first and UNSM 2414 the second complete mounted dinosaur skulls in the United States, respectively. YPM 2182 was displayed in 1901 and USNM 2414 were displayed in 1904.
Due to a lack of knowledge about hadrosaurids, Claosaurus annectens, Marsh’s son, was classified in three species: Trachodon, Thespesius, and Claosaurus. There were many opinions. Encyclopedias and textbooks made a distinction between Claosaurus annectens, which is “Iguanodon-like”, and Hadrosaurus annectens, based on the remains of adult Edmontosaurus. Hatcher however explicitly identified C.annectens with the hadrosaurid represented in those same duck-billed skulls. Hatcher’s 1902 revision was extensive. He considered nearly all the hadrosaurid genera that were then synonyms of Trachodon. These included Cionodon and Diclonius, Hadrosaurus and Pteropelyx as well as Claorhynchus (fragmentary genera) now believed to be horned dinos. Hatcher’s research led to a short consensus. However, new material from Canada as well as Montana revealed a greater variety of hadrosaurids after 1910. Charles W. Gilmore, in 1915, reassessed hadrosaurids. He recommended that Thespesius should be reintroduced to hadrosaurids of the Lance Formation and rock units with equivalent age. Trachodon, which was based on insufficient material, should be limited to a hadrosaurid of the older Judith River Formation or its equivalents. Claosaurus occidentalis was recommended by Gilmore to be treated the same way as Thespesius occidentalis. Thespesius would be reinstated for Lance-age hadrosaurids. This would have other implications for Edmontosaurus’ taxonomy in the next decades.
Two additional important C. annectens specimens were found during this period (1902-1915). Charles Hazelius Sternberg, his sons, and the Lance Formation rocks near Lusk in Wyoming, discovered the first specimen, AMNH 5060. Sternberg was working at the British Museum of Natural History. Henry Fairfield Osborn, American Museum of Natural History, was able to buy the specimen for $2,000. Sternbergs also recovered another similar specimen from the same location in 1910. It was not as well preserved, but it was also found with skin impressions. This specimen (SM 4036), was sold to the Senckenberg Museum, Germany.
Side note: Trachodon selwyni was originally described in 1902 by Lawrence Lambe as a lower jaw of what is now the Dinosaur Park Formation, Alberta. However, Glut (1997) incorrectly stated that it had been assigned to Edmontosaurus regalis, Lull, and Wright. Instead, it was deemed “of very questionable validity”. Recent reviews on hadrosaurids agree.
Lawrence Lambe, a 1917 Canadian scientist, coined the term Edmontosaurus for two partial skulls found in Horseshoe Canyon Formation (formerly known as the lower Edmonton Formation), along the Red Deer River in southern Alberta. These rocks are older than those in which Claosaurus Annectens was discovered. Edmontosaurus’ name is derived from the Edmonton Formation. E. regalis, the type species, or more loosely “king-sized”, is based upon NMC 2288. It consists of a skull and articulated vertebrae, up to the sixth tail vertebra. Ribs, partial hips, a skull, and most of an upper arm bone. Levi Sternberg discovered it in 1912. Paratype NMC 2289 is the second specimen. It consists of a skull, skeleton, and part or all of the feet. George F. Sternberg discovered it in 1916. Lambe discovered that his new dinosaur was most similar to Diclonius mirabilis (specimens currently assigned to Edmontosaurus Annectens). He also noted the robustness and size of Edmontosaurus. Lambe initially only described the skulls for the two skeletons. However, he returned to the genus to write about NMC 2289’s skeleton in 1920. It is not possible to describe the postcrania of this type specimen, as it remains in its plaster jackets.
Edmontosaurus would soon include two more species. These were named from Canadian remains dating back to the 1920s. However, both would be initially assigned to Thespesius. Gilmore named Thespesius edmontoni the first species in 1924. T. edmontoni was also a Horseshoe Canyon Formation specimen. It was based upon NMC 8399 which was another almost complete skeleton that lacked most of its tail. Sternberg’s 1912 discovery of NMC 8399 on the Red Deer River led to NMC 8399 being named. Lambe briefly described its forelimbs and ossified tendon, as well as skin impressions in 1913-1914. He initially thought that it was a specimen of Trachodon marginatus but later changed his mind. It was the first Canadian museum to mount a dinosaur skeleton. Gilmore discovered that his new species was very similar to Thespesius, which he called Thespesius. However, the details of the arms or hands made it difficult to tell the difference. He also noticed that his species had more vertebrae in Marsh’s neck and back, but suggested that Marsh was wrong in thinking that annectens specimens were complete there.
Charles Mortram Sternberg, an 18-year-old man, named Thespesius. This specimen was found in rocks belonging to the Lance Formation, now known as the Frenchman Formation. NMC 8509 contained a complete skull, many vertebrae, partial hip girdles and hind limbs. This was the first significant dinosaur specimen to be recovered from Saskatchewan. Sternberg chose to give it to Thespesius as that was the only hadrosaurid genera from the Lance Formation. T. saskatchewanensis, which was small at 7 to 7.3 meters (23 to 24 ft), was considered unusual at the time.
Lull and Wright tried to solve the complex taxonomy surrounding crestless hadrosaurids in 1942 by naming Anatosaurus a new genus to include several species not found under their prior genera. Anatosaurus is a name that means “duck lizard” because of its broad, duck-like beak. (Latin anas = duck + Greek salvaros = lizard). Its type species was Marsh’s Claosaurus thenectens. This genus also included T. saskatchewanensis and Thespesius edmontoni. Marsh had previously named Trachodon longiceps, a large lower jaw, Anatosaurus copei. The American Museum of Natural History has two skeletons that were long known as Diclonius Mirabilis or variations thereof. The various species were renamed Anatosaurus annectens to A. copei and A. edmontoni to A. longiceps and A. saskatchewanensis. Anatosaurus was to be known as the “classic duck-billed dinosaurus.”
This was the case for many decades until Michael K. Brett–Surman, a graduate student in the 1970s and 80s, reexamined the material. He found that A. annectens was the type Anatosaurus species and that A. copei was unique enough to merit its own genus. Theses and dissertations cannot be considered official publications of the International Commission on Zoological Nomenclature. However, other paleontologists were aware of his findings and they were adopted in many popular works. In 1990, Ralph Chapman and Brett-Surman established a new genus to accommodate A. copei (Anatotitan). A. saskatchewanensis, A. edmontoni, and A. longiceps were also assigned to Edmontosaurus. A. longiceps was then added to Anatotitan either as a second or synonym to A. copei. Anatosaurus was dropped into Edmontosaurus because it contained the Anatosaurus type species (A. annectens).
Three valid species were included in the Edmontosaurus concept: E. regalis (along with Anatosaurus Edmontoni, which was later changed to edmontonensis), E. annectens (including Anatosaurus Edmontoni) and E. Saskatchewanensis. The debate continues about the correct taxonomy for the A. copei specimens. Jack Horner and Catherine Forster, returning to Hatcher’s argument of 1902 said Anatotitan copei represented specimens of Edmontosaurus nectens with broken skulls. Another “mummy”, nicknamed “Dakota”, was announced in 2007. It was discovered by Tyler Lyson in 1999 and was from North Dakota’s Hell Creek Formation.
Nicolas Campione, David Evans and their colleagues conducted the first ever morphometric analyses to compare different specimens that were assigned to Edmontosaurus in a 2011 study. Only two species were valid, E. regalis from the late Campanian and E. annectens from the late Maastrichtian. Anatotitan copei was further confirmed by their study. This is because the long and low skulls of A. copei are the result of ontogenetic changes.