Episode 129 is all about Edmontosaurus, a hadrosaurid that lived in the Cretaceous in what is now western North America.

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In this episode, we discuss:

News:

The dinosaur of the day: Edmontosaurus

Hadrosaurid (duck-billed) that lived in the Cretaceous in what is now western North America

Two known species: Edmontosaurus regalis and Edmontosaurus annectens

Type species is Edmontosaurus regalis

The species name regalis means “regal” or “king-sized”

Edmontosaurus is named after Edmonton, the capital of Alberta (fossils were first found in southern Alberta)

Edmontosaurus regalis was named in 1917 by Lawrence Lambe, based on two specimens found in Alberta (that George Sternberg found in 1912 and 1916)

However, there are other species that are now classified as Edmontosaurus that were named earlier, including Edmontosaurus annectens, which Charles Marsh named in 1892 (originally was Claosaurus, then known as Trachodon, then Anatosaurus annectens. Anatosaurus and Anatotitan are now usually considered to be synonyms of Edmontosaurus

Charles Marsh named Claosaurus annectens in 1892, based on a partial skull-roof and skeleton and a second skull and skeleton (specimens were collected in 1891 by John Bell Hatcher, in Wyoming)

Charles Marsh described in 1889 a lower jaw that John Bell Hatcher found in the Lance Formation. He named it Trachodon longiceps, and it was larger than Cope’s specimen but had some similarities. In 1904 a second mostly complete skeleton was found in the Hell Creek Formation, by Oscar Hunter, a rancher in Montana. He and a friend debated over whether what he found was a fossils. Hunter showed it was brittle (and therefore stone) by kicking off the tops of the vertebrae, which Barnum Brown, who eventually collected the fossil, was unhappy about. Alfred Sensiba, another rancher, bought the specimen for a pistol and sold it to Brown, who excavated it in 1906. In 1907 this and Cope’s specimen were mounted next to each other at the AMNH, as Trachodon mirabilis

Hadrosaurids weren’t well known at the time, and after Marsh died in 1897 Claosaurus annectens was classified as a number of genera, Claosaurus, Thespesius, Trachodon. Textbooks and encyclopedias mentioned the difference between Claosaurus that was “Iguanodon-like” and Hadrosaurus with the “duck-bill”. In 1902, Hatcher said Claosaurus annectens was synonymous with the duck-billed skull hardosaurid, and he thought nearly all then known hadrosaurids were synonyms of Trachodon (which included Cionodon, Diclonius, Hadrosaurus, Ornithotarsus, Pteropelyx, Thespesius, Claorhynchus, Polyoanx). Then in 1910 new fossils from Canada and Montana showed more diversity in hadrosaurids. Charles Gilmore said in 1915 that Claosaurus annectens was the same as Thespesius occidentalis

Between 1902 and 1915, two more Claosaurus annecten specimens were found. The first was the “Trachodon mummy” found in 1908 by Charles Hazleius Sternberg and his sons, in Wyoming. Sternberg was working for the British Museum of Natural History, but Henry Fairfield Osborn bought the specimen for $2000 for the American Museum of Natural History. In 1910 the Sternbergs found a second similar specimen in the same area, which had skin impressions (they sold it to the Senckenberg Museum in Germany)

Lawrence Lambe described Trachodon selwyni in 1902 based on a lower jaw found in Alberta. It was described as having been assigned to Edmontosaurus regalis, but not many people think this is right

Trachodon is now considered to be a dubious genus

Two other species were included with Edmontosaurus in the 1920s but were initially called Thespesius. In 1926, Charles Sternberg named a new specimen Thespesius saskatchwanensis. In 1942, Lull and Wright wanted to simplify the taxonomy of crestless hadrosaurids and named a new genus, Anatosaurus, to include multiple species. The name Anatosaurus means “duck lizard” Assigned to this new genus were Thespesius, Trachodon longiceps (named based on a lower jaw), and a new species called Anatosaurus copei, based on two skeletons on display at the AMNH that were previously known as Diclonius. Anatosaurus became known as the “classic duck-billed dinosaur”

Anatosaurus was a wastebasket taxon for hadrosaurs

Anatosaurus copei (then Anatotian, then Edmontosaurus annectens) was found in 1882 by Dr. J. L. Wortman and R. S. Hill in 1882, for Edward Cope. They found it in the Hell Creek Formation, and Cope described it as Diclonius mirabilis. It was a combination of Diclonius, a hardosaur Cope had named earlier based on teeth, and Trachodon mirabilis, which was also named based on teeth, but named by Joseph Leidy. Cope thought Leidy did not properly characterize Trachodon and had abandoned it, so he assigned the older Trachodon species to the new genus Diclonius (Leidy had found that Trachodon was based on multiple types of dinosaurs, and he was working on revising the genus, but didn’t formally declare anything)

Lambe noted that the two Edmontosaurus specimens he described in 1917 were similar to Diclonius mirabilis

In the 1970s and 1980s Michael K. Brett-Surman rexamined this material and found that Anatosaurus annectens, the type species, was actually a species of Edmontosaurus, and said that Anatosaurus copei was different enough to be a separate genus. This was part of his graduate work, and is not considered to be an official publication by the International Commission on Zoological Nomenclature. In 1990, Brett-Surman and Ralph Chapman designed a new genus for Anatosaurus copei, Anatotitan. Then Anatosaurus saskatchewanensis and Anatosaurus edmontoni were reassigned to Edmontosaurus, Anatosaurus longiceps became Anatotitan (either as a second species or synonym of Anatotitan copei). Because the type species, Anatosaurus annectens, became Edmontosaurus, Anatosaurus is no longer considered to be a junior synonym

At this time, there were considered to be three species of Edmontosaurus: regalis, annectens (which included Anatosaurus edmontoni) and saskatchewanensis

Nicolás Campione and David Evans said in a 2007 study that there were only two valid Edmontosaurus specimens: regalis and annectens, and they found that Anatotitan copei was a synonym of Edmontosaurus annectens (the Anatotitan skull was a mature Edmontosaurus annecten)

In 2011, Campione and Evans looked at all known Edmontosaurus skulls and found that the shape of the skulls changed as it grew. The skull became longer and flatter. This lead to mistakes in classification, and means that Thespesius edmontoni, a.k.a. Edmontosaurus annectens, was more likely a subadult Edmontosaurus regalis. Also Edmonstosaurus saskatchewanensis represented juveniles, Edmontosaurus annectens were subadults, and Anatotitan copei were mature adults

It’s possible Trachodon longiceps is also a synonym of Edmontosaurus annectens

Edmontosaurus specimens found in Alaska and western Texas have been reassigned to other genera (Ugrunaaluk kuukpikensis and Kritosaurus)

It’s a saurolophine hadrosaurid, which is the group that had solid crests or fleshy combs (instead of large, hollow crests, like lambeosaurinae)

One of the largest hadrosaurids

Up to 39 ft (12 m) long and weighing 4 tons (possibly even larger, up to 49 ft or 15 m long and weighing 9 metric tons, based on a couple specimens that are still being studied)

Very large Edmontosaurus were probably rare because of environmental stress, disease, and being prey

Lots of bonebeds found. One in the Lance Formation has remains from 10,000 to 25,000 Edmontosaurus

Possibly lived in groups and may have migrated, based on several bone beds being found

Phil R. Bell and Eric Snively said in 2008 that Edmontosaurus may have migrated annually 1,600 mi (2,600 km) round trip (from Alaska to Alberta), but not everyone agrees

Chisamy and others in 2012 found that hadrosaur remains in more polar regions were from groups that lived there all the time (and didn’t migrate)

Herbivore, and could move on both two and four legs

Probably walked on two legs when moving fast

Had powerful leg muscles

Could run possibly up to 28 mph (45 kph)

Bulky with a long, flat tail and a head with a duck-like beak

Held tail horizontally (tail had ossified tendons so it was “ramrod” straight)

Stiff tail may have helped counterbalance, especially when changing between two and four legs

Hadrosaurs are sometimes called the “cows” of the Cretaceous, but they may have been more powerful than we realized (had large back legs and a muscled tail, and could run faster than a T.rex)

Largest known skull was 46 in (118 cm) long

Had a comb-like crest on its head

Skull was triangular

Some Edmontosaurus skulls were so well preserved scientists could make casts of the brain cavity (had a proportionately small brain)

Bones around its nasal openings had deep indentations, which may have held inflatable air sacs

Scientists have found sclerotic rings in the eye sockets and stapes (reptilian ear bone) in Edmontosaurus specimens, which is rarely preserved

Edmontosaurus annectens has a longer, less robust skull than Edmontosaurus regalis, and Edmontosaurus regalis comes from an older formation than Edmontosaurus annectens (though they’ve both been found in the same area)

Found in the Horseshoe Canyon and St. Mary River formations (older) and Frenchman, Hell Creek, and Lance formations (younger)

Had a frilly ridge of soft tissue down the center of its neck and back

Had four fingers on each hand (2nd, 3rd, and 4th digits were about the same length and were together via a fleshy covering); little finger was shorter and not connected to the other three

Had three toes on each foot, and they had hoof-like tips

Cope had originally thought hadrosaurids were amphibious, based on the lower jaw being weakly connected and might break off if eating non-aquatic food (he also thought the beak was weak). But this turned out to not be true

Short fingers were not great for swimming, and same with rigid tail

Scientists used to think Edmontosaurus was aquatic and ate aquatic plants (until the 1960s and 70s). William Morris in 1970 said it had a diet like modern ducks, and used its beak to filter plants and aquatic invertebrates, but this is now considered false

Scientists have found skin impressions and possible gut contents of Edmontosaurus

Had a toothless beak that were covered in keratin

The “mummy” Edmontosaurus at the Senckenberg Museum has some of the keratinous material on the beak

Used its beak to cut food (cropped it or clamped jaws on twigs and branches and stripped off leaves and shoots)

Could eat food on the ground to about 13 ft (4 m) tall

Probably grazed its food, based on wear patterns on the teeth

Had cheek-like structures to keep food in the mouth

Could probably slice and grind, based on tooth structure

Had dental batteries

Had up to 2,000 teeth at the back of its jaws

Only had teeth in the upper cheeks and dentaries

Continually replaced teeth, and they took about half a year to form

Teeth grew in columns, and the number of columns depended on the size of the Edmontosaurus (Edmontosaurus regalis had between 51-53 columns and Edmontosaurus annectens had 52)

From the 1980s to early 2000s, it was thought that hadrosaurids could chew by moving its lower jaw backward and forward, based on a model by David Weishampel in 1984. But in 2008 Casey Holliday and Lawrence Witmer published a study that found Edmontosaurus did not have skull joints that would allow this motion. A 2009 study by Vincent Wililams and others said there may have been a combination of movements, including an oblique motion

There were reports of gastroliths found in Edmontosaurus annectens (then known as Claosaurus, when Barnum Brown found it in 1900), but now it’s thought the gastroliths were actually gravel that washed in after the animal died

The Sternberg “mummy” specimens may have had gut contents. Sternberg reported on carbonized gut contents for the AMNH specimen, but it hasn’t been described yet. Plant remains in the Senckenberg Museum specimen were described but were not easy to interpret (plants may be gut contents, or were washed into the animal’s carcass after it died)

Edmontosaurus annectens specimens have been found with skin impressions, such as the “Trachodon mummy”, and another specimen nicknamed “Dakota” (found in 1999 by Tyler Larson in the Hell Creek Formation in North Dakota, and announced in 2007). Found that most of the body was covered in scales

Not as many specimens with skin impressions have been found for Edmontosaurus regalis, but some specimens have been studied, including one with a soft tissue crest on the head

Not as many specimens with skin impressions have been found for Edmontosaurus regalis, but some specimens have been studied, including one with a soft tissue crest on the head Not clear if Edmontosaurus annectens had a crest, and whether the crest indicated sexual dimorphism

Edmontosaurus lived all over western North America, and seemed to prefer coasts and coastal plains

The Lance formation, where some Edmontosaurus specimens have been found, had a bayou setting, with tropical conifers and palm trees around hardwood forests, a humid, subtropical climate. Lived among fish, salamanders, turtles, lizards, snakes, shorebirds, and small mammals

Lived at the same time and place as Triceratops and Tyrannosaurus (one of the last non-avian dinosaurs)

Edmontosaurus bones were described as having tumors in 2003 (hemanglomas, desmoplastic fibroma, metastatic cancer, and osteoblastoma). May have been genetic or from environmental factors

Osteochondrosis has also been found in 2.2% of 224 Edmontosaurus toe bones (pits in bone in places where bones articulate, which happens when cartilage is not replaced by bone during growth). Not clear if that’s from genetics, trauma, feeding intensity, or other factors

One specimen of Edmontosaurus annectens from South Dakota has tooth marks from small theropods on its lower jaws (partially healed). Maybe the theropods attacked its throat, and it died of its injuries

Can see an adult Edmontosaurus annectens at the Denver Museum of Nature and Science (has a theropod bite in its tail, probably a T.rex); died before it healed, and had a bone infection. It survived the attack somehow, either outmaneuvered, outran, or used its tail as a weapon

Can see two Edmontosaurus specimens at the Museum of the Rockies

Can see Edmontosaurus in Dinosaurs in their Time, an exhibit in the Carnegie Museum (two T.rexes are fighting over a carcass)

Fun Fact:

Pachypodosauria (potential new name for Saurischians w/o Theropods) was named by Friedrich von Huene in 1914. Ironically Pachypodosauria was originally used to group theropods and sauropodomorphs (he also named Sauropodomorpha)

This isn’t the first time the Saurischian-Ornithischian framework has been questioned. Bob Bakker proposed some major changes in The Dinosaur Heresies in 1986. He proposed putting herrarasaurids on their own, Theropods on their own, and Phytodinosauria “plant dinosaurs” on its own. Which effectively separating out herbivores from carnivores. This was part of a larger argument to remove Dinosauria from Reptilia to emphasize their bird-like warm bloodedness. In the book he says “I proposed this sort of classification in 1975 in an article I published in in Scientific American. Most taxonomists, however, have viewed such new terminology as dangerously destabilizing to the traditional well-known shcheme that has been with us since the time of Baron Cuvier.”

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