Edmontosaurus (Edmonton Lizard, named after the Lower Edmonton Formation, which is now called the Horseshoe Canyon Formation) is a genus of saurolophine hadrosaurid dinosaur that lived in western North America 73 - 66 million years ago, from the Campanian to the Maastrichtian stage of the Late Cretaceous Period. Next to Triceratops, it is one of the most common dinosaurs of its place and time, as well as one of the largest non-sauropod dinosaurs that ever lived in North America.
Edmontosaurus is a massive animal, one of the largest hadrosaurs ever discovered. It measured around 11 - 13 meters (36 - 43 feet) long, and weighed around 5.6 - 7 metric tons (6.2 - 7.7 short tons) according to a study in 2022.[5] Some remains indicate that Edmontosaurus could have reached sizes similar to that of its larger Chinese relative, Shantungosaurus, which is the biggest non-sauropod dinosaur ever known, reaching lengths of 15 - 16.6 meters (50 - 54 feet) and masses of 13 - 16 metric tons (14 - 18 short tons), though it is believed that these were exceptional, rare cases as opposed to being an indication of the animal's large size.[9][10]Edmontosaurus came in a variety of lightly-built and robust forms, though it is yet to be confirmed if this is a sign of sexual dimorphism.[11] As with most ornithopods, Edmontosaurus had a latticework (criss-crossed arrangement) of fleshy sinews that ran along the backbone as strengthening supports, with these tendons ending up ossified (turned to bone) as the dinosaur grew older.[12]
When it comes to the large size and growth rate of hadrosaurs, one study in 2008 brings up Hypacrosaurus stebingeri specimen MOR 549, which reached sexual maturity (during which the animal becomes fertile and ready to mate) in 2 - 3 years, attained 95% skeletal maturity (the extent to which its body can grow) in 10 - 12 years, and died at 13 years of age, with all these suggesting that the quick growth of hadrosaurs was an adaptation against large predatory dinosaurs, which tended to grow at a rate 2 - 4 times slower. In that study, it is said that Albertosaurus took around 23 years, and Tyrannosaurus rex around 36 years (though a new study in 2020 suggests that T. rex reached skeletal maturity in 16 - 22 years).[13][14] This is also consistent with Majungasaurus of the Maevarano Formation in Madagascar, as it is said to take 20 years to grow.[15]
Jaws and Dentition[]
Hadrosaur beaks were not shaped like a duck's bill, instead bearing keratinized sheaths that curved downwards
The skull of Edmontosaurus is approximately 1.18 meters (3 feet, 11 inches) long.[6] Like all hadrosaurs, its mouth is said to resemble a duck's beak. However, as proven by the remains of Edmontosaurus annectens specimen LACM 23502, hadrosaur bills are not actually as duck-like as once thought. The face of LACM 23502 has what appears to be a rhamphotheca (beak tissue), or, at the very least, the supporting structure beneath the actual rhamphotheca, indicating that hadrosaur beaks actually extended past the premaxilla (upper jaw tip), curving downwards in a hooked shape, giving the bill a form closer to that of a shovel.[16][DN 2][DN 3] This hooked shape allowed Edmontosaurus to grip, rip, and snap off the tough materials seen in its stomach and coprolites (fossilized dung), like the needles of Cunninghamites elegans (an extinct species of conifer), the twigs of conifers and broadleaf trees, several small seeds and fruits, and even tree bark, food that simply cannot be grabbed or broken off with a flat duck-like bill.[17][DN 2]
A herd of Edmontosaurus feeding on vegetation close to the ground
To help mash up the tough plant materials they fed on, hadrosaurs evolved dental batteries, tightly-packed, diamond-shaped teeth arranged in approximately 60 "tooth families" (columns) that interlocked to form surfaces that grinded against each other like rasps. One jaw ramus of a hadrosaur can hold around 300 teeth, and the entire mouth would have had a thousand or more at any given time.[18][19] Due to constant wear and tear, these teeth would have been quickly replaced, growing in less than 0.65 years (7 - 8 months), and younger animals would have likely grown their teeth even faster than older ones.[7] Unlike mammals, dinosaurs did not chew from side to side the way mammals did (in the case of hadrosaurs, they just moved their jaws back and forth),[20] and hence did not need cheeks to retain food in their mouth, unlike what older studies propose.[AN 1] Even so, they may have had "cheeks" as a result of jaw muscles extending across the parts where true cheeks would be, an idea supported by osteological and microwear evidence.[AN 2]
Limbs and Speed[]
An Edmontosaurus juvenile hobbling towards its mother, having narrowly escaped the currents of a raging icy river
Edmontosaurus lacks a first digit (the "thumb"), leaving it with only four fingers on each of its hands, which are mostly enclosed in a fleshy covering, hence, the individual fingers cannot move independently, instead acting more like a single unit. The second digit (the "index finger") has a spade-shaped claw. The fifth digit (the "little finger" or "pinkie") is not part of the "mitten" of flesh (hence, it pops out from the rest of the hand), and lacks a claw entirely. The fourth digit (equivalent to the "ring finger") is completely enclosed in the "mitten", and thus cannot be seen. The third digit has a weight-bearing hoof-like nail.[21][22] As for the hind limbs, the feet only have three toes that also end in hoof-like tips, and these digits, unlike those of the hadrosaur's hands, are clearly separate from each other, not united within a "glove" of flesh. Like other hadrosaurids, Edmontosaurus is quadrupedal by default. However, it can switch to a bipedal stance when needed. On its robust, straight thigh bone, a prominent flange can be found halfway down its back side, serving as the attachment of powerful muscles connected to the hips and tail, which pulled the thighs (and, therefore, the hind legs, which were longer and more robust than the front legs) backwards so that the animal can use its long, heavy, laterally flattened tail to balance itself as it stood up, walked, and ran on two legs.[21]
An Edmontosaurus running away from a T. rex closing in on it
“ A group of Edmontosaurs. They lack armor, but they're as big as T. rex, and twice as fast. To catch one needs cunning. ”
Despite its bulky physique, Prehistoric Planet states that Edmontosaurus can be twice as fast as T. rex. In 2009, studies indicate that Edmontosaurus can reach a speed of 15.7 meters (52 feet) per second, or 57 kilometers (35 miles) per hour, when galloping on all fours, and 14 meters (46 feet) per second, or 50 kilometers (31 miles) per hour, when running on two legs.[23] By comparison, a 2017 study indicates that T. rex could only run up to 27 kilometers (17 miles) per hour, and it would likely exhaust itself before reaching its top speed,[8] though a study in 2021 also calculated a rhythmic, energy-efficient walking speed of 1.28 meters (4 feet, 2 inches) per second, or 4.6 kilometers (3 miles) per hour for T. rex.[24]
A T. rex grabbing an Edmontosaurus by the neck
However, Dr. Darren Naish, Prehistoric Planet's lead consultant, later clarified that the idea of Edmontosaurus being twice as fast as T. rex was an error in the narration, and both animals actually had a similar top speed, meaning that, given the modern estimates of the maximum speed of T. rex (which was calculated almost a decade after the studies regarding the running speed of Edmontosaurus, and thus, are more in-line with the current understanding of these animals), Edmontosaurus likely also ran at speeds of around 25 - 30 kilometers (15.5 - 19 miles) per hour, making it easier for a T. rex to catch up to one of these hadrosaurs.[DN 1] Although ambushing prey is more preferable for predators since it would help conserve effort, energy, and time, the fact that at least two cases show T. rex biting an Edmontosaurus on the tail imply that Edmontosaurus is not fast enough to escape unscathed at all times (and also that the robust theropod is not averse to chasing after prey when necessary), as tail bites are more likely inflicted by a predator attempting to grab its fleeing target from behind during a pursuit.[25][26]
There are at least two recognized species of Edmontosaurus, the earlier E. regalis (the type species, with a species name meaning "king-sized") of the Horseshoe Canyon Formation (formerly known as the lower Edmonton Formation) in southwest Alberta, Canada, and the later E. annectens, which lived in the Hell Creek Formation (which stretches from Montana to South Dakota in USA), the Lance and Laramie Formations in Wyoming, USA, and the Frenchman Formation in Saskatchewan, Canada. A hadrosaur in the Prince Creek Formation was originally seen as an Edmontosaurus species, then was classified as a distinct animal known as Ugrunaaluk kuukpikensis in 2015,[27] though this idea was called into question given the lack of differences to properly distinguish it from Edmontosaurus.[1][2] Currently, the Prince Creek hadrosaur is considered as possibly being E. regalis based on similarities in skull and mandibles.[3]E. annectens differs from E. regalis in that its skull is longer, lower, and less robust. E. regalis is also known to have a crest or wattle of soft tissue on its head, though it is yet to be confirmed if E. annectens also had such a comb.[28][29] It has been suggested that both E. regalis and E. annectens represent two different sexes of a single species, but this is contradicted by the fact that E. regalis came from different, older formations, indicating that it lived earlier than E. annectens, and was therefore distinct from it. Despite all these, Prehistoric Planet does not depict either of the two species as looking distinct from each other, as both species use the same design on the show, with the sleeker, crestless head implying that E. annectens served as the basis for the animal's portrayal in the series.
An adult female, a juvenile, and an adult male Edmontosaurus traveling across the Prince Creek Formation, along with dozens more
On Prehistoric Planet, Edmontosaurus is depicted as being mostly brown with a white underside that travels upwards in vertical stripes, providing the hadrosaur with countershading to help enhance camouflage, while its legs bear similarly-colored horizontal bands, perhaps to help further break its outline while blending in with the environment. This coloration may be based on specimen NDGS 2000 (nicknamed "Dakota") of the Hell Creek Formation, as the areas of its arm's joints have textures forming a striped pattern. Conversely, the eumelanin found within the fossilized flank tissue of hadrosaur specimen YPMPU 016969 suggests that hadrosaurs may have been as gray as elephants and rhinoceros, which may in turn imply that hadrosaurs occupied similar ecological niches as these large mammals, though these findings are far from conclusive given a lack of other variables (e.g. chromatophores) that can actually determine a reptile's skin color.[30]Edmontosaurus is known to come in various lightly-built and robust forms, though it is unknown if this is meant to indicate sexual dimorphism. Instead, the show depicts the adult males as being mostly the same as the adult females, save for their bright green and yellow markings on the face and neck area, fitting given how it is usually male animals that appear more vibrant in order to intimidate rivals and attract females.
Shaken yet still mostly (but not entirely) intact following their chaotic river crossing, the Edmontosaurus herd continues their journey
The Prince Creek species of Edmontosaurus was featured in the first segment of Ice Worlds trying to cross an icy river while being harassed by dromaeosaurs, with two of the hadrosaurs appearing briefly in the second segment of Ice Worlds, walking down a river while an Ornithomimus tries to keep them away from his nest. The fifth segment of Forests shows the Horseshoe Canyon Formation on fire, with an Edmontosaurus regalis escaping the flames with her two young. Edmontosaurus annectens appears in the fifth and final segment of Swamps, with a herd being attracted to the lush wetlands of the Hell Creek Formation, though they themselves were viewed as food by two subadult Tyrannosaurus brothers,[PhP 1][DN 4] which successfully ambush and bring down one of the hadrosaurs while they were grazing through a forest at night. Footage of Edmontosaurus from the fifth segment of Swamps is used in the Uncovered segment "How Good Were T. rex Senses?", which is dedicated to the means by which T. rex perceived and hunted its prey.
A herd of Edmontosaurus traveling alongside an icy river in the Prince Creek Formation, Alaska
“ Although at this time in Earth's history, the polar regions are relatively warm, these lands are nonetheless ruled by extreme seasonal change. When the sun rises for the first time in almost three months, every animal must be ready to make the most of the daylight, and the warmer days that are to come. ”
Edmontosaurus lived in Laramidia, an island continent that would one day become western North America, which, by that time, was split in half by an inland sea, with the earlier E. regalis existing around 73 - 70 million years ago, and the later E. annectens living approximately 69 - 66 million years ago (with the age of the earliest remains based on the age of the Laramie Formation, which is 69 - 68 million years old according to magnetostratigraphic dating).[4] It is known from places as far north as Alaska and Canada, though it also lived in more southern areas. Edmontosaurus appears to prefer subtropical inland forests, swamps, and rivers (as seen in the Hell Creek Formation, which, though warmer than Montana and South Dakota today, was kept humid by sufficient levels of rainfall), and, like some animals today, is believed to move depending on resources (this does not necessarily mean that they are migratory animals, periodically moving in response to seasonal changes and conditions).
The environments that Edmontosaurus lived in resulted in exceptional "mummified" specimens (in truth, they are still true fossils, as their tissues have been mineralized, transformed into rock), like SMF R 4036, AMNH 5060, and NDGS 2000, nicknamed "Dakota", mostly preserved by rivers.
Paleofauna[]
A trio of Dromaeosaurus feasting on a juvenile Edmontosaurus that drowned while crossing a river in the Prince Creek Formation
Edmontosaurus lived in a wide range of habitats. Up north in the Prince Creek Formation, specimens considered to be possibly Edmontosaurus regalis coexisted with animals like Pachyrhinosaurus perotorum, the pachycephalosaur Alaskacephale, as well as unidentified lambeosaurines, leptoceratopsids, thescelosaurines, and ornithomimosaurs that may or may not be Ornithomimus. It also coexisted with carnivorous theropods like Saurornitholestes, Dromaeosaurus, troodontids (which made up two-thirds of all theropod fossils in the area, and are almost twice as big as their relatives in Alberta and Montana),[31][32][33] and the tyrannosaurine Nanuqsaurus, the region's top predator and the only animal in the area that could conceivably hunt fully-grown Edmontosaurus directly.
Two young Edmontosaurus following their mother as she leads them out of a burnt forest in the Horseshoe Canyon Formation
In the Horseshoe Canyon Formation of Alberta, Canada, Edmontosaurus regalis dwelled near shorelines (preferring habitats described as bald cypress swamps and peat bogs on delta coasts), while other hadrosaurs like fellow saurolophine Saurolophus osborni and the lambeosaurine Hypacrosaurus altispinus lived in lowlands further inland.[34][35] This allows for niche partitioning, something further supported by the fact that Edmontosaurus regalis is usually not found together with Saurolophus. It was even assumed that they lived in different times and thus never met, until a discovery in 2007 revealed the fossils of both E. regalis and S. osborni in the same locality, proving that they coexisted, at least, to some degree.[36]
Adult Edmontosaurus would have been safe from small hunters like the troodontid Albertavenator and the saurornitholestine dromaeosaur Atrociraptor. However, it would have been one of the preferred targets of Albertosaurus sarcophagus, the largest predator in the Horseshoe Canyon Formation, since its lighter and sleeker physique (compared to tyrannosaurines) is better adapted for the pursuit of fleet-footed, less-armored prey like hadrosaurs as opposed to heavily-armored prey like Edmontonia and Anodontosaurus.
Edmontosaurus regalis is only known from the lower, earlier units of the Horseshoe Canyon Formation like the Horsethief and possibly the older Drumheller Members, as it appears to have been replaced by Hypacrosaurus in the upper portions, units younger than the two aforementioned layers, with its disappearance (and the apparent absence of ceratopsians in those later times) being attributed to possible climate change.[37] It died out 70 million years ago, and thus never reached the end of the Mesozoic Era.
A selection of non-avian dinosaurs that lived in the Hell Creek, Lance, and Scollard Formations (Edmontosaurus annectens on the left side, in green)
“ Here, in spring, new plant growth creates new feeding grounds for the gathering herds. But where there are large numbers of plant-eaters, there are great hunters... ”
In the more southern parts of its range, Edmontosaurus coexisted with animals like Triceratops, Ankylosaurus, and Pachycephalosaurus, as well as some dromaeosaurs like Acheroraptor and troodontids like Pectinodon. Given their large size, adult Edmontosaurus would have only needed to be wary of one hunter, the apex predator of the regions it lived in, Tyrannosaurus rex. Given the large size of their bodies, they would have, however, attracted several scavengers upon death. The NDGS 2000 "Dakota" specimen, for example, bears marks left by non-serrated conical teeth with cutting ridges ("carinae"), suggesting that, by the time it died, it was immediately feasted upon by any of the various crocodyliforms of the Hell Creek Formation (e.g. Brachychampsa montana, Borealosuchus sternbergii, and Thoracosaurus neocesariensis), which ironically released the gases, fluids, and microbes that developed within it during decomposition, allowing its soft tissues to dry out without significant degradation prior to the specimen's burial and fossilization.[38]
A herd of Edmontosaurus walking towards a swamp in the Hell Creek Formation
In a 2011 study that estimated the proportions of large-bodied dinosaurs in the Hell Creek Formation, it was revealed that Edmontosaurus was the third most abundant dinosaur in the Hell Creek Formation, making up 20% of the area's dinosaur population. The most common is Triceratops, which made up 40% of all dinosaurs found in the region, followed by T. rex, which made up 24% of Hell Creek's dinosaur population.[39]
As one of the last non-avian dinosaurs, Edmontosaurus annectens, along with most of the animals it coexisted with, would have bore witness to the Cretaceous-Paleogene Extinction Event 66.043 million years ago,[40] a catastrophe that would ultimately wipe out three-quarters of all life on Earth, including all non-avian dinosaurs.
Social Lifestyle and Parental Habits[]
An Edmontosaurus tending to her young
Several bonebeds indicate that Edmontosaurus lived in large herds (said to be headed by several leaders on the show, though it is also possible that this implies that several herds, each with a single leader, combined to form a larger head for this occasion). However, it is also possible that some individuals were solitary, or, as shown in Forests, only lived with their offspring or other family members. Herding behavior allows for safety in numbers, though this comes at the expense of the few that are focused on and attacked while the rest get away from the threat.
An Edmontosaurus escaping a forest fire with her two offspring
“ Most animals flee. But this Edmontosaurus has a family to care for. She doesn't abandon them. Now, they must keep one step ahead of the blaze until it burns out. ”
Prehistoric Planet also depicts female Edmontosauruses as caring for their young, with one mother urging her calf out of a river in Ice Worlds (though she doesn't actually help it), and another carefully guiding her two offspring out of the burning woods in Forests. Even so, Dr. Darren Naish brings up how Edmontosaurus likely laid 20 - 30 eggs like most dinosaurs, hence, they live by the r-selection strategy, since they have many offspring, many of which are not expected to survive up to adulthood, a fact that some predators may take advantage of,[DN 5] as shown when a pack of dromaeosaurs harass an Edmontosaurus herd by a river crossing with the knowledge that some won't survive raging rapids.
Traveling Lifestyle[]
A herd of Edmontosaurus come across an icy river
“ These duckbilled dinosaurs pass through here every year, nomads in search of the fresh vegetation brought by the spring. They're huge. The only chance the dromaeosaurs will have is to work as a team. ”
Some studies support the idea that Edmontosaurus was a migratory animal, stocking up on fat and other energy resources to make a 2,600-kilometer (1,600-mile) round trip every year, which would require a pace of 2 - 10 kilometers (1 - 6 miles) per hour, and could explain the animal's presence in Alaska and Canada.[41] Other studies, however, conclude that Edmontosaurus did not migrate and simply endured wintertime.[42] As clarified by Dr. Darren Naish, several lines of evidence suggest that the Edmontosauruses of the far north were actually not migratory, with one form of proof being babies in the north of Alaska. Hence, Prehistoric Planet simply refers to them as "nomads", constantly moving to where food is plentiful.[DN 6] Regardless, due to this sort of lifestyle, Edmontosauruses would have faced several dangers on their journey, from predators to the environmental terrain and conditions.
Defensive Tactics[]
A herd of Edmontosaurus stampeding, putting their own young at risk of wandering closer to danger, being dragged away by predators, or getting trampled underfoot
Edmontosaurus is roughly just as fast as its main predator, Tyrannosaurus rex.[DN 1] Hence, when confronted with threats, the hadrosaurs prefer to flee. In response, predators tend to use different tactics to bypass or even exploit their tendency to run from danger. In Ice Worlds, dromaeosaurs several times smaller than them successfully get the whole herd to panic, stampede, and frantically try to cross an icy river even though they are no threat to adults, and are only trying to harass the juveniles, exploiting the pandemonium to indirectly get a few of them killed by the river. In Swamps, a pair of T. rexes hunt in the darkness of the night, also cause panic to a degree, and ambush their prey, forcing a single targeted Edmontosaurus into a position where the pair can close in on it and kill it.
An Edmontosaurus struggling and attempting to fight back against a T. rex
Even so, given its size, Edmontosaurus is far from defenseless. Despite lacking armor or visible weapons of any kind, these large, powerful animals are capable of enduring a few of the bone-crushing bites of a T. rex (with specimens like DMNH 1943 and another E. annectens from the Hell Creek Formation bearing healed T. rex bites on their tails).[25][26] The original plan for the fifth segment of Swamps even involved two juvenile T. rexes attacking an adult Edmontosaurus, only to be beaten up.[DN 7] While this particular idea ultimately never came to pass, the final version of events showed that it still takes a considerable amount of experience, skill, and even luck for a T. rex to bring down an Edmontosaurus.[DN 8]
Gallery[]
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↑ 4.04.1Hicks, J.F., Johnson, K.R., Obradovich, J. D., Miggins, D.P., and Tauxe, L. 2003. Magnetostratigraphy of 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.
↑Gould, Rebecca; Larson, Robb; Nellermoe, Ron (2003). "An allometric study comparing metatarsal IIs in Edmontosaurus from a low-diversity hadrosaur bone bed in Corson Co., SD". Journal of Vertebrate Paleontology. 23 (3, suppl): 56A–57A
↑ 21.021.1Lull, Richard Swann; Wright, Nelda E. (1942). Hadrosaurian Dinosaurs of North America. Geological Society of America Special Paper 40. Geological Society of America.
↑Russell, Dale A.; Chamney, T. P. (1967). "Notes on the biostratigraphy of dinosaurian and microfossil faunas in the Edmonton Formation (Cretaceous), Alberta". National Museum of Canada Natural History Papers. 35: 1–35.
↑Russell, Dale A. (1989). An Odyssey in Time: Dinosaurs of North America. Minocqua, Wisconsin: NorthWord Press, Inc. pp. 170–171.
