Diet and feeding of
E. annectens as semi-aquatic animals that could only chew soft water plants, a popular idea at the time which is now outdated As a hadrosaurid,
Edmontosaurus was a large terrestrial
herbivore. Its teeth were continually replaced and packed into dental batteries that contained hundreds of teeth, only a relative handful of which were in use at any time. The animal's feeding range would have been from ground level to around above. An example of this is William Morris's 1970 interpretation of an edmontosaur skull with nonbony beak remnants. He proposed that the animal had a diet much like that of some modern ducks, filtering plants and aquatic invertebrates like
mollusks and
crustaceans from the water and discharging water via V-shaped furrows along the inner face of the upper beak. In high latitude regions like Alaska, conifers would have been the dominant food source, although the diet of
Edmontosaurus would have been seasonally variable. The tooth structure indicates combined slicing and grinding capabilities. but this material has not been described. The plant remains in the Senckenberg Museum specimen have been described, but have proven difficult to interpret. The plants found in the carcass included needles of the
conifer Cunninghamites elegans, twigs from conifer and broadleaf trees, and numerous small seeds or fruits. Upon their description in 1922, they were the subject of a debate in the German-language journal
Paläontologische Zeitschrift. Kräusel, who described the material, interpreted it as the gut contents of the animal, At the time, hadrosaurids were thought to have been aquatic animals, and Kräusel made a point of stating that the specimen did not rule out hadrosaurids eating water plants. until it was brought up by
John Ostrom in the course of an article reassessing the old interpretation of hadrosaurids as water-bound. Instead of trying to adapt the discovery to the aquatic model, he used it as a line of evidence that hadrosaurids were terrestrial herbivores. Other authors have noted that because the plant fossils were removed from their original context in the specimen and were heavily prepared, it is no longer possible to follow up on the original work, leaving open the possibility that the plants were washed-in debris.
Isotopic studies The diet and
physiology of
Edmontosaurus have been probed by using
stable isotopes of
carbon and
oxygen as recorded in
tooth enamel. When feeding, drinking, and breathing, animals take in carbon and oxygen, which become incorporated into bone. The isotopes of these two elements are determined by various internal and external factors, such as the type of plants being eaten, the physiology of the animal,
salinity, and climate. If isotope ratios in fossils are not altered by fossilization and later
changes, they can be studied for information about the original factors;
warmblooded animals will have certain isotopic compositions compared to their surroundings, animals that eat certain types of plants or use certain digestive processes will have distinct isotopic compositions, and so on. Enamel is typically used because the structure of the mineral that forms enamel makes it the most resistant material to chemical change in the skeleton. Such a motion would parallel the effects of
mastication in mammals, although accomplishing the effects in a completely different way. Work in the early 2000s has challenged the Weishampel model. A study published in 2008 by Casey Holliday and Lawrence Witmer found that ornithopods like
Edmontosaurus lacked the types of skull joints seen in those modern animals that are known to have kinetic skulls (skulls that permit motion between their constituent bones), such as
squamates and birds. They proposed that joints that had been interpreted as permitting movement in dinosaur skulls were actually
cartilaginous growth zones. An important piece of evidence for Weishampel's model is the orientation of scratches on the teeth, showing the direction of jaw action. Other movements could produce similar scratches though, such as movement of the bones of the two halves of the lower jaw. Not all models have been scrutinized under present techniques. Weishampel developed his model with the aid of a computer simulation. Natalia Rybczynski and colleagues have updated this work with a much more sophisticated
three-dimensional animation model, scanning a skull of
E. regalis with lasers. They were able to replicate the proposed motion with their model, although they found that additional secondary movements between other bones were required, with maximum separations of between some bones during the chewing cycle. Rybczynski and colleagues were not convinced that the Weishampel model is viable, but noted that they have several improvements to implement to their animation. Planned improvements include incorporating soft tissue and tooth wear marks and scratches, which should better constrain movements. They note that there are several other hypotheses to test as well.
Growth 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. In a 2022 study, Wosik and Evans proposed that
E. annectens reached maturity in 9 years of age based on their analysis for various specimens from different localities. They found the result to be similar to that of other hadrosaurs. and
E. regalis, have been studied in this way. The brain was not particularly large for an animal the size of
Edmontosaurus. The space holding it was only about a quarter of the length of the skull,
Osteochondrosis, or surficial pits in bone at places where bones articulate, is also known in
Edmontosaurus. This condition, resulting from
cartilage failing to be replaced by bone during growth, was found to be present in 2.2% of 224 edmontosaur toe bones. The underlying cause of the condition is unknown. Genetic predisposition, trauma, feeding intensity, alterations in blood supply, excess
thyroid hormones, and deficiencies in various growth factors have been suggested. Among dinosaurs, osteochondrosis (like tumors) is most commonly found in hadrosaurids.
Locomotion Like other hadrosaurids,
Edmontosaurus is thought to have been a
facultative biped, meaning that it mostly moved on four legs, but could adopt a bipedal stance when needed. It probably went on all fours when standing still or moving slowly, and switched to using the hind legs alone when moving more rapidly. While long thought to have been aquatic or semiaquatic, hadrosaurids were not as well-suited for swimming as other dinosaurs (particularly theropods, who were once thought to have been unable to pursue hadrosaurids into water). Hadrosaurids had slim hands with short fingers, making their forelimbs ineffective for propulsion, and the tail was also not useful for propulsion because of the ossified tendons that increased its rigidity, and the poorly developed attachment points for muscles that would have moved the tail from side to side.
Social behavior Extensive
bone beds are known for
Edmontosaurus, and such groupings of hadrosaurids are used to suggest that they were gregarious, living in groups. Unlike many other hadrosaurids,
Edmontosaurus lacked a bony crest. It may have had soft-tissue display structures in the skull, though: the bones around the nasal openings had deep indentations surrounding the openings, and this pair of recesses are postulated to have held inflatable air sacs, perhaps allowing for both visual and auditory signaling.
Edmontosaurus has been considered a possibly migratory hadrosaurid by some authors. A 2008 review of dinosaur migration studies by Phil R. Bell and Eric Snively proposed that
E. regalis was capable of an annual round-trip journey, provided it had the requisite
metabolism and fat deposition rates. Such a trip would have required speeds of about , and could have brought it from Alaska to Alberta. In contrast to Bell and Snively,
Anusuya Chinsamy and colleagues concluded from a study of bone microstructure that polar
Edmontosaurus overwintered. ==Paleoecology==