📸 Hadrosaur paleoart
By the end of the Age of Dinosaurs, life had begun to stagnate, struggling under the climate change wrought by the volcanic Deccan Traps. But among the dinosaur clade’s many evolutionary branches, there were some that continued to strive. The duck-billed Hadrosaurs had a worldwide distribution, extending into desert wastes and freezing arctic environments. Wherever they went, they relied on an efficient grazing style, using their many teeth to process all kinds of plant material. With these attributes, Hadrosaurs staked a claim to the Late Cretaceous, a fascinating bookend to the end of the dinosaurs.
📸 Edmontosaurus annectens skull
Hadrosaurs have an extensive fossil record, with the majority of species under the Hadrosauridae family having complete skulls. It is with these skulls that the dinosaur family can be identified, specifically its duck-bill shape. This elongated rostral bone housed the dinosaur’s dental battery, with each tooth stocked with up to five replacements. With their hundreds of teeth, these herbivores were able to grind through all manner of plant material, including twigs, berries, and even rotten wood. This grazing style of eating was supported by Hadrosaurs’ hooved, often quadruped posture, a result of the dinosaur’s missing manual digit I, another identifying feature. Other species could stand bipedally for a browsing eating style, securing higher food sources that competitors could not reach.
📸 Hadrosaur's evolutionary branches
Studies of bone density have shown that these voracious eaters continued to grow throughout their lives. This was a common characteristic of dinosaurs, but Hadrosaurs grew faster and reached maturity sooner than predatory species, suggesting a possible survival strategy to outgrow their predators. For example, Hypacrosaurus, a striking member of the cranial crest-bearing lambeosaurine Hadrosaurs, typically topped out at 30 ft (9 m) in length. This is just shy of a full-grown Tyrannosaurus rex, but unlike the fearsome theropod, Hypacrosaurus reached maturity in just 10 years whereas the Tyrant Lizard took nearly three times as long to reach that size.
📸 Sources of Edmontosaurus specimens. (source: Chinsamy paper)
The extent of the Hadrosaur fossil record testifies to the many environments the dinosaur lived in, with remains found across the Americas, Europe, and Asia. They were even at home in polar environments. A 2012 study compared Edmontosaurus fossils from Alaska’s Prince Creek Formation against the Horseshoe Canyon Formation in Alberta. In the polar specimens, the Edmonotosaurus fossils showed evidence of cyclical changes in the bone’s blood vessels, suggesting seasonal adaptations to one location, as opposed to migration to warmer climates. Even during a harsh winter, Hadrosaurs were able to thrive.
Hadrosaurs’ discovery stems from two specimens, both identified by paleontologist Joseph Leidy. The first was a number of fossil teeth found by geologist Ferdinand V. Hayden in 1855 at the meeting point of Montana’s Judith and Missouri Rivers, later named by Leidy as Trachodon mirabilis. Three years later, another Hadrosaur fossil was pulled from a marl pit in Haddonfield, New Jersey, this specimen dubbed Hadrosaurus foulkii. Leidy believed that Hadrosaurs were aquatic feeders, their small teeth best suited to consuming watery plants. This view of Hadrosaurs held for decades, but later findings demonstrate just how extensive these herbivores’ distribution was.
📸 Dakota's skin impressions. (image credit: Kabacchi - Wikimedia)
Hadrosaurs are one of the rare dinosaurs to have a fossil record that includes soft tissue. Dakota, an Edmontosaurus found in the Hell Creek Formation, was naturally mummified before fossilization, such that its skin and underlying muscle tissue has been preserved. A 2022 paper theorized that Dakota’s soft remains were fossilized because of scavenging by aquatic crocodyliforms that punctured holes in the Edmontosaurus’ carcass, allowing for decomposition gases and fluids to be released instead of corrupting the dinosaur’s remains. This theory is supported by the identifiable bite marks on the specimen, as well as Dakota’s deflated appearance.
📸 Paleoart by Heinrich Harder, 1916
📸 An Edmontosaurus ischium specimen
Mini Museum has authentic Hadrosaur fossils available from a variety of genera! These specimens are fossilized Edmontosaurus, Hypacrosaurus, and Maiasaura bones, which were recovered on private land in the western United States.
The specimen shown here is from an Edmontosaurus ischium, a hip bone that is used to classify dinosaurs into two main groups: the “lizard-hipped” saurischians and the “bird-hipped” ornithischians. Also available are fossil vertebrae from several genera and a smaller riker display case specimen!
Check out our full Hadrosaur fossil collection, with riker box specimens, plus several Edmonontosaurus, Hypacrosaurus, and Maiasaura showcase specimens! Explore the Hadrosaur collection here!
Brett-Surman MK, Farlow JOrville, Holtz TR. The Complete Dinosaur. 2nd ed. Indiana University Press; 2012.
Chinsamy, Anusuya, et al. “Hadrosaurs Were Perennial Polar Residents.” Anatomical Record (Hoboken, N.J. : 2007), vol. 295, no. 4, 2012, pp. 610–14, https://doi.org/10.1002/ar.22428.
Drumheller SK, Boyd CA, Barnes BMS, Householder ML. Biostratinomic alterations of an Edmontosaurus “mummy” reveal a pathway for soft tissue preservation without invoking “exceptional conditions.” PloS one. 2022;17(10):e0275240-e0275240. doi:10.1371/journal.pone.0275240
Eberth DA, Evans DC. Hadrosaurs. 1st ed. Indiana University Press; 2014.