Creature Feature 8

Hope you all had a great weekend! This week, we're going to feature one of the most well-known of all the dinosaurs from Hell Creek, the ornithischian hadrosaur Edmontosaurus annectens!

Model of Edmontosaurus annectens.

Edmontosaurus was one of the largest hadrosaurs known, reaching approximately 12 meters in length and weighing in at an estimated 4.0 metric tons. It is also known from a few exceptionally preserved specimens displaying soft tissues such as scale impressions and possibly gut contents (Bell et al., 2013)!

As a hadrosaur, Edmontosaurus is a bulky animal with a long, laterally compressed tail and a head ending in a wide, duck-like beak (hence the term "duck-bill" often associated with hadrosaurs). The forelimbs were not quite as robust as the hindlimbs, but were sufficiently long to be used when standing or moving.

The dentition of Edmontosaurus was quite interesting. Its teeth were only present in the maxillae and dentaries, and were composed of 6 different types of tissue (Erickson et al., 2012). These teeth grew in large columns of at least six teeth, and the number of columns varied by the size of the animal (Lull and Wright, 1942). As with some other herbivorous dinosaurs (ie Triceratops), these teeth were replaced throughout the lifetime of the animal, each new tooth taking around six months to form (Stanton Thomas and Carlson, 2004).

The feeding habits of Edmontosaurus have been a matter of debate for many years. The most recent simulations based on preserved skulls and soft tissue suggest that Edmontosaurus was a grazer instead of a browser, as the microwear on the teeth was dominated by scratches that would be unlikely in a browsing herbivore (due to eating less abrasive foods). Suggested dietary components include Equisetum and other silica-rich plants, as well as soil accidentally ingested while grazing (Williams et al., 2009). Additionally, the structure of Edmontosaurus teeth suggests that they were capable of both slicing and grinding (Erickson et al., 2012).

Currently, evidence points to Edmontosaurus having a diet heavy in gymnosperms (Stanton Thomas and Carlson, 2004), based on enriched carbon isotope values in tooth enamel of multiple specimens. However, it is certainly possible that other factors were also contributing to the observed data, so this is by no means certain.

Emontosaurus walked with a quadrupedal gait, but its anatomy might allow it to run on its rear limbs alone should the need arise (for example, to escape a potential predator). The two fastest simulated gaits thought to be realistic were 15.7 meters per second for a gallop, and 14.0 meters per second for a bipedal run. The study in question found only weak support for bipedal running as the most likely option for a high-speed gait, but the possibility of galloping was not ruled out (Sellers et al., 2009).

There is also significant evidence for gregarious behavior in Edmontosaurus. There are extensive bone beds attributed to the genus, with one such bed estimated to contain the dissociated remains of between 10,000-25,000 Edmontosaurus specimens (Chadwick et al., 2006). While Edmontosaurus lacked the bony crests seen in other hadrosaurs, there is evidence for potential soft tissue structures related to auditory or visual signaling (Hopson, 1975). It has even been proposed that the gracile and robust forms observed in Edmontosaurus represent male and female specimens, but the validity of this claim has not yet been established (Gould et al., 2003).

Well, I hope you enjoyed this week's creature feature! Edmontosaurus was a fascinating creature, and it will be a joy to see it come to life in Dinosaur Battlegrounds!

Acknowledgements:













Bell, P. R.; Fanti, F.; Currie, P. J.; Arbour, V. M. 2013. A Mummified Duck-Billed Dinosaur with a Soft-Tissue Cock's Comb. Current Biology.
Erickson, Gregory M.; Krick, Brandon A.; Hamilton, Matthew; Bourne, Gerald R.; Norell, Mark A.; Lilleodden, Erica, Sawyer, W. Gregory. 2012. Complex dental structure and wear biomechanics in hadrosaurid dinosaurs. Science 338 (6103): 98-101.

Lull, Richard Swann, Wright, Nelda E. 1942. Hadrosaurian Dinosaurs of North America. Geological Society of America Special Paper 40. Geological Society of America. pp. 50-93.
Stanton Thomas, Kathryn J; Carlson, Sandra J. Microscale δ¹⁸O and δ¹³C isotopic analysis of an ontogenetic series of the hadrosaurid dinosaur Edmontosaurus: implications for physiology and ecology. Palaeogeography, Palaeoclimatology, and Palaeoecology 206 (2004): 257-287.
Williams, Vincent S.; Barrett, Paul M.; Purnell, Mark A. 2009. Quantitative analysis of dental microwear in hadrosaurid dinosaurs, and the implications for hypotheses of jaw mechanics and feeding. Proceedings of the National Academy of Sciences 106 (27) 11194-11199.
Sellers, W. I.,; Manning, P. L.; Lyson, T.; Stevens, K; Margetts, L. 2009. Virtual palaeontology: gait reconstruction of extinct vertebrates using high performance computing. Palaeontologia Electronica 12 (3): unpaginated. Retrieved 2016-2-23.
Chadwick, Arthur; Spencer, Lee; Turner, Larry. 2006. Preliminary depositional model for an Upper Cretaceous Edmontosaurus bonebed. Journal of Vertebrate Paleontology 26 (3, suppl.): 49A.
Hopson, James A. 1975. The evolution of cranial display structures in hadrosaurian dinosaurs. Paleobiology 1 (1): 21-43.
Gould, Rebecca; Larson, Robb; Nellermoe, Ron. 2003. An allometric study comparing metatarsal IIs in Emontosaurus from a low-diversity hadrosaur bone bed in Corson Co., SD. Journal of Vertebrate Paleontology 23 (3, suppl.): 56A-57A.