Edmontosaurus: Prehistoric Animal of the Week

Today we are checking out one of the largest and most well studied of the duck-billed dinosaurs.  Enter Edmontosaurus!  

Edmontosaurus annectens in watercolors by Christopher DiPiazza.

Edmontosaurus was a hadrosaur ("duck-billed") dinosaur that could grow to at least 39 feet (12 meters) long from beak to tail that lived during the late Cretaceous period in what is now western North America.  There are currently two recognized species within the genus, Edmontosaurus regalis and Edmontosaurus annectens.  E. regalis lived between 73 and 70 million years ago in what is now Alaska, Colorado, and Alberta, and had a more robust snout. Edmontosaurus annectens lived between 68 and 66 million years ago in what is now Montana, South Dakota, and Wyoming, and had a longer, lower snout.  The genus name translates to "Edmonton Reptile/Lizard" in reference to Edmonton, Alberta, where the first specimen was found.  Edmontosaurus also includes the dinosaurs that used to be called Anatosaurus and Anatotitan, which were initially thought to be distinct taxa.  (Part of me wishes Anatotitan, which translates to "Duck Titan" was still valid because the name "duck titan" brings me joy.)

Skeletons on display at the American Museum of Natural History in New York City.

Before we go further, describing this dinosaur, I think it's important to mention that one thing that makes Edmontosaurus particularly special, is the fact that we know an incredible amount about it compared to other dinosaurs.  This is because in addition to skeletons, we have not one, but SEVERAL mummified specimens that have been unearthed over the years.  Thanks to this we know more about Edmontosaurus' life appearance than almost any other prehistoric dinosaur.  So as you read the rest of this post if you notice I am able to describe Edmontosaurus in much more detail than normal, this is why.

Image from Sereno's recent paper (referenced below) showcasing the fleshy sail and lizard-like spines down the midline of a recently described Edmontosaurus mummy.

Out of all the hadrosaurs, which are characterized by having wide, flat bills in the front of their mouths, Edmontosaurus annectens had arguably the "duckiest" bill, which was particularly wide and almost squared off to a degree.  Initially hadrosaurs were believed to have been semi-aquatic, behaving like the ducks, swimming in fresh water and eating water plants.  Since then, we have found out that he bill of a hadrosaur, including Edmontosaurus, wasn't really similar to a duck's at all.  Thanks to a mummified specimen of Edmontosaurus which preserved the keratin that was growing over the skull in life, we know that the flat duck-like beak was only the shape of the skull and the whole beak would have been bigger and more downturned in life.  This appears to be more of an adaptation for clipping tough plant material, including pine needles and twigs which would the be processed in the back of the jaws by literally hundreds of small teeth that were arranged tightly together in units called dental batteries. These dental batteries were the dinosaur's way to grind food like some mammals do today with molars.  Like all reptiles, if a tooth became too worn down, it would fall out and be replaced with a fresh tooth.  Because of this hadrosaur teeth are among some of the most common fossils in locations where they lived. 

Edmontosaurus specimen on display at the American Museum of Natural History in New York.  This individual preserved soft tissue, including some of the beak's keratin.

Dental battery on the lower jaw of Edmontosaurus.

There is a mummified specimen of Edmontosaurus regalis (although it has been recently been suggested this may be a third species) which preserved the skin around the neck, which appears to have had a wide, wrinkled texture.  This same specimen also shows the animal had a fleshy crest, like a chicken's wattle, on its head.  We don't know if all members of the species had this feature or if it was just in one sex, nor do we know if it was present in Edmontosaurus annectens.  That being said there are also mummies of Edmontosaurus annectens which show us a lot about its scaly skin, including a fleshy sail-like crest that ran from the back of its neck down to the base of its tail, at which point it had a single row of triangular spines running down the midline of the tail, similar spines in some modern lizards, takes over.  Another Edmontosaurus annectens mummy, which preserved the skin on the tail, shows the mosaic-like scales are arranged in banding patterns, which may imply the dinosaur had colored stripes on its tail in life.  

Photograph and graphic showing the skin texture and fleshy crest of Edmontosaurus regalis.

Like all hadrosaurs, Edmontosaurus would had robust hind legs with three toes on each foot and slender, yet strong front limbs.  It likely would have been able to walk on all fours or on its hind legs depending on what its needs were.  Each hand had five fingers, but the middle three were fused together and ended in one large hoof-like claw.  The first finger also had a claw and jutted out to the side while the fifth also jutted out on the other end but had no claw.  When the animal was on all fours the middle three digits that formed the hoof would support most of the weight. The same mummy that showed the back crest mentioned earlier also preserved the feet, showing Edmontosaurus' nails were also extremely hoof-like and its toes were heavily padded.  

Photograph of the mummified hand of Edmontosaurus annectens.  Note the large hoof that encompasses the middle three fingers.  You an also see the fine scaly skin and folds on the wrists.  From paper by Drumheller et al. referenced below.

Edmontosaurus possessed an extremely muscular tail that was also reinforced with boney tendons running along its spine, causing the tail to be stiff and easier to hold off the ground in life.  The huge tail would have acted as a counterbalance to the dinosaur's torso as it walked or ran on its hind legs.  The tail could also have been an extremely effective weapon against potential predators or even members of its own species.  This is important to note, since I feel far too often hadrosaurs are depicted as fodder for meat-eating dinosaurs simply because they didn't have obvious weapons like horns, clubs, or spikes.  In reality they likely were probably more than capable of defending themselves and a healthy adult Edmontosaurus would have been a challenging target for even the hungriest tyrannosaur. 

Nanuqsaurus eyes a family of Edmontosaurus regalis.  The adult Edmontosaurus would have been too large and dangerous for the tyrannosaur to attempt to hunt.

That's all for this week.  As always feel free to comment below!

References

Campione, N.E.; Evans, D.C. (2011). "Cranial Growth and Variation in Edmontosaurs (Dinosauria: Hadrosauridae): Implications for Latest Cretaceous Megaherbivore Diversity in North America". PLOS ONE. 6 (9) e25186.

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. 24 (1): 70–75.

Brett-Surman, Michael K. (1979). "Phylogeny and paleobiogeography of hadrosaurian dinosaurs". Nature 277 (5697): 560–562

Campione, Nicolás E.; and Evans, David C. (2011). "Cranial growth and variation in Edmontosaurs (Dinosauria: Hadrosauridae): implications for latest Cretaceous megaherbivore diversity in North America". PLoS ONE 6 (9): e25186. 

Drumheller SK, Boyd CA, Barnes BMS, Householder ML (2022) Biostratinomic alterations of an Edmontosaurus “mummy” reveal a pathway for soft tissue preservation without invoking “exceptional conditions”. PLoS ONE 17(10): e0275240.

Lambe, Lawrence M. (1917). "A new genus and species of crestless hadrosaur from the Edmonton Formation of Alberta" (pdf (entire volume, 18 mb)). The Ottawa Naturalist 31 (7): 65–73. Retrieved 2009-03-08.

Lambe, Lawrence M. (1920). "The hadrosaur Edmontosaurus from the Upper Cretaceous of Alberta". Department of Mines, Geological Survey Memoirs 120: 1–79. 

Manning, Phillip L.; Morris, Peter M.; McMahon, Adam; Jones, Emrys; Gize, Andy; Macquaker, Joe H. S.; Wolff, G.; Thompson, Anu; Marshall, Jim; Taylor, Kevin G.; Lyson, Tyler; Gaskell, Simon; Reamtong, Onrapak; Sellers, William I.; van Dongen, Bart E.; Buckley, Mike; Wogelius, Roy A. (2009). "Mineralized soft-tissue structure and chemistry in a mummified hadrosaur from the Hell Creek Formation, North Dakota (USA)". Proceedings of the Royal Society B. 276 (1672): 3429–3437.

Morris, William J. (1970). "Hadrosaurian dinosaur bills — morphology and function". Contributions in Science (Los Angeles County Museum of Natural History). 193: 1–14.

Ostrom, John H. (1964). "A reconsideration of the paleoecology of the hadrosaurian dinosaurs". American Journal of Science 262 (8): 975–997

Sereno, Paul. (2025) Duck-billed dinosaur fleshy midline and hooves reveal terrestrial clay-template "mummification". Science 0

Sharpe, H. S., Bell, P. R., Baylatry, I., Sissons, R., & Sullivan, C. (2025). Re-evaluation of a soft crested Edmontosaurin, with implications for hadrosaurid life appearance and diversity. The Anatomical Record, 1–20. 

Nanotyrannus: Beast of the Week

 This week we will be learning about a dinosaur who's identity has been the subject of a lot of debate or decades.  Check out Nanotyrannus!

Nanotyrannus was a meat-eating dinosaur that lived in what is now Montana in the United States during the latest Cretaceous period, between 67 and 66 million years ago.  From snout to tail it measured between 17 and 20 feet (6.2 meters) long as an adult. The genus name translates to "Small/Dwarf Tyrant" because it was originally believed to be a close relative of Tyrannosaurus rex, but much smaller.  

Watercolor life reconstruction of Nanotyrannus lancensus attacking a baby Tyrannosaurus rex by Christopher DiPiazza.

The first known Nanotyrannus bones were fond in the 1940s and it was initially thought to be a kind of Gorgosaurus. Then in the 1980s it was re-examined and thought by many paleontologists to be worthy of its own genus and was renamed Nanotyrannus.  Then in the 1990s it was suggested by some to be a juvenile Tyrannosaurus and the discovery of a new skeleton, nicknamed "Jane", further strengthened that stance, since that skeleton was indeed of a juvene when it died.  It also exhibited the typical traits paleontologists already knew for sure juvenile tyrannosauroids had, thanks to confirmed juvenile specimens of other taxa, like Albertosaurus.  These traits include proportionally longer arms and legs, which experts suggested allowed younger individuals to fill a different ecological niche, specializing in running down smaller faster prey, before bulking into mature adults.  For decades there was a division among experts on this possibility.  Then finally much more recently in 2025, a formal paper on an extremely complete skeleton, nicknamed "Bloody Mary", deemed Nanotyrannus a valid taxon again.  "Bloody Mary" was not a juvenile, in fact when a cross section of one of their bones was examined, it was estimated they were in their twenties when they died, which is similar to the age of some of the largest adult Tyrannosaurus rex specimens when they died.  Based on this, plus a few other key differences in its skull and limb anatomy, it appeared that Nanotyrannus was indeed it's own kind of dinosaur, and not simply a young T. rex. (although Tyrannosaurus itself still likely looked similar to Nanotyrannus it when it was a juvenile)

Nanotyrannus lethaeus on display at the Burpee Museum in Illinois, USA.  This specimen was thought to be a juvenile Tyrannosaurus rex by many experts.

This latest paper also was able to identify that Nanotyrannus included two species.  Nanotyrannus lethaeus, which includes the skeleton, named "Jane", and was the slightly larger of the two.  Nanotyrannus lancensus was smaller, but had proportionally longer arms, which includes the newer "Bloody Mary" individual.  Another interesting point that the newest paper suggested, was that Nanotyrannus was much less closely related to the group that contains Tyrannosaurus and Gorgosaurus, called the tyrannosaurids, than previously believed.  Even those who thought it was a distinct taxon in the past thought it to be within the tyrannosaurid family.  Thanks to the "Boody Mary" skeleton, which preserved a lot of anatomy not known prior, the new paper suggests Nanotyrannus was outside tyrannosaurids, but still a tyrannosauroid, more similar to dinosaurs like Dryptosaurus, which also had proportionally longer arms, large hand claws, and lived during the late Cretaceous.

Nanotyrannus lancensus skull. (photo: James St. John)

As stated, Nanotyrannus had proportionally long and slender legs, implying it was a fast runner when alive, likely specializing in hunting smaller faster prey, while its much larger cousin, T. rex could take larger, more heavily armored prey.  That being said, juvenile Tyrannosaurus were still almost certainly similar in build to Nanotyrannus, so they would have likely competed with each other on that level at the very least.  

Close up of the skin preserved on Nanotyrannus lancensus' leg.

Nanotyrannus had a narrow, slender snout, filled with proportionally long, bladelike teeth, ideal for slashing meat, not for crushing like adult T. rex had.  Nanotyrannus also possessed little bony crests in front of its eyes, which may have had keratin growing over them in life, forming small display structures, which is a feature common in many tyrannosaurs.  As stated earlier it's arms were proportionally long for a tyrannosaur, and were tipped with two fingers on each hand, each with a hook-shaped claw.  One specimen preserves what appears to be scaly skin on it's leg like a bird, which anyone would have assumed it had there, but is still really exciting to have proof of.  Considering it was a tyrannosauroid which are known in the fossil record to have had feathers and were closely related to birds, it probably also had feathers of some kind on other parts of its body. 

That is all for this week!  Comment below!

References

Bakker, R.T.; Williams, M.; Currie, P.J. (1988). "Nanotyrannus, a new genus of pygmy tyrannosaur, from the latest Cretaceous of Montana". Hunteria. 1: 1–30.

Carr, T.D. (1999). "Craniofacial ontogeny in Tyrannosauridae (Dinosauria, Coelurosauria)". Journal of Vertebrate Paleontology. 19 (3): 497–520.

Eberth, David A.; Currie, Philip J. (2010). "Stratigraphy, sedimentology, and taphonomy of the Albertosaurus bonebed (upper Horseshoe Canyon Formation; Maastrichtian), southern Alberta, Canada". Canadian Journal of Earth Sciences. 47 (9): 1119–1143.

Gilmore, C.W. (1946). "A new carnivorous dinosaur from the Lance Formation of Montana". Smithsonian Miscellaneous Collections. 106: 1–19.

Henderson (2005). "Nano No More: The death of the pygmy tyrant." In "The origin, systematics, and paleobiology of Tyrannosauridae", a symposium hosted jointly by Burpee Museum of Natural History and Northern Illinois University.

Larson, P. (2013). The validity of Nanotyrannus lancensis (Theropoda, Lancian - Upper Maastrichtian of North America (PDF). Society of Vertebrate Paleontology 73rd Annual Meeting. p. 159.

Zanno, Lindsay E.; Napoli, James G. (2025-10-30). "Nanotyrannus and Tyrannosaurus coexisted at the close of the Cretaceous". Nature. doi:10.1038/s41586-025-09801-6.