Priconodon: Beast of the Week

 This week we will be checking out the coolest armored dinosaur most people never heard of.  Make way for Priconodon crassus!

Priconodon was an armored dinosaur that lived in what is now Maryland, United States, during the early Cretaceous period, about 115 million years ago.  It's name translates to "Pine Saw Tooth" in reference to its distinctive teeth, which it used to eat plants when alive.  Priconodon shows evidence of being the largest armored dinosaur ever discovered, possibly growing to 45 feet (13.7 meters) long from beak to tail.  

Watercolor of an adult Priconodon with two roughly human-sized Deinonychus in the foreground.  Fossil evidence suggests Priconodon may have been a behemoth of an armored dinosaur.

Despite being barely known even among dinosaur fans, Priconodon has been known on the fossil record for a very long time, being one of the first dinosaurs ever to be formally described from North America back in the late 1800s.  The first fossils from this dinosaur were in the form of teeth, which experts at the time were able to deduct were from some sort of armored dinosaur, and as time went on and more dinosaur bones were discovered elsewhere, more specifically a nodosaur.  Nodosaurs were armored dinosaurs in the ankylosaur group that were often adorned with large spikes but lacked tail clubs. (Europelta and Gargoyleosaurus are two examples of other nodosaurs that have been covered here)  Some of the Priconodon teeth unearthed were incredibly large, dwarfing the teeth of any other armored dinosaur.  Based on the size of the teeth compared to other more completely-known nodosaurs, it was known even back then that Priconodon was huge, likely the largest armored dinosaur known, but it was difficult to envision to what extent based on only teeth.  Another interesting trait of the teeth is that most of them show evidence of being water-worn, implying Priconodon may have preferred to feed on plants in or near the water.  This makes sense considering all of Priconodon's fossils have been found in what would have been a slow-moving riverbed or swamp during the early Cretaceous.

Priconodon tooth.  Image from the Smithsonian Museum of Natural History.

Priconodon tooth compared to the teeth of related nodosaur, Peloroplides.  Peloroplides measured about 20 feet from beak to tail.  Based on the difference in tooth size, Priconodon could likely have grown to be much larger.

Finally in 2023, over a century later, several fossils other than teeth from Priconodon were discovered from the same fossil site as its teeth in what is considered the first true dinosaur bone bed on the eastern part of the United States.  Several limb bones and osteoderms (armor pieces), including a large curved spike were uncovered.  Most impressive, however, was a GIGANTIC tail vertebra.  Combined with the largest teeth, when compared to the same parts of more completely known ankylosaurs, this vertebra implies that Priconodon may have grown to 45 feet long from beak to tail, making it the largest armored dinosaur ever discovered by a huge margin. (At the time of me writing this paper there is no formal paper describing any material from Priconodon other than teeth.  Bones from this dinosaur are still being found and prepped from the site in Maryland where it was found and a formal paper is still at least a few years away.  This is why there are no sources for the 45 foot estimate nor the bones below.  Please understand that estimate is a rough number and is of course subject to change.)

Priconodon tail vertebra (with one of the side processes missing) next to my hand, discovered in 2023.  Stay tuned for a formal paper on this and possibly more bones from this amazing armored giant in the future.

Priconodon would have shared its environment with a number of other dinosaurs known from the same fossil bed in Maryland where it was discovered, like Astrodon, Aquilops, Deinonychus, and Acrocanthosaurus, to name a few.  

References

Carpenter, K., and Kirkland, J.I. (1998). Review of Lower and middle Cretaceous ankylosaurs from North America. In: Lucas, S.G., Kirkland, J.I., and Estep, J.W. (eds.). Lower and Middle Cretaceous Terrestrial Ecosystems. New Mexico Museum of Natural History and Science Bulletin 14:249-270.

Coombs, Jr., W.P. (1978). The families of the ornithischian dinosaur order Ankylosauria. Palaeontology 21(1):143-170.

Marsh, O.C. (1888). Notice of a new genus of Sauropoda and other new dinosaurs from the Potomac Formation. American Journal of Science 135:89-94.