Creature Feature 20

Well, now that we've covered all of the dinosaur species from Hell Creek, it's time to start getting in to the other types of vertebrates! This week, we're going to look at the stagodont metatherian genus, Didelphodon!

Didelphodon template model, WIP. Texture variants will be used to represent the different species.

Didelphodon was a genus of metatherian mammals - this group includes the marsupials. There are two confirmed species that have been found in Hell Creek - D. vorax (the type species) as well as D. padanicus. There are other remains that may represent new species, but these are either too fragmentary to identify or have not been fully described yet (Kielan-Jaworowska et al., 2004). Didelphodon was a rather large mammal by Mesozoic standards, around the size of a small domestic cat (Fox and Naylor, 2006). Its dentition is indicative of a predatory lifestyle, with distinct bladelike cusps and carnassial notches. In addition, the short, massive jaws bear huge premolar teeth which appear to be well-suited for crushing (Kielan-Jaworowska et al., 2004).

While most mammals are only known from isolated teeth and occasional jaw fragments (such as Alphadon), Didelphodon skeletal material has been found. Its skull is similar to that of the modern Tasmanian devil (Sarcophilus harrisii), while the postcranial anatomy resembles that of a modern otter. It is suggested that it was semiaquatic (Fox and Naylor, 2006; Kielan-Jaworowska et al., 2004), possibly making its home by burrowing into the riverbanks. The diet for Didelphodon may have consisted of crawfish, mollusks, small lizards, plants, and even dinosaur eggs. Given that the skeletal material was found in sediment attributed to a riverbed, it is thought that the reason for the unusual preservation of the fossil (roughly 30% complete) was that it died in its burrow. In addition, a fossil water stain surrounded the specimen, suggesting that its remains were quickly buried by fluctuations in the water table (Rocky Mountain Dinosaur Research Center, 2010). Unfortunately, the paper that will formally describe the new specimen has not been published as of yet, but at some point in the future I hope to get in contact with the authors to see if they can help make sure our model is as accurate as possible.

The mollusk-heavy diet of Didelphodon certainly makes sense, as there was a great diversity of freshwater mollusks - in fact, at my count there are at least 7 genera known from Hell Creek. While as far as I know there are no remains of crawfish, it is not unreasonable to suspect they would have been present. In addition, it may have been preyed upon by Borealosuchus and Brachychampsa, though this relationship could be complicated by the possibility that Didelphodon may have opportunistically preyed upon very young hatchlings as many small opportunistic predators do today (raccoons, for example). Keep in mind that these are just hypotheses that I am proposing based on my own personal knowledge, and should not be taken as fact.

Well, I hope this post has taught you a little bit more about Didelphodon! We're gonna start showing more love to a lot of the lesser-known vertebrates from Hell Creek, so stay tuned!

Acknowledgements:

Kielan-Jaworowska, Z.; Cifelli, R. L.; Cifelli, R.; Luo, Z. X. 2004. Mammals from the Age of Dinosaurs: Origins, Evolution, and Structure. New York: Columbia University Press. pp. 441-462.

Fox, R. C.; Naylor, B. G. 2006. Stagodontid marsupials from the Late Cretaceous of Canada and their systematic and functional implications. Acta Palaeontologica Polonica 51 (6): 13-36.

Didelphodon vorax. Rocky Mountain Dinosaur Resource Center. 2010-12-07. Retrieved 2016-5-17.