Creature Feature 13

Greetings, fans! I apologize again for not having a Sci-Day last week, but I had preparations to make for my presentation and didn't have enough time. For this week's Creature Feature, we will be looking at the metatherian genus Alphadon!

Model of Alphadon marshi.

Those who may be more well-informed in scientific nomenclature may have noticed that, unlike the previous Sci-Day posts, I did not include a species name. That is because there were actually at least two species from this genus in the Hell Creek formation - A. marshi (the type species), A. wilsoni, two specimens tentatively assigned to those two specimens but may represent distinct forms (poor preservation of the specimens makes identification impossible), and a third, undescribed species. Since it would not be possible to get enough information on the distinct species to justify two separate Creature Features, I will be talking about the genus collectively. As we get into some of the less well-known lineages of creatures from Hell Creek (particularly those with very little information on them), I will be doing similar Creature Features that look at a group of animals rather than just a single species.

Alphadon was a metatherian - the group which contains living marsupials. While remains of this genus from Hell Creek are not very complete, we know that it was a rather small creature (as were most mammals of its time), estimated around 30 centimeters in length. Its dentition suggests an omnivorous diet, which would consist of fruits, insects (and other invertebrates), and possibly small vertebrates. 

 

The main differences between the two species from Hell Creek relates to the morphology of the molars. These differences are mainly based on differences in morphology of the upper molars, as the distinctions between lower molars and premolars are not as distinct (Johanson, 1992). In A. wilsoni, there is a stylar cusp at or slightly anterior to the deepest part of the ectoflexus, and the paracone and metacone are conical on the labial side, whereas in A. marshi they are flattened/concave (Johanson, 1992). Overall, the anatomy of the occlusal surface of the molars is the best way to distinguish between the two species (Johanson, 1992).

Unfortunately, like I said, there is not much information around on Alphadon, probably due to the fragmentary nature of the remains (consisting mostly of isolated teeth and occasional jaw fragments). However, I have done my best given the information available. Also, a sidenote - there was a third species originally referred to the genus Alphadon, but the species has since been reassigned to the genus Nortedelphys (Williamson et al., 2012). Depending on how much I can find about this other species, it may also get its own Creature Feature.

I hope you may have learned a bit more about the small but rather interesting Alphadon!

Acknowledgements:

Johanson, Zerina. 1992. A systematic revision of the North American late Cretaceous marsupial genus Alphadon Simpson, 1927. University of Alberta (Canada), ProQuest Dissertations Publishing. MM73236.

Williamson, T. E.; Brusatte, S. L.; Carr, T. D.; Weil, A.; Standhardt, B. R. 2012. The phylogeny and evolution of Cretaceous–Palaeogene metatherians: cladistic analysis and description of new early Palaeocene specimens from the Nacimiento Formation, New Mexico. Journal Of Systematic Palaeontology, 10(4), 625-651.