Originally thought to be a wolverine-like animal, (Plesiogulo relative) then viewed as an amphicynodontine ursoid and the third time, we might got it entirely correct… Drassonax harpagops was one of the first definitive ursids (true bear).
Drassonax is a genus with just incomplete remains preserved, like upper maxillary teeth and lower jaws. The only known basal ursoids (ursoids include the Ursidae as well as forms already showing ursid traits but still not belonging to the family) with preserved whole skeletals (therefore giving us much more clues about their anatomy and biology) are Amphicynodon and Eoarctos. Based on dental characteristics, Drassonax appears to be a close relative of the former.
Here is a rough hypothetical sketch of how could the skull of Drassonax look like. The proportions are based off of close relatives such as Amphicynodon and Campylocynodon.
The first true caniforms very likely evolved in North America, as it’s indicated by the oldest and most primitive forms of both arctoids (bear and musteloid ancestors) and cynoids (canids) appearing there as early as in the middle Eocene, and in the case of the first ursoids, the genus Subparictis in the Late Eocene during the Chadronian land mammal age, approximately 38-33 million years ago.
They all started out as largely very active mesocarnivores of rather compact dimensions with adaptations for arboreal or scansorial lifestyle. Drassonax likely possesed great climbing and grasping abilities, also being able to rapidly accelerate. As with its close relative Amphicynodon, it is possible that also Drassonax could reverse its feet, perhaps even up to 180°. This would enable it to descend and ascend trees headfirst.
Perhaps one of the best still-living examples of these small carnivorans that we can compare to our extinct species, in terms of ecology is the enigmatic african palm civet (Nandinia binotata). As well as with others, they resemble the ancestral body plan of the earliest arctoids that all others subsequently evolved from.
Literature:
- Wang, X., R. J. Emry, C. A. Boyd, J. J. Person, S. C. White, and R. H. Tedford. 2023. An exquisitely preserved skeleton of Eoarctos vorax (nov. gen. et sp.) from Fitterer Ranch, North Dakota (early Oligocene) and systematics and phylogeny of North American early arctoids (Carnivora, Caniformia). Society of Vertebrate Paleontology Memoir 22. Journal of Vertebrate Paleontology 42(2, Supplement). DOI: 10.1080/02724634.2022.2145900
- Galbreath, E. C. 1953. A contribution to the Tertiary geology and paleon- tology of northeastern Colorado. University of Kansas Paleontological Contributions 4:1–120.
- Baskin, J. A., and R. H. Tedford. 1996. 24. Small arctoid and feliform carnivorans; pp. 486–497 in D. R. Prothero and R. J. Emry (eds.), The terrestrial Eocene-Oligocene transition in North America, Part II: Common vertebrates of the White River Chronofauna. Cambridge University Press, Cambridge.
- Bonis, L. D., A. Gardin, and C. Blondel. 2019. Carnivora from the early Oligocene of the ‘Phosphorites du Quercy’ in southwestern France. Geodiversitas 41:601–621.
- Climbing Adaptations of an Enigmatic Early Arctoid Carnivoran: the Functional Anatomy of the Forelimb of Amphicynodon leptorhynchus From the Lower Oligocene of the Quercy Phosphorites (France)