Anacodon

Credit: Roman Yevseyev.

*Anacodon* is an extinct genus of arctocyonid "condylarth" mammal that lived in Canada, Wyoming and Montana from the Paleocene to the Eocene.

## Description

The only indicators of arctocyonid locomotion is pes from *Arctocyon*, which suggest semi-fossorial behaviours. However, USGS 25034 represents a distal right tibia, left astragalus, left and partial right calcaneus, right cuboid, left navicular, cuneiforms, metatarsals, unguals and phalanges attributable to *Anacodon*. These were found in the Bighorn Basin, where the postcrania were compared with *Arctocyon* and *Galecyon*. The trochlear ridge of the tibia is low, broad, similar to *Arctocyon mumak* and less prominent than *Arctocyon ferox*. These suggests more musculature ran between the tibia and astragalus. *Anacodon* has a medial malleolus greater (in the medial) than *Arctocyon mumak*. Since *Anacodon* has borders raised more, the sustentacular facet is shaped differently than *Galecyon*. The facet is most similar with *Arctocyon primaevus*, indicating an increased mobility in the joint. Additionally, the astragalar head does not continue with the sustentacular facet, which is similar with the latter, creating a ridge that supports the attachment of muscles and ligaments.

The calcaneal sulcus is wider than in *Arctocyon mumak* because the ectal facet differs in shape. The calcaneal cuneiform facet and plantar tubercle are more prominent than in *Galecyon*. Raised edges at the calcaneal tubercle are not present, suggesting muscles moved along its surface. The unguals strongly curve, with the proximal portion of such creating a broad flexor tubercle. This shape is associated with fossorial animals, as a strong ventral curve exists without a proximodorsal prominence. Anacodon represent extremely flexible joints, with morphology similar to terrestrial and semi-fossorial animals. The latter is represented based on strongly-developed proceses that bear muscle attachment, short and robust bones, strongly curved unguals, and an astragalar head that is narrow and extends medially to result in greater supination. The former is represented by a shallow astragalar trochlea, which leads to instability and low flexion-extension. Currently, the true style of Anacodon locomotion is still unknown, and more research will have to be done.

## Classification

Using discrete unconstrained trees, the following is recovered:

## References

1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 https://paleobiodb.org/classic/basicTaxonInfo?taxon\_no=42199
2. ↑ 2.0 2.1 Gould F., Rose K. 2014. Gnathic and postcranial skeleton of the largest known arctocyonid ‘condylarth’ Arctocyon mumak (Mammalia, Procreodi) and ecomorphological diversity in Procreodi. Journal of Vertebrate Paleontology 34(5):1180-1202.
3. ↑ Argot C. 2013. Postcranial analysis of a carnivoran-like archaic ungulate: the case of Arctocyon primaevus (Arctocyonidae, Mammalia) from the late Paleocene of France. Journal of Mammal Evolution 20:83-114.
4. ↑ Zack S., Rose K. 2015. The postcranial skeleton of Galecyon: Evidence for morphological and locomotor diversity in early Hyaenodontidae (Mammalia, Hyaenodontidae). Journal of Vertebrate Paleontology 35(6): 26-39
5. ↑ http://www.highpoint.edu/highpurcs/files/2018/04/Heather-Estes-Anacodon-Foot-and-Ankle-HighPURCS-Poster.pdf
6. ↑ https://onlinelibrary.wiley.com/doi/10.1111/brv.12242