I know nothing about Mixodectes as I write this.
But based on the abstract description, I will put it into a phylogenetic perspective.
Sargis et al. 2018 report:
“Mixodectids are eutherian mammals from the Paleocene of North America that have been considered close relatives of the extinct plagiomenids, microsyopid plesiadapiforms,and/or dermopterans, making them relevant to better understanding euarchontan relationships. We analyzed a new dentally associated skeleton of Mixodectes pungent (NMMNH P-54501). It is the most complete skeleton of a mixodectid known, preserving a partial skull with all teeth erupted and previously unknown elements of the axial skeleton, forelimbs, and hind limbs, all with epiphyses fused.”
The authors believe plesiadapiforms are basal to primates,
which is invalid based on the results in the large reptile tree (LRT, 1315 taxa). Plesiadapiforms are more closely related to carpolestids (including Daubentonia, the extant aye-aye) and multituberculates.
The NMMNH P-54501 mixodectid has
- Humeral traits indicating a mobile shoulder and elbow.
- The humerus has a large medial epicondyle and the proximal phalanges have
pronounced flexor sheath ridges, both indicating powerful flexion of the digits.
- Pelvis traits as in arboreal euarchontans.
- The femur suggests a habitually flexed knee.
- The astragalus and calcaneum indicates mobility in the ankle joints and is often present in arboreal taxa capable of pedal inversion.
- The authors do not discuss the teeth…which are important: are they rodent-like (with large incisors as in Glires)?… or carnivore like (with canine fangs as in other primates)?
Sargis et al. conclude: “In summary, the postcranial morphology of Mixodectes is very similar to that of arboreal euarchontans, including plesiadapiforms, supporting inferences based on less complete material that mixodectids were both arboreal and members of Euarchonta.”
Euarchonta (Waddell et al. 1999) = Scandentia (tree shrews), Dermoptera (colugos), Plesiadapiformes (Plesiadapis) and Primates (lemurs to humans). Together these taxa are not monophyletic in the LRT (subset Fig. 1).
Sargis EJ et al. (4 co-authors) 2018. Functional morphology of a remarkably complete skeleton of Mixodectes pnugens: evidence for arboreality in an enigmatic eutherian from the Early Paleocene. SVP abstracts.