Palaeanodonts are extinct placental mammals exhibiting myrmecophagous and fossorial adaptations. They have been viewed as the sister group to Pholidota (pangolins), which is the sister-clade to Carnivora within Ferae. Palaeanodonts display morphological features that are similar to those in pangolins and xenarthrans, which are likely related to their specialized ecological niche. Therefore, it has been challenging to decipher whether shared features are synapomorphies or convergences. Here, we describe in detail the brain virtual endocast anatomy of the middle Eocene palaeanodont Metacheiromys marshi and make morphological and quantitative comparisons with two extant African pangolins, Smutsia gigantea and Phataginus tricuspis. We found several differences between the fossil and extant taxa including in the olfactory bulbs, the cerebellum, and the venous and arterial systems. However, we propose an anatomical feature as a possible synapomorphy uniting palaeanodonts and pangolins in Pholidotamorpha: the presence of a well-developed orbital gyrus and a presylvian sulcus. These correlated features are present in some other groups but are likely derived traits acquired independently, for example in xenarthrans. In terms of the behavioural ecology of M. marshi and pangolins, we suggest that reduced olfaction and eye movement control is likely linked to fossoriality or slow arboreality as previously proposed for rodents. The expansion of the orbital gyrus of the neocortex is proposed to be related to the evolution of myrmecophagy and the emergence of a protrusile tongue in early Pholidotamorpha, acquired convergently in giant anteaters. Overall, this work provides a novel perspective on the evolution of palaeanodonts and pangolins and presents new hypotheses related to the impact of ecological adaptations on the brain evolution of mammals.
Bru et al. (Sat,) studied this question.