Palaechthon nacimienti (Wilson and Szalay 1972) ~4cm skull length, middle Palaeocene, was originally and subsequently considered a basal plesiadapiform.
Here derived from a sister to the pen-tailed tree shrew, Ptilocercus, Palaechthon phylogenetically precedes Cynocephalus, the colugo.
Distinct from Ptilocercus, the skull of Palaechthon was similar in size but had a smaller orbit, directed laterally and a smaller cranium. The interorbit area was wider A large infraorbital foramen (hole in front of the eye) was present. The posterior maxilla was not so deep. Upper premolar 4 was flat to match the molars. Lower premolar 3 was larger. The mandible was deeper.