Don’t know if you knew this, but the ecological niche of woodpeckers, that is, penetrating trees to reach and extract wood-boring invertebrates, has been also occupied by mammals. Living examples of such kind are: The marsupial genus of the-so-called trioks and Striped possum (Dactylopsila) and the lemuroid primate Aye-aye (Daubentonia). These species share several diagnostic traits that are associated with this kind of behaviour, such as: Massive, rodent-like incisors, used to rip off the bark of trees and one elongated, either third or fourth finger used to extract the insects out of the holes.

Interestingly, during the Paleogene (Paleocene to Oligocene) a whole order (and family) of mammals existed that specialized in such woodpecking behaviour, called Apatotheria. The members of Apatemyidae have been found all over the world. One species Heterohyus nanus, with different specimens being found in the Messel Pit even preserve soft tissue. This species (as well as others of its family) shows clear convergence between the formerly mentioned extant mammalian woodpeckers. They were small agile and active creatures spending much of their time foraging for food in the trees but being also able to run on the ground and leap short distances. Here are my attempts at reconstructing these critters:

One of the last known apatemyids, the genus Sinclairella, come from Arikareean North American Stage of the John Day Formation. When we compare its skull to the extant marsupial Dactylopsila (picture on the top), we find out that they look strikingly similar:

References:

• https://www.researchgate.net/profile/Julia-Schultz-7/publication/225698582_Virtopsy_of_the_controlled_decomposition_of_a_dormouse_Eliomys_quercinus_as_a_tool_to_analyse_the_taphonomy_of_Heterohyus_nanus_from_Messel_Eocene_Germany/links/09e41511b5e4cb4e7d000000/Virtopsy-of-the-controlled-decomposition-of-a-dormouse-Eliomys-quercinus-as-a-tool-to-analyse-the-taphonomy-of-Heterohyus-nanus-from-Messel-Eocene-Germany.pdf
• https://www.researchgate.net/publication/263714512_A_new_specimen_of_Heterohyus_nanus_Apatemyidae_Mammalia_from_the_Eocene_of_Messel_Germany_with_unusual_soft-part_preservation
• https://en.wikipedia.org/wiki/Aye-aye
• https://en.wikipedia.org/wiki/Striped_possum