The oldest bats

Rietbergen TB et al 2023 described
two more of the 30 bats found in the Green River Formation (early Eocene) of Wyoming. They wrote, “The relative stratigraphic position of these fossils indicates that they are the oldest bat skeletons recovered to date anywhere in the world. Taken in sum, our results indicate that Green River bats represent a separate chiropteran radiation of basal bats, and provide additional support for the hypothesis of a rapid radiation of bats on multiple continents during the early Eocene.”

Excellent description.
Unfortunately the authors’ outgroups, Sorex (shrew) and Erinaceus (hedgehog), were cherry-picked, are not arboreal and share no bat traits. Also missing is Tadarida, the Mexican free-tailed bat (finger claws lost convergently), which is more primitive than Icaronycteris and Onychonycteris in the LRT.

Just add taxa to solve this problem. Bat sisters are primates and Microcebus is a bat ancestor in the LRT, which minimizes taxon exclusion by adding taxa.

Several months ago,
I suggested (via email) to co-author and bat expert, Nancy Simmons, to add Microcebus (Figs 1, 2). That didn’t work this time. Not sure why bat workers, like pterosaur workers, are reticent to add pertinent taxa to their outgroup lists. There was no reply from Dr Simmons.

Bats likely appeared much earlier than the early Eocene.
The early appearance of bats and primates in the placental clade of the large reptile tree (LRT, 2227 taxa) indicates a MUCH earlier evolution of bats, likely in the Jurassic when arboreal placentals, like multituberculates, had free reign to evolve prior to the origin of birds and convergent predatory arboreal theropods, like Microraptor.

References
Rietbergen TB, van den Hoek Ostende LW, Aase A, Jones MF, Medeiros ED, Simmons NB 2023. The oldest known bat skeletons and their implications for Eocene chiropteran diversification. PLoS ONE 18(4): e0283505. https://doi.org/10.1371/journal.pone.0283505

wiki/Microcebus
wiki/Tadarida