Muizon, et al. 2019
describe the feeding behavior of Mystacodon selenensis (late Eocene, Fig. 1). They nest Mystacodon as ‘earliest known toothed mysticete’.
If this taxon sounds familiar, it is.
We looked at Mystacodon in February 2018 and nested it in the large reptile tree (LRT, 1505 taxa) as a big pakicetid, between Maiacetus and Llanocetus. These nest at the base of the clade that ultimately produces the toothed whales (odontocetes)… not the baleen whales (mysticetes).
Mystacodon selenensis (Lambert et al. 2017) was promoted as the earliest mysticete, but it nests with Maiacetus, only larger and with a smaller pelvis.
Lambert et al. (seven co-authors) 2017. Earliest Mysticete from the Late Eocene of Peru Sheds New Light on the Origin of Baleen Whales. Current Biology. in press. doi:10.1016/j.cub.2017.04.026.
Muizon C, Bianucci G, Martínez-Cáceres and Lambert O 2019. Mystacodon selenensis, the earliest known toothed mysticete (Cetacea, Mammalia) from the late Eocene of Peru: anatomy, phylogeny, and feeding adaptations. Geodiversitas 41 (11): 401-499. https://doi.org/10.5252/geodiversitas2019v41a11. http://geodiversitas.com/41/11