Data from: Echericetus novellus n. gen. n. sp. (Cetacea: Mysticeti: Eomysticetidae), an Oligocene baleen whale from Baja California Sur, Mexico

Among the several evolutionary lineages of the baleen whales (Mysticeti),
the eomysticetids are an ancient successful family that retain possibly
non-functional teeth and functional baleen, a transitional stage between
toothed and baleen-assisted filter-feeding mysticetes. However, the patchy
fossil record leaves gaps in eomysticetids palaeobiology interpretations
but their diversity and widespread geographical distribution can be a
relevant proxy to understanding the evolution of crown Mysticeti. Here, we
describe a new baleen whale, Echericetus novellus n. gen. n. sp., from the
Oligocene of Mexico (slightly older than 27.95 million years ago). This
new taxon has morphological features that show its affinity to
Eomysticetidae, such as the intertemporal region longer than wide,
elongate and oval temporal fossa, and a well-developed and lobate coronoid
process of the mandible. Similarly, our cladistic analyses confirm the
inclusion of Echericetus in the Eomysticetidae. Echericetus reinforces our
notion of the eomysticetid diversity and disparity. Geographically, the
existence of Echericetus from Mexico also indicates that eomysticetids
inhabited subtropical regions in the Northern Hemisphere. Lastly, our
discovery of a new eomysticetid from the Oligocene of Mexico provides new
insights into the distribution patterns and habitat use of Eomysticetidae,
essential to further explain the demise of this transitional lineage
between toothed and baleen-bearing whales.