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Earliest Mysticete from the Late Eocene of Peru Sheds New Light on the Origin of Baleen Whales
Mystacodon selenensis Lambert et al., 2017  *This image is copyright of its original author Reconstruction credits: Alberto Gennari  *This image is copyright of its original author Figure 1 Cranium, Mandible, and Teeth of Mystacodon selenensis gen. et sp. nov. MUSM 1917 Cranium in dorsal (A), left lateral (B), and ventral © views; detail of left posterior lower teeth in lateral view (D); left mandible in lateral (E) and dorsal (F) views; and three detached anterior lower teeth (from left to right: incisor, incisor/canine, and ?p1) in lingual or labial and occlusal views (G). aof, antorbital foramina; apm, antorbital process of maxilla; bn, bony nares; C, upper canine; c, lower canine; cp, coronoid process; ep, embrasure pit; I1–I3, upper incisors; i1–i3, lower incisors; iop, infraorbital plate; ju, jugal; la, lacrimal; M1 and M2, upper molars; m1–m3, lower molars; maf, mandibular fossa; mf, mental foramina; mg, mesorostral groove; mx, maxilla; na, nasal; nc, nuchal crest; P1–P4, upper premolars; p1–p4, lower premolars; pa, parietal; pmx, premaxilla; prpf, preorbital process of frontal; pspf, postorbital process of frontal; sq, squamosal; sym, mandibular symphysis; zpm, zygomatic process of maxilla; zyg, zygomatic process of squamosal. Scale bars for (A)–©, (E), and (F), 200 mm; for (D), 20 mm; and for (G), 10 mm. See also Figures S2 and S4 and Table S2. Highlights
Summary "Although combined molecular and morphological analyses point to a late middle Eocene (38–39 million years ago) origin for the clade Neoceti (Odontoceti, echolocating toothed whales plus Mysticeti, baleen whales, and relatives), the oldest known mysticete fossil dates from the latest Eocene (about 34 million years ago) of Antarctica [1, 2]. Considering that the latter is not the most stemward mysticete in recent phylogenies and that Oligocene toothed mysticetes display a broad morphological disparity most likely corresponding to contrasted ecological niches, the origin of mysticetes from a basilosaurid ancestor and its drivers are currently poorly understood [1, 3, 4, 5, 6, 7, 8]. Based on an articulated cetacean skeleton from the early late Eocene (Priabonian, around 36.4 million years ago) of the Pisco Basin, Peru, we describe a new archaic tooth-bearing mysticete, Mystacodon selenensis gen. et sp. nov. Being the geologically oldest neocete (crown group cetacean) and the earliest mysticete to branch off described so far, the new taxon is interpreted as morphologically intermediate between basilosaurids and later toothed mysticetes, providing thus crucial information about the anatomy of the skull, forelimb, and innominate at these critical initial stages of mysticete evolution. Major changes in the morphology of the oral apparatus (including tooth wear) and flipper compared to basilosaurids suggest that suction and possibly benthic feeding represented key, early ecological traits accompanying the emergence of modern filter-feeding baleen whales’ ancestors." Other articles related: This ancient whale likely sucked prey into its mouth like a giant vacuum cleaner 36m-year-old fossil discovery is missing link in whale evolution, say researchers Baleen whales' ancestors were toothy suction feeders |
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