Fig 1.
Generalized phylogeny showing the transition in mysticetes from toothed ancestors to the edentulous, baleen bearing extant taxa.
Phylogeny of Cetacea with an emphasis on mysticete evolution. Blue represents the ancestral condition of adults bearing teeth. Extant mysticetes (green) are edentulous as adults, bear baleen on the palate, and dorsal foramina on the mandible. Eomysticetidae is traditionally interpreted as edentulous, though some taxa preserve possible alveoli potentially indicative of a dentition [9–11].
Fig 2.
Alveolar groove on the mandible of Mysticeti.
(A) Medial view of the left mandible of USNM VZ 571487, Balaenoptera acutorostrata. (B) Enhanced view of the selected region on panel (A), specifically highlighting the alveolar groove and associated sulci.
Fig 3.
Internal canal system of the mammalian mandible.
3D model of a human mandible with line art illustration highlighting the generalized mammalian condition for innervation and vascularization of the mandible. The mandibular canal gives off dorsomedial branches to each root of each tooth, as well as mental branches that exit the mandible through mental foramina by which the lips and gums are vascularized and innervated.
Table 1.
List of specimens scanned, location of scan, and number of CT slices.
Fig 4.
3D model of the left mandible of Sus scrofa (USNM VZ 260907). 3D model figured in medial (A), dorsal (B), and lateral (C) views. White represents the external bony surface, pink the alveoli and teeth, green the mental branches, and blue the mandibular canal.
Fig 5.
Mandible of Odocoileus virginianus.
3D model of the right mandible of Odocoileus virginianus (USNM VZ 118627). 3D model figured in lateral (A), dorsal (B), and medial (C) views. White represents the external bony surface, pink the alveoli and teeth, green the mental branches, and blue the mandibular canal.
Fig 6.
3D model of the right mandible of Zygorhiza kochii (USNM PAL 11962). 3D model figured in lateral (A), dorsal (B), and medial (C) views. White represents the external bony surface, pink the alveoli, green the mental branches, and blue the mandibular canal.
Fig 7.
Mandible of Tursiops truncatus.
3D model of the right mandible of Tursiops truncatus (SDSNH 21212). 3D model figured in lateral (A), dorsal (B), and medial (C) views. White represents the external bony surface, pink the alveoli, green the mental branches, and blue the mandibular canal.
Fig 8.
Mandible of Balaenoptera acutorostrata.
3D model of the right mandible of Balaenoptera acutorostrata (USNM VZ 571847). 3D model figured in lateral (A), dorsal (B), and medial (C) views. (D) represents a magnification of the posterior end of the mandible in lateral view, highlight dorsal branches from the mandibular canal as distinct from mental branches. White represents the external bony surface, pink the dorsal branches, green the mental branches, and blue the mandibular canal.
Fig 9.
Mandible of Megaptera novaeangliae.
3D model of the left mandible of Megaptera novaeangliae (DFO 2408). 3D model figured in medial (A), dorsal (B), and lateral (C) views. (D) represents a magnification of the posterior end of the mandible in medial view, highlight dorsal branches from the mandibular canal as distinct from mental branches. White represents the external bony surface, pink the dorsal branches, green the mental branches, and blue the mandibular canal.
Fig 10.
Mandible of Caperea marginata.
3D model of the left mandible of Caperea marginata (DFO 2408). 3D model figured in medial (A), dorsal (B), and lateral (C) views. White represents the external bony surface, pink the dorsal branches, green the mental branches, and blue the mandibular canal.
Fig 11.
Internal morphology of mysticete mandibles are unique compared to those of toothed mammals.
Cross sections of the left mandible of Sus scrofa (A, B), the right mandible of Tursiops truncatus (C, D), and the right mandible of Balaenoptera acutorostrata (E, F). Label colors follow the scheme of previous figures: pink represents alveoli and/or teeth, green the mental branches, and blue the mandibular canal. Here, the dorsal branches observed in Balaenoptera acutorostrata are labeled in black to reflect the uncertainty of their homology to alveolar branches of the toothed taxa observed.