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FIG. 50 in Mystacodon selenensis, the earliest known toothed mysticete (Cetacea, Mammalia) from the late Eocene of Peru: anatomy, phylogeny, and feeding adaptations

FIG. 50. — Lateral view of the right pelvic bones of some extant mysticetes. A, Balaenoptera musculus; B, Balaenoptera musculus; C, Megaptera novaeangliae; D, E, Balaena mysticetus. The iliac, pubic and ischial portions are, respectively, in blue, yellow and green. Modified from Struthers (1893).

FIG. 49 in Mystacodon selenensis, the earliest known toothed mysticete (Cetacea, Mammalia) from the late Eocene of Peru: anatomy, phylogeny, and feeding adaptations

FIG. 49. — Lateral view of innominate of some extinct cetaceans. A, Georgiacetus vogtlensis (GSM 350); B, Basilosaurus isis (CGM 42176, cast); C, Basilosaurus cetoides (USNM 12261); D, Chrysocetus healyorum (SCSM 87-195, cast, right innominate, reversed); E, Mystacodon selenensis (MUSM 1917). Not to scale.

FIG. 48 in Mystacodon selenensis, the earliest known toothed mysticete (Cetacea, Mammalia) from the late Eocene of Peru: anatomy, phylogeny, and feeding adaptations

FIG. 48. — Mystacodon selenensis (MUSM 1917, holotype). Left innominate: A, lateral view; B, dorsal view; C, medial view; D, ventral view. Scale bar: 5 cm.

FIG. 39 in Mystacodon selenensis, the earliest known toothed mysticete (Cetacea, Mammalia) from the late Eocene of Peru: anatomy, phylogeny, and feeding adaptations

FIG. 39. — Ribs transverse sections of Mystacodon, basilosaurids, and chaeomysticetes. A, Mystacodon selenensis (MUSM 1917, holotype): section of an anterior-median (right?) rib of the thoracic cage in the median region of the diaphysis; B, Dorudon atrox (UM 101222): section of a left R4 at mid-diaphysis (reversed); C, Basilosaurus isis (WH 074): section of a left R4 at mid-diaphysis. B and C are reproduced from Houssaye et al. (2015). D, Piscobalaena nana (MNHN.F. SAS1618). E, Balaenoptera acutorostrata (IRSNB uncatalogued). Abbreviations: ant, anterior; med, medial. Scale bar: 1 cm.

FIG. 42 in Mystacodon selenensis, the earliest known toothed mysticete (Cetacea, Mammalia) from the late Eocene of Peru: anatomy, phylogeny, and feeding adaptations

FIG. 42. — Mystacodon selenensis (MUSM 1917, holotype). Right humerus: A, lateral view; B, medial view; C, anterior view; D, posterior view. Scale bar: 5 cm.

FIG. 6 in Mystacodon selenensis, the earliest known toothed mysticete (Cetacea, Mammalia) from the late Eocene of Peru: anatomy, phylogeny, and feeding adaptations

FIG. 6. — Lateral view of the skull of Mystacodon selenensis (MUSM 1917, holotype). Oblique lines and grey-shaded regions indicate respectively broken and reconstructed parts. Scale bar: 20 cm.

FIG. 1 in Mystacodon selenensis, the earliest known toothed mysticete (Cetacea, Mammalia) from the late Eocene of Peru: anatomy, phylogeny, and feeding adaptations

FIG. 1. — Views of the extraction of the postcranial skeleton of Mystacodon selenensis (MUSM 1917 holotype) at Playa Media Luna (Ica Department, Peru).

FIG. 27 in Mystacodon selenensis, the earliest known toothed mysticete (Cetacea, Mammalia) from the late Eocene of Peru: anatomy, phylogeny, and feeding adaptations

FIG. 27. — Mystacodon selenensis (MUSM 1917, holotype). A-C, right i2 or i3 (tooth I); D-F, left i3 or c (tooth II); G-I, right?p1 (tooth III); A, labial view; B, lingual view; C, occlusal view; D, labial view; E, lingual view; F, occlusal view; G, labial view, H, lingual view; I, occlusal view. Scale bar: 3 cm.

FIGURE 22 in A new group of late Oligocene mysticetes from México

FIGURE 22. Philogenetic position of Tlaxcallicetus. 1) Under equal weights, consensus tree recovered from 260 parsimonious trees (1327 steps, consistency index CI= 0.246, retention index RI= 0.686, rescaled consistency index RCI= 0.168756, tree total length 1474). 2) Under implied weights: k= 6, consensus tree from 3 parsimonious trees (85.63773 steps, CI= 0.271, RI= 0.724, RCI= 0.196204, tree total length 1338. Black squares mark unequivocal characters that support the different groups (see legend). Support branch belongs only to those clades with 50% or more consistency. Dashed lines suggest a probable inclusion of taxa in clade.

FIGURE 21 in A new group of late Oligocene mysticetes from México

FIGURE 21. Left thyrohyoid, Tlaxcallicetus sp. (MU EcSj5/18/95), dorsal (1), anterior (2), and posterior (3) views.

FIGURE 20 in A new group of late Oligocene mysticetes from México

FIGURE 20. Left bulla, Tlaxcallicetus sp. (MU EcSj5/18/95), ventral (1), dorsal (2), lateral (3), medial (4), posterior (5), and anterior (6) views.

FIGURE 19 in A new group of late Oligocene mysticetes from México

FIGURE 19. Left bulla with anatomical terms, Tlaxcallicetus sp. (MU EcSj5/18/95), ventral (1), dorsal (2), lateral (3), medial (4), posterior (5), and anterior (6) views.

FIGURE 18 in A new group of late Oligocene mysticetes from México

FIGURE 18. Left periotic, Tlaxcallicetus sp. (MU EcSj5/18/95), closer view of internal acoustic meatus, dorsal view.

FIGURE 17 in A new group of late Oligocene mysticetes from México

FIGURE 17. Left periotic, Tlaxcallicetus sp. (MU EcSj5/18/95), medial (1), lateral (2), ventral (3), dorsal (4), posterior (5), and anterior (6) views.

FIGURE 16 in A new group of late Oligocene mysticetes from México

FIGURE 16. Left periotic with anatomical terms, Tlaxcallicetus sp. (MU EcSj5/18/95), medial (1), lateral (2), ventral (3), dorsal (4), posterior (5), and anterior (6) views.

FIGURE 2 in A new group of late Oligocene mysticetes from México

FIGURE 2. General stratigraphy and observations at mesa El Tesoro; 1) view of the strata over the mined phosphatic Humboldt bed; 2-3) position of the gray phosphatic sandstone over the Humboldt bed; 4) fossils Tlaxcallicetus cf. guaycurae in situ in the gray phosphatic sandstone and 5) ventral view, left ear region of Tlaxcallicetus sp., field observation at mesa El Tesoro.

FIGURE 10 in A new group of late Oligocene mysticetes from México

FIGURE 10. Ear region and left periotic comparison between Tlaxcallicetus species, ventral view. Tlaxcallicetus sp. (MU EcSj5/18/95) (1-2), Tlaxcallicetus guaycurae (MU EcSj5/06/31) (3-4), and specimen found at mesa El Tesoro, Tlaxcallicetus sp., field observation (5-6).

FIGURE 8 in A new group of late Oligocene mysticetes from México

FIGURE 8. Tlaxcallicetus guaycurae (MU EcSj5/06/31), ear region (1) with the left periotic bone (2-4), ventral view. Pars cochlearis (3), posteromedial view.

FIGURE 1. Map locality, 1 in A new group of late Oligocene mysticetes from México

FIGURE 1. Map locality, 1) state of Baja California Sur, Mexico; 2) Oligocene outcrops of San Juan Member, El Cien Formation; 3) El Saladito and mesa El Tosoro fossilferous localities, north to San Juan de la Costa village.

FIGURE 9 in A new group of late Oligocene mysticetes from México

FIGURE 9. Detailed features of Tlaxcallicetus guaycurae (MU EcSj5/06/31), (1) pitted edge in the glenoid fossa that suggest a fibrocartilaginous joint; (2) inflated and rounded squamosal prominence; (3) external occipital sulcus on the posterior middle part of the supraoccipital.