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. 2006 Dec 7;273(1604):2955-63.
doi: 10.1098/rspb.2006.3664.

A bizarre new toothed mysticete (Cetacea) from Australia and the early evolution of baleen whales

Erich M G Fitzgerald  1
Affiliations

A bizarre new toothed mysticete (Cetacea) from Australia and the early evolution of baleen whales

Erich M G Fitzgerald. Proc Biol Sci. .

Abstract

Extant baleen whales (Cetacea, Mysticeti) are all large filter-feeding marine mammals that lack teeth as adults, instead possessing baleen, and feed on small marine animals in bulk. The early evolution of these superlative mammals, and their unique feeding method, has hitherto remained enigmatic. Here, I report a new toothed mysticete from the Late Oligocene of Australia that is more archaic than any previously described. Unlike all other mysticetes, this new whale was small, had enormous eyes and lacked derived adaptations for bulk filter-feeding. Several morphological features suggest that this mysticete was a macrophagous predator, being convergent on some Mesozoic marine reptiles and the extant leopard seal (Hydrurga leptonyx). It thus refutes the notions that all stem mysticetes were filter-feeders, and that the origins and initial radiation of mysticetes was linked to the evolution of filter-feeding. Mysticetes evidently radiated into a variety of disparate forms and feeding ecologies before the evolution of baleen or filter-feeding. The phylogenetic context of the new whale indicates that basal mysticetes were macrophagous predators that did not employ filter-feeding or echolocation, and that the evolution of characters associated with bulk filter-feeding was gradual.

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Figures

Figure 1
Figure 1
Janjucetus hunderi gen. et sp. nov. (NMV P216929) from the Upper Oligocene Jan Juc Marl, Victoria, Australia. Holotype skull and right mandible in: (a) dorsal view; (b) right lateral view; (c) anterior and slightly dorsal view; and (d) ventral view. Holotype left periotic and surrounding basicranium in (e) ventral view. Abbreviations: ap, anterior process of periotic; bo, basioccipital; boc, basioccipital crest; cm, coronoid process of mandible; eam, external acoustic meatus; eo, exoccipital; fer, fenestra rotunda; fpsq, falciform process of squamosal; fr, frontal; gl, glenoid fossa; jn, jugular notch; ju, jugal; la, lacrimal; lt, lateral tuberosity; m, mandible; mf, mallear fossa; mfo, mandibular foramen; mx, maxilla; na, nasal; nuc, nuchal crest; ol, outer lip of tympanic bulla; pa, parietal; pal, palatine; pc, pars cochlearis of periotic; pe, periotic; peo, paroccipital process of exoccipital; pmx, premaxilla; po, postorbital process of frontal; pp, posterior process of tympanoperiotic; pt, pterygoid; sac, sagittal crest; sgf, fossa on squamosal for sigmoid process of tympanic bulla; so, supraoccipital; spsq, spiny process of squamosal; sq, squamosal; st, stapes; sym, mandibular symphysis; t, loose left mandibular tooth; ty, tympanic bulla; vf, vascular foramen; vo, vomer; zmx, zygomatic process of maxilla; zsq, zygomatic process of squamosal. Scale bars: (a–d) 100 mm, (e) 10 mm.
Figure 2
Figure 2
Janjucetus hunderi gen. et sp. nov. (NMV P216929) from the Upper Oligocene Jan Juc Marl, Vic., Australia. Holotype skull in (a) left lateral view. Left upper dentition in (b) buccal view. Left C1–P2 in (c) lingual view. Left P3–M2 in (d) lingual view. Right lower post-canine dentition (p1–m3) in (e) lingual view. Note that the apex of the crown of P4 was lost during preparation. Abbreviations: ju, jugal; pal, palatine; sq, squamosal; I2, upper second incisor; I3, upper third incisor; C1, upper canine; P1, upper first premolar; p1, lower first premolar; P2, upper second premolar; p2, lower second premolar; P3, upper third premolar; p3, lower third premolar; P4, upper fourth premolar; p4, lower fourth premolar; M1, upper first molar; m1, lower first molar; M2, upper second molar; m2, lower second molar; m3, lower third molar. Scale bars: (a) 100 mm, (b–e) 20 mm.
Figure 3
Figure 3
Phylogeny and stratigraphic record of Mysticeti, including Janjucetus, and the evolution of feeding ecology in mysticetes. Phylogenetic relationships of Janjucetus based on strict consensus of three trees derived from parsimony analysis of 266 characters in 26 genera (some taxa pruned from tree). Cetacean skull reconstructions shown in dorsal view. Characters relevant to the evolution of feeding in mysticetes are optimized on to the tree at nodes where they appear. Taxa marked with * represent toothed mysticetes. Numbers, and numbers in parentheses, at nodes represent bootstrap and branch support values, respectively. Solid circles denote named clades. Solid black bars on branches represent stratigraphic range error bars of their respective clade. Ages are in millions of years, with the time-scale being linear only for Late Eocene through Oligocene. Time-scale after Gradstein et al. (2004). Abbreviations: ChM TM, Charleston Museum toothed mysticetes; C, Chaeomysticeti; M, Mysticeti. (See electronic supplementary material for further information.)
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