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| Chaeomysticete mandible fragments NMV P218462 (Museums Victoria) from the Aquitanian–Burdigalian of South Australia. in Rule, Duncan, Marx, Pollock, Evans & Fitzgerald, 2023. |
Abstract
Baleen whales (mysticetes) include the largest animals on the Earth. How they achieved such gigantic sizes remains debated, with previous research focusing primarily on when mysticetes became large, rather than where. Here, we describe an edentulous baleen whale fossil (21.12–16.39 mega annum (Ma)) from South Australia. With an estimated body length of 9 m, it is the largest mysticete from the Early Miocene. Analysing body size through time shows that ancient baleen whales from the Southern Hemisphere were larger than their northern counterparts. This pattern seemingly persists for much of the Cenozoic, even though southern specimens contribute only 19% to the global mysticete fossil record. Our findings contrast with previous ideas of a single abrupt shift towards larger size during the Plio-Pleistocene, which we here interpret as a glacially driven Northern Hemisphere phenomenon. Our results highlight the importance of incorporating Southern Hemisphere fossils into macroevolutionary patterns, especially in light of the high productivity of Southern Ocean environments.
Keywords: Mysticeti, Chaeomysticeti, Southern Hemisphere, body size, gigantism
Systematic palaeontology
Cetacea Brisson 1762
Neoceti Fordyce & Muizon 2001
Mysticeti Gray 1864
Chaeomysticeti Mitchell 1989
Chaeomysticeti gen. et sp. indet.
Referred specimen. NMV P218462, symphyseal regions of both mandibles, plus fragments of the left premaxilla and maxilla.
Locality and horizon. NMV P218462 was found by F.A. Cudmore (on 15 February 1921) eroding from limestone cliffs on the east bank of the Murray River, opposite Wongulla, about 5 km south of Devon Downs, South Australia. ...
Conclusion:
Baleen whales first evolved large body size in the Southern Hemisphere, perhaps facilitated by the onset of the ACC and high seasonal productivity in the Southern Ocean. Previous suggestions of an abrupt global Plio-Pleistocene shift towards mysticete gigantism are hampered by a strong collection bias against austral localities that obscures more gradual and regional trends. Medium-large mysticetes may have helped to engineer ocean ecosystems, albeit in a comparatively limited fashion, since the beginning of the Neogene. Further exploration of the Southern Hemisphere is crucial to constructing a truly global picture of the nature, timing and impacts of whale evolution.
James P. Rule, Ruairidh J. Duncan, Felix G. Marx, Tahlia I. Pollock, Alistair R. Evans† and Erich M.G. Fitzgerald. 2023. Giant Baleen Whales emerged from A Cold southern Cradle. Proc. R. Soc. B. 290: 20232177. DOI: 10.1098/rspb.2023.2177
