Juvenile morphology: A clue to the origins of the most mysterious of mysticetes?
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The origin of the pygmy right whale (Caperea marginata) has long been one of the most vexing conundrums of marine mammal evolution. The extremely disparate skeletal structure of Caperea and a patchy fossil record have left morphology and molecules at odds: whereas most morphological analyses ally Caperea with right whales (Balaenidae), most molecular studies instead suggest a close relationship with rorquals (Balaenopteridae) and grey whales (Eschrichtiidae). The morphological evidence supporting a Caperea-balaenid clade consists of several shared features of the skull and mandible, as traditionally observed in adult individuals. Here, we show that at least two of these features, the ascending process of the maxilla and the coronoid process, arise from substantially different precursors early during ontogeny and therefore likely do not represent genuine synapomorphies. Both of these juvenile morphologies have adult counterparts in the fossil record, thus indicating that the ontogenetic variation in the living species may be a genuine reflection of differing ancestral states. This new evidence contradicts previous morphological hypotheses on the origins of Caperea and may help to reconcile morphological and molecular evidence.
KeywordsCetacea Mysticeti Baleen whale Caperea Pygmy right whale Evolution
We thank M. Churchill for providing photographs of LACM 54763, as well as D. J. Bohaska, M. Boller, E. Burns, E. Crespo, E. M. G. Fitzgerald, C. Francou, N. Garcia, E. R. Gomez, P. Holroyd, H. Karasawa, C. de Muizon, C. W. Potter, N.D. Pyenson, M. Reguero, A. Sanders, A. Van Helden, D. Verzi, and R. Ziegler for access to collections. We thank the editor and referees for their constructive comments. This research was supported by the following grants: Geoscience Society of New Zealand (Wellman Research Award), Systematics Association/Linnean Society of London (Systematic Research Fund), Scottish Association for Marine Science (Research Bursary), Paleontological Society (Stephen Jay Gould Award), University of Otago Postgraduate Scholarship and Publication Bursary, and Otago Museum Linnaeus Taxonomy Fellowship to FGM; Cetacean Society International (CSI), American Museum of Natural History (Lerner Gray Fund for Marine Research), Society for Marine Mammalogy (Grant In Aid of Research), and Smithsonian Institution (Remington Kellogg Fund) to MRB; and University of Otago-Geology PBRF funds to REF.
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