[en] The fossil record of cetaceans documents how terrestrial animals acquired extreme adaptations and transitioned to a fully aquatic lifestyle1,2. In whales, this is associated with a substantial increase in maximum body size. Although an elongate body was acquired early in cetacean evolution3, the maximum body mass of baleen whales reflects a recent diversification that culminated in the blue whale4. More generally, hitherto known gigantism among aquatic tetrapods evolved within pelagic, active swimmers. Here we describe Perucetus colossus-a basilosaurid whale from the middle Eocene epoch of Peru. It displays, to our knowledge, the highest degree of bone mass increase known to date, an adaptation associated with shallow diving5. The estimated skeletal mass of P. colossus exceeds that of any known mammal or aquatic vertebrate. We show that the bone structure specializations of aquatic mammals are reflected in the scaling of skeletal fraction (skeletal mass versus whole-body mass) across the entire disparity of amniotes. We use the skeletal fraction to estimate the body mass of P. colossus, which proves to be a contender for the title of heaviest animal on record. Cetacean peak body mass had already been reached around 30 million years before previously assumed, in a coastal context in which primary productivity was particularly high.
Disciplines :
Earth sciences & physical geography Zoology
Author, co-author :
Bianucci, Giovanni; Dipartimento di Scienze della Terra, Università di Pisa, Pisa, Italy
Lambert, Olivier; D.O. Terre et Histoire de la Vie, Institut Royal des Sciences Naturelles de Belgique, Brussels, Belgium
Urbina, Mario; Departamento de Paleontología de Vertebrados, Museo de Historia Natural-Universidad Nacional Mayor de San Marcos, Lima, Perú
Merella, Marco; Dipartimento di Scienze della Terra, Università di Pisa, Pisa, Italy
Collareta, Alberto; Dipartimento di Scienze della Terra, Università di Pisa, Pisa, Italy
Bennion, Rebecca ; Université de Liège - ULiège > Geology ; D.O. Terre et Histoire de la Vie, Institut Royal des Sciences Naturelles de Belgique, Brussels, Belgium
Salas-Gismondi, Rodolfo ; Departamento de Paleontología de Vertebrados, Museo de Historia Natural-Universidad Nacional Mayor de San Marcos, Lima, Perú ; Facultad de Ciencias y Filosofía/Centro de Investigación para el Desarrollo Integral y Sostenible, Laboratorios de Investigación y Desarrollo, Universitad Peruana Cayetano Heredia Lima, Lima, Perú
Benites-Palomino, Aldo ; Departamento de Paleontología de Vertebrados, Museo de Historia Natural-Universidad Nacional Mayor de San Marcos, Lima, Perú ; Department of Paleontology, University of Zurich, Zurich, Switzerland
Post, Klaas; Natuurhistorisch Museum Rotterdam, Rotterdam, The Netherlands
de Muizon, Christian; Département Origines et Évolution, CR2P (CNRS, MNHN, Sorbonne Université), Muséum National d'Histoire Naturelle, Paris, France
Bosio, Giulia; Dipartimento di Scienze dell'Ambiente e della Terra, Università degli Studi di Milano-Bicocca, Milano, Italy
Di Celma, Claudio; School of Science and Technology, University of Camerino, Camerino, Italy
Malinverno, Elisa; Dipartimento di Scienze dell'Ambiente e della Terra, Università degli Studi di Milano-Bicocca, Milano, Italy
Pierantoni, Pietro Paolo; School of Science and Technology, University of Camerino, Camerino, Italy
Villa, Igor Maria; Institut für Geologie, Universität Bern, Bern, Switzerland
Amson, Eli ; Staatliches Museum für Naturkunde Stuttgart, Stuttgart, Germany. eli.amson@smns-bw.de
We thank A. Altamirano, A. Martinez Luna, E. Diaz Ramoz, G. Olmedo, J. Chauca-Luyo, M. Laime Molina, M. Burga, M. Martínez-Cáceres, N. Ramirez, P. Giuffra, R. Varas-Malca, and W. Aguirre Diaz for field fossil collection and laboratory assistance; A. Ball, L. Cornish and R. Sabin for access to the Wexford blue whale model and related data, as well as the rest of the staff in the Imaging and Analysis Centre at the NHM London who digitized the model; A. Martinez Luna for his help with the core drilling; A. Risplendente for EPMA analysis on biotite; A. Gioncada for tephra analyses; A. Larramendi for his advice on body density analyses; C. Wimmer-Pfeil and S. Morel for preparing the thin-sections; D. Hagmann, J. Schaeffer, G. Billet, F. Zachos and U. Göhlich for their help with surface models; E. Steurbaut for preliminary biostratigraphic investigation; F. Goussard for capturing the surface model of C. peruvianus’ holotype; G. Bagnoli, C. Chacaltana, T. J. DeVries, K. Gariboldi, W. Landini, G. Molli and G. Sarti for discussions about the geology and palaeontology of the East Pisco Basin; G. Carnevale for fossil fish identifications; N. Fusi for grain-size analysis; N. Valencia for his support both in the field and at the MUSM; Q. Martinez for discussions and help with CT data acquisition; V. Barberini for the assistance in Ar–Ar dating; V. de Buffrénil for preliminary assessment of bone histology at an early stage of the study; V. Fischer for the surface model of a vertebra of Basilosaurus cetoides; V. de Buffrénil and D. Germain for sharing CT data; and W. Aguirre Diaz for the fossil preparation. The stay of R.B. at the MUSM has been funded by a Stan Wood Award from the Palaeontological Association. Grants from the University of Pisa (PRA_2017_0032 to G. Bianucci) and the University of Camerino (FAR 2019, STI000102 to C.D.C.), and the Italian Ministero dell’Istruzione dell’Università e della Ricerca (PRIN Project 2012YJSBMK to G.B.) supported this work. 39 40We thank A. Altamirano, A. Martinez Luna, E. Diaz Ramoz, G. Olmedo, J. Chauca-Luyo, M. Laime Molina, M. Burga, M. Martínez-Cáceres, N. Ramirez, P. Giuffra, R. Varas-Malca, and W. Aguirre Diaz for field fossil collection and laboratory assistance; A. Ball, L. Cornish and R. Sabin for access to the Wexford blue whale model and related data, as well as the rest of the staff in the Imaging and Analysis Centre at the NHM London who digitized the model; A. Martinez Luna for his help with the core drilling; A. Risplendente for EPMA analysis on biotite; A. Gioncada for tephra analyses; A. Larramendi for his advice on body density analyses; C. Wimmer-Pfeil and S. Morel for preparing the thin-sections; D. Hagmann, J. Schaeffer, G. Billet, F. Zachos and U. Göhlich for their help with surface models; E. Steurbaut for preliminary biostratigraphic investigation; F. Goussard for capturing the surface model of C. peruvianus ’ holotype; G. Bagnoli, C. Chacaltana, T. J. DeVries, K. Gariboldi, W. Landini, G. Molli and G. Sarti for discussions about the geology and palaeontology of the East Pisco Basin; G. Carnevale for fossil fish identifications; N. Fusi for grain-size analysis; N. Valencia for his support both in the field and at the MUSM; Q. Martinez for discussions and help with CT data acquisition; V. Barberini for the assistance in39Ar–40Ar dating; V. de Buffrénil for preliminary assessment of bone histology at an early stage of the study; V. Fischer for the surface model of a vertebra of Basilosaurus cetoides; V. de Buffrénil and D. Germain for sharing CT data; and W. Aguirre Diaz for the fossil preparation. The stay of R.B. at the MUSM has been funded by a Stan Wood Award from the Palaeontological Association. Grants from the University of Pisa (PRA_2017_0032 to G. Bianucci) and the University of Camerino (FAR 2019, STI000102 to C.D.C.), and the Italian Ministero dell’Istruzione dell’Università e della Ricerca (PRIN Project 2012YJSBMK to G.B.) supported this work.
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