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A heavyweight early whale pushes the boundaries of vertebrate morphology

Nature volume 620, pages 824–829 (2023)Cite this article

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Abstract

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.

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Fig. 1: Partial skeleton of the P. colossus MUSM 3248 holotype.
Fig. 2: Pachyostosis in the P. colossus MUSM 3248 holotype.
Fig. 3: Bone histology of the P. colossus MUSM 3248 holotype.
Fig. 4: Scaling of the skeletal mass across amniotes’ body mass range.

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Data availability

All data generated or analysed during this study are included in the Article and the Supplementary Information as well as the following public repositories. Three-dimensional surface models of the holotype of P. colossus as well as Cynthiacetus peruvianus MNHN.F.PRU10 are available at MorphoMuseuM80; newly acquired CT data are available at MorphoSource (https://doi.org/10.17602/M2/M510260). The existing database AnAge69 was also used. All nomenclatural acts from this work were recorded at ZooBank: Perucetus (urn:lsid:zoobank.org:act:E5F92709-2F65-4C50-8F46-7C005F64CE03); P. colossus (urn:lsid:zoobank.org:act:CD837E76-E7B8-4E06-8F87-54AFE7AFB211).

Code availability

The code run for this study is provided at GitHub (https://github.com/eliamson/ColossalCode).

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Acknowledgements

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 39Ar–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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Authors and Affiliations

  1. Dipartimento di Scienze della Terra, Università di Pisa, Pisa, Italy

    Giovanni Bianucci, Marco Merella & Alberto Collareta

  2. D.O. Terre et Histoire de la Vie, Institut Royal des Sciences Naturelles de Belgique, Brussels, Belgium

    Olivier Lambert & Rebecca Bennion

  3. Departamento de Paleontología de Vertebrados, Museo de Historia Natural-Universidad Nacional Mayor de San Marcos, Lima, Perú

    Mario Urbina, Rodolfo Salas-Gismondi & Aldo Benites-Palomino

  4. Evolution & Diversity Dynamics Lab, UR Geology, Université de Liège, Liège, Belgium

    Rebecca Bennion

  5. 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

    Rodolfo Salas-Gismondi

  6. Department of Paleontology, University of Zurich, Zurich, Switzerland

    Aldo Benites-Palomino

  7. Natuurhistorisch Museum Rotterdam, Rotterdam, The Netherlands

    Klaas Post

  8. Département Origines et Évolution, CR2P (CNRS, MNHN, Sorbonne Université), Muséum National d’Histoire Naturelle, Paris, France

    Christian de Muizon

  9. Dipartimento di Scienze dell’Ambiente e della Terra, Università degli Studi di Milano-Bicocca, Milano, Italy

    Giulia Bosio & Elisa Malinverno

  10. School of Science and Technology, University of Camerino, Camerino, Italy

    Claudio Di Celma & Pietro Paolo Pierantoni

  11. Institut für Geologie, Universität Bern, Bern, Switzerland

    Igor Maria Villa

  12. Staatliches Museum für Naturkunde Stuttgart, Stuttgart, Germany

    Eli Amson

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  1. Giovanni Bianucci
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  2. Olivier Lambert
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  4. Marco Merella
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  10. Christian de Muizon
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  15. Igor Maria Villa
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  16. Eli Amson
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M.U. discovered and collected the fossil. E.A., G. Bianucci and O.L. conceived and designed the project. G. Bosio, A.C., C.D.C., E.M., I.M.V. and P.P.P. collected and analysed the stratigraphical data and wrote the corresponding Methods sections. A.B.-P., A.C., E.A., G. Bianucci, M.M., O.L., R.B. and R.S.-G. collected phenotypic data (including CT and/or surface scans and/or palaeohistological samples). E.A., G. Bianucci and O.L. analysed the phenotypic data. E.A., G. Bianucci and O.L. wrote the first draft of the manuscript. All of the authors discussed the analyses and reviewed the manuscript.

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Correspondence to Eli Amson.

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Extended data figures and tables

Extended Data Fig. 1 Three vertebrae of Perucetus colossus (MUSM 3248 holotype).

a,g,m. Anterior view. b,h,n. Posterior view. c,i,o. Dorsal view. d,j,p. Ventral view. e,k,q. Right lateral view. f,l,r. Left lateral view. Tentative position along the vertebral column: a–f = Th-a, penultimate thoracic; g–l = Th-b, last thoracic; m–r = L-a, first lumbar. All images were generated from three-dimensional surface models. Scale bar = 50 cm.

Extended Data Fig. 2 Three vertebrae of Perucetus colossus (MUSM 3248, holotype).

a,g,m. Anterior view. b,h,n., Posterior view. c,i,o. Dorsal view. d,j,p. Ventral view. e,k,q. Right lateral view. f,l,r. Left lateral view. Tentative position along the vertebral column: a–f = L-b, second lumbar; g–l = L-c, third lumbar; m–r = L-d, fourth lumbar. All images were generated from three-dimensional surface models. Scale bar = 50 cm.

Extended Data Fig. 3 Three incomplete vertebrae of Perucetus colossus (MUSM 3248, holotype).

a,g,m. Anterior view. b,h,n. Posterior view. c,i,o. Dorsal view. d,j,p. Ventral view. e,k,q. Right lateral view. f,l,r. Left lateral view. Tentative position along the vertebral column: a–f = L-e, fifth lumbar; g–l = L-f, sixth lumbar; m–r = L-g, seventh lumbar. All images were generated from three-dimensional surface models. Scale bar = 50 cm.

Extended Data Fig. 4 Two vertebrae (a–l) and three posterior ribs (m; R-b,c,d) of Perucetus colossus (MUSM 3248, holotype).

a,g. Anterior view. b,h. Posterior view. c,i. Dorsal view. d,j. Ventral view. e,k. Right lateral view. f,l Left lateral view. Tentative position along the vertebral column: a–f = L-j, eleventh lumbar; g–l = L-k, twelfth lumbar. a–l. Images generated from three-dimensional surface models. m. Photograph taken in the field. Scale bars = 50 cm.

Extended Data Fig. 5 Location and stratigraphic position of Perucetus colossus MUSM 3248.

a. Map showing the position of the Coastal Batholith and major trench-parallel structural highs along the coast of Peru (redrawn and modified after Travis et al.82. and Thornburg & Kulm83). b. Stratigraphic column of the Cenozoic succession exposed in the East Pisco Basin (redrawn and modified after Malinverno et al.84, Bianucci & Collareta85, and Bosio et al.86). c. Measured stratigraphic section of the type locality of P. colossus, indicating the stratigraphic height of the holotype MUSM 3248, the dated tephra layer, and the identified bioevents.

Extended Data Fig. 6 Vertebral and costal morphology of Perucetus colossus (MUSM 3248, holotype) compared to that of other cetaceans.

a, mean and maximum ratio of vertebral centrum anteroposterior length (CL) to mediolateral width (CW), computed with the thoracic and lumbar vertebrae of other cetaceans (Ba = Basilosaurinae; Dor = Dorudontinae; FM = fossil Mysticeti; FO = fossil Odontoceti; P = Pakicetidae+Ambulocetidae; Pa = Pachycetinae; Pr = Protocetidae; R = Remingtonocetidae). b, profile of vertebral centrum length in P. colossus (Pc) compared with the profiles of other basilosaurids (Aa = Antaecetus aithai; Bc = Basilosaurus cetoides; Bi = Basilosaurus isis; Cf = Chrysocetus fouadassii Cp = Cynthiacetus peruvianus; Da = Dorudon atrox; data of A. aithai and B. isis from Gingerich et al.15, fig. 11). c, curvature (length/chord) of the best preserved rib, R-a (red horizontal line) compared to those of Cynthiacetus peruvianus (MNHN.F.PRU10).

Extended Data Fig. 7 Vertebral microanatomy illustrated with binarized sections (black = bone) obtained with physical core drills (a) or µCT data (b–f).

a, Perucetus colossus (MUSM 3248, holotype, vertebra L-e for the centrum and transverse process and L-c for the neural spine). The global compactness (Cg) was measured in ten areas (orange outlines) to assess overall centrum compactness (see Supplementary Methods). b, common minke whale (Balaenoptera acutorostrata, LR M 523). c, Amazon river dolphin (Inia geoffrensis, ZMB_Mam_41500). d, common dolphin (Delphinus sp. ZMB_Mam_697.59). e, dugong (Dugong dugon, ZMB_Mam_69340). f, manatee (Trichechus manatus, ZMB_Mam_17377). (1) Centrum (anteroposterior mid-length, from its dorsal edge to its centre), external towards top; (2) Neural spine (dorsoventral mid-height), external towards right); (3) Transverse process (mediolateral mid-width), external towards top. Width of the virtual cross-sections were defined as representing 7.2% of the centrum dorsoventral height; this is the mean ratio between the centrum height of P. colossus and the width of the physical core drills. The core drills of the neural spine and transverse process do not reach the middle of the corresponding vertebral parts (but break surfaces indicate uniform structure throughout). See core drills’ location in Supplementary Fig. S6c,d. Scale bars: a = 13.9 mm, b = 23.6 mm, c = 2.2 mm, d = 2.7 mm, e = 3.2 mm, f = 3.0 mm.

Extended Data Fig. 8 Estimating the whole skeletal volume of Perucetus colossus based on Cynthiacetus peruvianus’ holotype (MNHN.F.PRU10).

a. Unmodified 3D model of Cynthiacetus peruvianus’ holotype. b,c. vertebral column scaled-up (top) and dilated (bottom). c,d. Rib cage scaled-up (top) and dilated (bottom) identifying the scanned rib of P. colossus as R17 (c) or R20 (d). Scale bars = 2 m.

Extended Data Fig. 9 Estimates of the osteological range of motion.

Extension and flexion of the preserved portion of vertebral column of Perucetus colossus holotype (MUSM 3248) is compared with an equivalent vertebral column portion of Cynthiacetus peruvianus holotype (MNHN.F.PRU10) using the respective 3D models. Intervertebral spaces were reconstructed based on the common dolphin (Delphinus delphis)81 (see Methods). Scale bar = 50 cm.

Extended Data Fig. 10 Reconstruction of Perucetus colossus in its coastal habitat.

Because portions of the skeleton are unknown, several aspects of the reconstruction are tentative: the overall proportions of the axial postcranium are based on a close relative Cynthiacetus peruvianus, which was scaled-up and dilated according to the elements recovered for P. colossus (see Extended Data Fig. 8); the skull and limbs were only scaled-up; the tail fluke and forelimb use (bottom-walking) are based on the manatee (Trichechus), the extant marine mammal with the closest degree of pachyosteosclerosis in the postcranial skeleton; the hind limb of P. colossus was not recovered, but the anatomy of its innominate indicates the presence of a reduced, articulated leg. The associated sawfish (Pristis) was recovered from the same unit in the East Pisco Basin, the Yumaque Member of the Paracas Formation87. Reconstruction by A. Gennari.

Supplementary information

Supplementary Information

Supplementary Methods (including Supplementary Figs. 1–9), Supplementary Discussion (including Supplementary Figs. 10–12), Supplementary References and Supplementary Tables 1–22.

Reporting Summary

Peer Review File

Supplementary Data 1

Rib curvature. Data table containing rib curvature values for Cynthiacetus peruvianus (MNHN.F.PRU10) and Perucetus colossus (MUSM 3248, holotype).

Supplementary Data 2

Skeletal and body mass data. Data tables containing measured skeletal and whole body masses for extant, terrestrial mammals and measured and estimated skeletal and whole body masses for aquatic mammals and other terrestrial taxa. All values in kg. See Supplementary Methods for the estimation procedures.

Supplementary Data 3

Vertebral proportions. Data tables containing extinct cetaceans’ vertebral proportions as well as the literature references from which they stem.

Supplementary Data 4

Vertebral parts’ volume. Data table containing the volume of individual vertebral parts for Cynthiacetus peruvianus (MNHN.F.PRU10) and Perucetus colossus (MUSM 3248, holotype).

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Bianucci, G., Lambert, O., Urbina, M. et al. A heavyweight early whale pushes the boundaries of vertebrate morphology. Nature 620, 824–829 (2023). https://doi.org/10.1038/s41586-023-06381-1

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