Enamel Microstructure in Eocene Cetaceans from Antarctica (Archaeoceti and Mysticeti)

  • Carolina LochEmail author
  • Monica R. Buono
  • Daniela C. Kalthoff
  • Thomas Mörs
  • Marta S. Fernández
Original Paper


Modern baleen whales have no adult teeth, whereas dolphins and porpoises have a homodont and polydont dentition, with simplified enamel microstructure. However, archaic cetaceans (archaeocetes and early mysticetes and odontocetes) had a complex and ornamented dentition, with complex enamel microstructure as in terrestrial mammals. This study describes the morphology of teeth and enamel microstructure in two fossil cetaceans from Antarctica: a basilosaurid archaeocete from the La Meseta Formation (middle Eocene); and Llanocetus sp. from the Submeseta Formation (late Eocene), one of the oldest mysticetes known. The two teeth analyzed were lower premolars, with transversely compressed triangular crowns composed of a main cusp and accessory denticles. The enamel microstructure of the basilosaurid and Llanocetus sp. is prismatic with Hunter-Schreger bands (HSB) and an outer zone of radial enamel. In the basilosaurid, the enamel is relatively thin and measures 150–180 μm, whereas in Llanocetus sp. it is considerably thicker, measuring 830–890 μm in the cusp area and 350–380 μm near the crown base. This is one of the thickest enamel layers among cetaceans, extinct and living. Structures resembling enamel tufts and lamellae were observed in both fossils at the enamel-dentine junction (EDJ) and extending along the thickness of the enamel layer, respectively. The presence of HSB and biomechanical reinforcing structures such as tufts and lamellae suggests prominent occlusal loads during feeding, consistent with raptorial feeding habits. Despite the simplification or absence of teeth in modern cetaceans, their ancestors had complex posterior teeth typical of most mammals, with a moderately thick enamel layer with prominent HSB.


Archaeocetes Hunter-Schreger bands La Meseta formation Mysticetes Teeth 



Enamel-dentine junction


Hunter-Schreger bands


Interprismatic matrix


Outer enamel surface


Prismless enamel


Radial enamel


Scanning electron microscopy



The authors would like to thank the Instituto Antártico Argentino (IAA-DNA) and Fuerza Aérea Argentina as well as the Swedish Polar Research Secretariat (SPFS) for logistical support during field work in Antarctica. J. Hagström (NRM), J. Moly (MLP), J. O’Gorman (MLP), M. Reguero (MLP), and C. Tambussi (CICTERRA) are thanked for their assistance in the field. M. Reguero (MLP) provided access to dental samples. We also acknowledge the facilities as well as scientific and technical assistance from staff at the Otago Centre for Electron Microscopy (OCEM) at the University of Otago, in particular Liz Girvan. CL acknowledges the University of Otago Faculty of Dentistry for a Sir Thomas Kay Sidey Research Grant. TM acknowledges financial support from the Swedish Research Council (VR Grant 2009-4447).

Compliance with Ethical Standards

No permits were required for the described study, which complied with all relevant regulations.

Conflict of Interest

The authors declare that they have no conflict of interest.


  1. Bajpai S, Gingerich PD (1998) A new Eocene archaeocete (Mammalia, Cetacea) from India and the time of origin of whales. Proc Natl Acad Sci USA 95:15464–15468CrossRefGoogle Scholar
  2. Bergqvist LP (2003) The role of teeth in mammal history. Braz J Oral Sci 2:249–257Google Scholar
  3. Borsuk-Białynicka M (1988) New remains of Archaeoceti from the Paleogene of Antarctica. Pol Polar Res 9: 437–445Google Scholar
  4. Buono MR, Fernández MS, Reguero MA, Marenssi SA, Santillana SN, Mörs T (2016) Eocene basilosaurid whales from the La Meseta Formation, Marambio (Seymour) Island, Antarctica. Ameghiniana 53:296–315CrossRefGoogle Scholar
  5. Deméré TA, Berta A (2008) Skull anatomy of the Oligocene toothed mysticete Aetioceus weltoni (Mammalia; Cetacea): implications for mysticete evolution and functional anatomy. Zool J Linn Soc 154:308–352CrossRefGoogle Scholar
  6. Deméré TA, McGowen MR, Berta A, Gatesy J (2008) Morphological and molecular evidence for a stepwise evolutionary transition from teeth to baleen in mysticete whales. Syst Biol 57:15–37CrossRefGoogle Scholar
  7. Fahlke JM (2012) Bite marks revisited - evidence for middle-to-late Eocene Basilosaurus isis predation on Dorudon atrox (both Cetacea, Basilosauridae). Palaeontol Electron 15: 1–16Google Scholar
  8. Fahlke JM, Bastl KA, Semprebon GM, Gingerich PD (2013) Paleoecology of archaeocete whales throughout the Eocene: dietary adaptations revealed by microwear analysis. Palaeogeogr Palaeoclimatol Palaeoecol 386:690–701CrossRefGoogle Scholar
  9. Fitzgerald EMG (2010) The morphology and systematics of Mammalodon colliveri (Cetacea: Mysticeti), a toothed mysticete from the Oligocene of Australia. Zool J Linn Soc Lond 158:367–476CrossRefGoogle Scholar
  10. Ford JKB, Ellis GM, Matkin CO, Wetklo MH, Barrett-Lennard LG, Withler RE (2011) Shark predation and tooth wear in a population of northeastern Pacific killer whales. Aquat Biol 11: 213–224CrossRefGoogle Scholar
  11. Fordyce RE (1985) Late Eocene archaeocete whale (Archaeoceti: Dorudontinae) from Waihao, South Canterbury, New Zealand. New Zeal J Geol Geop 28:351–357CrossRefGoogle Scholar
  12. Fordyce RE (1989) Origins and evolution of Antarctic marine mammals. Geol Soc Lond Spec Publ 47:269–281CrossRefGoogle Scholar
  13. Fordyce RE (2009) Cetacean evolution. In: Perrin WF, Würsig B, Thewissen JGM (eds) Encyclopedia of Marine Mammals, 2nd edn. Academic Press, San Diego, pp 201–207CrossRefGoogle Scholar
  14. Fordyce RE, Marx FG (2018) Gigantism precedes filter feeding in baleen whale evolution. Curr Biol 28:1670–1676CrossRefGoogle Scholar
  15. Fordyce RE, Muizon C de (2001) Evolutionary history of cetaceans: a review. In: Mazin J-M, de Buffrénil V (eds) Secondary Adaptation of Tetrapods to Life in Water. Verlag Dr. Friedrich Pfeil, München, pp 169–233Google Scholar
  16. Fostowicz-Frelik Ł (2003) An enigmatic whale tooth from the upper Eocene of Seymour Island, Antarctica. Pol Polar Res 24:13–28Google Scholar
  17. Geisler JH, Boessenecker RW, Brown M, Beatty BL (2017) The origin of filter feeding in whales. Curr Biol 27:2036–2042CrossRefGoogle Scholar
  18. Hocking DP, Marx FG, Fitzgerald EM, Evans AR (2017) Ancient whales did not filter feed with their teeth. Biol Letters 13: 20170348. CrossRefGoogle Scholar
  19. Ishiyama M (1987) Enamel structure in odontocete whales. Scan Microsc 1:1071–1079Google Scholar
  20. Kalthoff DC (2006) Incisor enamel microstructure and its implications to higher-level systematics of Eurasian Oligocene and early Miocene hamsters (Rodentia). Palaeontographica A 277:67–80Google Scholar
  21. Karlsen K (1962) Development of tooth germs and adjacent structures in the whalebone whale (Balaenoptera physalus (L.)). Hvalradets Skrifter 45:1–56Google Scholar
  22. Koenigswald W von (1997) Evolutionary trends in the differentiation of mammalian enamel ultrastructure. In: Koenigswald W von, Sander PM (eds) Tooth Enamel Microstructure. Balkema, Rotterdam, pp 203–235Google Scholar
  23. Koenigswald W von, Sander PM (1997) Glossary of terms used for enamel microstructures. In: Koenigswald W von, Sander PM (eds) Tooth Enamel Microstructure. Balkema, Rotterdam, pp 267–280Google Scholar
  24. Loch C, Duncan WJ, Simões-Lopes PC, Kieser JA, Fordyce RE (2013) Ultrastructure of enamel and dentine in extant dolphins (Cetacea: Delphinoidea and Inioidea). Zoomorphology 132:215–225CrossRefGoogle Scholar
  25. Loch C, Kieser JA, Fordyce RE (2015) Enamel ultrastructure in fossil cetaceans (Cetacea: Archaeoceti and Odontoceti). PLoS One 10:e0116557. CrossRefGoogle Scholar
  26. Maas MC, Thewissen JGM (1995) Enamel microstructure of Pakicetus (Mammalia: Archaeoceti). J Paleontol 69:1154–1163CrossRefGoogle Scholar
  27. Marx FG, Tsai CH, Fordyce RE (2015) A new Early Oligocene toothed ‘baleen’whale (Mysticeti: Aetiocetidae) from western North America: one of the oldest and the smallest. R Soc Open Sci 2: 150476Google Scholar
  28. Marx FG, Hocking DP, Park T, Ziegler T, Evans AR, Fitzgerald EMG (2016a) Suction feeding preceded filtering in baleen whale evolution. Mem Mus Vic 75: 71–82CrossRefGoogle Scholar
  29. Marx FG, Lambert O, Uhen MD (2016b) Cetacean Paleobiology. John Wiley & Sons, HobokenCrossRefGoogle Scholar
  30. McGowen MR, Spaulding M, Gatesy J (2009) Divergence date estimation and a comprehensive molecular tree of extant cetaceans. Mol Phylogenet Evol 53: 891–906CrossRefGoogle Scholar
  31. Mitchell ED (1989) A new cetacean from the late Eocene La Meseta Formation Seymour Island, Antarctic Peninsula. Can J Fish Aquat Sci 46: 2219–2235CrossRefGoogle Scholar
  32. Nanci A (2012) Ten Cate's Oral Histology: Development, Structure, and Function. Elsevier, St. LouisGoogle Scholar
  33. O’Leary MA, Uhen MD (1999) The time of origin of whales and the role of behavioral changes in the terrestrial-aquatic transition. Paleobiology 25:534–556CrossRefGoogle Scholar
  34. Peredo CM, Pyenson ND, Boersma AT (2017) Decoupling tooth loss from the evolution of baleen in whales. Front Mar Sci 4:67. CrossRefGoogle Scholar
  35. Peredo CM, Peredo JS, Pyenson ND (2018) Convergence on dental simplification in the evolution of whales. Paleobiology: 1–10.
  36. Sahni A, Koenigswald W von (1997) The enamel microstructure of some fossil and recent whales from the Indian subcontinent. In: Koenigswald W von, Sander PM (eds) Tooth Enamel Microstructure. Balkema, Rotterdam, pp 177–191Google Scholar
  37. Stefen C (2001) Enamel structure of arctoid Carnivora: Amphicyonidae, Ursidae, Procyonidae, and Mustelidae. J Mammal 82:450–462CrossRefGoogle Scholar
  38. Stefen C, Rensberger JM (1999) The specialized structure of hyaenid enamel: description and development within the lineage - including percrocutids. Scan Microsc 13:363–380Google Scholar
  39. Thewissen JGM, Sensor JD, Clementz MT, Bajpai S (2011) Evolution of dental wear and diet during the origin of whales. Paleobiology 37:655–669CrossRefGoogle Scholar
  40. Thewissen JGM, Williams EM, Roe LJ, Hussain ST (2001) Skeletons of terrestrial cetaceans and the relationship of whales to artiodactyls. Nature 413:277–281CrossRefGoogle Scholar
  41. Uhen MD (2000) Replacement of deciduous first premolars and dental eruption in archaeocete whales. J Mammal 81:123–133CrossRefGoogle Scholar
  42. Uhen MD (2008) New protocetid whales from Alabama and Mississippi, and a new cetacean clade, Pelagiceti. J Vertebr Paleontol 28:589–593CrossRefGoogle Scholar
  43. Uhen MD (2009) Evolution of cetacean dental morphology. In: Perrin WF, Würsig B, Thewissen JGM (eds) Encyclopedia of Marine Mammals, 2nd edn. Academic Press, San Diego, pp 302–307CrossRefGoogle Scholar
  44. Ungar PS (2010) Mammal Teeth: Origin, Evolution and Diversity. The Johns Hopkins University Press, BaltimoreGoogle Scholar
  45. Werth AJ (2001) How do mysticetes remove prey trapped in baleen? Bull Mus Comp Zool 156:189–203Google Scholar
  46. Werth AJ (2006) Mandibular and dental variation and the evolution of suction feeding in Odontoceti. J Mammal 87:579–588CrossRefGoogle Scholar
  47. Wiman C (1905) Über die alttertiären Vertebraten der Seymourinsel. Wiss Ergebn Schwed Südpol–Exp 3:1–37Google Scholar

Copyright information

© Springer Science+Business Media, LLC, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Sir John Walsh Research Institute, Faculty of DentistryUniversity of OtagoDunedinNew Zealand
  2. 2.Instituto Patagónico de Geología y Paleontología, CONICETPuerto MadrynArgentina
  3. 3.Department of ZoologySwedish Museum of Natural HistoryStockholmSweden
  4. 4.Department of PaleobiologySwedish Museum of Natural HistoryStockholmSweden
  5. 5.Facultad de Ciencias Naturales y MuseoUniversidad Nacional de La Plata, CONICETBuenos AiresArgentina

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