Enamel microstructure in Eocene cetaceans from Antarctica (Archaeoceti and Mysticeti)

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 complexand ornamented dentition, with complex enamel microstruc...

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Bibliographic Details
Published in:Journal of Mammalian Evolution
Main Authors: Loch, Carolona, BUONO, Monica, KALTHOFF, Daniela, Mörs, Thomas, FERNANDEZ, Martha
Format: Article in Journal/Newspaper
Language:English
Published: Enheten för zoologi 2020
Subjects:
Archaeocetes
Hunter-Schreger bands
La Meseta formation
Mysticetes
Teeth
Other Earth and Related Environmental Sciences
Annan geovetenskap och miljövetenskap
Antarc*
Antarctica
baleen whales
Online Access:http://urn.kb.se/resolve?urn=urn:nbn:se:nrm:diva-3412
https://doi.org/10.1007/s10914-018-09456-3
Description
Summary: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 complexand 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 cuspand 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.

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