When whales had teeth: dental morphology and ultrastructure in fossil cetaceans from Antarctica

LOCH, CAROLINA; BUONO, MÓNICA; KALTHOFF, DANIELA C.; MÖRS, THOMAS; FERNÁNDEZ, MARTA S.

Lima

Congreso; XII Congreso de la Sociedad Latinoamericana de Especialistas en Mamíferos Acuáticos RT; 2018

Modern whales have no teeth, using keratinized baleen plates to Òlter huge volumes of small prey from seawater, while dolphins possess simpliÒed, homodont and numerous teeth used to pierce and grasp Òsh and squid. However, cetacean ancestors had a heterodont dentition with complex and ornament teeth. This study describes the morphology of teeth and enamel ultrastructure intwo fossil cetaceans from Antarctica: a Basilosauridae archaeocete, representing an extinct lineage, and Llanocetus sp., one of the oldest known ancestors of baleen whales. The basilosaurid was collected from La Meseta Formation (middle Eocene) and Llanocetus sp. from Submeseta Formation (late Eocene), in Seymour (Marambio) Island, Antarctica. After being photographed and described,teeth were embedded in epoxy resin, sectioned, ground polished, etched and coated with gold palladium for SEM observation. The two teeth analysed were lower premolars, bearing a transversally compressed triangular crown with a main cusp and accessory denticles. The enamel of Basilosauridae and Llanocetus sp. is prismatic with Hunter-Schreger bands (HSB) and an outer layer of radial enamel. In Basilosauridae, the enamel was relatively thin and measures 150-180 µm,while in Llanocetus it was considerably thicker, measuring 830-890 µm in the coronal area and 350- 380 µm near the crown base. Structures resembling enamel tufts and lamellae were observed at the enamel-dentine junction (EDJ) and extending along the thickness of the enamel layer, respectively. Despite the simpliÒcation or complete absence of teeth in modern whales, their basalancestors had complex posterior teeth typical of most mammals. The same trend was observed in the ultrastructure of enamel, which is thin and either radial or prismless in most modern toothed cetaceans, but was moderately thick and with prominent HSB in basilosaurids and Llanocetus. The presence of HSB and biomechanical reinforcing structures such as tufts and lamellae suggest heavyocclusal loads during feeding.