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

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

Lima

Conferencia; XVIII Reunión de Trabajo de Expertos en Mamíferos Acuáticos y al XII Congreso de la SOLAMAC; 2018

Sociedad Latinoamericana de Especialistas en Mamíferos Acuáticos ? SOLAMAC

Modern whales have no teeth, using keratinized baleen plates to Òlter huge volumes of small preyfrom seawater, while dolphins possess simpliÒed, homodont and numerous teeth used to pierceand grasp Òsh and squid. However, cetacean ancestors had a heterodont dentition with complexand 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 atransversally compressed triangular crown with a main cusp and accessory denticles. The enamelof Basilosauridae and Llanocetus sp. is prismatic with Hunter-Schreger bands (HSB) and an outerlayer 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 atthe 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 inthe ultrastructure of enamel, which is thin and either radial or prismless in most modern toothedcetaceans, but was moderately thick and with prominent HSB in basilosaurids and Llanocetus. Thepresence of HSB and biomechanical reinforcing structures such as tufts and lamellae suggest heavy occlusal loads during feeding.