Carolina Loch, Robert Boessenecker, Morgan Churchill and Jules A. Kieser

doi: 10.1007/s00114-016-1366-z

Volume 103(44), May 2016, Pages 1-8 

This study aimed to assess the enamel ultrastructure in modern otariid pinnipeds and in the extinct walrus Pelagiarctos. Teeth of the New Zealand fur seal (Arctocephalus forsteri), sea lion (Phocarctos hookeri), and Pelagiarctos thomasi were embedded, sectioned, etched and analyzed via scanning electron microscopy. The enamel of NZ otariids and Pelagiarctos was prismatic and moderately thick, measuring 150-450 µm on average. It consisted of transversely oriented Hunter-Schreger bands (HSB) from the enamel-dentine junction (EDJ) to near the outer surface, where it faded into prismless enamel less than 10 µm thick. The width of HSB was variable and averaged between 6-10 prisms, and they presented an undulating course both in longitudinal and cross sections. The overall organization of the enamel was similar in all teeth sampled; however, the enamel was thicker in canines and postcanines than in incisors. The crowns of all teeth sampled were uniformly covered by enamel; however, the grooved incisors lacked an enamel cover on the posterior side of the buccal face. Large tubules and tuft-like structures were seen at the EDJ. HSB enamel as well as tubules and tufts at the EDJ suggest increased occlusal loads during feeding, a biomechanical adaptation to avoid enamel cracking and failure. Despite overall simplification in tooth morphology and reduced mastication, the fossil and modern pinnipeds analyzed here retained the complex undulating HSB structure of other fossil and living Carnivora, while other marine mammals such as cetaceans developed simplified radial enamel.

Full text is available at: http://link.springer.com/article/10.1007/s00114-016-1366-z