Dear MARMAM subscribers,
We are pleased to announce the publication of the following paper in
PLOS One:
Loch C, Kieser JA, Fordyce RE (2015) Enamel Ultrastructure in Fossil Cetaceans
(Cetacea: Archaeoceti and Odontoceti). PLoS ONE 10(1): e0116557.
doi:10.1371/journal.pone.0116557
Abstract
The transition from terrestrial ancestry to a fully pelagic life profoundly
altered the body systems of cetaceans, with extreme morphological changes in
the skull and feeding apparatus. The Oligocene Epoch was a crucial time in the
evolution of cetaceans when the ancestors of modern whales and dolphins
(Neoceti) underwent major diversification, but details of dental structure and
evolution are poorly known for the archaeocete-neocete transition. We report
the morphology of teeth and ultrastructure of enamel in archaeocetes, and
fossil platanistoids and delphinoids, ranging from late Oligocene (Waitaki
Valley, New Zealand) to Pliocene (Caldera, Chile). Teeth were embedded in epoxy
resin, sectioned in cross and longitudinal planes, polished, etched, and coated
with gold palladium for scanning electron microscopy (SEM) observation. SEM
images showed that in archaeocetes, squalodontids and Prosqualodon (taxa with
heterodont and nonpolydont/limited polydont teeth), the inner enamel was
organized in Hunter-Schreger bands (HSB) with an outer layer of radial enamel.
This is a common pattern in most large-bodied mammals and it is regarded as a
biomechanical adaptation related to food processing and crack resistance.
Fossil Otekaikea sp. and delphinoids, which were polydont and homodont, showed
a simpler structure, with inner radial and outer prismless enamel. Radial
enamel is regarded as more wear-resistant and has been retained in several
mammalian taxa in which opposing tooth surfaces slide over each other. These
observations suggest that the transition from a heterodont and nonpolydont/limited
polydont dentition in archaeocetes and early odontocetes, to homodont and
polydont teeth in crownward odontocetes, was also linked to a marked
simplification in the enamel Schmelzmuster. These patterns probably reflect
functional shifts in food processing from shear-and-mastication in archaeocetes
and early odontocetes, to pierce-and-grasp occlusion in crownward odontocetes,
with the implication of less demanding feeding biomechanics as seen in most
extant odontocetes.
Full text is available at:
Best regards,
________________________________________
Carolina Loch Silva, PhD
Research Assistant
Sir John Walsh Research Institute
Faculty of Dentistry, University of Otago
Dunedin 9054, New Zealand
Phone: +(64) 03 479-5667
&
Research Collaborator
Geology Department, University of Otago
and
Laboratório de Mamíferos Aquáticos UFSC
Florianópolis, SC - Brasil