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Pliosaurid tooth ontogeny and replacement (free pdf)

Ben Creisler

A new paper in open access:

Judyth Sassoon, Davide Foffa & Ryan Marek (2015)
Dental ontogeny and replacement in Pliosauridae
Royal Society Open Science 2015 2: 150384
DOI: 10.1098/rsos.150384

Dental morphology and patterns of tooth replacement in representatives
of the clade Pliosauridae (Reptilia, Sauropterygia) are evaluated in
detail. The jaws of one basal (Thalassiodracon hawkinsii) and two
derived species (Pliosaurus carpenteri, Pliosaurus kevani) were
visualized by μCT scans, and the ontogenetic patterns, or ‘movement
paths’, of replacement teeth could be mapped. Other specimens
(Peloneustes philarchus and Pliosaurus westbuyensis) with
well-preserved jaws containing functional and replacement teeth in
situ were also examined directly, and waves of tooth replacement could
be inferred from the degree of in situ tooth development and the
fusion between functional and replacement alveoli. The analysis
revealed symmetrical tooth eruption over the medial axis throughout
the length of the jaw in the basal pliosaurid Thalassiodracon. By
contrast, symmetrical tooth eruption patterns occur only along the
anterior sections of the jaws of derived pliosaurids. In Pliosaurus,
replacement schedules differ in the anterior and posterior portions of
the jaws and appear to correlate with differences in tooth morphology
and symmetrical replacement. The anterior teeth exhibit longer
replacement cycle periods and symmetrical replacement, while shorter
cycle periods and asymmetry are seen posteriorly. A longer period
suggests slower replacement and is characteristic of large,
specialized caniniform teeth in the longer snouted Late Jurassic taxa.
Smaller posterior teeth have a shorter period and therefore a faster
replacement cycle. The transition from long to short replacement
period over the length of the jaw is thought to account for the loss
of symmetry. This differentiation could relate to differential tooth
function and a type of heterodonty. We therefore propose a new model
of pliosaurid tooth replacement patterns and present it in a
phylogenetic context.