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Stenopterygius (Ichthyosauria) Ontogenetic Tooth Reduction

Ben Creisler

A recent paper in PLoS ONE:

Daniel G. Dick & Erin E. Maxwell (2015)
Ontogenetic Tooth Reduction in Stenopterygius quadriscissus (Reptilia:
Ichthyosauria): Negative Allometry, Changes in Growth Rate, and Early
Senescence of the Dental Lamina.
PLoS ONE 10(11): e0141904.

We explore the functional, developmental, and evolutionary processes
which are argued to produce tooth reduction in the extinct marine
reptile Stenopterygius quadriscissus (Reptilia: Ichthyosauria). We
analyze the relationship between mandible growth and tooth size,
shape, and count, to establish an ontogenetic trend. The pattern in S.
quadriscissus is consistent with hypotheses of tooth size reduction by
neutral selection, and this unusual morphology (a functionally
edentulous rostrum) was produced by a series of different evolutionary
developmental changes that are known for other taxa showing tooth
reduction and loss. Specifically, this species evolved functional
edentulism by evolutionary changes in the growth allometry of the
dentition and by altering growth rates through ontogeny. This
observation supports previous hypotheses that S. quadriscissus
underwent ontogenetic tooth reduction. Tooth reduction in S.
quadriscissus may be caused by unique selective pressures resulting
from prey choice and feeding behavior, expanding our current
understanding of the mechanisms producing tooth reduction.