Abstract
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.
Highlights
Dentition has been convergently reduced in size or lost completely several times throughout vertebrate evolution, despite its importance in individual survival [1]
We demonstrate the existence of a previously hypothesized ontogenetic trend of increasing tooth reduction in the extinct marine reptile Stenopterygius quadriscissus (Reptilia: Ichthyosauria), and explore a potential mechanism producing gradual tooth reduction related to feeding behavior
The Reduced Major Axis (RMA) slope a for logMandible against logCrownHeight for S. quadriscissus (Fig 3), with a value of 0.67 shows strong negative allometry
Summary
Dentition has been convergently reduced in size or lost completely several times throughout vertebrate evolution, despite its importance in individual survival [1]. Loss of such a critical structure requires a complex interaction of developmental and environmental factors, and most extant species which show evolutionary “tooth reduction” are more accurately described as completely edentulous (and we use the term “tooth loss” to refer to this condition). Our understanding of processes producing gradual tooth size reduction (without complete tooth loss) is PLOS ONE | DOI:10.1371/journal.pone.0141904. We demonstrate the existence of a previously hypothesized ontogenetic trend of increasing tooth reduction in the extinct marine reptile Stenopterygius quadriscissus (Reptilia: Ichthyosauria), and explore a potential mechanism producing gradual tooth reduction related to feeding behavior. We expand our understanding of dental morphological evolution to include species which show functional edentulism without complete tooth loss
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