Specimen list and measurement data for Stenopterygius quadriscissus; Plot of lower jaw length against stratigraphic occurrence for all specimens of S. quadriscissus

Supplementary Table 1.—Specimen list and measurement data for Stenopterygius quadriscissus. Note that only approximate geographic provenance is available as these are historical finds. All measurements are in millimetres. Specimens for which all 6 measurements were not available were included in the lower jaw mean length analysis, but not the PCA analysis.; Supplementary Figure 1.—Plot of lower jaw length against stratigraphic occurrence for all specimens of S. quadriscissus (juveniles included)

Maxwell&DececchiSI

Supplementary Table 1 (list of specimens examined) and Table 2 (results of the partial correlation analyses

RMA analysis of tooth crown shape through ontogeny in <i>Stenopterygius quadriscissus</i>.

<p>Tooth Shape calculated as per Massare (1987).</p

An example of a belemnite with a shattered phragmocone, interpreted as a bite mark (SMNS 60863).

<p>Scale bar = 1 cm.</p

Diagram showing measurements used throughout the analysis.

<p>Diagram showing measurements used throughout the analysis.</p

Ontogenetic Tooth Reduction in <i>Stenopterygius quadriscissus</i> (Reptilia: Ichthyosauria): Negative Allometry, Changes in Growth Rate, and Early Senescence of the Dental Lamina

<div><p>We explore the functional, developmental, and evolutionary processes which are argued to produce tooth reduction in the extinct marine reptile <i>Stenopterygius quadriscissus</i> (Reptilia: Ichthyosauria). We analyze the relationship between mandible growth and tooth size, shape, and count, to establish an ontogenetic trend. The pattern in <i>S</i>. <i>quadriscissus</i> 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 <i>S</i>. <i>quadriscissus</i> underwent ontogenetic tooth reduction. Tooth reduction in <i>S</i>. <i>quadriscissus</i> may be caused by unique selective pressures resulting from prey choice and feeding behavior, expanding our current understanding of the mechanisms producing tooth reduction.</p></div

Plot showing the allometric slopes of the different tooth quadrants included in the One-way ANCOVA.

<p>Each vertical group of four points is a single specimen. Values = log mm.</p

RMA analysis of tooth count through ontogeny in <i>Stenopterygius quadriscissus</i>.

<p>RMA analysis of tooth count through ontogeny in <i>Stenopterygius quadriscissus</i>.</p

Dental growth in <i>S</i>. <i>quadriscissus</i> modelled using the von Bertalanffy growth model.

<p>Symbols: red-colored upward pointing triangles = embryos, red-colored downward pointing triangles = pregnant females. Values are raw measurements.</p

Supplementary Information

All specimen numbers, recorded gut contents, mandible lengths, stratigraphic information, and tooth measurements used in this study. Please see the attached references document for relevant bibliographic citations