A Cambrian Peak in Morphological Variation Within Trilobite Species
Mark Webster
Department of the Geophysical Sciences, University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637, USA. E-mail: mwebster{at}geosci.uchicago.edu
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Fig. 1. Temporal pattern of the frequency (A) and relative proportion (B) of trilobite species coded as polymorphic in at least one character in cladistic analyses. Hatched and solid shading in (A) denotes polymorphic and nonpolymorphic species, respectively. Geologic period abbreviations: Ordov., Ordovician; Sil., Silurian; Dev., Devonian; Carb., Carboniferous; E, early; M, middle; L, late. Error bars indicate two-unit profile likelihood confidence intervals. Data are from table S2.
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Fig. 2. Frequency distributions for the proportion of characters coded as polymorphic within trilobite species for the Early Cambrian (A, median = 2.8%), Middle Cambrian (B, median = 3.6%), and post-Cambrian (C, median = 0.0%). Approximate duration (in millions of years, my) of each temporal bin is shown; duration for Early Cambrian is based on trilobite-bearing portion only. Frequency distributions at higher temporal resolution are shown in fig. S2. Data are from table S2.
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Fig. 3. (A and B) Differences among trilobite orders in the frequency (A) and relative proportion (B) of species coded as polymorphic in at least one character in cladistic analyses. (C and D) Temporal pattern of the frequency (C) and relative proportion (D) of proetid trilobite species coded as polymorphic in at least one character in cladistic analyses. (E and F) Temporal pattern of the frequency (E) and relative proportion (F) of phacopid trilobite species coded as polymorphic in at least one character in cladistic analyses. Hatched and solid shading in (A), (C), and (E) denote polymorphic and nonpolymorphic species, respectively. Error bars indicate two-unit profile likelihood confidence intervals. Data are from table S2. Abbreviations as for Fig. 1.
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