Abstract

T. striatopunctatus, from the Henryhouse Formation of early Late Silurian age exposed in the Lawrence Uplift and Arbuckle Mountains of southern Oklahoma, is interpreted to be sexually dimorphic. This is the first report of dimorphism in the Thlipsuridae and is based on the study of 128 specimens, mainly dissociated valves, from one sample. The individuals of one group of adults are considerably longer than adults of the other group and always have a distinct posteroventral spine, a feature very poorly developed or absent from the shorter adults. The longer specimens with well developed spines are considered to be females.

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