Relatively few fossil dytiscids have been described. This is unfortunate since fossils can provide useful phylogenetic and evolutionary information including unique character combinations not present in extant taxa and minimum ages for divergences. However, even when fossils are found, important characters are often not visible since they may be poorly preserved or obscured. The fossil insects present in calcareous nodules from the Miocene Barstow Formation of the Calico Mountains in Southern California are exceptionally well preserved (Palmer, 1957). The original organisms are replaced by silica or other minerals and when the nodules are dissolved in formic acid, the...

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