Evolution of the subgenus Cyphelophorus (Genus Helophorus, Hydrophilidae, Coleoptera): description of two new fossil species and discussion of Helophorus tuberculatus Gyll.

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Abstract
Exposures of late Tertiary sediments in the North American Arctic contain well-preserved fossils of Coleoptera (beetles). Two sites, Lava Camp in western Alaska and locality 2-73 on Meighen Island (Canadian Arctic Archipelago), have yielded fragments referable to two fossil species of the helophoran subgenus Cyphelophorus (Hydrophilidae). The only extant species in the subgenus, Helophorus tuberculatus Gyll., is characterized by a distinctive array of elytral tubercles, the intraspecific variation of which is documented here as an aid for distinguishing H. tuberculatus from the two fossil species.The two fossil species are obviously related to H. tuberculatus and probably represent sequential species in the lineage leading to H. tuberculatus. If so, they provide information on evolutionary trends within the Cyphelophorus lineage, and when examined in the light of the morphological features of species in other Helophorus subgenera, show that the tuberculate elytron seen in H. tuberculatus is probably a derived character that developed by modification of an elytron initially having raised alternate interstices.