Toward a Phylogenetic Classification of the Ephemeroptera (Insecta): a Commentary on Systematics

Abstract

Higher classifications of Ephemeroptera formulated in light of phylogenetic hypotheses have been essentially evolutionary in that they have incorporated paraphyletic taxa. The term “paraphyletic” has had a confused history because systematists have applied it to different concepts; for Ephemeroptera, it has denoted one type of nonpolyphyletic grouping. Such paraphyletic taxa were used so that large degrees of character (presumably adaptive) differentiation could be expressed, but resulting classifications lack any means of consistently expressing such gaps, and their ability to express genealogy is compromised. Phylogenetic classifications are now strongly advocated. Not only can the increasing number of phylogenetic hypotheses based on cladistic analysis be objectively expressed, but many traditional taxa and categories can be conserved by employing sequencing conventions. The philosophy and history of competing classificatory systems are discussed. A phylogenetic methodology is employed when possible in proposed revisions of the higher taxa of Ephemeroptera. New cladistic data are presented and previous data reviewed. Major lineages formerly part of the paraphyletic family Siphlonuridae are classified as families within several higher taxa to express phylogeny and at the same time maintain other traditional family units. Assignment of superfamilies within the new suborder Pisciforma (new infraorder Arenata [Acanthametropodidae, Ametropodidae, Analetrididae, Metretopodidae, Pseudironidae] and new infraorder Imprimata [Ameletidae, Ameletopsidae, Baetidae, Metamoniidae, Rallidentidae, Siphlaenigmatidae, Siphlonuridae]) awaits additional cladistic analysis. Considerable evidence is available, however, for the new suborder Rectracheata (new infraorder Vetulata [Oniscigastridae], new infraorder Lanceolata [Leptophlebioidea, Behningioidea, Ephemeroidea], and infraorder Pannota, new status [Caenoidea, Neoephemeroidea, Baetiscoidea]), and new suborder Setisura (Coloburiscidae, Isonychiidae, Oligoneuriidae, Heptageniidae). A new revision of Ephemeroidea serves as a prima facie example of phylogenetic classification in the order. Changes in Ephemeroidea include the removal of Behningiidae, the addition of the new fossil family Australiphemeridae, incorporation of the former Euthyplociidae and the new fossil subfamily Pristiplociinae in Polymitarcyidae, and the incorporation of Pentageniinae and Palingeniinae (formerly Palingeniidae) and the new subfamily Hexageniinae in Ephemeridae. Derivations are expressed mainly by sequencing of taxa recognized at the subfamily rank. Phylogenetic systematics is shown to have predictive and heuristic value for interpreting comparative biology, inferring adaptive evolution and biogeography, and also to have an important function in paleontological and ecological analyses.