Springtail - Systematics and Evolution

Systematics and Evolution

Traditionally, the springtails were divided into the orders Arthropleona, Symphypleona and occasionally also Neelipleona. The Arthropleona were divided into two superfamilies, the Entomobryoidea and the Poduroidea. But actually, these two and the Symphypleona form three lineages, each of which is equally distant from the other two. Thus, the Arthropleona are abolished in modern classifications, and their superfamilies are raised in rank accordingly, being now the Entomobryomorpha and the Poduromorpha. Technically, the Arthropleona are thus a partial junior synonym of the Collembola. The term "Neopleona" is essentially synonymous with Symphypleona + Neelipleona.

The Neelipleona were originally seen as a particular advanced lineage of Symphypleona, based on the shared global body shape. But the global body of Neelipleona is realised in a completely different way than in Symphypleona. Subsequently, the Neelipleona were considered as being derived from the Entomobryomorpha. But analysis of 18S and 28S rRNA sequence data suggests that they form the most ancient lineage of springtails, which would explain their peculiar apomorphies.

Springtails are attested to since the Early Devonian. The fossil from 400 million years ago, Rhyniella praecursor, is the oldest terrestrial arthropod, and was found in the famous Rhynie chert of Scotland. Given its morphology resembles extant species quite well, the radiation of the Hexapoda can be situated in the Silurian, 420 million years ago or more.

Fossil collembola are rare. Most fossils are found in amber. Even these are rare and many amber deposits carry few or no collembola. The best deposits are from the early Eocene of Canada and Europe, Miocene of Central America, and the mid-Cretaceous of Burma and Canada. They display some unusual characteristics: first, all but one of the fossils from the Cretaceous belong to extinct genera, whereas none of the specimens from the Eocene or the Miocene are of extinct genera; second, the species from Burma are more similar to the modern fauna of Canada than are the Canadian Cretaceous specimens.