On time and place of origin of continental calanoid families: a hypothesis

Abstract

Several independent methods: molecular-genetic, biogeographical, and morphological analyses — were applied to explain the origin of the continental calanoid fauna and the distribution of their recent genera. The theory of Continental Drift and the evolution of the Tethys Sea were also used for that purpose. The molecular-genetic-based phylogenetic tree that we constructed, as well as the largest number of genera and species in Diaptomidae, allow us to support the idea that this family of fresh- and brackishwater Copepoda arose earlier than the Temoridae and Centropagidae. The ancestors of the Diaptomidae likely invaded, and were distributed across, the supercontinent Pangaea before its division into two continental plates in the Mesozoic Era, i.e., not later than 180-200 Ma. Therefore, various genera of this family can be found almost everywhere on all continents, except Antarctica. The family Temoridae is known only from Europe, Asia and North America. These three continental plates stayed together long after separation of Pangaea into two parts: Laurasia and Gondwana (until circa 50 Ma). At approximately the same time (50 Ma), the genus Eurytemora should have been created, as its representatives are known from North America and Eurasia. The family Centropagidae seems to have invaded inland waters somewhere between Temoridae and Diaptomidae, as its representatives can be found on all continents except Africa. Also, as a possibly alternative option, this centropagid invasion could have happened independently in the northern and southern Pangaea blocks, by different marine ancestors, at the same time as Temoridae, as is shown herein in the molecular-genetic-based phylogenetic tree. Using the evolution model of the Tethys Sea proved to be very productive for explaining the modern ranges of continental calanoids, both within families and in individual genera, including the genus Eurytemora.