Phylogeny of the Thysanoptera
Phylogeny of the Thysanoptera
Within insects, the Acercaria represent a large group showing exceptional evolutionary success. They include Hemiptera (true bugs, cicadas, aphids, whiteflies and scale insects) and the smaller sister lineages Psocodea (barklice, lice) and the superorder Thripida. Considering extant species, Thripida is generally used as synonym of Thysanoptera. However, actually Thripida includes Thysanoptera sensu stricto and the fossil order Lophioneurida, discussed as an immediate, ancestral thysanopteran clade, a closely related stemgroup or as an early paraphyletic lineage. The actual relationship between both has been a contentious issue.
About 50 species are known from Lophioneurida that had their main distribution during the Permian. During the Mid-Permian, one of the subgroups of the Lophioneurida – presumably the lineage including Zoropsocus – gave rise to the Thysanoptera. Only a few fossils are available from the Triassic, but this period is probably a very important time in terms of evolution within Thripida, as thysanopteran forms emerged (Triassothrips virginicus, Kazachothrips triassicus; Triassothripidae). Within the Jurassic Lophioneurids were still more common and widespread but their decline is evident since the Early Cretaceous, when aeolothripid Thysanoptera became more diverse. Lophioneurida most likely had disappeared before the dawn of the Paleogene.
Fossils reveal the close relationship of Lophioneurida and Thysanoptera. Lophioneurids provided fundamental features that constitute the head and mouthparts of modern Thysanoptera including an asymmetrical mouth cone with a stylet-like mandible and laciniae, and the reduction or loss of the right mandible. Moreover, at least some species had eversible arolia and wings with long fringe hairs (a character that independently evolved in many small flying insects). Recent studies suggest a similar feeding behaviour in Lophioneurida and Thysanoptera. Tiny holes that have been found in fossil Progymnosperm spores from the Permian indicate punch-and-suck feeding, as known from extant thrips that feed on pollen grains. They pierce the pollen wall with their left mandible by pressing and nodding their head against it, then the fluid contents are sucked out. Thysanoptera that fed on fungal spores, like many extant species of Phlaeothripidae and Merothripidae do, are, also known from the Cretaceous.
As mentioned above, the origin of Thysanoptera lies between the Permian and Triassic. In later Mesozoic strata (particularly from the Cretaceous), fossils of Thysanoptera are found increasingly. Most of them can be attributed to families that still exist. Inclusions in Lebanese amber indicate that Cretaceous thrips already had developed most character states of modern species.
Finds of fossil thrips in amber are quite common, but most of these inclusions date from much younger periods. A large number of species has been described from Eocene Baltic amber (40 million years old) and many of these species have been included in more or less useful identification keys. Unfortunately, these works usually focus only on diagnostic descriptions and lack information that allows conclusions to be drawn on past ecological conditions.