In addition, while this type of feeding damage was not referred to any particular holometabolan clade, it is closest to symphytan Hymenoptera in overall features, an informal similarity buttressed by recent phylogenetic analyses indicating that the Hymenoptera is the earliest derived lineage within the Holometabola (Schlumeister et al., 2002; Schlumeister, 2003; Savard et al., 2005; Wiegmann et al., 2009), supported by morphological studies of adults (Vilhelmsen, 1997a, b), from which can be inferred an endophytic larva resembling P.
Hennig (1969) provided a context for his views regarding the origin of the Holometabola by stating that the ancestral larva was active, predatory and campodeiform.
The Lag between the origin of the Holometabola and its eventual dominance
For the Holometabola, this is best explained by the presence of sufficient climatic oscillation in the Pangaean equatorial belt such that fitness benefits gradually would accrue to holometabolous clades through heightened interspecies competition and through creation of underutilized or otherwise ecologically transformed niches during the Permian (Roscher and Schneider, 2006; DiMichele et al., 2010).
There are important examples of ecologically important clades, which exhibit delayed lags in the fossil record that may differ or parallel the pattern exhibited by the Holometabola of the late Paleozoic and Triassic.
There are five summary points resulting from this exploration of the origin and early history of the Holometabola. These statements reflect recent paleobiological and molecular phylogenetic developments and hopefully will serve as a template for further investigation.
Four fossils assigned to the Holometabola have been identified throughout Early to Late Pennsylvanian (Late Carboniferous) deposits from the Illinois Basin and a site in Western Europe.
Divergence time estimate for the Holometabola. These four occurrences of the currently earliest documented Holometabola suggest an earlier divergence time of Late Mississippian (Serpukhovian Stage), from 328 to 318 million years ago.
Major temporal lag between the origin and eventual diversification of the Holometabola. There was an approximate 80 million-year time lag between the estimated origin of holometaboly during the Late Mississippian and its eventual, dramatic diversification during the Middle to Late Triassic.
A priority for future paleobiological investigations of Paleozoic Holometabola. Considerable effort should be directed toward investigating suspect terrestrial deposits from the later Mississippian Subperiod that likely would yield fossil insect material, including a common ancestor to the multiple holometabolous lineages present during the Pennsylvanian.
18S ribosomal RNA genes of insects: primary structure of the genes and molecular phylogeny of the Holometabola. Annals of the Entomological Society of America 89: 788-803.