New Carboniferous fossils of Spilapteridae enlighten postembryonic wing development in Palaeodictyoptera
Abstrakt
A new palaeodictyopterid nymph Bizarrea obscura gen. n.etsp. n. (Spilapteridae) and a new adult specimen of Homaloneura cf. dabasinskasi Carpenter are described from the Pennsylvanian (Moscovian) ironstone nodules of Mazon Creek (IL, U.S.A.). Both taxa share enlarged prothoracic lobes (interpreted by some as winglets), heteronomous meso- and metathoracic wing pads or wings, a slender abdomen with pointed laterotergites, and a unique division of the abdominal segments by two transverse sulci.
An alternative hypothesis for the placement of Bizarrea within Homoiopteridae is considered on the basis of its large body size and relatively short wing pads. Based on the morphology of the new material, postembryonic development of wing pads in Palaeodictyoptera (Palaeodictyopterida) is reconsidered.
Detailed investigation of the abdominal segments, including examination by scanning electron microscopy, reveals the presence of subcircular, sclerotized structures partially covered at the bases of the nymphal laterotergites I- VII, ?VIII. Based on their position and shape, these structures are interpreted as abdominal spiracles, and thus a terrestrial or semiaquatic habitat for these immatures is hypothesized.
Moreover, our discovery of the same, supposedly homologous structures in the enigmatic Vogesonymphidae (Permoplectoptera), from the Middle Triassic of Grès a Voltzia in France, is evidence for the parallel coexistence of ancestrally terrestrial and derived aquatic lineages of Ephemerida (Ephemeropterida) in early Mesozoic ecosystems.