Palaeoptera

The name Palaeoptera (from Greek Template:Wikt-lang ( 'old') + Template:Wikt-lang ( 'wing')) has been traditionally applied to those ancestral groups of winged insects (most of them extinct) that lacked the ability to fold the wings back over the abdomen as characterizes the Neoptera. The Diaphanopterodea, which are palaeopteran insects, had independently and uniquely evolved a different wing-folding mechanism. Both mayflies and dragonflies lack any of the smell centers in their brain found in Neoptera. Their midgut epithelium has a dual origin: the anterior and posterior regions develop through cellular differentiation, while the central region originates from yolk cells. In all other winged insects, the midgut epithelium is formed solely by cellular differentiation, whereas in the remaining hexapods, including Apterygota, it develops entirely from yolk cells. Which suggests that Palaeoptera represent a transitional stage between these two developmental strategies.

Disputed status

The complexities of the wing-folding mechanism, as well as the mechanical operation of the wings in flight (indirect flight muscles), are such that it indicates that Neoptera is a monophyletic lineage. The plesiomorphic absence of wing-folding does not necessarily mean the Palaeoptera form a natural group – they may be an assemblage containing all insects, closely related or not, that "are not Neoptera", an example of a wastebasket taxon. If the extinct lineages are taken into account, it is likely that the concept of Palaeoptera will eventually be discarded or changed in content to more accurately reflect insect evolution.

In any case, three main palaeopteran lineages, traditionally treated as superorders, are recognized. Of these, the Palaeodictyopteroidea themselves might be a paraphyletic assemblage of basal Pterygota, too. As it stands, the relationship of the two living Paleopteran groups – Ephemeroptera (mayflies) and Odonata (dragonflies and damselflies) – to the Neoptera has not yet been resolved; there are three main competing hypotheses with many variations. In two of these – those that treat the ephemeropteran or the odonatan lineage as closer to the Neoptera than to the other "palaeopterans" – the Palaeoptera appear to be paraphyletic.

See also

• Archedictyon
• Neoptera

References

• Maddison, David R. (2002): Tree of Life Web Project – Pterygota. Winged insects. Version of 2002-JAN-01. Retrieved 2008-DEC-15.
• Trueman, John W.H. [2008]: Tree of Life Web Project – Pterygote Higher Relationships. Retrieved 2008-DEC-15.
• Trueman, John W.H. & Rowe, Richard J. (2008): Tree of Life Web Project – Odonata. Dragonflies and damselflies. Version of 2008-MAR-20. Retrieved 2008-DEC-15.