Fossilized leaf-mimic lacewings

Lacewings, or Neuroptera, are a order of insects with very distinctively patterned wings, as their names (both in English and Latin) suggest. Among insects in general, many species, especially the well-known leaf katydids, are mimics of flowering-plant leaves. Such leaf mimicry presumably is a form of camouflage that functions in either defence or in aid of predation.

Paleontologists working in China have discovered a rare set of lacewing fossils (open access article) from Middle Jurassic rocks at a site in Inner Mongolia which are leaf mimics - a useful adaptation given their large size. However, their age means that they pre-date the Cretaceous radiation of flowering plants. The relationship between flowering plants (angiosperms) and insects has been characterized as a synergistic adaptive radiation - both groups flourished in diversity on similar timescales, an observation explained by pointing to the frequent close relationships and associations between insects and angiosperms. Therefore, leaf mimicry has long been thought to be a post-angiosperm phenomenon, and virtually all known leaf-mimics pretend to be angiosperm leaves. These lacewings, however, appear to mimic cycads or bennettiales, both of which are non-flowering seed plants (gymnosperms) that dominated the pre-angiosperm plant world. Both fossil and extant cycads have distinctive pinnate leaves, which the lacewings resemble. These are very different in form from the typical angiosperm leaf.

On the whole this is a very neat story - close insect-plant associations or coevolution appeared long before the rise of the angiosperms. The change in plant communities from gymnosperm-dominated to angiosperm-dominated, however, would have diminished the effectiveness of these cycad mimics, and might explain their disappearance. Perhaps some later fossil discoveries, likely coming from China, the new hot-bed for paleontology, might shed more light on the affair....