Fossils of Early Stick Insects

Stick insects are fascinating and beautiful creatures, exquisitely mimicking leaves, twigs, and bark to hide themselves from hunters on the prowl. Some species even sway and rustle to complete the illusion. Even the group's scientific name, Phasmatodea, is evocative, coming from the Ancient Greek phasma, meaning "phantom". Unfortunately for researchers, the group's origins are equally well enshrouded thanks to a paucity of fossils from their early evolution. In a paper published in the open access journal PLoS ONE, a team of researchers have described a trio of fossils uncovered in Inner Mongolia which shed light on the early history of these enigmatic insects.

The specimens, two females and a male, represent a new species, Cretophasmomima melanogramma, which lived around 130 million years ago. Remarkably well-preserved, they show several traits characteristic of stick insects, including a 'shoulder pad' found at the base of the forewings of all living Phasmatodea, as well as some differences. These ancient stick insects still hadn't evolved a curved notch on their forelegs in which they could hide their head, for example. Likewise, the drastic size difference between modern male and female stick insects still hadn't evolved when these critters were hiding on Cretaceous plants.

The researchers were also able to make out dark lines running the length of the insects' wings, offering them a hint of where C. melanogramma might have lived. In their resting position, the wings would have made a tongue-like outline covered with parallel dark lines. Based on this, the researchers believe C. melanogramma probably hid on the ancient plant Membranifolia admirabilis, camouflaged by its similarity to the leaves. Not only have these fossils pushed back the date for the emergence of Phasmatodea, but they also suggest that leaf mimicry predated other forms of disguise in this group. Together with the morphological differences with extant forms, this enables researchers to start piecing together a picture of early Phasmatodean evolution, an ongoing dance between plants, insects, and their predators.

Reference
Wang M, et al. Under Cover at Pre-Angiosperm Times: A Cloaked Phasmatodean Insect from the Early Cretaceous Jehol Biota. PLoS ONE 9(3): e91290. (2014) doi:10.1371/journal.pone.0091290

Image credit
The reconstruction, a copy of Fig. 7 from the paper, is by S. Fernandez and is distributed under a CC-BY license.