An ancient stick insect species,
Cretophasmomima melanogramma from in Inner Mongolia at the Jehol locality, may have mimicked plant leaves for defense as far back as 126 million years ago, during the Cretaceous period, according to a new study.

Many insects have developed defense mechanisms, including the ability to mimic the surrounding environment. Stick and leaf insects mimic plants from their environment, but scientists know little about the original of this interaction due to little or no previous stick insect fossil records showing this adaptation.

The scientists discovered three specimens of
Cretophasmomima melanogramma, one female and two males. The species possessed adaptive features that make it resembling a plant recovered from the same locality.

At left: Cretophasmomima melanogramma at right: Membranifolia admirabilis. Credit: left: O. Béthoux, right: F. Jacques

The insects' wings have parallel dark lines and when in the resting position, likely produced a tongue-like shape concealing the abdomen.

Fossils from a relative of the ginkgo plant have been documented in the area with similar tongue-shaped leaves along with multiple longitudinal lines. The authors suggest the insect used this plant as a model for concealment. The new fossils indicate that leaf mimicry was a defensive strategy performed by some insects as early as in the Early Cretaceous, but that additional refinements characteristic of recent forms, such as a curved part of the fore legs for hiding the head, were still lacking.

The new fossil suggests that leaf mimicry predated the appearance of twig and bark mimicry in these types of insects. The diversification of small-sized, insect-eating birds and mammals may have triggered the acquisition of such primary defenses.