A 126-million-year-old fossil of the oldest stick insect was discovered in Mongolia.

The insect, named Cretophasmomima melanogramma, was found in Liaoning province in northeastern China, part of the Jehol rock formation. This discovery has confirmed that an insect's ability to blend in with the foliage is no recent adaptation and existed in ancient times too.

The insect most likely existed during the dinosaur age. It was long and narrow and used its wings as a leaf-like cloak to fool birds and rat-like mammals, according to L.A. Times.

"This new record suggests that leaf mimicry predated the appearance of twig and bark mimicry in Phasmatodeans," the authors wrote. "Additionally, it complements our growing knowledge of the early attempts of insects to mimic plant parts."

Three fossils of the insect were uncovered - two male and one female. Researchers speculated that the female species grew about 2.2 inches (55 mm) long and the males were a bit smaller.

Describing the creatures, researchers said that their wings appeared to have dark, parallel lines. When folded back, the wings assumed a "tongue-like" shape that covered the insect's abdomen.

Researchers also said that the insect's wings resembled a leaf-shaped plant organ called Membranifolia admirabilis, a relative of the Ginkgo tree.  The arrival of small insect-eating birds and agile, branch-walking mammals provided good reason for insects to develop new predator-avoidance strategies like mimicking the appearance of a leaf. According to a Reuters report, researchers that made this discovery believe that the insects evolved to look like these leaves so that they could hide from their predators. 

"Cretophasmomima melanogramma is one of the grand-cousins of today's stick and leaf insects," said paleontologist Olivier Béthoux of the Center for Research on Paleobiodiversity and Paleoenvironments, according to Reuters.

Considering the fact that today's stick insects mimic the same plants they eat, the Cretophasmomima melanogramma may have had a similar eating habit. The creature lived in a warm and wet environment with a large array of plants, dominated by conifers but also featuring relatives of the Gingko, cycas and others. However, the researchers found that the insect lacked some characteristics of similar insects seen today, such as a curved part of the front legs that hide the head.

Currently, there are roughly 3,200 known species of stick and leaf insects, which are members of the insect order known as Phasmatodea. Their name is derived from the ancient Greek word for phantom because of their ability to disguise themselves.

Stick insects are reportedly the longest insects in the world. In 2008, Phobaeticus chani, a 56.7cm-long stick-insect from Borneo was declared the world's longest insect and displayed at the Natural History Museum. Only three specimens of the insect have been found so far. Previous to this, a stick-insect called Phobaeticus serratipes found in Malaysia and Indonesia held the record of being the longest insect in the world.

Though the newly discovered insect comes nowhere close to the size of the Phobaeticus chain, it still holds the title of being the oldest known stick insect.

The current study was published online in the journal PLOS ONE. The study was funded by the National Basic Research Program of China, National Science Foundation of China, Project of Great Wall Scholar, KEY project of Beijing Municipal Commission of Education and China Geological Survey.