From its ancestral beginnings, it seems, the cockroach has been built to survive.
Fossils of Archimylacris eggintoni, a time-lost relative of the
modern pest, are common enough and found all around the world. Finding intact specimens,
however, is not easy, and so there are a number of mysteries surrounding the insect.
Using a partially intact specimen stored at the Natural History
Museum in London and an x-ray computed tomography (CT) system, researchers at Imperial
College London have created a 3-D virtual fossil that has revealed hidden features
of the creature.
The modern relative of A. eggintoni.
When alive, A. eggintoni and its relations grew to about 2 to
9 cm long and 4 cm wide and roamed the floors of the primeval forests looking for
decayed matter to feed on and a nice place to lay their eggs. The insects, which
eventually evolved into termites and mantises as well as modern cockroaches, flourished
during the Carboniferous geologic period from 359 million to 299 million years ago.
The fossils they left behind typically show bodies and wings, but very few limbs
or other small parts survive in the fossil record.
Using x-ray microtomography and digital reconstruction, Russell
Garwood and his colleague Mark D. Sutton examined a protoroach that was a fossilized
void inside siderite (ferrous carbonate). They used an x-ray CT system made by Metris
NV (now owned by Nikon Metrology NV) and installed at the Natural History Museum
to acquire two sets of 3000+ x-ray images: one of the entire fossil at a resolution
of 22.5 µm and one of the anterior portion – to focus on the limbs –
at a resolution of 17.7 µm. They report their findings in the April 14, 2010, online
edition of Biology Letters.
X-ray computed tomography helped create a three-dimensional
“virtual fossil”
of Archimylacris eggintoni, the ancestor of mantises, termites and
cockroaches.
Courtesy of Imperial College London and the Natural History Museum.
With software developed by Sutton, they created virtual models
of the fossil that showed features of A. eggintoni that have never been seen before.
They found that the insect had claws at the base of its legs, which likely facilitated
tree climbing, and adhesive limb structures called euplantulae that helped it walk
across slick surfaces such as leaves. These specializations likely allowed the
creature to lay eggs well away from predators.
The researchers also noted that the insect’s legs –
fairly long and pitched at a low angle to the body – were built for running
quickly across uneven ground, and that its mandibles were perfectly suited for its
diet of decomposing plants and insects. In fact, old A. eggintoni wasn’t that
different from its present-day cousins.