杏吧原创

A cockroach preserved in amber is the earliest cave-dwelling animal identified from the dinosaur era. All other known cave-dwellers have lived much more recently.

The specimen was found in amber in the Hukawng Valley in Myanmar. The rocks where it was discovered are 99 million years old 鈥� they were laid down halfway through the Cretaceous period, when the last dinosaurs lived.

This new Cretaceous cockroach has been dubbed Mulleriblattina bowangi by a team led by Peter Vr拧ansk媒 at the Slovak Academy of Sciences in Bratislava, Slovakia. He has previously discovered extraordinary modern cockroaches.

鈥淚t鈥檚 clearly a cave inhabitant,鈥� says Vr拧ansk媒. It is a pale white colour, having lost its pigments, and its eyes and wings are drastically reduced compared with other cockroaches. It also has unusually long antennae, which presumably helped it navigate in the dark.

Finally, its legs have none of the sensitive spines that normally help a cockroach feel its surroundings. 鈥淎ll cockroaches have spines because it鈥檚 passive protection against predators,鈥� he says. 鈥淭hese don鈥檛 have these spines, because in caves there is no threat.鈥�

It is strange that a cave-dwelling organism became trapped in amber, which comes from tree sap. The most likely explanation is that it wandered close to the cave entrance, and trees were growing nearby, says Vr拧ansk媒.

No other cave-dwelling animal, of any kind, can be confidently attributed to the dinosaur era or earlier, he says.

M. bowangi belongs to a cockroach family called Nocticolidae. Many modern members live in caves. However, it seems the modern cave dwellers aren鈥檛 directly descended from the Cretaceous cave dweller.

Vr拧ansk媒鈥檚 team has reconstructed the family tree of Nocticolidae and thus its history. 鈥淭his group originated about 127 million years ago,鈥� he says. At that time, many continents were connected in a supercontinent called Gondwana. However, Gondwana soon broke up, so groups of Nocticolidae species became isolated on separate continents.

When Nocticolidae lineages entered caves, they began evolving rapidly, the team found. 鈥淎fter entering caves, organisms begin behaving very strangely from the evolutionary point of view,鈥� says Vr拧ansk媒. 鈥淚n a very short time, their evolution becomes very rapid and very strange, because bizarre and strange forms originate.鈥�

However, these cave-dwelling lineages then tended to die out relatively quickly, within about 30 million years. It is unclear why they died out, he says, but it could have been that their isolated lives led to inbreeding or a lack of viruses bringing in new genetic material. Most modern cave-dwelling organisms have probably evolved their unusual bodies within the past few million years, he says.