‘Living fossil’ spiders hitched a ride to get to Asia

Primitive spiders known as liphistiids started diversifying between four and 24 million years ago, about the same time the subcontinent of India collided with Eurasia. Because the burrow-dwelling spiders couldn't travel over water, they must have traveled with the land masses. (Credit: Xu Xin)

The geographical distribution of the most “primitive” spiders that exist today may provide new insights into the movement of Earth’s land masses millions of years ago.

The group of spiders named liphistiids, regarded as “living fossils” because they closely resemble their extinct ancestors with segmented abdomen and spinnerets located in the middle of the lower abdomen, currently inhabit East Asia and Southeast Asia.

However, the only fossil of their ancient relatives dating back some 295 million years was discovered in France. Researchers say the cross-continental migrating arachnids could shed light on continental drift, when at its beginning, Earth was a supercontinent that broke up and shifted apart.

89 species

Scientists examined about 2,000 liphistiid specimens in Asia. With a “molecular clock” method using DNA analysis, they were able to determine when the extant spiders originated and diversified.

The findings, published in the Proceedings of the Royal Society B, show for the first time that the original liphistiid branched out from their ancestors about 39 to 58 million years ago, says Li Daiqin, associate professor of biological sciences at the National University of Singapore.

This “new” group started diversifying to eight genera between four and 24 million years ago, giving rise to some 89 species. Only one genus is found in Southeast Asia while the rest are in East Asia.

The relatively recent branching and quick evolution coincided with the time when the subcontinent of India collided with Eurasia. Because this group of burrow-dwelling spiders cannot be dispersed over water, Li says they must have traveled with the land masses.

3 ways to get there

The researchers suggested three possible hypotheses explaining the eastward dispersal routes of the spiders’ ancestors from Europe:

  • Out of Gondwana, in which the spiders traveled along the southern supercontinent of Gondwana and then drifted north.
  • Stepping-on Middle East, in which the animals traversed south of the ancient northern supercontinent Laurasia via the Middle East to Southeast Asia.
  • Silk Road, in which the spiders crossed Central Asia to China.

The study findings refute previous research that suggests short-term land bridges formed during the glacial cycles between the mainland and southern Japanese islands such as Kyushu and Okinawa, allowed migration of the creatures to these islands.

Researchers from the Smithsonian Institution and the Slovenian Academy of Sciences and Arts contributed to the work.

Source: National University of Singapore