These horseshoe crabs crawled beneath dinosaurs

BEIJING, Jan. 29 (Xinhuanet) -- Two nearly complete small horseshoe crab fossils discovered in Canada reveal a new genus, pushing their origins back at least 100 million years earlier than previously thought.

Named Lunataspis aurora, the ancient horseshoe crab is estimated to have been just 1.5 inches (4 centimeters) from head to tail-tip, much smaller than its modern-day relatives that can reach nearly 20 inches (50 centimeters).

"We do not know if the fossils were small because they were simply young animals or because Lunataspis just didn't grow any bigger," said researcher David Rudkin of the Royal Ontario Museum in Canada.

Rudkin and his colleagues, including Graham Young of the Manitoba Museum, found the fossils buried in 445-million-year-old rocks from the Ordovician period in central and northern Manitoba. They describe the discovery in the January issue of the journal Paleontology. The specimens included patches of the animals' outer-covering and even evidence of their compound eyes.

Horseshoe crabs are not true crabs. They are instead more closely related to spiders and scorpions. And like their eight-legged relatives, horseshoe crabs sport a flexible exoskeleton made of chitin rather than the hard-shell armoring worn by crabs.

Chitin degrades over time. For that reason, ancient specimens of horseshoe crabs have been sparse. Until now, the oldest fossils dated back 350 million years ago, from the Carboniferous period. Fossils have also been found in rocks from the Jurassic Period, suggesting the animals were crawling around beneath dinosaurs.

Both the Carboniferous and the Jurassic fossil discoveries indicate the ancient horseshoe crabs greatly resembled their modern-day counterparts.

"We wouldn't necessarily have expected horseshoe crabs to look very much like the modern ones, but that's exactly what they look like," Rudkin said. "This body plan that they've invented, they've stayed with it for almost a half a billion years. It's a good plan."

(Agencies)