Fwd: [Archaeology] Oldest Horseshoe Crab Fossil Discovered
- From another post on Archaeology Group......---------- Forwarded message ----------
Date: Jan 30, 2008 10:16 AM
Subject: [Archaeology] Oldest Horseshoe Crab Fossil Discovered
On Yahoo and LiveScience
Nearly a half a billion years ago, tiny horseshoe crabs crept along
the shorelines much like today's larger versions do, new fossil
Two nearly complete fossil specimens discovered in Canada reveal a
new genus of horseshoe crab, pushing their origins back at least 100
million years earlier than previously thought.
Dubbed Lunataspis aurora, the ancient horseshoe crab is estimated to
have been just 1.5 inches (4 centimeters) from head to tail-tip.
That's much smaller than its modern-day relatives that can span
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, spotted 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 and 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
Analysis of the recent finds also indicates the ocean creatures
haven't changed much over the eons.
"We wouldn't necessarily have expected horseshoe crabs to look very
much like the modern ones, but that's exactly what they look like,"
"This body plan that they've invented, they've stayed with it for
almost a half a billion years. It's a good plan," Rudkin told
LiveScience. "They've survived almost unchanged up until the present
day, whereas lots of other animals haven't."
And whereas major extinction events have wiped even the mightiest,
non-avian dinosaurs from our planet, this primitive-looking organism
has come out unscathed.
"The horseshoe crab, the lowly little animal that crawls out of the
sea every once in a while to mate, it's survived for at least 445
million years in more or less the same form," Rudkin said.
He added that understanding how horseshoe crabs adapted to their
ecological niche so early and then weathered natural crises will give
scientists broader insights about how ocean ecosystems changed over
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