杏吧原创

WHY did trilobites鈥攐ne of Earth鈥檚 most successful
creatures鈥攕uddenly die out? According to a new study, it was simply
because they couldn鈥檛 shed their skins fast enough.

Trilobites evolved into more than 1500 genera. They survived for about 300
million years, but vanished around 250 million years ago. 杏吧原创s usually
attribute the trilobite鈥檚 demise to newly evolved predators, like fish. But why
the trilobites succumbed to these new dangers when other arthropods remained is
a mystery.

Having examined thousands of trilobite fossils found in rocks near
Cincinnati, Ohio, Danita Brandt of Michigan State University in East Lansing
says that their unusual moulting habits may have been the cause. All arthropods
moult by shedding their exoskeletons periodically so that they can grow into new
and larger ones. Modern arthropods like lobsters moult in a few minutes: a
single suture splits like a zip.

But Brandt found that trilobites had several patterns of opening. Each of the
many segments of their bodies could moult separately, taking several days. This
left their bodies vulnerable to primitive fish and squid. 鈥淢oulting is a very
dangerous time for an arthropod,鈥� says Brandt, who will present her findings at
a meeting in Ontario next month.

Trilobites may have made a last-ditch attempt to improve the situation.
Brandt says the last trilobites tended to have fewer body segments, so that they
could moult slightly faster. 鈥淲hy didn鈥檛 trilobites take the next step and
develop a consistent moulting pattern?鈥� asks Brandt. 鈥淲e may never know.鈥�