The principal animal lineages diverged in the Cambrian period, but most diversity at lower taxonomic ranks arose more gradually over the subsequent 500 million years. Annelid worms, or segmented worms, seem to exemplify this pattern, based on molecular analyses and the fossil record. However, 15 new specimens of the annelid worm Iotuba chengjiangensis challenge this picture.
Iotuba chengjiangensis is a species of annelid worm that lived during the Cambrian period, some 515 million years ago.
The fossilized remains of this worm, also known as Eophoronis chengjiangensis, came from the Early Cambrian Chengjiang Lagerstätte in China.
The specimens included evidence of the worms’ guts and kidneys and revealed they had an unexpectedly complex structure similar to that of other annelid worms.
This means that annelids diversified into different lineages some 200 million years earlier than previously thought and were part of the evolutionary leap known as the Cambrian explosion.
“We know that the main animal lines we see today emerged during the Cambrian explosion, but we always thought annelid worms were late to the party, and their major subgroups didn’t begin to diversify until nearly 200 million years later,” said Dr. Martin Smith, a paleontologist at Durham University.
“But the amazingly preserved fossils we have studied and the structure of these amazing little creatures challenge this picture, and show that annelid worms — including Iotuba chengjiangensis — seemed to follow the pattern of events initiated by the Cambrian explosion.”
“Detailed fossils of this type of worm are extremely rare, so it was great to be able to study the fossilized record of this tiny animal in such detail.”
“It turns out they weren’t late to the party at all, they were just hiding in a side room.”
Iotuba chengjiangensis was able to move its head in and out of a cage made of bristly spines.
This makes the species a close relative of families of annelids…
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