Cambrian Explosion: punctuated trilobites (Introduction)

by David Turell , Thursday, June 09, 2022, 19:43 (877 days ago) @ David Turell

A male trilobite fossil is found:

https://www.scientificamerican.com/article/sex-life-of-one-of-earth-rsquo-s-earliest-an...

"Yet despite their abundance, nobody has been able to figure out how trilobites reproduced—until now. In a very unusual fossil, scientists have found one of the first examples of sexual anatomy in the fossil record: a small pair of grasping appendages that let the male trilobite hold the female close during mating.

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"Trilobites’ delicate bits, such as legs, antennae and reproductive structures, were made of soft tissues that rarely petrified. Paleontologists can infer the existence of legs based on sockets in some species’ outer shells and trace impressions. But reproductive organs were frustratingly elusive.

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"The species, Olenoides serratus, is about as well-known as ancient arthropods get: it makes up many of the Burgess Shale’s fossils and the genus even lends its name to a Yu-Gi-Oh fantasy game card.

"Losso’s specimen was in an unusual position, however. It fossilized lying on its side rather than on its back or belly like most Olenoides fossils. What’s more, its appendages were stretched out and preserved in remarkable detail, down to the joints. Among them, researchers found two sets of short, grasping appendages that looked an awful lot like reproductive structures called claspers.

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"The looks of claspers in horseshoe crabs helped Losso and her team verify that the Olenoides appendages were more than just malformed feet. Claspers suggest that, in some species, male and female trilobites had different looking bodies. “They have found that Rosetta stone fossil that allows us to really confirm these theories about sexual dimorphism,” Bicknell says. “This is just a really nice, fundamentally important addition.”

"Losso cautions that the feature might not be universal. “Finding claspers in Olenoides serratus doesn’t mean that all trilobites reproduced that way,” she says. Nevertheless, the study marks an important milestone in trilobite paleontology, one which will help inform future research. It hints the animals evolved a wider variety of specialized limbs than previously thought and did so early in their evolutionary history. “It speaks to a really cool underlying modularity,” Hegna says. “They’re an armored Swiss Army knife.”

Comment: our favorite Cambrians are yielding more secrets. It has alwasy bee presumed sex appeared in the Cambrian, but Edicraran 'frond-like animals could have had sex earlier.