Sea Creature Unchanged for 500 Million Years

Humans tend to think that change means progress, always leading to something better, but tiny sea creatures known as rhabdopleurids prove that staying the course can sometimes be even more successful.

These animals reside on the ocean floor where they build their homes out of collagen on the shells of dead clams. It may not be an extravagant existence, but they've lived this way for 500 million years, according to a new study in the journal Lethaia.

What's even more interesting is that they've outlasted a more elaborate species that descended from a common ancestor.

"We think that change is always going to lead us to a better place, that evolution is always going to lead to something better," said lead author Charles Mitchell, a University of Buffalo geology professor. "But all this progress in making all these wonderful pelagic graptolites didn't lead them to take over the world. They didn’t survive, but these simple dudes, these bottom-dwelling creatures, did."

"Pelagic graptolites" were ancient zooplankton that went extinct around 350 million years ago. They evolved rapidly, splitting into many new species and evolving many new traits. Some of this happened because they were living closer to the ocean's surface, which tends to be more unstable.

In the meantime, the rhabdopleurids hardly changed, doing their clam and collagen thing over the eons. (They secrete the collagen themselves, so that's not coming from the shellfish.)

Here's what a colony of them looks like:

In this case, the conservative approach won out and the rhabdopleurids lived happily ever after until the present. You can still find them now, living in areas from Bermuda to the Bering Sea.

"High speciation rates generally go hand in hand with high extinction rates, and likewise low with low," Mitchell said. "Conservative lineages may weather the storms of climate change and other events, but do not become big parts of the ecosystem, whereas the major players are impressive but often brought low by mass extinction and other ‘slings and arrows of outrageous fortune.'"

Read more at Discovery News