September 8, 2012
Ancient Sea Creatures Show Newer Doesn’t Always Mean Better
April Flowers for redOrbit.com - Your Universe Online
"Out with the old and in with the new" is an adage we have all heard and probably lived by in this world of fast changing technology and fads. But some tiny sea critters are showing us, newer isn't always better.
Rhabdopleurids are small worm shaped animals that live on the ocean floor. They build tube like homes of collagen on the shells of dead clams. Rhabdopleurid colonies are small, and they are definitely not the dominant animal in their ecosystem.
The impressive thing about rhabdopleurids is that they have lived this way, and survived, for more than 500 million years. They have outlasted other, more elaborate species that descended from a common ancestor, according to a new study led by the University of Buffalo.
Rhabdopleurids' age and modern existence are well documented, however, where the new study breaks ground is by identifying them as a predecessor to ancient zooplankton — known as pelagic graptolites — that went extinct about 350 million years ago.
"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 Charles Mitchell, a University at 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."
Mitchell led the research team, which included Michael J. Melchin from St. Francis Xavier University in Nova Scotia, Canada; Chris B. Cameron of the Universite de Montreal; and Jorg Maletz from the Frei Universitat Berlin. The results of their study were published online in the journal Lethaia.
The team used the rhabdopleurids' structure and form to determine that they were some of the most primitive graptolites that ever existed. The rhabdopleurids stayed pretty much the same over the course of history, while their zooplankton relatives evolved slowly and split into many new species.
Other differences evolved as well. Zooplankton developed ways to live closer to the surface and became important players in their new ecosystems, while rhabdopleurids, on the other hand, continued dwelling on the ocean floor and remained relatively inconspicuous.
The conservative approach won out: the rhabdopleurids survived and are still around today, living in areas from Bermuda to the Bering Sea. The zooplankton graptolites went extinct.
"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.'"
Rhabdopleurids and the colonies they build are beautiful to behold under a microscope. The animals are about a millimeter long and Y-shaped, with a pair of tentacled arms extending from a narrow body to filter food from the water. The colonies they create are whimsical-looking structures, consisting of a network of copper-colored tubes that resemble tiny elephant trunks, each one bearing numerous ridges.
The knowledge that rhabdopleurids are ancient graptolites will enable researchers to gain insight into poorly understood aspects of graptolite biology. Studying rhabdopleurids could reveal new clues about how early graptolites looked and reproduced, and even what they ate.