Evolution doesn’t always end in success for every organism. In fact, for some, it seems to result in exactly what a species most fears: extinction. A new study by Charles Mitchell from the University of Buffalo’s geology department found that a tiny, long-lived, marine organism far outlived its evolutionary successors. Mitchell, working with Michael J. Melchin of St. Francis Xavier University in Nova Scotia, Canada, Chris B. Cameron from the Universite de Montre,l; and Jorg Maletz of the Frei Universitat Berlin, analyzed the morphology of these marine creatures, known as rhabdopleurids to determine their evolutionary lineage. Rhabdopleura compacta are millimeter-long seafloor-dwelling creatures that use their two tentacled arms to filter through ocean water and pick out their microscopic food. They form orange, tube-like colonies on the shells of dead clams in oceans worldwide. Their most amazing feat: they have been living like this for the past 500 million years.
Mitchell and colleagues compared the structure and form of rhabdopleurids to that of ancient zooplankton, known as pelagic graptolites. They found that rhabdopleurids were the evolutionary precursor to these prehistoric zooplankton. Most interesting is that pelagic graptolites went extint 350 million years ago, whereas rhabdopleurids remain a thriving species today. Zooplankton evolved to live near the ocean surface; but the un-evolved rhabdopleurids took the conservative approach and stayed on the bottom of the sea. Zooplankton did survive for a period of time and in fact played important roles in this new, surface-water ecosystem. But their extinction shows that sometimes remaining unchanged may in fact be more advtanageous for a species. "Conservative lineages may weather the storms of climate change and other events,” said Mitchell, “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.” (listen to Mitchell tell more about his study in this radio short). Surpiringly enough, not evolving can be more advantageous in the long run and sometimes the simpler organisms do win that game each and every organism on Earth plays: that of survival.
Find this study in the journal Lethaia.
Read the press release for Mitchell's study at www.buffalo.edu.
The Paleontological Research Institution, Ithaca, New York, is pleased to sponsor Paleontology content for This View of Life. Founded in 1932, PRI has outstanding programs in research, collections, and publications, and is a national leader in development of informal Earth science education resources for educators and the general public.
