How Old is Old?
How long ago did the earliest comb jelly diverge" "Unfortunately, we don't have fossils of the oldest comb jelly," laments Dunn. "Therefore, there is no way to date the earliest jelly and determine when it diverged."
After diverging from other species, the comb jelly probably continued to evolve, says Herendeen. Therefore, today's comb jelly--a common creature--probably looks very different that did the earliest comb jelly.
Moreover, the tentacled, squishy but bell-less comb jelly developed along a different evolutionary path than did the classically bell-shaped jellyfish, says Patrick Herendeen, an NSF program director. Such divergences mean that "the jellyfish type of body form has independently evolved several times," says Herendeen.
Remaining Gaps in the Tree of Life
While reversing the evolutionary order of the sponge and comb jelly, Dunn's study also resolved some long-standing questions about other species. Among these was whether millipedes and centipedes are more closely related to spiders than to insects. The answer: spiders.
But despite these and other important evolutionary insights provided by Dunn's team, the tree of life remains a work in progress. "Scientists currently estimate that there are a total of about 10 million species of organisms on earth," says Dunn. "But so far, only about 1.8 million species--most of which are animals--have been described by science. Very few of these species have, so far, been positioned in the tree of life."
A Methodological Breakthrough
But at least some of the tree of life's remaining gaps will
|Contact: Lily Whiteman|
National Science Foundation