Functional diversity in animals began at a slow pace and sped up over time, according to a new study from the Stanford School of Earth, Energy and Environmental Sciences.
The Cambrian explosion 542 million years ago gave rise to nine basic body forms among marine animals that are still found in the world in the modern age. As species evolved over hundreds of millions of years, variations in these same basic body forms assisted species in thriving within specific environmental niches. Despite these changes, the basic body plan remains the same as those seen in the ancient seas.
Stanford University researchers examined how the behavior of animals, known as ecological diversity, changed over time. They expected to find that the two sets of changes would largely parallel one another. Instead, investigators discovered that ecological diversity developed at a much slower rate than physical changes.
"The fossil record provides clear evidence that the basic body plans that all marine animals follow today evolved around the time of the Cambrian explosion 542 million years ago and almost all subsequent new species are variations on those themes. But what animals have been able to do with those body plans has changed dramatically and took much longer to reach the point that we see today," Jonathan Payne, a paleobiologist with Stanford University, said.
Data from around two-thirds of all marine fossils were studied, and placed into categories based on ecological functions. These groups were based on the habitat of the animal, its feeding habits and mobility. An example of this would be the difference between stationary sponges and free-roaming fish.
Stephen Jay Gould, a well-known evolutionary biologist who passed away in 2002, had proposed the idea that ecological functions evolved quickly during the Cambrian Explosion before settling into slower changes.
"Our evidence is very clear that, unlike basic body plans, the ecological functions of animals did not appear in an early burst at all. Rather, it's quite the opposite," Matthew Knope, lead author of the new study, said.
The study also revealed how ecological functions recovered following the two greatest extinctions in the history of the world, the Permian extinction 252 million years ago, as well as the extinction, 66 million years ago, that marked the end of the age of dinosaurs. The diversity of behaviors not only rebounded during these events, but filled an even greater number of niches than before, as predominant species died out, and were replaced with other forms of life.
Analysis of how functional differentiation in animals changed over time was published in the journal Nature Communications.
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