It turns out that the meek really may inherit the Earth. Bigger animals were more prevalent during ancient times but in the last 40 million years since the global mass extinction, the marine world was dominated by tiny fish. A new study by Lauren Sallan, a University of Pennsylvania researcher, found that a mass extinction 359 million years ago called the Hangenberg event caused a sudden and long term change in the vertebrate community.
This study suggests that small, fast-reproducing fish was naturally equipped with evolutionary benefit over larger species.
After a deep study by the researchers it was found that, in line with Cope’s rule, vertebrates slowly kept increasing in body size during the Devonian Period (419 to 359 million years ago).
Changes in the size of animals has been a debatable topic for a long time among paleontologists and evolutionary biologists. One of the most significant theories is Cope’s rule.
According to this rule the size of a particular group of animals has a tendency to increase gradually over time owing to the evolutionary benefits of larger body size, which include the ability to catch prey and avoid being hunted.
The research was reported in Science.
Sallan, an assistant professor in Penn’s Department of Earth and Environmental Science in the School of Arts & Sciences stated, “Rather than having this thriving ecosystem of large things, you may have one gigantic relict, but otherwise everything is the size of a sardine.”
“It doesn’t matter what is eliminating the large fish or what is making ecosystems unstable,” Sallan said. “These disturbances are shifting natural selection so that smaller, faster-reproducing fish are more likely to keep going, and it could take a really long time to get those bigger fish back in any sizable way.”
Additional theories suggest that animals also have a tendency to be larger in the presence of more oxygen, or in colder climates. Lilliput Effect is another similar theory and suggests that following mass extinctions, there is a short-term trend supporting small body size.
Michael J. Benton had earlier stated that the Lilliput effect in terrestrial ostracods is characterized by the extinction of large taxa and the rise of small-sized and elongate new forms.
Due to very little understanding of body-size trends after mass-extinctions, “a glaring oversight considering current declines in global fish populations.”
Sallan and her coauthor, Andrew K. Galimberti, now a graduate student at the University of Maine, aim to understand the body-size trends around the Hangenberg Event, collected dataset of 1,120 fish fossils.
All of these fossils were from the period between 419 to 323 million years ago. They also amassed body-size information from published papers, museum specimens, photographs and bits of fossils.
Once the Devonian period ended, “there were fish called arthrodire placoderms with large slashing jaws that were the size of school buses, and there were relatives of living tetrapods, or land-dwelling vertebrates, that were almost as large,” Sallan said.
After this was a period of mass extinction that witnessed over 97 percent vertebrate species vanishing from the face of this Earth.
Researchers concluded that after this, body size reduced and kept decreasing for quite some time – at least 40 million years.
Sallan says that many global fish populations are now endangered and ecologists fear that Earth may now be on the brink of a sixth major extinction event caused by human activities. She adds that this is an alarming issue because no one knows how long it will take for larger species to come back.