Size of marine creatures averages 150 times bigger than 540 million years ago
NOAA Photo Library/Wikimedia Commons
Marine animals have become much bigger over time, scientists report February 20 in Science. This finding lends evidence to Cope’s rule, which states that animals often evolve to be larger than their distant ancestors. The hypothesis takes its name from 19th century paleontologist Edward Drinker Cope, who noticed this trend in the fossil record.
The researchers compared body size measurements of animals over a period spanning from 542 million years ago, during the Cambrian Period, to today. The animals included species from more than 17,000 genera, among them trilobites, plesiosaurs (extinct reptiles with a long neck and flippers), whales and clams, as well as many less familiar creatures.
Marine animals today are on average 150 times larger than they were during the Cambrian, the researchers found. The smallest animals alive today — tiny crustaceans called ostracods —