The blue whale is over 100,000 times bigger in size than the largest animal of the Cambrian period
Ever since animals first originated on the Earth about 550 million years ago (based on fossil records), evolution has favored larger animals. According to an extensive new study conducted by researchers at Stanford University, marine animals have been getting bigger since the Cambrian period (500-544 million years ago).
Average size of animals increased 150-fold
The increase in body size was not by chance. It can’t be explained by “random drift,” says Noel Heim, the lead author of the study. It indicates that bigger animals tend to fare better. Over the past 544 million years, the average size of marine animals has increased 150-fold. Today’s smallest sea creature is 10 times smaller than its counterpart of the Cambrian period.
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On the other hand, the big blue whale is over 100,000 times bigger in size than the largest animal of the Cambrian period. It shows that evolution over time skewed decisively towards bigger animals. The finding follows a more than a century old theory called “Cope’s Rule.” It was named after 19th century American paleontologist Edward Drinker Cope.
Cope observed that ancient ancestors of modern animals such as horses were much smaller. That means horses grew in size over time. Though the rule applies to most animals, it is not without exceptions. Most dinosaurs grew bigger until they died out. But birds that evolve from dinosaurs became smaller and lighter as they needed to fly.
Why evolution favored larger animals?
Dr Noel Heim wanted to test the Cope’s rule on marine animals. Heim’s team compiled a dataset of 17,208 groups, or genera, of marine animals. It included more than 60% of all the animal genera ever lived on Earth. To collect the body size data, they relied on the Treatise on Invertebrate Paleontology, a 50-volume book set. It contains detailed information of every invertebrate whose fossil records are known.
Soon, a pattern became apparent. The groups that included bigger animals tended to become more diverse over time. Researchers said larger species likely took advantage of being able to capture larger prey, burrow more efficiency and deeply in sediment, and move faster.
Findings of the study appeared in the latest issue of the journal Science.