Over evolutionary history, many different species of animals have evolved very large body sizes. The general consensus has been that an animal grows to a large size based on an increase in growth rate. However, very few studies have explored this question across many species within a comparative phylogenetic framework. In new research, paleontologists looked across a large dataset of theropod dinosaurs, which had an array of body sizes. They found evidence supporting changes in growth rate contributing to body size change, but also found that changes in the duration of growth played a large role.
“Most animals are thought to evolve to be larger by growing faster than their ancestors, but this study shows that it’s just as likely that bigger and smaller animals grew for longer or shorter periods of time during growth spurts,” said Dr. Michael D. D’Emic, a paleontologist at Adelphi University.
“The bones of many animals, including dinosaurs, slowed or paused growth every year, leaving marks like tree rings that indicate the animal’s age and can be used to estimate the rate of growth. Rings like these are called cortical growth marks.”
“Widely spaced rings indicate faster growth and narrowly spaced rings tell us that an animal was growing more slowly.”
In the study, the researchers measured about 500 such growth rings in about 80 bones of theropod dinosaurs.
“We found that there was no relationship between growth rate and size,” Dr. D’Emic said.
“Some gigantic dinosaurs grew very slowly, slower than alligators do today. And some smaller dinosaurs grew very fast, as fast as mammals that are alive today.”
“Extinct animals like dinosaurs inspire awe because of how different they seem from our modern world, but they were animals that grew under similar constraints and environmental factors as those that exist today,” said Thomas Pascucci, a paleontologist at Adelphi University.
The study opens the door to future investigations of how…
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