Theropods are meat-eating dinosaurs that inhabited the prehistoric Earth and varied in size from the bus-sized Tyrannosaurus rex to the tiny Velociraptor that is the size of a dog.
A team of scientists led by Ohio University investigated how such radically disparate dinosaur sizes evolved recently discovered, Phys.org reported. Surprisingly, they found that smaller and bigger theropod dinosaurs like these did not always become that way just by growing slower or faster.
What Tree Rings in Dinosaur Bones Reveal
In the new paper titled "Developmental Strategies Underlying Gigantism and Miniaturization in Non-avialan Theropod Dinosaurs," published in Science, researchers including Ohio University professor Patrick O'Connor and Ph.D. student Riley Sombathy discovered through bone analysis that there was no relationship between growth rate and body size.
Paleontologist Michael D. D'Emic, the lead author of the study from Adelphi University, said that most animals are thought to evolve to be larger by growing faster, but the new research shows that it is just as likely as bigger and smaller animals grow for longer or shorter periods during growth spurts.
Bones of many animals, like dinosaurs, slowed or paused growth each year and left tree rings that show the age of an animal and can be used to estimate their rate of growth. D'Emic added that these rings are called cortical growth marks. Widely spaced rings imply faster growth, whereas narrowly spaced rings indicate a slower growth rate.
The team measured about 500 tree rings in 80 theropod bones, wherein most of them are carnivorous species closely related to birds. They found no relationship between the growth rate and size, as some gigantic dinosaurs grew more slowly than modern alligators. More so, some small dinosaurs grew very fast, like mammals today.
O'Connor noted that the study opens the door to more research in the future, specifically on how animals regulate their growth. Changes in different growth control mechanisms at molecular or genetic levels majorly affect developmental strategies in theropod dinosaurs. Future research on modern organisms provides an opportunity to elucidate how they evolve in body size.
Implications of Findings Relate to Other Land Animals
Theropods are distinguished by their bipedal posture and a collection of physical characteristics. Theropods may have existed as long as 230 million years ago in South America during the Triassic Era.
According to Japan Times, the new study is the first to consider developmental mechanisms linked to bone growth and body size variation in a large group of carnivorous dinosaurs.
O'Connor said that although the study is focused on theropod dinosaurs, its implications extend to most land animals, enabling scientists to constrain the interplay among development, environment, genetics, and diversity of life.
For instance, birds are believed to have evolved from small feathered theropods during the Jurassic Period. D'Emic said that large birds grow quickly, while alligators grow very slowly and take years to reach the same weight as big birds.
RELATED ARTICLE : Ancestors of Sauropod Dinosaurs Were Bipedal, Likely Quick to Move 205 Million Years Ago
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