The long-necked dinosaurs, sauropods, are famous for their extreme body sizes, evolving body masses several times greater than the next-heaviest terrestrial animals, elephant-like and rhinoceros-like mammals and duck-billed dinosaurs. New research provides insights into how these giant creatures achieved their record-breaking sizes over time.
“It was previously thought that sauropods evolved their exceptional sizes independently a few times in their evolutionary history, but through a new analysis, we now know that this number is much higher, with around three dozen instances over the course of 100 million years around the globe,” said Dr. Michael D’Emic, a vertebrate paleontologist at Adelphi University.
To investigate sauropod body size evolution, Dr. D’Emic compiled measurements of the circumferences of hundreds of weight-bearing bones, correlated with the weight of the animal they belonged to.
The researcher then used a technique called ancestral state reconstruction to map the reconstructed body masses of nearly 200 sauropod species onto their evolutionary tree.
The results show that sauropods reached their exceptional sizes early in their evolution and that with each new sauropod family to evolve, one or more lineages independently reached superlative status.
“Before going extinct with the other dinosaurs (besides birds) at the end of the Cretaceous period, sauropods evolved their unrivaled sizes a total of three dozen times,” Dr. D’Emic said.
“These largest-of-the-largest sauropods were ecologically distinct, having differently shaped teeth and heads and differently proportioned bodies, indicating that they occupied the ‘large bodied’ niche somewhat differently from one another.”
The microscopic study of their bones revealed that sauropods had different growth rates as well, suggesting that the record-setters were metabolically distinct.
This mirrors the pattern in mammals, which evolved very large body sizes quickly in the wake…
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