New research conducted at Adelphi University has shed light on the remarkable size of sauropods, the largest creatures to have ever roamed the Earth. According to the study, these long-necked dinosaurs, such as Brachiosaurus and Apatosaurus, achieved their enormous sizes multiple times over a span of 100 million years. Contrary to previous beliefs, the analysis suggests that around three dozen instances of size evolution occurred globally within the sauropod family.
The study, titled “The Evolution of Maximum Body Size in Sauropod Dinosaurs” and authored by paleontologist Michael D’Emic, employed a technique called ancestral state reconstruction. D’Emic gathered measurements of weight-bearing bones’ circumferences and correlated them with the weight of the corresponding animals. By mapping the reconstructed body masses of nearly 200 sauropod species onto their evolutionary tree, the researcher uncovered key insights into their size evolution.
The results indicate that sauropods attained their impressive sizes early on in their evolutionary history. Furthermore, with the emergence of each new sauropod family, one or more lineages independently reached extraordinary sizes. The largest sauropods, which arose approximately 100 million years ago, possessed unique characteristics, including distinct teeth and head shapes, as well as varying body proportions. This suggests that they occupied the ecological niche of large-bodied creatures in diverse ways.
The study also delved into the microscopic analysis of sauropod bones, revealing different growth rates among these dinosaurs. This implies that the record-setting sauropods had distinct metabolic traits. Interestingly, this pattern resembles that observed in mammals, which rapidly evolved substantial body sizes following the extinction of dinosaurs but later stabilized within the range of mammoth-sized creatures.
D’Emic’s findings challenge Cope’s rule, a popular theory from the 19th century that posits a gradual evolution of animal size over time. Instead, the study proposes that animals achieve varying body sizes based on their ecological context and the available niches, which may appear random when viewed on a larger scale.
While previous researchers have attributed sauropods’ immense size to their unique combination of features, D’Emic emphasizes that no single feature or set of features can differentiate the sauropods that surpassed the size of terrestrial mammals from those that did not.
Further research will focus on unraveling the reasons why certain sauropod lineages evolved into super-giants while others did not.