Title: Study Reveals Surprising Evolutionary Process Behind Sauropods’ Massive Sizes
Subtitle: Sauropods achieved colossal sizes multiple times, defying popular theory
Date: May 10, 2023
A groundbreaking study conducted by Adelphi University has shed new light on the awe-inspiring size of sauropods, the largest creatures to have ever walked the Earth. Through meticulous measurements of weight-bearing bones and mapping the body masses of nearly 200 sauropod species, researchers have revealed that these super-giants evolved their massive sizes multiple times, challenging the widely accepted “Cope’s Rule” of the 19th century. The study suggests that ecological context and available niches played a crucial role in dictating the sizes of these prehistoric giants.
Sauropods, including iconic dinosaurs like Brachiosaurus and Apatosaurus, towered over all other land-dwelling animals. According to Professor Michael D’Emic, a paleontologist at Adelphi University and the author of the study published in Current Biology, sauropods’ remarkable sizes were previously believed to have evolved independently a few times. However, the new analysis reveals that this happened approximately three dozen times over a span of 100 million years worldwide.
To investigate the evolution of sauropod body sizes, D’Emic compiled measurements of bone circumferences and correlated them with each animal’s weight. He then utilized ancestral state reconstruction, a technique in evolutionary biology, to map the reconstructed body masses of nearly 200 sauropod species onto their evolutionary tree.
The results of the study indicate that sauropods achieved their exceptional sizes early on in their evolutionary history. With the emergence of each new sauropod family, one or more lineages independently reached superlative sizes. The analysis also found that these immense sauropods were ecologically distinct, featuring unique teeth, head shapes, and body proportions, suggesting they occupied the “large-bodied” niche differently from one another.
Moreover, microscopic examination of sauropod bones revealed different growth rates among these colossal creatures, implying that metabolic differences contributed to their record-breaking sizes. This parallel with mammals, which rapidly evolved large sizes after the extinction of dinosaurs, before reaching a plateau seen in mammoths, further reinforces the findings.
This new research challenges the widely accepted theory of “Cope’s Rule,” which suggests that animals’ sizes evolve over time. Instead, the study proposes that the attainment of different body sizes is closely linked to ecological context and the availability of niches, which may appear random when viewed on a larger scale.
While scientists have previously attributed sauropods’ immense size to a unique combination of features, Professor D’Emic highlights that there is no single defining feature that distinguishes sauropods that surpassed terrestrial mammal size from those that did not.
Untangling why certain sauropod lineages achieved super-giant sizes while others did not will be the next area of focus for researchers, as they strive to unravel the mysteries behind these incredible prehistoric creatures.
Reference:
“The evolution of maximum terrestrial body mass in sauropod dinosaurs” by Michael Daniel D’Emic, 8 May 2023, Current Biology.
DOI: 10.1016/j.cub.2023.02.067