2023-05-09 10:37:45
Of all the creatures that have ever walked the Earth, sauropods, long-necked herbivorous dinosaurs, were undoubtedly the largest. Brachiosaurus, Apatosaurus, Titanosaurus… The Patagotitan swimsuitWithout going any further, with its almost 40 meters in length and 70 tons in weight, it is so far the ‘king among kings’, the largest animal of all time. But how did these giants manage to reach such enormous sizes? And why did they do it? A new study carried out by researchers at Adelphi University in New York has just revealed part of the secret. The results have just been published in ‘Current Biology’.
“Until now,” explains the paleontologist Michael D’Emiclead author of the study – sauropods were thought to have developed their exceptional sizes independently several times in their evolutionary history, but through new analysis, we now know that number is much higher, with around three dozen cases in over the course of 100 million years and around the entire world.”
To understand how the body size of sauropods evolved, D’Emic collected measurements of the circumferences of hundreds of the weight-bearing bones of those dinosaurs, and then related them to the estimated weights of the animals to which they belonged. He then used a technique called ‘ancestral state reconstruction’ to map the reconstructed body masses of nearly 200 sauropod species along their evolutionary tree.
The results show that sauropods already had exceptional sizes early in their history. But what was most interesting was that, with each new evolutionary family, one or more lineages independently reached superlative size. Something that, in total, happened about 36 times.
“Before becoming extinct with the other dinosaurs at the end of the Cretaceous Period -explains the researcher- the sauropods evolved to their incomparable sizes a total of three dozen times. These sauropods, the largest of the largest, were ecologically distinct, had differently shaped teeth and heads, and bodies of different proportions, indicating that they filled the ‘big body’ niche somewhat differently from each other.”
not all were the same
Microscopic study of their bones revealed that these dinosaurs also had different growth rates, suggesting that those that reached record sizes were metabolically different. Which, surprisingly, mirrors the pattern of mammals, which also rapidly evolved to very large body sizes in the wake of the extinction of the dinosaurs, before stagnating in the range of giant mammoths.
D’Emic’s findings contradict the so-called ‘Cope Rule’, the popular 19th century theory that the size of animals evolves over time. Instead, the new study envisions animals reaching different body sizes depending on their ecological context and available niches, which can appear random when viewed on a large scale.
“While, in general, other researchers have explained the immense size of sauropods based on their unique combination of features,” concludes D’Emic, “the truth is that there is no one feature or set of features that distinguishes sauropods that exceeded the size of land mammals of those that did not.
Unraveling why precisely these lineages developed to their supergiant sizes while most did not will be the next step in the research.
#Sauropods #supergiants #times #history