Sauropod dinosaurs — the largest-ever animals to roam the Earth — evolved to reach colossal body sizes several dozen times over. This is the conclusion of a new study from the US, which involved the analysis of hundreds of fossilised bones from the ancient behemoths. The researcher says that the apparently “random” way that different sauropods reached different sizes is, in fact, a reflection of each species’ particular ecological circumstances.
Paper author and palaeontologist Professor Michael D’Emic of New York’s Adelphi University said: “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.”
In his study, the researcher compiled the measurements of hundreds of weight-bearing sauropod bones, correlated with the weight of the particular species they belonged to.
He then used a technique called “ancestral state reconstruction” to map the estimated body masses of nearly 200 different sauropod species onto their evolutionary tree.
The analysis indicated that sauropods reached their exceptional sizes early on in their evolutionary history.
Moreover, with each new sauropod family to evolve, one or more lineages reached colossal sizes independently of each other.
Professor D’Emic said: “Before going extinct with the other dinosaurs (besides birds) at the end of the Cretaceous period, sauropods evolved their unrivalled sizes a total of three dozen times.
“These largest-of-the-largest sauropods were ecologically distinct, having differently shaped teeth and heds and differently proportioned bodies.”
This, he added, indicates that “they occupied the ‘large bodied’ niche somewhat differently from one another.”
When Professor D’Emic studied sauropod bones under the microscope, he found that different species also exhibited different rates of growth.
This, he said, suggests that the species that achieved record-setting sizes were metabolically distinct from their smaller counterparts.
This mirrors the pattern seen in mammals, which evolved relatively large body sizes quickly in the wake of the extinction of the dinosaurs some 66 million years ago.
According to the academic, sauropods would have evolved different body sizes depending on which ecological niches were available to them at the time.
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He said: “Other researchers have explained sauropods’ immense size in general based on their unique combination of features.”
However, he noted, “there is no one feature or set of features that characterises the sauropods that did surpass terrestrial mammal size from the ones that didn’t.”
With his initial study complete, Prof. D’Emic is now looking to untangle why certain lineages of sauropods reached “super-giant” sizes while others did not.
The full findings of the study were published in the journal Current Biology.
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