[ad_1]
A strange group of raptors dinosaurs, known as alvarezsaures, declined dramatically around 100 million years ago, from ostrich-sized predators that hunted early mammals and baby dinosaurs to anteaters the size of an chicken, according to paleontologists.
Alvarezsaures were slender theropods – a diverse group of two-legged dinosaurs with hollow bones and three-toed limbs, including Tyrannosaurus Rex and Velociraptor – which may have been feathered. There are 21 confirmed species of alvarezsaures dating from the late Jurassic period about 160 million years ago and the end of the Cretaceous about 66 million years ago.
In a new study, paleontologists examining the fossils of these dinosaurs found that the group’s size massively declined between 110 million and 85 million years ago. Before that, alvarezsaures weighed between 22 and 154 pounds (10 and 70 kilograms), but they quickly shrunk to under 11 pounds (5 kg), a species shrinking to just 0.3 pounds (0.15 kg).
Related: 7 surprising facts about dinosaurs
“Size reduction is very rare in Cretaceous theropod dinosaurs,” lead author Zichuan Qin, a doctoral student at the University of Bristol in the UK and the Institute of Paleontology and Paleoanthropology, told Live Science. vertebrates in China. By this time, most of the other dinosaurs were getting bigger, and the only other group to decrease in size was the theropod lineage that eventually evolved in modern day birds, he added.
Researchers suspect that a significant change in global ecosystems during the Cretaceous Period could be behind the change in diet and the rapid miniaturization of alvarezsaures.
Compare species
Until now, paleontologists had been baffled by the remarkable size differences within species of alvarezsaures. The largest species, The last Bonapartenykus, is over 460 times heavier than the smallest species, Parvicursor deleted, Qin said.
To understand why there was such a size discrepancy, the researchers compared the size and age of the alvarezsaures specimens they had collected, along with data from other studies, while taking extra care to s ‘ensure that the specimens were fully, or nearly fully, grown. They relied on growth rings in bones (much like tree rings) to estimate the maturity of their specimens.
“Including juveniles in the data set would profoundly influence the accuracy of the results,” Qin said.
The results revealed a threefold decrease in the average body size of alvarezsaurs over a period of about 25 million years, which is a “rapid jump” in terms of evolutionary time, Qin said.
As the alvarezsaures got smaller, they also exhibited physiological changes, the most notable of which was that their arms became much shorter and they lost all but one of their fingers. This change of arms was probably the result of a change in diet. The larger species had long arms with fingers and claws that would have allowed them to catch the prey they were hunting, while the smaller species would have been adapted to sting and sting social insects, such as ants and termites, inside their mounds.
The researchers also found that as the alvarezsaures shrank, their growth rate dropped dramatically, meaning it would have taken them longer to reach their maximum size, Qin said. But growth rates also varied widely between these smaller species, he added.
Change tactics
Next, the researchers looked into what might have caused this rapid shrinkage. Their main theory is that miniaturization is the result of an equally rapid change in the dinosaur ecosystem.
Around the same time the alvarezsaurs started to shrink, Earth known what is known today as the Terrestrial Revolution of the Cretaceous. During this time, between 125 million and 80 million years ago, there was a massive increase in the diversity and abundance of flowering plants.
With such flowering in these plants, social insects like ants, termites and the bees would have flourished, creating a new ecological niche that was most likely exploited by alvarezsaures who shrank to take advantage of the new food, Qin said. This new ecological niche has also led to the emergence of more species of alvarezsaurs than ever before, he added.
“At that time, this anthill niche was rare, which gave Alvarezsaurus a huge space to explore, ”Qin said.
The study was published online July 6 in the journal Current biology.
Originally posted on Live Science.
[ad_2]
Source link