"Dinosaurs that adapted their diets to consume termites saw a significant decrease in size"
In a groundbreaking discovery, a new study led by PhD student Zichuan Qin has shed light on a remarkable transformation in the evolution of alvarezsaurids, a group of two-legged predators that lived during the Late Jurassic to Late Cretaceous period (160 to 70 million years ago) in various parts of the world, including China, Mongolia, and South America.
The study, co-authored by experts such as Professor Michael Benton from the University of Bristol, Dr Qi Zhao, an expert on bone histology, and Professor James Clark, one of the first discoverers of tiny alvarezsaurs from Mongolia, was conducted at the University of Bristol and Institute of Vertebrate Paleontology and Paleoanthropology in Beijing. The findings of this study were published in the journal Current Biology under the title 'Growth and miniaturization among alvarezsauroid dinosaurs'.
According to the study, alvarezsaurs, which were slender predators that pursued lizards, early mammals, and baby dinosaurs as their diet for most of their time on Earth, underwent a significant change around 100 million years ago. They reduced in size and became specialized ant-eaters.
Zichuan Qin's calculations show that the body sizes of alvarezsaurs ranged from turkey to ostrich-sized for the first 90 million years they existed, averaging 30-40 kg. However, around 100 million years ago, there was a sudden drop in their body size, with the average size plummeting to that of a chicken. Some of the alvarezsaur specimens, especially the chicken-sized ones, were not all adults, and the study ensured to exclude those identified as babies and juveniles from the calculations.
This second miniaturization event in dinosaurs, as the study suggests, was not for flight, but to accommodate a completely new diet, switching from flesh to termites. The study's findings indicate that Zichuan Qin's ancestors had sharp teeth, flexible forelimbs, and big eyes, suggesting they had a mixed diet.
Interestingly, the claw shapes of alvarezsaurs also changed from grabbing and cutting to punching around the same time their body size dropped. Mononykus, a small alvarezsaur, had a short and stout arm with a modified finger that looked like a punchy little arm, ideal for punching a hole in the side of a termite mound.
Professor Xing Xu, a co-supervisor to Zichuan in Beijing, states that this is a very strange result, but it seems to be true. The study was also co-authored by Professor Jonah Choiniere, an expert who was first to report the earliest alvarezsaurs in China.
The Cretaceous Terrestrial Revolution occurred during this time, marking the emergence of modern-style forests and woodlands, with diverse plants and animals, including insects that specialized to pollinate the new flowers and to feed on their leaves, petals, and nectar. This revolution could have played a role in the evolution of alvarezsaurs, pushing them towards a diet change and subsequent miniaturization.
While the university where Zichuan Qin attended for his work on Alvarezsaurids is not yet known, this study has opened up a new chapter in our understanding of dinosaur evolution, revealing a fascinating transformation in the history of alvarezsaurs.
