Say dinosaurs or dinos for short and the image of those gigantic creatures with sharp teeth and/or huge tails swishing to and fro, towering over all the other creatures, immediately comes to mind! Yet, they were also there in small packages!

In fact the twist in the tale is that a new study suggests that alvarezsaurs reduced in size as they became ant-eaters. This was 100 million years ago.

In a new study which is led by Zichuan Qin, looks at this unusual alvarezsaurs. Qin, is a PhD student at the University of Bristol and Institute of Vertebrate Paleontology and Paleoanthropology in Beijing.

Also read: New species of dinosaur — among the largest in the world – discovered in Australia

Qin took measurements of the body sizes of dozens of specimens of alvarezsaurs. They ranged from 10 to 70 kilograms. Thus they were in the size of a large turkey to that of a small ostrich. This was the norm through most of their existence when they reduced, reduced rapidly to the size of chickens. Strangely, their diet too changed as they became ant-eaters.

The period these dinosaurs lived is from the Late Jurassic to Late Cretaceous, that is 160 to 70 million years ago. They were found in several regions of the world including South America, China and Mongolia.

This species has been described as two-legged, and were predatory by nature at least for most of their time. Their diet included lizards, early mammals, and baby dinosaurs.

In an article in sciencedaily.com Prof. Michael Benton, said: "Perhaps competition with other dinosaurs intensified through the Cretaceous. The Cretaceous was a time of rapidly evolving ecosystems and the biggest change was the gradual takeover by flowering plants. Flowering plants changed the nature of the landscape completely, and yet dinosaurs mostly did not feed on these new plants. But they led to an explosion of new types of insects, including ants and termites."

Benton is one of Qin’s supervisors at Bristol’s School of Earth Sciences.

The revamping of the ecosystem is known as the Cretaceous Terrestrial Revolution. It marks the period during which modern-style forests and woodlands emerged. These had a variety of plants and animals, which included insects. The insects specialised in pollinating the new flowers and their diet included their leaves, petals and nectar.

Also read: A complete ban on wildlife trade key to contain Covid and other pandemics — AI expert

A major challenge in the study was to make sure that the many alvarezsaur specimens under the scanner, especially those which were chicken sized, were adults. Elaborating on this aspect for ScienceDaily, Dr. Qi Zhao, a co-author who is an expert on bone histology said: “Some of the skeletons clearly came from juveniles, and we could tell this from sections through the bone. These showed the ages of the dinosaurs when they died, depending on the number of growth rings in the bone. We were able to identify that some specimens came from babies and juveniles and so we left them out of the calculations."

In the first instance, eating of ants in dinosaurs may seem strange and amazing. Elaborating on this point for ScienceDaily, Professor James Clark in Washington DC said: "This was suggested years ago when the arms of Mononykus were reported from Mongolia. Mononykus was one of the small alvarezsaurs, just about 1 metre long, but probably weighing 4-5 kilograms, a decent-sized Christmas turkey. Its arm was short and stout and it had lost all but one of its fingers which was modified as a short spike. It looked like a punchy little arm, no good for grabbing things, but ideal for punching a hole in the side of a termite mound."

Incidentally, Clark is a co-author of the paper being discussed and also one of the first discoverers of tiny alvarezsaurs from Mongolia.

Throwing further light on alvarezsaur dinosaurs, Professor Jonah Choiniere in South Africa, who too is a co-author of the paper remarked: "Interestingly, alvarezsaur dinosaurs were indeed not small in size or ant eaters at start. Their ancestors, like Haplocheirus, are relatively large, close to the size of a small ostrich, and their sharp teeth, flexible forelimbs and big eyes suggest they had a mixed diet."

Choiniere was the first to report the earliest alvarezsaurs in China.

Qin who after taking all the body size measurements went ahead to map them across a dated evolutionary tree of the alvarezsaurs. Qin said: "My calculations show how body sizes went up and