Sharp measurement discount in dinosaurs that modified eating regimen to termites

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Painting: Artistic reconstruction of four representative Alvarez sauroids, Haplocheirus sollers (left), Patagonykus puertai (top center), Linhenykus monodactylus (bottom center) and Bannykus wulatensis (bottom right), which illustrate the body size and nutritional changes in Alvarez sauroid dinosaurs. Photo credit: Zhixin Han / artstation.com / xinyanjun

Dinosaurs were generally huge, but a new study of the unusual alvarez dinosaurs shows that they were reduced in size about 100 million years ago when they became specialized ant-eaters.

The new work is by Zichuan Qin, a Ph.D. Student at the University of Bristol and the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing. He measured the height of dozens of specimens and showed that for most of their existence they ranged from 10-70 kg, the size of a large turkey to a small ostrich, and then quickly fell on chicken-sized animals as they began a remarkable new diet Assumptions: Ant eating.

The alvarez dinosaurs lived in many parts of the world, including China, Mongolia, and South America, from the Late Jurassic to the Late Cretaceous (160 to 70 million years ago). They were slender, two-legged predators most of the time on Earth, chasing lizards, early mammals, and baby dinosaurs for food.

“Perhaps the Cretaceous period increased competition with other dinosaurs,” says Prof. Michael Benton, one of Zichuan’s supervisors at the Bristol School of Earth Sciences. “The Cretaceous Period was a time of rapidly evolving ecosystems and the biggest change was the gradual takeover by flowering plants. Flowering plants completely changed the nature of the landscape, and yet dinosaurs mostly did not feed on these new plants. But they led to an explosion of new insect species, including ants and termites. “

This restructuring of ecosystems was called the Cretaceous Terrestrial Revolution and marks the time when forests and forests emerged in the modern style with a variety of plants and animals, including insects, which specialized in pollinating the new flowers and getting off their leaves, petals and nectar to feed.

Great reduction in the size of the dinosaurs who changed their diet to include termites

Graphic: Bone tissue (osteohistological) sampling, development of body mass and explosive diversification of Alvarez sauroid. Photo credit: Zichuan Qin

A major problem with many specimens of alvarsaur, especially the chicken-sized ones, was that they were all fully grown. “Some of the skeletons were clearly from teenagers,” says Dr. Qi Zhao, co-author and expert in bone histology, “and we could see this from cuts through the bone. These showed the age of the dinosaurs when they died, depending on the number of annual rings in the bone. We were able to determine that some specimens come from babies and young animals and have therefore removed them from the calculations. “

Eating ants may be an amazing diet for dinosaurs. “This was suggested years ago when the arms of Mononykus were reported from Mongolia,” says Professor James Clark in Washington, DC, co-author of this work and also one of the first discoverers of tiny alvarez dinosaurs from Mongolia. “Mononykus was one of the little alvarez dinosaurs, only about 1 meter long but probably weighing 4-5 kilograms, a decent Christmas turkey. His arm was short and stocky and he had lost all but one finger, which was modified as a short thorn. It looked like a sturdy little arm, not good to grip, but ideal for punching a hole in the side of a termite mound. “

“Interestingly, alvarez dinosaurs were indeed not small or ant-eaters in the beginning,” says Professor Jonah Choiniere of South Africa, a co-author of the article who first reported on the earliest alvarez dinosaurs in China. “Their ancestors, like Haplocheirus, are relatively large, almost the size of a small ostrich, and their sharp teeth, flexible forelegs, and large eyes suggest they had a mixed diet.”

Zichuan Qin took all the measurements of his height and mapped them using a dated evolutionary tree of the alvarez dinosaurs. “My calculations show how body sizes increased and decreased in the first 90 million years in which they existed, from turkey to ostrich size and an average of 30-40 kg,” says Zichuan. “Then, 95 million years ago, their height suddenly dropped to 5 kg and their claws changed from grasping and cutting to striking.”

“This is a very strange finding, but it seems to be true,” said Professor Xing Xu, co-supervisor of Zichuan in Beijing. “All the other dinosaurs kept getting bigger, but one group of carnivores was shrinking and this was being linked to tree life and flying. They eventually became birds. We identified a second miniaturization event – but it wasn’t for” flight but to meet a completely new diet, the switch from meat to termites. ”

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More information:
Growth and miniaturization among alvarez sauroid dinosaurs, Zichuan Qin, Qi Zhao, Jonah N. Choiniere, James M. Clark, Michael J. Benton, and Xing Xu. Current Biology, 2021. Provided by the University of Bristol

Quote: Large size reduction in dinosaurs who changed their diet to include termites (2021, July 6), accessed on July 6, 2021 from https://phys.org/news/2021-07-sharp-size-reduction-dinosaurs- diet.html

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