Most people think of dinosaurs as big, ferocious and extinct reptiles. That’s largely true, but there are some misconceptions. Dinosaurs came in all shapes and sizes. Dinosaurs were the largest land animals of all time, but a great number of dinosaurs were smaller than a turkey.
Scientists have discovered the fossilized skeleton of a baby dinosaur representing a new species of coelurosaur, a group of theropods that includes ancient beasts like T. rex.
With a skull that’s barely taller than the diameter of a quarter, the remains are thought to have belonged to a dinosaur that was less than a year old when it died, and researchers think it measured just 3 feet (1 meter) long and weighed only 3 lbs. (1.3 kilogram).
But the baby may have grown into a bruiser in adulthood, possibly comparable to the 16-foot-long (5 meters) Monolophosaurus, a theropod dinosaur with a long bony crest on its head, or the 25-foot-long (7.6 m) Sinraptor, which means “Chinese plunderer.”
The discovery was made by James Clark, the Ronald B. Weintraub Professor of Biology, in the Department of Biological Sciences of GW’s Columbian College of Arts and Sciences. Dr. Clark, along with his then doctoral student Jonah Choiniere and a team of international researchers, found the dinosaur specimen in a remote region of Xinjiang in China in 2006.
Dinosaurs first appeared about 230 million years ago. They ruled the Earth for about 135 million years until an extinction event 65 million years ago wiped out all but bird-like dinosaurs. Scientists don’t agree entirely on what happened, but the extinction likely was a double or triple whammy involving an asteroid impact, choking chemicals from erupting volcanoes, climate change and possibly other factors.
Named Aorun zhaoi after a character in the Chinese epic tale “Journey to the West,” this dinosaur lived more than 161 million years ago, when the Late Jurassic Period was just getting underway, according to scientists at George Washington University who made the discovery in northwestern China.
James Clark, a GW biologist, and a team that included his then doctoral student Jonah Choiniere made the find in 2006 at the Shishugou Formation in a remote part of Xinjiang. Aorun is the fourth coelurosaur found in this formation, which has yielded a remarkable diversity of theropods, a group of mostly carnivorous dinosaurs that walked on two legs.
Dr. Choiniere, now a senior researcher at the Evolutionary Studies Institute at the University of the Witwatersrand in Johannesburg, South Africa, was a doctoral student in Biological Studies at GW when the discovery was made. He was also a Kalbfleisch Fellow and Gerstner Scholar at the American Museum of Natural History.
Aorun lived more than 161 million years ago, in the earliest part of the Late Jurassic Period. Its small, numerous teeth suggest that it would have eaten prey like lizards and small relatives of today’s mammals and crocodilians.
The beasts preserved in the Shishugou deposits date back to a period straddling the Middle and Late Jurassic Period, a time when dinosaurs had just begun to reach enormous sizes and dominate ecosystems on land, Clark’s website notes.
“All that was exposed on the surface was a bit of the leg,” Clark said in a statement. “We were pleasantly surprised to find a skull buried in the rock too.”
A closer look at the fossils showed that the bones had not fully developed.
The Jurassic Period was the second segment of the Mesozoic Era. It occurred from 199.6 to 145.5 million years ago, following the Triassic Period and preceding the Cretaceous Period.
During the Jurassic Period, the supercontinent Pangaea split apart. The northern half, known as Laurentia, was splitting into landmasses that would eventually form North America and Eurasia, opening basins for the central Atlantic and the Gulf of Mexico. The southern half, Gondwana, was drifting into an eastern segment that would form Antarctica, Madagascar, India and Australia, and a western portion that would form Africa and South America. This rifting, along with generally warmer global temperatures, allowed for diversification and dominance of the reptiles known as dinosaurs.
“We were able to look at microscopic details of Aorun’s bones and they showed that the animal was less than a year old when it died on the banks of a stream,” said Choiniere.
Choiniere is now a senior researcher at the Evolutionary Studies Institute at the University of the Witwatersrand in Johannesburg, South Africa. In addition to being a GW doctoral student at the time of the discovery, Choiniere was also a Kalbfleisch Fellow and Gerstner Scholar at the American Museum of Natural History.
This is the fifth new theropod discovered at the Wucaiwan locality by the team, co-led by Dr. Clark and Dr. Xu Xing of the Chinese Academy of Sciences.
This research was funded by the National Science Foundation Division of Earth Sciences and the Chinese National Natural Science Foundation.