Dinosaurs are Not Extinct, One Lineage Survives as Birds

Dinosaurs are not extinct and nearly 10,000 species exist in today's world in the form of birds, a new study reveals.

Despite the fact that the prehistoric large bodied dinosaurs vanished from Earth some 65 million years ago, the new finding led by scientists at Oxford University and the Royal Ontario Museum claims that one dinosaur lineage survived and evolved into birds.

The researchers suggest that shrinkage of their body size was the key to survival.

"Dinosaurs aren't extinct; there are about 10,000 species alive today in the form of birds. We wanted to understand the evolutionary links between this exceptional living group, and their Mesozoic relatives, including well-known extinct species like T. rex, Triceratops, and Stegosaurus," said Dr Roger Benson of Oxford University's Department of Earth Sciences, who led the study.

In this study the researchers estimated the body mass of 426 dinosaur species based on the thickness of their leg bone.  They noticed a rapid rate of body size evolution after their origin, which gradually declined and just a single evolutionary line led to birds that continued to alter the size and did so for 170 million years.

The dinosaurs were weighed using the thickness of leg bones like femur. They found that Argentinosaurus, the biggest dinosaur at 90 tons was 6  million times the weight of the smallest Mesozoic dinosaur, a sparrow-sized bird Qiliania that weighed 15 grams.

A great variation in the body mass was seen in the feathered dinosaur maniraptorans. This dinosaur line led to birds.  Velociraptor, birds and other forms weighed between 15 grams -3 tons and fed on meat, plants and more omnivorous diet.

 The rate of body size evolution on the dinosaur family tree was examined throughout the first 160 million years. If the close relatives were found to be of similar size it was evident that the evolution was slow.  But if the sizes varied that indicated a speedy evolution.

"What we found was striking. Dinosaur body size evolved very rapidly in early forms, likely associated with the invasion of new ecological niches. In general, rates slowed down as these lineages continued to diversify," said Dr David Evans at the Royal Ontario Museum, who co-devised the project. "But it's the sustained high rates of evolution in the feathered maniraptoran dinosaur lineage that led to birds -- the second great evolutionary radiation of dinosaurs."

The finding was published in PLOS Biology.