New find sheds light on dinosaur flight

Wednesday, July 16, 2014

The dinosaur's long tail probably worked like the elevator and flaps of an aircraft, helping to control the animal's pitch and reduce speed for landing (Stephanie Abramowicz/Dinosaur Institute NHM)

Stuart Gary

Fossils of the largest dinosaur capable of flight have been discovered in China, according to a new study.

A report in the journal Nature Communications, says the 1.2-metre-long raptor named Changyuraptor yangi, was covered with plumage, including 30-centimetre-long tail feathers.

This discovery shows this 125-million-year-old raptor was flying long before birds split off from dinosaurs, says one of the study's authors Dr Luis Chiappe, a palaeontologist at the Natural History Museum of Los Angeles County.

"What makes this special is its size," says Chiappe.

"This four-kilogram dinosaur is much bigger than previous dinosaurs that we thought could fly, so it extends our understanding of what these animals were capable of doing."

The long feathered tail is thought to have played an important flight role, given the raptor's relatively large body size.

Chiappe and colleagues believe the long tail worked like the elevator and flaps of an aircraft, helping the dinosaur to control up and down pitch movements, and reduce speed for landing.

"If you're a heavy animal you could injure yourself unless you can slow down to land safely," says Chiappe.

Four-winged dinosaur

Changyuraptor is part of a group of predatory, feathered, non-avian dinosaurs called Microraptorines which include several small 'four-winged' species.

"We refer to these as 'four-winged', not because they had four wings, but because they had very long feathers on their hind legs," says Chiappe.

He says the dinosaur's sharp steak-knife-like serrated teeth indicate "it was definitely a predator."

"Stomach contents from its close cousin the microraptor showed bird and fish remains," says Chiappe. "Presumably they also ate small mammals and lizards."

The dinosaur was discovered in north-eastern China's Liaoning Province, a region which has developed into a prolific dinosaur fossil bed over the last decade.

"This is an incredible place with spectacular fossils, offering us a ten-million-year window on an ecosystem that existed between 130 and 120 million years ago," says Chiappe.

Changyuraptor yangi lived in what was a temperate forest of mostly conifers, with an undergrowth of ferns and some of the earliest flowering plants.

The forest surrounded a series of interconnected lakes and streams, dominated by active volcanos erupting clouds of ash and deadly pyroclastic flows.

These flows pushed the remains of these animals into the lakes where they were covered by volcanic ash and sediments.

"This quick burial and lack of oxygen helped preserve this animal from predators and microbial decay, allowing us to find it," says Chiappe.

"To many people the idea of flying dinosaurs is a novel concept, feathered flight has always been assumed to be the domain of birds," says Chiappe.

"There's now plenty of evidence to show that birds were descended from dinosaurs, and we're also learning that these dinosaurs were also capable of flight."

Dinosaurs not warm or cold-blooded

Tuesday, July 8, 2014

Dinosaurs' higher metabolic rate allowed them to move faster making them a more dangerous predator.

Rachel Sullivan

Dinosaurs were neither warm-blooded like mammals, nor cold-blooded like reptiles, instead they were somewhere in between, suggests a new study.

Exploiting the middle ground as a strategy may have helped dinosaurs rule the Earth for more than 100 million years, scientists report today in the journal Science .

The question of whether dinosaurs were lumbering cold-blooded or active warm-blooded animals has been debated for decades, but finding a definitive answer has proven difficult.

Now, biologist John Grady from the University of New Mexico and colleagues, have developed a new method for analysing dinosaurs' metabolic rates.

Building on previous work by palaeontologists and physiologists, they created a large database on growth and energy in both living and extinct groups of vertebrates including 21 species of dinosaurs.
They then used statistical analyses and energetic models to determine the relationship between growth rate and energy use.

Annual growth rings in fossils were used to determine growth rates, while metabolic rates were estimated by using changes in body size as an animal grows from birth to adult (known as ontogenetic growth).

"We found that growth rate is a good indicator of energy use in living animals. Warm-blooded (endothermic) mammals grow 10 times faster than cold-blooded (ectothermic) reptiles, and metabolise 10 times faster; in general doubling one's metabolic rate leads to a doubling in growth rate," Grady explains.

However, when they examined the growth rates of dinosaurs, although there was some variation in the rate they grew, they had neither the high metabolic rate of mammals and birds, nor the low metabolic rate of reptiles.

"Surprisingly we found that, instead, they occupied the middle energetic ground."

Today, mesothermic animals are uncommon, but living species come from across the evolutionary spectrum, and include leatherback turtles, tuna, great white sharks and the echidna.

These animals at times rely on internally-generated metabolic heat to maintain body temperatures, while being subject to external temperatures in others.

"They generate enough heat to warm their blood above ambient temperature, but don't do anything to maintain it, such as shivering which humans do when they are cold," says Grady.

"Meanwhile, echidna body temperatures can fluctuate by up to 10 degrees when they are active."

Evolutionary advantage

Dinosaurs evolved around 200 million years ago, and competed for resources with ectothermic animals like lizards.

Their higher metabolic rate meant they could move faster making them a more dangerous predator, or more elusive prey, says Grady.

"A higher metabolic rate gave them other competitive advantages as well: they could grow faster and reproduce faster.

"But being completely warm-blooded like a mammal limits the maximum size an animal can reach — it is doubtful that a lion the size of T. rex would be able to eat enough wildebeasts (or elephants) without starving to death.

"With their lower food demands, however, the real T. rex was able to get really big while still maintaining their advantage over their competition."

As well as helping us understand how warm-blooded animals evolved, understanding dinosaurs' energy use challenges our understanding of how life operates, Grady explains.

"They were ecologically dominant for more than 100 million years, and understanding how they lived and what contributed to their dominance helps us understand why some animals win over others.

"Dinosaurs' intermediate lifestyle may have been the key to their evolutionary success. Against today's polarised landscape, dinosaurs stand out as a successful middle way."