How Dinosaurs Grew the World's Longest Necks
As paleontologists increasingly unearth evidence of feathers in prehistoric fossils, our conceptions of what dinosaurs looked like when they roamed the earth has gradually evolved.
Instead of the reptilian appearance we all recognize from childhood toys and films like Jurassic Park, many dinosaurs in fact more closely resembled birds, kind of like this recently discovered little guy, Eosinopteryx brevipenna, a flightless theropod dinosaur that roamed China during the Middle/Late Jurassic period.
Archaeopteryx, also known as Urvogel, the German word for "original bird" or "first bird," was first discovered in 1860 and later fossils of this species presented some of the earliest evidence of flight in these prehistoric animals.
An intermediate creature that was not quite dinosaur but not exactly a bird either when it lived 150 million years ago, Archaeopteryx had teeth, a long tail, and wings capable of flight with claws at the end for grabbing prey.
A century after the discovery of Archaeopteryx, paleobiologists increasingly found anatomical connections between birds and dinosaurs. In the 1970s, artists began to portray dinosaurs with feathers based on accumulating evidence.
Megapnosaurus, shown here, was another species with whom researchers began early to identify with feathers. A lightweight animal that could reach up to 10 feet in length and roamed Jurassic Zimbabwe, Megapnosaurus, also known as Syntarsus, traveled in packs and preyed on small reptiles and fish.
Many of the fossils unearthed that provided evidence of feathers had deteriotated over the eons they remained buried. It wasn't until 2010 that researchers identified color pigments in feathers from dinosaurs and early birds.
Sinosauropteryx, illustrated here, was a theropod dinosaur that had "simple bristles -- precursors of feathers -- in alternate orange and white rings down its tail," according to a description of the study's findings.
Given that so many feathered dinosaurs were in fact flightless, the purpose of the feathers has been a subject of debate. Some dinosaurs may have evolved feathers for social signaling; others had plumage to provide insulation.
In the cases of some dinosaurs, such as the two oviraptors, herbivores related to T. rex that lived during the Cretaceous period, researchers believe the feathers were used for mating displays, similar to modern-day peacocks and turkeys.
Jason Brougham/University of Texas
You might be fooled into thinking the animals in this illustration are something between a murder of crows and a band of blue jays. In fact they are Microraptors that lives more than 130 million years ago.
These four-winged, plumed dinosaurs were no larger than modern-day pigeons and sported iridescent tail feathers.
Researchers believe the shimmering plumage was likely used in mating and other social interactions.
Like the diversity among birds today, not all feathered dinosaurs were lightweight, agile animals. A massive tyrannosaur that lived in China until about 65 million years ago, Yutyrannus huali, meaning "beautiful feathered tyrant," grew up to 30 feet long and could weigh more than 3,000 pounds.
This titanic tyrannosaur, as it was described, significantly increases the size range for feathered dinosaurs.
In a stunning find published in the journal Science in 2011, paleontologists uncovered dinosaur feather preserved in amber that dated back some 79 million years ago.
This discovery provided scientists a new window into the evolution of feathers in terms of structure in the evolutionary timeline from dinosaurs to birds. Even shades of color remained well preserved in the amber.
How did the largest of all dinosaurs evolve necks longer than any other creature that has ever lived? One secret: mostly hollow neck bones, researchers say.
The largest creatures to ever walk the Earth were the long-necked, long-tailed dinosaurs known as the sauropods. These vegetarians had by far the longest necks of any known animal. The dinosaurs' necks reached up to 50 feet (15 meters) in length, six times longer than that of the current world-record holder, the giraffe, and at least five times longer than those of any other animal that has lived on land.
"They were really stupidly, absurdly oversized," said researcher Michael Taylor, a vertebrate paleontologist at the University of Bristol in England. "In our feeble, modern world, we're used to thinking of elephants as big, but sauropods reached 10 times the size elephants do. They were the size of walking whales."
To find out how sauropod necks could get so long, scientists analyzed other long-necked creatures and compared sauropod anatomy with that of the dinosaurs' nearest living relatives, the birds and crocodilians.
"Extinct animals — and living animals, too, for that matter — are much more amazing than we realize," Taylor told LiveScience. "Time and again, people have proposed limits to possible animal sizes, like the five-meter (16-foot) wingspan that was supposed to be the limit for flying animals. And time and again, they've been blown away. We now know of flying pterosaurs with 10-meter (33-foot) wingspans. And these extremes are achieved by a startling array of anatomical innovations." [Image Gallery: 25 Amazing Ancient Beasts]
Among living animals, adult bull giraffes have the longest necks, capable of reaching about 8 feet (2.4 m) long. No other living creature exceeds half this length. For instance, ostriches typically have necks only about 3 feet (1 m) long.
When it comes to extinct animals, the largest land-living mammal of all time was the rhino-like creature Paraceratherium, which had a neck maybe 8.2 feet (2.5 m) long. The flying reptiles known as pterosaurs could also have surprisingly long necks, such as Arambourgiania, whose neck may have exceeded 10 feet (3 m).
The necks of the Loch Ness Monster-like marine reptiles known as plesiosaurs could reach an impressive 23 feet (7 m), probably because the water they lived in could support their weight. But these necks were still less than half the lengths of the longest-necked sauropods.
In their study, Taylor and his colleagues found that the neck bones of sauropods possessed a number of traits that supported such long necks. For instance, air often made up 60 percent of these animals' necks, with some as light as birds' bones, making it easier to support long chains of the bones. The muscles, tendons and ligaments were also positioned around these vertebrae in a way that helped maximize leverage, making neck movements more efficient.
In addition, the dinosaurs' giant torsos and four-legged stances helped provide a stable platform for their necks. In contrast, giraffes have relatively small torsos, while ostriches have two-legged stances.
auropods' necks reached up to 50 feet (15 meters) in length, six times longer than that of the current world-record holder, the giraffe.Courtesy of PeerJ
Sauropods also had plenty of neck vertebrae, up to 19. In contrast, nearly all mammals have no more than seven, from mice to whales to giraffes, limiting how long their necks can get. (The only exceptions among mammals are sloths and aquatic mammals known as sirenians, such as manatees.)
Moreover, while pterosaur Arambourgiania had a relatively giant head with long, spear-like jaws that it likely used to help capture prey, sauropods had small, light heads that were easy to support. These dinosaurs did not chew their meals, lacking even cheeks to store food in their mouths; they merely swallowed it, letting their guts break it down.
"Sauropod heads are essentially all mouth. The jaw joint is at the very back of the skull, and they didn't have cheeks, so they came pretty close to having Pac Man-Cookie Monster flip-top heads," researcher Mathew Wedel at the Western University of Health Sciences in Pomona, Calif., told LiveScience.
"It's natural to wonder if the lack of chewing didn't, well, come back to bite them, in terms of digestive efficiency. But some recent work on digestion in large animals has shown that after about 3 days, animals have gotten all the nutrition they can from their food, regardless of particle size.
"And sauropods were so big that the food would have spent that long going through them anyway," Wedel said. "They could stop chewing entirely, with no loss of digestive efficiency."
What's a Long Neck Good For?
Furthermore, sauropods and other dinosaurs probably could breathe like birds, drawing fresh air through their lungs continuously, instead of having to breathe out before breathing in to fill their lungs with fresh air like mammals do. This may have helped sauropods get vital oxygen down their long necks to their lungs.
"The problem of breathing through a long tube is something that's very hard for mammals to do. Just try it with a length of garden hose," Taylor said.
As to why sauropods evolved such long necks, there are currently three theories. Some of the dinosaurs may have used their long necks to feed on high leaves, like giraffes do. Others may have used their necks to graze on large swaths of vegetation by sweeping the ground side to side like geese do. This helped them make the most out of every step, which would be a big deal for such heavy creatures.
Scientists have also suggested that long necks may have been sexually attractive, therefore driving the evolution of ever-longer necks; however, Taylor and his colleagues have found no evidence this was the case.
In the future, the researchers plan to delve even deeper into the mysteries of sauropod necks. For instance, Apatosaurus, formerly known as Brontosaurus, had "really sensationally strange neck vertebrae," Taylor said. The scientists suspect the necks of Apatosaurus were used for "combat between males — fighting over women, of course."
Taylor and Wedel detailed their findings online Feb. 12 in the journal PeerJ.
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