by David Braun
“If I could shoot you back in a time machine, it would have been like going on safari, except you’d want something more robust than a Land Rover—maybe a tank,” he said. “The sauropods were probably beautiful animals if you were a long way away with binoculars,” he added.
“But up close, [they were] probably a nightmare.”
THE NOT-SO-FRIENDLY SKIES
Giant Bugs Once Roamed the Earth
Predatory dragonflies the size of modern seagulls ruled the air 300 million years ago, and it’s long been a mystery how these and other bugs grew so huge.
Dragonflies as big as seagulls? Oversized giant cockroaches? Why did these bugs get so big? To avoid oxygen overdose, one study hints.
Too Much of a Good Thing
The leading theory is that ancient bugs got big because they benefited from a surplus of oxygen in Earth’s atmosphere. But a new study suggests it’s possible to get too much of a good thing: Young insects had to grow larger to avoid oxygen poisoning.
“We think it’s not just because oxygen affects the adults but because oxygen has a bigger effect on larvae,” said study co-author Wilco Verberk of Plymouth University in the United Kingdom. “So a larval perspective might lead to a better understanding of why these animals existed in the first place, and maybe why they disappeared.”
Baby Bugs Can’t Control Their Gases
Fossils show that giant dragonflies and huge cockroaches were common during the Carboniferous period, which lasted from about 359 to 299 million years ago. During this time, the rise of vast lowland swamp forests led to atmospheric oxygen levels of around 30 percent—close to 50 percent higher than current levels.
According to previous theories about insect gigantism, this rich oxygen environment allowed adult bugs to grow to ever larger sizes while still meeting their energy needs.
For the new study, Verberk and colleague David Bilton instead focused on how varying oxygen levels affect stonefly larvae, which, like dragonflies, live in water before becoming terrestrial adults. Higher concentrations of oxygen in air would have meant higher concentrations dissolved in water.
TRUTH:
SEVENTY-FIVE PERCENT OF ALL ANIMALS ARE INSECTS.
The results showed that juvenile stoneflies are more sensitive to oxygen fluctuations than their adult counterparts living on land. This may be because insect larvae typically absorb oxygen directly through their skin, so they have little or no control over exactly how much of the gas they take in. By contrast, adult insects can regulate their oxygen intake by opening or closing valvelike holes in their bodies called spiracles.
While crucial for life, oxygen can be poisonous in large quantities: Humans exposed to excess oxygen can suffer cell damage leading to vision problems, difficulty breathing, nausea, and convulsions. It’s likely the larvae of many ancient insects also passively absorbed oxygen from water and were not able to regulate their oxygen intake very well—a big danger when oxygen levels were so high.
One way to decrease the risk of oxygen toxicity would have been to grow bigger, since large larvae would absorb lower percentages of the gas, relative to their body sizes, than small larvae. “If you grow larger, your surface area decreases relative to your volume,” Verberk explained.
Lower Oxygen Levels
The new theory could also explain why giant insects continued to exist even after Earth’s atmospheric oxygen levels began decreasing, he said. “If oxygen actively drove increases in body mass to avoid toxicity, lower levels would not be immediately fatal, although in time, they [would] probably diminish performance of the larger insects,” since adults would have evolved to require more oxygen and would get sluggish in air with lower levels, Verberk said.
“Such reduced performance will eventually have made it possible for other species to outcompete the giants.”
BIRD BRAINS
Brainy Birds
Out-Thought Doomed Dinosaurs?
Having a bird brain wasn’t such a bad thing 65 million years ago. It was these bigger bird brains that kept them alive while the dinosaurs and their teeny brains went extinct.
Birds survived the global catastrophe that wiped out their dinosaur relatives due to superior brainpower, a 2009 study suggests.
Bird Brains = Big Brains
A pair of prehistoric seabirds found in southeast England by Victorianera fossil hunters were examined by researchers from the Natural History Museum in London. The two 55-million-year-old skulls suggest the ancestors of modern birds developed larger, more complex brains than previously thought.
TRUTH:
RESEARCHERS HAVE FOUND THAT PREHISTORIC SEABIRDS’ BRAINS WERE NEARLY THE SAME SIZE AS THOSE IN BIRDS ALIVE TODAY.
This implies that bird ancestors had a mental edge over non-birdlike dinos and flying reptiles, so they were better able to adapt after the so-called K-T mass extinction event around 65 million years ago, said study co-author Angela Milner.
Some ancient groups of birds did go extinct, she noted, so it wasn’t feathers or warm-bloodedness that gave modern birds a leg up. “It had to be something else,” she said, “and it seems to be this bigger brain.”
Advantage, Birds
The study, published in 2009 in the Zoological journal of the Linnean Society, was based on two specimens from the Natural History Museum’s vast fossil collection. Odontopteryx toliapica belonged to an extinct group of giant, bony-toothed seabirds, while Prophaethon shrubsolei was a prehistoric relative of ternlike tropical seabirds.
Milner and colleagues used CT scans of the skulls to make models of the size and shape of the fossil birds’ brains. What they found is that the ancient bird brains were almost the same size as those in birds alive today. The older noggins also showed early growth of a brain region known as the wulst.
“It seems to be the area that’s involved in more complex behavior and cognition, such as being able to learn about your environment and remember it,” Milner said. So after the K-T event, she said, these birds “were just better equipped to deal with challenging physical conditions.”
Fossil bird skulls that have not been flattened out over time are extremely rare, and no examples are known from the time of the K-T event. But Milner says the brain advances seen in the 55-million-year-old birds would probably have begun more than 65 million years ago.
And fossils of the oldest known bird, Archaeopteryx, which lived 147 million years ago, reveal its brain was “nowhere near as well developed as the ones we looked at,” she said.
Desperately Seeking Fossils
Julia Clarke, a geoscientist at the University of Texas at Austin who was not involved with the study, says there are various competing theories to explain why birds outlived the dinosaurs. One idea is that the ancestors of all living birds came from the southernmost part of the southern supercontinent Gondwana, where they escaped the worst of the environmental fallout from the K-T event.
Another theory is that modern bird lines evolved in coastal habitats that also were less heavily impacted. As well as providing valuable new evidence for the evolution of birds, she said, the latest study offers an intriguing new theory that will motivate paleontologists to look harder and farther to find more fossils.
“We still desperately need good fossils sampling brain and skeletal features in the species that are very close but outside the [evolutionary tree] of all living birds,” Clarke said. “We can only get so close to understanding the brains of the earliest birds with the sample of known species currently available.”
IMPRESSIVE HEAD GEAR
Prehistoric “Shield”-Headed Croc Found
The prehistoric “ShieldCroc” had a fierce look, but weak jaws. Paleontologists say this “one of a kind” creature was more pelican than pro-wrestler when it hunted.
A new prehistoric croc sporting an odd head “shield” has been found in Morocco, paleontologists say. Dubbed ShieldCroc, the animal’s head appendage was surrounded by blood vessels and covered with a sheath like those seen in frilled din
osaurs, including Triceratops.
Scoop Like a Pelican
At 30 to 35 feet (9 to 11 meters) long, the river-dwelling monster would have preyed on other giant animals of the late Cretaceous, such as 13-foot-long (4-meter-long) coelacanths. But ShieldCroc likely boasted relatively weak jaws, at least compared with those of today’s crocodiles.
“It’s fairly certain that it belonged to a group of crocodyliforms—including the flat-headed crocs—that had really thin, weak jaws and weak chin joints,” said researcher Casey Holliday, a paleontologist at the University of Missouri. Crocodyliforms are part of a group known as the crocodilians, which includes modern-day alligators, caimans, and more.
TRUTH:
SCIENTISTS OFTEN USE THE HEAD SIZE OF AN ANIMAL TO ESTIMATE ITS TOTAL LENGTH.
“So they weren’t wrestling dinosaurs on the water’s edge. They would have been quick, snap feeders waiting for prey to come by and then grabbing it and swallowing it with large, basket-shaped mouths—something like a pelican would do,” Holliday said.
Showy Headpiece
A piece of ShieldCroc’s skull landed in Canada’s Royal Ontario Museum in the early 2000s, but Holliday and colleagues have only recently studied the specimen and its odd headpiece. It’s difficult to determine what purpose the shield served when the animal lived, some 99 million years ago, Holliday noted.
But after rigorous evaluation of the fossil and studies of comparative behaviors with modern crocodilians, scientists suggest the shield may have helped ShieldCroc regulate its temperature and communicate with other ShieldCrocs.
For instance, some crocodyliforms and living crocodilians, such as the Cuban crocodile, have horns on the sides of their heads, which males use to impress females and scare away other males. “We kind of see ShieldCroc having similar behaviors and showing off the roof of its head,” Holliday said.
An illustration of ShieldCroc snatching its prey (Photo Credit 10.7)
Despite these possible similarities with modern crocodilians, the animal appears to have been one of a kind, said Christopher Brochu, a University of Iowa paleontologist, who wasn’t involved in the study. “There’s nothing quite like this among the birds or the crocodilians, which are the two closest living relatives of this thing.”
Five Oddball Prehistoric Crocs
1. RatCroc—rodent-like, with buck teeth for rooting through the ground for tubers and simple animals
2. PancakeCroc—flat-bodied, lying motionless and waiting for prey to swim into its thin, 3-foot-long jaws
3. DuckCroc—used its long, smooth, sensitive nose to poke through vegetation and its hook-shaped teeth to capture frogs and small fish in shallow water
4. DogCroc—a plant-eater with lanky legs, which indicates it was quick enough to run into water if threatened
5. BoarCroc—a 20-foot-long “saber-toothed cat in armor” that preyed on dinosaurs with its three sets of fangs
Croc Evolution
ShieldCroc’s discovery in Morocco could suggest that modern crocs evolved in what’s now the Mediterranean—a theory that remains hotly debated among crocodilian experts. But there’s no doubt the animal provides evidence of astonishing crocodyliform diversity in the Southern Hemisphere during the late Cretaceous, said Holliday, who described the new species at the 2011 Annual Meeting of the Society of Vertebrate Paleontology in Las Vegas.
“It definitely points to … Africa [as] a melting pot of different crocodyliforms living in the same region at the same time,” Holliday said. “One lineage, including DogCroc, BoarCroc, and others tended to be terrestrial, while another group, including SuperCroc, were big, aquatic, predatory crocs. ShieldCroc represents another group and a more modern flavor of crocs.”
Widespread Crocodyliforms
With the discoveries of ShieldCroc and related species, University of Iowa’s Brochu said, “We’re beginning to realize just how diverse and even bizarre the crocodyliforms were in the Southern Hemisphere,” he said. “The group was extremely widespread, and in some places crocodyliforms may have been among the major predators and even herbivores. And in some places they really were simply bizarre.” For instance, “in the southern Mediterranean, including North Africa, we’re seeing these animals that look nothing like any living crocodilian.”
TOO BIG TO FLAP
Largest Flying Bird
Could Barely Get off Ground, Fossils Show
Taking off was no easy task for an enormous bird that lived in the Andes mountains six million years ago. How did this big bird get airborne?
The largest bird that ever flew was an expert glider but was too heavy to fly by flapping its wings, researchers say.
Getting off the ground was a challenge for the 155-pound (70-kilogram) Argentavis magnificens, a condorlike bird that lived in the Andes mountains and the pampas of Argentina about six million years ago. Despite its massive flight muscles and 21-foot (6.4-meter) wingspan, the giant bird probably could not generate enough lift to take off from a level surface, according to a new study.
Fly Like a Bird
NASA engineers have programmed a model airplane to look for rising columns of hot air called thermals and use them to soar like a bird, similar to the way the prehistoric Argentavis magnificens probably flew. This way of flight allows air currents to do most of the work required to gain altitude.
Excellent Glider
Like human hang gliders, Argentavis probably had to run downhill into a headwind to become airborne, said Sankar Chatterjee of Texas Tech University in Lubbock. “Takeoff capability is the limiting factor for the size of flying birds, and Argentavis almost reached the upper limit,” Chatterjee said. “Heavier birds such as the ostrich had to give up flight.” Once aloft, however, Argentavis was no ostrich. Despite weighing as much as 16 bald eagles, Chatterjee said, “it was an excellent glider, like a sail plane.”
“Mythological versions of giant soaring birds appear in religions all over the world. What we have done is shown that it would have been possible for a so-called monster bird to fly.”
Sankar Chatterjee
curator of paleontology, Texas Tech University
Going Up
The new understanding of Argentavis flight comes from an unusual collaboration between paleontologists and a retired aeronautical engineer. The researchers took measurements from Argentavis fossils and then conducted their analysis using a computer program designed to study flight performance in helicopters.
“Birds are commonly compared with aircraft, but in reality helicopters are a better analogy,” Chatterjee said. Unlike engine-powered airplanes, he noted, birds rely on their wings for both forward thrust and vertical lift, the two components necessary for flight.
Although Argentavis could not wing skyward on its own, the researchers say, it could have reached high altitudes by riding winds deflected upward over mountains. More commonly, particularly in open terrain, Argentavis probably gained elevation by circling inside rising columns of warm air, known as thermals.
The huge flyer may have traveled hundreds of miles by repeatedly riding thermal “elevators” and then soaring gradually back to earth, Chatterjee said.
(Photo Credit 10.8)
Some of the largest flying birds today, such as condors and eagles, pursue a similar strategy. Although capable of powered flight, these species save energy by letting air currents do most of the work required to gain altitude.
Predator or Scavenger?
In the past, researchers have disagreed as to whether Argentavis was a predator, like most hawks and eagles, or a scavenger. Chatterjee and co-author Kenneth Campbell, of the Natural History Museum of Los Angeles County, say fossil details indicate the species was an active predator.
“[The birds’ skull] was adapted for catching prey and swallowing it whole,” Campbell said. “Its jaw mechanics were not suited for tearing flesh from carcasses, as in vultures, nor for tearing prey animals apart for swallowing, as in eagles and owls.”
TRUTH:
O
NE OF THE LARGEST BIRDS TODAY IS THE ANDEAN CONDOR, WHICH HAS A WINGSPAN OF ABOUT 9 FEET AND WEIGHS 25 POUNDS.
But Paul Palmqvist, of the University of Malaga in Spain, has argued that a flying species as large as Argentavis must have been a scavenger. Palmqvist’s argument is based in part on a predictable relationship between body size and foraging area seen in predatory hawks and eagles today.
Given its huge size, Palmqvist says, a predatory Argentavis would not have been able to cover enough ground and locate enough prey to meet its daily needs. “A vulturelike behavior is more reasonable, as vultures have smaller range areas,” Palmqvist said. “Carrion is more available than living flesh.”
The new flight analysis, he said, also tends to support his view. “Given its lack of maneuverability, a predator this size would have a problem landing on its prey,” Palmqvist noted. But Chatterjee and Campbell said the species was certainly a capable enough flyer to attack live prey—probably rabbit-size mammals—from the air.
300-MILLION-YEAR-OLD BRAIN
Oldest Fossil Brain
Found in Kansas
Found in “bizarre” prehistoric fish, scientists have found a 300-million-year-old brain-the oldest fossil of its kind.
Digital x-ray images of a “bizarre” 300-million-year-old shark relative have revealed the oldest known fossilized brain, researchers announced in 2009.
