Earliest bat shows flight developed before echolocation

Blogging on Peer-Reviewed ResearchTheir heads and bodies of bats have amassed an extraordinary array of adaptations that have make them lords of the night sky. Today, the thousand-plus types of bats make up a fifth of living mammal species. Richard Dawkins once described the evolution of bats as “one of the most enthralling stories in all natural history” and as of this week, the story has a clearer beginning.

OnychonycterisThe success of bats hinges on two key abilities: their mastery of flight, a feat matched only by birds and insects; and echolocation, the ability to navigate their way through pitch-blackness by timing the reflections of high-pitched squeaks. For evolutionary scientists, the big question has always been: which came first?

The ‘clawed bat’

Until now, fossil bats haven’t provided any clues for all of them show signs of both echolocation and flight. But a stunning new fossil, discovered by Nancy Simmons from the American Museum of Natural History is an exception and it provides a categorical answer to the long-running debate – the earliest bats could fly but could not echolocate.

The new creature hails from the Green River in Wyoming and is known as Onychonycteris, meaning “clawed bat”. Its fossils date back to about 52.5 million years ago and by comparing it to other prehistoric bats, Simmons found that it is the most ancient member of this lineage so far discovered. It acts as a ‘missing link’ in bat evolution, much like the famous Archaeopteryx hinted that birds may have evolved from dinosaurs.

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Dinosaurs grew fast, had teen pregnancies and died young

Blogging on Peer-Reviewed ResearchTyrannosaurusFor some dinosaurs, the best strategy was to grow fast and breed early. New fossil evidence suggests that at least three species, including celebrities like Tyrannosaurus and Allosaurus, were having sex in their teens. In this way, their pace of growth and maturity was closer to that of modern birds and mammals than it would be to a reptile scaled-up to the same size.

They also started to breed well before they had finished growing, which suggests that they lived relatively short and brutal lives and needed as much time as possible to reproduce before they met an untimely demise. Modern back-boned animals with high adult death rates use a similar strategy.

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Prehistoric meat-eating fungus snared microscopic worms

Blogging on Peer-Reviewed ResearchCowboys have been lassoing cattle for several centuries, but it turns out that fungi developed the same trick 100 million years ago when dinosaurs still walked the Earth.

A nematode-trapping fungal lassoAlexander Schmidt and colleagues from the Humboldt University of Berlin found evidence of this ancient Wild West scene in a beautiful chunk of French amber.

The amber piece lacked the transparent clear beauty of a jeweller’s piece and the debris and dirt inside it suggests that it came from tree sap that had fossilised after it had fallen to the ground. There, it perfectly preserved the species living in the leaf litter, including a species of predatory fungi and the small worms – nematodes – that Schmidt thinks it hunted.

The fungus’s weapons were single cells coiled into rings just 10 micrometres in diameter. A thousand of these tiny loops could fit in a centimetre, but they were more than large enough to accommodate a blundering nematode. Once a worm swam through, the fungi constricted its snare, trapping the animal.

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The social life of our extinct relatives

Blogging on Peer-Reviewed ResearchOne of our extinct evolutionary cousins, Paranthropus robustus, may have walked like a man but it socialised like a gorilla. Using only fossils, UCL scientists have found that P.robustus males were much larger than females, competed fiercely for mates and led risky lives under heavy threat from predators.

I wrote an article about the cool new finding for Nature Network. Here’s the opening and you can read the full article here.

A single fossil can tell you about the shape, diet and movements of an extinct animal but with enough specimens, you can reconstruct their social lives too.

Charles Lockwood of University College London used an unusually large collection of fossils to peer back in time at the social structures of one of our closest extinct relatives, Paranthropus robustus, which inhabited southern Africa between 1.2 million and 2 million years ago.

Sabre-toothed cats had weak bites

The sabre-toothed cat is one of the most famous prehistoric animals and there is no question that it was a formidable predator, capable of bringing down large prey like giant bison, horses, and possibly even mammoths. The two massive canines – the largest teeth of any mammal – are a powerful visual. But while they were clearly powerful weapons, scientists have debated their use for over 150 years.

Now, a new study shows that Smilodon, the most iconic of the sabre-tooths, had a surprisingly weak bite. They were a precision weapon that were used to deliver a single, final wound to an already subdued victim – the equivalent of an assasin’s stiletto rather than a swordsman’s blade.

Earlier suggestions pictured Smilodon using its teeth to hang onto the back of large prey, to slash their abdomens open, or to impale them at the end of a flying pouce. One of the most popular theories said that the cat would have used its teeth to sever arteries and airways with a decisive bite to the throat – a quicker technique than the suffocating neck bites used by modern lions.

Working out how strongly Smilodon could bite would go a long way towards deciding on one of these theories and to do that, palaeontologists have studied the animal’s fossilised skull. Even then, opinions have gone either way depending on which bit of the skull they looked at. The muscle attachment points suggest it has small jaw muscles, but the bite could have been powered from the neck. The lower jaw is smaller, but strongly built, lending weight to the idea of a powerful bite.

To get some clearer answes, Colin McHenry and colleagues from the University of Newcastle, Australia decided to put Smilodon‘s skull through a digital crash-test. They used a technique called ‘finite element analysis‘ or FEA, which is typically used in mechanical engineering and crash-testing for cars.

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Evidence that Velociraptor had feathers

In Jurassic Park, the role of Velociraptor was played by computer-generated reptilian actors, that bore little resemblance to the real deal. The actual dinosaur was smaller, slower and used its infamous claw to stab rather than disembowel. And now, scientists have found conclusive proof that it was covered in feathers.

Since Jurassic Park aired, dinosaurs like Velociraptor have received something of a makeover. It began in the late 1990s when Chinese palaeontologists found a stunning series of dinosaur fossils with distinct traces of feathers around their bodies. Some were just covered in a downy fluff, while others like Microraptor had fully-formed wings and were probably capable of true flight.

Quill knobs on the forearm of a VelociraptorThese species were primitive members of the dromaeosaurids, a group of small, agile predators that Velociraptor also belongs to. With feathered ancestors and evolutionary cousins, it was always extremely likely that Velociraptor also had a feathered coat but until now, that was always an educated guess.

Quill knobs

The breakthrough came from Alan Turner and Mark Norell from the American Museum of Natural History and Peter Makovicky of the Field Museum of Chicago. They were studying the forearm of a Velociraptor unearthed in 1998, when they noticed six evenly spaced knobs of bone on the back edge.

The team recognised these as quill knobs, small lumps of bone that act as attachment points for feathers. These knobs are direct evidence that Velociraptor carried a row of feathers on its forearm, probably about 14 by Turner’s count. You can see them in the top two images above. The bottom two show the equivalent structures in a modern vulture, and how feathers are attached to them.

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Did climate change kill off the Neanderthals? Not likely…

The reasons why the Neanderthals died off remain a mystery. One of the major theories says that they were the victims of major climate changes, but new evidence suggests that this is an unlikely scenario.

In an age where climate change driven by our own hand is poised to cause catastrophic changes to human life, it seems fitting to work out if shifting climates also doomed our evolutionary cousins, the Neanderthals.

A Neanderthal hunter - did he fail to compete with humans?The question of why the Neanderthals died out has been the source of fierce debate since the first bones were discovered in the early 19th century. Some scientists turned the finger of blame inwards, suggesting that early humans killed them off, either directly, through violence and the spread of new diseases, or indirectly by gradually out-competing them.

Others have accused changing climates. According to them, Neanderthals were adapted to cold environments and, being less flexible than humans, they were unable to cope with a warming post-Ice Age world.

Now, Chronis Tzedakis from the University of Leeds has found compelling evidence that the Neanderthals extinction was unlikely to have coincided with the extreme shifts in climate at the end of the last Ice Age.

While their findings don’t rule out the climate change model completely, they strongly suggest that it wasn’t a major factor in the Neanderthals’ downfall.

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Dinosaurs provide clues about the shrunken genomes of birds

I’m baaaack! So, newly married and after two weeks of honeymooning, I return to my regular blogging schedule, refreshed and relaxed.

Today is also an auspicious day – it’s been a year since I first started this blog and it’s completely exceeded all my expectations (in that some people are reading it, which is more than my predicted no people).

So, without further ado, the science. I haven’t had time to pen a new article, but here’s a slightly old one.

 

 

Tyrannosaurus had a genome half the size of a house mouseThere is a reason why there are no dinosaur geneticists – their careers would quickly become as extinct as the ‘terrible lizards’ themselves. Bones may fossilise, but soft tissues and molecules like DNA do not. Outside of the fictional world of Jurassic Park, dinosaurs have left no genetic traces for eager scientists to study.

Nonetheless, that is exactly what Chris Organ and Scott Edwards from Harvard University have managed to do. And it all started with a simple riddle: which came first, the chicken or the genome?

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Argentavis, the largest flying bird, was a master glider

The largest ever flying bird, Argentavis, was a giant predator, as big as a light aircraft. But how did such a giant take to the skies and stay there?

An artist rendering of ArgentavisSix million years ago, the skies of Argentina were home to fearsome predator – Argentavis magnificens, the largest bird to ever take to the air. It weighed in at 70kg and had a wingspan of 7m, about the same size as a Cessna 152 light aircraft.

Argentavis was a member of an extinct group of predatory birds understandably called the teratorns – ‘monster birds’. They are related to storks and New World vultures such as turkey vultures and condors. But Argentavis completely dwarfed even the massive Andean condor, weighing six times more and with a wingspan over twice as long (in the picture below, its silhouette is placed next to a bald eagle for scale).

There is no question that Argentavis flew. It has all the characteristics of modern flyers including light, hollow bones and strong, sturdy wings. It’s how it flew that palaeontologists have puzzled over, given its massive size in relation to modern birds.

Take-off

For a start, how did it get its large bulk off the ground in the first place? The heaviest living flier, the Great Kori Bustard, is over three times lighter than Argentavis, and even it can only take off after arduously ‘taxiing’ like a airplane.

Sankar Chatterjee from the Museum of Texas Tech University decided to model the giant’s flying style by running simulations with known fossils. He found that Argentavis simply couldn’t have generated enough lift from a running-take-off.

It needed height to get airborne, but it could manage with surprisingly little. Even a gentle down-slope of 10° and a light headwind would have given it enough extra power to avoid an embarrassing crash. Albatrosses and hang-glider pilots use the same technique today.

In the air

Argentavis’s formidable skeleton, in comparison to a bald eagle.Once in the air, the flapping flight that small birds use was out of the question for the giant predator. By studying its skeleton, Chatterjee estimated the maximum amount of power that its flight muscles could have generated. And while substantial, it was still 3.5 times less than the minimum amount of power needed to fly.

Instead, Chatterjee believes that Argentavis was a master glider. It was capable of soaring for great distances at a shallow angle of 3°, continually re-shaping its wings to control its glide.

Unlike flapping, the efficiency of gliding doesn’t change very much with size, if a bird sticks to the standard body plan. So despite its enormity, Argentavis sailed through the air with as much grace as much smaller species like the buzzard or white stork.

Like modern soarers, Chatterjee believes that Argentavis used two techniques. By flying along the Andean ridges, it stayed aloft using upwards air currents produced by wind deflected up the cliffs. The several fossils found at the Andean foothills support his idea.

Because of its efficient gliding, it could stay aloft using relatively slow drafts of wind. Chatterjee calculated its top speed at about 70 km/h, allowing it scan vast tracts of land for prey. It’s a very energy-efficient style and today, eagles and vultures use it to great effect, sometimes covering hundreds of miles without a single wing flap.

Hot air

When the bird switched from the mountains to the wide, open spaces of the pampas, it switched to a different method – thermal soaring, where rising columns of hot air provided it with lift.

Thermals are hot rising columns of air.Popcorn-like cumulus clouds betray the location of thermals, and by circling around one, Argentavis could have risen through the air, giving itself enough height to soar to the next thermal. Despite its large size, Chatterjee calculated that Argentavis was manoeuvrable enough to manage the tight circular turns needed to stay within a thermal column.

Even with this reliance of thermals, Argentavis was pushing the limits of even gliding flight. Any heavier and it would have exceeded the maximum weight for safe gliding. So why are there no equally sized giants today?

Chatterjee thinks that the late Miocene’s climate provided the answer. Six million years ago, Argentina was much hotter and drier than it is today – just the weather needed for generating the powerful thermals needed to lift such a large bird.

Argentavis was beautifully adapted to take advantage of this large, open habitat, where it could travel across large distances in search of prey. And unlike modern condors, it was no mere scavengers. Its skull was as long as my forearm and ended in a formidable hooked beak – it was an active hunter, possibly taking prey on the wing. .

Reference: Chatterjee, Templin & Campbell. The aerodynamics of Argentavis, the world’s largest flying bird from the Miocene of Argentina. PNAS doi.10.1073/pnas.0702040104.

Images from PNAS paper and Apokryltaros

Related posts on extinct animals:
Bone-crushing super-wolf went extinct during last Ice Age
Microraptor – the dinosaur that flew like a biplane
How many types of dinosaur were there?
Tracks provide evidence of swimming dinosaurs

Bone-crushing super-wolf went extinct during last Ice Age

Being confronted with a pack of wolves is bad enough, but if you happened to be in Alaska some 12,000 years ago, things would be much, much worse. Back then, the icy forests were patrolled by a sort of super-wolf. Larger and stronger than the modern gray wolf, this beast had bigger teeth and more powerful jaws, built to kill very large prey.

The gray wolf - smaller than the Beringian variety, and with weaker jawsThis uber-wolf was discovered by Jennifer Leonard and colleagues from the University of California, Los Angeles. The group were studying the remains of ancient gray wolves, frozen in permafrost in eastern Beringia, a region that includes Alaska and northwest Canada.

These freezer-like conditions preserved the bodies very well, and the team found themselves in a unique position. They could not only analyse the bones of an extinct species, but they could extract DNA from said bones, and study its genes too.

For their first surprise, they found that these ancient wolves were genetically distinct from modern ones. They analysed mitochondrial DNA from 20 ancient wolves and none of them was a match for over 400 modern individuals. Today’s wolves are clearly not descendants of these prehistoric ones, which must have died out completely. The two groups shared a common ancestor, but lie on two separate and diverging branches on the evolutionary tree.

Hunter/scavenger

The genes were not the only differences that Leonard found. When she analysed the skulls of the Beringian wolves, she found that their heads were shorter and broader. Their jaws were deeper than usual and were filled with very large carnassials, the large meat-shearing teeth that characterise dogs, cats and other carnivores (the group, not meat-eaters in general).

The overall picture is that of a skull specially adapted to bite with tremendous force. These ancient wolves were hypercarnivores, specialised for eating only meat and killing prey much larger than themselves. Leonard even suggests that the mighty mammoths may have been on their menu.

The eastern Beringian wolf was a formidable hunter that could also turn to scavenging - just like modern hyenas.Once prey was dismembered, the wolves would have left no bones to waste. With its large jaws, it could crush the bones of recent kills, or scavenge in times between hunts. Today, spotted hyenas lead a similar lifestyle.

The wolves’ teeth also suggest that bone-crushing was par for the course. The teeth of almost all the specimens showed significant wear and tear, and fractures were very common.

Their powerful jaws allowed the Beringian wolves to quickly gobble down carcasses, bones and all, before having to fend off the competition. And back then, the competition included many other fearsome and powerful hunters, including the American lion and the short-faced bear, the largest bear to have ever lived.

Evolution of a super-wolf

Leonard suggests that the ancestor of today’s gray wolf reached the New World by crossing the Bering land bridge from Asia to Alaska. There, it found a role as a middle-sized hunter, sandwiched between a smaller species, the coyote, and a larger one, the dire wolf.

When the large dire wolves died out, the gray wolf split into two groups. One filled the evolutionary gap left behind by the large predators by evolved stronger skulls and teeth. The other carried on in the ‘slender and fast’ mold.

The extinct super-wolf would have been able to hunt prey even larger than this bison.But in evolution, the price of specialisation is vulnerability to extinction. When its large prey animals vanished in the Ice Age, so too did the large bone-crushing gray wolf. Its smaller and more generalised cousin, with its more varied diet, lived to hunt another day.

Similar things happened in other groups of meat-eaters. The American lion and sabre-toothed cats went extinct, but the more adaptable puma and bobcat lived on. The massive short-faced bear disappeared, while the smaller and more opportunistic brown and black bears survived.

Leonard’s findings suggests that the casualties of the last Ice Age extinction were more numerous than previously thought. What other predators still remain to be found in the permafrost?

Reference: Leonard, Vila, Fox-Dobbs, Koch. Wayne & van Valkenburgh. 2007. Megafaunal extinctions and the disappearance of a specialized wolf ecomorph. Curr Biol doi:10.1016/j.cub.2007.05.072

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Related posts on studying extinct animals:

Inner ear size can predict a mammal’s agility
Tracks provide evidence of swimming dinosaurs
Death of dinosaurs did not lead to rise of modern mammals

Microraptor – the dinosaur that flew like a biplane

Tracks provide evidence of swimming dinosaurs

It’s amazing how much you can learn about an animal from the tracks it leaves behind. In the case of dinosaurs, tracks that have lasted for millions of years tell us how fast they moved or whether they travelled in groups. Now, a unique set of tracks discovered in Spain tell us that at least some types of dinosaur could swim*.

The track in question is preserved in the sandstone of the Cameros Basin, one of the richest known sources of dinosaur tracks from the Cretaceous period. It stretches across 15 metres but consists of just six pairs of footprints; their maker was clearly a large animal.

A drawing of a swimming theropodThe ‘footprints’ are few in number, but their size and shape speak volumes. Each is actually a series of two or three long, slender scratch marks. That rules out a walking animal or a tip-toeing crocodile, both of which would have produced a broader, flatter print.

Ruben Ezquerra from the Fundación Patrimonio Paleontológico de La Rioja, who discovered the tracks, thinks that they are clear signs of a paddling carnivorous dinosaur.

Reconstruction

During the late Cretaceous, these sandstone flats would have been submerged under metres of water. As the predator swam through the lake, its torso would have floated near the surface while its legs propelled it along. As it swam, the tips of its toes lightly scratched at the sediment, creating the tracks that exist today.

Each of its paddling strides spanned about 2.5 metres; this was a large animal. Even so, its tracks suggest that it swam with exaggerated walking motions, in the same way that modern (and less fearsome) water-birds do.

The tracks even tell Ezquerra that the predator was swimming against the current. They are asymmetric with the right prints angled forty-five degrees to the left. These were caused by the animal pushing harder with its right foot, while its body was slightly angled against upriver.

Baryonyx, a fishing dinosaur from Cretaceous Spain - could it have left the Camperos tracks?In a way, we shouldn’t be surprised. The dinosaurs filled ecological vacancies that modern mammals now inhabit, and many large mammals from bears to (surprisingly) elephants prove to be surprisingly capable swimmers.

Some dinosaur species were even thought to be specialised fishermen and one of these, Baryonyx (above), lived in Spain during the early Cretaceous. Could it have made the tracks that Ezquerra found?

Reference: Ezquerra, Doublet, Costeur, Galton, Perez-Lorente. 2007. Were non-avian theropod dinosaurs able to swim? Supportive evidence from an Early Cretaceous trackway, Cameros Basin (La Rioja, Spain). Geology 35: 507-510.

Drawing: by Guillaume Suan, University Lyon.

*Note that prehistoric marine reptiles, like plesiosaurs and icthyosaurs, were not dinosaurs. All dinosaurs were land-living creatures.

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Death of dinosaurs did not lead to rise of modern mammals

New research has disproved the idea that the extinction of the dinosaurs allowed mammals the chance to take over the earth. Modern mammal groups only diversified sometime after the mass extinction. But if dinosaurs weren’t holding them back, what was?

While the mighty dinosaurs walked the earth, the ancestors of modern mammals were scurrying through the undergrowth beneath their feet, biding their time. Sixty-five million years ago, their opportunity came.

After the dinosaurs died out, the mammals took their time before inheriting the earth.During a massive extinction event, the majority of life on earth including the entire dinosaur line (with the exception of the birds) went extinct. And like ambitious young graduates whose boss got the sack, the mammals took their ecological place.

They rapidly diversified into a variety of different forms, eventually giving rise to the four thousand plus species that exist today. Right?

Wrong.

This is the picture that has been painted by scientists, textbooks and popular culture for decades. But in the light of new evidence, it just doesn’t measure up.

Olaf Bininda-Emonds, Andy Purvis and a team of international scientists reconstructed the tree of life that unites almost all living species of mammals. Using both fossils and genetic evidence, they worked out how modern species split apart from common ancestors over the last several million years.

The ancestors of modern mammals bided their time before diversifying after the dinosaurs died out.Their study turned up many surprises. For a start, they found that the seeds of modern mammal dynasties were planted much earlier than expected.

Almost twice the expected number of mammal groups were around to see the K/T boundary ­– the point in time where the dinosaurs and their peers went extinct. While the dinosaurs were still stomping about, the early mammals were busy exploiting smaller ecological niches.

But after the K/T boundary, the researchers found no sign of the expected rapid expansion of mammal lineages. As it turns out, mammals – or our forefathers at the very least – were not impatient go-getters ready to spring into action when opportunity knocked. In evolutionary terms, they were slackers.

The fuse that led up to the explosion of modern mammal groups was clearly longer than we thought. And Bininda-Emonds’s work suggests a reason for that too.

Mammals like Andrewsarchus evolved after the dinosaurs died out but went extinct themselves.As it happens, some mammal groups did diversify quickly after the dinosaurs’ coup de grace, giving rise to species like Andrewsarchus (right), a ferocious hooved predator. But these animals too eventually went extinct. Today, they have no living descendants.

These temporarily dominant groups, like the dinosaurs before them, may have kept our own ancestors in the evolutionary shade. As Purvis explains, “For the first 10 or 15 million years after the dinosaurs were wiped out, present day mammals kept a very low profile, while these other types of mammals were running the show.”

Perhaps they adapted to a still-changing climate only to be wiped out mere geological moments later. The forefathers of today’s mammals could have fared better because they played it slow and steady, and waited until conditions settled down before diversifying.

Reference: Bininda-Emonds, Cardillo, Jones, MacPhee, Beck, Grenyer, Price, Vos, Gittleman & Purvis. 2007. The delayed rise of present-day mammals. Nature 446: 507-512.

 

Related posts on dinosaurs and mammal evolution:
How many types of dinosaur were there?
Microraptor – the dinosaur that flew like a biplane
Tracks provide evidence of swimming dinosaurs
Bone-crushing super-wolf went extinct during last Ice Age
Orang-utan study suggests that upright walking may have started in the trees
Human cone cell lets mice see in new colours

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