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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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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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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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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Microraptor – the dinosaur that flew like a biplane

Modern aircraft went through a bi-plane phase before settling on today’s two-wing design. Now, new research birds did the same thing. One of their ancestors was a dinosaur called Microraptor, that flew on two sets of wings arranged like a biplane.

We believe dinosaurs to be extinct but in truth, they surround us every day. All the world’s birds, from the pigeons of our cities to the gulls of our seasides, are descended from dinosaurs, and modern science now classifies the birds with their long-dead kin.

The gulf between dinosaurs and modern birds may seem huge, but the discovery of several feathered dinosaurs are seriously blurring the line between the two. And now, new research on the feathered dinosaur Microraptor reveals that birds may have evolved from dinosaur ancestors that flew not on two wings, but on four.

A Microraptor fossil with leg feathers highlightedThe link between dinosaur and bird was cemented in the last two decades, when palaeontologists unearthed hundreds of beautifully preserved fossils in the Liaoning province of China. Many of the newcomers were small predators, belonging to the same group as the famous Velociraptor (and indeed, most scientists believe that this Hollywood star was also covered in primitive feathers).

The new species run the full evolutionary gamut from flightless dinosaurs to flying birds. They range from Sinosauropteryx with its primitive, downy, proto-feathers to Caudipteryx, a dinosaur with proper flight-capable feathers, to Confuciusornis, a true bird.

Together, these species provide a tantalising snapshot of how small prehistoric predators transformed into the familiar fliers of today’s skies.

One of these species, Microraptor, stood out among the rest, for it had winged legs as well as arms (see image above, white arrow). The animal’s metatarsal bones were covered in long, asymmetric flight feathers.

Their shape is clearly designed to produce lift during flight, but how Microraptor used its four wings has puzzled scientists. The species’ discoverers believed that by splaying its legs out sideways from its body, it held its wings in tandem like a dragonfly. But for Sankar Chatterjee and R. Jack Templin of Texas Tech University, the facts didn’t add up.

For a start, no bird or dinosaur has shown the ability to splay its legs out sideways and doing so would probably have dislocated the hip. Microraptor must have tucked its legs vertically beneath its body, like modern birds of prey do when they pounce.

Its leg flight feathers would only produce lift if the leading edge faced forward, against the flow of air. The leg feathers must therefore have protruded horizontally from the tucked legs.

A re-creation of Microraptor's biplane flight postureChatterjee’s revised pose makes Microraptor look like a feathered biplane, with the leg wings sitting below and just behind the main pair.

This new posture may also answer a long-standing debate about the origin of flight. Some scientists believe that bird flight evolved when ground-dwelling dinosaurs began to take to the skies. In contrast to this ‘ground-up’ theory, the ‘trees-down’ camp believes that tree-dwelling dinosaurs evolved flight to glide from tree to tree.

And this is exactly what Microraptor did. It lacked the muscles for a ground take-off and couldn’t get a running start for fear of damaging its leg feathers. But a computer simulation showed that Microraptor could successfully fly between treetops, covering over forty metres in an undulating glide.

It is unclear if Microraptor could truly fly or was just an exceptional glider. Certainly, its body plan shows many features that would make its avian descendants such great aeronauts. It had a large sternum for attaching powerful flight muscles and strengthened ribs to withstand the heavy pressures of a flight stroke.

Its long, feathered tail acted a stabiliser and rudder and its tibia (shin bone) was covered in smaller, backwards-facing feathers. Modern birds of prey carry similar feather ‘trousers’ and Chatterjee believes that they helped to reduce drag by breaking up turbulent airflow behind the animal’s leg.

A biplaneIt could be that Microraptor’s biplane design was just a failed evolutionary experiment. But Chatterjee thinks otherwise. He believes that the biplane model was a stepping stone to the two-wing flight of modern birds. As the front pair of wings grew larger and produced more lift, they eventually took over the responsibilities formerly shared with the hind pair.

This series of events stunningly mirrors the evolution of man-made aircraft. When the Wright brothers unveiled their new plane in 1903, little did they no that dinosaurs had got there first 125 million years ago.

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How many types of dinosaurs were there?

According to a new study, we have only scratched the surface of dinosaur diversity. With over 1300 new groups left to discover, fossil-hunters should be kept busy for decades to come.

Few creatures, living or dead, can capture our imaginations like dinosaurs. But those of us who were mesmerised by these creatures as children may find today’s cast strange and unfamiliar. Our well-known mainstays like Tyrannosaurus have been joined by Hollywood-sponsored favourites like Velociraptor, while new names are cropping up at great pace. Clearly, many new species are waiting to join the ranks. The question is: how many?

How many types of dinosaur were there?

There are many problems with estimating dinosaur numbers. For a start, the fossil record is incomplete and many species are known only from small fragments. The best information we have comes from the Dinosauria ­­– the dinosaur enthusiast’s bible – which put the number of known genera at 285 in its 1990 edition. ‘Genera’ is a term referring to groups of closely related species. For dinosaurs, it is a good an indicator of diversity as any, as most genera have only one representative.

Fossil-hunting renaissance

Since 1990, palaeontologists have been busy. Countries like China and Argentina have proven to be particularly rich digging grounds and the number of new groups being unearthed has accelerated at a tremendous rate. About 15 new genera are discovered every year, and the total has almost doubled to 527. The newcomers have included several record-breakers, including the massive Argentinosaurus, the tyrannosaur-trumping Giganotosaurus, and the minute Microraptor.

Now, Steve Wang and Peter Dodson from the University of Pennsylvania have plugged the data from the Dinosauria into an established mathematical model to work out how many genera are still undiscovered. By their reckoning, we have only begun to scratch the surface of dinosaur diversity. We have found less than a third of all possible groups, and a further 1300 or so are still hidden beneath our feet.

Extinction

The study also provides some tantalising hints as to what killed off the dinosaurs – a topic that is still hotly contested today. Wang and Dodson looked at the change in dinosaur diversity towards the end of the Cretaceous period and found that it remained fairly constant. While the analysis is not accurate enough to provide concrete answers, it weighs against the idea that the dinosaur dynasty was already in decline towards the end of their reign. Instead, their doom most likely came suddenly crashing down from the heavens in asteroid form.Birds probably evolved from small predatory dinosaurs like Microraptor.

Obviously, the method is not perfectly accurate, but if anything, the total estimate of about 1850 genera is most likely to be too low. For a start, Wang and Dodson have deliberately ignored the dinosaurs’ biggest triumphs – the birds, evolutionary descendants of dinosaurs and technically part of their group. The statistics also cannot account for the large number of genera that will never be discovered because by chance, they left no fossils.

For those genera that did fossilise, the researchers believe that they will not stay hidden for long. According to their study, will we have discovered about 75-90% of the remaining groups by the turn of the century. But this will only happen if we can sustain the current golden age of discovery. With China and Argentina rapidly yielding their secrets, new veins of fossils will need to be found and tapped.

These statistics should act as a clarion call to budding palaeontologists looking to make an impact. Go grab your shovel, here be dragons.

 

Reference: Wang & Dodson. 2006. PNAS Epub before print

Related posts on 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