Shrinking helped dinosaurs and birds to keep evolving
Although most dinosaurs went extinct 65 million years ago, one dinosaur lineage survived and lives on today as a major evolutionary success story -- the birds.
A study that has 'weighed' hundreds of dinosaurs suggests that shrinking their bodies may have helped the group that became birds to continue exploiting new ecological niches throughout their evolution, and become hugely successful today.
An international team, led by scientists at Oxford University and the Royal Ontario Museum, estimated the body mass of 426 dinosaur species based on the thickness of their leg bones. The team found that dinosaurs showed rapid rates of body size evolution shortly after their origins, around 220 million years ago. However, these soon slowed: only the evolutionary line leading to birds continued to change size at this rate, and continued to do so for 170 million years, producing new ecological diversity not seen in other dinosaurs.
A report of the research is published in PLOS Biology.
'Dinosaurs aren't extinct; there are about 10,000 species alive today in the form of birds. We wanted to understand the evolutionary links between this exceptional living group, and their Mesozoic relatives, including well-known extinct species like T. rex, Triceratops, and Stegosaurus,' said Dr Roger Benson of Oxford University's Department of Earth Sciences, who led the study. 'We found exceptional body mass variation in the dinosaur line leading to birds, especially in the feathered dinosaurs called maniraptorans. These include Jurassic Park's Velociraptor, birds, and a huge range of other forms, weighing anything from 15 grams to 3 tonnes, and eating meat, plants, and more omnivorous diets.'
The team believes that small body size might have been key to maintaining evolutionary potential in birds, which broke the lower body size limit of around 1 kilogram seen in other dinosaurs.
'How do you weigh a dinosaur? You can do it by measuring the thickness of its leg bones, like the femur. This is quite reliable,' said Dr Nicolás Campione, of the Uppsala University, a member of the team. 'This shows that the biggest dinosaur Argentinosaurus, at 90 tonnes, was 6 million times the weight of the smallest Mesozoic dinosaur, a sparrow-sized bird called Qiliania, weighing 15 grams. Clearly, the dinosaur body plan was extremely versatile.'
The team examined rates of body size evolution on the entire family tree of dinosaurs, sampled throughout their first 160 million years on Earth. If close relatives are fairly similar in size, then evolution was probably quite slow. But if they are very different in size, then evolution must have been fast.
'What we found was striking. Dinosaur body size evolved very rapidly in early forms, likely associated with the invasion of new ecological niches. In general, rates slowed down as these lineages continued to diversify,' said Dr David Evans at the Royal Ontario Museum, who co-devised the project. 'But it's the sustained high rates of evolution in the feathered maniraptoran dinosaur lineage that led to birds -- the second great evolutionary radiation of dinosaurs.'
The evolutionary line leading to birds kept experimenting with different, often radically smaller, body sizes -- enabling new body 'designs' and adaptations to arise more rapidly than among larger dinosaurs. Other dinosaur groups failed to do this, got locked in to narrow ecological niches, and ultimately went extinct. This suggest that important living groups such as birds might result from sustained, rapid evolutionary rates over timescales of hundreds of millions of years, which could not be observed without fossils.
'The fact that dinosaurs evolved to huge sizes is iconic,' said team member Dr Matthew Carrano of the Smithsonian Institution's National Museum of Natural History. 'And yet we've understood very little about how size was related to their overall evolutionary history. This makes it clear that evolving different sizes was important to the success of dinosaurs.'
Story Source:
The above story is based on materials provided by University of Oxford. Note: Materials may be edited for content and length.
Journal Reference:
- Roger B. J. Benson, Nicolás E. Campione, Matthew T. Carrano, Philip D. Mannion, Corwin Sullivan, Paul Upchurch, David C. Evans. Rates of Dinosaur Body Mass Evolution Indicate 170 Million Years of Sustained Ecological Innovation on the Avian Stem Lineage. PLoS Biology, 2014; 12 (5): e1001853 DOI: 10.1371/journal.pbio.1001853
Revealing the healing of 'dino-sores': Examining broken bones in 150-million-year-old predatory dinosaur
Scientists have used state-of-the-art imaging techniques to examine the cracks, fractures and breaks in the bones of a 150 million-year-old predatory dinosaur.
The University of Manchester researchers say their groundbreaking work – using synchrotron-imaging techniques – sheds new light, literally, on the healing process that took place when these magnificent animals were still alive.
The research, published in the Royal Society journal Interface, took advantage of the fact that dinosaur bones occasionally preserve evidence of trauma, sickness and the subsequent signs of healing.
Diagnosis of such fossils used to rely on the grizzly inspection of gnarled bones and healed fractures, often entailing slicing through a fossil to reveal its cloying secrets. But the synchrotron-based imaging, which uses light brighter than 10 billion Suns, meant the team could tease out the chemical ghosts lurking within the preserved dinosaur bones.
The impact of massive trauma, they discovered, seemed to be shrugged off by many predatory dinosaurs – fossil bones often showed a multitude of grizzly healed injuries, most of which would prove fatal to humans if not medically treated.
Dr Phil Manning, one of the paper's authors based in Manchester's School of Earth, Atmospheric and Environmental Sciences, said: "Using synchrotron imaging, we were able to detect astoundingly dilute traces of chemical signatures that reveal not only the difference between normal and healed bone, but also how the damaged bone healed.
"It seems dinosaurs evolved a splendid suite of defence mechanisms to help regulate the healing and repair of injuries. The ability to diagnose such processes some 150 million years later might well shed new light on how we can use Jurassic chemistry in the 21st Century."
He continued: "The chemistry of life leaves clues throughout our bodies in the course of our lives that can help us diagnose, treat and heal a multitude of modern-day ailments. It's remarkable that the very same chemistry that initiates the healing of bone in humans also seems to have followed a similar pathway in dinosaurs."
Co-author Jennifer Anné said: "Bone does not form scar tissue, like a scratch to your skin, so the body has to completely reform new bone following the same stages that occurred as the skeleton grew in the first place. This means we are able to tease out the chemistry of bone development through such pathological studies.
"It's exciting to realise how little we know about bone, even after hundreds of years of research. The fact that information on how our own skeleton works can be explored using a 150-million-year-old dinosaur just shows how interlaced science can be."
Professor Roy Wogelius, another co-author from The University of Manchester, added: "It is a fine line when diagnosing which part of the fossil was emplaced after burial and what was original chemistry to the organism. It is only through the precise measurements that we undertake at the Diamond Synchrotron Lightsource in the UK and the Stanford Synchrotron Lightsource in the US that we were able to make such judgments."
Story Source:
The above story is based on materials provided by Manchester University. Note: Materials may be edited for content and length.
Journal Reference:
- Jennifer Anné, Nicholas P. Edwards, Roy A. Wogelius, Allison R. Tumarkin-Deratzian, William I. Sellers, Arjen van Veelen, Uwe Bergmann, Dimosthensis Sokaras, Roberto Alonso-Mori, Konstantin Ignatyev, Victoria M. Egerton, Phillip L. Manning. Synchrotron imaging reveals bone healing and remodeling strategies in extinct and extant vertebrates. Interface Focus, 2014
My, What Big Claws! Dino Talons Used for Digging
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| New research has found that during their transition from carnivores to herbivores, therapod dinosaurs developed a large variety of claw shapes adapted to specific functions such as digging, grasping or piercing. Shown here, different claw shapes with functions. Credit: Dr. Stephan Lautenschlager, University of Bristol, UK, Single use only |
Giant, razor-sharp claws seen on herbivorous dinosaurs may have been used for digging, grasping or piercing, a researcher says.
The new findings shed light on the changes in claw form and function that occurred as birds evolved from their ancient dinosaur ancestors, the scientist added.
Meat-eating dinosaurs such as Tyrannosaurus rex and Velociraptor were all reptiles known as theropods; they relied on sharp teeth and claws to capture and kill prey. Many theropods may have possessed feathers, and research suggests modern birds evolved from these dinosaurs. [In Images: The Life of T. Rex]
However, not all theropods were carnivores.
"The stereotypical image of theropod dinosaurs is that of large, predatory and carnivorous animals," said study author Stephan Lautenschlager, a vertebrate paleontologist at the University of Bristol in England. "However, fossil findings in the last 15 to 20 years have shown that a number of different groups among theropods did not conform to this classical view. Many of these had apparently adapted to a different diet and become omnivores or herbivores — that is evident from the shape of the teeth and the morphology of the skull."
Lautenschlager investigated an unusual group of theropods known as therizinosaurs, which lived between 66 million and 145 million years ago in Asia and North America. These long-necked dinosaurs, which possessed coats of primitive downlike feathers, could reach up to 23 feet (7 meters) long with massive, razor-sharp claws more than 19 inches (50 centimeters) in length.
Credit: Dr. Stephan Lautenschlager, University of Bristol, UK, Single use only
"The large claws of Therizinosaurus cheloniformis have been enigmatic since they were first discovered in the 1950s," Lautenschlager said. "Originally it was thought they belonged to some sort of giant turtle. Later it became clear that they belonged to the group of dinosaurs known as therizinosaurs, and that other members of this group also had enlarged claws."
However, despite gigantic claws that might seem like ideal weapons for killing prey, therizinosaurs were herbivores. To understand how these plant eaters might have used their claws, Lautenschlager digitally scanned the claws of 65 theropod species and generated computer models to simulate how the dinosaurs might have used such talons. He also compared those reptile talons with claws from 40 mammal species, which scientists know the function of.
Lautenschlager discovered therizinosaurs may have used their giant claws for digging, grasping or piercing.
"The grasping function can roughly be compared with a rake or grappling hook," Lautenschlager said. "These claws were probably used to grasp a branch and pull it closer to the animal to reach parts of the vegetation otherwise out of reach." The dinosaurs may have used digging claws to unearth tasty roots.
Lautenschlager noted the changes seen in therizinosaur claws paralleled changes seen in their skulls and teeth that helped the animals adapt to changes in what they ate. This suggests changes in theropod diet were major drivers for skeletal changes in theropod evolution.
These findings might shed light on the evolution of modern birds from ancient theropods.
"Therizinosaurs were not directly ancestral to birds," Lautenschlager said. "Nevertheless, by understanding how different dinosaurs adapted to different ecological situations — for example, different food — we can better understand what changes in the skeleton were related to diet, to flight or something completely different."
Lautenschlagerdetailed his findings online May 7 in the journal Proceedings of the Royal Society B.
http://www.livescience.com/45401-dinosaur-claws-used-for-digging.html
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