Category: Environment

{New research challenges a long-held hypotheses about how flight first developed in birds.}

Research by post-doctoral fellow Alexander Dececchi challenges long-held hypotheses about how flight first developed in birds. Furthermore, his findings raise the question of why certain species developed wings long before they could fly.

Dr. Dececchi, a William E. White Post-Doctoral Fellow in the Department of Geological Sciences and Geological Engineering, used measurements from fossil records and data from modern birds to test the evolutionary explanation for the origin of birds. Dr. Dececchi and his colleagues determined that none of the previously predicted methods would have allowed pre-avian dinosaurs to take flight.

“By disproving the idea that the predicted models led to the development of flight, our research is a step towards determining how flight developed and whether it can evolve once or developed multiple times in different evolutionary lines,” he says.

Dr. Dececchi and his colleagues examined 45 specimens, representing 24 different non-avian theropod species, as well as five bird species. After determining some critical variables from the fossils — such as body mass and wing size — they used measurements from living birds to estimate wing beat, flap angle and muscular output.

These values were used to build a model for different behaviours linked to the origins of flight such as vertical leaping and wing-assisted incline running (WAIR) — a method of evasion for many ground-based modern birds that has become a favoured pathway towards the origin of flapping flight in the paleontological literature. They also tested if any species met the requirements to take-off from the ground and fly under their own power.

“We know the dimensions and we know how modern birds muscles and anatomy work,” Dr. Dececchi says. “Using our model, if a particular species doesn’t reach the minimum thresholds for function seen in the much more derived birds — such as the ability to take off or to generate a certain amount of power — it’s safe to say they would not have been able to perform these behaviours or fly.”

The researchers found that none of the behaviours met the criteria expected in the pathway models. In fact, they found that almost all the behaviours had little or no benefit, outside of those species which evolved right before the origin of birds. When looking at WAIR specifically — the method that has been touted as an explanation for some early wing adaptations — the researchers found that it only was possible in a handful of large winged, small bodied species such as Microraptor, but found no evidence to suggest its use was widespread.

Dr. Dececchi says that the group’s findings suggest that wings, even those with large or ornately coloured feathers, could have initially served different purposes rather than flying such as signaling or sexual selection before the development of flight.

Dr. Dececchi explains that the question of whether flight evolved once or multiple times in multiple evolutionary tracks is an ongoing topic of debate. Many of the species studied lived tens of millions of years and thousands of miles apart, with a last common ancestor that existed 50 or 100 million years earlier — leading researchers to wonder if flight evolved once but was lost, or if different species stumbled upon the same solution.

“There is some evidence that they evolved in parallel — there may be some differences in the details between how each taxon flew, but they tend to converge on these same answers,” says Dr. Dececchi. “That, to me, is one of the most exciting questions that has come out of the past few decades of work in theropods.”

{New observations on urban versus rural birds shed light on the effects of human population expansion on wildlife, say authors of a new report.}

No need to head to the movie theater or download the video game app: Angry Birds can be found right in your backyard this summer–if you live in the suburbs, that is.

Virginia Tech researchers recently found that birds that live in suburban areas exhibit significantly higher levels of territorial aggression than their country counterparts. The results were recently published in Biology Letters.

“A possible reason for this is that these birds have less space but better resources to defend,” said Scott Davies, a postdoctoral associate in biological sciences in the College of Science. “Living near humans provides better food and shelter, but it also means more competition for these limited resources.”

Davies and co-author Kendra Sewall, an assistant professor of biological sciences in the College of Science, measured territorial aggression in 35 urban and 38 rural male song sparrows at three rural and three urban sites in the New River Valley during the spring of 2015.

The Virginia Tech and Radford University campuses served as the (sub)urban sites due to their levels of human impact. Rural sites included Kentland Farm and Heritage Park. In these settings, the researchers played a recording of a male song sparrow and observed how the territory-holding birds responded to a simulated intrusion from a neighbor.

Campus birds showed a higher level of aggression: they approached and remained near the speaker, flapped their wings furiously, engaged in loud singing and then began to produce ‘soft song’–a term that researchers use to describe the quiet, garbled noise that a bird makes, which is predictive of an impending attack.

Though rural birds still responded to a song intrusion, they did not respond as vigorously.

The researchers placed small leg bands on the birds to identify individuals, and recorded each individual’s responses twice, several weeks apart. The suburban birds were more territorial on both occasions, showing that their increased aggression persists throughout a breeding season.

The researchers’ observations shed light on the effects of human population expansion on wildlife. The world population is projected to reach 9.6 billion by 2050, according to the United Nations, increasing by more than 2 billion people. Though many animals avoid habitats that are impacted by humans, some species can adjust and live in suburban and even urban habitats.

“This finding supports past research showing that urban birds are more aggressive in defending their territories,” said Dr. Kiki Sanford, neurophysiologist and host of the This Week in Science and Stem Cell podcasts, who was not involved in the study. “We need to understand widespread behavioral differences between various species of urban and rural bird populations to get an idea of how urbanization will affect their survival and diversity in the future. Testosterone and population density are the usual predictors for aggression, but there are other influential factors like increased food availability in urban environments that need to be examined.”

Ongoing work in the Sewall lab addresses how expanding suburbanization impacts bird species, permitting them to adjust and persist despite changes in their habitat. Sewall is affiliated with the Fralin Life Science Institute and the Global Change Center at Virginia Tech.

“Predicting the impact that human population growth will have on wildlife requires studying the species that adjust and persist in human impacted habitats,” said Sewall. “Suburban sprawl is a primary form of human habitat change and though many species can survive in our backyards, their behavior and physiology may change to cope with shifts in resources and with new disturbances.”

{Scientists from the University of Oxford have shown that newly hatched ducklings can readily acquire the concepts of ‘same’ and ‘different’ — an ability previously known only in highly intelligent animals such as apes, crows and parrots.}

Ducklings and other young animals normally learn to identify and follow their mother through a type of learning called imprinting, which can occur in as little as 15 minutes after hatching. Imprinting is a powerful form of learning that can allow ducklings to follow any moving object, provided they see it within the species’ typical ‘sensitive period’ for imprinting.

In this new study, published in the journal Science, ducklings were initially presented with a pair of objects either the same as or different from each other — in shape or in colour — which moved in a circular path.

The ducklings therefore ‘imprinted’ on these pairs of moving objects before being tested for their preferences between different sets of objects. In these subsequent choice tests, each duckling was allowed to follow either of two pairs of objects composed of shapes or colours to which the duckling had not previously been exposed.

For example, if an individual duckling had originally been exposed to a pair of spherical objects, in the choice test it may have had to choose between following a pair of pyramids (same) or a pair made up of one cube and one cuboid (different).

If the birds had learned the relationship between members of the original moving pair, then they should have followed the pairs of novel objects showing that same relationship (either ‘same’ or ‘different’), even if they had never seen the test objects.

In the example above, ducklings that had been imprinted on two spheres should have followed the set of two pyramids, because they were the same as each other. This is exactly what the ducklings did.

About three-quarters of the ducklings preferred to follow the stimulus pair exhibiting the relationship they had learned in imprinting, and their accuracy was as good whether they had to learn the concept of equal or different, or whether they were tested with shapes or colours.

Professor Alex Kacelnik of Oxford University’s Department of Zoology, who has worked extensively on learning and decision-making in animals, said: ‘To our knowledge this is the first demonstration of a non-human organism learning to discriminate between abstract relational concepts without any reinforcement training. The other animals that have demonstrated this ability have all done so by being repeatedly rewarded for correct performance, while our ducklings did it spontaneously, thanks to their predisposition to imprint when very young.

‘And because imprinting happens so quickly, the ducklings learned to discriminate relational concepts much faster than other species, and with a similar level of precision.’

Antone Martinho, a doctoral student in Oxford’s Department of Zoology and the study’s first author, said: ‘While it seems surprising at first that these one-day-old ducklings can learn something that normally only very intelligent species can do, it also makes biological sense. When a duckling is young, it needs to be able to stay near its mother for protection, and an error in identifying her could be fatal.

‘Ducks walk, swim and fly, and are constantly changing their exact shape and appearance as they extend their wings or become partially submerged, or even change angle with respect to the viewer. If the ducklings just had a visual “snapshot” of their mother, they would lose her. They need to be able to flexibly and reliably identify her, and a library of concepts and characteristics describing her is a much more efficient way to do so, compared with a visual memory of every possible configuration of the mother and her environment.

‘Still, this is an unexpected feat for a duckling, and a further reminder that “bird-brain” is quite an unfair slur.’

The discovery of relational concept learning in a new species and in a newly hatched baby bird suggests that this ability may not be as rare or as difficult as previously thought.

Professor Kacelnik added: ‘It may mean that relational concepts are adaptively useful or even necessary to a wider variety of animal. Most animals will, like the ducklings, need identification mechanisms that are robust to natural variation. A challenge we face now is to identify the processes by which the animals’ brains achieve it.’

{Dinosaurs are often depicted in movies as roaring ferociously, but it is likely that some dinosaurs mumbled or cooed with closed mouths, according to a study published online in the journal Evolution that will be in the August print edition.}

The research examines the evolution of a specialized way birds emit sound — closed-mouth vocalization. The study emerges from a new collaboration, funded by a grant from the Gordon and Betty Moore Foundation, to understand the origin and evolution of the unique vocal organ of birds and the large array of sounds it can produce. Because birds descended from dinosaurs, the research may also shed light on how dinosaurs made sound.

Closed-mouth vocalizations are sounds that are emitted through the skin in the neck area while the beak is kept closed. To make them, birds typically push air that drives sound production into an esophageal pouch rather than exhale through the open beak. The coos of doves are an example of this behavior. Compared with sounds emitted through an open beak, closed-mouth vocalizations are often much quieter and lower in pitch. Birds making closed-mouth vocalizations usually do so only to attract mates or defend their territory. At other times, they emit sounds through an open mouth.

To understand when and how closed-mouth vocalization evolved, researchers with The University of Texas at Austin, Midwestern University in Arizona, Memorial University of Newfoundland and the University of Utah used a statistical approach to analyze the distribution of this vocal ability among birds and other reptilian groups. In total, the researchers identified 52 out of 208 investigated bird species that use closed-mouth vocalization.

“Looking at the distribution of closed-mouth vocalization in birds that are alive today could tell us how dinosaurs vocalized,” said Chad Eliason, a postdoctoral researcher at The University of Texas Jackson School of Geosciences and the study’s co-author. “Our results show that closed-mouth vocalization has evolved at least 16 times in archosaurs, a group that includes birds, dinosaurs and crocodiles.

Interestingly, only animals with a relatively large body size (about the size of a dove or larger) use closed-mouth vocalization behavior.”

Tobias Riede, a physiology professor at Midwestern University and the study’s first author, said the association with large bodies is a matter of physics.

“The inflation of an elastic cavity could present a size-dependent challenge,” Riede said. “The lung pressure required to inflate a cavity depends on the tension in the wall of the cavity, and this tension increases for smaller body sizes.”

Researchers still are not certain about how the ancestors of modern archosaurs vocalized. But the occurrence of closed-mouth vocalization across birds and crocodiles — the two surviving groups of archosaurs — indicates that closed-mouth vocalization can emerge in diverse archosaur species depending on behavioral or environmental circumstances, Riede said.

“A cool thing about this work is the demonstration that closed-mouth behavior evolved many times,” Riede said. “That suggests it can emerge fairly easily and be incorporated into mating displays.”

Because dinosaurs are members of the archosaur group, and many had large body sizes, it is likely that some dinosaurs made closed-mouthed vocalizations in a manner similar to birds today, perhaps during mating displays. However, at this point in time, no direct fossil evidence exists to reveal what dinosaurs sounded like.

Julia Clarke, a professor at the Jackson School of Geosciences and co-author, said the study offers clues.

“To make any kind of sense of what nonavian dinosaurs sounded like, we need to understand how living birds vocalize,” she said. “This makes for a very different Jurassic world. Not only were dinosaurs feathered, but they may have had bulging necks and made booming, closed-mouth sounds.”

Future research by this collaboration will integrate information from fossils, experimental physiology, gene expression and sound modeling to understand the sounds that extinct early avian species, and perhaps their dinosaur ancestors, produced.

{Researchers have produced the first detailed study of the impact of solar parks on the environment, opening the door to smarter forms of farming and better land management.}

Environmental Scientists at Lancaster University and the Centre for Ecology and Hydrology monitored a large solar park, near Swindon, for a year.

They found that solar parks altered the local climate, measuring cooling of as much as 5 degrees Centigrade under the panels during the summer but the effects varied depending on the time of year and the time of day.

As climate controls biological processes, such as plant growth rates, this is really important information and can help understand how best to manage solar parks so they have environmental benefits in addition to supplying low carbon energy.

Their paper ‘Solar park microclimate and vegetation management effects on grassland carbon cycling’ is published in the Journal Environmental Research Letters.

Increasing energy demands and the drive towards low carbon energy sources have prompted a rapid increase in ground-mounted solar parks across the world.

This means a significant land use change on a global scale and has prompted urgent calls for a detailed understanding of the impacts of solar parks on the fields beneath them.

Dr Alona Armstrong, of Lancaster University, said the new study raises some key questions for the future.

She said: “Solar parks are appearing in our landscapes but we are uncertain how they will affect the local environment.”

“This is particularly important as solar parks take up more space per unit of power generated compared with traditional sources. This has implications for ecosystems and the provision of goods, for example crops, and services, such as soil carbon storage. But until this study we didn’t understand how solar parks impacted climate and ecosystems.”

“With policies in dominant economies supporting solar energy, it is important that we understand the environmental impacts to ensure we get more than just low carbon energy from the land they occupy.”

The authors of the study say understanding the climate effects of solar parks will give farmers and land managers the knowledge they need to choose which crops to grow and how best to manage the land; there is potential to maximise biodiversity and improve yields.

Dr Armstrong added: “This understanding becomes even more compelling when applied to areas that are very sunny that may also suffer water shortages.The shade under the panels may allow crops to be grown that can’t survive in full sun. Also, water losses may be reduced and water could be collected from the large surfaces of the solar panels and used for crop irrigation.”

{The well-known documentary “Plastic Planet” by Werner Boote starkly illustrates the dangers of plastic and synthetics for human beings and also shows how ubiquitous plastic is. Motivated by this multiple award-winning film, a family of five from Styria completely avoided plastics in their home environment for several months. Environmental medicine experts monitored them and analyzed their urine samples at the start of the experiment and again two months in. The main finding of this human biomonitoring study: even if one avoids plastics as far as possible in the home, a certain amount of exposure is inevitable from chemicals and from the environment.}

The well-known documentary “Plastic Planet” by Werner Boote starkly illustrates the dangers of plastic and synthetics for human beings and also shows how ubiquitous plastic is. Motivated by this multiple award-winning film, a family of five from Styria completely avoided plastics in their home environment for several months. Environmental medicine experts from MedUni Vienna monitored them and analyzed their urine samples at the start of the experiment and again two months in. The main finding of this human biomonitoring study: even if one avoids plastics as far as possible in the home, a certain amount of exposure is inevitable from chemicals and from the environment. The study has now been published in the leading journal “Environmental Research.”

In the middle of November 2009, family K started to eliminate plastics from their home, the first experiment of its kind in the world. All everyday items made of plastic were replaced by corresponding plastic-free products, as far as possible. This even went as far as replacing plastic toothbrushes with toothbrushes made from wood and animal hair (pig bristles). At the same time, they took great care only to eat food that had not (or hardly) been in contact with plastic.

“There are many aspects to the plastics problem. It concerns not only plasticizers (phthalates) but also flame retardants, fragrances and dye-stuffs. For example, even very low concentrations of phthalates can affect essential biological processes such as enzyme activity or the hormone system,” explains Hans-Peter Hutter of MedUni Vienna’s Institute of Environmental Hygiene. “In this human biomonitoring study, we wanted to find out whether complete avoidance of plastics could modify our bioburden.”

{{Bioburden unchanged}}

The family’s morning urine was measured at the start of the experiment and after a two-month period, during which they had avoided plastics at home — this only being possible to a limited extent at work and in school — to measure 14 phthalate metabolites and Bisphenol A (BPA), which have a health impact. The outcome: even though they avoided every possible contact with plastics at home, they still had a certain bioburden, so that the health effects are minimal. Hutter: “The experiment and study show: there is no way for us to avoid this exposure.” Moreover, the family in question was already very aware of following a healthy lifestyle, so that their exposure to plastics was already below average. That meant that the plastic avoidance campaign had even less effect upon their bioburden. Hutter: “In their case, it was impossible to achieve any further lasting reduction in the concentration of these ever-present substances.”

{{Call for a stricter chemicals policy}}

The environmental medicine experts therefore emphasize that it is very important to redouble efforts to implement a more restrictive chemicals policy, to help avoid plastics in everyday life — not only because of various substances that are harmful to health but also to avoid waste and to avoid spreading these substances into the environment (keyword: microplastics). Hutter: “For example, even just by using glass bottles instead of plastic bottles for mineral water, we could reduce environmental damage.”

In some cases the harmful exposure due to individual products is very small, says Hutter. This has always been the argument put forward by individual companies. “However, what is important is the total exposure due to the widespread use of plastics. Nowadays, this is very high.” Apart from plasticizers (phthalates), problematic substances include other so-called industrial chemicals, such as polybrominated diphenyl ethers, nonylphenol and Bisphenol A, which are associated with plastics. This is an area of research that the environmental medicine experts at MedUni Vienna and scientists from MedUni Vienna’s Centre of Public Health have been addressing for a long time.

{{No home for plastics}}

By following the link http://www.keinheimfuerplastik.at/ you can find a blog written by the family, describing the problems they encountered when trying to avoid plastic — whether out shopping, in the kitchen or when selecting toys.

{{Story Source:}}

The above post is reprinted from materials provided by Medical University of Vienna.

{The ability of finches, sparrows, and many other birds to see a visual world hidden to us is explained in a study published in the journal eLife.}

Birds can be divided into those that can see ultraviolet (UV) light and those that cannot. Those that can live in a sensory world apart, able to transmit and receive signals between each other in a way that is invisible to many other species. How they unlock this extra dimension to their sight is revealed in new findings from the Washington University School of Medicine in St. Louis.

The study reveals two essential adaptions that enable birds to expand their vision into the UV range: chemical changes in light-filtering pigments called carotenoids and the tuning of light-sensitive proteins called opsins.

Birds acquire carotenoids through their diets and process them in a variety of ways to shift their light absorption toward longer or shorter wavelengths. The researchers characterized the carotenoid pigments from birds with violet vision and from those with UV vision and used computational models to see how the pigments affect the number of colors they can see.

“There are two types of light-sensitive cells, called photoreceptors, in the eye: rods and cones. Cone photoreceptors are responsible for color vision. While humans have blue, green, and red-sensitive cones only, birds have a fourth cone type which is either violet or UV-sensitive, depending on the species,” says senior author Joseph Corbo, MD, PhD, Associate Professor of Pathology and Immunology.

“Our approach showed that blue-cone sensitivity is fine-tuned through a change in the chemical structure of carotenoid pigments within the photoreceptor, allowing both violet and UV-sighted birds to maximize how many colors they can see.”

The study also revealed that sensitivity of the violet/UV cone and the blue cone in birds must move in sync to allow for optimum vision. Among bird species, there is a strong relationship between the light sensitivity of opsins within the violet/UV cone and mechanisms within the blue cone, which coordinate to ensure even UV vision.

Taken together, these results suggest that both blue and violet cone cells have adapted during evolution to enhance color vision in birds.

“The majority of bird species rely on vision as their primary sense, and color discrimination plays a crucial role in their essential behaviors, such as choosing mates and foraging for food. This explains why birds have evolved one of the most richly endowed color vision systems among vertebrates,” says first author Matthew Toomey, a postdoctoral fellow at the Washington University School of Medicine.

“The precise coordination of sensitivity and filtering in the visual system may, for example, help female birds discriminate very fine differences in the elaborate coloration of their suitors and choose the fittest mates. This refinement of visual sensitivity could also facilitate the search for hidden seeds, fruits, and other food items in the environment.”

The team now plans to investigate the underlying molecular mechanisms that help modify the carotenoid pigments and light-sensitive protein tuning in a wide range of bird species, to gather further insights into the evolution of UV vision.

{When early terrestrial animals began moving about on mud and sand 360 million years ago, the powerful tails they used as fish may have been more important than scientists previously realized. That’s one conclusion from a new study of African mudskipper fish and a robot modeled on the animal.}

Animals analogous to the mudskipper would have used modified fins to move around on flat surfaces, but for climbing sandy slopes, the animals could have benefitted from using their tails to propel themselves forward, the researchers found. Results of the study, reported this week in the journal Science, could help designers create amphibious robots able to move across granular surfaces more efficiently — and with less likelihood of getting stuck in the mud.

Sponsored by the National Science Foundation, the Army Research Office and the Army Research Laboratory, the project involved a multidisciplinary team of physicists, biologists and roboticists from the Georgia Institute of Technology, Clemson University and Carnegie Mellon University. In addition to a detailed study of the mudskipper and development of a robot model that used the animal’s locomotion techniques, the study also examined flow and drag conditions in representative granular materials, and applied a mathematical model incorporating new physics based on the drag research.

“Most robots have trouble moving on terrain that includes sandy slopes,” said Dan Goldman, an associate professor in the Georgia Tech School of Physics. “We noted that not only did the mudskippers use their limbs to propel themselves in a kind of crutching motion on sand and sandy slopes, but that when the going got tough, they used their tails in concert with limb propulsion to ascend a slope. Our robot model was only able to climb sandy slopes when it similarly used its tail in coordination with its appendages.”

Based on fossil records, scientists have long studied how early land animals may have gotten around, and the new study suggests their tails — which played a key role in swimming as fish — may have helped supplement the work of fins, especially on sloping granular surfaces such as beaches and mudflats.

“We were interested in examining one of the most important evolutionary events in our history as animals: the transition from living in water to living on land,” said Richard Blob, alumni distinguished professor of biological sciences at Clemson University. “Because of the focus on limbs, the role of the tail may not have been considered very strongly in the past. In some ways, it was hiding in plain sight. Some of the features that the animals used were new, such as limbs, but some of them were existing features that they simply co-opted to allow them to move into a new habitat.”

With Ph.D. student Sandy Kawano, now a researcher at the National Institute of Mathematical and Biological Synthesis, Blob’s lab recorded how the mudskippers (Periopthalmus barbaratus) moved on a variety of loose surfaces, providing data and video to Goldman’s laboratory. The small fish, which uses its front fins and tail to move on land, lives in tidal areas near shore, spending time in the water and on sandy and muddy surfaces.

Benjamin McInroe was a Georgia Tech undergraduate who analyzed the mudskipper data provided by the Clemson team. He applied the principles to a robot model known as MuddyBot that has two limbs and a powerful tail, with motion provided by electric motors. Information from both the mudskipper and robotic studies were also factored into a mathematical model provided by researchers at Carnegie Mellon University.

“We used three complementary approaches,” said McInroe, who is a now a Ph.D. student at the University of California Berkeley. “The fish provided a morphological, functional model of these early walkers. With the robot, we are able to simplify the complexity of the mudskipper and by varying the parameters, understand the physical mechanisms of what was happening. With the mathematical model and its simulations, we were able to understand the physics behind what was going on.”

Both the mudskippers and the robot moved by lifting themselves up to reduce drag on their bodies, and both needed a kick from their tails to climb 20-degree sandy slopes. Using their “fins” alone, both struggled to climb slopes and often slid backward if they didn’t use their tails, McInroe noted. Early land animals likely didn’t have precise control over their limbs, and the tail may have compensated for that limitation, helping the animals ascend sandy slopes.

The Carnegie Mellon University researchers, who have worked with Goldman on relating the locomotion of other animals to robots, demonstrated that theoretical models developed to describe the complex motion of robots can also be used to understand locomotion in the natural world.

“Our computer modeling tools allow us to visualize, and therefore better understand, how the mudskipper incorporates its tail and flipper motions to locomote,” said Howie Choset, a professor in the Robotics Institute at Carnegie Mellon University. “This work also will advance robotics in those cases where a robot needs to surmount challenging terrains with various inclinations.”

The model was based on a framework proposed to broadly understand locomotion by physicist Frank Wilczek — a Nobel Prize winner — and his then student Alfred Shapere in the 1980s. The so-called “geometric mechanics” approach to locomotion of human-made devices (like satellites) was largely developed by engineers, including those in Choset’s group. To provide force relationships as inputs to the mudskipper robot model, Georgia Tech postdoctoral fellow Jennifer Rieser and Georgia Tech graduate student Perrin Schiebel measured drag in inclined granular materials.

Information from the study could help in the design of robots that may need to move on surfaces such as sand that flows around limbs, said Goldman. Such flow of the substrate can impede motion, depending on the shape of the appendage entering the sand and the type of motion.

But the study’s most significant impact may be to provide new insights into how vertebrates made the transition from water to land.

“We want to ultimately know how natural selection can act to modify structures already present in organisms to allow for locomotion in a fundamentally different environment,” Goldman said. “Swimming and walking on land are fundamentally different, yet these early animals had to make the transition.”

{Molecular dating from DNA sequences challenges dominant scientific theory}

Humans’ early mammal relatives likely diversified 66 million years ago, after the extinction of dinosaurs opened up space for animals such as big cats, horses, elephants and eventually apes to evolve.

QUT evolutionary biologist Dr Matthew Phillips used molecular dating from DNA sequences to challenge the dominant scientific theory that placental mammals diversified 20 million years before dinosaurs became extinct.

In a paper published in the journal Systematic Biology and delivered at the Society for Molecular Biology and Evolution Conference this week, Dr Phillips said biases in models of DNA evolution inflated estimates of when modern mammals, which were once no larger than a guinea pig, diversified and evolved into the animals familiar to us today.

“We can infer that some placental mammals did co-exist with dinosaurs,” he said.

“But for 20 years or so the current dominant theory has suggested that their diversification happened more than 80 million years ago, well before dinosaurs became extinct.

“It now appears that the major diversification of placental mammals closely followed the extinction of dinosaurs 66 million years ago, an event that would have opened up ecological space for mammals to evolve into.”

Dr Phillips said that for molecular dating to work, scientists had to calibrate the rate of DNA evolution with fossils of known age.

“I re-examined fossil calibrations, excluding those that were contentious or based on poorly resolved fossil placements and also fossil calibrations from within groups of very large or long-lived mammals, such as whales, for which parallel changes in the rate of DNA evolution in different lineages could distort dating estimates.

“When I took the remaining set of calibrations, the major diversification of placental mammals coincided with the extinction of dinosaurs,” Dr Phillips said.

“Fossil records have long indicated that the ancestors of many modern placental mammal groups can be traced back to the period immediately following the dinosaur extinction.

“But many scientists focused on DNA sequencing have brushed aside aspects of the fossil data, but when you minimise the potential biases in molecular dating you instead get a story that matches the fossil evidence.”

Dr Phillips is presenting these findings at the Society for Molecular Biology and Evolution Conference this week.

{Over 90 percent of mammal species were wiped out by the same asteroid that killed the dinosaurs in the Cretaceous period 66 million years ago, significantly more than previously thought, a new study concludes.}

Over 90 per cent of mammal species were wiped out by the same asteroid that killed the dinosaurs in the Cretaceous period 66 million years ago, significantly more than previously thought.

A study by researchers at the Milner Centre for Evolution at the University of Bath and published in the Journal of Evolutionary Biology, reviewed all mammal species known from the end of the Cretaceous period in North America. Their results showed that over 93 per cent became extinct across the Cretaceous-Paleogene (K-Pg) boundary, but that they also recovered far more quickly than previously thought.

The scientists analysed the published fossil record from western North America from two million years before the Cretaceous-Paleogene boundary, until 300,000 years after the asteroid hit. They compared species diversity before and after this extinction event to estimate the severity of the event and how quickly the mammals recovered. The extinction rates were much higher than previous estimates based on more limited data sets.

Dr Nick Longrich from the Milner Centre for Evolution, in the University of Bath’s Department for Biology & Biochemistry, explained: “The species that are most vulnerable to extinction are the rare ones, and because they are rare, their fossils are less likely to be found. The species that tend to survive are more common, so we tend to find them.

“The fossil record is biased in favour of the species that survived. As bad as things looked before, including more data shows the extinction was more severe than previously believed.”

The researchers say this explains why the severity of the extinction event was previously underestimated. With more fossils included, the data includes more rare species that died out.

Following the asteroid hit, most of the plants and animals would have died, so the survivors probably fed on insects eating dead plants and animals. With so little food, only small species survived. The biggest animals to survive on land would have been no larger than a cat. The fact that that most mammals were small helps explain why they were able to survive.

Yet the researchers found that mammals also recovered more rapidly than previously thought, not only gaining back the lost diversity in species quickly but soon doubling the number of species found before the extinction. The recovery took just 300,000 years, a short time in evolutionary terms.

Dr Longrich added: “Because mammals did so well after the extinction, we have tended to assume that it didn’t hit them as hard. However our analysis shows that the mammals were hit harder than most groups of animals, such as lizards, turtles, crocodilians, but they proved to be far more adaptable in the aftermath.

“It wasn’t low extinction rates, but the ability to recover and adapt in the aftermath that led the mammals to take over.”

Surprisingly, the recovery from the extinction took place differently in different parts of the continent. The species found in Montana were distinct from those in nearby Wyoming, for example.

“You might expect to see the same few survivors all across the continent. But that’s not what we found,” said Longrich. “After this extinction event, there was an explosion of diversity, and it was driven by having different evolutionary experiments going on simultaneously in different locations.

“This may have helped drive the recovery. With so many different species evolving in different directions in different parts of the world, evolution was more likely to stumble across new evolutionary paths.”