Tuesday, December 22, 2009

Venomous Dinosaur Discovered in China

ScienceDaily (Dec. 22, 2009) — A group of University of Kansas researchers working with Chinese colleagues have discovered a venomous, birdlike raptor that thrived some 128 million years ago in China. This is the first report of venom in the lineage that leads to modern birds.

"This thing is a venomous bird for all intents and purposes," said Larry Martin, KU professor and curator of vertebrate paleontology at the Natural History Museum and Biodiversity Institute. "It was a real shock to us and we made a special trip to China to work on this."

The KU-China team's findings will be published in the early edition of the Proceedings of the National Academy of Sciences during the week of Dec. 21.

"We think it's going to make a big splash," said Martin.

The article's authors are Enpu Gong, geology department at Northeastern University in Shenyang, China, and researchers Martin, David Burnham and Amanda Falk at the KU Natural History Museum and Biodiversity Institute.

The dromaeosaur or raptor, Sinornithosaurus (Chinese-bird-lizard), is a close relative to Velociraptor. It lived in prehistoric forests of northeastern China that were filled with a diverse assemblage of animals including other primitive birds and dinosaurs.

"This is an animal about the size of a turkey," said Martin. "It's a specialized predator of small dinosaurs and birds. It was almost certainly feathered. It's a very close relative of the four-winged glider called Microraptor."

The venom most likely sent the victim into rapid shock, shrinking the odds of retaliation, escape or piracy from other predators while the raptor manipulated its prey.

"You wouldn't have seen it coming," said Burnham. "It would have swooped down behind you from a low-hanging tree branch and attacked from the back. It wanted to get its jaws around you. Once the teeth were embedded in your skin the venom could seep into the wound. The prey would rapidly go into shock, but it would still be living, and it might have seen itself being slowly devoured by this raptor."

The genus had special depressions on the side of its face thought by the investigators to have housed a poison gland, connected by a long lateral depression above the tooth row that delivered venom to a series of long, grooved teeth on the upper jaw. This arrangement is similar to the venom-delivery system in modern rear-fanged snakes and lizards. The researchers believe it to be specialized for predation on birds.

"When we were looking at Sinornithosaurus, we realized that its teeth were unusual, and then we began to look at the whole structure of the teeth and jaw, and at that point, we realized it was similar to modern-day snakes," Martin said.

Sinornithosaurus is represented by at least two species. These specimens have features consistent with a primitive venom-delivery system. The KU-China research team said it was a low-pressure system similar to the modern Beaded lizard, Heloderma, however the prehistoric Sinornithosaurus had longer teeth to break through layers of feathers on its bird victims.

The discovery of features thought to be associated with a venom-delivery system in Sinornithosaurus stemmed from a study of the anatomy and ecology of Microraptor by the joint Chinese-KU team. They now are seeking to discover if Microraptor may have possessed a similar poison-delivery system.

Friday, December 18, 2009

'Screaming Roadrunner' Ran Circles Around Dinos

By Jennifer Viegas Thu Dec 17, 2009 05:00 PM ET Discovery News

During the Late Cretaceous, Mongolia's Gobi Desert was home to numerous dinosaurs, mammals and lizards. One of the most eye-catching, and possibly ear-splitting, residents was a newly identified bird.

The new species, which lived 71 to 75 million years ago, has been named Hollanda luceria, after the punk/country band Lucero and the Holland family, whose donations helped to support the research.

"Judging from the size of the hindlimb, Hollanda luceria most closely resembled the modern Southern Screamer," project leader Alyssa Bell, a researcher in the Dinosaur Institute at the Natural History Museum of Los Angeles County, told Discovery News.

The modern Southern Screamer's call has been likened to a blaring trumpet and a stadium horn.
For the study, which will appear in the February issue of the journal Cretaceous Research, Bell and her team analyzed the bird's remains, which were originally found in the southern Gobi Desert in 1997.

Previous research on avian anatomy concluded that bones in the third toe reflect how much time the bird spent moving on the ground.

The scientists studied these bones and compared them with those of other birds. Bell said the data "shows that our new bird was most likely a ground-foraging bird like a roadrunner or a chucao, implying that it spent a great deal of its time foraging or hunting on the ground."

Other fossils excavated at the site reveal that the newly identified bird was part of an ecosystem consisting of dinosaurs, such as Protoceratops and Velociraptor, mammals, lizards and other birds, like waterfowl Teviornis and the large, clawed Gobipteryx.

Bell doesn't think H. luceria preyed upon dinosaur eggs, "as they would have been too large for the bird to swallow; however, it probably would have been an active hunter of the small lizards and mammals as well as insects that lived in the environment."

The presence of so much diverse wildlife in the Gobi region during the Late Cretaceous, along with geological studies, suggests that this area was once similar to the Channel Country of central Australia or to the Nebraska Sand Hills.

"Thus, Hollanda's environment would have consisted of sand dunes, which had been stabilized by a covering of vegetation, and a continuous water supply that formed shifting streams and ponds," she said. "This interpretation is very different from early research that saw the Late Cretaceous Gobi as a desert of shifting sand dunes and sand storms."

Gareth Dyke, a paleontologist at University College Dublin, told Discovery News that the new research "is interesting," in part because, "Hollanda has quite an unusual ecology and is also well-preserved."

"It has very long legs compared to other birds known from the time and, from this part of the world, shows that early in their evolutionary history birds had evolved a range of ecological adaptations like fast 'road running,'" he added.

Given the Mongolian bird's connection to a musical group, Bell said Lucero "now joins the ranks of artists such as Mick Jagger, Neil Young, Simon and Garfunkel and Mozart in having a species named after them."

Tuesday, December 15, 2009

Woolly Mammoths Lasted Longer than Previously Thought

ScienceDaily (Dec. 15, 2009) — Extinct woolly mammoths and ancient American horses may have been grazing the North American steppe for several thousand years longer than previously thought. After plucking ancient DNA from frozen soil in central Alaska, a team of researchers used cutting-edge techniques to uncover "genetic fossils" of both species locked in permafrost samples dated to between 7,600 and 10,500 calendar years.

This new evidence suggests that at least one population of these now-extinct mammals endured longer in the continental interior, challenging the conventional view that these and other large species, or megafauna, disappeared from the Americas about 12,000 years ago.

"We don't know how long it takes to pinch out a species," says Ross MacPhee, Curator of Mammalogy at the American Museum of Natural History. "Extinctions often seem dramatic and sudden in fossil records, but our study provides an idea of what an extinction event might look like in real time, with imperiled species surviving in smaller and smaller numbers until eventually disappearing completely."

At the end of the Pleistocene, the geological epoch roughly spanning 12,000 to 2.5 million years ago, many of the world's megafauna, such as giant sloths, saber-toothed cats, dire wolves, stag-moose, and mammoths, vanish from the geological record. Some large species such as Equus caballus, the species from which the domestic horse derives, became extinct in North America but persisted in small populations elsewhere. Because of the apparent sudden disappearance of many megafaunal species in North America, some scientists have proposed cataclysmic explanations like human overhunting, an extraterrestrial impact, and the introduction of novel infectious diseases. The swiftness of the extinctions, however, is not suggested directly by the fossils themselves but is inferred from radiocarbon dating of bones and teeth discovered on the surface or buried in the ground. Current "macrofossil" evidence places the last-known mammoths and wild horses between 13,000 and 15,000 years ago.

But hard remains of animals are rarely preserved, difficult to find, and laborious to accurately date because of physical degradation. Because of this, MacPhee and co-authors Eske Willerslev of the University of Copenhagen in Denmark, Richard Roberts of the University of Wollongong in Australia, and Duane Froese of the University of Alberta in Canada decided to tackle the problem by dating the "last survivors" through dirt. Frozen sediments from the far north of Siberia and Canada can preserve small fragments of animal and plant DNA exceptionally well, even in the complete absence of any visible organic remains, such as bone or wood.

"In principle, you can take a pinch of dirt collected under favorable circumstances and uncover an amazing amount of forensic evidence regarding what species were on the landscape at the time," says Willerslev, director of the Centre for GeoGenetics at the University of Copenhagen. "The use of ancient DNA offers the possibility of being able to sample previous life within the last 400,000 years, freeing us from having to rely on skeletal and other macrofossil evidence as the only way to collect information about species that are no longer with us."

In order to prospect for genetic fossils, the team collected soil cores from undisturbed Alaskan permafrost. Wind-blown Stevens Village, situated on the bank of the Yukon River, fit the bill perfectly. Here, sediments were sealed in permafrost soon after deposition. Two independent methods (radiocarbon and optically stimulated luminescence) were used to date plant remains and individual mineral grains found in the same layers as the DNA.

"With these two techniques, we can be confident that the deposits from which the DNA was recovered haven't been contaminated since these lost giants last passed this way," said Roberts, director of the Centre for Archaeological Science at the University of Wollongong. "It's a genetic graveyard, frozen in time."

Cores collected at Stevens Village offer a clear picture of the local Alaskan fauna at the end of the last ice age. The oldest sediments, dated to about 11,000 years ago, contain remnant DNA of Arctic hare, bison, and moose; all three animals were also found in higher, more recent layers, as would be expected. But one core, deposited between 7,600 and 10,500 years ago, confirmed the presence of both mammoth and horse DNA. To make certain that the integrity of this sample had not been compromised by geologic processes (for example, that ancient DNA had not blown into the surface soils), the team did extensive surface sampling in the vicinity of Stevens Village. No DNA evidence of mammoth, horse, or other extinct species was found in modern samples, a result that supports previous studies which have shown that DNA degrades rapidly when exposed to sunlight and various chemical reactions.

"The fact that we scored with only one layer is not surprising," says MacPhee. "When you start going extinct, there will be fewer and fewer feet on the ground, and thus less and less source material for ancient DNA such as feces, shed dermal tissues, and decaying bodies."

The team also developed a statistical model to show that mammoth and horse populations would have dwindled to a few hundred individuals by 8,000 years ago.

"At this point, mammoths and horses were barely holding on. We may actually be working with the DNA of some of the last members of these species in North America," says permafrost expert Froese, associate professor in the Department of Earth and Atmospheric Sciences at the University of Alberta. "The Yukon Flats includes large shifting river bars with an abundance of high quality forage where large mammals can and could make a living. There may have been a handful of similar sites in Alaska, hosting small remnant populations," says Froese.

"Dirt DNA has lots of exciting potential to contribute to extinction debates in other parts of the world too, as well as a range of archaeological questions," said Willerslev, who also points out that the approach is not restricted to looking back at the past. "We can also use it to make a list of modern species living in any particular location," he said. "This kind of information is really valuable for studies of animals that are hard to detect, and there are some neat forensic applications too."

The new paper is published in the Proceedings of the National Academy of Sciences. In addition to Willerslev, MacPhee, Froese, and Roberts, authors include James Haile, Morten Rasmussen, and Thomas Gilbert of the University of Copenhagen in Denmark; Alberto Reyes, and Simon Robinson of the University of Alberta in Canada; Lee Arnold and Martina Demuro of the University of Wollongong in Australia; Rasmus Nielsen and Kasper Munch of the University of California at Berkeley; Barry Brook, Jeremy Austin, and Alan Cooper of the University of Adelaide in Australia; Ian Barnes of the Royal Holloway University of London in the United Kingdom; and Per Moller of Lund University in Sweden. The research was funded by the Danish National Research Foundation, the Natural Science and Engineering Research Council of Canada, the Alberta Ingenuity Foundation, the Australian Research Council; Discovery Communications, Inc.; the AHRB, and the Arts and Humanities Research Council.

Wednesday, November 25, 2009

Using Raptor Talons to Infer Predatory Behavior

A new study by students with the Montana State University Museum of the Rockies in Bozeman, Montana has shown that the morphology of the talons of birds of prey are related to how they are used during prey capture and feeding.

According to some reports, this is the first time a study on the functional morphology raptor talons has been conducted.

The study has shown that the enlarged talons of on the first digit of members of the family Accipitridae are utilized for restraining large prey items, whereas members of the family Pandionidae have recurved talons of uniform size on each toe which aids in capturing fish like fish hooks.

The study has also shown that many owls, which feed on smaller prey items, utilize the strength in their feet to constrict prey items more than they use their talons. Additionally, falcons typically dispatch prey by striking them and then killing the prey items by breaking the neck with a tomial tooth on the beak.

You can read more at:

Denver W. Fowler, Elizabeth A. Freedman, John B. Scannella. Predatory Functional Morphology in Raptors: Interdigital Variation in Talon Size Is Related to Prey Restraint and Immobilisation Technique. PLoS ONE, 2009; 4 (11): e7999

Saturday, November 21, 2009

Loss fo Mammoths & Mastodons Resulted in Landscape Change

Extinction of Giant Mammals Changed Landscape Dramatically
By Jeanna Bryner, Senior Writer--LIVE SCIENCE
posted: 19 November 2009 02:06 pm ET

Before ancient megafauna went extinct, mastodons kept broad-leaved vegetation, such as black ash trees, in check. Credit: Barry Roal Carlsen, University of Wisconsin-Madison.

The last breaths of mammoths and mastodons some 13,000 years ago have garnered plenty of research and just as much debate. What killed these large beasts in a relative instant of geologic time?

A question asked less often: What happened when they disappeared?

A new study, based partly on dung fungus, provides some answers to both questions. The upshot: The landscape changed dramatically.

"As soon as herbivores drop off the landscape, we see different plant communities," said lead researcher Jacquelyn Gill of the University of Wisconsin, Madison, adding the result was an "ecosystem upheaval."

Gill and her colleagues found that once emptied of a diversity of large animals equaling or surpassing that of Africa's Serengeti, the landscape completely changed. Trees once kept in check by the mammoth gang popped up and so did wildfires sparked by the woody debris.

The results, which are detailed in the Nov. 20 issue of the journal Science, could paint a picture of what's to come if today's giant plant-eaters, such as elephants, disappear.

"We know some of these large animals are among the most threatened that we have on the landscape today and they have a lot of large habitat requirements and they eat a lot of food," Gill told LiveScience. "If these animals go extinct we can expect the landscape will respond."

Dung fungus

Gill and her colleagues analyzed sediment samples collected from Appleman Lake in Indiana as well as data from sites in New York.

They focused on a dung fungus called Sporormiella that must pass through a mammal's gut to complete its life cycle and reproduce via spores. More of such spores indicate more dung and more megafauna around to contribute to the fecal contents. Within that same sediment, the team looked at pollen and charcoal as proxies for vegetation and fires, respectively.

Sediment layers accumulate over time and can indicate when the stuff embedded in it was around. By matching up the dung spores along with vegetation and fire indicators in certain layers, the researchers figured the large herbivores were already declining before the vegetation started changing or wildfires took off.

The changes in spore abundance suggest the megafauna began to decline some time between 14,800 and 13,700 years ago. By 13,500 years ago, the decline was in full force, Gill said.

Rather than getting vaporized in an instant, the results suggest the animals gradually dwindled for about 1,000 years.

Here's how it may have gone down: The large herbivores started to decline. Without such leafy eaters to keep broad-leaved species in check, trees such as black ash and elm took over a landscape once dominated by conifers. Soon after, the accumulation of woody debris sparked an increase in wildfires, another key shaper of landscapes, the researchers say.

What killed the mammoths?

As for what drove the beasts into their graves, Gill says the findings don't put the nail in the coffin, but do rule out some ideas. To explain the extinction, scientists have put forth climate change, hunting by humans such as the Clovis people (known for using advanced spear tips), and even impact by a comet. The answer could be a combination of several factors, scientists say.

Gill says this new study is a strong one because all of the evidence comes from one place, and so the researchers aren't making comparisons across different regions whose sediments may be off in terms of timing.

If the timing is accurate, as Gill says it should be, the findings can rule out the idea of a meteor or comet killing off the creatures some 13,000 years ago.

And since the plant community didn't change until after the big guys began to decline, that's a mark against climate change. (A warming climate was considered the cause of a revamping of vegetation, and thus animal habitat.)

"At this site, we can say that habitat loss didn't cause the decline, because the major habitat shift happens after the collapse [of the megafauna]," Gill said. "And habitat change is a big line of argument in the climate camp. If climate change is causing these extinctions, you'll have to evoke another process than habitat loss."

Hunting, at least that by the Clovis people, can also be ruled out at the site.

"It seems as though the animals were already in decline by the time [Clovis] people adopted this tool kit," Gill said, referring to the advanced spear tips thought to be more efficient at taking down large prey than hunting instruments used by humans prior to the Clovis.

The new study was funded by the Wisconsin Alumni Research Foundation, the UW-Madison Center for Climatic Research in the Nelson Institute for Environmental Studies, and the National Science Foundation.

Monday, November 16, 2009

Birds At Twilight

ScienceDaily (Nov. 16, 2009) — Research at the Lund University Vision Group can now show that the color vision of birds stops working considerably earlier in the course of the day than was previously believed, in fact, in the twilight. Birds need between 5 and 20 times as much light as humans to see colors.

It has long been known that birds have highly developed color vision that vastly surpasses that of humans. Birds see both more colors and ultraviolet light. However, it was not known what amount of light is necessary for birds to see colors, which has limited the validity of all research on this color vision to bright sunlight only.

"Using behavioral experiments we can now demonstrate that birds lose their color vision in the twilight and show just how much light is needed for birds to be able to interpret color signals," says Olle Lind, a doctoral candidate at the Department of Cell and Organism Biology.

For humans and horses, color vision ceases to work after dusk, at light intensities roughly corresponding to bright moonlight. However, the light threshold is not the same for all vertebrates. Geckos, for instance, can see colors at night. In the experiments performed by the Lund University Vision Group, the color vision of birds stopped working at light intensities corresponding to what prevails shortly after the sun goes down. Birds need between 5 and 20 times as much light as humans to see colors. Among all the vertebrates tested thus far, birds are the first to lose their color vision in the twilight, even though they are the vertebrates that probably see colors best of all in the daylight.

With these findings it is now possible to start to draw conclusions about how birds use their color vision at dawn and dusk. The findings also direct our focus to previous research about how important color is when it comes to eggs or begging baby birds in enclosed nests. Inside enclosed nests it is dark even when the sun is bright outside.

"Against the background of our new discoveries, we should now re-evaluate earlier research about how birds perceive the color of their eggs and their young in the nest," says Olle Lind.
The research findings were recently published in Journal of Experimental Biology 2009, 212: pp. 3693-3699.

Wednesday, November 11, 2009

Dinosaurs warm-blooded?

ScienceDaily (Nov. 11, 2009) — Were dinosaurs "warm-blooded" like present-day mammals and birds, or "cold-blooded" like present day lizards? The implications of this simple-sounding question go beyond deciding whether or not you'd snuggle up to a dinosaur on a cold winter's evening.

In a study published this week in the journal PLoS ONE, a team of researchers, including Herman Pontzer, Ph.D., assistant professor of anthropology in Arts & Sciences, has found strong evidence that many dinosaur species were probably warm-blooded.

If dinosaurs were endothermic (warm-blooded) they would have had the potential for athletic abilities rivalling those of present day birds and mammals, and possibly similar quick thinking and complicated behaviours as well¬. Their internal furnace would have enabled them to live in colder habitats that would kill ectotherms (cold-blooded animals), such as high mountain ranges and the polar regions, allowing them to cover the entire Mesozoic landscape. These advantages would have come at a cost, however; endothermic animals require much more food than their ectothermic counterparts because their rapid metabolisms fatally malfunction if they cool down too much, and so a constant supply of fuel is required.

Pontzer worked with colleagues John R. Hutchinson and Vivian Allen from the Structure and Motion Laboratory at the Royal Veterinary College, UK, to bring a combination of simple measurements, rigorous computer modeling techniques and their knowledge of physiology in present-day animals to bear in a new study on this hot topic. Using their combined experience, the authors set out to determine whether a variety of dinosaurs and closely related extinct animals were endothermic or ectothermic, and when, where and how often in the dinosaur family tree this important trait may have evolved.

"It's exciting to apply our studies of living animals back to the fossil record to test different evolutionary scenarios," Pontzer said. "I work on the evolution of human locomotion, using studies of living humans and other animals to figure out the gait and efficiency of our earliest fossil ancestors. When I realized this approach could be applied to the dinosaur record, I contacted John Hutchinson, an expert on dinosaur locomotion, and suggested we collaborate on this project. Our results provide strong evidence that many dinosaur species were probably warm-blooded. The debate on this issue will no doubt continue, but we hope our study will add a useful new line of evidence."

Studies of present-day animals have shown that endothermic animals are able to sustain much higher rates of energy use (that is, they have a higher "VO2max") than ectothermic animals can. Following this observation, the researches reasoned that if the energy cost of walking and running could be estimated in dinosaurs, the results might show whether these extinct species were warm- or cold-blooded. If walking and running burned more energy than a cold-blooded physiology can supply, these dinosaurs were probably warm-blooded.

But metabolism and energy use are complex biological processes, and all that remains of extinct dinosaurs are their bones. So, the authors made use of a recent work by Pontzer showing that the energy cost of walking and running is strongly associated with leg length -- so much so that hip height (the distance from the hip joint to the ground) can predict the observed cost of locomotion with 98% accuracy for a wide variety of land animals. As hip height can be simply estimated from the length of fossilized leg bones, Pontzer and colleagues were able to use this to obtain simple but reliable estimates of locomotor cost for dinosaurs.

To back up these estimates, the authors used a more complex method based on estimating the actual volume of leg muscle dinosaurs would have had to activate in order to move, using methods Hutchinson and Pontzer had previously developed. Activating more muscle leads to greater energy demands, which may in turn require an endothermic metabolism to fuel. Estimating active muscle volume in an extinct animal is a great deal more complicated than measuring the length of the legs, however, and so the authors went back to basic principles of locomotion.

First, how large would the forces required from the legs have to be to move the animal? In present-day animals, this is mainly determined by how much the animal weighs and what sort of leg posture it uses -- straight-legged like a human or bent-legged like a bird, for example. Second, how much muscle would be needed to supply these forces? Experiments in biological mechanics have shown that this depends mainly on the limb muscles' mechanical advantage, which in turn depends strongly on the size of the bony levers they are attached to.
To apply these principles to extinct dinosaurs, Pontzer and colleagues examined recent anatomical models of 13 extinct dinosaur species, using detailed measurements of the fossilized bony levers that limb muscles attached to. From this, the authors were able to reconstruct the mechanical advantage of the limb muscles and calculate the active muscle volume required for each dinosaur to walk or run at different speeds. The cost of activating this muscle was then compared to similar costs in present-day endothermic and ectothermic animals.

The results of both the simple and complex method were in very close agreement: based on the energy they consumed when moving, many dinosaurs were probably endothermic, athletic animals because their energy requirements during walking and running were too high for cold-blooded animals to produce. Interestingly, when the results for each dinosaur were arranged into an evolutionary family tree, the authors found that endothermy might be the ancestral condition for all dinosaurs. This pushes the evolution of endothermy further back into the ancient past than many researchers expected, suggesting that dinosaurs were athletic, endothermic animals throughout the Mesozoic era. This early adoption of high metabolic rates may be one of the key factors in the massive evolutionary success that dinosaurs enjoyed during the Triassic, Jurassic and Cretaceous periods, and continue to enjoy now in feathery, flying form.

Their methods add to the many lines of evidence, from bone histology to lung ventilation and insulatory "protofeathers," that are all beginning to support the fundamental conclusion that dinosaurs were generally endothermic. Ironically, indirect anatomical evidence for active locomotion in dinosaurs was originally some of the first evidence used by researchers John Ostrom and Robert Bakker in the 1960s to infer that dinosaurs were endothermic.
Pontzer and his colleagues provide a new perspective on dinosaur anatomy, linking limb design to energetics and metabolic strategies. The debate over dinosaur physiology will no doubt continue to evolve, and while the physiology of long-extinct species will always remain a bit speculative, the authors hope the methods developed in this study provide a new tool for researchers in the field.

Journal reference:
Pontzer H, Allen V, Hutchinson JR. Biomechanics of Running Indicates Endothermy in Bipedal Dinosaurs. PLoS ONE, 2009; 4 (11): e7783 DOI: 10.1371/journal.pone.0007783
Adapted from materials provided by Washington University in St. Louis, via EurekAlert!, a service of AAAS.

Monday, November 9, 2009

Colorful Males Less Confused?

ScienceDaily (Nov. 9, 2009) — Why do so many animal species -- including fish, birds and insects -- display such rich diversity in coloration and other traits? In new research, Gregory Grether, UCLA professor of ecology and evolutionary biology, and Christopher Anderson, who recently earned his doctorate in Grether's laboratory, offer an answer.

At least since Charles Darwin, biologists have noticed that species differ in "secondary sexual traits," such as bright coloring or elaborate horns, Grether said. Darwin attributed this diversity to sexual selection, meaning the traits increased an animal's ability to attract mates.

But Grether and Anderson, writing in the Oct. 28 issue of the journal Proceedings of the Royal Society B: Biological Sciences, emphasize another evolutionary factor.

"The cost of attacking the wrong type of male and of being attacked by the wrong type of male favors the rich diversity of coloration and of birdsong and chemical cues, such as odors, to identify rivals," Grether said.

Grether and Anderson studied several species of the Hetaerina damselfly (closely related to dragonflies) and found that differences in coloration served to help damselflies distinguish males of their own species, who are rivals, from those of other species, who are not.

"We found that male Hetaerina damselflies use species differences in wing coloration to distinguish between intruders of their own species and intruders of other damselfly species, but only at sites where the two species naturally occur together," he said. "This provides one of the clearest demonstrations yet of an evolutionary process that is probably very prevalent in nature but which has largely been overlooked. We tested for shifts in what animals recognize as competitors."

Nobel Prize-winning Austrian ethologist and zoologist Konrad Lorenz suggested in 1962 that the spectacularly diverse coloration of coral reef fish was likely due to selection against fighting with the wrong species.

"Just as there could be selection against mating with the wrong species, there can also be selection against fighting with the wrong species," Grether said. "Lorenz said there was no advantage to coral reef fish attacking species that are close in proximity but are not competitors. The idea never really reached the level of attention in evolutionary biology that it deserved."

Lorenz's idea may not accurately explain the color diversity of coral reef fish, Grether said, but it may explain the diversity of coloration of other animal groups.

"When species are found in the same location, they do a better job of telling apart males of their own species from males of the other species than they do in places where they do not occur together," Grether said.

At sites where only one damselfly species occurs naturally, the researchers tested their theory by using members of that species whose wings had been artificially colored to resemble males of another damselfly species.

"We can test their responses at both kinds of sites, and we found they show greater discrimination between males of their own species and of other species at places where they actually have to contend with the other species than at places where they don't. They differentiate based on color," Grether said. "That this ability has evolved as a result of selection against fighting with other species is suggested quite strongly by the fact that in places where the other species do not occur, they do not make that distinction.

"If there is no reason for two species to interact aggressively with each other -- as Lorenz argued with coral reef fish -- then you would expect evolution to favor the ability for them to tell the difference by, for example, an exaggeration in the initial difference in color between them," Grether said. "Differences in color might enable females to more readily tell their own males apart from males of other species. Selection against interspecies aggression could favor the evolution of increased differences between species in color."

Some damselflies species also differ more in coloration where they occur together than where they occur alone, but "this finding can be explained either by selection against mating with the wrong species or selection against fighting with the wrong species," Grether said.

In future research, Grether hopes to learn what proportion of species can tell the difference between members of their own species and members of other species and whether they respond more strongly to their own species in a competitive context. Interspecies aggression and the evolutionary effect it has are understudied scientific questions, Grether said.

In addition to studying several species of damselflies in Mexico and Texas, Grether and Anderson collaborated with modeler Kenichi Okamoto to construct a mathematical model of what happens when species with similar secondary sexual traits come into contact. The model, published in the November 2009 issue of the journal Biological Reviews, predicts rapid evolutionary shifts in secondary sexual traits and also in what the animals recognize as competitors.

"My reading of the evidence," Grether said, "is that these evolutionary processes are important."

The research is federally funded by the National Science Foundation, and by UC MEXUS.
Adapted from materials provided by University of California - Los Angeles.

Tuesday, November 3, 2009

New Analyses Of Dinosaur Growth May Wipe Out One-third Of Species

ScienceDaily (2009-10-31) -- Paleontologists Mark Goodwin and Jack Horner have dug for 11 years in Montana's Hell Creek Formation in search of every dinosaur fossil they can find, accumulating specimens of all stages of development. Their new report on the growth stages of dome-headed dinosaurs shows that two named species are really just young pachycephalosaurs. They say that perhaps one-third of all named dinosaurs may not be separate species, but juvenile or subadult stages of other known dinosaurs. ... > read full article

Terrible Teens Of T. Rex: Young Tyrannosaurs Did Serious Battle Against Each Other
ScienceDaily (2009-11-02) -- Teenage tyrannosaurs got into some serious fights with their peers. The evidence can be found on Jane, a prized juvenile Tyrannosaurus rex, discovered in 2001 in Montana. The dinosaur's fossils show that it sustained a serious bite that punctured through the bone of its upper jaw and snout. The researchers determined that another juvenile tyrannosaur was responsible for the injury. ...

Wednesday, September 30, 2009

Tyrannosaurus Pathological Autopsy reveals Connection to Birds

A team of researchers have revealed that holes commonly found in the jaws of Tyrannosaurs may be due to a protozoan infection. Many of these holes have previously been attributed to wounds inflicted by other Tyrannosaurs or struggles with their prey.

The hypothesized protozoan is a species of Trichomonas, possibly Trichomonas gallinae. T. gallinae is found in modern pigeon species as well as birds-of-prey that prey upon infected pigeons. Infections result in lesions on the jaws and interior of the mouth of infected birds. Infections can be severe enough to potentially prevent feeding by birds, which can result in the starvation of infected birds. Infections in birds-of-prey are also accompanied by holes in the mandible, which are similar to the holes found in a number of T. rex specimens including 'Sue' at the Chicago Field Museum.

Thursday, August 27, 2009

Iridescence Found in 40-Million-Year-Old Fossil Bird Feather

Known for their wide variety of vibrant plumage, birds have evolved various chemical and physical mechanisms to produce these beautiful colors over millions of years.

A team of paleontologists and ornithologists has now discovered evidence of vivid iridescent colors in fossil feathers more than 40 million years old.

The finding, published online August 26 in the journal Biology Letters, signifies the first evidence of a preserved color-producing nanostructure in a fossilized feather.

Iridescence is the quality of changing color depending on the angle of observation, such as the rainbow of colors seen in an oil slick.

The simplest iridescent feather colors are produced by light scattering off the feather's surface and a smooth surface of melanin pigment granules within the feather protein.

Examining feather fossils from the Messel Shale in Germany with an electron microscope, scientists funded by the National Science Foundation (NSF) have documented this smooth layer of melanin structures, called melanosomes.

"Although fossil feathers have been known for many years, determining their original color has not been done," said H. Richard Lane, a paleontologist and program director in NSF's Division of Earth Sciences.

"Discovery of a color-producing nanostructure in a fossil feather opens up the possibility that we may someday be able to determine such colors in fossil birds, as well as in feathered dinosaurs."

For more than 25 years, paleontologists have found microscopic tubular structures on fossilized feathers and hair. These were long interpreted as bacteria that had digested the feathers at the time they were fossilized.

The team had previously discovered that these structures were in fact not bacteria but melanosomes; this information allowed the scientists to document the original color patterns.

"The feathers produced a black background with a metallic greenish, bluish or coppery color at certain angles--much like the colors we see in starlings and grackles today," said Richard Prum, a scientist at Yale and one of the paper's authors.

Following up on the new finding, he and colleagues are racing to discover what additional coloration features may be found in fossil feathers.

"The discovery of ultra-structural detail in feather fossils opens up remarkable possibilities for the investigation of other features in soft-bodied fossils, like fur and even internal organs," said scientist Derek Briggs of Yale, a co-author of the paper.

"The ‘Holy Grail' is reconstructing the colors of feathered dinosaurs," said Yale graduate student and paper lead author Jakob Vinther. "We are working hard to determine if this will be possible."
Other authors of the paper include Julia Clarke (University of Texas at Austin) and Gerald Mayr (Senckenberg Research Institute, Germany). Funding also was provided by the National Geographic Society and Yale University.


Tuesday, July 21, 2009

A Dinosaur Named Jane

One of the more interesting discoveries over the past few years has been a dinosaur specimen nicknamed "Jane." "Jane" is a Tyrannosaur specimen discovered by researchers from the Burpee Museum of Natural History.

There has been much debate over the identification of this Tyrannosaur specimen. Some think it may represent a more complete specimen of a species called Nanotyrannus lancensis; the type specimen resides at the Cleveland Museum of Natural History. Others think "Jane" may be a representative of a juvenile Tyrannosaurus rex.
The current identification "Jane", at the Burpee Museum, is that of a juvenile Tyrannosaurus rex, however recent research may support the designation of "Jane" as a specimen of Nanotyrannus lancensis.

"Jane's" skull is remarkably similar to the Cleveland type specimen of Nanotyrannus, and CT scans of the type specimen seem to support its designation as a distinct species apart from Tyrannosaurus rex.

There is still much to learn about Nanotyrannus and "Jane." However, other sub-adult Trannosaur specimens, like "Bucky," may help shed greater light on the true identity of "Jane."

Thursday, June 4, 2009

Sexing Tyrannosaurs

The relationship between dinosaurs and birds has been pretty well established, especially in recent years as many new feathered dinosaur specimens have been discovered in China.

However, it can be sometimes difficult to imagine an animal like Tyrannosaurus rex being related to the small songbird visiting your backyard bird feeder.

Researchers from the Museum of the Rockies and North Carolina State University have illustrated that Tyrannosaurs did indeed share a very important characteristic with birds.
As female birds produce eggs their bodies borrow calcium from their skeletons to produce the protective eggshells. As eggs form, skeletal calcium is removed from the inner bone tissue that lines the marrow. This interior woven bone tissue is called medullary bone and is found in female birds primarily as they are the gender that lays eggs.

Dr. Mary Schweitzer of North Carolina State University, and colleagues, have found and identified medullary bone in a Tyrannosaur specimen, which was one of the first discoveries of this kind of bone structure in dinosaurs. It also allowed her to confirm that the gender of the Tyrannosaur specimen was a female animal that was pregnant at the time of its death.

Dr. Schweitzer's research has also revealed that the production of medullary bone was a unique characteristic shared by dinosaurs and birds but not basal archosaurs, like crocodillians. She found that American Alligators, as representatives of more basal archosaurians, do not produce medullary bone before, during, or after egg-laying in females and definitely not in males alligators. This makes sense given that crocodillians and other modern basal archosaurs (turtles) produce soft leathery eggs rather than the hard-shelled eggs of birds and dinosaurs.

Since the discovery of a pregnant female Tyrannosaurus, several other species of dinosaurs, including Tenontosaurus and Allosaurus, have been discovered with similar internal bone structure revealing gender and breeding status.

You can read more about Dr. Schweitzer's discovery in a recent book, titled "How to Build a Dinosaur," by Dr. Jack Horner and James Gorman.

Friday, April 3, 2009

"Cincinnati Warbler"

In 1880 in the village of Madisonville in greater Cincinnati, Dr. Frank Langdon discovered, what he thought, was a new species of warbler which he named the Cincinnati Warbler (Helminthophaga cincinnatiensis).

It was later determined that the "Cincinnati Warbler" was in fact a hybrid between a Kentucky Warbler and a Blue-winged Warbler.

You can find an excellent essay about the "Cincinnati Warbler" at the Birding in Cincinnati website.

Wednesday, March 25, 2009

Juvenile Triceratops were possibly social

Many herbivorous dinosaurs have been depicted as living in herds based on finding aggregations of multiple individuals in fossil deposits. One of the few exceptions to this has been adult Triceratops. There have been many Triceratops specimens found since paleontologists have been looking for fossil organisms, but these discoveries have typically been of solitary individuals.

A newly reported discovery in southeastern Montana may shed new light on the social behavior of Triceratops. Three juvenile individuals were found together in a formation by a volunteer of the Burpee Museum of Natural History. The three juveniles were killed together during a flood event. The finding suggests that young Triceratops formed small herds, possibly for defense against predators and became more solitary as adults.

While a variety of dinosaur species have been found to group together as adults, the finding of juvenile groups is much less common.

Triceratops was a Cretaceous genus that lived between 70 and 65 million years ago in parts of the U.S. and Canada.

The finding was published in the Journal of Vertebrate Paleontology.