Wednesday, November 25, 2009
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
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."
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
"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.
Wednesday, November 11, 2009
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.
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.
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.
Monday, November 9, 2009
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
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. ...