Monday, March 14, 2011

Abundance of Feathered Dinosaurs During Temperate Climate With Harsh Winters

Fragment of a jaw bone of a ceratopsian dinosaur, Archaeoceratops, from the Lower Cretaceous (Gansu province, China). (Credit: Copyright Romain Amiot)

Chilly Times for Chinese Dinosaurs: Abundance of Feathered Dinosaurs During Temperate Climate With Harsh Winters

ScienceDaily (Mar. 13, 2011) — Dinosaurs did not always enjoy mild climates. New findings show that during part of the Early Cretaceous, north-east China had a temperate climate with harsh winters. They explain the abundance of feathered dinosaurs in fossil deposits of that period.

The discovery was made by an international collaboration coordinated by Romain Amiot of the Laboratoire de géologie de Lyon: terre, planètes et environnement (CNRS/ENS de Lyon/Université Lyon 1).

Their work is published in the Proceedings of the National Academy of Sciences.

It has long been thought that the climate of the Mesozoic, the age of the dinosaurs, was generally warm across the planet. However, a recent study challenges this theory. The work focuses on a region of north-east China where the Jehol fauna developed during part of the Early Cretaceous (between 125 and 110 million years ago). The fossils found in this deposit include many dinosaurs covered with filamentous structures similar to bird feathers (such structures can take on various forms, ranging from filaments, down and 'protofeathers' to true feathers). But is this feature due simply to excellent conditions of preservation or to the adaptation of such species to environmental conditions? Since these dinosaurs were unable to fly, several scientists have suggested that their feathers acted as thermal insulation.

A team of paleontologists from France, China, Japan and Thailand examined the issue and tried to determine the temperatures at that time. Teeth and bones from dinosaurs, mammalian reptiles, crocodiles, turtles and freshwater fish from fossil deposits containing the Jehol fauna were collected. This selection of samples was then completed by fossil remains from contemporary deposits in other regions of China, Japan and Thailand. The scientists analyzed the oxygen isotopic composition of each sample. They based their analysis on the principle that the average local air temperature determines the relative quantity of oxygen isotopes contained in the rainwater drunk by the animals. This isotope record is passed on and stored within the bones and teeth of animals as they grow. Since the oxygen contained in the mineralized tissue is preserved during fossilization, the researchers were able to reconstruct the prevailing air temperatures in the environment of Asian dinosaurs during the Early Cretaceous.

The results show that average temperatures in this period of the Early Cretaceous were very similar to those of today at equivalent latitudes (such as the climate in Beijing today). The Jehol fauna therefore lived in a cool temperate climate characterized by harsh winters during which cold-blooded reptiles (turtles and lizards) had to hibernate, whereas the down, feathers and fur of warm-blooded animals (mammals, birds and dinosaurs) enabled them to maintain sustained activity in winter. "These results do not prove in any way that feathers appeared because of their insulating characteristics. They show that feathers would have given the dinosaurs of the Jehol fauna a physiological advantage over their fellow animals with scales," points out Amiot, lead author of the paper and currently a CNRS researcher at the Laboratoire de géologie de Lyon (ENS de Lyon/Université de Lyon 1/CNRS).

This work helps us to better understand the Early Cretaceous period, of which there are few geological records, and sheds new light on existing theories about Earth at the time of the dinosaurs.
The laboratories involved are: Laboratoire de géologie de Lyon: terre, planètes et environnement (CNRS/Université Lyon 1/ENS de Lyon); Laboratoire de géologie de l'École normale supérieure (CNRS/ENS Paris); Institut de physique du globe de Paris (CNRS/UPMC/Université Paris Diderot); and the Institute of Vertebrate Paleontology and Paleoanthropology , Beijing, China.

Story Source:
The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by CNRS (Délégation Paris Michel-Ange).

Journal Reference:
  1. R. Amiot, X. Wang, Z. Zhou, X. Wang, E. Buffetaut, C. Lecuyer, Z. Ding, F. Fluteau, T. Hibino, N. Kusuhashi, J. Mo, V. Suteethorn, Y. Wang, X. Xu, F. Zhang. Oxygen isotopes of East Asian dinosaurs reveal exceptionally cold Early Cretaceous climates. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1011369108

CNRS (Délégation Paris Michel-Ange). "Chilly times for Chinese dinosaurs: Abundance of feathered dinosaurs during temperate climate with harsh winters." ScienceDaily 13 March 2011. 14 March 2011 <­ /releases/2011/03/110311173104.htm>.

Thursday, March 10, 2011

Fossil Bird Study Describes Ripple Effect of Extinction in Animal Kingdom

Jessica Oswald, an NSF predoctoral fellow at the Florida Museum of Natural History on the UF campus, holds the mandible, or beak, of an extinct species of cowbird, Pandanaris convexa, recently discovered for the first time in Mexico. The bird has previously only been found at the Rancho La Brea fossil site in California and a site in Reddick, between Gainesville and Ocala in North Central Florida. Oswald is lead author of a new study in the March 8, 2011, print edition of the journal Palaeogeography, Palaeoclimatology, Palaeocology. The research shows the ripple effect throughout the animal kingdom caused by the extinction of large mammals 20,000 years ago, including the disappearance of a cowbird species. (Credit: Florida Museum of Natural History/UF photo by Kristen Grace)
ScienceDaily (Mar. 9, 2011) — A University of Florida study demonstrates extinction's ripple effect through the animal kingdom, including how the demise of large mammals 20,000 years ago led to the disappearance of one species of cowbird.

The study shows the trickle-down effect the loss of large mammals has on other species, and researchers say it is a lesson from the past that should be remembered when making conservation, game and land-use decisions today.

"There's nothing worse for a terrestrial ecosystem than the loss of large mammals -- and the loss of apex predators like sharks, tuna and other large fish will have the same negative impact on the oceans," said study co-author David Steadman, ornithology curator at the Florida Museum of Natural History on the UF campus. "We're seeing it with the loss of lions and elephants in parts of Africa, as well as in Florida with the decline of panthers. There's no question these losses will have a negative domino effect on our ecosystems."

The fossil study of eight songbird species from northern Mexico by Florida Museum ornithologists is currently available online and will appear in the March 8th print edition of the journal Palaeogeography, Palaeoclimatology, Palaeocology.

An extinct cowbird, Pandanaris convexa, is the most common bird found at the fossil site called Térapa, in Sonora, Mexico, about 150 miles south of Arizona. This is the first time fossils of the large bird, a member of the blackbird family, have been found in Mexico.

Finding the extinct cowbird at the fossil site was unpredictable and unexpected, according to Jim Mead, chair of the department of geosciences at East Tennessee State University, who has collected a variety of fossils at the site, including the birds used in the study. Mead described the findings at Térapa as "bizarre and exciting."
"The tropical environment is unusual because the site is so far from the coast," Mead said. "The fossil record also provides evidence animals migrated from north to south and, unexpectedly, from south to north."

The cowbird has previously only been found at the Rancho La Brea fossil site in California and a site in Reddick, between Gainesville and Ocala in North Central Florida. The study expands the bird's known range and creates new questions about whether it may have lived across the southern U.S.

"The extinct cowbird needed grasslands and these big mammals to survive," said lead author Jessica Oswald, a National Science Foundation predoctoral fellow at the Florida Museum. "Those two things play into each other because mega mammals maintain grasslands. They keep big trees from coming in and colonizing the areas because they graze, stomp and trample little saplings."

Like modern cowbirds, this species probably fed on seeds and insects large mammals exposed, Oswald said. The mammals included extinct species of ground sloth, mammoth, horse, tapir, camel and bison.
About 20,000 years ago, most of these large mammals went extinct, which lead to the extinction of scavengers like condors and vultures, as well as cowbirds, Steadman said. Extinctions, especially mass extinctions, can cause radical species loss and changes in species distribution.

"Big species can't exist in a vacuum, nor can smaller species," Steadman said. "When one piece of the puzzle goes extinct, there is no good way of predicting what sort of trickle-down effect, what kind of cascade effect that will have."

The study also confirms the area was once marshy grassland, possibly surrounded by a savanna near a river. Fossils of plants, reptiles and mammals of all sizes, and 31 species of birds other than songbirds have been recovered from the Térapa site over the past 10 years. Most of these species are found today in grasslands or wetlands, Steadman said.

Steadman and Oswald used the Florida Museum's more than 24,000 skeletal specimens of birds to identify the Mexican fossils.

Songbirds make up more than 50 percent of the world's living bird species, but the fossil record is poorly developed, especially in Central and South America. Oswald said this study helps build the fossil record of songbirds in Mexico.

Finding bird fossils, as well as bones of other small animals, is a time-consuming and labor-intensive process. Sediment is placed in a fine mesh sieve and water is used to remove dirt and debris from the bones.

Story Source:
The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Florida. The original article was written by Leeann Bright.

Journal Reference:
  1. Jessica A. Oswald, David W. Steadman. Late pleistocene passerine birds from Sonora, Mexico. Palaeogeography, Palaeoclimatology, Palaeoecology, 2011; 301 (1-4): 56 DOI: 10.1016/j.palaeo.2010.12.020

University of Florida. "Fossil bird study describes ripple effect of extinction in animal kingdom." ScienceDaily 9 March 2011. 10 March 2011 /releases/2011/03/110307124959.htm>.

Saturday, March 5, 2011

Fittest Adélie penguins appear to sustain colony populations

Penguins fighting each other.
Photo Credit: Jean Pennycook
Adélie penguins squabble at the Cape Royds colony on Ross Island. Scientists studying the population dynamics of these seabirds for the last 15 years have noted some "super breeders" seem to be consistently successful in producing chicks that reach adulthood.

Super breeders

For 15 years, U.S. researchers in Antarctica have watched the ebb and flow of Adélie penguin colony populations around the Ross Sea, recording the births and deaths, and the lives in between, of the continent’s iconic seabird in order to understand the patterns.

They’ve observed the large-scale changes over the summer seasons that have seen some colonies balloon to historic numbers, while at least one has plummeted to a near-record low. [See previous article: After the icebergs.] Now the scientists are focusing on why some individuals within the colonies are more successful than others in terms of foraging and breeding success.

Understanding the factors that determine which birds are better suited for the Darwinian dance of life can help the researchers predict how the penguins may fare in the future as climate change re-writes the script for survival.

“We’re getting a much better feeling with how individuals can cope with different scenarios,” said Grant Ballard , his face burnished nearly scarlet from the sun and wind of an Antarctic summer at Cape Crozier on Ross Island, home to one of the largest Adélie penguin colonies in the world.

Ballard and his co-principal investigators, David Ainley , an ecologist with H.T. Harvey and Associates  in California, and Katie Dugger at Oregon State University , are at the start of a new five-year grant from the National Science Foundation  that takes a bottom-up approach, focusing on individual capability, to learn how large populations will evolve and adapt over time.

Ainley said only about 20 percent of a given colony sustains the population consistently. More birds will breed successfully in “easy” years — when the journey across the sea ice from the rocky islands where the penguins nest to the open ocean where they forage is short.

But in tougher years, when the sea ice extends so far that the energy required to forage and feed their young causes many to fail, a special “breed” of penguin somehow manages to fledge their chicks to adulthood.
Fat Penguin Chick
Photo Credit: Jean Pennycook
A healthy, fat penguin chick.
An adult penguin guards its nest.
Photo Credit: Jean Pennycook
A penguin guards its nest.
“We found these super-breeders are much better foragers. They dive deeper; they have a shorter recovery period at the surface between dives. They bring back more food,” said Ainley, who first worked with the Ross Sea penguins in the 1970s as a PhD student.

Is it just a matter of genetics — a matter of being faster and stronger? Or does age and experience have anything to do with success?

It’s probably both, according to Ballard. The pattern the researchers have detected so far suggests that age and experience count, but older doesn’t necessarily equate to breeding success.

“There does seem to be variability at the individual level,” said Ballard, a staff scientist at PRBO Conservation Science  in California.

For each of the last 15 summers at Cape Crozier, the penguin team has banded 1,000 new adults, so the researchers have a large pool of known-age birds that they track. Most nest at a site called Area M, home to about 20,000 of the estimated 230,000 breeding pairs spread across about 5 kilometers of the moraines on the lower slopes of Mount Terror.
Still, not all the birds cooperate, so Ballard and his colleagues hike the length and breadth of the colony at least once a week to locate the stragglers. They randomly select “super-breeders” and their ordinary cohorts for putting on time-depth recorders.

The compact instruments, painlessly taped on the lower back of the animal, provide data on how deep and how long a penguin dives on a foraging trip. A simple V-shape dive means the critter likely came up with an empty stomach. A distinctive wiggle at the bottom of the dive signals success.

“There are some individuals that always have the biggest chicks, and they’re always in the colony,” Ballard said. In other words, the super-breeders get in, get out and get back to the colony more efficiently. That means not only more food, more often for its chicks, but more protection against predatorial skuas because super-breeders spend less time away from the nest.

Eventually, the team wants to determine to what extent the abilities of super-breeders are passed on to succeeding generations. Is it hereditary? Or are there enough “easy” years when the gene pool becomes flooded, diluted by the genes of the other 80 percent?

“There’s still a huge amount of mystery when it comes down to it,” Ballard said.

Dugger noted that one can’t be into instant gratification in this business of demographic research. “We get one data point each year with a huge amount of effort,” she said.

NSF-funded research in this story: David Ainley, H.T. Harvey and Associates, Award No. 0944411 ; Grant Ballard, PRBO, Award No. 0944141 ; and Katie Dugger, Oregon State University, Award No. 0944358 . 


Changes in Ross Sea environment, fishery cause demographic shift in species

Penguins float on iceberg.
Photo Credit: Nate Biletnikoff/Antarctic Photo Library
Adélie penguins float on an iceberg near Cape Crozier on Ross Island. Cape Crozier is home to one of the largest colonies of Adélies in the world. Scientists hypothesize its growth may, in part, be to shifts in the number of marine species in the Ross Sea due to pressures caused by a fishery that captures commercially available Chilean sea bass.

Population pressures

The penguin colony at Cape Royds on Ross Island in Antarctica is the southernmost breeding ground for any penguin in the world — seen by humans as an extreme place to raise chicks.

Still, the colony had grown to about 4,200 breeding pairs before 2001, one of the highest populations for that location in historic records dating back to 1907, according to David Ainley , senior ecologist at a SF Bay Area ecological consulting firm, H.T. Harvey and Associates . Ainley is the principal investigator for a long-term project trying to understand factors behind the population dynamics and trends at Royds and other colonies in the Ross Sea region. 

But then giant icebergs calved off the Ross Ice Shelf in 2000, locking in hundreds of additional square kilometers of sea ice beginning in 2001. That meant a long trek for the Adélies from Cape Royds to the open ocean to get food for their chicks.

The population crashed. In 2006, the dam of ice broke and open water appeared again farther south. Two years later, when The Antarctic Sun checked in with Ainley, the Royds colony was just “treading water,” though enjoying good reproductive success. He thought the young adults would start returning to the colony in the foreseeable future.

And, indeed, for the second straight year, there was a large influx of young birds (three to four years old) at the end of the breeding season. Ainley said that while last year’s “invasion” of young adults did contribute to the breeding population this year, the colony was further diluted in 2010 by the late arrival of former breeders.
That left the breeding population at Royds at about 1,400 pairs, its lowest total since 1970, when it started to recover from uncontrolled tourism in the 1960s. Since then, the location of the colony has been an Antarctic Specially Protected Area , a designation under the Antarctic Treaty system that controls access to the site.

One factor in the decline may be the lack of younger birds returning to the colony to try breeding, according to Ainley. Young adults will often set up nests around the exterior of the colony as they “practice” breeding skills.

Person weighs big fish.
Photo Credit: Melanie Connor/Antarctic Photo Library
Scientist Art DeVries weighs an Antarctic toothfish in November 2002, four years before the Ross Sea fishery began.
Person watches whale dorsal fins.
Photo Credit: Donald LeRoi/Antarctic Photo Library
A scientist observes killer whales in the Ross Sea. Researchers have reported that occurrence frequency of orcas has dropped since a fishery moved into the region.
Those nests serve as a sort of shield for the successful breeders against predatorial skuas, a clever species of seabird that uses all manner of trickery to steal chicks and eggs. A favored ploy is for the skuas to operate in pairs: One pulls an adult’s tail, while its partner pulls an egg out of the nest while the penguin is distracted.

“The skuas are just having a field day. They’re like people: They don’t manage their resources very well; they don’t believe in rainy days,” Ainley said. “There’s actually large areas of Royds now that are totally vacant of penguin nests where there were nests before the iceberg.”

Fishy business

Meanwhile, other colonies in the region have grown tremendously, buoyed to a limited extent by penguins from Royds that abandoned their colony in the tough iceberg years.

Cape Crozier on Ross Island now boasts an estimated 230,000 breeding pairs, which could place it at the top of the list for the largest Adélie colony in the world. That’s up by nearly 50,000 breeding pairs in the last decade before the icebergs moved in. On nearby Beaufort Island, the colony has expanded from 40,000 to 55,000 breeding pairs.
But immigration from Royds cannot explain the rapid expansion of these other colonies, Ainley said.

Instead, he suspects that the Adélie populations are skyrocketing because they face less competition from another predator in the Ross Sea food web — the Antarctic toothfish (Dissostichus mawsoni), known to seafood consumers as Chilean sea bass. Both prey extensively on the Antarctic silverfish (Pleuragramma antarcticum) in waters over the Ross Sea continental shelf.

Ainley believes a toothfish fishery that operates in the Ross Sea — authorized by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) , which oversees fishing in the Southern Ocean — may be taking too big of a bite out of the D. mawsoni population.

“Just as when thousands of food-competing Antarctic minke whales were removed from the wintering area of Ross Sea penguins during the 1970s, Adélies are exhibiting a spurt of colony growth not easily explained by climate change,” Ainley said.

He and others have argued in the scientific literature that too little is known about the life history of the toothfish, a late-maturing, slow-growing, long-lived species that can grow up two meters long. He said it was unwise to allow the fishery to operate without learning more about what the limits may be to its footprint.
The fishery began in the 1996-97 austral summer. In less than a decade, scientists who had been successfully capturing and releasing Antarctic toothfish in McMurdo Sound for research since the 1970s could no longer find any specimens.

Concurrently, Ross Sea killer whales, which prey on toothfish, have decreased in occurrence frequency, according to a paper in 2009 in the journal Aquatic Mammals by Ainley, Grant Ballard and Silvia Olmastroni. A staff scientist at PRBO Conservation Science , Ballard is a co-principal investigator on the Ross Sea penguin population dynamics study with Ainley and Katie Dugger at Oregon State University  (and collaborators Phil Lyver and Melanie Massaro of Landcare Research New Zealand).

Ainley noted that silverfish-eating emperor penguins (Aptenodytes forsteri) have also increased their presence in McMurdo Sound. “[It’s] the only part of the Ross Sea where these sorts of systematic observations are possible owing to the logistics available from the U.S. Antarctic Program ,” Ainley said.
Is the Ross Sea fishery to blame for the apparent shift in populations of whales, penguins and Antarctic toothfish?

“You can’t discount it, even though there are a lot of people who want to,” said Ainley, who is concerned that the fishery may skew data collected by researchers such as himself studying the effects of climate change on the marine ecosystem.

“You’re either studying climate change or you’re studying fish depletion, so what are you going to study?” he asked.

NSF-funded research in this story: David Ainley, H.T. Harvey and Associates, Award No. 0944411 ; Grant Ballard, PRBO, Award No. 0944141 ; and Katie Dugger, Oregon State University, Award No. 0944358 .