From: Kathleen Wong, California Academy of Sciences
Published October 28, 2004 12:00 AM

Carnivores Grew Too Big for Their Britches and Other Stories

Carnivores Grew Too Big for Their Britches


The world's biggest carnivores paid for their size with their lives. A new study demonstrates that conflicting natural forces keeps the magnitude of meat eaters within a distinct range.


Paleobiologist Blaire Van Valkenburgh and colleagues of the University of California, Los Angeles, studied the large animals who went extinct during the late Pleistocene, which occurred between 50,000 and 100,000 years ago. The researchers found that the largest "hypercarnivores" all died out within 6 million years, while smaller predator species were likely to survive for up to 11 million years. Being big offers an advantage at mealtimes, allowing animals to devour large quantities of food.


But as succeeding generations grow ever larger, they need wider ranges, and the only types of prey worth pursuing become animals larger than themselves. As the predators grow more specialized at hunting certain prey, they become vulnerable to extinction when conditions change and these animals become less available, the researchers report in the journal Science. Smaller predators have more food options and are thus able to weather more changes. The trend can be seen in modern endangered species lists populated by big cats, wolves, and bears.




Earth Hums to the Rhythms of Its Oceans


While studying earthquakes in 1988, Japanese seismologists noticed that the Earth emits a mysterious hum. The basso-profundo grumble persisted even when no earthquakes were shaking.


Now Barbara Romanowicz and Junkee Rhie of the University of California, Berkeley, say the seas emit these ultra-low-frequency sound waves. Using seismometer data from the United States and Japan, they were able to track the source of most of the sounds to the North Pacific Ocean at the start of the year. From March until October, the noise source shifted to the Southern Oceans, and then moved north once again.


The sounds coincided with the areas where marine weather was the most severe, the scientists report in the journal Nature. Both sloshing water and atmospheric turbulence may be contributing to the mechanism.





Big Climate Swings Could Be Normal


Global climate may have wobbled far more strongly over the past millennium than once thought. Published in the journal Science, the research questions current methods of interpreting climate records. Typically, models of past climate are based on markers like the width of tree growth rings, which have been matched to historic temperature records to create a width-to-temperature scale. Although temperature does affect the width of growth rings, so do factors such as rainfall and disease.


Now Hans von Storch of GKSS Research Institute in Geesthacht, Germany, demonstrates that climate models based on such proxy data don't register wider temperature fluctuations. von Storch and colleagues simulated Earth's climate over the last 1,000 years using a computer model. They then subtracted a few years of data here and there and added back some inaccurate estimates to simulate errors in climate record interpretation. They then used this doctored data to estimate climate using a popular statistical method employed by others.


The researchers found the model removed up to 80 percent of the original fluctuations in the original data, suggesting climate models are underestimating the amount of real temperature change by a factor of two or more. If true, today's dramatic global warming trends may not be unique, and human influences on climate might be weaker than now believed.





Head Lice Links Ancient Human Lineages


Lice genetics offers evidence that modern humans interacted with a now-extinct hominid species thousands of years ago. The two populations may have swapped personal pests through close contact in fights, traded clothing, cannibalism, or even sex, according to a new study in the journal PLoS Biology.


David Reed of the Florida Museum of Natural History in Gainesville, Florida, and colleagues analyzed the ancestry of the two species of human head lice found in modern people, one of which is found only in North America. Differences in the DNA indicate that the lice diverged about 1.18 million years ago — about when humans diverged from other hominids. The worldwide louse went through a population bottleneck in its history, while the North American louse population appears to have been more stable.


Lice cannot survive for long away from their hosts, so the hominids they lived on must have endured the same demographic trends. Our species, Homo sapiens, split from the rest of the hominid family tree about 1.2 million years ago and went through a population bottleneck like that found in the cosmopolitan louse. And an early hominid species called Homo erectus, which lived in Asia, is thought to have been isolated from other hominids for a good 900,000 years.


To explain the genetics of the lice, Reed and colleagues suggest that modern humans interacted with Homo erectus in Asia about 100,000 years ago, caught the rarer louse species, and carried it to North America. Meanwhile, populations of Homo erectus in Asia and elsewhere died out along with their lice.





Early Tyrannosaurs Wore Feathers


The ancestors of Tyrannosaurus rex were covered in primitive feathers. A team led by Xing Xu of the Institute for Vetebrate Paleontology and Paleoanthropology in Beijing, China, and colleagues have found a 128 million- to 139 million-year-old fossil bearing faint impressions of early feathers in Liaoning, China.


The scientists named it Dilong paradoxus, or "emperor dragon paradox," for the surprising link between the fuzzy, jackal-sized beast and its fearsome descendent, which appeared some 53 million years later. But the scientists themselves weren't surprised, as other feathered dinosaurs have been found in the same area.


The researchers report in the journal Nature that both species had broad, square skulls and extremely strong jaws. But unlike T. rex, Dilong had forelegs that could probably move food to its mouth. The feathers that covered its body were soft and hairlike and likely used for insulation. T. rex may have lost its feathers because its great size made it difficult to lose heat. However, the scientists say, young T. rexes may well have been covered in some sort of feathery down.





Related Links


Carnivores Grew Too Big for Their Britches: CNN (Associated Press) /


Discovery.com


Earth Hums to the Rhythms of Its Oceans: New Scientist


Big Climate Swings Could Be Normal: Nature News / New Scientist


Head Lice Links Ancient Human Lineages: BBC / New Scientist / Discovery.com


Early Tyrannosaurs Wore Feathers: New Scientist / Nature News





Source: California Academy of Sciences


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