It might look docile lolling among the water lilies, but bad-tempered and surprisingly swift on terra firma, the hippopotamus has a deservedly fearsome public image in its African homeland. It also has a formidable reputation among evolutionary biologists: the beast has defied attempts to pinpoint its origin for nearly two centuries. To that end, recent findings may finally put the hippo in its place.
With its gaping maw, hairless body and fy
eyes that sit high on its head, the semiaquat-ic hippo is one of the most distinctive members of Africa's mammalian menagerie. Two species exist today—the common Hippopotamus amphibius and the smaller Li-berian hippo, Choeropsis liberiensis—and 40 more are known from the fossil record. Experts agree that hippos belong to the mammalian order Artiodactyla, a group of even-toed, hoofed creatures whose extant representatives include camels, pigs and ruminants such as cows. But exactly where hippos sit on the artiodactyl family tree has proved devilishly difficult to discern.
Two hypotheses lead the pack. The first posits that the piglike peccaries, or tayas-suids, are the closest relatives of the hippo. The second proposes that extinct swamp-dwelling creatures called anthracotheres own that distinction. To evaluate the two scenarios, Jean-Renaud Boisserie, a postdoctoral researcher at the University of California at Berkeley, and his colleagues scrutinized all the characteristics ever used to support one or the other of these models, incorporating data from 32 artiodactyl species (including new fossil hippos from Chad and Ethiopia).
In presenting their work at a fall meeting and, more recently, in a paper published online January 24 by the Proceedings of the National Academy of Sciences USA, the investigators concluded that many of the putative resemblances between hippos and pec-caries—the rounded shape of the muzzle in cross section, for example—are in fact primitive artiodactyl traits and therefore not indicative of a deeper relationship. Other similarities were also judged meaningless. The anthracothere hypothesis fared much better: the team's analysis supports a link between hippos and anthracotheres, pointing to an especially close relationship with a dentally advanced subset of anthracotheres known as the Bothriodontinae. Although hippo teeth look rather different, the two groups have in common a number of features in the skull, lower jaw and limbs.
The results stand to elucidate not only the ancestry of hippos but also that of whales. In 2001 key fossil whale discoveries revealed the ocean dwellers to be descended from artiodactyls [see "The Mammals That Conquered the Seas," by Kate Wong, Scientific American, May 2002]. And sev eral DNA analyses have concluded that whales and hippos in particular share a common ancestor. But some paleontologists have been reluctant to embrace the molecular findings because whereas the oldest known whales date back to more than 53 million years ago, the earliest hippos yet found are only around 15 million years old. The fossil trail of anthracotheres, however, doesn't peter out until some 41 million years ago. An anthracothere origin of hippos could thus reduce the gap between them and whales to just 12 million years. "This is the best work so far to link anthracotheres to hippos," comments fossil-cetacean expert J.G.M. (Hans) Thewissen of the Northeastern Ohio Universities College of Medicine. The challenge now, he adds, will be to identify anthracothere ancestors from the right time and place to bridge the remaining break between hippos and whales.
The hippo will no doubt remain a force to be reckoned with in the wilds of Africa. But paleontologists may have at last wrestled with the river horse and won.
" Aerial Base Station
TRYING AGAIN: STRATOSPHERIC AIRSHIPS FOR COMMUNICATIONS BY STEVEN ASHLEY
The plan is familiar: park an antenna high in the stratosphere and then relay signals to and from devices below. Such an airborne transceiver could blanket urban areas with wireless coverage more cheaply than satellite-based alternatives while avoiding the need to build forests of mast-mounted base stations on the ground. In the past, various remote-controlled airplanes, balloons and blimps have been proposed to keep antennas aloft for months on end, but few have ever made it into the air, and none have operated commercially.
Previous failures, however, do not daunt the latest contender for the prize. This spring engineers at Sanswire Networks, an Atlanta-based Wi-Fi provider, plan to test a prototype of a high-tech airship that they claim could supply mobile communications service to major metropolitan areas for as long as 18 months at a stretch. "It's like a big pontoon
boat in the sky," says company chairman Michael K. Molen. If the concept proves successful, fleets of whale-shaped "Stratel-lites"—short for stratospheric satellites—will fly 20 kilometers up to where the air is so thin that solar-powered electric motors can keep the $10-million-plus ships in geostationary "orbits."
Beyond standard financial and political difficulties, these projects face formidable
The Stratellite program began three and a half years ago, when Sanswire Networks began to consider airborne telecommunications. If the airships prove successful, then the hope is "to build three to five Stratellites in the first 18 months of operation," says company chairman Michael K. Molen. After a year and a half in service, the rechargeable batteries onboard will need changing. "When refitting becomes necessary, a replacement ship will take the three-hour trip up to the stratosphere, where it will change places with the original ship to maintain uninterrupted service." Each Stratellite would provide Wi-Fi-based voice, video and data services across a 240-kilometer-diameter area defined by a line-of-sight signal.
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jT*} wtiat the Sclwmfic Amencan [Lustom Pubdshing F^ograrT; ^r do for TOUR ereanu technical difficulties, observes aerospace engineer James D. DeLaurier of the University of Toronto. A veteran of a late-1980s effort to fly a microwave beam-powered drone, DeLaurier explains that the region above "20 kilometers is no atmospheric Shangri-la, as was once thought." Despite the rarefied air in the stratosphere, wind pressures are still significant, he notes, adding that the "area is full of ozone, ultraviolet radiation and even atomic oxygen, all of which degrade materials over time." Helium management is another issue: the enclosing envelope bag, which has to be thin to reduce weight, "looks like Highway 95" to helium molecules, which zip right through it, DeLaurier says. "So you have to have a way to replenish lost lifting gas."
To overcome such obstacles, Sans-wire has hooked up with Vernon Koe-nig, an expert in lighter-than-air technology who designed an airship for an earlier, underfinanced effort. Called Sanswire 1, the one-third-scale prototype will rely on a lightweight skin of body-armor-grade polyethylene fibers and incorporate thousands of square meters of photovoltaic film on the upper exterior. Once builders install the engines, high-altitude propellers and a triple-redundant computer guidance system, flight-testing will be conducted above a California U.S. Air Force base.
A full-size Stratellite would be nearly as large as a football field. It would be able to loft a 1.5-ton payload using mostly helium and would employ nitrogen to maintain the shape of its outer skin as the craft rises and falls. Some 37,000 cubic meters of helium inside will expand nearly 17-fold by the time the ship reaches cruising altitude. The commercial airship will most likely include a technology to manufacture lifting gas, perhaps hydrogen, to replace lost helium.
Molen says the aerodynamic lifting body-type shape means the airship will be able to "fly" under power, maneuvering its way up rather than simply floating higher. Presumably this approach will enable the ship to navigate past the jet stream and maintain its position.
As with the earlier, similar efforts, it all sounds promising. But the question remains whether the idea will really fly.
; No Bath Time
IN SPACE, IT'S NOT EASY BEING CLEAN BY PHIL SCOTT
After a grimy day of tussling with yet another alien species, the crew of the average Star Trek franchise might shower off with sound waves and don fresh uniforms courtesy of the ship's replicator. "I wish we had those things," Stephanie Walker says of the replicators. As a systems manager for flight crew equipment at the NASA Johnson Space Center in Houston, Walker remains keenly aware of the limitations of life in space. We can send a human to the moon, but we cannot ensure that astronauts on the International Space Station (ISS) stay fresh for their six-month missions.
Of course, NASA ranks comfort well below safety and health. And the station has a ways to go before it resembles Mir, which "had its own odor, like 12 years in a sock closet," quips Marsha Ivins, a veteran of five shuttle flights who is currently assigned to the Johnson center. Future manned flights, however, will demand extended togetherness: a round-trip to Mars should last at least 18 months. That's a problem, because space alters an astronaut's sense of taste and smell. "Things that don't bother you normally may nauseate you over time," explains Jeff Jones, a Houston-based flight surgeon for the ISS.
Today's astronauts use various off-the-shelf waterless products, such as body wipes and no-rinse shampoos developed for hospitals. All conform to strict station parameters. "We send up extend nr enhance the reach of your confere ncefty rnposi urn deliver in-depth couerdge □( a product launch or s new corporate initiative build your corporate image ai a leader In cutting-edge technology connect
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nothing with alcohol in it, because the environmental-control system can't get the alcohols out," Walker says. Propyl-ene glycol, commonly used to keep cleansing ingredients in the proper physical state, also poses a problem in large quantities. Most space soaps are herbal instead.
As for astronauts and their laundry, "they can wash clothing with soap and rinse it out with a water-bag system and let it air-dry," Jones states. "Things dry pretty quickly" with good air movement, he adds, thanks to an onboard humidity that hovers around 30 to 40 percent—a relative Sahara compared with Mir's 80 to 90 percent. Clothes drying is especially popular in the station's Zvezda service module, where airflow is best.
Higher-tech hygiene might be possible. NASA astronauts have tried two T-shirts woven with silver thread. The metal inhibits bacterial growth. The results, though anecdotal, seem promising: the shirts "were encrusted with salt, but they did not smell," Ivins reports. Last year NASA began testing silver-laced bedsheets, blankets and other items in its Aquarius underwater habitat, off the Florida coast.
Ivins downplays the idea of silver-suited space travelers. But she notes that "we have now the opportunity to look at new materials and new technologies, and one of these may turn out to be the Velcro of the future." A springtime-fresh Velcro, perhaps.
Phil Scott showers daily in New York City.
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