- Bones Show Biggest Dinosaurs Had Hot Blood
- World’s Freakiest Worm Gets Expanded Family Tree
- Giant Asteroid Impact Could Have Stirred Entire Ocean
- Spirit Rover Wiggles Her Wheels
Posted: 11 Nov 2009 08:55 AM PST
The infamous T-Rex may have been a cold-blooded killer, but new evidence suggests he probably had warm blood.
Paleontologists have debated the issue of dinosaur metabolism for decades: Did those ancient, lumbering beasts rely on the sun's warmth to regulate their body temperature, like today's reptiles and amphibians, or could they generate their own body heat like mammals and birds? Respected scientists have come down on both sides of the issue, and there's a host of arguments to support each theory.
Now, using a biomechanical model that predicts the energy cost of walking and running based on the size of an animal's leg bones, researchers have shown that the biggest dinos couldn't have gotten around without a warm-blooded metabolism.
"Using studies of living animals, we can figure out the relationship between limb design and the amount of muscle an animal needs to support its body weight as it walks and runs," said anthropologist Herman Pontzer of Washington University in St. Louis, who co-authored the paper published Thursday in PLoS ONE. "The size of muscle is very good predictor of how much energy you need, because to turn on muscle, you need oxygen."
Because warm-blooded animals have much greater aerobic capacity than their cold-blooded counterparts, finding bigger muscles and higher energy demands in dinosaurs would favor the warm-blooded hypothesis. Indeed, when Pontzer and colleagues looked at anatomical models of 14 different species of extinct dinosaurs, they were surprised to find that even at a slow walk, most dinos needed more energy than a cold-blooded metabolism could provide.
Of course, drawing conclusions about extinct dinosaurs from a model based on modern-day animals involves making some assumptions. Pontzer acknowledges that it's possible dinosaurs had a physiology completely unlike anything alive today, a cold-blooded metabolism that provided enough energy to meet the needs of these fast, muscular creatures.
"That's a limitation of this analysis," he said, "and maybe a limitation of any similar analysis that uses what we see in the world today. But it just seems to us more likely that they're warm-blooded than that they have some bizarre form of physiology that we have no record of today."
The new research fits well with a previous study on dinosaur cardiovascular anatomy, based on a CT scan of a 66-million year old dinosaur fossil with a preserved heart. Imaging revealed a four-chambered, double-pump heart with a single aorta — essentially, the heart of a warm-blooded mammal or bird, not a cold-blooded reptile. But other anatomical studies have led to different conclusions: A study of dinosaur noses, for example, revealed that dinos lack special bones in their nose, called turbinates, that protect against water loss during rapid breathing and are found in 99 percent of warm-blooded animals.
Pontzer, whose primary research involves the biomechanics of ancient human locomotion, says the argument over dinosaur metabolism isn't going to end son. "Our data, as far as the method goes, are pretty clear that the big guys are probably warm-blooded," he said. "But it won't be the last word, surely. These big debates will, and perhaps should, be debated for awhile."
Image: Figure 1 from "Biomechanics of Running Indicates Endothermy in Bipedal Dinosaurs." Pontzer H, Allen V, Hutchinson JR, PLoS ONE 4(11), 2009.
Posted: 10 Nov 2009 12:52 PM PST
Five years after discovering some of the strangest creatures in the world — mouthless worms that live in the bones of dead whales — scientists have taken a peek into their genes. Though not complete, the glimpse shows these creatures to be far more complicated than was known.
The worms, found in a gray whale skeleton off the coast of California, prompted scientists to designate them as representatives of an entirely new genus, dubbed Osedax. They belonged to a taxonomic family of marine worms that lack mouths and anuses, and rely entirely on bacteria to absorb and excrete nutrients. But Osedax was unique: Adult males were extremely small, and lived in colonies inside the females. Even more strikingly, they occupied an evolutionary niche comprised entirely of fallen whales.
"Picture the bottom of the ocean. Anything below 1000 meters is fed entirely by 'marine snow' — the things that are supported by photosynthesis at the top of the ocean, and the things that eat them, and eventually fall to the ocean floor," said Robert Vrijenhoek, a senior scientist at the Monterey Bay Aquarium Research Institute. "When a whale drops into your neighborhood, it's roughly equivalent to 2000 years of marine snow falling in a millisecond."
Since the discovery by Vrijenhoek and other MBARI researchers of Osedax, other species have been found in whalebones off the coast of Sweden and Japan. (Some of their names hint at the genus' weirdness: Osedax mucofloris roughly translates to "bone-eater snot-flower," in honor of its appearance.) A total of five species have now been named, enough for a comparison of their genetic characteristics to provide insight into their evolutionary history.
In a study published Tuesday in BMC Biology, Vrijenhoek looked for similarities and differences in five genes across the species. In much the same way that comparing genes from humans and Neanderthals would hint at the existence of other members of the Homo genus, the analysis suggested at least 12 more as-yet-unidentified lineages of Osedax. The worms might still be out there, though some may have gone extinct. It's believed that modern whaling, which drove many whale species to the brink of extinction, may have had equally profound effects on Osedax.
The genetic results also raise the question of just how long the whalebone-eating worms have existed. The five species appear to have shared a common ancestor at least 45 million years ago, when whales arose and diversified. But Osedax might have emerged even earlier, during the Cretaceous, and moved to whales when marine dinosaurs died out.
To figure that out, scientists will need to look for traces of Osedax in the fossils of dinosaurs and early whales. In the meantime, Vrijenhoek and others are learning more about how the worms live now. Since whale carcasses are hard to come by, the researchers have lured them with carcasses of other animals.
"The worms can live perfectly happily on cowbones," said Vrijenhoek. "We've also put down sea lion bones and pig bones. The worms don't seem to care."
Images: 1) MBARI. 2) University of Copenhagen. To see Osedax in real-time, visit the Monterey Bay Aquarium Research Institute's ocean-floor webcam, near which the researchers recently sank a pig.
Citation: "A remarkable diversity of bone-eating worms (Osedax; Siboglinidae; Annelida)." By Robert C. Vrijenhoek, Shannon B. Johnson and Greg W. Rouse. BMC Biology, Vol. 7, No. 74, published online November 10, 2009.
Posted: 10 Nov 2009 12:39 PM PST
The collision of a large extraterrestrial object with Earth almost 2 billion years ago may have stirred the seas worldwide and delivered a huge serving of oxygen to the deep ocean.
The Sudbury impact, named after the Canadian city located near the center of what remains of the ancient crater, happened around 1.85 billion years ago (SN: 6/15/02, p. 378). Despite erosion since then, the impact structure —at least 200 kilometers across — is recognized to be the second-largest on the face of the planet, says William Cannon, a geologist with the U.S. Geological Survey in Reston, Va., and coauthor on a paper in the November Geology. The event fundamentally affected the concentrations of dissolved oxygen in the deep sea — enough to almost instantly shut down the accumulation of marine sediments known as banded iron formations, report Cannon and coauthor John F. Slack, also of the USGS in Reston.
Banded iron formations, massive deposits rich in iron oxides, have accumulated at several periods in Earth's long-distant geological past, mostly when atmospheric concentrations of oxygen were low (SN: 6/20/09, p. 24).
One extended episode of banded iron formation (or BIF) buildup suddenly — and without an obvious explanation — ended about 1.85 billion years ago, says Cannon. Over a very short interval, he notes, "the environment shifted from one happily making banded iron to one that wasn't."
In northern Minnesota and other areas nearby, the formations lie directly underneath a thick layer of material only recently recognized as ejecta from the Sudbury impact. Mark Jirsa, a geologist with the Minnesota Geological Survey in St. Paul, was a member of the team that identified the ejecta layer. "We intuitively connected the Sudbury impact with the shutdown of BIF accumulation," he says. "But now [Cannon and Slack] have come up with a model for how that might have happened."
About 1.85 billion years ago, Earth's now separate landmasses were joined in a single supercontinent. That also means there was one large ocean, says Cannon. Many scientists suggest that the object that slammed into Earth then — probably an asteroid abut 10 kilometers across — splashed down in that ocean, in waters about 1 kilometer deep on the shallow shelf surrounding the supercontinent. Models hint that the tsunami spawned by the event would have been 1 kilometer tall at the impact site and remained at least 100 meters tall about 3,000 kilometers away, Cannon adds.
Those immense waves and large underwater landslides triggered by the impact stirred the ocean, bringing oxygenated waters from the surface down to the ocean floor, the researchers propose. Sediments deposited on the seafloor before the impact, including BIFs, contained little if any iron in its Fe(III) form but were high in Fe(II), a sign that most parts of the ocean were oxygen-free. But marine sediments deposited after the impact included substantial amounts of Fe(III) but very little Fe(II) — and, therefore, sizable amounts of dissolved oxygen. The team's analyses suggest that after the impact, dissolved iron spewed into the deepest parts of the ocean by hydrothermal vents would have reacted with oxygen within a day or so, thereby choking off most of the supply of Fe(II) to shallower waters where BIFs typically accumulated.
While Cannon and Slack's model explains how BIF accumulation might have suddenly ceased 1.85 billion years ago, it doesn't prove that's how it happened, Jirsa warns. Nevertheless, he notes, "scientists are closer to an explanation than we previously were." The geological record suggests that environmental changes were happening in oceans worldwide even before the Sudbury impact, he adds, "and the role that the impact played, if any, in shutting down BIF accumulation isn't well understood."
Images: 1) Geological map of the Sudbury Nickel Region, A.P. Coleman, 1913. / Aerial radar and digital elevation maps, Planetary and Space Science Centre, University of New Brunswick. / Wired.com. 2) Flickr/unforth.
Posted: 10 Nov 2009 11:04 AM PST
The Spirit Mars rover wiggled her wheels for the first time in months. The rover has been stuck in Martian soil for half a year.
The movement, seen in the image above, doesn't mean that Spirit has been extricated, but it did provide some excitement for the rover's operators and fans.
"First drive sequence in 145 sols," wrote Scott Maxwell, aka @marsroverdriver.
Planetary Society blogger, Emily Lakdawalla, summed up the general excitement among Mars watchers.
"[I]t's a thrill to see Spirit doing anything like roving again," Lakdawalla wrote.
Spirit and Opportunity landed on Mars in January 2004 and have been exploring the planet ever since. In recent months, while Spirit's been stuck, she's also been a bit glitchy, experiencing what the engineers are calling "amnesia." Despite the problems, the rovers are considered a tremendous success for NASA, having traveled the planet for 20 times longer than the 90 days that were originally planned for.
NASA will hold a press conference on Thursday to discuss further attempts to free the rover. Jet Propulsion Laboratory engineers have mocked up the Martian surface to model her predicament in hopes of finding just the right series of moves to unstick her wheels.
Image: NASA / JPL / animation by Damien Bouic
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