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VOL.441 NO.7094 DATED 08 JUNE 2006
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* Summaries of newsworthy papers:
Palaeobiology: Earliest fossil evidence for life on Earth?
Planetary science: Another look beneath Titan's haze
Fossils: Dwarf dinosaurs lived an island life
Sleep: Brain region linked to fly slumber
Organic chemistry: Twisted logic leads to elusive molecule
Earth science: Earthquake aftershocks mainly triggered by shaking, not static stress
And finally… World's leggiest animal leaps back into limelight
* Mention of papers to be published at the same time with the same embargo
* Geographical listing of authors
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 Palaeobiology: Earliest fossil evidence for life on Earth? (pp 714-718; N&V)
Strangely shaped rock formations in Western Australia’s Pilbara region may be the earliest fossil evidence of life on Earth, according to an article in Nature. A comprehensive study of the layered sediments called stromatolites suggests that microbes were alive and well in tidal reefs some 3,430 million years ago.
Australia’s stromatolites, which were first described almost three decades ago, are a source of spirited debate. Some think they were formed by primitive microbes, whereas others believe they were formed chemically by hydrothermal vents.
In an attempt to resolve the dispute, Abigail Allwood and her colleagues studied a stretch of stromatolite-rich rock over 10 kilometres long, and identified seven differently shaped types of stromatolite, each in their own environmental niche.
Some look like upside-down ice cream cones, others like egg cartons. Their complexity, the team argue, makes them too complex to be chemical in nature. Viewed as a whole, the stromatolites resemble a reef formation, suggesting the presence of a complex ecosystem.
 Planetary science: Another look beneath Titan's haze (pp 709-713)
A new view of Saturn's moon Titan reported in this week's Nature shows the striking variety of surface structures on this haze-shrouded world, including a first glimpse of craters formed by other bodies hitting the surface.
The remarkable thing about Titan's surface is that in fact there are so few craters, compared with the pock-marked face of the bare, icy Saturnian moon Rhea. A team led by Steve Wall conclude that Titan's surface is either geologically active, so that tectonic movements or outflows of material from 'cold volcanoes' have covered over the traces of old craters, or that it has such a thin icy crust lying over softer material below that the craters flatten out like dents in soft sand and then become covered over by dust.
As well as two craters of 450 and 80 kilometres across, the new images of Titan show a range of other features. Cassini's Titan Radar Mapper imaged a long swath of the surface, reaching from high in the southern hemisphere to high in the northern and covering nearly two million square kilometres of the moon's surface. This was only the third close fly-by of Titan by Cassini, which passed just 1,579 kilometres above the surface and showed features as small as a few hundred metres across.
Titan's atmosphere is full of organic (carbon-based) substances, which account for the tawny haze that normally hides the surface. Before the Cassini mission it had been thought that the moon might have lakes or even oceans of liquid hydrocarbons below this shroud. Cassini hasn't confirmed that, but the images acquired in this and previous fly-bys have revealed what seem to be sinuous, river-like dark channels that may have been formed by the flow of such liquids, perhaps methane. Wall's team has also seen dark streaks that might be dunes formed from particles of ice or solid organic materials.
 Fossils: Dwarf dinosaurs lived an island life (pp 739-741)
A new species of dwarf dinosaur has been discovered in northern Germany. It’s thought that the tiny plant-munching sauropod lived on an island during the Late Jurassic period, making it the first known example of island dwarfism for dinosaurs.
Martin Sander and colleagues studied the remains of over 11 sauropods found in the Kimmeridgian marine beds of northern Germany. With total body lengths ranging from 1.7 to 6.2 metres, the team originally thought that the dinosaurs were juveniles. But bone histology indicated that they were dwarfed adults, and the new species is unveiled in this week’s Nature.
With the central Europe of Jurassic times submerged by sea, the little dinosaurs probably lived on one of the large islands around the Lower Saxony basin. Here, physical isolation and limited resources would have favoured the survival of smaller dinosaurs with lesser appetites.
 &  Sleep: Brain region linked to fly slumber (pp 753-756; 757-760)
Researchers have pinpointed a brain area in flies that is crucial to sleep, raising interesting speculation over the purpose of sleep and its possible link with learning and memory.
In two separate Nature papers, teams lead by Ravi Allada and Amita Sehgal use different methods to show that the so-called mushroom bodies are essential for sleep regulation in the fruitfly Drosophila melanogaster. Quite how the mushroom bodies control sleep is uncertain, but Allada and colleagues show that if the area is destroyed chemically, flies sleep less.
Mushroom bodies are known to have a role in learning and memory, raising the possibility that sleep and learning are somehow linked in the fly brain. This lends weight to the notion that, in flies, sleep may function to consolidate memories that are formed during the day - something that is known to occur in vertebrates.
Sleeping flies are similar to sleeping humans. Both are groggy when woken suddenly, and need extra slumber if sleep deprived. It’s therefore possible, the authors argue, that a mechanism regulating both sleep and learning could be evolutionarily conserved. So studying the mushroom bodies may help to throw light on the mechanisms governing vertebrate and invertebrate sleep.
 Organic chemistry: Twisted logic leads to elusive molecule (pp 731-734; N&V)
The amino-acid building blocks of protein molecules are held together by so-called amide bonds, a subject of deep interest for chemists and biochemists. Kousuke Tani and Brian Stoltz have now succeeded in making an unusual amide-containing molecule that has been sought for almost 70 years. Publishing in Nature this week, they say that it should lead to a better understanding of the behaviour and properties of this crucial chemical linkage.
An amide group consists of a nitrogen atom linked to a carbon atom that is also joined to an oxygen atom by a double bond: in chemical notation, it can be written -N-CO-. What is unusual about the version created by Tani and Stoltz is that the nitrogen atom is linked into two six-atom rings, making a so-called bicyclic framework. This twists and distorts the amide group, making it behave differently from those in ordinary amide molecules - for one thing, the nitrogen atom becomes a stronger base (the opposite of an acid).
This molecule, called 2-quinuclidone, has defeated the attempts of some of the world's top chemists to make it, because the twist renders it rather unstable and hard to put together. Tani and Stoltz succeeded where others had failed by using a new strategy that involves kicking out a nitrogen molecule from the parent compound, providing a strong driving force for the reaction. They have been able to isolate a salt of 2-quinuclidone and verify using crystallography that they have made the right molecule.
 Earth science: Earthquake aftershocks mainly triggered by shaking, not static stress (pp 735-738; N&V)
The aftershocks produced by earthquakes are mainly triggered by seismic waves, rather than changes in static stress caused by the 'mainshock', as was previously thought.
In this week's Nature, Karen Felzer and Emily Brodsky present an analysis of the aftershocks produced by a range of mainshocks in Southern California between 1984 and 2002. At greater distances from the mainshock, the probability of finding an aftershock declines in such a way that suggests dynamic stresses, carried by seismic waves, are the culprits. This means that even relatively small earthquakes can sometimes trigger aftershocks up to 100 kilometres away, and could have important implications for predicting where aftershocks will occur.
"This comes as something of a surprise," comments Ian Main in a related News and Views article. "Further work is required to pin down the exact mechanisms at work."
Karen RF Felzer (U.S. Geological Survey, Pasadena, CA, USA)
Tel: +1 626 583 7822; E-mail: [email protected] <mailto:[email protected]>
Please note the author is travelling and it may be easier to reach her on her mobile: +1 310 569 4688.
 And finally… World's leggiest animal leaps back into limelight (p 707)
The world's leggiest millipede - and the one that comes closest to actually living up to its name - has made a surprise reappearance decades after it was first discovered. Illacme plenipes, which has up to 750 legs, has been spotted in a tiny patch of San Benito County, California, the first time it had been seen since 1926.
Although there are some 10,000 known millipede species, none actually possesses the mythical 1,000 legs. I. plenipes comes close, however, although the 12 new specimens unveiled by Paul Marek and Jason Bond have a wide range of different tallies. Females definitely wear the (presumably rather complicated) trousers in this species: the three adult females described here each have more than 660 legs, compared with between 318 and 402 for the four adult males, and fewer still for the five juveniles.
The variation may be because these creatures continue to add to their collection even after reaching sexual maturity, the authors suggest in a Brief Communication in this week's Nature. Females can reach more than 30 millimetres in length, and yet the millipedes are a mere half a millimetre wide, which makes the complexity of their legs and reproductive organs all the more surprising.
ALSO IN THIS ISSUE…
 Noise-resistant and synchronized oscillation of the segmentation clock (pp 719-723)
 Stabilization of the disk around beta Pictoris by extremely carbon-rich gas (pp 724-726)
 A constitutive law for dense granular flows (pp 727-730)
 Intensity of sexual selection along the anisogamy-isogamy continuum (pp 742-745)
 Social interactions among epithelial cells during tracheal branching morphogenesis (pp 746-749)
 Importance of SoxE in neural crest development and the evolution of the pharynx (pp 750-752)
 Germline transmission of genetically modified primordial germ cells (pp 766-769)
 SAGA interacting factors confine sub-diffusion of transcribed genes to the nuclear envelope (pp 770-773)
 Nuclear pore association confers optimal expression levels for an inducible yeast gene (pp 774-778)
GEOGRAPHICAL LISTING OF AUTHORS…
The following list of places refers to the whereabouts of authors on the papers numbered in this release. For example, London: 4 - this means that on paper number four, there will be at least one author affiliated to an institute or company in London. The listing may be for an author's main affiliation, or for a place where they are working temporarily. Please see the PDF of the paper for full details.
Marseille: 10, 11
Paris: 16, 17
UNITED STATES OF AMERICA
Pasadena: 2, 6, 7, 14
Santa Cruz: 7
Stanford: 2, 13
District of Columbia
New York: 2
For North America and Canada
For Japan, Korea, China, Singapore and Taiwan
For the UK/Europe/other countries not listed above
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