New Very Large Ordovician Anomalocaridid Discovered

aleontologists have discovered that a group of remarkable ancient sea creatures existed for much longer and grew to much larger sizes than previously thought, thanks to extraordinarily well-preserved fossils discovered in Morocco.

The creatures, known as anomalocaridids, were already thought to be the largest animals of the Cambrian period, known for the "Cambrian Explosion" that saw the sudden appearance of all the major animal groups and the establishment of complex ecosystems about 540 to 500 million years ago. Fossils from this period suggested these marine predators grew to be about two feet long. Until now, scientists also thought these strange invertebrates—which had long spiny head limbs presumably used to snag worms and other prey, and a circlet of plates around the mouth—died out at the end of the Cambrian.

Now a team led by former Yale researcher Peter Van Roy (now at Ghent University in Belgium) and Derek Briggs, director of the Yale Peabody Museum of Natural History, has discovered a giant fossilized anomalocaridid that measures one meter (more than three feet) in length. The anomalocaridid fossils reveal a series of blade like filaments in each segment across the animal's back, which scientists think might have functioned as gills.

In addition, the creature dates back to the Ordovician period, a time of intense biodiversification that followed the Cambrian, meaning these animals existed for 30 million years longer than previously realized.

"The anomalocaridids are one of the most iconic groups of Cambrian animals," Briggs said. "These giant invertebrate predators and scavengers have come to symbolize the unfamiliar morphologies displayed by organisms that branched off early from lineages leading to modern marine animals, and then went extinct. Now we know that they died out much more recently than we thought."

Note: There is a Devonian anomalocaridid already, Schinderhannes bartelsi, which already extended the clades' existence furter than the Ordovician already. This one IS the biggest by far though.

Kepler/Spitzer Telescopes Find, Confirm New Multi ExoPlanet System

A new planetary member of the Kepler-10 solar system was announced today. Using data from NASA's Spitzer Space Telescope, members of the Kepler science team confirmed a new planet, dubbed Kepler-10c.

The Kepler-10 star system is located about 560 light-years away near the Cygnus and Lyra constellations. The Kepler telescope has discovered two planets around this star. Kepler-10b is, to date, the smallest known rocky exoplanet, or planet outside our solar system (dark spot against yellow sun). This planet, which has a radius of 1.4 times that of Earth's, whips around its star every .8 days. Its discovery was announced in Jan. 2011.

Now, in May 2011, the Kepler team is announcing another member of the Kepler-10 family, called Kepler-10c. It's bigger than Kepler-10b with a radius of 2.2 times that of Earth's, and it orbits the star every 45 days. Both planets would be blistering hot worlds.

Kepler-10c was first identified by Kepler, and later validated using a combination of a computer simulation technique called "Blender," and NASA's Spitzer Space Telescope. Both of these methods are powerful ways to validate the Kepler planets that are too small and faraway for ground-based telescopes to confirm using the radial-velocity technique. The Kepler team says that a large fraction of their discoveries will be validated with both of these methods.

In the case of Kepler-10c, scientists can be 99.998 percent sure that the signal they detected is from an orbiting planet. Part of this confidence comes from the fact that Spitzer, an infrared observatory, saw a signal similar to what Kepler detected in visible light. If the signal were coming from something other than an orbiting planet -- for example an indistinguishable background pair of orbiting stars -- then scientists would expect to see different signals in visible and infrared light.

No time...but awesome.

The Most Expensive Part Is Not the First Two Steps

I'm working on a lunar resources chimera post like what James did for us about He-3.

Mammalian Brain Expansion Due to Increased Sense of Smell?

Mammals first evolved their characteristic large brains to enable a stronger sense of smell, according to a new study published this week in the journal Science by paleontologists from The University of Texas at Austin, Carnegie Museum of Natural History and St. Mary's University in San Antonio.

This latest study is the first to use CT technology, similar to medical scanners, to reconstruct the brains of two of the earliest known mammal species, both from the Jurassic fossil beds of China. The 3D scans revealed that even these tiny, 190-million-year-old animals had developed brains larger than expected for specimens of their period, particularly in the brain area for smell.

Among living animals, mammals have the largest brains relative to body size. Scientists have proposed many explanations, but because fossil skulls of early mammals are extremely rare, have been reluctant to cut them open for closer study, thus destroying the fossils. Scientists have mostly relied on comparative studies of living mammals.

"We studied the outside features of these fossils for years," said Tim Rowe, professor in the Jackson School of Geosciences and director of the Vertebrate Paleontology Laboratory at The University of Texas at Austin, and lead author of the new study. "But until now, studying the brains meant destroying the fossils. With CT technology, we can have our cake and eat it, too."

According to the study, other factors leading to larger brains in early mammals included greater tactile sensitivity and enhanced motor coordination. Fossils of some of the earliest mammals, such as Hadrocodium, bore full coats of fur, explaining the need for enhanced tactile sensitivity.

Rowe's co-authors are Thomas E. Macrini, assistant professor of biological sciences at St. Mary's University in San Antonio, and Zhe-Xi Luo, curator and associate director for research and collections at the Carnegie Museum of Natural History.

Macrini conducted much of this research for his doctoral dissertation at The University of Texas at Austin, in which he scanned the heads of numerous fossil and living species to visualize the size and shape of their brains.

"This is the most comprehensive study yet undertaken using computed tomography to study the evolution of the mammalian skull," said Macrini. "And it is exciting to see these new insights emerging from years of intense labor."

Luo was involved in the discovery and research on the fossils for this study. When he first described the paper clip-sized mammal Hadrocodium ten years ago, he named it for its relatively large cranium despite its appearance so early in the mammalian lineage ("hadro" means "fullness" in Latin and "codium" means "head").

hm. Do we see a similar trend for gorgons? They had an awesome sense of smell.

Another Xenopermian Teaser

Zach did it.

Can you guess the lineage?

It LOVES walrodonts.

Cryptolacerta hassiaca: A New Basal Amphisbaenian

The recent discovery by researchers from the University of Toronto Mississauga and the Museum für Naturkunde Berlin, Germany of a tiny, 47 million-year-old fossil of a lizard called Cryptolacerta hassiaca provides the first anatomical evidence that the body shapes of snakes and limbless lizards evolved independently.

"This fossil refutes the theory that snakes and other burrowing reptiles share a common ancestry and reveals that their body shapes evolved independently," says lead author Professor Johannes Müller of Humboldt-Universität, Berlin.

The fossil reveals that amphisbaenians are not closely related to snakes, but instead are related to lacertids, a group of limbed lizards from Europe, Africa and Asia. "This is the sort of study that shows the unique contributions of fossils in understanding evolutionary relationships," says Professor Robert Reisz from the University of Toronto Mississauga, the senior author of the study. "It is particularly exciting to see that tiny fossil skeletons can answer some really important questions in vertebrate evolution".

The German research team, led by Müller and American graduate student Christy Hipsley, used X-ray computed tomography to reveal the detailed anatomy of the lizard's skull and combined the anatomy of Cryptolacerta and other lizards with DNA from living lizards and snakes to analyze relationships. Their results showed that Cryptolacerta shared a thickened, reinforced skull with worm lizards and that both were most closely related to lacertids, while snakes were related to monitor lizards like the living Komodo dragons.

The press release was badly written, IMNSHO.

Triassic Archosaur Pushes Back Archosaurian Origins

A fossil unearthed in China in the 1970s of a creature that died about 247 million years ago, originally thought to be a distant relative of both birds and crocodiles, turns out to have come from the crocodile family tree after it had already split from the bird family tree, according to research led by a University of Washington paleontologist.

The only known specimen of Xilousuchus sapingensis has been reexamined and is now classified as an archosaur. Archosaurs, characterized by skulls with long, narrow snouts and teeth set in sockets, include dinosaurs as well as crocodiles and birds.

The new examination dates the X. sapingensis specimen to the early Triassic period, 247 million to 252 million years ago, said Sterling Nesbitt, a UW postdoctoral researcher in biology. That means the creature lived just a short geological time after the largest mass extinction in Earth's history, 252 million years ago at the end of the Permian period, when as much as 95 percent of marine life and 70 percent of land creatures perished. The evidence, he said, places X. sapingensis on the crocodile side of the archosaur family tree.

"We're marching closer and closer to the Permian-Triassic boundary with the origin of archosaurs," Nesbitt said. "And today the archosaurs are still the dominant land vertebrate, when you look at the diversity of birds."

The work could sharpen debate among paleontologists about whether archosaurs existed before the Permian period and survived the extinction event, or if only archosaur precursors were on the scene before the end of the Permian.

"Archosaurs might have survived the extinction or they might have been a product of the recovery from the extinction," Nesbitt said.

The research is published May 17 online in Earth and Environmental Science Transactions of the Royal Society of Edinburgh, a journal of Cambridge University in the United Kingdom.

The paper is here.

16th Annual CESM Workshop: Final Agenda

16th Annual CESM Workshop

20 - 23 June 2011

The Village, Breckenridge, Colorado

Monday, 20 June 2011
10:00 a.m. Registration
12:00 – 1:00 p.m. Lunch (on your own)
1:00 – 2:00 p.m. “State of the CESM” by Jim Hurrell, NCAR
2:00 – 3:00 p.m. CESM Distinguished Achievement Award
3:00 – 3:30 p.m. Break
3:30 – 5:00 p.m. Poster Session (Forest Room)
5:00 – 6:30 p.m. Reception (light appetizers and cash bar) (Elk Room; Antlers A; Antlers B)

Tuesday, 21 June 2011
7:00 – 8:30 a.m. Registration and Continental Breakfast
8:30 – 12:00p.m. Atmosphere Model Working Group Meeting (Ten Mile Room)
8:30 – 12:00p.m. Paleoclimate Working Group Meeting (Tarn Room)
8:30 – 12:00p.m. Polar Climate Working Group Meeting (Aspen / Blue Spruce Room)
10:30 – 11:00 a.m. Break
12:00 – 1:30 p.m. Lunch (on your own)
1:30 – 5:00 p.m. Ocean Model Working Group Meeting (Ten Mile Room)
1:30 – 5:00 p.m. Chemistry Climate Working Group Meeting (Tarn Room)
1:30 – 5:00 p.m. Land Model Working Group Meeting (Aspen / Blue Spruce Room)
3:00 – 3:30 p.m. Break
6:30 – 8:00 p.m. Interest Group on Uncertainty Quantification in Climate (Ten Mile Room)

Wednesday, 22 June 2011
7:00 – 8:30 a.m. Registration and Continental Breakfast
8:30 – 12:00 a.m. Biogeochemistry Working Group Meeting (Ten Mile Room)
8:30 – 12:00 a.m. Climate Variability Working Group Meeting (Tarn Room)
8:30 – 12:00 a.m. Land Ice Working Group Meeting (Aspen / Blue Spruce Room)
10:30 – 11:00 a.m. Break
12:00 – 2:00 p.m. Lunch (on your own)
2:00 – 3:00 p.m. Plenary Presentation – GFDL's ESM2 Series Simulations of Coupled Carbon, Climate and Ecosystems by John Dunne, NOAA / GFDL
3:00 – 3:30 p.m. Break
3:30 – 4:30 p.m. Plenary Presentation – Communicating the Credibility of Climate Change Science by Jeff Kiehl, NCAR

Thursday, 23 June 2011
7:00 – 8:30 a.m. Registration and Continental Breakfast
8:30 – 12:00 p.m. Software Engineering Working Group Meeting (Aspen / Blue Spruce Room)
8:30 – 12:00 p.m. Climate Change Working Group Meeting (Ten Mile Room)
8:30 – 12:00 p.m. WACCM Working Group Meeting (Tarn Room)
10:30 – 11:00 a.m. Break
12:00 – 1:30 p.m. Discussion and Wrap-up (Ten Mile Room)
1:30 p.m. Adjourn

Anyone Have a Copy?

H. -D. Sues, J. A. Hopson, and N. H. Shubin. 1992. Affinities of Scalenodontoides plemmyridon Hopson, 1984 (Synapsida: Cynodontia) from the Upper Triassic of Nova Scotia. Journal of Vertebrate Paleontology 12(2):168-171 [R. Butler/R. Butler/R. Butler]

Any other more recent papers on Arctotraversodon would be welcome, too.

Thanx.

Climatically driven biogeographic provinces of Late Triassic tropical Pangea

Climatically driven biogeographic provinces of Late Triassic tropical Pangea

1. Jessica H. Whiteside (a,*),

2. Danielle S. Grogan (a)

3. Paul E. Olsen (b,*)

4. Dennis V. Kent (b,c)

a. Department of Geological Sciences, Brown University, 324 Brook Street, Box 1846, Providence, RI 02912;

b. Lamont-Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, NY 10964

c. Department of Earth and Planetary Sciences, Rutgers University, Piscataway, NJ 08854

*. To whom correspondence may be addressed. E-mail: Jessica_Whiteside@Brown.edu or polsen@ldeo.columbia.edu.

Abstract:

Although continents were coalesced into the single landmass Pangea, Late Triassic terrestrial tetrapod assemblages are surprisingly provincial. In eastern North America, we show that assemblages dominated by traversodont cynodonts are restricted to a humid 6° equatorial swath that persisted for over 20 million years characterized by “semiprecessional” (approximately 10,000-y) climatic fluctuations reflected in stable carbon isotopes and sedimentary facies in lacustrine strata. More arid regions from 5–20°N preserve procolophonid-dominated faunal assemblages associated with a much stronger expression of approximately 20,000-y climatic cycles. In the absence of geographic barriers, we hypothesize that these variations in the climatic expression of astronomical forcing produced latitudinal climatic zones that sorted terrestrial vertebrate taxa, perhaps by excretory physiology, into distinct biogeographic provinces tracking latitude, not geographic position, as the proto-North American plate translated northward. Although the early Mesozoic is usually assumed to be characterized by globally distributed land animal communities due to of a lack of geographic barriers, strong provinciality was actually the norm, and nearly global communities were present only after times of massive ecological disruptions.

ha! Called it! Over at Chineleana some time ago, I asked if anyone had looked at the difference in climates between the the American SW and the Newark Basin.

Note: SF Authors. If you have a supercontinent, its just as likely to have multiple ecosystems as a world broke up into multiple continents.

Another interesting note is that the procolophonids and the traversodont cynodonts seem to have been ecological equivalents. I don't know of any procs the size of Arctotraversodon though. It had a 40 cm skull, iirc.

Could Leakage from the Agulhas Current System Moderate Europe's Changed Climate?

Neandertals Had Second Late Survival Locale in Russia?

Scientists have identified what may be one of the last northern refuges of Neanderthals, a spot near the Arctic Circle in Russia with artifacts dated to 31,000 to 34,000 years ago.

Stone tools and flakes found there look like the work of Neanderthals, the stocky, muscular hunters who lived in Europe and western Asia until they were replaced by modern humans, researchers reported Thursday in the journal Science.

The site lies along the Pechora River west of the Ural Mountains, about 92 miles south of the Arctic Circle. Researchers dated it from animal bones and sand grains. Nobody has found any human bones or DNA that could provide stronger evidence that Neanderthals lived there, report the scientists, from Russia, France and Norway. The artifacts had been collected during various expeditions.

Neanderthals first appeared more than 200,000 years ago. They died out sometime after modern humans arrived in Europe, which occurred some 40,000 to 45,000 years ago.

Richard Klein, a Stanford University professor of anthropology, said the artifacts do look like the work of Neanderthals, but that it's also possible they were made by modern people instead.

Neanderthals were not previously known to be in that area, nor convincingly shown to be present anywhere at such a recent time, he said. Finding another site or human bones would help settle the question, he said.

paper here.

Paleocene Marsupials Demonstrate Social Behavior

Evidence of lifestyle and social behavior is almost never preserved in the fossil record. Now, a group of researchers from the Muséum national d'Histoire naturelle (Paris), CNRS (Paris) and Museo de Historia naturel Alcide d'Orbigny de Cochabamba (Bolivia) has excavated a remarkable collection of dozens of small mammal skulls and skeletons from the Tiupampa site in the central Andes in Bolivia that provides compelling fossil evidence of social behavior. A study of these remains, published this week in Nature, reveals the oldest example of group-living in mammals.

Today, many mammals live in groups. Others, such as most marsupials (which include the South American opossums and Australian koalas and wombats), are strictly solitary. We know very little about social behavior of fossil mammals, because only rarely is the number of preserved individuals large enough to provide evidence of community life.

Now, the discovery of a population of a mouse-sized ancient relative of marsupials (Pucadelphys andinus) from the early Tertiary (64 million years ago) in Bolivia demonstrates that group-living appeared early in the mammalian history, and may even represent the ancestral condition for mammals as a whole.

Basal synapsids have already been shown to be social, just an fyi.

More on NASA's Discovery Mission Down Select

Dollo's Law Has Exceptions?

Ever since Charles Darwin proposed his theory of evolution in 1859, scientists have wondered whether evolutionary adaptations can be reversed.

Answering that question has proved difficult, partly due to conflicting evidence. In 2003, scientists showed that some species of insects have gained, lost and regained wings over millions of years. But a few years later, a different team found that a protein that helps control cells' stress responses could not evolve back to its original form.

Jeff Gore, assistant professor of physics at MIT, says the critical question to ask is not whether evolution is reversible, but under what circumstances it could be. "It's known that evolution can be irreversible. And we know that it's possible to reverse evolution in some cases. So what you really want to know is: What fraction of the time is evolution reversible?" he says.

By combining a computational model with experiments on the evolution of drug resistance in bacteria, Gore and his students have, for the first time, calculated the likelihood of a particular evolutionary adaptation reversing itself.

They found that a very small percentage of evolutionary adaptations in a drug-resistance gene can be reversed, but only if the adaptations involve fewer than four discrete genetic mutations. The findings will appear in the May 13 issue of the journal Physical Review Letters. Lead authors of the paper are two MIT juniors, Longzhi Tan and Stephen Serene.

Gore and his students used an experimental model system developed by researchers at Harvard University to study the evolution of a gene conferring resistance to the antibiotic cefotaxime in bacteria.

The Harvard team identified five mutations that are crucial to gaining resistance to the drug. Bacteria that have all five mutations are the most resistant, while bacteria with none are very susceptible to the drug. Susceptible bacteria can evolve toward resistance by gaining each of the five mutations, but they can't be acquired in any old order. That's because evolution can only proceed along a given path if each mutation along the way offers a survival advantage.

Scientists study these paths by creating a "fitness landscape": a diagram of possible genetic states for a particular gene, and each state's relative fitness in a given environment. There are 120 possible paths through which bacteria with zero mutations could accumulate all five, but the Harvard team found that only 18 could ever actually occur.

The MIT team built on that study by asking whether bacteria could evolve resistance to cefotaxime but then lose it if they were placed in a new environment in which resistance to the original drug hindered their ability to survive.

Genetic states that differ by only one mutation are always reversible if one state is more fit in one environment and the other is more fit in the other. The MIT researchers were able to study how the possibility of reversal decreases as the number of mutations between the two states increased.

"This is the first case where anyone's been able to say anything about how reversibility behaves as a function of distance," Gore says. "What we see in our system is that once the system gets four mutations, it's unable to get back to where it started."

Daniel Weinreich, assistant professor of biology at Brown University, says the study's most important contribution is its analysis of the reversibility between every possible intermediate state in the fitness landscape.

"What Jeff has done is show that there's another layer of mathematical complexity that enters when you ask questions about reversing environmental pressure," says Weinreich, who was not involved in this research.

In the late 19th century, paleontologist Louis Dollo argued that evolution could not retrace its steps to reverse complex adaptations — a hypothesis known as Dollo's law of irreversibility. Gore says his team's results offer support for Dollo's law, but with some qualifications.

"It's not that complex adaptations can never be reversed," he says. "It's that complex adaptations are harder to reverse, but in a sense that you can quantify."

The study also helps explain why organs no longer needed, such as the human appendix, do not readily disappear. "You can only ever really think about evolution reversing itself if there is a cost associated with the adaptation," Gore says. "For example, with the appendix, it may just be that the cost is very small, in which case there's no selective pressure to get rid of it."

hmmm.

Phantom Ray Takes Flight

While China works on its J-20 - an interesting, if questionable analysis of the J-20 here and the F-22 fleet has oxygen generator problems - the US is rapidly working on its UCAVs. The Phantom Ray is the one above and conducted its first flight last month.

Also being worked on are the X-47B and Avenger.

Note the F-35 in the background above. The F-35 program delivered its first production aircraft this week as well. Still a ways from IOC though.

NASA Selects Next Discovery Missions

ASA has selected three science investigations from which it will pick one potential 2016 mission to look at Mars' interior for the first time; study an extraterrestrial sea on one of Saturn's moons; or study in unprecedented detail the surface of a comet's nucleus.

Each investigation team will receive $3 million to conduct its mission's concept phase or preliminary design studies and analyses. After another detailed review in 2012 of the concept studies, NASA will select one to continue development efforts leading up to launch. The selected mission will be cost-capped at $425 million, not including launch vehicle funding.

NASA's Discovery Program requested proposals for spaceflight investigations in June 2010. A panel of NASA and other scientists and engineers reviewed 28 submissions. The selected investigations could reveal much about the formation of our solar system and its dynamic processes. Three technology developments for possible future planetary missions also were selected.

"NASA continues to do extraordinary science that is re-writing textbooks," said NASA Administrator Charles Bolden. "Missions like these hold great promise to vastly increase our knowledge, extend our reach into the solar system and inspire future generations of explorers."

The planetary missions selected to pursue preliminary design studies are:

1. * Geophysical Monitoring Station (GEMS) would study the structure and composition of the interior of Mars and advance understanding of the formation and evolution of terrestrial planets. Bruce Banerdt of NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif., is principal investigator. JPL would manage the project. [Editorial note: This previous post describes a two station Mars geophysical network, while the short description for this candidate proposal suggests it may be for a single station.]
2. * Titan Mare Explorer (TiME) would provide the first direct exploration of an ocean environment beyond Earth by landing in, and floating on, a large methane-ethane sea on Saturn's moon Titan. Ellen Stofan of Proxemy Research Inc. in Gaithersburg, Md., is principal investigator. Johns Hopkins University's Applied Physics Laboratory in Laurel, Md., would manage the project.
3. * Comet Hopper would study cometary evolution by landing on a comet multiple times and observing its changes as it interacts with the sun. Jessica Sunshine of the University of Maryland in College Park is principal investigator. NASA's Goddard Space Flight Center in Greenbelt, Md., would manage the project.

"This is high science return at a price that’s right," said Jim Green, director of NASA’s Planetary Science Division in Washington. "The selected studies clearly demonstrate a new era with missions that all touch their targets to perform unique and exciting science."

Torn between Titan and Mars here...

Parareptiles Not Hit as Badly by Permian Extinction?

The end-Permian extinction, by far the most dramatic biological crisis to affect life on Earth, may not have been as catastrophic for some creatures as previously thought, according to a new study led by the University of Bristol.

An international team of researchers studied the parareptiles, a diverse group of bizarre-looking terrestrial vertebrates which varied in shape and size. Some were small, slender, agile and lizard-like creatures, while others attained the size of rhinos; many had knobbly ornaments, fringes, and bony spikes on their skulls.

The researchers found that, surprisingly, parareptiles were not hit much harder by the end-Permian extinction than at any other point in their 90 million-year history. Furthermore, the group as a whole declined and diversified time and time again throughout its history, and it was not until about 50 million years after the end-Permian crisis that the parareptiles finally disappeared.

During the end-Permian extinction, some 250 million years ago, entire groups of animals and plants either vanished altogether or decreased significantly in numbers, and the recovery of the survivors was at times slow and prolonged before new radiations took place.

By studying the fossil record, palaeontologists can examine how individual groups of organisms responded to the end-Permian event and assess just how dramatic it was. However, as the quality and completeness of the fossil record varies considerably, both geographically and stratigraphically, palaeontologists need to find a way to ‘join the dots’ and piece together the fragments of a complex mosaic to give a more satisfactory and better picture of ancient life’s diversity.

Paper here.

CAM Plants Spread During Miocene When Habitat Expanded

n a paper published in the early edition of the Proceedings of the National Academy of Sciences, Brown University biologists and colleagues have discovered that the rapid speciation of cacti occurred between 5 and 10 million years ago and coincided with species explosions by other succulent plant groups around the world. The researchers propose that a prolonged dry spell and possibly lower levels of atmospheric carbon dioxide during that time, known as the late Miocene, opened habitat that contributed to the rise of these plants and a broad vegetative makeover on Earth.

"The cacti, as a group, have been around for a while, but most of the species diversity that we see today was generated really recently," said Monica Arakaki, a postdoctoral researcher at Brown and the paper's lead author.

The Brown team and colleagues from Oberlin College and the University of Zurich, Switzerland, were interested primarily in dating the origins of the cacti (scientific name Cactaceae). The team sequenced the chloroplast genomes (the organelles inside plant leaves that engineer photosynthesis) for a dozen cacti and their relatives and combined their new genomic data with existing genomes to build a phylogeny, or evolutionary tree, for angiosperms, the genealogical line of flowering plants that represents roughly 90 percent of all plants worldwide. From there, the scientists deduced that Cactaceae first diverged from its angiosperm relatives roughly 35 million years ago but didn't engage in rapid speciation for at least another 25 million years.

"Cacti were actually present on the landscape for millions of years — looking like cacti and acting like cacti — before they began their major diversification," said Erika Edwards, assistant professor of biology in the Department of Ecology and Evolutionary Biology at Brown and corresponding author on the paper.

The team then sifted through the literature on the timing of diversification in other succulents from regions around the globe. Succulents include aloes, the agaves of North America, the ice plants of South Africa and other lineages. Their comfort zone is in water-limited climates, and they have adapted physical characteristics to cope in those locales, such as shallow root systems, specialized water-storing tissue and exchanging gas at night, when it is cooler and less humid and so less water is lost. What struck the researchers was that all the succulent lineages, across habitats and continents, underwent major speciation between 5 and 10 million years ago, during roughly the same time period as the cacti.

C4 grasses, the tropical grasses that are now up to 20 percent of our planet's vegetative covering, burst onto the scene as well during this same window of time.

This must be more than a coincidence, the researchers thought. "It isn't overly surprising that most of the standing cactus diversity is relatively young. But when you put these species radiations in the context of all the other changes in plant communities that were happening at that very moment, all over the world, it begs some sort of global environmental driver," Edwards said.

The most plausible causes, the scientists thought, were a drying out of the planet and lowering of atmospheric carbon-dioxide levels. A wealth of research involving oxygen isotopes from a deep-sea organism showed the Earth underwent a drop in temperature, which the researchers believe led to reduced rainfall and increased aridity worldwide.

The carbon-dioxide link is more nuanced and controversial. The authors highlight one study that inferred atmospheric CO2 levels spiraled downward beginning roughly 15 million years ago. Combined with global cooling, "a drop in CO2 concentration would therefore immediately expand the ecological space in which drought-adapted succulent plants, with their high photosynthetic water use efficiency, would be competitive," the authors write.

"We suggest that a rapid expansion of available habitat (rather than any particular new 'key' innovation) during the late Miocene was a primary driver of the global diversification of plant lineages already possessing a preadapted succulent syndrome," the researchers write. "Against a backdrop of increasing global aridity, a sharp CO2 decline is a plausible driver of the simultaneous expansion of C4 grasslands, the clustering of new C4 origins, and the diversification of succulent lineages."

New High Quality J-20 Picture