Scientists decoded the genome of living fossil Coelacanth

April 18th, 2013 Riffin

An international team of researchers has decoded the genome of a creature whose evolutionary history is both enigmatic and illuminating: the African coelacanth. A sea-cave dwelling, five-foot long fish with limb-like fins, the coelacanth was once thought to be extinct. A living coelacanth was discovered off the African coast in 1938, and since then, questions about these ancient-looking fish — popularly known as “living fossils” — have loomed large. Coelacanths today closely resemble the fossilized skeletons of their more than 300-million-year-old ancestors. Its genome confirms what many researchers had long suspected: genes in coelacanths are evolving more slowly than in other organisms.

“We found that the genes overall are evolving significantly slower than in every other fish and land vertebrate that we looked at,” said Jessica Alföldi, a research scientist at the Broad Institute and co-first author of a paper on the coelacanth genome, which appears in Nature this week. “This is the first time that we’ve had a big enough gene set to really see that.”

Living fossil fish, Coelacanth. (Credit: © alessandrozocc / Fotolia)

Living fossil fish, Coelacanth. (Credit: © alessandrozocc / Fotolia)

Researchers hypothesize that this slow rate of change may be because coelacanths simply have not needed to change: they live primarily off of the Eastern African coast (a second coelacanth species lives off the coast of Indonesia), at ocean depths where relatively little has changed over the millennia.

“We often talk about how species have changed over time,” said Kerstin Lindblad-Toh, scientific director of the Broad Institute’s vertebrate genome biology group and senior author. “But there are still a few places on Earth where organisms don’t have to change, and this is one of them. Coelacanths are likely very specialized to such a specific, non-changing, extreme environment — it is ideally suited to the deep sea just the way it is.”

Because of their resemblance to fossils dating back millions of years, coelacanths today are often referred to as “living fossils” — a term coined by Charles Darwin. But the coelacanth is not a relic of the past brought back to life: it is a species that has survived, reproduced, but changed very little in appearance for millions of years. “It’s not a living fossil; it’s a living organism,” said Alföldi. “It doesn’t live in a time bubble; it lives in our world, which is why it’s so fascinating to find out that its genes are evolving more slowly than ours.”

The coelacanth genome has also allowed scientists to test other long-debated questions. For example, coelacanths possess some features that look oddly similar to those seen only in animals that dwell on land, including “lobed” fins, which resemble the limbs of four-legged land animals (known as tetrapods). Another odd-looking group of fish known as lungfish possesses lobed fins too. It is likely that one of the ancestral lobed-finned fish species gave rise to the first four-legged amphibious creatures to climb out of the water and up on to land, but until now, researchers could not determine which of the two is the more likely candidate.

In addition to sequencing the full genome — nearly 3 billion “letters” of DNA — from the coelacanth, the researchers also looked at RNA content from coelacanth (both the African and Indonesian species) and from the lungfish. This information allowed them to compare genes in use in the brain, kidneys, liver, spleen and gut of lungfish with gene sets from coelacanth and 20 other vertebrate species. Their results suggested that tetrapods are more closely related to lungfish than to the coelacanth.

However, the coelacanth is still a critical organism to study in order to understand what is often called the water-to-land transition. Lungfish may be more closely related to land animals, but its genome remains inscrutable: at 100 billion letters in length, the lungfish genome is simply too unwieldy for scientists to sequence, assemble, and analyze. The coelacanth’s more modest-sized genome (comparable in length to our own) is yielding valuable clues about the genetic changes that may have allowed tetrapods to flourish on land.

By looking at what genes were lost when vertebrates came on land as well as what regulatory elements — parts of the genome that govern where, when, and to what degree genes are active — were gained, the researchers made several unusual discoveries:

  • Sense of smell. The team found that many regulatory changes influenced genes involved in smell perception and detecting airborne odors. They hypothesize that as creatures moved from sea to land, they needed new means of detecting chemicals in the environment around them.
  • Immunity. The researchers found a significant number of immune-related regulatory changes when they compared the coelacanth genome to the genomes of animals on land. They hypothesized that these changes may be part of a response to new pathogens encountered on land.
  • Evolutionary development. Researchers found several key genetic regions that may have been “evolutionarily recruited” to form tetrapod innovations such as limbs, fingers and toes, and the mammalian placenta. One of these regions, known as HoxD, harbors a particular sequence that is shared across coelacanths and tetrapods. It is likely that this sequence from the coelacanth was co-opted by tetrapods to help form hands and feet.
  • Urea cycle. Fish get rid of nitrogen by excreting ammonia into the water, but humans and other land animals quickly convert ammonia into less toxic urea using the urea cycle. Researchers found that the most important gene involved in this cycle has been modified in tetrapods.

The coelacanth genome may hold other clues for researchers investigating the evolution of tetrapods. “This is just the beginning of many analyses on what the coelacanth can teach us about the emergence of land vertebrates, including humans, and, combined with modern empirical approaches, can lend insights into the mechanisms that have contributed to major evolutionary innovations,” said Chris Amemiya, a member of the Benaroya Research Institute and co-first author of the Nature paper. Amemiya is also a professor at the University of Washington.

Sequencing the full coelacanth genome was uniquely challenging for many reasons. Coelacanths are an endangered species, meaning that samples available for research are almost nonexistent. This meant that each sample obtained was precious: researchers would have “one shot” at sequencing the collected genetic material, according to Alföldi. But the difficulties in obtaining a sample and the challenges of sequencing it also knit the community together.

“The international nature of the work, its evolutionary value and history, and the fact that it was a technically challenging project really brought people together,” said Lindblad-Toh. ” We had representatives from every populated continent on earth working on this project.”

Although its genome offers some tantalizing answers, the research team anticipates that further study of the fish’s immunity, respiration, physiology, and more will lead to deep insights into how some vertebrates adapted to life on land, while others remained creatures of the sea.

Tulip tree’s genome is ‘molecular fossil’

April 17th, 2013 Riffin

The “extraordinary level of conservation” of genetic data in the tulip tree remains largely unchanged since the dinosaurs, a study suggests.The species’ genomic change is about 2,000 times slower than in humans, making it a “molecular fossil”, a team of US researchers said.

The new information has affected our understanding of flowering plants’ evolution, they added.The findings have been published in the open access journal BMC Biology.

The team from the universities of Indiana and Arkansas sequenced the mitochondrial genome of the species (Liriodendron tulipifera), only to discover it had one of the slowest silent mutation rates (a process that does not affect gene function).

They added that the sequencing showed that many of the genes that had been lost during 200 million years of flowering plants’ (angiosperms) evolution had been preserved.

“Based on this, it appears that the genome has been more-or-less frozen in time for millions and millions of years,” explained co-author Prof Jeffrey Palmer.

Prehistoric powerhouses

Mitochondria are found within organisms’ cells and their job is to generate power. They do this by converting food stuffs into chemical energy that the organism uses to function.

 Tulip tree

Tulip tree leaves and flower (Image: Gary Cot/Radford University)
  • Scientific name: Liriodendron tulipifera
  • Average height: 20m-30m
  • Native to the eastern US, and is considered to be one of the region’s tallest native trees
  • Generally flowers in mid-summer
  • Distinctive-shaped leaves, which are said to resemble dinosaur footprints
  • Popular parkland species, as its flowers look similar to tulips
  • Seeds are wind dispersed, often travelling up to seven times the distance of the mother tree
  • The timber has a reputation of being resistant to termites

In an accompanying commentary, Prof Ian Small from the University of Western Australia – who was not involved in the research – said the vast variations between the genetic data of angiosperms gleaned from mitochondrial genome sequencing made “untangling their evolutionary histories difficult“.

However, he added, the paper by Prof Palmer et al turned out to be ” an extremely useful window into the past”.

Prof Small said the species was a member of an “early branching lineage” that was distinct from other groups that housed most of the world’s crop plants, which had been the target of most sequencing efforts around the globe.

As a result of the slow mutation rate, he explained: “This ‘fossilised’ genome gives us some important clues as to what mitochondrial looked like (and how they functioned) as flowering plants evolved and took over the land in the time of the dinosaurs.”

He added that the increasing cost-effectiveness of the sequencing process was making it easier to choose strategically informative species rather than focusing on economically important ones, ie food crops.

He explained that data gaps remained: “The coverage of early diverging plants is still from optimal, with many large and important groups still badly sampled – for example, gymnosperms and ferns.”

He concluded: “I look forward to being able to analyse the next molecular ‘fossil’ to roll off the sequencing machines.”

Source: article by  Mark Kinver Environment reporter, BBC News

WFS Profile: Dr. Rinchen Barsbold

April 17th, 2013 Riffin

Dr. Rinchen Barsbold born December 21, 1935 in Ulan Bator is a Mongolian paleontologist and geologist. He works with the Institute of Geology, at Ulaanbaatar, Mongolia. He is recognized around the world as a leader in vertebrate paleontology and Mesozoic stratigraphy.

Barsbold has been instrumental in the discovery and recovery of one of the largest dinosaur collections in the world. His work has projected Mongolian paleontology into world prominence and helped to form a more modern understanding of the later stages of dinosaur evolution in Eurasia.

Barsbold has had considerable influence on dinosaur paleontology in the Communist world. Barsbold’s scientific work has made him a leading authority on theropods of the Gobi Desert, starting with his doctoral dissertation on these dinosaurs. As early as 1983, he noted that in different lineages of theropods, many features hitherto only known from birds had evolved in various combinations (Barsbold 1983). He postulated that as a result of this “ornithization”, one or several lineages of theropods that happened to acquire the proper combination of such traits went on to evolve into actual birds.

Paleontologist Rinchen Barsbold with Two Tarbosaurs

Paleontologist Rinchen Barsbold with Two Tarbosaurs

Since the identification of a number of feathered dinosaurs beginning in the late 1990s, Barsbold’s ideas are more fully appreciated. When he initially published his conclusions – a list of generally rather obscure anatomical features – in 1983, there was little exchange between the Mongolian scientific community and that of Western countries. Moreover, Barsbold’s early papers were usually published in Russian, in which few Western scientists are fluent. In addition, Evgeny Kurochkin – probably the leading specialist on bird paleontology in the then-Communist world – was critical of the theropod-bird link, working with and teaching mostly Cenozoic bird paleontology. Therefore, Barsbold’s theories initially had more impact among “dinosaur” paleontologists in Mongolia, the USSR, and allied countries.

2010 Romer-Simpson Medal Recipient Rinchen Barsbold Wrote…….

             “I was born (1935.12.21) in the capital of Mongolia, Ulaanbaatar city, or UB as its’s well-known among the foreigners who have now visited our country. During the most of 20th century my country has been “defended” by the iron curtain from the west and east, and, probably, UB appeared as an abbreviated name only after 1990 while Gorbachev’s perestroika had changed the situation that now seems to be so stable and steady. Hopefully, our Mongolia is now quite free and democratic country.

But my field research at the Gobian dinosaur sites started long before these remarkable changes took place. Being the leader of the Joint Mongolian-Soviet expeditions, I had the best possibilities to research many times all the great dinosaur sites over the Gobi Desert, and to include notable fossils into the Mongolian Dinosaur Collection, which is well-known in the world. During that time in Warsaw, thanks to the efforts of Z.Kielan-Jaworowska, an outstanding scientist and 1995 Romer-Simpson Medalist, I had a happy opportunity to meet J.H. Ostrom, who worked out his idea on the bird ancestry. Many years after the iron curtain had been taken off, I met again the great scientist in his Peabody Museum. We were no longer so young, and the meeting was very sincere and touching. Ostrom has advanced our knowledge on the dinosaur evolution, having opened the new approaches to the fruitful “dinosaur-bird” concept, a remarkable achievement of the evolutionary biology at the end of 20th century. I dare think that researchers in the Mongolian Gobi are not only simple eye-witnesses, but may also have promoted, even a little, this remarkable concept. Indeed, the divergence and unique state of preservation so characteristic of the Mongolian fossil record allow us to show a number of unusual aspects in the dinosaur morphology, and even to open slightly this fundamental and hidden sphere of the behavior of dinosaurs. Surely, the Fighting Dinosaurs, the Flock of Protoceratops babies, as well as Oviraptorid Citipati in brooding position say much about the dinosaur behavioral aspects, which were absolutely unknown in the science of the last century.

I always keep in mind R.C. Andrews’ words: “Mongolia, a land of mystery, of paradox and promise!” Our friendly cooperations with the colleagues from US, Japan, South Korea, Canada, China, as well as with our old friends from Russia and Poland, have extended the possibilities of the Mongolian Paleontology in which my collaborators and I live. I have had a happy chance to work in many joint expeditions being always their indispensable participant. Now we here understand more deeply the ancient history of the past wild nature of Mongolia and Central Asia as a whole. We see the similarity of the Mongolian dinosaurs with the North American relative groups, and their difference from the Chinese dinosaurs, even though our countries are close neighbours. The great dinosaur sites of the Mongolian Gobi preserve their mystery, paradox and promise. Let’s work further! “

 

Dinosaur Was a Strong Swimmer, Doggy-Paddle Style

April 16th, 2013 Riffin

Claw marks on a 100-million-year-old riverbed in China reveal how some dinosaurs doggy-paddled over long distances, scientists say.

“What we have are scratches left by the tips of a two-legged dinosaur’s feet,” study researcher Scott Persons, of the University of Alberta, said in a statement. “The dinosaur‘s claw marks show it was swimming along in this river and just its tippy toes were touching bottom.”

Stretching over a distance of 50 feet (15 meters), the markings show that the dinosaur had a coordinated, left-right, left-right swimming style, Persons said. The researchers believe the scratches belong to a carnivorous theropod — a type of dinosaur that walked on two legs — that stood roughly 3 feet (1 meter) at the hip.

Dinosaur swimmer

Dinosaur swimmer

While it’s tough to determine the identity of the swimming dinosaur from these marks alone, Persons suspects it could have been an early tyrannosaur or a Sinocalliopteryx, predators known to have roamed this prehistoric landscape in China.

The paddle-scratches were found in a dried-up river in China’s Szechuan Province, which Persons described as a “dinosaur super-highway,” full of the footprints of other Cretaceous-era theropods and long-necked, four-legged sauropods.

The research was detailed April 8 in journal Chinese Science Bulletin.

It’s not the first time dinosaur paddle prints have turned up in the fossil record. In 2007, paleontologists found S-shaped prints on the bottom of what was a lake in the Cameros Basin in Spain 125 million years ago. The unusual tracks indicate the animal’s body was floating in about 10 feet (3.2 m) of water when it scratched the lakebed, researchers said at the time.

Earlier this year, a group of scientists published a study in the Journal of Vertebrate Paleontology arguing that a set of up to 4,000 fossilized footprints in Australia is evidence of a dinosaur river crossing — not a stampede over land, as was long thought.

Source : live science.com

Fossilized shell-breaking Crab

April 15th, 2013 Riffin

While waiting for colleagues at a small natural history museum in the state of Chiapas, Mexico last year, Cornell paleontologist Greg Dietl chanced upon a discovery that has helped rewrite the evolutionary history of crabs and the shelled mollusks upon which they preyed.

In a museum display case he recognized a 67- to 69-million-year-old fossil from the Late Cretaceous period of a big crab with an oversized right claw. Such crabs with claws of different sizes were not known to exist until the early Cenozoic era, about 20 million years later.

Aside from being larger than most known Late Cretaceous crabs (about the size of today’s Florida stone crabs) and having asymmetrical claws, this ancient crab also sported a curved tooth on the movable finger of the larger right claw. This was another specialized adaptation that paleontologists thought developed millions of years later for peeling snail shells open.

“I immediately had to point it out to my colleagues around me,” said Dietl, an adjunct professor in Cornell’s Department of Earth and Atmospheric Sciences and director of collections at the Cornell-affiliated Paleontological Research Institution in Ithaca. “I was really excited when I found it. The fossil re-opens the question of the role crabs played in the well-documented restructuring of marine communities that occurred during the Mesozoic era [251 million years ago to 65 million years ago].”

The discovery led to a study, published March 10 in the online version of the Royal Society’s Biology Letters journal, coauthored by Francisco J. Vega, a geologist at the Universidad Nacional Autónoma de México.

In a museum display case, Cornell paleontologist Greg Dietl recognized a 69 million-year-old crab fossil with an oversized right claw, a feature previously thought to appear more than 20 million years later. Credit: Cornell University

In a museum display case, Cornell paleontologist Greg Dietl recognized a 69 million-year-old crab fossil with an oversized right claw, a feature previously thought to appear more than 20 million years later. Credit: Cornell University

 

The museum’s staff showed Dietl and colleagues another fossil of the same species in a back room. Both specimens, found near the town of Ocozocoautla in southeastern Mexico, are the oldest fossils with these unique features on record and represent a new species, Megaxantho zogue.

The large right “crusher” claw generated a great deal of force to break shells, while the smaller left cutter claw moved faster and could manipulate prey into position. Also, the curved tooth increased the power of the claw.

 

Dietl hopes the discovery will spur other researchers to search for similar examples of these curved tooth structures from the Late Cretaceous period, just prior to the extinction of the dinosaurs.

Although Megaxantho crabs became extinct around 65 million years ago, these features evolved again in other crab species throughout the Cenozoic era, leading to present-day crabs, according to the study. The repeated evolution suggests that such power-enhancing adaptations may evolve during times and places where resources are abundant and accessible, Dietl said.

The study may be relevant to the current stresses of habitat loss, overfishing, climate change and other human-influenced activities that are reducing the productive capacity of the environment.

“We may be diminishing the capacity of organisms to adapt in novel ways,” a consideration that conservationists may need to account for in future strategies for protecting natural areas, he said.

Note:  from a news release issued by Krishna Ramanujan, Cornell University in 2008

Organic Remains from world’s oldest Dinosaur Embryo Bonebed

April 14th, 2013 Riffin

The great age of the embryos is unusual because almost all known dinosaur embryos are from the Cretaceous Period. The Cretaceous ended some 125 million years after the bones at the Lufeng site were buried and fossilized.

Led by University of Toronto Mississauga paleontologist Robert Reisz, an international team of scientists from Canada, Taiwan, the People’s Republic of China, Australia, and Germany excavated and analyzed over 200 bones from individuals at different stages of embryonic development.

“We are opening a new window into the lives of dinosaurs,” says Reisz. “This is the first time we’ve been able to track the growth of embryonic dinosaurs as they developed. Our findings will have a major impact on our understanding of the biology of these animals.”

The bones represent about 20 embryonic individuals of the long-necked sauropodomorph Lufengosaurus, the most common dinosaur in the region during the Early Jurassic period. An adult Lufengosaurus was approximately eight metres long.

This is a flesh reconstruction of embryonic dinosaur inside egg. (Credit: Artwork by D. Mazierski)

This is a flesh reconstruction of embryonic dinosaur inside egg. (Credit: Artwork by D. Mazierski)

The disarticulated bones probably came from several nests containing dinosaurs at various embryonic stages, giving Reisz’s team the rare opportunity to study ongoing growth patterns. Dinosaur embryos are more commonly found in single nests or partial nests, which offer only a snapshot of one developmental stage.

To investigate the dinosaurs’ development, the team concentrated on the largest embryonic bone, the femur. This bone showed a consistently rapid growth rate, doubling in length from 12 to 24 mm as the dinosaurs grew inside their eggs. Reisz says this very fast growth may indicate that sauropodomorphs like Lufengosaurus had a short incubation period.

Reisz’s team found the femurs were being reshaped even as they were in the egg. Examination of the bones’ anatomy and internal structure showed that as they contracted and pulled on the hard bone tissue, the dinosaurs’ muscles played an active role in changing the shape of the developing femur. “This suggests that dinosaurs, like modern birds, moved around inside their eggs,” says Reisz. “It represents the first evidence of such movement in a dinosaur.”

The Taiwanese members of the team also discovered organic material inside the embryonic bones. Using precisely targeted infrared spectroscopy, they conducted chemical analyses of the dinosaur bone and found evidence of what Reisz says may be collagen fibres. Collagen is a protein characteristically found in bone.

“The bones of ancient animals are transformed to rock during the fossilization process,” says Reisz. “To find remnants of proteins in the embryos is really remarkable, particularly since these specimens are over 100 million years older than other fossils containing similar organic material.”

Only about one square metre of the bonebed has been excavated to date, but this small area also yielded pieces of eggshell, the oldest known for any terrestrial vertebrate. Reisz says this is the first time that even fragments of such delicate dinosaur eggshells, less than 100 microns thick, have been found in good condition.

“A find such as the Lufeng bonebed is extraordinarily rare in the fossil record, and is valuable for both its great age and the opportunity it offers to study dinosaur embryology,” says Reisz. “It greatly enhances our knowledge of how these remarkable animals from the beginning of the Age of Dinosaurs grew.”

Fossil Pollen sheds light on early Pollinators

April 13th, 2013 Riffin

The collapse of honeybee colonies across North America is focusing attention on the honeybees’ vital role in the survival of agricultural crops, and a new study by University of Florida and Indiana University Southeast researchers shows insect pollinators have likely played a key role in the evolution and success of flowering plants for nearly 100 million years.

The origins of when flowers managed to harness insects’ pollinating power has long been murky. But the new study, published online this week on the Proceedings of the National Academy of Sciences Web site and appearing in its Dec. 24 print edition, is the first to pinpoint a 96-million-year-old timeframe for a turning point in the evolution of basal angiosperm groups, or early flowering plants, by demonstrating they are predominantly insect-pollinated.

This 96-million-year-old fossilized angiosperm pollen clump of Phimopollenites striolata was extracted by careful processing of sediment from three sites in Minnesota's Dakota Formation. Florida Museum of Natural History researchers found about 40 separate clumps in the pollen samples used for a study published in the Proceedings of the National Academy of Sciences Dec. 24 print edition. Each individual grain within the clump in this image measures approximately 14-by-19 microns. Clumping is generally found only in animal-pollinated flowering plants.

This 96-million-year-old fossilized angiosperm pollen clump of Phimopollenites striolata was extracted by careful processing of sediment from three sites in Minnesota’s Dakota Formation. Florida Museum of Natural History researchers found about 40 separate clumps in the pollen samples used for a study published in the Proceedings of the National Academy of Sciences Dec. 24 print edition. Each individual grain within the clump in this image measures approximately 14-by-19 microns. Clumping is generally found only in animal-pollinated flowering plants.

 

“Our study of clumping pollen shows that insect pollinators most likely have always played a large role in the evolution of flowering plants,” said David Dilcher, a graduate research professor of paleobotany at the Florida Museum of Natural History. “It was true 96 million years ago and we are seeing it today with the potential threat to our agricultural crops because of the collapse of the honeybee colonies. The insect pollinators provide for more efficient and effective pollination of flowering plants.”

 

The study provides strong evidence for the widely accepted hypothesis that insects drove the massive adaptive radiation of early flowering plants when they rapidly diversified and expanded to exploit new terrestrial niches. Land plants first appear in the fossil record about 425 million years ago, but flowering plants didn’t appear until about 125 million years ago in the Early Cretaceous period.

 

The study also is the first to describe the biological structure of pollen clumping in the early Late Cretaceous, which holds clues about the types of pollinators with which they were coevolving, said lead author Shusheng Hu, who started the study while at the Florida Museum but is currently at Indiana University Southeast. Hu said previous scientists found examples of early clumped pollen from a slightly earlier time period but these were interpreted as immature parts of anther from a flower, or dismissed as insect packaging activity or fecal pellets.

 

“We really had to jump out of the box and think in a new way on these widespread pollen clumps,” said Hu, who completed the research in 2006 as part of his UF doctoral work.

 

Today, flowers specialized for insect pollination disperse clumps of five to 100 pollen grains. Clumped grains are comparatively larger and have more surface relief than wind- or water-dispersed pollen, which tend to be single, smaller and smoother.

 

“These clumps represent an amazing new strategy in the evolution of flowering plants,” Dilcher said. “For me, the excitement here lies in the early times of these fossil flowers, when angiosperms were making these huge evolutionary steps. What we found with the fossil pollen clumps folds nicely into what has been suggested by molecular biologists that those plants that are basal in angiosperm evolutionary relationships seem to have been dominated by insect pollination.”

 

The nine species of fossil pollen clumps, combined with known structural changes occurring in flowering plants at this time, led the researchers to suggest that insect pollination was well established by the early Late Cretaceous – only a few million years before the explosion in diversity and distribution of flowering plant families. Known structural changes include early prototypes of stamen and anther, plant organs which lift pollen up and away from the plant, positioning the plants’ genetic material to be passed off to visiting insects.

 

The researchers sampled pollen from three sites in Minnesota’s Dakota Formation, which represents a time period when a shallow seaway covered North America’s interior.

 

Co-author David Jarzen, a Florida Museum pollen scientist, refined existing pollen processing techniques for extracting intact fossil pollen from the calcareous Minnesota limestone and silicate mudstone rock matrix. Co-author David Taylor, a botanist from Indiana University Southeast contributed a statistical analysis of pollination methods among living and early plants.

 

A Smithsonian Institution paleobiologist, Conrad Labandeira, who specializes in insect-plant associations, and who is unassociated with the study, said that the authors’ ability to demonstrate pollen clumping in basal angiosperms adds one more piece to the puzzle of several pollination types established in the mid-Cretaceous.

 

“These data are very comparable with parallel data such as flower structure, pollen structure, and insect mouthpart morphology, that now documents a wide variety of pollination types that occurred before the Cenomanian,” Labandeira said.

 

Note: This story has been adapted from a news in 2007 release issued by the University of Florida

The Origin and Initial Rise of Pelagic Cephalopods in the Ordovician

April 12th, 2013 Riffin

During the Ordovician the global diversity increased dramatically at family, genus and species levels. Partially the diversification is explained by an increased nutrient, and phytoplankton availability in the open water. Cephalopods are among the top predators of todays open oceans. Their Ordovician occurrences, diversity evolution and abundance pattern potentially provides information on the evolution of the pelagic food chain.

 

Methodology/Principal Findings

We reconstructed the cephalopod departure from originally exclusively neritic habitats into the pelagic zone by the compilation of occurrence data in offshore paleoenvironments from the Paleobiology Database, and from own data, by evidence of the functional morphology, and the taphonomy of selected cephalopod faunas. The occurrence data show, that cephalopod associations in offshore depositional settings and black shales are characterized by a specific composition, often dominated by orthocerids and lituitids. The siphuncle and conch form of these cephalopods indicate a dominant lifestyle as pelagic, vertical migrants. The frequency distribution of conch sizes and the pattern of epibionts indicate an autochthonous origin of the majority of orthocerid and lituitid shells. The consistent concentration of these cephalopods in deep subtidal sediments, starting from the middle Tremadocian indicates the occupation of the pelagic zone early in the Early Ordovician and a subsequent diversification which peaked during the Darriwilian.

Nodule with masses of orthoconic nautiloids from La Maurerie Formation, earliest Floian, Montagne Noire, France. Arrow highlights Bactroceras. Scale bar equals 1 cm. doi:10.1371/journal.pone.0007262.g001

Nodule with masses of orthoconic nautiloids from La Maurerie Formation, earliest Floian, Montagne Noire, France.
Arrow highlights Bactroceras. Scale bar equals 1 cm.
doi:10.1371/journal.pone.0007262.g001

 

Early Ordovician cephalopod occurrences in distal and deep marine depositional settings. Map simplified from [97]. doi:10.1371/journal.pone.0007262.g002

Early Ordovician cephalopod occurrences in distal and deep marine depositional settings.
Map simplified from Cocks LRM, Torsvik TH (2004).
doi:10.1371/journal.pone.0007262.g002

Habitats of selected Late Ordovician cephalopods (dotted lines). doi:10.1371/journal.pone.0007262.g010

Habitats of selected Late Ordovician cephalopods (dotted lines).
doi:10.1371/journal.pone.0007262.g010

Conclusions/Significance

The exploitation of the pelagic realm started synchronously in several independent invertebrate clades during the latest Cambrian to Middle Ordovician. The initial rise and diversification of pelagic cephalopods during the Early and Middle Ordovician indicates the establishment of a pelagic food chain sustainable enough for the development of a diverse fauna of large predators. The earliest pelagic cephalopods were slowly swimming vertical migrants. The appearance and early diversification of pelagic cephalopods is interpreted as a consequence of the increased food availability in the open water since the latest Cambrian.

Citation: Kröger B, Servais T, Zhang Y (2009) The Origin and Initial Rise of Pelagic Cephalopods in the Ordovician. PLoS ONE 4(9): e7262. doi:10.1371/journal.pone.0007262

Editor: Matthew Kosnik, Smithsonian Institution, National Museum of Natural History, United States of America

Diversification in Ancient Tadpole Shrimps Challenges the Term ‘Living Fossil’

April 11th, 2013 Riffin

The term ‘living fossil’ has a controversial history. For decades, scientists have argued about its usefulness as it appears to suggest that some organisms have stopped evolving. New research has now investigated the origin of tadpole shrimps, a group commonly regarded as ‘living fossils’ which includes the familiar Triops. The research reveals that living species of tadpole shrimp are much younger than the fossils they so much resemble, calling into question the term ‘living fossil’.

This is an image of a Triops cancriformis, the European Tadpole Shrimp. (Credit: Africa Gomez, available for full re-use under a CC-BY 3.0 license.)

This is an image of a Triops cancriformis, the European Tadpole Shrimp. (Credit: Africa Gomez, available for full re-use under a CC-BY 3.0 license.)

Darwin informally introduced the term ‘living fossil’ in On the Origin of Species when talking about the platypus and lungfish, groups that appear to have diversified little and appear not to have changed over millions of years. For him living fossils were odd remnants of formerly more diverse groups, and suggestive of a connection between different extant groups. Ever since, the term has been widely used to describe organisms such as the coelacanth, the horseshoe crab and the ginkgo tree. The term has been controversial, as it appears to suggest that evolution has stopped altogether for these organisms, and some scientists have argued that it should be abandoned.

Tadpole shrimps are a small group of ancient crustaceans (a group which includes the familiar Triops) that are often called ‘living fossils’, because the living species look virtually identical to fossils older than the dinosaurs. Analysing DNA sequences of all known tadpole shrimps, and using fossils from related crustacean groups — such as the water flea and the brine shrimp — the team of researchers, from the University of Hull, University of Leicester and the Natural History Museum in London, showed that tadpole shrimps have in fact undergone several periods of radiation and extinction. The new study is published today in PeerJ, a new peer reviewed open access journal in which all articles are freely available to everyone (https://PeerJ.com).

Different species of tadpole shrimp often look very similar (they are called ‘cryptic species’), and so it is only with the advent of DNA sequencing that scientists have realized that they are a surprisingly diverse group. The team’s results uncovered a total of 38 species, many of them still undescribed. This abundance of ‘cryptic species’ makes it very difficult for fossils to be assigned to any particular species as they all look remarkably similar. For example, 250-million-year-old fossils have been assigned to the living European species Triops cancriformis whereas the team’s results indicate that the living T. cancriformis evolved less than 25 million years ago. First author Tom Mathers says “In groups like tadpole shrimps where cryptic speciation is common, the fossil record says very little about patterns of evolution and diversification and so the term ‘living fossil’ can be quite misleading. For this reason, we used fossils from related groups to gain an understanding about the evolution of tadpole shrimps.”

The lead author Africa Gómez said, “Living fossils evolve like any other organism, they just happen to have a good body plan that has survived the test of time. A good analogy could be made with cars. For example the Mini has an old design that is still selling, but newly made Minis have electronic windows, GPS and airbags: in that sense, they are still ‘evolving’, they are not unchanged but most of the change has been ‘under the hood’ rather than external. By comparison, organisms labeled as ‘living fossils’ such as tadpole shrimps, are constantly fine-tuning their adaptation to their environment. Although outwardly they look very similar to tadpole shrimp fossils from the age of the dinosaurs, their DNA and reproductive strategies are relatively hidden features that are constantly evolving. The flexibility of their reproductive strategies, which our research has revealed, could be the evolutionary trick that has allowed them to persist as a morphologically conservative group for so long.”

Background

Tadpole shrimps include the familiar Triops — which is often sold as dried eggs in toy shops — that can easily be grown at home. Their fossils can be found from the Carboniferous, 300 million years ago, and the group has survived several mass extinction events. Currently, tadpole shrimps occupy a range of temporal aquatic habitats with different water chemistry conditions, such as hypersaline Australian lakes, rice fields, coastal pools, river floodplains and arctic ponds. Their eggs can survive in a dry state for several decades, only hatching when suitable conditions return.

volcanic eruptions triggered mass extinction Before dinosaurs’ era

April 10th, 2013 Riffin

More than 200 million years ago, a massive extinction decimated 76 percent of marine and terrestrial species, marking the end of the Triassic period and the onset of the Jurassic.

Back to the future? Ancient rocks in Hartford Basin, Conn., offer a look into geologic time. - Terrence Blackburn and Paul Olsen

Back to the future? Ancient rocks in Hartford Basin, Conn., offer a look into geologic time. – Terrence Blackburn and Paul Olsen

The event cleared the way for dinosaurs to dominate Earth for the next 135 million years, taking over ecological niches formerly occupied by other marine and terrestrial species.

It’s not clear what caused the end-Triassic extinction, although most scientists agree on a likely scenario.

Over a relatively short time period, massive volcanic eruptions from a large region known as the Central Atlantic Magmatic Province (CAMP) spewed forth huge amounts of lava and gas, including carbon dioxide, sulfur and methane.

This sudden release of gases into the atmosphere may have created intense global warming, and acidification of the oceans, which ultimately killed off thousands of plant and animal species.

Now, researchers at MIT, Columbia University and other institutions have determined that these eruptions occurred precisely when the extinction began, providing strong evidence that volcanic activity did indeed trigger the end-Triassic extinction.

Results of the research, funded by the National Science Foundation (NSF), are published this week in the journal Science.

“These scientists have come close to confirming something we had only guessed at: that the mass extinction of this ancient time was indeed related to a series of volcanic eruptions,” says Lisa Boush, program director in NSF’s Division of Earth Sciences.

“The effort is also the result of the EARTH TIME initiative, an NSF-sponsored project that’s developing an improved geologic time scale for scientists to interpret Earth’s history.”

The scientists determined the age of basaltic lavas and other features found along the East Coast of the United States, as well as in Morocco–now-disparate regions that, 200 million years ago, were part of the super continent Pangaea.

The rift that ultimately separated these landmasses was also the site of CAMP’s volcanic activity.

Today, the geology of both regions includes igneous rocks from the CAMP eruptions as well as sedimentary rocks that accumulated in an enormous lake. The researchers used a combination of techniques to date the rocks and to pinpoint CAMP’s beginning and duration.

From its measurements, they reconstructed the region’s volcanic activity 201 million years ago, discovering that the eruption of magma–along with carbon dioxide, sulfur and methane–occurred in repeated bursts over a period of 40,000 years, a short span in geologic time.

“This extinction happened at a geological instant in time,” says Sam Bowring, a geologist at MIT. “There’s no question the extinction occurred at the same time as the first eruption.”

In addition to Bowring, the paper’s co-authors are Terrence Blackburn and Noah McLean of MIT; Paul Olsen and Dennis Kent of Columbia; John Puffer of Rutgers University; Greg McHone, an independent researcher from New Brunswick, N.J.; E. Troy Rasbury of Stony Brook University; and Mohammed Et-Touhami of the Université Mohammed Premier (Mohammed Premier University) Oujda, Morocco.

Blackburn is the paper’s lead author.

More than a coincidence

The end-Triassic extinction is one of five major mass extinctions in the last 540 million years of Earth’s history.

For several of these events, scientists have noted that large igneous provinces, which provide evidence of widespread volcanic activity, arose at about the same time.

But, as Bowring points out, “just because they happen to approximately coincide doesn’t mean there’s cause and effect.”

For example, while massive lava flows overlapped with the extinction that wiped out the dinosaurs, scientists have linked that extinction to an asteroid collision.

“If you want to make the case that an eruption caused an extinction, you have to be able to show at the highest possible precision that the eruption and the extinction occurred at exactly the same time,” Bowring says.

For the time of the end-Triassic, Bowring says that researchers have dated volcanic activity to right around the time fossils disappear from the geologic record, providing evidence that CAMP may have triggered the extinction.

 

But these estimates have a margin of error of one to two million years. “A million years is forever when you’re trying to make that link,” Bowring says.

For example, it’s thought that CAMP emitted a total of more than two million cubic kilometers of lava.

If that amount of lava were spewed over a period of one to two million years, it wouldn’t have the same effect as if it were emitted over tens of thousands of years.

“The timescale over which the eruption occurred has a big effect,” Bowring says.

Tilting toward extinction

To determine how long the volcanic eruptions lasted, the group combined two dating techniques: astrochronology and geochronology.

The former is a technique that links sedimentary layers in rocks to changes in the tilt of the Earth.

For decades, scientists have observed that the Earth’s orientation changes in regular cycles as a result of gravitational forces exerted by neighboring planets.

The Earth’s axis tilts at regular cycles, returning to its original tilt every 26,000 years. Such orbital variations change the amount of solar radiation reaching the Earth’s surface, which in turn has an effect on the planet’s climate, known as Milankovich cycles.

This cyclical change in climate can be seen in the types of sediments deposited in the Earth’s crust.

Scientists can determine a rock’s age by first identifying cyclical variations in deposition of sediments in quiet bodies of water, such as deep oceans or large lakes.

A cycle of sediment corresponds with a cycle of the Earth’s tilt, established as a known period of years.

By seeing where a rock lies in those sedimentary layers, scientists can get a good idea of how old it is. To obtain precise estimates, researchers have developed mathematical models to determine the Earth’s tilt over millions of years.

Bowring says the technique is good for directly dating rocks up to 35 million years old, but beyond that, it’s unclear how reliable the technique is.

He and colleagues used astrochronology to estimate the age of the sedimentary rocks, then tested those estimates against high-precision dates from 200-million-year-old rocks in North America and Morocco.

The geologists broke apart rock samples to isolate tiny crystals known as zircons, which they analyzed to determine the ratio of uranium to lead.

The technique enabled the team to date the rocks to within approximately 30,000 years–a precise measurement in geologic terms.

Taken together, the geochronology and astrochronology techniques gave the geologists precise estimates for the onset of volcanism 200 million years ago.

The techniques revealed three bursts of magmatic activity over 40,000 years–a short period of time during which massive amounts of carbon dioxide and other gas emissions may have drastically altered Earth’s climate.

While the evidence is the strongest thus far for linking volcanic activity with the end-Triassic extinction, Bowring says that more work can be done.

“The CAMP province extends from Nova Scotia all the way to Brazil and West Africa,” he says. “I’m dying to know whether those are exactly the same age.”

Note: This story has been adapted from a news release issued by the National Science Foundation

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