Kenyan fossils show evolution of hippos

A French-Kenyan research team has just described a new fossil ancestor of today’s hippo family. This discovery bridges a gap in the fossil record separating these animals from their closest modern-day cousins, the cetaceans. It also shows that some 35 million years ago, the ancestors of hippos were among the first large mammals to colonize the African continent, long before those of any of the large carnivores, giraffes or bovines. This work, co-signed by researchers of the Institut des sciences de l’évolution de Montpellier (CNRS/Université de Montpellier/IRD/EPHE) and Institut de paléoprimatologie et paléontologie humaine : évolution et paléo-environnements (CNRS/Université de Poitiers) is published in the journal Nature Communications.

The ancestry of hippopotamuses is somewhat of an enigma. For a long time, paleontologists thought these semi-aquatic animals, with their unusual morphology (canines and incisors with continual growth, primitive skull and trifoliate tooth-wear pattern), to be related to the Suidae family, which includes pigs and peccaries. But in the 1990s and 2000s, DNA comparisons showed that the hippo’s closest living relatives were the cetaceans (whales, dolphins, etc.), which disagreed with most paleontological interpretations. Moreover, the lack of fossils significantly hindered attempts to uncover the truth about hippo evolution.

Right, a hemi mandible of Epirigenys lokonensis with premolars 3 and 4 and molars 1 and 2. Compared with, to the left, a hemi mandible from a hippopotamid fossil. Credit: © LPRP/J.-R. Boisserie

Right, a hemi mandible of Epirigenys lokonensis with premolars 3 and 4 and molars 1 and 2. Compared with, to the left, a hemi mandible from a hippopotamid fossil.
Credit: © LPRP/J.-R. Boisserie

New paleontological work by a group of French and Kenyan researchers has now revealed that hippos are not related to suoids but instead descend from another, now extinct, group. The new fossils studied have made it possible to build the first evolutionary scenario that is compatible with both genetic and paleontological data. By analyzing a half-jaw and several teeth discovered at Lokone (in the Lake Turkana basin, Kenya), the French-Kenyan team described a new fossil species (belonging to a new genus (2)), dating back to about 28 million years. They named it Epirigenys lokonensis, from the word “Epiri” which means hippo in the Turkana language and the site of discovery, Lokone.

By comparing the characteristics of fossil teeth with those of ruminants, suoids, hippos and fossil anthracotheres (an extinct family of ungulates), the scientists reconstructed the relationships between these groups. The results show that Epirigenys forms a kind of evolutionary transition between the oldest known hippo in the fossil record (about 20 million years ago) and an anthracothere lineage. This position in the tree of life is compatible with the genetic data, confirming that the cetaceans are the hippos’ closest living cousins.

This kind of discovery may one day enable scientists to draw a picture of the common ancestor of cetaceans and hippos. Indeed, analysis of Epirigenys (28 million years old) has linked today’s hippos to a lineage of anthracotheres, the oldest of which date back about 40 million years. However, until now, the earliest known ancestor of the hippos was about 20 million years old, while the first fossils of cetaceans are 53 million years old. The time gap between today’s hippos and the oldest cetaceans is thereby filled by nearly 75% according to the present scenario.

Furthermore, this discovery shows the whole history of the African fauna in a new light. Africa was an isolated continent from about 110 to 18 million years ago. Most of the iconic African fauna (lions, leopards, rhinos, buffaloes, giraffes, zebras, etc.) are relatively recent arrivals on the continent (they have been there less than 20 million years). Until now, the same was believed to be true of hippos, but the discovery of Epirigenys demonstrates that their anthracothere ancestors migrated from Asia to Africa some 35 million years ago.

Source: Fabrice Lihoreau, Jean-Renaud Boisserie, Fredrick Kyalo Manthi, Stéphane Ducrocq. Hippos stem from the longest sequence of terrestrial cetartiodactyl evolution in Africa. Nature Communications, 2015; 6: 6264 DOI: 10.1038/ncomms7264

Were dinosaurs destined to be big? Testing Cope’s rule

In the evolutionary long run, small critters tend to evolve into bigger beasts — at least according to the idea attributed to paleontologist Edward Cope, now known as Cope’s Rule. Using the latest advanced statistical modeling methods, a new test of this rule as it applies dinosaurs shows that Cope was right — sometimes.

“For a long time, dinosaurs were thought to be the example of Cope’s Rule,” says Gene Hunt, curator in the Department of Paleobiology at the National Museum of Natural History (NMNH) in Washington, D.C. Other groups, particularly mammals, also provide plenty of classic examples of the rule, Hunt says.

To see if Cope’s rule really applies to dinosaurs, Hunt and colleagues Richard FitzJohn of the University of British Columbia and Matthew Carrano of the NMNH used dinosaur thigh bones (aka femurs) as proxies for animal size. They then used that femur data in their statistical model to look for two things: directional trends in size over time and whether there were any detectable upper limits for body size.

In the evolutionary long run, small critters tend to evolve into bigger beasts -- at least according to the idea attributed to paleontologist Edward Cope, now known as Cope's Rule. Using the latest advanced statistical modeling methods, a new test of this rule as it applies dinosaurs shows that Cope was right -- sometimes. Credit: © Derrick Neill / Fotolia

In the evolutionary long run, small critters tend to evolve into bigger beasts — at least according to the idea attributed to paleontologist Edward Cope, now known as Cope’s Rule. Using the latest advanced statistical modeling methods, a new test of this rule as it applies dinosaurs shows that Cope was right — sometimes.
Credit: © Derrick Neill / Fotolia

“What we did then was explore how constant a rule is this Cope’s Rule trend within dinosaurs,” said Hunt. They looked across the “family tree” of dinosaurs and found that some groups, or clades, of dinosaurs do indeed trend larger over time, following Cope’s Rule. Ceratopsids and hadrosaurs, for instance, show more increases in size than decreases over time, according to Hunt. Although birds evolved from theropod dinosaurs, the team excluded them from the study because of the evolutionary pressure birds faced to lighten up and get smaller so they could fly better.

As for the upper limits to size, the results were sometimes yes, sometimes no. The four-legged sauropods (i.e., long-necked, small-headed herbivores) and ornithopod (i.e., iguanodons, ceratopsids) clades showed no indication of upper limits to how large they could evolve. And indeed, these groups contain the largest land animals that ever lived.

Theropods, which include the famous Tyrannosaurus rex, on the other hand, did show what appears to be an upper limit on body size. This may not be particularly surprising, says Hunt, because theropods were bipedal, and there are physical limits to how massive you can get while still being able to move around on two legs.

Hunt, FitzJohn, and Carrano will be presenting the results of their study on Nov. 4, at the annual meeting of The Geological Society of America in Charlotte, North Carolina, USA.

As for why Cope’s Rule works at all, that is not very well understood, says Hunt. “It does happen sometimes, but not always,” he added. The traditional idea that somehow “bigger is better” because a bigger animal is less likely to be preyed upon is naïve, Hunt says. After all, even the biggest animals start out small enough to be preyed upon and spend a long, vulnerable, time getting gigantic.

Abstract: https://gsa.confex.com/gsa/2012AM/webprogram/Paper211594.html

Source: Geological Society of America. “Were dinosaurs destined to be big? Testing Cope’s rule.” ScienceDaily. ScienceDaily, 2 November 2012. <www.sciencedaily.com/releases/2012/11/121102151954.htm>.

Eonatator coellensis: New marine fossil from Columbia

A nearly complete fossil of a prehistoric marine reptile with preserved soft tissue has been found in central-western Colombia, at a spot several hundred miles from the Caribbean coast, a university in this capital said.

Experts have given the reptile the name “Eonatator coellensis” because the find was made in a dry stream bed in Coello, a town in Tolima province, the National University of Colombia’s news agency said Tuesday.Professor Luis Enrique Calderon and his son Ricardo discovered the fossil in rocks dating back 80 million years, during the Cretaceous period (145-66 million years ago), and informed the Colombian Geological Service.

Eonatator coellensis

Eonatator coellensis

The animal was a mosasaurus with a full body length of 2.8 meters (9.1 feet) and a head length of 41.5 centimeters (16 inches), according to experts from that institution, which said it was a member of the genus Eonatator.

Colombian paleontologist Maria Paramo, a National University professor who is heading up the investigation, discovered that the remains have a cream-pink coloration and have been almost entirely preserved with the exception of the tail.Her findings include 15 of the reptile’s teeth, its thoracic wall and part of its vertebral column.Based on the quantity, morphology and length of the preserved vertebrae, she estimates that the length of the animal’s tail was similar to that of the rest of its body.The soft tissue remains are located in the lungs and the pancreas, as well as the muscle fibers that extend to the ribs.

“One thing that troubled us was why the skin wasn’t preserved if what was inside was preserved,” the researcher said.

“From the geological characteristics, it’s apparent that it didn’t go frequently into the open sea, but rather stayed closer to the coast,” Paramo said.

“The anatomical shape of its front and hind limbs indicate it could have gone a little away from the mainland,” the paleontologist added.

Courtesy: Fox News

Life Possible On Earth 3.2 Billion Years Ago

A spark from a lightning bolt, interstellar dust, or a subsea volcano could have triggered the very first life on Earth. But what happened next? Life can exist without oxygen, but without plentiful nitrogen to build genes — essential to viruses, bacteria and all other organisms — life on the early Earth would have been scarce.

The ability to use atmospheric nitrogen to support more widespread life was thought to have appeared roughly 2 billion years ago. Now research from the University of Washington looking at some of the planet’s oldest rocks finds evidence that 3.2 billion years ago, life was already pulling nitrogen out of the air and converting it into a form that could support larger communities.

“People always had the idea that the really ancient biosphere was just tenuously clinging on to this inhospitable planet, and it wasn’t until the emergence of nitrogen fixation that suddenly the biosphere become large and robust and diverse,” said co-author Roger Buick, a UW professor of Earth and space sciences. “Our work shows that there was no nitrogen crisis on the early Earth, and therefore it could have supported a fairly large and diverse biosphere.”

The results were published Feb. 16 in Nature.

The authors analyzed 52 samples ranging in age from 2.75 to 3.2 billion years old, collected in South Africa and northwestern Australia. These are some of the oldest and best-preserved rocks on the planet. The rocks were formed from sediment deposited on continental margins, so are free of chemical irregularities that would occur near a subsea volcano. They also formed before the atmosphere gained oxygen, roughly 2.3 to 2.4 billion years ago, and so preserve chemical clues that have disappeared in modern rocks.

The oldest samples are sedimentary rocks that formed 3.2 billion years ago in northwestern Australia. They contain chemical evidence for nitrogen fixation by microbes. Credit: R. Buick / UW

The oldest samples are sedimentary rocks that formed 3.2 billion years ago in northwestern Australia. They contain chemical evidence for nitrogen fixation by microbes.
Credit: R. Buick / UW

Even the oldest samples, 3.2 billion years old — three-quarters of the way back to the birth of the planet — showed chemical evidence that life was pulling nitrogen out of the air. The ratio of heavier to lighter nitrogen atoms fits the pattern of nitrogen-fixing enzymes contained in single-celled organisms, and does not match any chemical reactions that occur in the absence of life.

“Imagining that this really complicated process is so old, and has operated in the same way for 3.2 billion years, I think is fascinating,” said lead author Eva Stüeken, who did the work as part of her UW doctoral research. “It suggests that these really complicated enzymes apparently formed really early, so maybe it’s not so difficult for these enzymes to evolve.”

Genetic analysis of nitrogen-fixing enzymes have placed their origin at between 1.5 and 2.2 billion years ago.

“This is hard evidence that pushes it back a further billion years,” Buick said. Fixing nitrogen means breaking a tenacious triple bond that holds nitrogen atoms in pairs in the atmosphere and joining a single nitrogen to a molecule that is easier for living things to use. The chemical signature of the rocks suggests that nitrogen was being broken by an enzyme based on molybdenum, the most common of the three types of nitrogen-fixing enzymes that exist now. Molybdenum is now abundant because oxygen reacts with rocks to wash it into the ocean, but its source on the ancient Earth — before the atmosphere contained oxygen to weather rocks — is more mysterious.

The authors hypothesize that this may be further evidence that some early life may have existed in single-celled layers on land, exhaling small amounts of oxygen that reacted with the rock to release molybdenum to the water.

“We’ll never find any direct evidence of land scum one cell thick, but this might be giving us indirect evidence that the land was inhabited,” Buick said. “Microbes could have crawled out of the ocean and lived in a slime layer on the rocks on land, even before 3.2 billion years ago.”

Future work will look at what else could have limited the growth of life on the early Earth. Stüeken has begun a UW postdoctoral position funded by NASA to look at trace metals such as zinc, copper and cobalt to see if one of them controlled the growth of ancient life.

Source: Eva E. Stüeken, Roger Buick, Bradley M. Guy, Matthew C. Koehler. Isotopic evidence for biological nitrogen fixation by molybdenum-nitrogenase from 3.2 Gyr. Nature, 2015; DOI: 10.1038/nature14180

Docofossor,Agilodocodon : mammal fossils discovered

The fossils of two interrelated ancestral mammals, newly discovered in China, suggest that the wide-ranging ecological diversity of modern mammals had a precedent more than 160 million years ago.

With claws for climbing and teeth adapted for a tree sap diet, Agilodocodon scansorius is the earliest-known tree-dwelling mammaliaform (long-extinct relatives of modern mammals). The other fossil, Docofossor brachydactylus, is the earliest-known subterranean mammaliaform, possessing multiple adaptations similar to African golden moles such as shovel-like paws. Docofossor also has distinct skeletal features that resemble patterns shaped by genes identified in living mammals, suggesting these genetic mechanisms operated long before the rise of modern mammals.

Photos of the fossils of Docofossor (left) and Agilodocodon (right). Credit: Zhe-Xi Luo, University of Chicago

Photos of the fossils of Docofossor (left) and Agilodocodon (right).
Credit: Zhe-Xi Luo, University of Chicago

These discoveries are reported by international teams of scientists from the University of Chicago and Beijing Museum of Natural History in two separate papers published Feb. 13 in Science.

“We consistently find with every new fossil that the earliest mammals were just as diverse in both feeding and locomotor adaptations as modern mammals,” said Zhe-Xi Luo, PhD, professor of organismal biology and anatomy at the University of Chicago and an author on both papers. “The groundwork for mammalian success today appears to have been laid long ago.”

Agilodocodon and Docofossor provide strong evidence that arboreal and subterranean lifestyles evolved early in mammalian evolution, convergent to those of true mammals. These two shrew-sized creatures — members of the mammaliaform order Docodonta — have unique adaptations tailored for their respective ecological habitats.

Agilodocodon, which lived roughly 165 million years ago, had hands and feet with curved horny claws and limb proportions that are typical for mammals that live in trees or bushes. It is adapted for feeding on the gum or sap of trees, with spade-like front teeth to gnaw into bark. This adaptation is similar to the teeth of some modern New World monkeys, and is the earliest-known evidence of gumnivorous feeding in mammaliaforms. Agilodocodon also had well-developed, flexible elbows and wrist and ankle joints that allowed for much greater mobility, all characteristics of climbing mammals.

“The finger and limb bone dimensions of Agilodocodon match up with those of modern tree-dwellers, and its incisors are evidence it fed on plant sap,” said study co-author David Grossnickle, graduate student at the University of Chicago. “It’s amazing that these arboreal adaptions occurred so early in the history of mammals and shows that at least some extinct mammalian relatives exploited evolutionarily significant herbivorous niches, long before true mammals.”

Docofossor, which lived around 160 million years ago, had a skeletal structure and body proportions strikingly similar to the modern day African golden mole. It had shovel-like fingers for digging, short and wide upper molars typical of mammals that forage underground, and a sprawling posture indicative of subterranean movement.

Docofossor had reduced bone segments in its fingers, leading to shortened but wide digits. African golden moles possess almost the exact same adaptation, which provides an evolutionary advantage for digging mammals. This characteristic is due to the fusion of bone joints during development — a process influenced by the genes BMP and GDF-5. Because of the many anatomical similarities, the researchers hypothesize that this genetic mechanism may have played a comparable role in early mammal evolution, as in the case of Docofossor.

The spines and ribs of both Agilodocodon and Docofossor also show evidence for the influence of genes seen in modern mammals. Agilodocodon has a sharp boundary between the thoracic ribcage to lumbar vertebrae that have no ribs. However, Docofossor shows a gradual thoracic to lumber transition. These shifting patterns of thoracic-lumbar transition have been seen in modern mammals and are known to be regulated by the genes Hox 9-10 and Myf 5-6. That these ancient mammaliaforms had similar developmental patterns is an evidence that these gene networks could have functioned in a similar way long before true mammals evolved.

“We believe the shortened digits of Docofossor, which is a dead ringer for modern golden moles, could very well have been caused by BMP and GDF,” Luo said. “We can now provide fossil evidence that gene patterning that causes variation in modern mammalian skeletal development also operated in basal mammals all the way back in the Jurassic.”

Early mammals were once thought to have limited ecological opportunities to diversify during the dinosaur-dominated Mesozoic era. However, Agilodocodon, Docofossor and numerous other fossils — including Castorocauda, a swimming, fish-eating mammaliaform described by Luo and colleagues in 2006 — provide strong evidence that ancestral mammals adapted to wide-ranging environments despite competition from dinosaurs.

“We know that modern mammals are spectacularly diverse, but it was unknown whether early mammals managed to diversify in the same way,” Luo said. “These new fossils help demonstrate that early mammals did indeed have a wide range of ecological diversity. It appears dinosaurs did not dominate the Mesozoic landscape as much as previously thought.”

The fossils of two interrelated ancestral mammals, newly discovered in China, suggest that the wide-ranging ecological diversity of modern mammals had a precedent more than 160 million years ago.

With claws for climbing and teeth adapted for a tree sap diet, Agilodocodon scansorius is the earliest-known tree-dwelling mammaliaform (long-extinct relatives of modern mammals). The other fossil, Docofossor brachydactylus, is the earliest-known subterranean mammaliaform, possessing multiple adaptations similar to African golden moles such as shovel-like paws. Docofossor also has distinct skeletal features that resemble patterns shaped by genes identified in living mammals, suggesting these genetic mechanisms operated long before the rise of modern mammals.

These discoveries are reported by international teams of scientists from the University of Chicago and Beijing Museum of Natural History in two separate papers published Feb. 13 in Science.

“We consistently find with every new fossil that the earliest mammals were just as diverse in both feeding and locomotor adaptations as modern mammals,” said Zhe-Xi Luo, PhD, professor of organismal biology and anatomy at the University of Chicago and an author on both papers. “The groundwork for mammalian success today appears to have been laid long ago.”

Agilodocodon and Docofossor provide strong evidence that arboreal and subterranean lifestyles evolved early in mammalian evolution, convergent to those of true mammals. These two shrew-sized creatures — members of the mammaliaform order Docodonta — have unique adaptations tailored for their respective ecological habitats.

Agilodocodon, which lived roughly 165 million years ago, had hands and feet with curved horny claws and limb proportions that are typical for mammals that live in trees or bushes. It is adapted for feeding on the gum or sap of trees, with spade-like front teeth to gnaw into bark. This adaptation is similar to the teeth of some modern New World monkeys, and is the earliest-known evidence of gumnivorous feeding in mammaliaforms. Agilodocodon also had well-developed, flexible elbows and wrist and ankle joints that allowed for much greater mobility, all characteristics of climbing mammals.

“The finger and limb bone dimensions of Agilodocodon match up with those of modern tree-dwellers, and its incisors are evidence it fed on plant sap,” said study co-author David Grossnickle, graduate student at the University of Chicago. “It’s amazing that these arboreal adaptions occurred so early in the history of mammals and shows that at least some extinct mammalian relatives exploited evolutionarily significant herbivorous niches, long before true mammals.”

Docofossor, which lived around 160 million years ago, had a skeletal structure and body proportions strikingly similar to the modern day African golden mole. It had shovel-like fingers for digging, short and wide upper molars typical of mammals that forage underground, and a sprawling posture indicative of subterranean movement.

Docofossor had reduced bone segments in its fingers, leading to shortened but wide digits. African golden moles possess almost the exact same adaptation, which provides an evolutionary advantage for digging mammals. This characteristic is due to the fusion of bone joints during development — a process influenced by the genes BMP and GDF-5. Because of the many anatomical similarities, the researchers hypothesize that this genetic mechanism may have played a comparable role in early mammal evolution, as in the case of Docofossor.

The spines and ribs of both Agilodocodon and Docofossor also show evidence for the influence of genes seen in modern mammals. Agilodocodon has a sharp boundary between the thoracic ribcage to lumbar vertebrae that have no ribs. However, Docofossor shows a gradual thoracic to lumber transition. These shifting patterns of thoracic-lumbar transition have been seen in modern mammals and are known to be regulated by the genes Hox 9-10 and Myf 5-6. That these ancient mammaliaforms had similar developmental patterns is an evidence that these gene networks could have functioned in a similar way long before true mammals evolved.

“We believe the shortened digits of Docofossor, which is a dead ringer for modern golden moles, could very well have been caused by BMP and GDF,” Luo said. “We can now provide fossil evidence that gene patterning that causes variation in modern mammalian skeletal development also operated in basal mammals all the way back in the Jurassic.”

Early mammals were once thought to have limited ecological opportunities to diversify during the dinosaur-dominated Mesozoic era. However, Agilodocodon, Docofossor and numerous other fossils — including Castorocauda, a swimming, fish-eating mammaliaform described by Luo and colleagues in 2006 — provide strong evidence that ancestral mammals adapted to wide-ranging environments despite competition from dinosaurs.

“We know that modern mammals are spectacularly diverse, but it was unknown whether early mammals managed to diversify in the same way,” Luo said. “These new fossils help demonstrate that early mammals did indeed have a wide range of ecological diversity. It appears dinosaurs did not dominate the Mesozoic landscape as much as previously thought.”

Swimming reptiles make their mark in the Early Triassic

Vertebrate tracks provide valuable information about animal behavior and environments. Swim tracks are a unique type of vertebrate track because they are produced underwater by buoyant trackmakers, and specific factors are required for their production and subsequent preservation. Early Triassic deposits contain the highest number of fossil swim track occurrences worldwide compared to other epochs, and this number becomes even greater when epoch duration and rock outcrop area are taken into account.

This image shows a swim traceway from Capitol Reef National Park. Credit: Tracy J. Thomson and Mary L. Droser, Geology, 5 Feb. 2015.

This image shows a swim traceway from Capitol Reef National Park.
Credit: Tracy J. Thomson and Mary L. Droser, Geology, 5 Feb. 2015.

This spike in swim track occurrences suggests that during the Early Triassic, factors promoting swim track production and preservation were more common than at any other time. Coincidentally, the Early Triassic period follows the largest mass extinction event in Earth’s history, and the fossil record indicates that a prolonged period of delayed recovery persisted throughout this time period.

During this recovery interval, sediment mixing by animals living within the substrate was minimal, especially in particularly stressful environments such as marine deltas. The general lack of sediment mixing during the Early Triassic was the most important contributing factor to the widespread production of firm-ground substrates ideal for recording and preserving subaqueous trace fossils like swim tracks.

Source:Geological Society of America. “Swimming reptiles make their mark in the Early Triassic.” ScienceDaily. ScienceDaily, 9 February 2015. <www.sciencedaily.com/releases/2015/02/150209143531.htm>.

 

15-million-year-old mollusk protein found

A team of Carnegie scientists have found “beautifully preserved” 15 million-year-old thin protein sheets in fossil shells from southern Maryland. Their findings are published in the inaugural issue of Geochemical Perspectives Letters.

The team–John Nance, John Armstrong, George Cody, Marilyn Fogel, and Robert Hazen–collected samples from Calvert Cliffs, along the shoreline of the Chesapeake Bay, a popular fossil collecting area. They found fossilized shells of a snail-like mollusk called Ecphora that lived in the mid-Miocene era–between 8 and 18 million years ago.

Ecphora is known for an unusual reddish-brown shell color, making it one of the most distinctive North American mollusks of its era. This coloration is preserved in fossilized remains, unlike the fossilized shells of many other fossilized mollusks from the Calvert Cliffs region, which have turned chalky white over the millions of years since they housed living creatures.

A 15-million year old fossil gastropod, Ecphora, from the Calvert Cliffs of southern Maryland is depicted. The golden brown color arises from the original shell-binding proteins and pigments preserved in the mineralized shell. Credit: John Nance

A 15-million year old fossil gastropod, Ecphora, from the Calvert Cliffs of southern Maryland is depicted. The golden brown color arises from the original shell-binding proteins and pigments preserved in the mineralized shell.
Credit: John Nance

Shells are made from crystalline compounds of calcium carbonate interleaved with an organic matrix of proteins and sugars proteins and sugars. These proteins are called shell-binding proteins by scientists, because they help hold the components of the shell together.They also contain pigments, such as those responsible for the reddish-brown appearance of the Ecphora shell. These pigments can bind to proteins to form a pigment-protein complex.

The fact that the coloration of fossilized Ecphora shells is so well preserved suggested to the research team that shell proteins bound to these pigments in a complex might also be preserved. They were amazed to find that the shells, once dissolved in dilute acid, released intact thin sheets of shell proteins more than a centimeter across. Chemical analysis including spectroscopy and electron microscopy of these sheets revealed that they are indeed shell proteins that were preserved for up to 15 million years.

“These are some of the oldest and best-preserved examples of a protein ever observed in a fossil shell,” Hazen said.

Remarkably, the proteins share characteristics with modern mollusk shell proteins. They both produce thin, flexible sheets of residue that’s the same color as the original shell after being dissolved in acid. Of the 11 amino acids found in the resulting residue, aspartate and glutamate are prominent, which is typical of modern shell proteins. Further study of these proteins could be used for genetic analysis to trace the evolution of mollusks through the ages, as well as potentially to learn about the ecology of the Chesapeake Bay during the era in which Ecphora thrived.

Courtesy: Carnegie Institution. “15-million-year-old mollusk protein found.” ScienceDaily. ScienceDaily, 5 February 2015. <www.sciencedaily.com/releases/2015/02/150205083702.htm>.

NOW Explains Earth’s magnetic field

Earth’s magnetic field is crucial for our existence, as it shields the life on our planet’s surface from deadly cosmic rays. It is generated by turbulent motions of liquid iron in Earth’s core. Iron is a metal, which means it can easily conduct a flow of electrons that makes up an electric current. New findings from a team including Carnegie’s Ronald Cohen and Peng Zhang shows that a missing piece of the traditional theory explaining why metals become less conductive when they are heated was needed to complete the puzzle that explains this field-generating process. Their work is published in Nature.

The center of the Earth is very hot, and the flow of heat from the planet’s center towards the surface is thought to drive most of the dynamics of the Earth, ranging from volcanoes to plate tectonics. It has long been thought that heat flow drives what is called thermal convection — the hottest liquid becomes less dense and rises, as the cooler, more-dense liquid sinks — in Earth’s liquid iron core and generates Earth’s magnetic field. But recent calculations called this theory into question, launching new quests for its explanation.

This is a conception of Earth's core overlaid by the electronic structure of iron; the width (fuzziness) of the lines results from the electron-electron scattering. Image courtesy of Ronald Cohen. Credit: Ronald Cohen

This is a conception of Earth’s core overlaid by the electronic structure of iron; the width (fuzziness) of the lines results from the electron-electron scattering. Image courtesy of Ronald Cohen.
Credit: Ronald Cohen

In their work, Cohen and Zhang, along with Kristjan Haule of Rutgers University, used a new computational physics method and found that the original thermal convection theory was right all along. Their conclusion hinges on discovering that the classic theory of metals developed in the 1930’s was incomplete.

The electrons in metals, such as the iron in Earth’s core, carry current and heat. A material’s resistivity impedes this flow. The classic theory of metals explains that resistivity increases with temperature, due to atoms vibrating more as the heat rises. The theory says that at high temperatures resistivity happens when electrons in the current bounce off of vibrating atoms. These bounced electrons scatter and resist the current flow. As temperature increases, the atoms vibrate more, and increasing the scattering of bounced electrons. The electrons not only carry charge, but also carry energy, so that thermal conductivity is proportional to the electrical conductivity.

The work that had purportedly thrown the decades-old prevailing theory on the generation of Earth’s magnetic field out the window claimed that thermal convection could not drive magnetic-field generation. The calculations in those studies said that the resistivity of the molten metal in Earth’s core, which is generated by this electron scattering process, would be too low, and thus the thermal conductivity too high, to allow thermal convection to generate the magnetic field.

Cohen, Zhang, and Haule’s new work shows that the cause of about half of the resistivity generated was long neglected: it arises from electrons scattering off of each other, rather than off of atomic vibrations.

“We uncovered an effect that had been hiding in plain sight for 80 years,” Cohen said. “And now the original dynamo theory works after all!”

Journal Reference: Peng Zhang, R. E. Cohen, K. Haule. Effects of electron correlations on transport properties of iron at Earth’s core conditions. Nature, 2015; 517 (7536): 605 DOI: 10.1038/nature14090

Evolution: Rock sponges split up

A study led by researchers at Ludwig-Maximilians-Universitaet (LMU) in Munich throws new light on the evolution of the so-called rock sponges, and reveals that conventional, morphology-based taxonomies do not accurately reflect the true genealogical relationships within the group.

Modern approaches to biological systematics have demonstrated that the evolutionary relationships between organisms can best be teased out by combining morphological analysis of fossil material with molecular genetic investigation of the genomes of living species. “This is a challenging task, particularly when fossil evidence is sparse, as in the case of most families of sponges,” says Professor Gert Wörheide of the Geobio-CenterLMU and LMU’s Department of Earth and Environmental Sciences. “The so-called rock sponges represent an exception to this rule insofar as they provide among the richest fossil record of sponges. With the aid of these fossils and the most comprehensive analysis yet carried out of gene sequences from extant species, an international team led by Wörheide has now reassessed the genealogy of the rock sponges — and show that, in many cases, traditional taxonomy does not correctly depict the evolutionary history of the group as a whole.

Rock sponges have a highly characteristic and extremely robust rock-like skeleton, which consists of barbed needles called spicules made of silicon dioxide (i.e., glass), which interlock to form a rigid network.
Credit: Professor Gert Wörheide

Rock sponges belong to the class Demospongiae, which account for the great majority of contemporary species assigned to the phylum Porifera. Demosponges are found in tropical, subtropical and temperate regions of the world’s oceans and occur at all depths from shallow reefs to abyssal depths. More than 300 extant species of rock sponges have been recognized, and classified into 41 genera that are assigned to 13 families. However, by comparison with the range of species represented in the fossil record, with over 300 genera comprising 34 families, the degree of diversity found in the contemporary demosponge fauna is comparatively modest. “The origins of modern rock sponges can be traced back over more than 500 million years into the Paleozoic, and this suggests that much more research will be needed before we understand their evolutionary history,” Wörheide adds.

Rock sponges have a highly characteristic and extremely robust rock-like skeleton, which consists of barbed needles called spicules made of silicon dioxide (i.e., glass), which interlock to form a rigid network. The form and structure of the skeletal elements provide some of the most important characters used to classify the rock sponges. “However, their precise classification and many aspects of their evolutionary history are still the subject of controversial debate,” says Astrid Schuster, a doctoral student in Wörheide’s group, who is first author of the new study. “Previous classifications were largely based on morphological similarities, and these led taxonomists to place many genera in the order ‘Lithistida‘, a dubious grouping which is still cited frequently in the literature,” she explains. With the aid of international colleagues, the team has now extended earlier molecular systematic studies and sequenced a specific pair of genes in each of 68 individual species of rock sponge, which had previously been assigned to 21 genera and 12 families. In addition, the team made use of previously reported gene sequences that were available in public databases.

The researchers correlated the molecular genetic results with characteristic features of the skeletal morphology, such as the type and configuration of the siliceous spicules. “The new findings refute some of the assumptions that have been made regarding the course of rock sponge evolution, and demonstrate that some species have been assigned to genera to which they do not actually belong,” says Schuster. Indeed, it is now abundantly clear that ‘Lithistida’ does not constitute a natural group, i.e., not all of its members can be derived from a direct common ancestor. In particular, the new work shows that classifications based on skeletal elements require thorough reassessment, because some of the different types of spicules that are characteristic for rock sponges arose, or were lost, several times independently during evolution. “So morphological similarities are not a reliable guide for the reconstruction of the genealogical relationships between these organisms,” Wörheide affirms, “and this is certainly also true of the other classes of sponge.”

The new study lays the groundwork for further investigations, in which the researchers will try to pinpoint the times at which the different sponge lineages diverged from one another. To do so, they will exploit the principle of the “molecular clock,” which reflects the fact that the extent of molecular divergence between sequences of the same (“homologous”) genes in any given pair of species provides a measure of the time elapsed since they diverged from one another. By dating divergence times, this strategy promises to enhance our understanding of sponge evolution, and should help to explain why Porifera are among the oldest groups of multicellular organisms still in existence.

Courtesy: Ludwig-Maximilians-Universität München. “Evolution: Rock sponges split up.” ScienceDaily. ScienceDaily, 12 January 2015. <www.sciencedaily.com/releases/2015/01/150112135622.htm>.

Geophysicists find reason for sudden tectonic plate movements

Yale-led research may have solved one of the biggest mysteries in geology — namely, why do tectonic plates beneath the Earth’s surface, which normally shift over the course of tens to hundreds of millions of years, sometimes move abruptly?

A new study published Jan. 19 in the journal Proceedings of the National Academy of Sciences says the answer comes down to two things: thick crustal plugs and weakened mineral grains. Those effects, acting together, may explain a range of relatively speedy moves among tectonic plates around the world, from Hawaii to East Timor.

Of course, in this case “speedy” still means a million years or longer.

“Our planet is probably most distinctly marked by the fact that it has plate tectonics,” said Yale geophysicist David Bercovici, lead author of the research. “Our work here looks at the evolution of plate tectonics. How and why do plates change directions over time?”

Traditionally, scientists believed that all tectonic plates are pulled by subducting slabs — which result from the colder, top boundary layer of the Earth’s rocky surface becoming heavy and sinking slowly into the deeper mantle. Yet that process does not account for sudden plate shifts. Such abrupt movement requires that slabs detach from their plates, but doing this quickly is difficult since the slabs should be too cold and stiff to detach.

Yale-led research may have solved one of the biggest mysteries in geology -- namely, why do tectonic plates beneath the Earth's surface, which normally shift over the course of tens to hundreds of millions of years, sometimes move abruptly? Credit: © Mopic / Fotolia

Yale-led research may have solved one of the biggest mysteries in geology — namely, why do tectonic plates beneath the Earth’s surface, which normally shift over the course of tens to hundreds of millions of years, sometimes move abruptly?
Credit: © Mopic / Fotolia

According to the Yale study, there are additional factors at work. Thick crust from continents or oceanic plateaux is swept into the subduction zone, plugging it up and prompting the slab to break off. The detachment process is then accelerated when mineral grains in the necking slab start to shrink, causing the slab to weaken rapidly.

The result is tectonic plates that abruptly shift horizontally, or continents suddenly bobbing up.

“Understanding this helps us understand how the tectonic plates change through the Earth’s history,” Bercovici said. “It adds to our knowledge of the evolution of our planet, including its climate and biosphere.”

The study’s co-authors are Gerald Schubert of the University of California-Los Angeles and Yanick Ricard of the Université de Lyon in France.