WFS

Formation of sedimentary layers of white clay, Tamilnadu, India

Fossil site for wood fossils, Tamilnadu, India

Fossil site in Kerala, India

Fossil wood park maintained by geological survey of India at Tamilnadu

Cretaceous fossil sites india

Fossils in rack:-Cyad

Fossils in rack:-echiniderms

Fossils in rack:-Rastellum sp

Pre-historic seabed, Cretaceous period

Fossil Remains Reveal New Species of Marine Fish from 408 Million Years Ago in Teruel, Spain

June 4th, 2013

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Researchers from the University of Valencia and the Natural History Museum of Berlin have studied the fossilised remains of scales and bones found in Teruel, Spain, and the south of Zaragoza, ascertaining that they belong to a new fish species called Machaeracanthus goujeti that lived in that area of the peninsula during the Devonian period. The fossils are part of the collection housed in the Palaeontology Museum of Zaragoza.

This is Machaeracanthus goujeti. (Credit: SINC)

In the journal Geodiversitas, a research team led by the University of Valencia describes a new species of spiny shark (Acanthodii), a primitive type of fish that shared characteristics with sharks and bony fish. Remains of scales, bones and scapular joint bones were found in Devonian (approximately 408 million years ago) in Teruel and the south of Zaragoza.

The paper also includes an analysis of fossils of a fragmented spine and isolated scales from the Lower Devonian found in northern Spain (Palencia and Cantabrian Mountains) and western France (Saint-Céneré commune), originally attributed to the Machaeracanthus sp species.

“The discovery of this new species, which we call Machaeracanthus goujeti and belongs to the Acanthodii group -of which very little is known-, expands our knowledge of the biodiversity that existed on the peninsula 480 million years ago, when the modern-day region of Teruel was covered by the sea,” Héctor Botella, professor in the palaeontology unit in the University of Valencia and the study’s lead author, explained.

The Acanthodii group of fish are also known as ‘spiny sharks’ owing to their appearance and, from what we know to date, they only lived during the Palaeozoic Era and reached their maximum level of diversity in the Devonic period. However, the bones typically found in the Acanthodii group grow differently to the bones found, therefore this type could be even more similar to sharks and would date from the very early stages of the radiation of jawed vertebrates (gnathostomata).

A fish fossil no more than one metre in length

The majority of the samples found by the researchers are juveniles. Based on the fossilised remains, the researchers estimate that the largest fish in this species would not reach one metre in length. “This is just an estimation because there are animals that can have large bones and be small, and vice versa,” Botella stated.

For their part, the fossils found in the sediment layers of the Iberian mountain range must surely have belonged to fish that swam close to the coast. “In other words, they must have lived in an epicontinental sea -an extensive but shallow salt water mass-, and it is therefore possible that this area was used as a breeding ground,” he concludes. Larger fossils were found in sediment layers a little further down.

The fossils form part of the collection housed in the Palaeontology Museum of Zaragoza.

world class fossils finds in Leicestershire

June 3rd, 2013

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Geologists say thousands more fossils exist at a Leicestershire site than previously realised.

The fossils, which are almost impossible to see with the naked eye, were found at Charnwood Forest.

This cast shows two of the newly-found fossils

Scientists from the British Geological Survey, in Nottinghamshire, made casts of the fossils which are on display at New Walk Museum in Leicester.

In 1957, schoolboy Roger Mason famously found one of the world’s earliest-recorded fossils at Charnwood.

The scientists discovered the fossils by painting silicone rubber on to rock surfaces.

They let the silicone set, peeled it off and brought it back to the labs where they made casts of the fossils to study them.

“By using the silicon moulds we have discovered there are literally thousands of fossils and they are gobsmackingly beautiful,” said Dr Phil Wilby, team leader.

“They are absolutely world class. Some of them are substantial in size but it’s almost impossible to see them in the forest because they only become visible when the sun is at the right angle.”

Until the project began, five years ago, only a handful of fossils had ever been discovered at Charnwood.

“The fossils at Charnwood were considered so important because it was the one place in the world where we could definitively say fossils were of Precambrian age,” added Dr Wilby.

The scientists have used isotopic dating to determine how old the fossils are.

It is believed they date back as far as 570 million years.

Geochronologist Daniel Condon said: “The level of detail you can see is now comparable to what you can see at some of the best sites in the world, such as Newfoundland.”

The team is now debating how the fossils fit into the history of life.

Dr Wilby describes the fern-like imprints as “pre-animals”.

“They are not plants or fungi but they are some major higher order of organisms,” he said.

He believes the community was killed en masse.

“It has been frozen in time,” he said. “The obvious comparison is with Pompeii.”

Albertadromeus syntarsus extends knowledge of dinosaur ecosystems

June 2nd, 2013

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Dinosaurs are often thought of as large, fierce animals, but new research highlights a previously overlooked diversity of small dinosaurs. In the Journal of Vertebrate Paleontology, a team of paleontologists from the University of Toronto, Royal Ontario Museum, Cleveland Museum of Natural History and University of Calgary have described a new dinosaur, the smallest plant-eating dinosaur species known from Canada. Albertadromeus syntarsus was identified from a partial hind leg, and other skeletal elements, that indicate it was a speedy runner. Approximately 1.6 m (5 ft) long, it weighed about 16 kg (30 lbs), comparable to a large turkey.

This is a life reconstruction of the new small-bodied, plant-eating dinosaur Albertadromeus syntarsus. – Art by Julius T. Csotonyi.

Albertadromeus lived in what is now southern Alberta in the Late Cretaceous, about 77 million years ago. Albertadromeus syntarsus means “Alberta runner with fused foot bones”. Unlike its much larger ornithopod cousins, the duckbilled dinosaurs, its two fused lower leg bones would have made it a fast, agile two-legged runner. This animal is the smallest known plant-eating dinosaur in its ecosystem, and researchers hypothesize that it used its speed to avoid predation by the many species of meat-eating dinosaurs that lived at the same time.

Albertadromeus was discovered in 2009 by study co-author David Evans of the Royal Ontario Museum as part an on-going collaboration with Michael Ryan of the Cleveland Museum of Natural History to investigate the evolution of dinosaurs in the Late Cretaceous of North America. The known dinosaur diversity of this time period is dominated by large bodied plant-eating dinosaurs.

Why are so few small-bodied dinosaurs known from North America some 77 million years ago? Smaller animals are less likely to be preserved than larger ones, because their bones are more delicate and are often destroyed before being fossilized. “We know from our previous research that there are preservational biases against the bones of these small dinosaurs,” said Caleb Brown of the University of Toronto, lead author of the study. “We are now starting to uncover this hidden diversity, and although skeletons of these small ornithopods are both rare and fragmentary, our study shows that these dinosaurs were more abundant in their ecosystems than previously thought.”

The reason for our relatively poor understanding of these small dinosaurs is a combination of the taphonomic processes (those related to decay and preservation) described above, and biases in the way that material has been collected. Small skeletons are more prone to destruction by carnivores, scavengers and weathering processes, so fewer small animals are available to become fossils and smaller animals are often more difficult to find and identify than those of larger animals.

“Albertadromeus may have been close to the bottom of the dinosaur food chain but without dinosaurs like it you’d not have giants like T. rex,” said Michael Ryan. “Our understanding of the structure of dinosaur ecosystems is dependent on the fossils that have been preserved. Fragmentary, but important, specimens like that of Albertadromeus suggest that we are only beginning to understand the shape of dinosaur diversity and the structure of their communities.”

“You can imagine such small dinosaurs filling the niche of animals such as rabbits and being major, but relatively inconspicuous, members of their ecological community” said Anthony Russell of the University of Calgary.

Note: This story has been adapted from a news release issued by the Society of Vertebrate Paleontology

Billion-Year-Old Water Could Hold Clues to Life On Earth and Mars

June 1st, 2013

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A UK-Canadian team of scientists has discovered ancient pockets of water, which have been isolated deep underground for billions of years and contain abundant chemicals known to support life.

This water could be some of the oldest on the planet and may even contain life. Not just that, but the similarity between the rocks that trapped it and those on Mars raises the hope that comparable life-sustaining water could lie buried beneath the Red Planet’s surface.

The findings, published in Nature today, may force us to rethink which parts of our planet are fit for life, and could reveal clues about how microbes evolve in isolation.

Researchers from the universities of Manchester, Lancaster, Toronto and McMaster analysed water pouring out of boreholes from a mine 2.4 kilometres beneath Ontario, Canada.

They found that the water is rich in dissolved gases like hydrogen, methane and different forms — called isotopes — of noble gases such as helium, neon, argon and xenon. Indeed, there is as much hydrogen in the water as around hydrothermal vents in the deep ocean, many of which teem with microscopic life.

The hydrogen and methane come from the interaction between the rock and water, as well as natural radioactive elements in the rock reacting with the water. These gases could provide energy for microbes that may not have been exposed to the sun for billions of years.

The crystalline rocks surrounding the water are thought to be around 2.7 billion years old. But no-one thought the water could be the same age, until now.

Using ground-breaking techniques developed at the University of Manchester, the researchers show that the fluid is at least 1.5 billion years old, but could be significantly older.

NERC-funded Professor Chris Ballentine of the University of Manchester, co-author of the study, and project director, says:

‘We’ve found an interconnected fluid system in the deep Canadian crystalline basement that is billions of years old, and capable of supporting life. Our finding is of huge interest to researchers who want to understand how microbes evolve in isolation, and is central to the whole question of the origin of life, the sustainability of life, and life in extreme environments and on other planets.’

Water droplets (stock image). Scientists have discovered ancient pockets of water, which have been isolated deep underground for billions of years and contain abundant chemicals known to support life. (Credit: © Alekss / Fotolia)

Before this finding, the only water of this age was found trapped in tiny bubbles in rock and is incapable of supporting life. But the water found in the Canadian mine pours from the rock at a rate of nearly two litres per minute. It has similar characteristics to far younger water flowing from a mine 2.8 kilometres below ground in South Africa that was previously found to support microbes.

Ballentine and his colleagues don’t yet know if the underground system in Canada sustains life, but Dr Greg Holland of Lancaster University, lead author of the study says:

‘Our Canadian colleagues are trying to find out if the water contains life right now. What we can be sure of is that we have identified a way in which planets can create and preserve an environment friendly to microbial life for billions of years. This is regardless of how inhospitable the surface might be, opening up the possibility of similar environments in the subsurface of Mars.’

Professor Ballentine, based in Manchester’s School of Earth, Atmospheric and Environmental Sciences, adds:

‘While the questions about life on Mars raised by our work are incredibly exciting, the ground-breaking techniques we have developed at Manchester to date ancient waters also provide a way to calculate how fast methane gas is produced in ancient rock systems globally. The same new techniques can be applied to characterise old, deep groundwater that may be a safe place to inject carbon dioxide.’

David Willetts, Minister for Universities and Science, says:

‘This is excellent pioneering research. It gives new insight into our planet. It has also developed new technology for carbon capture and storage projects. These have the potential for growth, job creation and our environment.’

Antarctic Polar Icecap Is 33.6 Million Years Old

May 31st, 2013

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Seasonal primary productivity of plankton communities appeared with the first ice. This phenomenon, still active today, influences global food webs. These findings, reported in the journal Science, are based on fossil records in sediment cores at different depths.

The study was led by the Andalusian Institute of Earth Sciences, a Spanish National Research Council-University of Granada joint centre.

The Antarctic continental ice cap came into existence during the Oligocene epoch, some 33.6 million years ago, according to data from an international expedition led by the Andalusian Institute of Earth Sciences (IACT) — a Spanish National Research Council-University of Granada joint centre. These findings, based on information contained in ice sediments from different depths, have recently been published in the journal Science.

A typical, simple dinoflagellate associated with the early Oligocene epoch and found in 33 million year-old sediments. (Credit: IODP)

Before the ice covered Antarctica, Earth was a warm place with a tropical climate. In this region, plankton diversity was high until glaciation reduced the populations leaving only those capable of surviving in the new climate.

The Integrated Ocean Drilling Program international expedition has obtained this information from the paleoclimatic history preserved in sediment strata in the Antarctic depths. IACT researcher Carlota Escutia, who led the expedition, explains that “the fossil record of dinoflagellate cyst communities reflects the substantial reduction and specialization of these species that took place when the ice cap became established and, with it, marked seasonal ice-pack formation and melting began.”

The appearance of the Antarctic polar icecap marks the beginning of plankton communities that are still functioning today. This ice-cap is associated with the ice-pack, the frozen part that disappears and reappears as a function of seasonal climate changes.

The article reports that when the ice-pack melts as the Antarctic summer approaches, this marks the increase in primary productivity of endemic plankton communities. When it melts, the ice frees the nutrients it has accumulated and these are used by the plankton. Dr Escutia says “this phenomenon influences the dynamics of global primary productivity.”

Since ice first expanded across Antarctica and caused the dinoflagellate communities to specialize, these species have been undergoing constant change and evolution. However, the IACT researcher thinks “the great change came when the species simplified their form and found they were forced to adapt to the new climatic conditions.”

Pre-glaciation sediment contained highly varied dinoflagellate communities, with star-shaped morphologies. When the ice appeared 33.6 million years ago, this diversity was limited and their activity subjected to the new seasonal climate.

Archaeopteryx restored in fossil reshuffle

May 30th, 2013

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What may be the earliest creature yet discovered on the evolutionary line to birds has been unearthed in China.

The fossil animal, which retains impressions of feathers, is dated to be about 160 million years old.

Scientists have given it the name Aurornis, which means “dawn bird”.

The significance of the find, they tell Nature magazine, is that it helps simplify not only our understanding for how birds emerged from dinosaurs but also for how powered flight originated.

Aurornis xui, to give it its full name, is preserved in a shale slab pulled from the famous fossil beds of Liaoning Province.

About 50cm tail to beak, the animal has very primitive skeletal features that put it right at the base of the avialans – the group that includes birds and their close relatives since the divergence from dinosaurs.

How it might have looked: Aurornis would have lived in forested environment

Pascal Godefroit from the Royal Belgian Institute of Natural Sciences is the lead author on the paper that describes Aurornis.

His Nature publication also reports details of an across-the-board re-analysis of how the many bird-like creatures living in Jurassic and Cretaceous times were related to each other.

This was done by comparing the detail in the shape of their bones.

The major consequence of this phylogenetic re-assessment is that it restores one of the most famous fossils ever found to the bird line.

Archaeopteryx, dubbed “the first true bird” when first identified in the 19th Century, was shunted recently into a pool of non-avian but bird-looking dinosaurs as a result of the many exquisite feathered creatures emerging in Liaoning. The skeletal features seen in these new specimens had appeared to make Archaeopteryx less pivotal.

However, this demotion caused some consternation because Archaeopteryx, which lived roughly 150 million years ago, could clearly fly; and by re-classifying the animal it had implied also that powered flight must have evolved at least twice – once on the real line to birds and again in this parallel pool of dinosaurs that merely shared some bird features.

But the re-analysis conducted following the discovery of Aurornis has once again simplified the picture.

The first Archaeopteryx fossils were discovered in the 1860s

“Previous phylogenetic investigations were based on maybe only 200 morphological characteristics. Here, we recognise almost 1,500 characteristics,” explained Dr Godefroit.

“So it’s a much bigger and more robust analysis, and according to this new investigation Archaeopteryx is again considered an ancestor of birds and the new creature we describe is also a basal bird; and in fact it is even more primitive than Archaeopteryx,” he told BBC News.

As well as placing Archaeopteryx at one of the earliest points of divergence within the avialans, the study also re-shuffles the Troodontidae, a family of bird-like dinosaurs. Dr Godefroit and colleagues now consider these to be a sister group of the avialans.

“What we’re arguing over here is actually very small, esoteric features of the anatomy,” commented Dr Paul Barrett from the Natural History Museum, London, UK.

“We’re looking at a nexus of animals around bird origins – birds themselves and a bunch of dinosaurs that are almost, but not quite, birds.

“There is a really grey, wobbly line between the two. Just one or two changes across a huge body of data can make the difference between an animal being on one side of this bird-dinosaur divide or the other.

Dr Barrett said the fossils now being unearthed were providing fascinating insights into the emergence of the bird line and the evolutionary “experimentation” that preceded it: “The beginnings of the bird line is all about fine-tuning parts of their anatomy – of their wings, of their hips, of their chest muscles and shoulder girdles, and so on – to make them flight-ready,” he told BBC News.

Source: Article By Jonathan Amos Science correspondent, BBC News

Tiny ‘Spherules’ Reveal Details About Earth’s Asteroid Impacts

May 28th, 2013

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Researchers are learning details about asteroid impacts going back to Earth’s early history by using a new method for extracting precise information from tiny “spherules” embedded in layers of rock.

The spherules were created when asteroids crashed into Earth, vaporizing rock that expanded into space as a giant vapor plume. Small droplets of molten and vaporized rock in the plume condensed and solidified, falling back to Earth as a thin layer. The round or oblong particles were preserved in layers of rock, and now researchers have analyzed them to record precise information about asteroids impacting Earth from 3.5 billion to 35 million years ago.

Researchers are learning details about asteroid impacts going back to the Earth’s early history by using a new method for extracting precise information from tiny “spherules” embedded in layers of rock. The spherules were created when asteroids crashed into Earth, vaporizing rock that expanded as a giant vapor plume. Small droplets of molten rock in the plume condensed and solidified, falling back to the surface as a thin layer. This sample was found in Western Australia and formed 2.63 billion years ago in the aftermath of a large impact. (Credit: Oberlin College photo/Bruce M. Simonson)

“What we have done is provide the foundation for understanding how to interpret the layers in terms of the size and velocity of the asteroid that made them,” said Jay Melosh, an expert in impact cratering and a distinguished professor of earth and atmospheric sciences, physics and aerospace engineering at Purdue University.

Findings, which support a theory that Earth endured an especially heavy period of asteroid bombardment early in its history, are detailed in a research paper appearing online in the journal Nature on April 25. The paper was written by Purdue physics graduate student Brandon Johnson and Melosh. The findings, based on geologic observations, support a theoretical study in a companion paper in Nature by researchers at the Southwest Research Institute in Boulder, Colo.

The period of heavy asteroid bombardment — from 4.2 to 3.5 billion years ago — is thought to have been influenced by changes in the early solar system that altered the trajectory of objects in an asteroid belt located between Mars and Jupiter, sending them on a collision course with Earth.

“That’s the postulate, and this is the first real solid evidence that it actually happened,” Melosh said. “Some of the asteroids that we infer were about 40 kilometers in diameter, much larger than the one that killed off the dinosaurs about 65 million years ago that was about 12-15 kilometers. But when we looked at the number of impactors as a function of size, we got a curve that showed a lot more small objects than large ones, a pattern that matches exactly the distribution of sizes in the asteroid belt. For the first time we have a direct connection between the crater size distribution on the ancient Earth and the sizes of asteroids out in space.”

Because craters are difficult to study directly, impact history must be inferred either by observations of asteroids that periodically pass near Earth or by studying craters on the moon. Now, the new technique using spherules offers a far more accurate alternative to chronicle asteroid impacts on Earth, Melosh said.

“We can look at these spherules, see how thick the layer is, how big the spherules are, and we can infer the size and velocity of the asteroid,” Melosh said. “We can go back to the earliest era in the history of Earth and infer the population of asteroids impacting the planet.”

For asteroids larger than about 10 kilometers in diameter, the spherules are deposited in a global layer.

“Some of these impacts were several times larger than the Chicxulub impact that killed off the dinosaurs 65 million years ago,” Johnson said. “The impacts may have played a large role in the evolutional history of life. The large number of impacts may have helped simple life by introducing organics and other important materials at a time when life on Earth was just taking hold.”

A 40-kilometer asteroid would have wiped out everything on Earth’s surface, whereas the one that struck 65 million years ago killed only land animals weighing more than around 20 kilograms.

“Impact craters are the most obvious indication of asteroid impacts, but craters on Earth are quickly obscured or destroyed by surface weathering and tectonic processes,” Johnson said. “However, the spherule layers, if preserved in the geologic record, provide information about an impact even when the source crater cannot be found.”

The Purdue researchers studied the spherules using computer models that harness mathematical equations developed originally to calculate the condensation of vapor.

“There have been some new wrinkles in vapor condensation modeling that motivated us to do this work, and we were the first to apply it to asteroid impacts,” Melosh said.

The spherules are about a millimeter in diameter.

The researchers also are studying a different type of artifact similar to spherules but found only near the original impact site. Whereas the globally distributed spherules come from the condensing vaporized rock, these “melt droplets” are from rock that’s been melted and not completely vaporized.

“Before this work, it was not possible to distinguish between these two types of formations,” Melosh said. “Nobody had established criteria for discriminating between them, and we’ve done that now.”

One of the authors of the Southwest Research Institute paper, David Minton, is now an assistant professor of earth and atmospheric sciences at Purdue.

Findings from the research may enable Melosh’s team to enhance an asteroid impact effects calculator he developed to estimate what would happen if asteroids of various sizes were to hit Earth. The calculator, “Impact: Earth!” allows anyone to calculate potential comet or asteroid damage based on the object’s mass.

The research has been funded by NASA.

Earth’s Iron Core Is Surprisingly Weak

May 27th, 2013

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Researchers have used a diamond anvil cell to squeeze iron at pressures as high as 3 million times that felt at sea level to recreate conditions at the center of Earth. The findings could refine theories of how the planet and its core evolved.

Through laboratory experiments, postdoctoral researcher Arianna Gleason, left, and Wendy Mao, an assistant professor of geological and environmental sciences and of photon science, determined that the iron in Earth’s inner core is about 40 percent as strong as previously believed.

The massive ball of iron sitting at the center of Earth is not quite as “rock-solid” as has been thought. (Credit: © KristijanZontar / Fotolia)

The massive ball of iron sitting at the center of Earth is not quite as “rock-solid” as has been thought, say two Stanford mineral physicists. By conducting experiments that simulate the immense pressures deep in the planet’s interior, the researchers determined that iron in Earth’s inner core is only about 40 percent as strong as previous studies estimated.

This is the first time scientists have been able to experimentally measure the effect of such intense pressure — as high as 3 million times the pressure Earth’s atmosphere exerts at sea level — in a laboratory. A paper presenting the results of their study is available online in Nature Geoscience.

“The strength of iron under these extreme pressures is startlingly weak,” said Arianna Gleason, a postdoctoral researcher in the department of Geological and Environmental Sciences, and lead author of the paper. Wendy Mao, an assistant professor in the department, is the co-author.

“This strength measurement can help us understand how the core deforms over long time scales, which influences how we think about Earth’s evolution and planetary evolution in general,” Gleason said.

Until now, almost all of what is known about Earth’s inner core came from studies tracking seismic waves as they travel from the surface of the planet through the interior. Those studies have shown that the travel time through the inner core isn’t the same in every direction, indicating that the inner core itself is not uniform. Over time and subjected to great pressure, the core has developed a sort of fabric as grains of iron elongate and align lengthwise in parallel formations.

The ease and speed with which iron grains in the inner core can deform and align would have influenced the evolution of the early Earth and development of the geomagnetic field. The field is generated by the circulation of liquid iron in the outer core around the solid inner core and shields Earth from the full intensity of solar radiation. Without the geomagnetic field, life — at least as we know it — would not be possible on Earth.

“The development of the inner core would certainly have some effect on the geomagnetic field, but just what effect and the magnitude of the effect, we can’t say,” said Mao. “That is very speculative.”

Gleason and Mao conducted their experiments using a diamond anvil cell — a device that can exert immense pressure on tiny samples clenched between two diamonds. They subjected minute amounts of pure iron to pressures between 200 and 300 gigapascals (equivalent to the pressure of 2 million to 3 million Earth atmospheres). Previous experimental studies were conducted in the range of only 10 gigapascals.

“We really pushed the limit here in terms of experimental conditions,” Gleason said. “Pioneering advancements in pressure-generation techniques and improvements in detector sensitivity, for example, used at large X-ray synchrotron facilities, such as Argonne National Lab, have allowed us to make these new measurements.”

In addition to intense pressures, the inner core also has extreme temperatures. The boundary between the inner and outer core has temperatures comparable to the surface of the sun. Simultaneously simulating both the pressure and temperature at the inner core isn’t yet possible in the laboratory, though Gleason and Mao are working on that for future studies. (For this study, Gleason mathematically extrapolated from their pressure data to factor in the effect of temperature.)

Gleason and Mao expect their findings will help other researchers set more realistic variables for conducting their own experiments.

“People modeling the inner core haven’t had many experimental constraints, because it’s so difficult to make measurements under those conditions,” Mao said. “There really weren’t constraints on how strong the core was, so this is really a fundamental new constraint.”

Drill Holes and Predation Traces versus Abrasion-Induced Artifacts Revealed by Tumbling Experiments

May 26th, 2013

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Drill holes made by predators in prey shells are widely considered to be the most unambiguous bodies of evidence of predator-prey interactions in the fossil record. However, recognition of traces of predatory origin from those formed by abiotic factors still waits for a rigorous evaluation as a prerequisite to ascertain predation intensity through geologic time and to test macroevolutionary patterns. New experimental data from tumbling various extant shells demonstrate that abrasion may leave holes strongly resembling the traces produced by drilling predators. They typically represent singular, circular to oval penetrations perpendicular to the shell surface. These data provide an alternative explanation to the drilling predation hypothesis for the origin of holes recorded in fossil shells. Although various non-morphological criteria (evaluation of holes for non-random distribution) and morphometric studies (quantification of the drill hole shape) have been employed to separate biological from abiotic traces, these are probably insufficient to exclude abrasion artifacts, consequently leading to overestimate predation intensity. As a result, from now on, we must adopt more rigorous criteria to appropriately distinguish abrasion artifacts from drill holes, such as microstructural identification of micro-rasping traces.

Holes generated by tumbling experiments on various shells.

Citation: Gorzelak P, Salamon MA, Trzęsiok D, Niedźwiedzki R (2013) Drill Holes and Predation Traces versus Abrasion-Induced Artifacts Revealed by Tumbling Experiments. PLoS ONE 8(3): e58528. doi:10.1371/journal.pone.0058528

Editor: David Caramelli, University of Florence, Italy

Fourteen Closely Related Crocodiles Existed Around 5 Million Years Ago

May 22nd, 2013

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Today, the most diverse species of crocodile are found in northern South America and Southeast Asia: As many as six species of alligator and four true crocodiles exist, although no more than two or three ever live alongside one another at the same time. It was a different story nine to about five million years ago, however, when a total of 14 different crocodile species existed and at least seven of them occupied the same area at the same time, as an international team headed by paleontologists Marcelo Sánchez and Torsten Scheyer from the University of Zurich is now able to reveal.

The deltas of the Amazonas and the Urumaco, a river on the Gulf of Venezuela that no longer exists, boasted an abundance of extremely diverse, highly specialized species of crocodile that has remained unparalleled ever since.

Two new fossil crocodile species discovered

While studying the wealth of fossil crocodiles from the Miocene in the Urumaco region, the scientists discovered two new crocodile species: the Globidentosuchus brachyrostris, which belonged to the caiman family and had spherical teeth, and Crocodylus falconensis, a crocodile that the researchers assume grew to well over four meters long. As Sánchez and his team reveal, Venezuela’s fossils include all the families of crocodile species that still exist all over the world today: the Crocodylidae, the so-called true crocodiles; the Alligatoridae, which, besides the true alligators, also include caimans; and the Gavialidae, which are characterized by their extremely long, thin snouts and are only found in Southeast Asia nowadays.

Crocodylus falconensis, a crocodile that probably grew to well over four meters long. (Credit: UZH)

On account of the species’ extremely different jaw shapes, the researchers are convinced that the different crocodilians were highly specialized feeders: With their pointed, slender snouts, the fossil gharials must have preyed on fish. “Gharials occupied the niche in the habitat that was filled by dolphins after they became extinct,” Sánchez suspects. With its spherical teeth, however, Globidentosuchus brachyrostris most likely specialized in shellfish, snails or crabs. And giant crocodiles, which grew up to 12 meters long, fed on turtles, giant rodents and smaller crocodiles. “There were no predators back then in South America that could have hunted the three-meter-long turtles or giant rodents. Giant crocodiles occupied this very niche,” explains Scheyer.

Andean uplift led to extinction

The unusual variety of species in the coastal and brackish water regions of Urumaco and Amazonas came to an end around 5 million years ago when all the crocodile species died out. The reason behind their extinction, however, was not temperature or climate changes — temperatures in the Caribbean remained stable around the Miocene/Pliocene boundary. Instead, it was caused by a tectonic event: “The Andean uplift changed the courses of rivers. As a result, the Amazon River no longer drains into the Caribbean, but the considerably cooler Atlantic Ocean,” explains Sánchez. With the destruction of the habitat, an entirely new fauna emerged that we know from the Orinoco and Amazon regions today. In the earlier Urumaco region, however, a very dry climate has prevailed ever since the Urumaco River dried up.