Meet PLOS at the Society of Vertebrate Paleontology 2014

SVP Blog Image

We are excited to announce that PLOS will be exhibiting at the Society of Vertebrate Paleontology 2014 Annual Meeting from 5-8th November in Berlin. This is only the second time that the meeting takes place outside North America, and the … Continue reading »

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The New PLOS ONE Collection on “Sauropod Gigantism – A Cross-Disciplinary Approach”

Sauropod-Collection-600x600 (3) (2)The exceptional gigantism of sauropod dinosaurs has long been recognized as an important stage in the evolution of vertebrates, the presence of which raises questions as to why no other land-based lineage has ever reached this size, how these dinosaurs functioned as living animals, and how they were able to maintain stable populations over distinct geological periods.

We are pleased to announce the publication of a PLOS Collection featuring new research on the complex Evolutionary Cascade Theory that attempts to answer  these questions and  explain how the unique gigantism of sauropod dinosaurs was possible. The fourteen papers that make up the collection address sauropod gigantism from a number of varied disciplinary viewpoints, including ecology, engineering, functional morphology, animal nutrition, evolutionary biology, and paleontology.

Sauropod dinosaurs were the largest terrestrial animals to roam the earth, exceeding all other land-dwelling vertebrates in both mean and maximal body size. While convergently evolving many features seen in large terrestrial mammals, such as upright, columnar limbs and barrel-shaped trunks, sauropods evolved some unique features, such as the extremely long necks and diminutive heads they are famous for. Dr Martin Sander, Professor of Paleontology at Universität Bonn and coordinating author for this series of 14 papers, said of the collection:

“This new collection brings together the latest research on the biology of sauropod dinosaurs, the largest animals to ever walk on Earth. Having been extinct for 65 million years, reconstructing sauropod biology represents a particular challenge. Using a wide array of scientific expertise, often from seemingly unlikely fields, has led to some amazing insights. For example, principles of soil mechanics have been used to ‘weigh a dinosaur’ based on its trackways, whilst the latest in computer modeling can make a dinosaur walk again.

The ultimate question underlying this research is how sauropods were able to evolve their uniquely gigantic body size. The wide-ranging disciplines covered in the collection means that there is a -broad, multi-disciplinary audience for the research, as well as general interest in dinosaurs; therefore, we felt that it was essential to publish such a volume in a leading open-access journal such as PLOS ONE to ensure the widest possible dissemination of our work.”

Readers are able to download “Sauropod Gigantism: A Cross-Disciplinary Approach” not only as a PDF but also as an ebook (.mobi and .epub formats) from the collection page. It will also be available on Flipboard (search “PLOS Collections”).

www.ploscollections.org/sauropodgigantism

Image credits:
Collection Image: Kent A. Stevens, University of Oregon

The Power of the Claw: Not Your Average “Soft” Material

Sep blog-tiger cropped

Earlier this month we gave you cuddling between affectionate lions. Lest we become overwhelmed by the desire to cuddle one of these (albeit adorable) feline predators ourselves, here is a look at exactly what one of their clawed paws could do to us, including to one of our toughest components: bone. In a PLOS ONE study published earlier this month, researchers tested the ability of claws to scratch the surface of bone. The effects of claw damage are often overlooked because claws are made of a material softer than bone. Contrary to expectations, however, these researchers found that claws produced recognizable bone damage.

The setup was simple: let a Kansas zoo tiger participating in their enrichment program spend an afternoon leisurely playing with carefully nested cow thigh bones, also called femora. To ensure that the cow femora were only accessible to tiger claws and not to tiger teeth, researchers bolted femora down into a log that was narrowly hollowed out—preventing the big cat from sticking his snout in.

Sep blog- cow femora

The result: impressively lacerated cow femora. Once tiger playtime was over, researchers removed the log, unbolted the femora, and microscopically examined the bone. Four scratches were clearly visible upon the bone’s surface. The scanning electron microscope (SEM) image below further highlights the depths of the tiger claw handiwork.

Sep blog-fomora scratches microscope

In this particular gouge, the main diagonal chasm in the image, the gulf made by the tiger’s claw penetrated the outer covering and subadjacent bone into the bony matrix. As we can see, tiger claws can do some damage.

Damage done to bone, however, is for the most part attributed to the effects of a predator’s teeth and not its claws, the reason being that measures of scratch resistance adhere to a so-called Mohs scale of mineral hardness. The Mohs scale is graded, with talc (1) as the softest material and diamond (10) as the hardest. On the scale, harder materials damage softer materials, but not vice versa. And in our case, bones are, in fact, harder than claws. Claws are made of the protein keratin—the same stuff is in hair, wool, nails, horns, and hooves—which scores a meager 2.5 on the Mohs scale. Bone, on the other hand, scores a much more formidable 5.0.

The current research, however, shows that we can expand our understanding of scratch resistance and mineral hardness to include the effects of softer materials striking harder materials, as long as we consider the kinetic energy involved, like the action of a tiger swatting or grabbing with its paw. In essence, more could be going on in the fossil record than previously thought.

Paleontologist and PLOS ONE Section Editor Andy Farke points out in the PLOS ONE blog The Integrative Paleontologist that fossils inevitably resurface as imperfect objects, which is, in part, what makes them so interesting: These fossils bear the visible marks in postpartum decay of a long and varied history. When studying bone narratives, paleontologists encounter everything from water damage to the bore marks of little critters. Including big-critter claw marks in the repertoire of possible bone modifications broadens this narrative and evidences, as the researchers themselves so aptly put it, the power of the claw.

For more information from the paleontologist perspective, check out blog posts on this article in The Integrative Paleontologist  by Dr. Farke and National Geographic.

Citation:

Rothschild BM, Bryant B, Hubbard C, Tuxhorn K, Kilgore GP, et al. (2013) The Power of the Claw. PLoS ONE 8(9): e73811. doi:10.1371/journal.pone.0073811

Image 1: Tiger by Dave Stokes

Image 2: doi:10.1371/journal.pone.0073811

Image 3: doi:10.1371/journal.pone.0073811

Pristine Fossil Reveals Unlikely Pair

Fernandez_Fig1 mediumThe small but sharp-toothed Thrinaxodon probably spent much of its time dining on its Triassic cohabitants, but a study published today reports a pristine fossil of the meat-eater apparently peacefully sharing its burrow with a small amphibian – until they were both buried in a flood.

The researchers uncovered the odd couple through non-destructive imaging 0f a burrow cast from South Africa, where the animals appeared to have died together. In the image of the cast itself, along with the ghostly outlinescast of the animal skeletons you can see that layer 1 is the original bed of the burrow, and layers 2 and 3 correspond to subsequent “pulses” of the flooding event.

The two skeletons are remarkably complete and well-preserved (in the image above Thrinaxodon is shown in brown, and the amphibian in grey), and the artifact provides an excellent opportunity to study the interactions between two different species. Given Thrinaxodon‘s carnivorous ways, it may at first seem most likely that the amphibian was about to be eaten for lunch, but its undisturbed skeleton and lack of expected bite marks rule out this possibility, the authors write. They also conclude that the flood responsible for burying the animals couldn’t have randomly washed the amphibian into the burrow once the animals were already dead because the burrow’s opening was too small.

To find the most likely answer, the researchers turned to modern creatures for insight. They note that animals today will live in a burrow built by another species if it is abandoned, if they can chase away the host, or if the host tolerates their presence. The Thrinaxodon was still in the den, so neither of the first two possibilities seem to apply in this case, leaving the last option as the most likely. As strange as it may seem, it appears that for whatever reason the Thrinaxodon graciously tolerated its amphibian partner’s presence.

If you want to see more, this video shows how the authors virtually dissected the burrow using synchrotron scanning to create an exquisitely detailed reconstruction of the burrow’s contents without cracking it open.

Citation: Fernandez V, Abdala F, Carlson KJ, Cook DC, Rubidge BS, et al. (2013) Synchrotron Reveals Early Triassic Odd Couple: Injured Amphibian and Aestivating Therapsid Share Burrow. PLoS ONE 8(6): e64978. doi:10.1371/journal.pone.0064978 

Meet Vectidraco, a European pterosaur the size of a crow

Fossil records show that pterosaurs of all sizes and shapes flew through the skies of China and Central Asia about 145 to 66 million years ago. A new species of small pterosaurs described in a PLOS ONE paper reveals that western Europe may have had a similar diversity of these ancient animals. Author Darren Naish discusses the importance of the new species, named Vectidraco.

How did you begin studying dinosaurs (or pterosaurs in particular)?

Most of my research is and has been based on the Lower Cretaceous fossils that come from the Isle of Wight and elsewhere  in southern England. The rocks here are famous for their dinosaurs, but fossil crocodilians, marine reptiles like plesiosaurs and rare pterosaurs are found here too. I’ve always been interested in pterosaurs and for several years have had a special research interest in a highly peculiar pterosaur group called the azhdarchoids – I’ve been working continuously on this group since 2007 or so and have been especially interested in their ecology, functional anatomy and evolutionary relationships. The finding of a new azhdarchoid in the Lower Cretaceous rocks of the Isle of Wight thus combined several of my special interests.

Where and how did you find the new fossil described in your study?

Most Cretaceous Isle of Wight fossils come from a rock unit termed the Wealden Supergroup. The new specimen – we’ve called it Vectidraco – is from a different, younger unit called the Atherfield Clay Formation, and as such it’s (so far as we know) only the second pterosaur reported from this unit.

I should say that the discovery of Vectidraco itself is interesting in that the find was made by a young girl, Daisy Morris (aged just 5 at the time!), while she was on holiday with her family. Daisy’s family wanted this fossil to be studied and cared for properly, so they did what I and many of my colleagues would say is “the right thing” and donated it to The Natural History Museum in London. So, we only know of Vectidraco thanks to Daisy: for this reason we named it in her honour. It’s full name is Vectidraco daisymorrisae.

What was previously known about this group of flying reptiles, the azhdarchoid pterosaurs?

So far as we know right now, azhdarchoids are unique to the Cretaceous period (that is, they were alive between about 145 and 66 million years ago) and all were toothless. They’re actually a pretty diverse group of pterosaurs, with some – like the tapejarids – being relatively small, withwingspans of about 3 feet or slightly less and others – namely the azhdarchids – being gigantic, withwingspans of more than 32 feet.

Tapejarids have short, deep snouts while azhdarchids have incredibly long, pointed jaws, and other kinds of azhdarchoid were intermediate between these two groups. Particularly good azhdarchoid fossils are known from South and North America and China, but their remains have been found right across Europe, Asia and Africa too.

Working out what azhdarchoids did when they were alive has been one of the great questions about the group, but it seems that they were mostly omnivores or carnivores that lived in terrestrial environments.

The paper describes the new fossil as “small-bodied”. How much larger are other known pterosaurs of this kind usually?

Azhdarchoids span a diversity of species that range from ‘small-bodied’ all the way up to gigantic. The biggest kinds –  like the famous Quetzalcoatlus from Texas – were something like 10 feettall at the shoulder and over 450 pounds heavy while small ones, and Vectidraco is one of them, had wingspans of just 30 inches or so and would have been similar in size to crows or gulls. I would say that Vectidraco belonged to an azhdarchoid group where small size was normal and widespread, with large and even giant size evolving in other azhdarchoid lineages.

How did you determine that the new fossil belonged to the same group as these other specimens?

Vectidraco is known only from its pelvis, but even with only a pelvis to go on, we could see several features of the new specimen that made it especially azhdarchoid-like, mostly to do with the weird anatomy of the big, T-shaped bony structure that projects upwards and backwards from the rear part of the pelvis. In an effort to better test the idea that Vectidraco is an azhdarchoid, we included it in a few different phylogenetic analyses and it came out as an azhdarchoid in these too. It also has several unique features, not seen in any other pterosaurs, and for these reasons we were able to name it as a new species.

How does this discovery change what we know about this group of pterosaurs?

We’ve known for a while that small-bodied azhdarchoids lived in western Europe during the Early Cretaceous: a new species called Europejara olcadesorum was described in PLOS ONE last year. Now we’ve found that Vectidraco lived in the same region during the same period, so we’re seeing a pattern: small-bodied azhdarchoids were living alongside longer-snouted, small-bodied pterosaurs and also alongside large, toothy kinds called ornithocheiroids.

This is essentially the same kind of pterosaur community that we  see in Chinese rocks of the same age – the great difference is that the Chinese fossils are relatively numerous, and frequently preserved as complete or near-complete skeletons. In fact, one of the things that we comment on in our paper is the fact that western Europe’s pterosaur assemblage looks far less rich than that of China due to differences in the way these fossils were preserved. Chinese pterosaur and small dinosaur fossils were buried rapidly by volcanic ash and hence preserved whole, while those of western Europe were usually broken apart on floodplains, extensively scavenged, and eventually preserved in fragmentary form.

The western European and Chinese assemblages might actually have contained similar sorts of species, but the conditions local to both places meant that their fossil records ended up being very different.

Read more about this exciting new fossil at Darren Naish’s own blog, Tetrapod Zoology.

Citation: Naish D, Simpson M, Dyke G (2013) A New Small-Bodied Azhdarchoid Pterosaur from the Lower Cretaceous of England and Its Implications for
Pterosaur Anatomy, Diversity and Phylogeny. PLoS ONE 8(3): e58451. doi:10.1371/journal.pone.0058451

Vullo R, Marugán-Lobón J, Kellner AWA, Buscalioni AD, Gomez B, et al. (2012) A New Crested Pterosaur from the Early Cretaceous of Spain: The First European Tapejarid (Pterodactyloidea: Azhdarchoidea). PLoS ONE 7(7): e38900. doi:10.1371/journal.pone.0038900

Images: Specimen and speculative reconstruction of Vectidraco from 10.1371/journal.pone.0058451, Life restoration of the head of Europejara from 10.1371/journal.pone.0038900

A geologist finds his way in a fossil forest (and makes a map for the rest of us)

 

The rich colors and textures of Petrified Forest National Park represent millions of years of geological time, climate change, and peculiar plants and animals. Now you can find your way through these historic layers with the first digitized map of the region, created largely based on research published in a 2010 PLOS ONE study by William Parker and Jeffrey Martz.

In the winter of 2001, Parker had just found the remains of a large dinosaur in the park under a ledge of sandstone; the trouble was establishing when it had lived since existing geological maps were unclear on what period of time the rocks around him represented. Maps available at that time divided the park into two parts separated by a layer of sandstone called the Sonsela Member, but researchers had differing opinions about which bits of sandstone were part of this formation. Though several previous studies had tried to improve these maps, the changes they made on paper didn’t always match up to the real distances and measurements that field researchers encountered.

Parker and his colleague Jeffrey Martz began to map the Sonsela Member as accurately as possible, walking over large sections of the park to take their measurements. As Parker told the National Parks Traveler, his colleague Jeff Martz “literally wore his boots down to ‘sandals’” before they finished the project. The results of their study were published in 2010, one of the first strictly geology studies to appear in PLOS ONE.

PLOS ONE academic editor Andy Farke noted on his blog that their paper helped resolve several questions about the geological events that shaped the Sonsela Member. The research also provided additional explanation for a layer in the geological record that marks a sudden extinction of plants and animals, and has implications for further research studying this major event.

Perhaps most importantly, however, anyone interested can check whether their results are correct.

“One of the things we have tried to do with the PLOS ONE paper is to make our study completely reproducible”, Parker explained in his blog post. “To this end we have provided (and advocate that all future studies also do this) GPS coordinates as well as photos of all measured outcrops. (..) Furthermore, any proposed mistakes in our work can be easily verified or refuted by future workers by using the map. Very important!”

Their study from 2010 formed the foundation for a now-completed geological map that covers 93,000 acres of the park, and is freely available on the Arizona Geological Survey website. According to the National Parks Traveler, the new map is a “rock star” in geological circles, with over 1100 recorded site visitors in a week. Follow the trail back to where it began by reading the PLOS ONE study here. But if you still find yourself getting lost, it might not hurt to carry a carp on your next hike.

Citation: Martz JW, Parker WG (2010) Revised Lithostratigraphy of the Sonsela Member (Chinle Formation, Upper Triassic) in the Southern Part of Petrified Forest National Park, Arizona. PLoS ONE 5(2): e9329. doi:10.1371/journal.pone.0009329

Image: Owl Rock Member, Chinle Formation, Petrified Forest National Wilderness Area. (NPS) by PetrifiedForestNPS on Flickr

New fossil suggests giant ‘killer walrus’ was just a toothy fish-eater

Sea lions, otters, humpback whales and harbor seals are familiar sights to most native Californians today, but the waters off this coastline once harbored a much stranger fauna: giant bony-toothed birds, sharks the size of whales, flightless penguin-like auks, sea cows and giant predatory sperm whales.

Several species of walruses also lived among these animals, but only one survived to the present-day. Robert Boessenecker, author of a paper published in PLOS ONE today, explains what one rare fossil of an extinct walrus reveals about life on Sharkstooth Hill about 15 million years ago:

How did you become interested in studying extinct walruses?

I was always interested in paleontology as a kid, but where I grew up in California, there aren’t any dinosaurs – so I went out collecting shark teeth in high school. As an undergraduate, my adviser encouraged me to start a field-based research project, so I began studying fossil sharks, birds, and marine mammals from the San Francisco region. This turned me on to marine mammal paleontology in general, and I started looking at fossil walruses from other areas in California and Oregon.

What was previously known about the extinct walrus Pelagiarctos?

Pelagiarctos, and close relatives – probably looked a bit more like a sea lion than the modern walrus, as they lacked long tusks.

The first fossils of Pelagiarctos included just the “chin” end of the jaw, and a handful of large teeth, and were discovered in the 1980′s at the famous Sharktooth Hill fossil site near Bakersfield, California. The jaw  fragment is very large and the two jawbones were fused at the chin – like humans, but not typical for pinnipeds. The large teeth are somewhat similar to those of terrestrial “bone-cracking” carnivores like hyenas, and so Pelagiarctos was interpreted as an apex predator that was adapted to feed upon warm blooded prey, perhaps including smaller pinnipeds and marine birds, in addition to the typical pinniped diet of fish. The large size and fusion of the lower jaws also suggested that Pelagiarctos could produce a large bite force – also pointing towards it being an apex predator, or “killer walrus” if you will.

Lastly, fossils of Pelagiarctos are extremely rare. Although there are hundreds of specimens of other pinnipeds  from Sharktooth Hill – there are only seven known specimens of Pelagiarctos from that site.

In your paper, you describe the discovery of a new jaw bone with teeth. What did this reveal about this walrus’ feeding habits?

The discovery of a more complete specimen allowed us to test the hypothesis that Pelagiarctos was a “killer walrus”. When we examined the new specimen and the original fossils, we found that the teeth really weren’t that sharp at all – in fact, the teeth looked like scaled up versions of the teeth of a much smaller sea lion. This told us that the tooth shape is really just a consequence of Pelagiarctos retaining primitive teeth, rather than being a feeding adaptation.

What about body size? My coauthor, Morgan Churchill, developed a method to reconstruct body size of fossil pinnipeds based on the size of the lower jaw. As mentioned already, Pelagiarctos was indeed large, about the size of large male sea lions. However, when you try to correlate the weight of modern pinnipeds with what they eat , there isn’t really any distinct trend. This is because most modern pinnipeds are generalists, and tend to eat fish, squid, and even krill and mollusks. Even the modern walrus, a mollusk specialist and an exception to the generalist ‘rule’ occasionally kills and eats marine birds and even other pinnipeds. The only pinniped to regularly hunt warm blooded prey – the leopard seal – spends a good deal of the year feeding on krill.

These alternative interpretations and observations – combined with the lack of feeding adaptations, suggests Pelagiarctos was also a generalist fish eater rather than a “killer walrus” that only hunted marine birds and warm blooded prey.

Does this tell us anything about the walruses that exist today?

This new find and reinterpretation of Pelagiarctos as a fish-eater gives us a slightly more accurate picture of the evolutionary background of the modern walrus. Right now, there is only one modern walrus species but back then, walruses were a very diverse group. Many of these other extinct walruses had strange adaptations – such as the development of upper and lower tusks, gigantic body size, ultradense bones, unusually short forelimbs, and even the loss of all teeth aside from tusks. The myriad types of extinct walruses – Pelagiarctos included – beautifully demonstrate the often convoluted path that evolution can take.

What is the most important aspect of your results?

Pelagiarctos lived roughly 15-18 million years ago; this period is also referred to as the “middle Miocene Climatic Optimum”, and global temperatures increased for a little while. After the optimum, the earth began to cool again.

Any information we can get that improves our knowledge of extinct marine mammal food webs – especially during times of climatic change – is a step forward towards putting together a “deep time” context for understanding modern marine mammal ecology.

Read more about this fossil at the author’s blog.

Image: Artist’s restoration of Pelagiarctos, Robert Boessenecker

Citation: Boessenecker RW, Churchill M (2013) A Reevaluation of the Morphology, Paleoecology, and Phylogenetic Relationships of the Enigmatic Walrus Pelagiarctos. PLoS ONE 8(1): e54311. doi:10.1371/journal.pone.0054311