In their recent study published in PLOS ONE, paleoecologist Larisa DeSantis and her team find out whether diet and climate have an effect on tooth wear in two species of kangaroo and one species of
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 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”).
Collection Image: Kent A. Stevens, University of Oregon
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.
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.
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.
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 2: doi:10.1371/journal.pone.0073811
Image 3: doi:10.1371/journal.pone.0073811
The 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 outlines 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