Most of us hope that we’ll only have to lose one set of teeth during our lifetime, but for most animals, replacing their teeth is just another fact of life. These so-called polyphyodont animals have
[Above image: Polar Bear jumping, in Spitsbergen Island, Svalbard, Norway. Arturo de Frias Marques, Wikimedia] This December, the Press team is reflecting on some of the PLOS ONE articles covered in the news in 2015.
The size, shape, and solidity of an egg can tell us a lot, but until we can see inside, there is still an opportunity for surprise. Unfortunately, when you have an ancient fossilized lizard egg, you can’t just crack it … Continue reading
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Whether tromping alone or running in a pack, all prehistoric creatures got around somehow. Paleontologists can use fossilized bones to learn more about what dinosaurs ate, what they looked like, and even how they might have moved, but bones are … Continue reading
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The toothpick —an often unnoticed tool for post-meal rituals and appetizer stability—has played a greater role in our ancestors’ health and comfort than many would imagine. In a world before dentists, Neanderthals and modern humans took oral hygiene into their own hands using the only tools they had readily available: little bits of nature they found surrounding them.
Researchers from Spain have presented evidence in PLOS ONE that Neanderthals used small sticks or blades of grass not only to remove fragments of food from between their teeth, but also to lessen the pain caused by periodontal disease, a form of gum disease. While multiple human and Neanderthal remains have been found showing evidence of toothpick use, the authors propose that the combined evidence of toothpick use and gum disease suggests that Neanderthals were perhaps practicing an early form of dental care.
The samples in the image above show an adult’s upper jaw with three teeth left intact found at the Cova Foradà cave site in Valencia, Spain, amidst animal remains and tools dated to the Mousterian era (300,000-30,000 years ago). The adult teeth, believed to belong to an individual between 35-45 years old, show heavy wear on the top surface and exposed roots, the result of a lifetime’s consumption of fibrous and abrasive foods like meats and grains. There are no signs of cavities in the remaining teeth, though decayed bone and the porous surface texture of the left side of the jaw indicate the presence of gum disease.
Two distinct grooves are present on the sides of the existing premolar and molar above the crown of the tooth. These grooves were caused by consistent dragging of a tool across the side of the tooth. The existence of these marks above the gum line indicates heavy dental wear and disease. Here, the gums had receded and left the base of the tooth unprotected. With the roots exposed, it would be easy for leftover debris from meals to get stuck and put pressure on already inflamed gums. The use of a foreign object pushed between the teeth would remove any particles lodged in this sensitive area. Without the extra burden of invasive food detritus, force on the gums would be reduced and irritation and pain would decrease.
Over the last few years, studies have shown that Neanderthals were capable of complex behaviors and emotions, may have used a sophisticated language, were more often right-handed than left, and were generally not the inferior cousins some thought they were. As this study shows, they practiced dental care as well. So, the next time you’re heading out of your favorite restaurant, take a good look at that bowl of toothpicks at the front: the contents could very well be evidence of one of our oldest habits.
Citation: Lozano M, Subirà ME, Aparicio J, Lorenzo C, Gómez-Merino G (2013) Toothpicking and Periodontal Disease in a Neanderthal Specimen from Cova Foradà Site (Valencia, Spain). PLOS ONE 8(10): e76852. doi:10.1371/journal.pone.0076852
Image Credit: Image from Figure 2 of the manuscript
18,000 years ago, the remote Indonesian island of Flores was home to a population of tiny humans. They stood only about 3.5 feet tall on their large feet, and their skulls housed unusually small brains approximately the size of a grapefruit. The identity of these ‘hobbits’ has been hotly debated for years: Were they modern humans suffering a disease, or a new species, Homo floresiensis?
Biological anthropologist Karen Baab first studied a model of LB1, the only skull recovered from the site, at the American Museum of Natural History in 2005. In a recently published PLOS ONE study, she and other researchers compare this specimen to a range of other modern human and extinct hominin skulls to get closer to settling the identity of Homo floresiensis, or ‘Flores man’.
The origins of ‘Flores man’ have been debated for quite a while now. What are the possible origins that are being discussed, and why the uncertainty?
The primary debate has centered on whether LB1 (and possibly the other individuals found on Flores) represents a new species that descended from an extinct species of the genus Homo or whether it is instead a pathological modern Homo sapiens, i.e the same species as us. If the Flores remains do in fact represent a distinct species, then the next question is whether they descended from Homo erectus, a species that may be our direct ancestor, or an even more primitive species. The latter scenario implies an otherwise undocumented migration out of Africa.
What makes it so hard to settle the argument one way or the other?
One of the difficulties in settling this particular argument is that most studies have focused on one or the other of these ideas and compared the Flores remains to either fossil hominins or to pathological modern humans, each using a different set of features. This makes it challenging to compare the alternative hypotheses side-by-side.
What kind of diseases might have caused modern humans to have features similar to these ‘hobbits’?
The three that have been discussed most prominently (and the three we looked at) are microcephaly, endemic hypothyroidism (“cretinism”) and Laron Syndrome. Microcephaly is not a disease per se, but rather a symptom of many different disorders. It refers to having an abnormally small brain and therefore skull. “Cretins” suffer from a lack of thyroid hormone before and after birth, which leads to stunted growth and possibly a slight decrease in skull size. Laron Syndrome individuals produce growth hormone, but their bodies do not properly recognize it, again leading to stunted growth and other developmental issues.
Only a few specimens of this hominin have been found, and there’s only one known skull, from the specimen named LB1. Are there reasons why these specimens have not been discovered elsewhere?
If Homo floresiensis descended from Homo erectus, then their closest relative lived just “next door” on the nearby island of Java. In this case, the unique features of the Homo floresiensis species probably evolved in the isolated island environment of Flores. If, however, the ancestor was a more primitive species, and Homo floresiensis didn’t branch off from H.erectus, it is possible that they might have migrated earlier than known, and we could still find older sites in mainland Asia containing this ancestral species.
You compared the morphology of the LB1 skull to many hominin ancestors and modern human populations from around the world. What were some of the most striking similarities and differences?
The LB1 skull is very distinct from the typical modern human’s, as it has a lower, more elongated silhouette when viewed from the side, , greater width at the rear of the braincase, and a flatter frontal bone (the bone underlying the forehead) with a more pronounced brow ridge. Interestingly, these are some of the same features that distinguish archaic species like Homo erectus from modern humans.
Specimens of Laron Syndrome and “cretin” skulls from modern Homo sapiens presented large, round, globular braincases, which are very different from the smaller, lower and less rounded braincase of LB1. The microcephalic human skulls present a closer comparison to LB1, but still show clear distinctions from LB1 in much the same way that they differ from species like Homo erectus or Homo habilis.
Overall, the LB1 braincase is most similar in its overall shape to small-brained Homo erectus from Eurasia that are 1.8 million years old.
How does this analysis add to, or change, what we knew about Flores man?
This analysis provides a unique opportunity to evaluate these evolutionary and pathological hypotheses side-by-side based on the same criterion – of cranial shape similarity. The results support a stronger affiliation of LB1 with fossil Homo than with any of the proposed pathologies. This study also offers an improvement over previous assessments of the microcephaly hypothesis by using a more extensive sample that better captures the variability in this disorder.
Do these results conclusively settle the discussion? What other possibilities still exist for the origins of H. floresiensis?
While very little in paleoanthropology is ever “settled,” I do think this study represents an important step forward in terms of putting the pathological hypotheses to rest. The question that remains to be answered definitively is which species of archaic Homo is the most likely ancestor of Homo floresiensis – Homo erectus or an earlier and more primitive species of Homo?
Citation: Baab KL, McNulty KP, Harvati K (2013) Homo floresiensis Contextualized: A Geometric Morphometric Comparative Analysis of Fossil and Pathological Human Samples. PLoS ONE 8(7): e69119. doi:10.1371/journal.pone.0069119
The rhino is an iconic animal. With their tough demeanor and unforgettable horn, what’s not to love?
This majestic creature has been on earth more than 9.2 million years, according to a recent PLOS ONE article, where researchers describe a fossil belonging to a large two-horned rhinocerotine species in central Turkey. This rhino was preserved in volcanic rock, a process which accounts for less than two percent of the earth’s fossils. The scientists believe an eruption similar to that of Mt. Vesuvius must be responsible for the impeccable preservation. This study gave us a sense of just how long these brilliant beasts have been among us; however their existence is in grave danger today.
Yesterday May 1st, was Save the Rhino day. The purpose of this day is to bring awareness to rhino conservation and the threats this animal faces in the wild. The rhinoceros does not have any known predators, except for us! Humans have been poaching the rhino at astounding rates for their distinctive horn. The horn is made of keratin, the same protein in our finger nails and hair, and is thought to offer health benefits in traditional medicine. The horn has also been poached for luxury items in other parts of the world.
Today, there are fewer than 29 thousand rhinos on earth, with the white rhino on the brink of extinction. In a recent PLOS ONE article, authors have investigated how potential losses in conservation efforts would affect the white rhino population in South Africa. The authors specifically looked into Kruger National Park where the rhino population increased from 1998 to 2008. Despite this increase, researchers have predicted that by 2015 more white rhinos will be poached than bred, bringing the species into a negative growth phase. Due to the high demand for rhino horns, the authors urge conservationists to find innovative approaches to curb the financial incentive driving the poaching.
Global awareness and conservation is desperately needed to ensure the rhinoceros continues to graze the earth for millions of years to come. For more research on conservation and the glorious rhinoceros, visit our site here.
Citation: Antoine P-O, Orliac MJ, Atici G, Ulusoy I, Sen E, et al. (2012) A Rhinocerotid Skull Cooked-to-Death in a 9.2 Ma-Old Ignimbrite Flow of Turkey. PLoS ONE 7(11): e49997. doi:10.1371/journal.pone.0049997
Citation: Ferreira SM, Botha JM, Emmett MC (2012) Anthropogenic Influences on Conservation Values of White Rhinoceros. PLoS ONE 7(9): e45989. doi:10.1371/journal.pone.0045989
Image on Flickr by wwarby
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
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