Many of us have heard the haunting call of a whale ‘song,’ but how do the whales themselves hear sound? Similar to the way that animals see color in different ranges of the visible light spectrum, the mechanism by which they hear sound can also vary and in some cases is still not well understood.
The authors of the recently published PLOS ONE article, “Fin Whale Sound Reception Mechanisms: Skull Vibration Enables Low-Frequency Hearing,” investigated how sound interacts with a fin whale’s skull. Specifically they looked at low-frequency sounds such as those used by whales, likely to communicate across long distances. The researchers obtained a whale skull after an unsuccessful attempt to rescue a beached newborn fin whale on Sunset Beach, Orange County, CA. They took a computed tomography (CT) scan of the skull and used it to construct a finite element model, which allowed them to simulate and make predications regarding the mechanism by which fin whales hear sound.
For the majority of animals that have what we normally anatomically identify as ears, the vibration of bones within the ear allows them to hear sounds. Fin whale ears work the same way, and by watching the simulated response of the bones in their model to sound, the authors were able to identify two main mechanisms by which fin whales hear. The first, and most prevalent, is known as the ‘bone conduction mechanism,’ where the vibration of the ear bones is caused by the movement of the skull in reaction to sound. The second mechanism is called the ‘pressure mechanism,’ which describes the way sound directly interacts with the whale ear bones after moving through the water and head tissue. In the figure below, the authors provide a colorful image from their model of the ear bones interacting with sound.
It is important to note that while the authors found that the ‘bone conduction mechanism’ seemed to be the main mechanism for hearing in their model, it may only be applied specifically to fin whales since it was the only skull type that they studied. However since fin whales are a type of baleen whale, distinguished from toothed whales by their baleen which filters food out of the water in place of teeth, it is possible that other baleen whales utilize the ‘bone conduction mechanism’ as well. The physiology of most toothed whales is much different than baleen whales, and a group of ligaments actually separates the ear bones from the rest of the skull making it more difficult for skull vibrations to reach the ear bones.
The fact that fin whales communicate using low-frequency vocalizations also pairs with the authors’ findings. Low-frequency sounds tend to scatter and therefore do not have the ability to apply much direct pressure on ear bones. Therefore the sound’s contact with the skull would account for the majority of how they hear these low-frequency sounds and the ‘pressure mechanism’ would be less impactful. Although a calf skull (see below) was used in this study, the authors note that these mechanisms should not change in the adult skull, as the components of hearing physiology develop at a young age.
How marine animals perceive sound has been a topic of growing discussion as the amount of man-made noise increases in the ocean. Tools such as sonar, often used by the military to detect objects underwater, have been suggested as a cause of some fin whale behavior that has been interpreted as confusion or even a possible cause of beaching. The authors mention that the results of their study may assist policy-making bodies, to protect our ocean’s species from things such as the inadvertent effects of sonar. Keep an ear to the ocean and if you are lucky enough to hear a whale call, you can now listen with a well-informed ear.
Citation: Cranford TW, Krysl P (2015) Fin Whale Sound Reception Mechanisms: Skull Vibration Enables Low-Frequency Hearing. PLoS ONE 10(1): e0116222. doi:10.1371/journal.pone.0116222 Images: Fin Whale by Amila Tennakoon via Flickr. Fig. 1 and Figs. S4 and S9 of the published article.
A house is not a home without a dog, and a dog isn’t a “D-O-double-G” without its microbial “crew.”
Human microbiome research is progressing rapidly, and we are always learning how the bacteria living on and inside of us contribute to our survival and well-being. Although we are making some headway to understanding the role of human flora in our bodies and in disease progression, we know far less about the microbial flora in our pooch friends.
The diverse microbial landscape on skin is essential for all animals, as it helps maintain essential oils and plays “guard” in the first line of immune defense. However, living on animal skin isn’t easy—it’s exposed to the world and all its creatures, and endures some serious physical contact with them. There are many skin diseases that may alter skin microbe colonization, such as atopic dermatitis (AD), one of the most common skin infections in dogs (and people). Dogs that do develop AD have an increased sensitivity to many allergens. Additionally, many dogs with allergic AD are subject to bacterial skin infections. With this in mind, a group of researchers at Texas A&M recently published a study in PLOS ONE where they identify the microbial makeup of dog skin. The authors “hired” a crew of healthy dogs, as well as a group of dogs with allergic AD, to characterize the differences in their bacterial communities.
To obtain samples of as many skin-inhabiting critters as possible, the researchers brushed swabs back and forth on 12 different skin sites from the “healthy” dog squad, and 4 different skin sites from the allergic AD dogs, with the sites shown in the image below.
After extracting and sequencing the DNA from the swab culture samples, the authors were able to characterize the microbial inhabitants of the dogs’ skin for each site, and compare the species distribution found on the healthy dogs’ skin to those found on the allergic dogs. In healthy dogs, the lowest abundance of species, also called species richness, were found in their mucosal areas, such as the nostrils; whereas the haired-skin areas, such as the groin and axilla, had the highest species richness. Notably, ears took the “bone” with 866 different species present!
Among all dogs tested, the authors found a total of 17 different phyla, with Proteobacteria being the most abundant phylum. Ralstonia was the most abundant genus, likely because it’s found in dirt and water, the favorited doggy playground. Although there was high variability among the individual dogs tested, the authors found that the proportion of Ralstonia was much lower in all allergic dogs.
The species richness was much lower in the allergic dogs as compared to healthy dogs, as seen in the image above. The authors suggest that this difference may be the result of the antimicrobial washes that allergic dogs are often prescribed by vets for treatment, as well as skin changes induced by the allergic inflammation response.
While there is much work to be done characterizing the full doggie microbiome, and this study had a limited sample size, the authors have made steps toward characterizing the bacterial ecology of dog skin, and discovered that dog skin may contain much richer and more diverse microbial communities than were previously suggested. Like with the human microbiome, researchers might now investigate the role of the dog microbiome in normal function, disease progression, and better treatments for our favorite co-pilots. So next time you let the dogs out, give a thought to their bacterial companions!
Citation: Rodrigues Hoffmann A, Patterson AP, Diesel A, Lawhon SD, Ly HJ, et al. (2014) The Skin Microbiome in Healthy and Allergic Dogs. PLoS ONE 9(1): e83197. doi:10.1371/journal.pone.0083197
We are excited to announce the publication of the PLOS ONEconference page. The page serves as a one-stop shop for announcements and information regarding upcoming conferences, including when and where to meet up with PLOS ONE journal staff.
You can easily navigate to the page by selecting the ‘Conferences’ tab from the EveryONE menu at the top of the page (also pictured below).
We hope you’ll check out the page and come meet us in person at one of the many conferences we plan on attending throughout the year.
Of all the environmental resources we take for granted, large, older trees might be near the top of the list. Not only do we rely on trees for oxygen and wood products, but about 180 different animal species rely on the hollow-bearing features of these trees for shelter, roosting, and nesting. Unfortunately, rapid urbanization poses an enormous threat to the existence of these trees.
Large old trees take centuries to mature, and scientists are paying particular attention to the changes in wooded areas as urbanization spreads. The authors of a recent study published in PLOS ONE utilized a simulation model to determine the future of older trees in and around Canberra, Australia. In this urban area of Australia where the population is projected to double from 375,000 people by 2056, the authors found that dramatic changes to the terrestrial environment could occur.
The simulation model developed by the authors calculated the average number of trees in a given area using pre-defined rates of tree mortality and existing data for trees they had catalogued and measured. The data collection included the total number of trees, how fast new ones were growing, and how quickly existing ones were dying or being removed. By extrapolating from this data, they were able to assess tree population changes in the coming years.
Unfortunately, building for a growing human population means clearing out these older trees that may pose a safety threat or may simply be in the way. By projecting the current rate of decline for existing trees in the next 300 years, the researchers found that these trees die or are removed at a rate so rapid that it could lead to their eventual disappearance. To put that threat into numbers, it seems that the population of these hollow-bearing trees will decline by nearly 87% over the next 300 years. In a worst case scenario, we could lose all old, hollow-bearing trees within 115 years. That’s a terrifying thought.
According to the authors’ review of tree population changes, several policies may need to change to reverse the decline of these trees. Only with a combined management strategy, including planting more trees and forming more hollow-bearing habitats, would the population of the trees increase over 250 years after a short period of decline. A decline in older, hollow-bearing trees, including some endangered Eucalyptus varieties, means a decline in shelter for the birds, bats, squirrels, and invertebrates that inhabit them.
Luckily, urbanization brings new innovation, and innovation inspires new solutions to important problems. Environmental consciousness in the public requires a discussion about improving tree management, community engagement, conservation strategies, and biodiversity offsets. For example, we now have the technology to give hollow-bearing features to trees in urban areas by using other hollow-structures or artificial nest boxes.
If large older trees are facing almost certain decline due to urbanization, we need to put forth significant efforts to develop conservation and management strategies to change that. With the research available today, we can develop strategies to protect the large trees in existence, improve regeneration for ones we lose, and develop plans to build structures for animals who are displaced. We are not the only living beings on Earth, and we need to take into consideration how we effect change in our environments.
Citation: Le Roux DS, Ikin K, Lindenmayer DB, Manning AD, Gibbons P (2014) The Future of Large Old Trees in Urban Landscapes. PLoS ONE 9(6): e99403. doi:10.1371/journal.pone.0099403
“I never quit until I get what I’m after. Negative results are just what I’m after. They are just as valuable to me as positive results.” – Thomas A. Edison
The publication of negative results is vitally important for many reasons, not least that it helps prevent duplication of research effort and potentially expedites the process of finding positive results. However, the struggle to find a home to publish the work, and the effort necessary to submit and publish what can feel like negligible scientific contributions, has led to concerns that negative findings are becoming the missing pieces in the scientific literature.
Today PLOS ONE launches a new collection to highlight studies that present inconclusive, null findings or demonstrate failed replications of other published work. The collection has been titled ‘Missing Pieces’ in reference to the many null results filed away indefinitely and ultimately excluded from the scientific record.
Selected examples focus on the lack of a significant effect of postpartum psychological distress on mothers in rural Bangladesh, despite differing positive findings in India.
Frequency discrimination training (FDT) using integrated training with computer-gameplay has previously been reported to show limited improvement in treating the symptoms of tinnitus, however, recent results from a randomised controlled trial did not translate to therapeutic benefit.
The failure to replicate previously published work is prominently highlighted in the popular PLOS ONE psychology paper, Failing the Future. Three attempted replications on the existence of precognition failed to support the previously significant results supporting retroactive facilitation of recall.
The publication of negative results, such as the works featured in the collection, is essential to research progress. Many journals, however, reject studies reporting negative or inconclusive results because the work is not considered impactful enough. In contrast, PLOS ONE does publish such studies; our publication criteria state that we will consider all work that makes a contribution to the field independent of impact.
Through this collection we hope to demonstrate that negative results are valuable to the community in cases where the result is illuminating in the context of previous work.
This collection serves to highlight negative result studies and to encourage the submission of negative results to PLOS ONE. If you would like your work to be considered for the Missing Pieces Collection, please contact firstname.lastname@example.org
As winter grips the Northern Hemisphere tightly, many of us are happy to retreat to the comfort of our warm homes. But for some animals, this season plays a vital role in the formation of something necessary for their survival, ice. There is one thing that we are becoming increasingly sure about: not all winters are created equal. In some years, ice and snow blanket the ground until mid-spring, and in others, light dustings of snow only last for a couple days. For animals that depend on ice for survival, varying winter conditions year to year may provide challenges to finding food, breeding, and making it from one day to the next.
PLOS ONE has recently published several studies that take a closer look at three different animals’ relationship with ice: penguins, polar bears, and ivory gulls.
Searching for Emperor Penguin Breeding Grounds
Emperor penguins rely on Antarctic sea ice for breeding and foraging, but a recent study published in PLOS ONE may have uncovered a new breeding behavior, where the penguins utilize a different type of ice.
Using satellite and aerial surveys to observe four emperor penguin breeding colonies, the authors of this study discovered something unusual. Two of the penguin colonies always appeared on the ice shelf rather than where we expected them to be—on sea ice—but the other two colonies were on both ice shelves and on sea ice in different breeding seasons. Researchers used synthetic aperture radar to assess how the largest of the four colonies may sometimes breed on the shelf and other times on the sea ice.
The authors found that in years where sea ice forms late in the season, the colony relocates onto the ice shelf. Three of the four breeding colonies were in the warmest northern conditions in Antarctica, where sea ice formation is less reliable. What may be a new breeding behavior at these warmer sites could provide clues for understanding how this near threatened penguin species may cope with future sea ice loss.
Polar Bears on the Move
On the other side of the globe, Arctic polar bears also rely heavily on ice for hunting and breeding, but sea ice has declined by over 9% in the Arctic over the past 20 years. The authors of a recent PLOS ONEstudy investigated how these changes may impact polar bear movement around the Arctic. The authors of this study analyzed genes from over 2,700 polar bears to evaluate whether polar bear genetic diversity and structure have changed in the past two decades. They then compared current polar bear genetic patterns with past patterns during ancient climate fluctuations.
Scientists identified four geographic polar bear populations: Eastern Polar Basin, Western Polar Basin, Canadian Archipelago, and Southern Canada (pictured above). They found evidence of gene flow within the past three generations, from Southern Canada and the Eastern Polar Basin toward the Canadian Archipelago, an area thought by scientists to be a possible future refuge for polar bears as climate-induced habitat decline continues.
They also found that the current population shift may differ from previous periods with respect to sea ice variation during the Holocene, where polar bears may have used both the Canadian Archipelago cluster and part of the Eastern Polar Basin cluster as an interglacial refuge. The scientists suggest more genetic samples are needed, but documenting population changes in the past and present may aid in conservation efforts as sea ice continues to decline.
Ivory Gulls on the Icy Edge
Living their entire lives in the Arctic, the near-threatenedivory gulls have scheduled their activities around ice. Foraging, migrating, and breeding are all dependent on ice, but little data exists on their year-round location and timing of these activities. In a recent PLOS ONEstudy, scientists interested in following the ivory gulls’ movement around their Arctic habitat attached satellite transmitters to 12 ivory gulls on Seymour Island, Canada in 2010, and tracked their migration over four breeding seasons.
Scientists have long thought the ivory gulls migrate along the Greenland coast, but the tracking data shows that individual birds varied the timing and their routes greatly. Ivory gulls avoid flying over open water, and scientists suggest birds may vary their migration route with the variations in sea ice formations. Further analysis of their movement revealed that the ivory gulls overwintered near the ice edge in Davis Strait and the Labrador Sea, which likely provided them with a consistent source of food, like fish, or scavenging opportunities, like polar bear remains.
Further research is needed to better understand these patterns, but may aid in predicting their ability to adapt to future sea ice changes.
While scientists are finding evidence that sea ice formation may be changing, they are also working to gain insight into animal behavior and develop conservation measures that might be designed around their current activities. While we humans in the Northern Hemisphere may be ready for winter to be over, animals at the Antarctic and Arctic poles may be hoping that more ice is on the way.
Citations: Fretwell PT, Trathan PN, Wienecke B, Kooyman GL (2014) Emperor Penguins Breeding on Iceshelves. PLoS ONE 9(1): e85285. doi:10.1371/journal.pone.0085285
Peacock E, Sonsthagen SA, Obbard ME, Boltunov A, Regehr EV, et al. (2015) Implications of the Circumpolar Genetic Structure of Polar Bears for Their Conservation in a Rapidly Warming Arctic. PLoS ONE 10(1): e112021. doi:10.1371/journal.pone.0112021
Spencer NC, Gilchrist HG, Mallory ML (2014) Annual Movement Patterns of Endangered Ivory Gulls: The Importance of Sea Ice. PLoS ONE 9(12): e115231. doi:10.1371/journal.pone.0115231
While humans may be the only ones with a day dedicated to celebrating romantic love, rest assured that the semblance of ‘love’ is alive and well in the animal kingdom too. While ‘love’ in this context may not hold the same meaning we normally think of, animals on land, air, and sea are diligently working to keep their species alive. In honor of them, the PLOS ONE staff has gathered a few of our favorite ‘animal love’-themed research articles to share with you this Valentine’s Day.
Letting people know you’re taken can be important, and no one knows this better than the male stony creek frog. The males of this species change color from boring brown to a ‘look at me!’ yellow in a matter of a few minutes during mating (pictured above). The authors of “The Neuro-Hormonal Control of Rapid Dynamic Skin Colour Change in an Amphibian during Amplexus” aimed to determine the hormones behind this color change. Previous studies, showing that stress in this species may trigger the color change during mating, helped the authors narrow down their focus to look specifically at stress hormones. By exposing captured, wild male frogs to epinephrine (also known as adrenaline), testosterone, and a control substance, they were able to determine that epinephrine likely plays a key role in turning the frogs yellow. Based on their observations, the authors hypothesize that the bright yellow color is a signal to other males that they have secured a female, and a way to possibly prevent other males from getting in the way of an all-important mating session.
Fighting among males for mates is fairly common in the animal kingdom, but a group of researchers investigated whether there were any evolutionary patterns in snakes exhibiting this behavior. The authors of “Phylogeny of Courtship and Male-Male Combat Behavior in Snakes” looked at 33 male snake courtship behaviors across 76 species, retrieving these details from pre-existing literature. Some of these behaviors included ‘biting,’ ‘tail whipping,’ and ‘spur poking.’ They also note that since snake behavior often goes unrecorded, future data collection is needed. They mapped these behaviors on a phylogeny, an evolutionary map that included 30 species of snakes belonging to the superfamily Colubroidea. After analyzing this comparison, they were able to discern a pattern (see image above) and gain idea of the time period that certain behaviors were introduced to a species. Based on this evaluation, a “head raise with simultaneous downward push” and “spur poking” were some of the earliest attack methods deployed in combat between these male snakes, all in the name of ‘love,’ of course!
While there are many species of birds that are ‘monogamous,’ many also mate outside social pairs. The authors of “Steller Sex: Infidelity and Sexual Selection in a Social Corvid (Cyanocitta stelleri)” aimed to determine what role male ornamental plumage plays in Steller jay chick paternity. The authors worked with a population of Steller jays in which 25 social pairs (life partners) were known and collected blood samples from the birds and their chicks. They were then able to determine the number of chicks that hatched after extra-pair mating. After analysis, the authors found that 15% of chicks in this Steller jay population were the product of extra-pair mating. Additionally, they found that jays whose male mates had lower quality plumage had more extra-pair chicks, while those whose mates had higher quality plumage had fewer extra-pair chicks. However, a nest full of extra-pair chicks does not go unpunished. Other studies have shown that bird nests with a higher percentage of extra-pair chicks result in less effort toward parental care on the part of the male.
My Sweet Little Dumpling [Squids]: Getting Frisky in Front of Flatheads
Being a “third wheel” can be an uncomfortable situation, but Nature takes that to another level when a predator “third wheel” approaches two mating creatures. You would think that the presence of predators would put animals on high alert and deter them from mating, but that may not always be the case. Many animals face a trade-off between survival and reproduction, and sometimes reproduction is their most viable option. Female dumpling squid (one pictured above) produce ink to mask their coupling from hungry sand flathead predators, but male dumpling squid do not bother to produce any defense mechanisms when they are mating.
To observe this mating behavior, the authors of “Does Predation Risk Affect Mating Behavior? An Experimental Test in Dumpling Squid (Euprymna tasmanica)” matched fifteen pairs of dumpling squid, and then subjected each pair to three separate predation simulations. The dumpling squid couple and the sand flathead were separated by a clear acrylic sheet with holes in the top, so that they could see and hear one another. The predator was introduced before, during, and after the squid couples’ mating, to observe whether its introduction would interrupt or stop the squids from getting busy. They found that females inked significantly more when a predator was introduced before mating, but the males did not ink. Males would not cease mating to protect themselves because an interruption would mean fewer sperm would be transferred, and he would be less likely to impregnate the female. In addition, predation risk did not influence the squids’ likelihood or duration of their mating. The image above depicts a pair of mating dumpling squid, and you can watch a video of their inking, jetting, and copulation behaviors here:
Reindeer (Rangifer tarandus) may look cute and innocent, but they can be aggressive when it comes to mating. During the rutting season, female reindeer move in large groups either to sample mates, or to avoid harassment from the males—not exactly the most romantic of situations. Often the dominant males will herd the females in a group, rather than follow an individual female, both to act as their protector and to increase their chances of successful reproduction. The authors of “Highly Competitive Reindeer Males Control Female Behavior during the Rut” investigated these behaviors by observing 11 male and 34 female semi-domestic reindeer during the breeding season, tracking and recording their GPS position every 15 minutes, for a total of 3800 recordings. They measured the average number in a group and how long the group remained together, and compared those measurements with the length of the mating season and the social rank of the dominant male, which is established based on several variables, such as a large body mass and antler size. Through this model, the researchers demonstrated that the dominant reindeer males, through herding and other mating-related activities, strongly influence the females’ movement patterns. In other words, the reindeer males were a bit machismo when it came to ‘love.’ The females, however, may not have as much choice in their mating partner—quite a double-standard, and not a very modern romance relationship for this animal pairing!
In contrast to the female reindeers’ relative lack of choice in a mate, female moths (Spodoptera litura) may be a bit pickier when choosing a mate. The authors of “Female and Male Moths Display Different Reproductive Behavior when Facing New versus Previous Mates” found that female moths can tell if they’ve mated with a male moth before, and they prefer to mate with new partners. Male moths, on the other hand, will generally mate with whichever female is present—in other words, he won’t mind if she’s an old flame. In the study, the researchers played a little moth matchmaker, pairing moths up in boxes in the lab to see if they’d mate with one another. They recorded the mating behaviors of the females when they were exposed to new mates, taking note of their expansion of the pheromone gland to attract a male mate (known as calling), the male’s courtship of the female by fanning his wings around her, and the mating of the two moths. They found that females called earlier and more often when paired with a new male partner, but males courted new and previous female mates the same way. This isn’t to say the males’ wooing techniques were boring by any means—in fact, male moths can create some lovely melodies to serenade their lovers.
We hope you enjoyed exploring the mating behaviors of some of our favorite animals— who knows, maybe you were even able to relate to some of them. Such behaviors show that many animals seem to subscribe to the “all’s fair in love and war” mantra—or at least the males do! Whether you’re “assertive” or not when it comes to love, rest assured there’s probably a member or two of the animal kingdom that has recently behaved the same way. Happy Valentine’s Day from PLOS ONE!
Written by PLOS staff members Tessa Gregory and Kaitlyn Keller
Kindermann C, Narayan EJ, Hero J-M (2014) The Neuro-Hormonal Control of Rapid Dynamic Skin Colour Change in an Amphibian during Amplexus. PLoS ONE 9(12): e114120. doi:10.1371/journal.pone.0114120
Senter P, Harris SM, Kent DL (2014) Phylogeny of Courtship and Male-Male Combat Behavior in Snakes. PLoS ONE 9(9): e107528. doi:10.1371/journal.pone.0107528
Overeem KR, Gabriel PO, Zirpoli JA, Black JM (2014) Steller Sex: Infidelity and Sexual Selection in a Social Corvid (Cyanocitta stelleri). PLoS ONE 9(8): e105257. doi:10.1371/journal.pone.0105257
Franklin AM, Squires ZE, Stuart-Fox D (2014) Does Predation Risk Affect Mating Behavior? An Experimental Test in Dumpling Squid (Euprymna tasmanica). PLoS ONE 9(12): e115027. doi:10.1371/journal.pone.0115027
Body G, Weladji RB, Holand Ø, Nieminen M (2014) Highly Competitive Reindeer Males Control Female Behavior during the Rut. PLoS ONE 9(4): e95618. doi:10.1371/journal.pone.0095618
Li Y-Y, Yu J-F, Lu Q, Xu J, Ye H (2014) Female and Male Moths Display Different Reproductive Behavior when Facing New versus Previous Mates. PLoS ONE 9(10): e109564. doi:10.1371/journal.pone.0109564
PLOS ONE and PLOS Biology are excited to return to the Biophysical Society’s Annual Meeting. The event will be held at the Baltimore Convention Center located in downtown Baltimore, Maryland. All are encouraged to stop by booth #636 to speak with PLOS staff and learn more about our journals. We look forward to meeting current and prospective authors, Academic Editors, reviewers, and anyone else interested in PLOS!
Be sure to grab a copy of the PLOS Editors’ Picks for Biophysical Sciences Articles postcard. PLOS editors’ picks include:
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 only part of the “rocky” story. We can study fossils of all shapes, sizes, and sources to piece together missing information about how these creatures moved, interacted, and lived. Trace fossils, which include fossilized impressions like footprints and belly drag marks left in the ground, can tell us a surprising amount about how animals of the past lived and moved. They are more common than you might think, but typically aren’t studied as often as fossilized bones. PLOS ONE recently published two separate studies where authors used trace fossils to provide insight on tyrannosaurs social life and the slow and slithering movements of an ancient temnospondyl, bringing two prehistoric creatures to ‘life.’
Many tyrannosaur bones have been collected and documented, but few scientists have studied their footprints. In a new PLOS ONEstudy, researchers found three 75 million-year-old three-toed tyrannosaurid footprint with claw marks tracks heading southeast within an 8.5 meter-wide corridor in British Columbia, Canada (shown in the image above). Scientists took molds and measurements of the prints (shown in the image below) to understand the track-makers’ behavior. Scientists aren’t sure exactly which species of tyrannosaur made the prints, but similarities in depth and preservation of the tracks indicate that these three trackways were made by dinosaurs walking alongside each other in the same direction at a normal pace, around 8.50 kilometers per hour.
These trackways add to previous research about tyrannasaurid social behavior and locomotion, but the authors acknowledge that there is the possibility, although unlikely, that three dinosaurs could have passed through the same spot separately within a short period of time. Either way, the tracks make up the first record of the walking gait of tyrannosaurids and provide insight about how they moved across Western Canada.
A 200 million-year-old mysterious trackway, called Episcopopus ventrosus, in southern Africa may have been made by a dinosaur, or maybe by an early ancestor of the crocodile. Researchers that mapped, cast, and laser-scanned the best-preserved part of the Episcopopus ventrosus trackway found that the track belongs to a primitive amphibian-like animal from one of the earliest groups of limbed vertebrates, temnospondyls. The author’s estimate the track-maker was 3.5 meters long and dragged the hind portion of its body along a wet sand bar on the bank of a river bend, using only the claw-less tips of its digits (pictured above).
The movements were likely made by a large-headed, slithering, and slow-moving amphibian-like animal. Researchers usually use hind-limb-driven salamanders as a model for temnospondyl locomotion, but this discovery is causing researchers to re-examine their use of salamander models for this front-limb-driven temnospondyl.
Socializing and Slithering
From signs of dinosaurs moving in packs to amphibian-like animals slithering across river banks, trace fossils can support what we already know about prehistoric creatures, but they can also shake up the assumptions we’ve made, and in the case of the tetrapod, potentially change the way we study them. Fossilized bones may still be the better known field of study, but footprints and other trace fossils may help shape our understanding of patterns, reconstructing of past lives, and bringing of prehistoric animals back to “life.”
Citation: McCrea RT, Buckley LG, Farlow JO, Lockley MG, Currie PJ, et al. (2014) A ‘Terror of Tyrannosaurs’: The First Trackways of Tyrannosaurids and Evidence of Gregariousness and Pathology in Tyrannosauridae. PLoS ONE 9(7): e103613. doi:10.1371/journal.pone.0103613
Marsicano CA, Wilson JA, Smith RMH (2014) A Temnospondyl Trackway from the Early Mesozoic of Western Gondwana and Its Implications for Basal Tetrapod Locomotion. PLoS ONE 9(8): e103255. doi:10.1371/journal.pone.0103255
For most animals, the sex of their offspring is determined by genetics. However, for tuatara, a lizard-like reptile that inhabits select New Zealand islands, the number of males versus females is related to the temperature during a specific period of the egg’s development.
The name for the scientific concept of temperature influencing the sex of your offspring is environmental sex determination (ESD) and is a trait found in many reptiles. For tuatara, the warmer it is, the more likely an egg is to develop into a male, and an incubation temperature of 69.8˚F gives about an equal chance of either gender developing.
What’s so special about these creatures? Tuatara are native to New Zealand, the only place in the world that they can be found. They are special for another reason, too: they are the only living members of the order Rhynchocephalia, which has earned them the nickname “living fossils.”
Tuatara stand out reproductively as well. It can take them up to 20 years to reach the age of reproduction, and once they do, the females only lay eggs every 2 to 5 years. They can also live to be more than 100 years old.
In a recent PLOS ONEstudy, the authors looked at a population of Tuatara living on North Brother Island in New Zealand to investigate the current male-to-female ratios and predict what these numbers may look like if temperatures increase based on current climate models.
For this study, the authors first looked at surveys conducted between 1988 and 2001 and found that approximately 60% of the population was male. They then looked at more recent surveys conducted between 2005 and 2011 to compare temperatures and sex ratios, the results of which revealed a 70% male population.
The authors then used a model to predict the ratio of males to females that might be born in future years, based on the soil temperature in various nesting sites. From this, they estimated that an increase of less than 1 degree Celsius would over time shift the population to 57% male, and an increase by 3-4 degrees Celsius could eventually shift the entire population to be male. Unfortunately, a large sex bias, especially toward males, has the potential to put tuatara at risk for extinction.
Though this population of tuatara has not yet been classified as endangered, the authors suggest that the potentially large effect a small temperature change could have on the population means that further population monitoring will be important. Increases in the temperature of their environment, combined with their slow reproductive cycle, means that it could be difficult for them to “bounce back” from population shifts toward fewer females. The authors note that in such a case, human interventions, such as artificially incubating eggs or modifying habitat, may be necessary to save the species.
The loss of tuatara would not only result in an extinct species, but the entire order Rhynchocephalia would be lost. However, since this species has not yet reached an endangered status, we are provided with an opportunity to take action. Future studies and monitoring of tuatara may allow us to prevent the grim fate that all other species of this order have reached.