Wednesday, January 28, 2015

New - old snakes - revise the earliest date for snake origins



 
Fossilized remains of four ancient snakes between 140 and 167 million years old are changing the way we think about the origin of snakes, and how and when it happened.
Ancient snakes: (top left) Portugalophis lignites (Upper 
Jurassic) in a gingko tree, from coal swamp deposits at 
Guimarota, Portugal; (top right) Diablophis gilmorei 
(Upper Jurassic), hiding in a ceratosaur skull, from the 
Morrison Formation in Fruita, Colorado; (bottom) 
Parviraptor estesi (Upper Jurassic/Lower Cretaceous) 
swimming in freshwater lake with snails and algae, from
 the Purbeck Limestone in Swanage, England. Artist 
Credit: Julius Csotonyi
 The discovery by an international team of researchers, including University of Alberta professor Michael Caldwell, rolls back the clock on snake evolution by nearly 70 million years.
"The study explores the idea that evolution within the group called 'snakes' is much more complex than previously thought," says Caldwell, professor in the Faculty of Science and lead author of the study published today in Nature Communications. "Importantly, there is now a significant knowledge gap to be bridged by future research, as no fossils snakes are known from between 140 to 100 million years ago."

The oldest known snake, from an area near Kirtlington in Southern England, Eophis underwoodi, is known only from very fragmentary remains and was a small individual, though it is hard to say how old it was at the time it died. The largest snake, Portugalophis lignites, from coal deposits near Guimarota in Portugal, was a much bigger individual at about a metre long. Several of these ancient snakes (Eophis, Portugalophis and Parviraptor) were living in swampy coastal areas on large island chains in western parts of ancient Europe. The North American species, Diablophis gilmorei, was found in river deposits from some distance inland in western Colorado.

This new study makes it clear that the sudden appearance of snakes some 100 million years ago reflects a gap in the fossil record, not an explosive radiation of early snakes. From 167 to 100 million years ago, snakes were radiating and evolving toward the elongated, limb-reduced body shape characterizing the now well known, ~100-90 million year old, marine snakes from the West Bank, Lebanon and Argentina, that still possess small but well-developed rear limbs.
Caldwell notes that the identification of definitive snake skull features reveals that the fossils -- previously associated with other non-snake lizard remains -- represent a much earlier time frame for the first appearance of snakes.

These ancient snakes share features with fossil and modern snakes (for example, recurved teeth with labial and lingual carinae, long toothed suborbital ramus of maxillae) and with lizards (for example, pronounced subdental shelf/gutter). The paleobiogeography of these early snakes is diverse and complex, suggesting that snakes had undergone habitat differentiation and geographic radiation by the mid-Jurassic. Phylogenetic analysis of squamates recovers these early snakes in a basal polytomy with other fossil and modern snakes, where Najash rionegrina is sister to this clade. Ingroup analysis finds them in a basal position to all other snakes including Najash.
"Based on the new evidence and through comparison to living legless lizards that are not snakes, the paper explores the novel idea that the evolution of the characteristic snake skull and its parts appeared long before snakes lost their legs," he explains.

He adds that the distribution of these newly identified oldest snakes, and the anatomy of the skull and skeletal elements, makes it clear that even older snake fossils are waiting to be found.

Caldwell MW, Nydam RL, Palci A, Apesteguía S. 2015. The oldest known snakes from the Middle Jurassic-Lower Cretaceous provide insights on snake evolution. Nature Communications, 2015; 6: 5996 DOI: 10.1038/ncomms6996


Thursday, January 22, 2015

Parental care in the middle Jurassic

Illustration Credit: Chuang Zhao
New research details how a preserved fossil found in China could be the oldest record of post-natal parental care from the Middle Jurassic.

The specimen, found by a farmer in China, is of an apparent family group with an adult, surrounded by six juveniles of the same species. Given that the smaller individuals are of similar sizes, the group interpreted this as indicating an adult with its offspring, apparently from the same clutch.

A fossil specimen discovered by a farmer in China represents the oldest record of post-natal parental care, dating back to the Middle Jurassic.

The tendency for adults to care for their offspring beyond birth is a key feature of the reproductive biology of living archosaurs -- birds and crocodilians -- with the latter protecting their young from potential predators and birds, not only providing protection but also provision of food.

This behavior seems to have evolved numerous times in vertebrates, with evidence of a long evolutionary history in diapsids -- a group of amniotes which developed holes in each side of the skull about 300 million years ago and from which all existing lizards, snakes and birds are descended
However, unequivocal evidence of post-natal parental care is extremely rare in the fossil record and is only reported for two types of dinosaurs and varanopid 'pelycosaurs' -- a reptile which resembled a monitor lizard.

A new study by the Institute of Geology, Chinese Academy of Geological Sciences, Beijing; the University of Lincoln, UK; and Hokkaido University, Japan, presents new evidence of post-natal parental care in Philydrosauras, a choristodere from the Yixian Formation of western Liaoning Province, China. Choristoderes are a group of relatively small aquatic and semi-aquatic diapsid reptiles which emerged in the Middle Jurassic Period more than 160 million years ago.

The team reviewed the fossil record of reproduction in this group using exceptionally preserved skeletons of the aquatic choristoderan Philydrosauras. The specimen was donated to the Jinzhou Paleontological Museum in Jinzhou City four years ago by a local farmer who discovered the skeleton.

The skeletons are of an apparent family group with an adult, surrounded by six juveniles of the same species. Given that the smaller individuals are of similar sizes, the group interpreted this as indicating an adult with its offspring, apparently from the same clutch.

Dr Charles Deeming, from the School of Life Sciences, University of Lincoln, UK, said: "That Philydrosauras shows parental care of the young after hatching suggests protection by the adult, presumably against predators. Their relatively small size would have meant that choristoderes were probably exposed to high predation pressure and strategies, such as live birth, and post-natal parental care may have improved survival of the offspring. This specimen represents the oldest record of post-natal parental care in diapsids to our knowledge and is the latest in an increasingly detailed collection of choristoderes exhibiting different levels of reproduction and parental care."

A test of whether post-natal parental care is an ancestral behavior that has persisted in the evolutionary development of amniotes will depend on future fossil discoveries.

Citation

Junchang Lü, Yoshitsugu Kobayashi, D. Charles Deeming, Yongqing Liu. 2014. Post-natal parental care in a Cretaceous diapsid from northeastern China. Geosciences Journal, 2014; DOI: 10.1007/s12303-014-0047-1

Monday, January 19, 2015

Different selection forces at work on coral snake and rattlesnake venoms

Eastern Diamondback Rattlesnake
If you're one of the unfortunate few to be bitten by a venomous snake, having access to effective antivenom to combat the swelling, pain and tissue damage to these bites is critical.
But new research by a team of biologists at Florida State University has revealed that creating antivenom is a bit tricky.

That's because the type of venom a snake produces can change according to where it lives.

Mark Marges, a Florida State doctoral student in Professor Darin Rokyta's laboratory, led a research study that examined the venom of 65 eastern diamondback rattlesnakes and 49 eastern coral snakes from all over the state of Florida to determine whether snake venoms varied by geography.

The venom from an eastern diamondback rattlesnake in the Florida panhandle is very different than the venom from a rattlesnake 500 miles south in the Everglades, and this has huge implications for snakebite treatment.

"So if you use just southern venoms when making the antivenom, it would be ineffective against some of the more common toxins found in northern diamondback rattlesnakes," said Florida State University doctoral student Mark Margres.

In the rattlesnakes, they found significant variation linked to geography. But, in the coral snakes, they found the venom to be identical no matter where the snakes were found.

"This can tell us a bit of the history and evolutionary patterns of the snakes," said Kenny Wray, a post-doctoral research associate in Rokyta's lab. "This suggests that the coral snakes may be recent invaders to the region and haven't had time to evolve different venoms in different areas."

This information also will help with the development of coral snake antivenom, because scientists now know there is uniformity in coral snake venom. According to a 2012 estimate by the Center for Disease Control, 7,000 to 8,000 people in the United States are bitten by venomous snakes every year.

Not only are there medical implications, this information is also important for conservation purposes.

The eastern diamondback rattlesnake is being considered for federal protection under the Endangered Species Act. But, if the snakes are removed from one geographic area, they will be irrevocably deleted from the ecosystem altogether.

"If we lose some of these populations, we lose a whole venom type," Rokyta said. "That really changes conservation."

Venom from an eastern diamondback rattlesnake in the Everglades is distinct from the cocktail of toxins delivered by the same species in the Florida panhandle area, some 500 miles away. But no matter where you go in the Southeastern United States, the venom of the eastern coral snake is always the same.

Each venomous snake species produces a unique venom, a mixture of around 50-200 toxic proteins and protein fragments that co-evolve with the typical prey of the snake, such as the smaller reptiles eaten by the eastern coral snake or the rodents preferred by rattlesnakes. In this cycle of evolutionary attack and counterattack, any genetic variants that enhance venom resistance tend to spread through the prey population, prompting tweaks to the snake venom recipe that restore its effectiveness.

The result should be distinctive local co-adaptations between predator and prey, as well as considerable regional diversity in the types and amounts of the different venom proteins. But when Darin Rokyta (Florida State University) and his colleagues collected and profiled venom from eastern coral snakes at many sites within Florida, they found no variation at all. The mix of proteins in coral snake venom from one part of the state was indistinguishable from that collected anywhere else. In contrast, eastern diamondbacks, which live in the same parts of the country as the coral snakes, produce venom with different ratios of toxic proteins in nearly every sub-population across their range. For example, two venom components, including one known to cause paralysis in prey, are found at high levels in the northernmost populations, and were completely absent in the snakes from Caladesi Island, near Tampa.

"We were shocked," Rokyta said. "This is the first time anyone has looked at venom variation at this scale, and everybody has assumed that the co-evolutionary arms race would cause local populations to diverge quickly."

Rokyta says there could be several explanations for the lack of variation in eastern coral snake venom. For example, a small population of the species might have recently expanded and taken over the entire range, displacing other populations and reducing genetic diversity. Or it could reflect a difference in co-evolutionary dynamics between the species and its typically reptilian prey, compared to the small mammals preferred by rattlesnakes. The team is now using genetic clues to the population histories of each species to investigate possible explanations.

The results of the study will be helpful to researchers developing eastern coral snake antivenom. Making an antivenom requires samples of venom, but if the mix varies substantially from place to place, this will affect the drug's effectiveness and reliability. For this species, sampling from many populations should not be necessary. "This tells us it doesn't matter where we catch these relatively elusive snakes; we can stick to using those locations where they're easy to find," Rokyta said.

The variation between eastern diamondback populations could provide crucial information to authorities managing the conservation of this species, which is in decline and under consideration for listing as threatened under the Endangered Species Act. Eastern diamondback rattlesnake declines are thought to have been caused by habitat loss compounded by hunting and persecution by humans. The data from this study can be used for population management, to ensure the full range of venom subtypes are conserved for the long-term viability of the species.

"The received wisdom was that venoms are rapidly-evolving, but now we know that's not necessarily the case." said Mark Johnston, Editor-in-Chief of GENETICS. "Clearly, venom evolution in these two snake species has been shaped by different forces. The next challenge is to understand why."

Citation
Margres MJ, McGivern JJ, Seavy M, Wray KP, Facente J, Rokyta DR. 2014. Contrasting Modes and Tempos of Venom Expression Evolution in Two Snake Species. Genetics, 2014; DOI: 10.1534/genetics.114.172437

Tuesday, January 13, 2015

Sand swimming in snakes and lizards

For swimming through sand, a slick and slender snake can perform better than a short and stubby lizard.

That's one conclusion from a study of the movement patterns of the shovel-nosed snake, a native of the Mojave Desert of the southwest United States. The research shows how the snake uses its slender shape to move smoothly through the sand, and how its slippery skin reduces friction -- both providing locomotive advantages over another sand-swimmer: the sandfish lizard native to the Sahara Desert of northern Africa.

The study provides information that could help explain how evolutionary pressures have affected body shape among sand-dwelling animals. And the work could also be useful in designing search and rescue robots able to move through sand and other granular materials.

Using X-ray technology to watch each creature as it moved through a bed of sand, researchers studied the waves propagating down the bodies of both the snakes and sandfish lizards. Granular resistive force theory, which considers the thrust provided by the body waves and the drag on the animals' bodies, helped model the locomotion and compare the energy efficiency of the limbless snake against that of the four-legged lizard -- which doesn't use its legs to swim through the sand.

"We were curious about how this snake moved, and once we observed its movement, how it moved so well in the sand," said Dan Goldman, an associate professor in the School of Physics at the Georgia Institute of Technology. "Our model reveals how both the snake and the sandfish move as fast as their body shapes permit while using the least amount of energy. We found that the snake's elongated shape allowed it to beat the sandfish in both speed and energy efficiency."

Information about the factors enabling the snake to move quickly and efficiently could help the designers of future robotic systems. "Knowing how the snake moves could be useful, for instance, in helping robots go farther on a given amount of battery power," Goldman said.

Supported by the National Science Foundation and the Army Research Office, the research was published online December 18, 2014, in the Journal of Experimental Biology. The study is believed to be the first kinematic investigation of subsurface locomotion in the long and slender shovel-nosed snake, Chionactis occipitalis.

Measurements made by former Ph.D. student Sarah Sharpe revealed that the snake propagates traveling waves down its body, from head to tail, creating a body curvature and a number of waves along its body that enhance its movement through the sand. As a consequence of the kinematics, the snake's body travels mostly in the same "tube" through the sand that is created by the movement of its wedge-shaped head and body.

Because the snake essentially follows its own tracks through the sand, the amount of slip generated by its motion is small, allowing it to move through the sand using less energy than the sandfish (Scincus scincus), whose movement pattern generated a larger fluidized region of sand around its body.

Overall, the research showed that each animal had optimized its ability to swim through the sand using its specific body plan.

"For each body wave the snake generates, it moves farther than the sandfish does within a single wave of motion of its body," Goldman noted. "Having a long and slender body allows the snake to bend its body with greater amplitude while generating more waves on its body, making it a more efficient sand swimmer."

The snake's skin is also more slippery than that of the sandfish, further reducing the amount of energy required to move through the sand.

Scientists had suspected that long and slender animals would have a sand-swimming advantage over creatures with different body shapes. The research showed that the advantage results from a high length-to-width ratio that allows the formation of more waves.

"If you have the right body shape and slick skin, you can get a very low cost of transport," explained Goldman.

To study the snakes as they moved through sand, Sharpe -- from Georgia Tech's Interdisciplinary Bioengineering Program -- and undergraduate Robyn Kuckuk, from the Wallace H. Coulter Department of Biomedical Engineering at Georgia Tech and Emory University, glued tiny lead markers onto the scales of the snakes. The markers, which fall off when the snakes shed their skin, allowed the researchers to obtain X-ray images of the snakes moving beneath the surface of the sand. Sharpe, now a biomechanical engineer with a research and consulting firm in Phoenix, created detailed videos showing how the snakes moved.

Associate professor Patricio Vela and graduate student Miguel Serrano, both from Georgia Tech's School of Electrical and Computer Engineering, developed software algorithms that allowed detailed analysis of the wave-forms seen on the X-ray movies as a function of time.

Stephen Koehler, a research associate in applied physics at Harvard University, applied resistive force theory to obtain data on the snakes' movement and energy efficiency. Animals swimming in sand can only move if the thrust provided by their bodies exceeds the drag created. The theory predicted that the snakes' skin would have about half as much friction as that of the sandfish, and that prediction was verified experimentally.

Joe Mendelson, director of research at Zoo Atlanta, assisted the research team in obtaining and managing the snakes.
Understanding how animals move through granular materials like sand could help the designers of robotic systems better understand how to optimize the use of energy, which can be a significant limiting factor in robotics.

"This research is really about how body shape and form affect movement efficiency, and how we can go between experiment and theory to improve our understanding of these issues," said Goldman. "What we are learning could help search and rescue robots maneuver in complex terrain and avoid obstacles."

Beyond the robotics concerns, the work can help scientists understand biological issues, such as how the body plans of desert-dwelling lizards and snakes converge to optimize their ability to move through their environment.

"These granular swimming systems turn out to be quite useful for understanding fundamental questions about evolutionary biology, biomechanics and energetics because they are simple to analyze and they can describe a good number of systems," Goldman added.




Citation
Sharpe SS., Koehler SA, Kuckuk RM, Serrano M, Vela PA, Mendelson J, Goldman DI. 2014. Locomotor benefits of being a slender and slick sand-swimmer." The Journal of Experimental Biology (2014): jeb-108357.


Sarah Sharpe, et al. 2014  Locomotor benefits of being a slender and slick sand swimmer. Journal of Experimental Biology, 2014 DOI: 10.1242/jeb.108357

Tuesday, January 6, 2015

New look at the evolution of snake bodies

Snake skeletons are just as regionalized as lizards, despite loss of 
limbs and increase in number of vertebrae. Photo Credit: Craig Chandler, 
Angie Fox, Jason Head, University of Nebraska-Lincoln
Sakes may not have shoulders, but their bodies aren't as simple as commonly thought, according to a new study that could change how scientists think snakes evolved.
Paleobiologists Jason Head of University of Nebraska-Lincoln and P. David Polly of Indiana University Bloomington found distinctions among snakes' vertebral bones that matched those found in the backbones of four-legged lizards.
Rather than snakes evolving from a lizard ancestor to a more simplified body form, the researchers say their findings suggest other animals gained more complex vertebral columns as they evolved.
The study provides new perspective on Hox genes, which govern the boundaries of the neck, trunk, lumbar, sacral and tail regions of limbed animals. The functions of Hox genes previously were thought to have been disrupted in snakes, resulting in seemingly simplified body forms.
Snakes differ from mammals, birds and most other reptiles because they lack forelimbs, shoulder girdles and breastbones. It was thought that when they lost their limbs, they also lost the regional distinctions that separated their backbones into neck, trunk, lumbar and other regions.
Yet when Head and Polly examined the shapes of individual vertebral bones in snakes, lizards, alligators and mice, they found snakes had regional differentiation like that of lizards.
"If the evolution of the snake body was driven by simplification or loss of Hox genes, we would expect to see fewer regional differences in the shapes of vertebrae," Head said. "Instead, what we found was the exact opposite. Snakes have the same number of regions and in the same places in the vertebral column as limbed lizards."
Not only did Head and Polly find that snakes were as differentiated as lizards, but when they compared regions in snakes with Hox gene expression, they found the two matched.
"This suggests that Hox genes are functioning in the evolution and development of the vertebral column in snakes, but instead of patterning distinct, rib-less regions like the neck and lumbar spine of mice, they control more subtle, graded changes in shape," Head said.
When combined with information from fossils, these findings indicate that the direction of snake evolution is the opposite of what had been concluded from developmental genetics alone, Head and Polly say.
"Our findings turn the sequence of evolutionary events on its head," Polly said. "It isn't that snakes have lost regions and Hox expression; it is that mammals and birds have independently gained distinct regions by augmenting the ordinary Hox expression shared by early amniotes."
Amniotes are the group of vertebrates that lay shelled eggs. They include reptiles, mammals and their predecessors.
"Snakes have a lot more vertebrae compared to lizards and they have lost the shoulder girdle, but they are just as regionalized," Polly said.
Head and Polly reached their conclusions using a method called geometric morphometrics and a regression-based analysis of the size and shape of vertebral structures. To determine where one segment ends and the next begins, they use a statistical method called maximum likelihood estimation.
"Analysis of gene functions are necessary, but not sufficient in studying evolutionary transitions," Head concludes. "In order to fully understand the mechanisms by which new body forms evolve, it is crucial to study the anatomy of modern and fossil organisms."

Citation
Jason J. Head, P. David Polly. Evolution of the snake body form reveals homoplasy in amniote Hox gene function. Nature, 2015; DOI:10.1038/nature14042


Thursday, January 1, 2015

A new frog that gives birth to tadpoles


University of California, Berkeley, herpetologist Jim McGuire was slogging through the rain forests of Indonesia's Sulawesi Island one night this past summer when he grabbed what he thought was a male frog and found himself juggling not only a frog but also dozens of slippery, newborn tadpoles.
He had found what he was looking for: direct proof that the female of a new species of frog does what no other frog does. It gives birth to live tadpoles instead of laying eggs.

Limnonectes larvaepartus. (a) MVZ 268323 (male, left) and MVZ 268307 (female,right) collected from Desa Uaemate along the Tasio-Tibo Road, Kabupatan Mamuju, Provinsi Sulawesi Barat, Sulawesi Island (02.61287S, 119.14238 E, 89 m elev.); (b) Limnonectes larvaepartus female (MVZ 268426) with tadpoles removed from the oviduct. Note the large yolk reserves available to the tadpoles; (c) An in situ adult male L. larvaepartus (JAM 14234) observed calling while perched on the edge of a small pool 2 m away from a 2 m wide stream; several L. larvaepartus tadpoles were present in the pool including the two visible within the yellow circle; (d) dorsal and ventral views of ~stage 25 L. larvaepartus tadpoles (JAM 14271) released by a pregnant female (JAM 14237) at the moment of capture.

A member of the Asian group of fanged frogs, the new species was discovered a few decades ago by Indonesian researcher Djoko Iskandar, McGuire's colleague, and was thought to give direct birth to tadpoles, though the frog's mating and an actual birth had never been observed before.

"Almost all frogs in the world -- more than 6,000 species -- have external fertilization, where the male grips the female in amplexus and releases sperm as the eggs are released by the female," McGuire said. "But there are lots of weird modifications to this standard mode of mating. This new frog is one of only 10 or 12 species that has evolved internal fertilization, and of those, it is the only one that gives birth to tadpoles as opposed to froglets or laying fertilized eggs."

Iskander, McGuire and Ben Evans of McMaster University in Ontario, Canada, named the species Limnonectes larvaepartus and fully describe it in this week's issue of the journal PLOS ONE.

Frogs have evolved an amazing variety of reproductive methods, says McGuire, an associate professor of integrative biology and curator of herpetology at UC Berkeley's Museum of Vertebrate Zoology. Most male frogs fertilize eggs after the female lays them. About a dozen species, including California's tailed frogs, have evolved ways to fertilize eggs inside the female's body. However, the mechanisms of internal fertilization are poorly understood in all but California's two species of tailed frogs, the latter of which have evolved a penis-like organ (the "tail") that facilitates sperm transfer. Whereas the tailed frogs deposit their fertilized eggs under rocks in streams, the other frogs previously known to have internal fertilization give birth to froglets -- miniature replicas of the adults.

Although internal fertilization is extremely rare among frogs, there are many other bizarre reproductive variations. Some frogs carry eggs in pouches on their back, brood tadpoles in their vocal sac or mouth, or transport tadpoles in pits on their back. The two known species of female gastric brooding frogs, both of which are now extinct, were famous for swallowing their fertilized eggs, brooding them in their stomach, and giving birth out of their mouths to froglets. Two genera in Africa engage in internal fertilization and give birth to froglets without going through a free-living tadpole stage.

Fanged frogs -- so-called because of two fang-like projections from the lower jaw that are used in fighting -- may have evolved into as many as 25 species on Sulawesi, though L. larvaepartus is only the fourth to be formally described. They range in size from 2-3 grams - the weight of a couple of paper clips -- to 900 grams, or two pounds. L. larvaepartus is in the 5-6 gram range, McGuire said.
The new species seems to prefer to give birth to tadpoles in small pools or seeps located away from streams, possibly to avoid the heftier fanged frogs hanging out around the stream. There is some evidence the males may also guard the tadpoles.

McGuire first encountered the newly described frog in 1998, the year he began studying the amazing diversity of reptiles and amphibians on Sulawesi, an Indonesian island east of Borneo and south of the Philippines. The island is a geographical hodgepodge, having formed from the merger of several islands about 8-10 million years ago.

"Sulawesi is an incredible place from the standpoint of species diversity endemic to the island as well as in situ diversification," he said, noting that most places on the island are home to at least five species of fanged frogs living side by side.

Although many vertebrate species have diversified on the island after arriving by overwater "sweepstakes" dispersal, most - such as the flying lizards and black-crested macaque monkeys - have speciated in such a way that their geographic ranges are non-overlapping, with their ranges meeting like pieces in a jigsaw puzzle. The fanged frogs are special, McGuire says, because they appear to represent a virtually unexplored adaptive radiation with many species occurring at the same sites but adapted to occupy distinct ecological niches.

"We are really interested in understanding how much of Sulawesi's in situ diversification was initiated on the paleo-islands, or if much or even all of the diversification was postmerger," he said.
Much of McGuire's work to date has been with the simpler non-adaptive radiations of the flying lizards and macaques. Fanged frogs present an even more exciting challenge, he says, because their diversification likely was influenced not only by the dynamic tectonics of Sulawesi, but also by adaptive radiation via ecological diversification.

McGuire and his colleagues and students have collected reptiles and amphibians throughout the island - flying lizards are his particular love - and taken genetic samples to reconstruct the evolution of species over time and perhaps shed light on how and when the islands came together.
He also is working with Iskandar to prepare a monograph on the identification, distribution and biology of the fanged frogs on the island.

Citation
Iskandar DT, Evans BJ, McGuire JA. 2014. A Novel Reproductive Mode in Frogs: A New Species of Fanged Frog with Internal Fertilization and Birth of Tadpoles. PLoS ONE, 2014; 9 (12): e115884 DOI:10.1371/journal.pone.0115884