Saturday, July 30, 2011

Raptors Avoid Snakes With Triangular Heads

Vipera latastei gaditana. Photo courtesy of Harold van der Ploeg.
Looking like a venomous species can have advantages for mimics, and a triangular-shaped head similar to that found in many vipers may convey a message to predators that says I am dangerous. Janne K. Valkonen, Ossi Nokelainen, and Johanna Mappes tested this idea using snake modles made of non-toxic grey plasticine. Four different kinds of artificial snakes were used: 1) zigzag-patterned snakes with triangular (viper type) heads and 2) with narrow (colubrid type) heads and 3) plain (grey) snakes with triangular heads and 4) with narrow heads. The use of plain snakes was crucial to separate the effect of the head shape from the overall appearance of vipers. The length and diameter of artificial models were identical in all treatments and in correspondence to the size Vipera latastei gaditana. The experiment was conducted in Coto Doñana National Park, southern Spain. Six transects were conducted in 2009 and thirteen in 2010 and a total of 595 snake models were used. The replicas were placed on the natural background in random order at approximately 15 metre (15 paces) intervals following features of the terrain. The authors found a a significant difference in the number of raptor attacks among treatments. Plain snakes with narrow heads were attacked significantly more often by raptors than were plain snakes with triangular heads. There was no difference in the number of raptor attacks on patterned, triangular-headed snake replicas and on patterned replicas with narrow heads. When attack data was pooled on snake replicas based on their patterns, plain snakes were attacked by raptors significantly more frequently than were zigzag patterned replicas. 8.2% of the 595 snake replicas were attacked by raptors and 18.5% by mammalian predators. Attacks by mammalian predators did not differ between treatments.

Citation: Valkonen JK, Nokelainen O, Mappes J (2011) Antipredatory Function of Head Shape for Vipers and Their Mimics. PLoS ONE 6(7): e22272. doi:10.1371/journal.pone.0022272

Thursday, July 28, 2011

Saving Amphibian Diversity by Mitigating Bd

A new article by Woodhams et al. suugests that amphibian diversity can be resuced from the emerging chytrid fungus Batrachochytrium dendrobatidis (Bd). The fungus can exist in amphibians populations as a transient commensal to lethal pathogen. And they suggest a combined strategy of halting pathogen spread and developing survival assurance colonies, as well as prophylactic or remedial disease treatment. Epidemiological models of Bd suggest that mitigation strategies can control disease without eliminating the pathogen. Sustainable conservation of amphibians in nature is dependent on long-term population persistence and co-evolution with potentially lethal pathogens. Therefoe the authors suggest that disease mitigation not focus exclusively on the elimination or containment of the pathogen, or on the captive breeding of amphibian hosts. Instead, successful disease mitigation must be context specific with epidemiologically informed strategies to manage already infected populations by decreasing pathogenicity and host susceptibility. A three step treatment for populations is proposed: first, identify mechanisms of disease suppression; second, parameterize epizootiological models of disease and population dynamics for testing under semi-natural conditions; and third, begin a process of adaptive management in field trials with natural populations. Below is one of the figures from the artlcle.
Some of the rediscovered species in Costa Rica including. A. Craugastor ranoides, B. Atelopus varius, C. Lithobates vibicarius, and D. Pristimantis lemur. Locality data are retained to discourage poaching. E. Climatic refuge in Costa Rica indicated by arrow. The core distribution of Batrachochytrium dendrobatidis (Bd)occurs in humid environments and coincides with the distribution of most declining populations of amphibians. Low abundance relict populations are being rediscovered within Bd enzootic zones, often with subclinical infections. Other species are found outside Bd enzootic zones. Healthy populations, in which a susceptible species maintained high abundance, were found at the edge of the distribution of the robber frog, Craugastor ranoides, in a climatic refuge [138]. Puschendorf et al. ([139]; including details of the bioclimatic model pictured in E) hypothesized that this relict population in the dry forest of Santa Elena Peninsula, Costa Rica, survives because climatic conditions in that habitat make pathogen establishment or persistence on hosts less likely.

Locomotion in Early Reptiles

Modern scientists would have loved the sight of early reptiles running across the Bromacker near Tambach-Dietharz (Germany) 300 million years ago. Unfortunately this journey through time is impossible. But due to Dr. Thomas Martens and his team from the Foundation Schloss Friedenstein Gotha numerous skeletons and footprints of early dinosaurs have been found and conserved there during the last forty years. "It is the most important find spot of primitive quadruped vertebrates from the Perm in Europe," says Professor Dr. Martin S. Fischer from the University Jena (Germany). The evolutionary biologist and his team together with the Gotha scientists and other partners are now starting a research project not only to analyze the locomotion of these primeval saurians. They also want to set them back into motion - at least in animation. The Volkswagen Foundation (VolkswagenStiftung) will support the project with about 288.000 Euro during the next two years. "Our first major palaeontologic project", as zoologist Fischer delightedly calls it. 
Heloderma suspectum. JCM
 How did the locomotion system of amniotes change?

The fossils found on the Bromacker date back to the oldest fully terrestrial vertebrates. These so-called amniotes are the first real "land-dwelling animals". This became possible through a first evolutionary step in which they laid a completely encapsulated egg in whose 'watery inside' the offspring could develop. Therefore tadpoles and gills became redundant. "The Bromacker fossils are the closest relatives of the last mutual ancestor of the amniotes that have been found so far," Dr. John A. Nyakatura, who oversees the new research project points out, stressing the evolutionary-biological importance of the finds. How did the locomotion system of those amniotes change? They are according to Nyakatura "pivotal to the genealogical tree for evolutionary biologists". The Jena expert in locomotion research says the crucial questions of the new project are: "Which functionally anatomical consequences does 'cutting the cord' to water have for the locomotion system of the animals?"

The Jena zoologists and their partners in Gotha, Dresden (both Germany), England and the USA wanted to find out. In their research they cannot only rely on years of expertise but also on one of the fastest X-ray video systems worldwide, which is used at the Friedrich Schiller University. With the help of this system, Dr. Nyakatura and the Paleo-Biomechanist Dr. Vivian Allen who will change from London to Jena in autumn, plan to analyze the locomotion systems of diverse animals resembling the early reptiles. They will observe skinks, tiger salamanders, green iguanas and small crocodiles. In order to do so the animals will move on a treadmill in front of the X-ray video camera that can take up to 2.000 pictures per seconds. Moreover the pressure on the joints will be investigated and footprints will be generated on wet clay. At the end of these analysis a comprehensive locomotion profile of the species is to be created - which in itself will bring science forward.

Three-dimensional, animated reconstructions of the fossil skeletons

The protocol of the footprints will then be compared to the primeval footprints, in order to get an understanding of the early saurians movements. "And this in turn will allow conclusions to be drawn about the find spot and what happened there," Dr. Martens adds. This is only possible because the Gotha researchers could not only recover numerous footprints but also complete skeletons of unique quality. "The fossils are mind-blowing," Nyakatura stresses. The entire animal relics encapsulated in stone slabs are being scanned with the help of the TU Dresden in order to create three-dimensional reconstructions of the skeletons. At the end of the project animated studies of the early saurians will be generated from the scans and the locomotion protocols. "Thanks to the support of the VolkswagenStiftung and the co-operation with the University Jena we will finally be able to give an insight into the world of the early saurians to the visitors of the 'Museum of Nature' in Schloss Friedenstein," says Dr. Martin Eberle, director of the Foundation Schloss Friedenstein Gotha. Now the researchers are hoping their project will be successful so that they cannot only mount an exhibition on the subject in two years' time. They will also be able to travel 300 million years back in time due to the innovative animations - and they will watch the early reptiles running.

Tuesday, July 26, 2011

Turtles + Lizards Form A Clade?

Famous for their sluggishness, turtles have been slow to give up the secrets of their evolution and place on the evolutionary tree. For decades, paleontologists and molecular biologists have disagreed about whether turtles are more closely related to birds and crocodiles or to lizards. Now, two scientists from the Mount Desert Island Biological Laboratory in Bar Harbor, Maine, and their colleagues from Dartmouth College and Harvard and Yale Universities have developed a new technique using microRNAs for classifying animals, and the secret is out. Turtles are closer kin to lizards than crocodiles.

To reach their conclusion, published in Nature News and Biology Letters, the research team looked at a newly discovered class of molecules called microRNA. Most of the genetic material or DNA that scientists study provides the code for building proteins, large molecules that form an essential part of every organism. But microRNAs are much smaller molecules that can switch genes on and off and regulate protein production. They are also remarkably similar within related animal groups and provide important clues for identification.

“Different microRNAs develop fairly rapidly in different animal species over time, but once developed, they then remain virtually unchanged,” said Kevin Peterson, a paleobiologist at MDIBL and Dartmouth College. “They provide a kind of molecular map that allows us to trace a species’ evolution.”

Peterson worked with Ben King, a bioinformatician at MDIBL. “My role in the study was to enhance our software so we could find new and unique microRNAs in the lizard genome,” King said. “We identified 77 new microRNA families, and four of these turned out to also be expressed in the painted turtle. So we had the evidence we needed to say that turtles are a sister group to lizards and not crocodiles.”

Though few creatures have been as puzzling as the turtle, the research team plans to use its microRNA analysis on other animals to help determine their origins and relationships as well. It is also developing a web-based platform to share the software with other researchers around the world.

In addition to King and Peterson, the research team included Tyler Lyson and Jacques Gauthier from Yale University, Eric Sperling from Harvard University, and Alysha Heimberg from Dartmouth College.

Citation
Tyler R. Lyson, Erik A. Sperling, Alysha M. Heimberg, Jacques A. Gauthier, Benjamin L. King and Kevin J. Peterson. 2011. MicroRNAs support a turtle + lizard clade. Biology Letters doi: 10.1098/rsbl.2011.0477.

Monday, July 25, 2011

Why Are Some Snakes More Common Than Others?

Ringnecked Snakes, Diadophis punctatus 
reach some of the most dense populations 
found in snakes. JCM

There is a reason why more people study lizards than snakes, snakes are notorious for being difficult to find. Undoubtedly their cryptic nature and in some cases low population densities are likely contributors to this situation. A paper in Science this week by Hechinger et al. examined parasites (there are no known parasitic snakes), but the authors produced two general rules that they suggest can be applied to animal abundance – for any species. The following quotes were taken from a press release associated with this article. 


First they said that, "In addition to body size, the general rule for animal abundance must factor in the food chain and let both small and large animals be top consumers." The second rule was, "that the amount of biomass produced by a population does not depend on the body size of the animals in the population, or on what type of animal -- bird, fish, crab, or parasite. So, "If this rule is general, it means an aphid population can produce the same amount of biomass as a deer population," said Lafferty. "Furthermore, tapeworms that feed on the deer population produce less biomass than the deer, but can produce the same as a mountain lion population that also feeds on the deer. Predicting animal abundance is one of the most basic and useful things ecological science can provide for management and basic research," said Hechinger. "This simple rule helps with that because it may apply to all life forms and can easily be applied to complex ecosystems in the real world." So, does this apply to snakes? Snakes are all predators or facultative scavengers. Does it explain why many snakes are very difficult to find, while other species seem quiet abundant in their habitats?

Parker and Plummer (1987) compiled a table of population densities of snakes, undoubtedly many more have been published since - but this information was readily available for this post. I added column for size.

In looking at the table below, Hechinger et al seem to be correct, the snakes with the most dense populations are small species (Carphophis and Diadophis), species feeding on invertebrates that are close to their food source - a short food chain; or they are piscivorous species that are probably taking prey that are feeding on autotrophic protists, scavenging decomposing material, or have other abundant food resources. The rarer snakes tend to feed on mammals, have larger body sizes, or live in environments with low productivity (Lampropeltis, Pantherophis, Eryx).


Species
Density,
 no/ha
Size (m)
Acrochordus arafurae
19-97
1.5
Eryx tataricus
<1
0.7
Carphophis amoenus
373-729
0.28
Coronella austriaca
11-17
0.8
Diadophis punctatus
719-1849
0.45
Elaphe dione
<1
1.2
Pantherophis obsoleta
<1
2.0
Elaphe quadrivirgata
4-46
2.6
Pantherophis vulpina
1-3
1.0
Heterodon nasicus
2-10
0.6
Heterodon platirhinos
1-7
0.8
Lampropeltis calligaster
<1
1.1
Lampropeltis triangulum
<1
0.9
Lycodonomorphus bicolor
380
0.7
Protobothrops flavoviridis
2-3
1.5
Vipera berus
3-14
0.65
Vipera ursinii
7
0.5


Citations
Hechinger, R. F., K. D. Lafferty,. A. P. Dobson, J. H. Brown, A. M. Kuris. 2011. A Common Scaling Rule for Abundance, Energetics, and Production of Parasitic and Free-Living Species. Science, 2011; 333 (6041): 445-448 DOI: 10.1126/science.1204337.

Parker, W. S. and M. V. Plummer. 1987. Population Ecology. Pages 253-301 In: R. Seigel et al. (eds.) Snakes, Ecology and Evolutionary Biology. New York: McMillian Publishing.

Sunday, July 24, 2011

Endangered River Turtle's Genes Reveal Ancient Influence of Mayans

A genetic study focusing on the Central American
river turtle (Dermatemys mawii) recently turned
up surprising results for a team of Smithsonian
scientists involved in conserving this critically
endangered species. Small tissue samples collected
from 238 wild turtles at 15 different locations
across their range in Southern Mexico, Belize
and Guatemala revealed a "surprising lack"
of genetic structure.
Photo Credit: Gracia González-Porter.
A genetic study focusing on the Central American river turtle (Dermatemys mawii) recently turned up surprising results for a team of Smithsonian scientists involved in the conservation of this critically endangered species. Small tissue samples collected from 238 wild turtles at 15 different locations across their range in Southern Mexico, Belize and Guatemala revealed a "surprising lack" of genetic structure, the scientists write in a recent paper in the journal Conservation Genetics.

The turtles, which are entirely aquatic, represent populations from three different river basins that are geographically isolated by significant distance and high mountain chains.

"We were expecting to find a different genetic lineage in each drainage basin," explains the paper's main author Gracia González-Porter of the Center for Conservation and Evolutionary Genetics at the Smithsonian Conservation Biology Institute. "Instead, we found the mixing of lineages. It was all over the place." Despite appearing isolated, the genetic data showed the different turtle populations had been in close contact for years.

"But how?" the researchers wondered.

The best possible explanation, González-Porter and her colleagues say, is that for centuries humans have been bringing them together. The turtles have been used as food, in trade and in rituals for millennia, widely transported and customarily kept in holding ponds till they were needed.

"For centuries, this species has been part of the diet of the Mayans and other indigenous people who lived in its historic distribution range," the scientists point out in their paper. "D. mawii was a very important source of animal protein for the ancient Mayans of the Peten (Preclassic period 800-400 B.C.)…. And it is possible that these turtles were part of the diet of the Olmec culture more than 3,000 years ago."

One specimen of D. mawii was found in an ancient Teotihuacan burial site in Mexico, a spot located more than 186 miles from the known range of this turtle, the researchers say. An ancient sculpture of a Central American river turtle at the National Museum of Anthropology in Mexico City was found in the Basin of Mexico, more than 217 miles from the turtle's range.

"The Central American River turtle is tame and resilient," González-Porter explains, "which makes it easy to transport. Their shells give them lots of protection. People don't have refrigeration so they put the turtles in ponds in their back yards."

During the rainy season in the tropics, the water flows are huge, she says. Rivers and ponds flood, captive turtles escape and mix with the local turtles.

This ancient practice still persists today. In Guatemala, Central American river turtles are kept in medium-sized ponds where they can be easily captured when needed. Similarly, in the State of Tabasco, Mexico, captured turtles are kept in rustic ponds and raised until they are either consumed or sold.

The genetic analysis of the Central American River turtle was initiated because these animals are critically endangered, González-Porter says.

They are the last surviving species of the giant river turtles of the family Dermatemydidae. D. mawii is currently the most endangered turtle species in Central America. A recent increase in the commercial demand for its meat has pushed it to the brink of extinction—2.2 pounds of their meat can fetch $100. Most local populations have disappeared and this turtle is now largely restricted to remote areas that are inaccessible to humans.

The article "Patterns of genetic diversity in the critically endangered Central American river turtle: human influence since the Mayan age?" was co-authored by Gracia González-Porter and Frank Hailer of the Center for Conservation and Evolutionary Genetics at the Smithsonian Conservation Biology Institute; Jesús Maldonado of Center for Conservation and Evolutionary Genetics at the Smithsonian Conservation Biology Institute and the Department of Vertebrate Zoology at the Smithsonian's National Museum of Natural History; Oscar Flores-Villela of the Museo de Zoología Facultad de Ciencias, México; and Rony Garcia-Anleu of the Wildlife Conservation Society-Guatemala Program, Guatemala.

Friday, July 22, 2011

Baenid Turtles Survived the K-T Extinction

New fossil localities from North Dakota and Montana have produced the remains of a turtle that survived the 65 million-year-old meteorite impact that wiped out the dinosaurs. The resulting study, published in the latest issue of the Journal of Vertebrate Paleontology, suggests that Boremys, a turtle that belongs to a group known as the baenids (bay-een-ids) survived the extinction event unharmed. Baenids are a group of extinct river turtles native to North America that flourished from approximately 80 million to 42 million years ago.
Diagram of the many types of turtles that survived the K/T extinction event. The skulls of these turtles are illustrated (as viewed from above) as are their fossil record (thick blue bars) and evolutionary relationships (thin lines connecting bars). The red line marks the extinction event, and is matched with the photographic of the geologic section in the background. The rocks below the red line were deposited during the Age of Dinosaurs (Mesozoic Era), whereas those above the line were deposited at the beginning of the Age of Mammals (Cenozoic Era). Note that eight different lineages of turtles survived the event, while only two went extinct at the event. Image courtesy of Erik Freeman.

The lead author, Tyler Lyson from Yale University, has been collecting turtles from the western United States for years, and immediately realized the importance of these new specimens, "This find further confirms that turtles were not fazed by the meteorite that killed the dinosaurs 65 million years-ago."

The survival of turtles during this massive extinction event appears counterintuitive with what we know about other organisms. While other groups of animals show high rates of extinction at the Cretaceous/Paleocene (K/T) boundary 65-million-years ago, this new discovery provides more data indicating that turtles were largely unaffected by the meteorite impact. Lyson and colleagues found that if you just looked at turtles during this time, you would not even notice that one of the largest extinction events in Earth’s history had occurred.

The researchers recovered the new Boremys turtle remains from rocks in southwestern North Dakota and eastern Montana. These rock formations, known as the Hell Creek and Fort Union, respectively, have been actively collected for fossils by paleontologists for more than 100 years.  This new study proves that even in well-searched localities, new fossil discoveries can still be uncovered. Co-author Dr. Walter Joyce acknowledged his surprise with the new discovery, "At first I did not believe Tyler when he told me that he had found Boremys in Paleocene deposits."

Lyson and his co-authors believe that features of the shell of Boremys did not help its chances of preservation in the fossil record. The turtle had very thin shell bones relative to other baenids, and they remained unfused throughout the turtle’s life. These features likely led to its skeleton being scattered after death, making the chances of a whole shell being preserved very low. The authors also noted that the features of the shell were very similar to another turtle species living at the same time, which lead to initial misidentification.

With the discovery of this turtle, Lyson and his colleagues can now say that at least eight types of baenid turtles survived the meteorite impact that killed so many other animals.

Citation: Lyson, T. R. et al. 2011.  BOREMYS (TESTUDINES, BAENIDAE) FROM THE LATEST CRETACEOUS AND EARLY PALEOCENE OF NORTH DAKOTA: AN 11-MILLION-YEAR RANGE EXTENSION AND AN ADDITIONAL K/T SURVIVOR. JOURNAL OF VERTEBRATE PALEONTOLOGY 31(4):1-9.

Thursday, July 21, 2011

Oldest Viviparous Squamata

The embryonic skeletons can be seen in 
side of their mother's remains. Photo
Credit: Susan Evans.

The lizard genus Yabeinosaurus Endo and Shikama 1942 was first described from Early Cretaceous deposits from the Jehol Group of northeastern China. Early interpretations suggested, Yabeinosaurus  was a small, weakly ossified lizard with gekkotan affinities. However, Evans et al. (2005) reported adults exceeded  300 mm snout–pelvis length, and lizard had a large, heavily ossified and strongly sculptured skull. Their results suggested Yabeinosaurus was close to the iguanian–scleroglossan dichotomy and they hypothesized that Yabeinosaurus may represent a relict species in the Jehol Biota, a survivor of the Pan-Laurasian lizard fauna of the Jurassic. Now, Wang and Evans (2011) document viviparity in Yabeinosaurus with the remains of a gravid female that contains more than 15 young with skeletal development that suggests they are near full term. Because Yabeinosaurus occupies a relatively basal position within crown-group squamates, they suggests that the anatomical and physiological preconditions for viviparity arose early within Squamata. It is the oldest terrestrial reptile known to give live birth, and it extends the evolution of viviparity to at least 120 million years ago. Yabeinosaurus probably lived on the banks of a stream and the remains were associated with hundreds of exquisitely preserved specimens of dinosaurs, fish, amphibians, reptiles, birds and mammals, plants and invertebrates.

Evans, S. E.; Wang, Y.; Li C. (2005). "The Early Cretaceous lizard genus Yabeinosaurus from China: resolving an enigma". Journal of Systematic Palaeontology 3 (4): 319–335. doi:10.1017/S1477201905001641.

Yuan Wang and Susan E. Evans. 2011. A gravid lizard from the Cretaceous of China and the early history of squamate viviparity. Naturwissenschaften

A 25-foot Crocodilian from the Cretaceous of Texas

Making its first appearance in Texas, a prehistoric crocodile thought to have originated in Europe now appears to have been a native of the Lone Star State.

The switch in origins for the genus known as Terminonaris is based on the identification of a well-preserved, narrow fossil snout that was discovered along the shoreline of a lake near Dallas.

The 96-million-year-old fossil from Texas is the oldest prehistoric crocodile of its kind in the world, according to paleontologist Thomas L. Adams at Southern Methodist University, Dallas, who identified the reptile.

SMU paleontologist Thomas L. Adams reconstructed the skull of Texas
Terminonaris from 3D scans of a 96-million-year-old fossil and a 
line-drawing. Adams identified the reptile primarily from its long snout, 
which measures more than 2 feet long and 7 inches wide, or 62 
centimeters. With a snout that long, Adams estimates the head 
would have been about one meter long. Art Credit: Thomas 
Adams, SMU


A distant cousin of modern crocodiles and alligators, Terminonaris was similar to the modern-day Indian gharial, only much larger.

"With the recognition of Terminonaris here in Texas, this actually changes a lot about what we thought we knew about this group," Adams said.

"Now we know the group had a wider distribution range, and that it's much older. It represents a unique find for Texas. This is the first occurrence of Terminonaris in Texas. It's also the oldest occurrence of Terminonaris in the world, and it's also the southernmost occurrence of Terminonaris anywhere."

There are six other known Terminonaris fossil specimens: five from North America and one from Europe. The European specimen, from Germany, previously was thought to be the oldest. Scientists had concluded that Terminonaris originated in Europe and then traversed the Atlantic and dispersed throughout North America.

"Now we know Terminonaris most likely originated here in Texas and dispersed northward," said Adams, a doctoral candidate in SMU's Roy M. Huffington Department of Earth Sciences at SMU.

Big Texas crocodile swam the shores of North America's prehistoric seaway

Adams identified the reptile primarily from its long snout, which measures more than 2 feet long and 7 inches wide, or 62 centimeters. With a snout that long, Adams estimates the head would have been about one meter long.

"Based on Nile crocodiles and the Indian gharial, which are both large crocodiles, a regression analysis indicates this Terminonaris probably would have been 23 to 25 feet long," said Adams. "The largest living crocodile today is the saltwater crocodile, which can reach up to 20 feet in length."

The Texas Terminonaris was an adult and most likely weighed more than a ton, he said.

Adams identified the fossils in "First Occurrence of the Long-Snouted Crocodyliform Terminonaris (Pholidosauridae) from the Woodbine Formation (Cenomanian) of Texas" in the Journal of Vertebrate Paleontology.

Prehistoric crocodiles such as Terminonaris together with living crocodiles make up a large group called crocodyliformes. While technically there are differences between living crocodiles and each of the different types of fossil crocodile forms, all of them are often commonly referred to as crocodiles.

Today there are only 23 species of living crocodiles, a small number compared to the many species of mammals, birds, lizards, snakes and fish alive today, Adams said. That's in stark contrast to prehistoric times.

"In the past, the crocodilian forms were very diverse and they were very successful. There were hundreds of species. Even at the time of the Texas Terminonaris, they were found everywhere," Adams said.

Texas specimen fills gap, expands age and range of group

Texas Terminonaris was discovered by Dallas-area amateur fossil enthusiast Brian Condon, a rural mail carrier. Condon discovered the heavy pieces of the snout and a vertebrate in 2005 while fossil hunting near his home on Lake Lewisville, a 26,000-acre recreational and fishing lake managed by the U.S. Army Corps of Engineers. He spotted the first of the pieces along the shoreline. Condon donated the fossils to SMU's Shuler Museum of Paleontology.

In prehistoric times, Texas Terminonaris would have made its home in a marine setting, along the eastern shore of North America's vast prehistoric Western Interior Seaway. One hundred million years ago the seaway was a wide, shallow sea that split the North American continent in half from the Arctic to the Gulf of Mexico, said Adams, lead author on the scientific article. The seaway would have covered Lake Lewisville's location.

In its day-to-day life on the seaway, Terminonaris would have kept close to shore, perhaps in a shallow lagoon or estuary, also venturing into the seaway's warm salty water to hunt for fish. Like modern crocodiles and alligators, Terminonaris would have eaten whatever it could catch, Adams said. Its long, slender snout was well-suited for devouring fish, small mammals and even small dinosaurs.

North America's other Terminonaris fossil specimens also were found along the seaway. A Kansas specimen is the youngest, about 91 million years, while those from Saskatchewan, Canada, and Montana are 93 million years old. The German specimen is 94 million years old.

"Terminonaris now here in Texas fills in a gap that we didn't have information for," Adams said. "It tells us that as a group, as a genus, they were around much longer, because we extend the age back to 96 million years. The range for them is now expanded, because this is the most southern occurrence of them."

Well-preserved fossil offers no clues to adult reptile's cause of death

While the Texas fossil is well-preserved, how the reptile died remains a mystery since only the snout was found.

It probably died in the water or washed out into the open sea, where it floated to the bottom and was buried very quickly, said Adams. The discovery of seven Terminonaris fossil specimens worldwide is significant, he said.

"To be fossilized, it requires they die at the right time in the right place, be buried very quickly, then eventually be exposed and uncovered," he said. "So the odds of being fossilized and being found as a fossil are very slim."

Condon found one piece at the water's edge of Lake Lewisville. The other pieces were further up a bank that sloped toward the shore, Condon said. The pieces had been deposited on the ground by receding water, pulled from the Woodbine Formation by constant waves that had washed away a soil bank and uncovered the heavy fossils. The outcrop of the Woodbine Formation visible at Lake Lewisville starts at the Red River in North Texas and thins as it nears Dallas.

Condon, who had previously found other fossils in the area, initially thought the pieces were petrified wood.

"This piece looked like a loaf of bread from Subway. It was all wrinkled," Condon said. "Then I picked it up and turned it over and saw it had teeth -- big, round conical teeth -- and I thought, 'This is amazing. It's a jaw.'"

Co-authors on the article were SMU paleontologists Michael J. Polcyn, Dale A. Winkler and Louis L. Jacobs, and also paleontologist Octavio Mateus, Universidade Nova de Lisboa, Portugal.

Wednesday, July 20, 2011

New Gymnophthalmids

The Luminous Lizard, Proctoporus shrevei 
Parker, 1935 from Trinidad's Northern
 Range. JCM Natural History Photography
The small teiid lizards, or microteiids are placed in the family Gymnophthalmidae lizards are small, (4-15cm body lengths) and range from southenr Mexico to Argentinia (with one species found on the continental island of Trinidad). About 190 species are known and are currently assigned to about 37 genera. The species in this family have adapted to specilized life styles and they often show limb reduction, body elongation, loss of eyelids and ear openings. They range from lowland tropical rainforests to high elevations in the Andes and may be terrestrial, arboreal, or semi-aquatic. The genus Riama contains small, forest-floor lizards, perhaps the most famous of which is the Luminous Lizard, Riama shrevei from Trinidad.

Sánchez-Pacheco and colleagues (2011) have now described the 28th species in the genus, Riama crypta, a species known only from Pilaló, Cotopaxi, and adjacent areas on the western slope of the Cordillera Occidental at elevations of 2320–2700 m, in Ecuador. Like most species of Riama, R. crypta seems to have a very restricted distribution

Pedro Peloso and colleagues (2011) have described a new genus and species of Gymnophthalmidae with a robust head, elongate body, well developed pentadactyl limbs, and a tail longer than the body. They named the genus, Marinussaurus, in honor of herpetologist Marinus S. Hoogmoed. The specific name M. curupira is derived from the mythical Curupira, an anthropomorphic creature known from many regions in South America which is short, with dark skin and feet pointed backward. The Curupira protects the forest and its inhabitants, severely punishing those who hunt for pleasure and the Curupira is sometimes much feared. The new species is known only from the type locality, located a few kilometers west of the intersection of the Rio Negro and Rio Amazonas/Solimões, in Brazil.

Citations
Peloso, Pedro L. V.; Pellegrino, Katia Cristina Machado.; Rodrigues, Miguel Trefaut Urbano.; Ávila-Pires, Teresa C. S. 2011. Description and phylogenetic relationships of a new genus and species of lizard (Squamata, Gymnophthalmidae) from the Amazonian rainforest of northern Brazil. American Museum Novitates, no. 3713, 1-24.

Sánchez-Pacheco, Santiago J.; Kizirian, David A.; Nunes, Pedro M. Sales. (2011) A new species of Riama from Ecuador previously referred to as Riama hyposticta (Boulenger, 1902) (Squamata, Gymnophthalmidae). American Museum Novitates, no. 3719, 1-20.

Molecules From the Skin of Hyla simplex

The skin of tree frogs tells a story of peril. Constantly assaulted by predators, these amphibians survive by waging chemical warfare using skin secretions. The potent molecules within may help humans too, as a potential source of new medications. Researchers have now analyzed the skin secretions of Chinese tree frogs, Hyla simplex, and found a potent mix of deadly snake-venom-like toxins as well as therapeutic chemicals (J. Proteome Res., DOI: 10.1021/pr200393t).

Han Liu of the Kunming Institute of Zoology at the Chinese Academy of Sciences, and colleagues captured and collected secretions of tree frogs from forests in Guangxi province. They determined the amino acid sequences of 27 proteins and peptides using a standard sequencing method coupled with mass spectrometry. The researchers also confirmed the protein and peptide identities using DNA sequences derived from RNA samples in the skin secretions.

The researchers subjected the agents to a battery of tests to check whether they could act as antimicrobials, painkillers, neurotoxins, or promoters of blood vessel regrowth. These studies revealed that some skin secretions are toxic to mice, water snakes, insects, and birds. Others seemed capable of helping the frog heal its own wounded flesh or dull its perception of pain.

The researchers also found that the amino acid sequences of several of the proteins bear remarkable similarity to those of neurotoxins from snake venom. Because snakes are predators of tree frogs, Liu says that the similarity in their toxins may indicate an arms race in which each species evolves increasingly sophisticated chemical weaponry and resistance. Though more work is needed to confirm this relationship, Liu says, frog skin could shed light on how a small amphibian survives in a snaky wilderness.

The above is a press release from the Kunming Institute of Zoology at the Chinese Academy of Sciences.

Monday, July 18, 2011

Snake Venom Evolution & Possum Predation

Research published recently in PLoS One delivers new insight about rapid toxin evolution in venomous snakes: pitvipers such as rattlesnakes may be engaged in an arms race with opossums, a group of snake-eating American marsupials. Although some mammals have long been known to eat venomous snakes, this fact has not been factored into previous explanations for the rapid evolution of snake venom. Instead, snake venom is usually seen as a feeding, or trophic, adaptation. But new molecular research on snake-eating opossums by researchers affiliated with the American Museum of Natural History suggests that predators factor into the rapid evolution of snake venom.

Possums frequently eat snakes. Are snakes 
rapidly evolving venom molecules to adapt
to possums predation? Photo: JCM Natural 
History.

"Snake venom toxins evolve incredibly rapidly," says Robert Voss, curator in the Department of Mammalogy at the American Museum of Natural History. "Most herpetologists interpret this as evidence that venom in snakes evolves because of interactions with their prey, but if that were true you would see equally rapid evolution in toxin-targeted molecules of prey species, which has not yet been seen. What we've found is that a venom-targeted protein is evolving rapidly in mammals that eat snakes. That suggests that venom has a defensive as well as a trophic role."

Several groups of mammals are known for their ability to eat venomous snakes, including hedgehogs, mongooses, and some opossums. Opossums, which belong to the marsupial family Didelphidae, consist of about one hundred known and several dozen undescribed species. Most of these opossums live in Central and South America, although there is one representative in the north that is familiar to those who spend time outside at night: the Virginia opossum.

Some didelphids, including the Virginia opossum, are known to eat rattlesnakes, copperheads, and some species of tropical pitvipers known as lanceheads. All of these pitvipers have venom containing dozens of highly toxic compounds, including many that attack blood proteins, causing massive internal hemorrhaging in nonresistant warm-blooded prey species, mainly rodents and birds.

The new research came out of a previous phylogenetic study of marsupials, published as a Bulletin of the American Museum of Natural History, that suggested unusually rapid evolution in one gene among a group of snake-eating opossums. The rapidly evolving gene codes for von Willebrand's factor, an important blood-clotting protein that is known to be the target of several snake-venom toxins. The association of rapid evolution in a venom-targeted gene among just those opossums known to eat pitvipers was the essential clue that prompted further study.

"This finding took us by surprise," says Sharon Jansa, associate professor in the Department of Ecology, Evolution and Behavior at the University of Minnesota and a Museum research associate. "We sequenced several genes—including the one that codes for von Willebrand Factor (vWF)—to use in a study of opossum phylogeny. Once we started to analyze the data, vWF was a real outlier. It was evolving much more rapidly than expected in a group of opossums that also, as it turns out, are resistant to pitviper venom."

The recently published research demonstrates that the rate of replacement substitutions (nucleotide changes that result in amino-acid changes) is much higher than the rate of silent substitutions (nucleotide changes that have no effect on the protein) in the von Willebrand Factor gene among pitviper-eating opossums. Typically, high rates of replacement substitutions means that the gene is under strong, sustained natural selection. That only happens in a few evolutionary circumstances.

"Most nucleotide substitutions have little or no effect on protein function, but that doesn't seem to be the case with vWF in these venom-resistant opossums," says Jansa. "The specific amino acids in vWF that interact with toxin proteins show unexpectedly high rates of replacement substitutions. These substitutions undoubtedly affect protein function, suggesting that the vWF protein can no longer be attacked by these snake toxins."

"It is so uncommon to find genes under strong positive selection, that the exceptions are really interesting and often conform to one evolutionary circumstance when two organisms are coevolving with each other," says Voss. "We've known for years that venom genes evolve rapidly in snakes, but the partner in this arms race was unknown until now. Opossums eat snakes because they can."

Recover of the Blue Iguana

The Grand Cayman blue iguana was decimated
by habitat destruction, car-related mortality, 
and predation by introduced cats and dogs. 
In 2002 the species numbered between 10-25 
individuals. A recovery program -- assisted 
by health experts from the Bronx Zoo  has 
brought the number of free-ranging iguanas 
within Grand Cayman's protected areas to 
more than 500 animals. Photo Credit: Julie 
Larsen Maher/Wildlife Conservation Society
While thousands of species are threatened with extinction around the globe, efforts to save the Grand Cayman blue iguana represent a rarity in conservation: a chance for complete recovery, according to health experts from the Wildlife Conservation Society's Bronx Zoo and other members of the Blue Iguana Recovery Program.

Coordinated by the National Trust for the Cayman Islands, the Blue Iguana Recovery Program—a consortium of local and international partners—has successfully released more than 500 captive-bred reptiles since the initiative's inception in 2002, when the wild population of iguanas numbered less than two dozen.

"For the past several years, we've succeeded in adding hundreds of animals to the wild population, all of which receive a health screening before release," said Dr. Paul Calle, Director of Zoological Health for WCS's Bronx Zoo.
Fred Burton, Director of the Blue Iguana Recovery Program, said: "We expect to reach our goal of 1,000 iguanas in managed protected areas in the wild in a few years. After that, we will monitor the iguanas to make sure they are reproducing in the numbers needed to maintain the wild population. If we get positive results, we will have succeeded."

The Grand Cayman blue iguana is the largest native species of its namesake island, growing to more than 5 feet in length and sometimes weighing more than 25 pounds. The iguana formerly ranged over most of the island's coastal areas and the dry shrub lands of the interior before becoming endangered by a combination of habitat destruction, car-related mortality, and predation by introduced dogs and cats. The entire island's wild population in 2002 was estimated at only 10-25 individuals.

Recovery efforts to save the Grand Cayman blue iguana have mostly centered on the Salina Reserve, a 625-acre nature reserve located on the eastern side of the island. After being hatched and raised for a year or two in a captive breeding facility, each iguana receives a complete health assessment before release. This involves veterinarians taking blood and fecal samples for analysis, as well as weighing and tagging each reptile. The samples are analyzed in a nearby lab at the St. Matthews Veterinary School while sampling continues. The iguanas are released after the lab results are reviewed and health is verified. This year, the recovery program is releasing iguanas into a new protected area, the Colliers Wilderness Reserve, established last year and managed by the National Trust.

Friday, July 15, 2011

Rotting Dinosaur Eggs Attracted Scavenger Insects

This is a side view of egg cocoons 
and fractured egg shell. Scale bar 
= 5 cm in both cases. Photo credit
 Jorge Genise.
Exceptionally preserved fossils of insect cocoons have allowed researchers in Argentina to describe how wasps played an important role in food webs devoted to consuming rotting dinosaur eggs. The research is published today (15th July) in the scientific journal Palaeontology.

The approximately 70 million year old eggs, from gigantic titanosaur sauropod dinosaurs were discovered in 1989 in the Patagonia region of Argentina, well known for yielding fossils of sauropod dinosaur eggs and even embryonic dinosaurs. Only recently it was discovered that one of the broken eggs contained tiny sausage-shaped structures, 2-3cm long and 1cm wide. The structures closely resembled fossilised insect cocoons, and were most similar in size and shape to the cocoons of some species of modern wasp.

There are many records of fossilised dinosaur eggs, and even several records of fossil cocoons, but, as author Dr Jorge Genise of the Museo Argentino de Ciencias Naturales states "this is the first time that these cocoons are found closely associated with an egg". Such a study of organismal behaviour (e.g. burrows, footprints) is known as ichnology.

The results indicate "that wasps probably participated in the food web, mostly composed of scavenging insects, which developed on the rotten egg". The make-up of carrion communities – spiders, beetles and other creatures populating rotting organic matter – is more familiar to us from the screens of crime scene investigation documentaries.

The numbers and different types of creatures indicate the length of deposition and the time since death. In this particular CSI, it appears that the dinosaur egg was broken by force, and subsequent fractures in the egg shell allowed scavenging creatures to feed upon the contents. At egg sizes of around 20cm, this represents a sizable amount of yolk! Other creatures later appeared to feed not upon the egg contents, but on the initial scavengers themselves. The wasps represent the top of the food web, and could have been feeding on insects or spiders gorging on rotting egg contents.

These scavengers also played an important role in cleaning up nest sites. Palaeontologists believe that some dinosaurs revisited nest sites year after year to lay new clutches of eggs. Carrion communities were essential to removing decaying material in advance of new nesting seasons. This new discovery gives us an insight into the murky world of insect communities that thrived at the feet of gigantic dinosaurs.