Friday, October 29, 2010

Resolving dinosaur phylogenies with fossil evidence of protofeathers

According to this article in Nature, a dinosaur skeleton was found in western Liaoning Province, China, that shows evidence of feathers.

Figure 1: Overview of a Tianyulong confuciusi skeleton.

What makes this particular find of a feathered dinosaur important is that it extends the known time period and geographic range of feathered dinosaurs. All previous records list feathered dinosaurs as living in Africa in the early Jurassic period. Now we know that they were also living in Asia, and were around all the way up to the early Cretaceous.

Figure 2: Close-up on evidence of protofeather structures.

This fossil of Tianyulong confuciusi (see figure 1 above) is an incomplete skeleton, but nevertheless it was detailed enough to conclusively prove that feathered dinosaurs (see figure 2 above) lived from the early Jurassic period to the early Cretaceous period, and in an area from Africa to Asia.

Finding this fossil also resolved the dispute over phylogeny. Tianyulong is closely related to Heterodontosaurus and Echinodon.  (See figure 3 below.)

Figure 3: The resolved phylogeny (or at least more resolved than before).

The filamentous integumentary structures are clear evidence that these dinosaurs had protofeathers. However, Zheng suggests that these feathers were geared more towards multicolored displays than for the flight we see in modern birds.

Source: Zheng, X.-T., You, H.-L., Xu, X. & Dong, Z.-M. An Early Cretaceous heterodontosaurid dinosaur with filamentous integumentary structures. Nature 458, 333–336 (2009).
DOI: 10.1038/nature07856.
Hyperlink to original article:

Sunday, October 24, 2010

Dino shows aquatic and terrestrial characteristics

I found a February 2010 article in Nature that gave detail on a dinosaur that may have lived similarly to an amphibian or even a fish, yet it did not display typical anatomical characteristics for living in water such as propelling tails, flexible fins, or webbing. It was known as a spinosaur (Baryonyx walkeri), and its head resembled a crocodile with unique cone-shaped teeth. Most people probably think of a dinosaur as a land-inhabiting creature, but research suggests that this specific group was not restricted to land.
One important find revealed that the long snout and tooth shape were evident of fish predation in spinosaurs. T. rex had serrated teeth that were perfect for its carnivorous diet, but B. walkeri displayed piercing teeth prime for fish feeding. This behavior was determined because of partially digested fish scales that were noticed in a 1983 fossil from England. Unfortunately, pterosaur (non-aquatic dinosaur) remains were also found in the fossilized spinosaur gut. The presence of oxygen isotope concentrations in turtle shells, and in the tooth enamel of spinosaurs, other dinosaurs, and crocodiles at this time period were looked into for further claim at whether the spinosaur was aquatic or not.
The reasoning was that the concentration of oxygen-18 in spinosaur tissues should match that of crocodiles and turtles if spinosaurs could be considered aquatic. There were obvious differences in concentrations between spinosaurs and terrestrial dinosaurs, but similar concentrations between spinosaurs and the aquatic animals used in this study. One argument against this states that a diet consisting of mainly fish would lower 0xygen-18 concentration levels to that of aquatic animals such as turtles and crocs. It is a controversial issue, but but may prove accurate with further studies. All in all, the central theme I found in this article is that it may be difficult to distinguish spinosaurs as aquatic dinosaurs since the limbs of their skeletons are completely atypical of common aquatic limbs utilized in propulsion and swimming.
Reference: doi: 10.1038/news.2010.84

Saturday, October 23, 2010

Lion vs. Saber-toothed Tiger. Who wins?

Saber-Toothed Cat Was More Like A Pussycat Than A Tiger

I guess the title speaks for itself, but also the fact that lions are still around should be proof enough that this Ice Age beast must have had some evolutionary fault that prevented it from persisting to present day. This evolutionary fault was the power and form of its jaw. Scientists had argued for years as to the strength of the Saber-toothed Cat's (Smilodon) bite. What they have now discovered may surprise you.

The Saber-toothed Tiger, although very powerfully built, with long, knife-like canines, rivaling the Tyrannosaurus Rex as one of the greatest killing machines of all time, had a very weak bite comparatively to the modern day lion. The force of the lion's bite is 3 times as strong as the bite of a Smilodon would have been. The Smilodon's jaw was also fairly narrow, limiting t he prey types it could hunt. However, this does not mean that the Saber-toothed Cat was any less of a hunter for not having a strong bite.

The Smilodon was not a predator of smaller prey like today's lion. It used its very powerful body to tackle the massive prey that existed during the ice age. It would use that body to wrestle the larger prey to the ground then use its weak bite on the neck which would usually kill the prey instantly. However, its build and jaw type are two of the main reasons why there are not Saber-toothed tigers around today, and why lion's are still around. Its body frame and jaw are extremely over-engineered to feed on today's smaller prey. So, once its larger prey began declining at the end of the the Ice Age, the Saber-tooth was left without a proper food source, and died off as well, leaving the lion as the victor because of its modified jaw strength and form.

I know we have not quite gotten to mammals yet, but I saw this article and thought it was very interesting. Plus, Saber-toothed tigers are one of my favorite prehistoric animals, so I thought we could jump ahead a little to this.

Friday, October 22, 2010

Lethal Ribs!

Many amphibians, as small to moderately sized soft-skinned organisms, exhibit different defensive strategies for protecting themselves from larger predators. A few of these defensive behaviors include cryptic coloration, toxicity, and defensive displays. In the case of the Spanish ribbed newt, Pleurodeles waltl, an entirely different defensive concept has been employed. This particular salamandrid is capable of projecting its ribs through its skin when faced by a predator that they are unable to escape from.

A study was conducted at the University of Vienna to determine details of this particular salamandrid's defensive capabilities. When the Spanish ribbed newt was first picked up, it began to squirm in attempt to escape from its handler. After it was unable to escape, a milky substance was secreted from glands in its neck, dorsal and lateral trunk, and tail (arrows in figure a). This secretion caused irritation to human mucous membranes but was lethal to mice in small doses, suggesting it is toxic. When these two defensive strategies did not work, the newt projected its ten pairs of ribs through its body wall as a final defensive maneuver (figure b)

In order to project its spines, the newt sat very still, straightened its vertebral column, and then shifted the ribs forward. These ribs have a two-headed costo-vertebral joint that allows for a maximum 65 degree shift forward. The final third of the distal portion of the ribs were found to be surrounded by a connective tissue sheath that was determined to be a protection layer between external pathogens and the internal body cavity. Furthermore, this newt has 10 pairs of orange spots which correspond to each rib that is projected through the body wall. These orange spots are thought to add an aposematic signal that is helpful in highlighting the rib projections to predators. After close examination, it was determined that pores were absent from these orange spots. This proved that the ribs were indeed piercing the body wall and not just projecting through an existing pore.

The researchers suggested that the newt was immune to its own toxins and used the general ability of amphibians to both produce anti-microbial agents from specialized glands and to heal quickly. These features allow for the Spanish ribbed newt to project its ribs from its body in order to defend itself.

Self injury for the benefit of self preservation is also found in Echinotriton, a member of a sister clade to Pleurodeles.

Brought to you by: Karie Charlton

Thursday, October 21, 2010

The Yolk on Egg Size

The article “Early development of Ensatina eschscholtzii: an amphibian with a large, yolky egg”, posted in EvoDevo Journal by Collazo and Keller, looks at early development in Ensatina eschscholtzii. This species is also commonly known as Ensatina, and is a plethodontidae (lungless) salamander that can be found in chaparrals, coniferous forests, and oak woodlands, throughout North and South America (there are seven total subspecies of Ensatina). Among amphibians there is some variability in the early processes of development that have once been thought to be derived during evolution. It is now believed that increased egg size could play a factor in affecting the early developmental functions such as gastrulation and cleavage patterns. Salamanders in the family Plethodontidae have very large yolky eggs that vary in size, making them a good candidate for observation regarding this theory.
As seen in hagfishes, elasmobranches, teleosts, coelacanths and amniotes, once an egg reaches a certain size it shifts from holoblastic to meroblastic cleavage. This shift in cleavage varies in different animal taxa. If different groups of amphibians were to be studied it might be discovered that these taxa also respond similarly to increases in egg size. In this study Egg size and embryonic developmental rate as well as cleavage pattern, which appeared to be holoblastic, were all noted to be different than that of other amphibians. Blastulation, gastrulation and formation of the embryonic disc were also observed and noted to be unlike the corresponding characteristics in other amphibians.

This paper thus concludes that large egg size and a large amount of yolk explain all of the developmental differences observed in Ensatina eschscholtzii.

EvoDevo Journal

Thursday, October 14, 2010

The New Tiny Frog

Because frogs have such a positive impact in controlling insect and pest populations and because of the recent declines in anuran populations, there has been a major push to find all of the species of frogs living around the world. Scientists and researchers have been interested in finding and describing all of the diverse species of amphibians before they are wiped out by habitat destruction, climate change, and infections and diseases.

Given that there has been so much research into frog populations and their distributions, there have been several new discoveries of novel frogs that have not previously been described or documented. There have also been groups of frogs that have been further broken down into different species due to further research. Museum specimens have also been used to determine whether “new” species have been collected before.

Microhyla nepenthicola, a new species of minifrog has recently been discovered in the forests of Borneo. This group of frogs is called mini or micro because of how small it is; they are less than 15 mm in length. The adult males of this new species are only about the size of a pea. They are found in pitcher plants which is how they got their name. They also have a distinctive call that consists of “a series of harsh rasping notes that last for a few minutes with brief intervals of silence.” Their call is distinctive enough that it helped researchers to collect and examine them.

Museum specimens of this minifrog were also found that had been collected over 100 years ago. They were mislabeled as immature stages of other frogs when, in fact, they were a completely different genus. This could be very interesting because there may be other museum specimens of frogs that have also been misidentified and need to be relooked at.

There is an arms race to find as many frog species as possible before they are wiped out by various environmental factors. It is important to determine the effects of environmental changes as well as effects of disease on different groups such as frogs and other amphibians. In studying these different populations and finding new species, light could be shed on the effects of these environmental changes on micro and even macrohabitats.

Abstract of original journal article

Science Daily Article

Tuesday, October 12, 2010

From Amphibian to Mice, Limb regeneration

It is commonly known that salamanders and newts have amazing regenerative abilities. If their tail or even a limb gets lobed off they are capable of regenerating a brand new one. According to the article in Nature entitled “Muscling in on limb regeneration” researchers have found a way to duplicate this regenerative ability in mice tissue. This research was lead by Helen Blau, a regenerative biologist at Stanford University of Medicine in California.

Previously the regenerative ability was attributed to stem-cells that remain in adult tissue, but the minimal number of these stem-cells in newts begs to differ. Now biologist lean toward the following conclusion: “in vertebrates endowed with regenerative ability, muscle cells surrounding injured tissue temporarily regress to a more primitive state, re-entering the cell cycle and then proliferating to produce more muscle cells.” The key factor in specialization of the muscle cells is retinoblastoma protein, Rb for short. When the Rb gene is suppressed in the muscles cells it sends the cells into the cell cycle again. But this process doesn’t work in mammal muscle cells.

Blau proposes the following: “that in mammals, an additional mechanism may have evolved atop the Rb pathway to confer tumour suppression. Unlocking regeneration in mammalian tissues may involve interfering with that pathway too.” The research team focused on a tumor-suppressing gene called Arf, which is present in mammals but not the regenerating vertebrates. Blau and her staff temporarily knocked down Arf and Rb in cultured mouse muscle cells. After doing this they found the treated cells re-entered the cell cycle and they began proliferating. The results were as follows: “When genes’ activities were restored, the cells returned to their differentiated state. Newly generated muscle cells transplanted into living mice were able to integrate into the animals’ muscle tissue.”

There are many questions and complications that arise with this research. One problem that arises is if the tumor suppressing gene is shut off, could this lead to tumors forming. Blau incorporation with Jason Pomerantz, a reconstruction surgeon from the University of California, believes that the tissue could be resolved by treating it as explants, and then implanted onto an organism. Another suggestion is to use drugs blocking the two genes injecting them into the spot that needs regenerated.

There are several unknowns that remain, which were pointed out in this article by Ken Poss, a cell biologist at Duke University Medical Center in California. Poss says, “regernation large chunks of tissue may involve recreating the connective-tissue scaffolding on which muscle cells grow—a step that’s not part of this technique.”

Nature paper:

Published online 5 August 2010 | Nature | doi:10.1038/news.2010.392

Image from the Nature paper

Sunday, October 10, 2010

Declines in Amphibian Populations

El Cope National Park has already felt the effects of population loss, losing over thirty species of amphibians.

One species from Panama, known as the golden frog (Atelopus zeteki), that has lately been struggling against Batrachochytrium dendrobatidis.

A Nature article from July 19, 2010 showed that species of amphibians have died off over the past ten years, giving biologists no clue to their existence. This might be one reason why Richard Lehtinen referred to cricket frogs as an "annual" species. A technique known as DNA barcoding has been used to identify amphibian species that were previously unknown. A park in Panama recently gave rise to eleven species, but only six of these are still extant. The cause seems to be due to the fungus Batrachochytrium dendrobatidis (same fungus that Lehtinen's cricket frog paper talked about). B. dendrobatidis affects almost 3,000 amphibian species across the globe, and it causes them to have difficulty breathing because of overly thick skin. The fungal disease has been studied using toe clippings and liver samples. Researchers have compared the effects of the epidemic before and after it struck back in 2004. El Cope, Panama was home to sixty-three species before the decline, but is now only home to thirty-three (five of these were previously unknown). Researchers are saying that things are being lost before they can be found and that there has been confusion regarding species of amphibians on whether certain ones are one species or two. Biologist Van Vredenburg stated that, "Up until now, we've only had a very crude estimate of what is lost."
Amphibians are being removed from their natural habitats by herpetologists for conservation purposes. Anti-fungal solutions are necessary to preserve these animals. Two of the three types of amphibians (frogs and and salamanders) are already capable of defending themselves against the fungus because of symbiotic bacteria growing on their skin. The bacteria is currently being swiped from healthy populations and taken to labs for culturing in order to then immunize amphibian populations with large amounts of this advantageous bacteria. It should be in everyone's best interest to insure that the oldest class of four-legged vertebrates continues to flourish worldwide.
Paper reference: doi: 10.1038/news.2010.360

Thursday, October 7, 2010

How some fish are predators on land.

Not only are catifish a terror in the water, but one particular species, Channallabes apus, terrorizes insects and it's prey on land at the waters edge. They found this "eel catfish" in the muddy swamps of tropical Africa. The reason that this fish is so interesting is because of it's ability to actually come out of the water to capture its prey on land at the waters edge. One of the main reasons that the fish is even able to do this is because of the flexibility of its head and the extraordinary way that it is able to bend its head. (Kind of like a neck? I think so)

The diet of the eel catfish consists of terrestrial insects that usually live right at the waters edge. The way that the catfish is able to capture these prey is in a class all its own. The fish literally lifts it's upper body up out of the water after propelling the head up and then bends its head down towards the ground allowing it to grasp on to the prey, while opening and closing it's mouth until the prey is safely in it's jaws. Along with this, the catfish has this rostro-caudal expansion wave, which is when the mouth opens wide, followed by an extensive hyoid depression (similar to the eel previously viewed in class). This allows there to be a little bit of suction on the prey however, on land this suction is not really enough to pull prey into the mouth.

As seen above, the bending of the neck is really not seen among other fish really at all, but is seen in mudskippers. Doing this action does require a type of ventral flex along the vertebral column. This catfish is incredible and one more fascinating fact is that although early stages of tetrapods had the ability to put weight on their pectoral fins, research on this animal shows that it is actually not necessary because of the way that the fish can dorsally flex and bend it's head.

Amanda Jones

Nature 440, 881 (13 april 2006) doi:10.1038/440881a; Published online 12 April 2006

Tuesday, October 5, 2010

How did turtles get their shells?

I was flipping through the channels last night and found an awesome documentary on Turtles and Tortoises. I wanted to know about where these guys split off on the tree and some common ancestors. What I found was Odontochelys semitestacea a 220 million year old ancestor to the turtle. The ancestor swam in China's costal waters long ago, and are now being studied by Chun Li of the Chinese Academy of Sciences in Beijing and his colleagues.
Before this the oldest know turtle ancestor was Proganochelys found in Germany. However, this new species sheds much more light on turtle evolution. These two differ in "in presence of teeth on premaxilla, maxilla and dentary; relatively long preorbital skull; distinct transverse process on pterygoid; absence of fully formed carapace; no acromial process on scapula; dorsal ribs articulating at midline of centrum; free sacral ribs; free caudal transverse processes; presence of long tail; four (rather than three) phalanges in digits III and IV of manus and pes; absence of osteoderms and tail-club." (Nature 456, 497-501 ) The most surprising feature here the absence of the carapace or top shell.
Since Odontochelys semitestacea spent its time swimming in aquatic environments, it is more likely that the bottom shell (Plastron) developed first, to protect from predators attacking from beneath. It has only a partially formed shell on top. Li believes this proves that the plastron developed before the carapace. The image of the skeleton above shows the lack of a top shell. More than likely, when turtles started walking on land their carapaces developed better because the ground was also protecting their undersides. However, some researchers believe that Odontochelys semitestacea lost its top shell and that an even older ancestor had the presence of both the carapace and plastron.

Article from Science Daily

Sunday, October 3, 2010

Fossil Link Between Frogs and Salamanders

Gerbatrachus hottoni is said to be the common ancestor of frogs and salamanders before they evolved separately. The fossils that were discovered of this species were found in 1995 but were not studied until 2008. Nicholas Hotton discovered the fossil but died two years later and was unable to finish studying the fossil. Jason Anderson and his team heard about the fossil at the Smithsonian and jumped on the opportunity to study it.

The fossil has a body plan similar to that of a salamander but has traits such as a short, mostly boneless tail. Also, he says "It's got a great big froggie ear and it's reduced the number of vertebrae in its back … but like salamanders, it shares a particular fusion of some ankle bones"(CBC news). Since this species has traits of both frogs and salamander Anderson like to call it a "Frogamander".

This species was walking the earth 50 million years before the dinosaurs and also predate the earliest frog and salamander fossils which did not occur until the dinosaur times as well. It was most likely living a large amount of its life in the water but was also able to move onto land similar to modern frogs. Given this information from the G. hottoni fossil, this species was most likely the common ancestor of both frogs and salamanders.

Also, you can listen to the frogamander segment from the Quirks and Quarks website

Nature paper: doi:10.1038/nature06865
CBC news article:
Quirks and Quarks:http: //