The pain of evolution: a big toothache for reptiles (Via Herp Digest)

The pain of evolution: a big toothache for reptiles - Study reveals infection in the jaw of 275-million-year-old reptile, highlighting the high cost of having permanent teeth
Springer Select - New York / Heidelberg, 4/18/11

Our susceptibility to oral infection has some parallels to those of ancient reptiles that evolved to eat a diet incorporating plants in addition to meat. That's according to Robert Reisz from the University of Toronto and his colleagues who found evidence of bone damage due to oral infec-tion in Paleozoic reptiles as they adapted to living on land. Their findings, published online in Springer's journal Naturwissenschaften - The Science of Nature, predate the previous record for oral and dental disease in a terrestrial vertebrate by nearly 200 million years.


The researchers investigated the jaws of several well-preserved specimens of Labidosaurus hama-tus, a 275-million-year-old terrestrial reptile from North America. One specimen stood out because of missing teeth and associated erosion of the jaw bone. With the aid of CT-scanning, Reisz and colleagues found evidence of a massive infection. This resulted in the loss of several teeth, as well as bone destruction in the jaw in the form of an abscess and internal loss of bone tissue.

As the ancestors of advanced reptiles diversified to life on land, many evolved dental and cranial specializations to feed more efficiently on other animals and to incorporate high-fiber plant leaves and stems into their diet. The primitive dental pattern in which teeth were loosely attached to the jaws and continuously replaced, changed in some lineages to be strongly attached to the jaw, with little or no tooth replacement. This was clearly advantageous to some early reptiles, allowing them to chew their food and thus improve nutrient absorption. The abundance and global distribution of Labidosauris and its kin attest to the evolutionary success of this strategy.

However, Reisz and his colleagues suggest that as this reptile lost the ability to replace teeth, the likelihood of infections of the jaw, resulting from damage to the teeth, increased substantially. This is because prolonged exposure of the dental pulp cavity of heavily worn or damaged teeth to oral bacteria was much greater than in other animals that quickly replaced their teeth.

The authors conclude: "Our findings allow us to speculate that our own human system of having just two sets of teeth, baby and permanent, although of obvious advantage because of its ability to chew and process many different foodstuffs, is more susceptible to infection than that of our distant ancestors that had a continuous cycle of tooth replacement."

Reference

Reisz R R et al (2011). Osteomyelitis in a Paleozoic reptile: ancient evidence for bacterial infection and its evolutionary significance. Naturwissenschaften - The Nature of Science. DOI 10.1007/s00114-011-0792-1

X-Rays Reveal Hidden Leg of an Ancient Snake (Via Herpdigest)

X-Rays Reveal Hidden Leg of an Ancient Snake: New Hints on How Snakes Were Getting Legless

ScienceDaily (Feb. 7, 2011) - A novel X-ray imaging technology is helping scientists better understand how in the course of evolution snakes have lost their legs. The researchers hope the new data will help resolve a heated debate about the origin of snakes: whether they evolved from a terrestrial lizard or from one that lived in the oceans. New, detailed 3-D images reveal that the internal architecture of an ancient snake's leg bones strongly resembles that of modern terrestrial lizard legs.

The team of researchers was led by Alexandra Houssaye from the Museum National d'Histoire Naturelle (MNHN) in Paris, France, and included scientists from the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, where the X-ray imaging was performed, and the Karlsruhe Institute of Technology (KIT), Germany, where a sophisticated technique and a dedicated instrument to take the images were developed.

Only three specimens exist of fossilised snakes with preserved leg bones. Eupodophis descouensi, the ancient snake studied in this experiment, was discovered ten years ago in 95-million-year-old rocks in Lebanon. About 50 cm long overall, it exhibits a small leg, about 2 cm long, attached to the animal's pelvis. This fossil is key to understanding the evolution of snakes, as it represents an intermediate evolutionary stage when ancient snakes had not yet completely lost the legs they inherited from earlier lizards. Although the fossil exhibits just one leg on its surface, a second leg was thought to be concealed in the stone, and indeed this leg was revealed in full detail thanks to synchrotron X-rays.

The high-resolution 3-D images, in particular the fine detail of the buried small leg, suggest that this species lost its legs because they grew more slowly, or for a shorter period of time. The data also reveal that the hidden leg is bent at the knee and has four ankle bones but no foot or toe bones.

"The revelation of the inner structure of Eupodophis hind limbs enables us to investigate the process of limb regression in snake evolution," says Alexandra Houssaye.

The scientists used synchrotron laminography, a recent imaging technique specially developed for studying large, flat samples. It is similar to the computed tomography (CT) technique used in many hospitals, but uses a coherent synchrotron X-ray beam to resolve details a few micrometers in size--some 1000 times smaller than a hospital CT scanner. For the new technique, the fossil is rotated at a tilted angle in a brilliant high-energy X-ray beam, with thousands of two-dimensional images recorded as it makes a full 360-degree turn. From these individual images, a high-resolution, 3-D representaton is reconstructed, which shows hidden details like the internal structures of the legs.

"Synchrotrons, these enormous machines, allow us to see microscopic details in fossils invisible to any other techniques without damage to these invaluable specimens," says Paul Tafforeau of the ESRF, a co-author of the study.


The results are published in the Feb. 8, 2011 issue of the Journal of Vertebrate Paleontology.

Rainforest collapse kickstarted reptile evolution

The fragmentation of tropical rainforests 300 million years ago helped pave the way for the rise of the dinosaurs, a new study suggests.By Paul Rincon Science reporter, BBC News


In the Carboniferous period, North America and Europe lay at the equator and were covered by steamy rainforest.

Global warming is thought to have brought about the collapse of these tropical habitats, triggering an evolutionary burst among reptiles.

The work, by a British team, is published in the journal Geology.

The forests that covered the ancient supercontinent of Euramerica are colloquially referred to as the Coal Forests.

The team used fossils to track the course of reptile evolution


They are so called because they accumulated a large amount of peat, which later turned into the coal that is mined today.

Towards the end of the Carboniferous, the Earth's climate is thought to have grown hotter and drier.

"Climate change caused rainforests to fragment into small 'islands' of forest," said co-author Howard Falcon-Lang, from Royal Holloway, University of London.

Dr Falcon-Lang continued: "This isolated populations of reptiles, and each community evolved in separate directions, leading to an increase in diversity."

To reach their conclusions, the scientists studied the fossil record of reptiles before and after the collapse of the rainforests.

They showed that reptiles became more diverse and even changed their diets as they struggled to adapt to a rapidly changing climate and environment.

Advantage reptiles
Professor Mike Benton, from the University of Bristol, said: "This is a classic ecological response to habitat fragmentation.

"You see the same process happening today whenever a group of animals becomes isolated from its parent population.

Reptiles diversified into forms such as Dimetrodon, a top predator in Permian times


"It's been studied on traffic islands between major road systems or, as Charles Darwin famously observed in the Galapagos, on oceanic islands."

His Bristol colleague Sarda Sahney commented: "It is fascinating that even in the face of devastating ecosystem-collapse, animals may continue to diversify."

Amphibians appear to have been hardest hit by the collapse of the rainforests. The relative success of reptiles may have been due to physical adaptations in which they differed from amphibians.

Firstly, the hard-shelled eggs of reptiles could be laid on dry land (most amphibians lay theirs in water). Secondly, reptiles possess protective scales that help them retain moisture (amphibian skin is very permeable to water).

"These key adaptations freed them from the aquatic habitats to which amphibians were tied and gave them ecologic advantage in the widespread drylands that developed," the researchers write in Geology.