How Snakes Lost Their Legs
A red-tailed boa. Research suggests snakes lost their limbs by growing them more slowly or for a shorter period of time.
New technologies could make it possible to bring extinct species back to life, concludes a paper published on April 4 in the journal Science. These advances include back-breeding (assembling or reassembling an extinct species' genes), cloning and genetic engineering.
A leading candidate for de-extinction is the woolly mammoth. Russian scientist Semyon Grigoriev, of the Sakha Republic's mammoth museum, plans to replace the nuclei of an elephant egg with nuclei extracted from woolly mammoth bone marrow. The elephant would theoretically become a surrogate mother to a baby mammoth.
Tasmanian tigers died out in 1936, in part because they had little genetic diversity which translates to "bad news for a species," said Katherine Belov, professor of comparative genomics at the University of Sydney. "Species are less able to adapt to change." Even if Tasmanian tigers -- or other animals -- are resurrected, it will take some time to build up diversity again.
Louis Agassiz Fuertes, Wikimedia Commons
Experts believe billions of these birds populated the Americas when Europeans arrived. Loss of habitat and commercial exploitation of the birds for their meat are thought to have killed them all off.
Efforts are now underway to revive the species by extracting DNA fragments from preserved specimens, and later, using band-tailed pigeons as surrogate parents.
Joseph Wolf, Wikimedia Commons
The Pyrenean ibex, a horned mammal once common in Europe, was one of the first subspecies targeted for de-extinction. Scientists began the attempts in late 1990s, when the last female Pyrenean ibex was still alive. Even if researchers could successfully clone that individual, there would be no males for her to breed with. Instead, genetic engineering might be required.
Cicero Moraes, Wikimedia Commons
Since saber-toothed cat bodies are sometimes found frozen, it might be possible to extract preserved DNA and clone the animal. About 5 years ago, scientists did just that with a mouse that was dead and frozen for 16 years. Woolly mammoth remains are also sometimes found in a well-preserved, frozen state.
Oxford Museum of Natural History, Wikimedia Commons
The dodo, a flightless bird, proved to be a tasty meal for humans and other predators. In 2007, scientists found a remarkably well-preserved dodo in a cave. Dodo DNA could be used to resurrect this avian species.
University of Texas at Austin, Wikimedia Commons
Ground sloths, relatively slow, lumbering animals, were easy targets for prehistoric big-game hunters. Scientists have found remains that still bear soft tissue. As with woolly mammoths, there's a chance extracted DNA could be used to back-breed or clone the large sloths.
Charles Knight, Wikimedia Commons
The Irish elk has been extinct for 11,000 years. Like the woolly mammoth, it inhabited colder regions. As a result, bodies are sometimes found frozen and in relatively good condition, making them candidates for DNA extraction.
UNiesert, Wikimedia Commons
Earlier this year, Harvard geneticist George Church -- with tongue in cheek -- said that he was seeing an "adventurous female human" to be a surrogate mother to a cloned Neanderthal. While Church was really just theorizing about what it would take to bring a Neanderthal back to life, the possibility could be a reality, should any scientist undertake such a controversial project.
Paleontologist Jack Horner is leading a project to create a dinosaur out of a chicken -- a "dinochicken." He told Discovery News that birds "are dinosaurs, so technically we're making a dinosaur out of a dinosaur." He and his colleagues have been genetically engineering chickens to reactivate ancestral traits, such as long tails, which are more associated with non-avian dinosaurs.
- Snakes lost their legs by growing them more slowly or for a shorter period of time until the legs eventually disappeared.
- Legs on snakes likely disturbed some form of movement, such as burrowing, rendering the legs useless.
- It's now believed that snakes either evolved from a lizard that burrowed on land or swam in the ocean.
Some, if not all, snakes used to have legs, and now new research suggests snakes lost their limbs by growing them more slowly or for a shorter period of time.
The research, outlined in the latest issue of the Journal of Vertebrate Paleontology, strengthens the belief that snakes evolved from a lizard that either burrowed on land or swam in the ocean.
In either case, its legs must have become less useful as the animal evolved over time.
"If something is not useful it can regress without any impact on the (animal's) survival, or regression can even be positive, as for here if the leg was disturbing a kind of locomotion, like for burrowing snakes or swimming snakes," lead author Alexandra Houssaye told Discovery News.
For the study, Houssaye, from the National Museum of Natural History in Paris, and her colleagues analyzed a fossil snake named Eupodophis descouensi. The prehistoric snake lived during the Cretaceous Period in what is now Lebanon.
To better examine the snake, the scientists used a new imagining technique called synchrotron-radiation computed laminography (SRCL). With an intense, high-energy beam of X-rays, the SRCL deeply penetrated the fossil as the researchers rotated it. The result was thousands of two-dimensional images that were later compiled into a three-dimensional model of the ancient snake's hips and ultra tiny .8-inch legs.
"Synchrotrons are enormous machines and allow us to see microscopic details in fossils invisible to any other techniques without damage to these invaluable specimens," said co-author Paul Tafforeau from the European Synchrotron Radiation Facility.
The new 3-D model determined that Eupodophis, in its lifetime, had two small regressed hind limbs and no front limbs. The leg visible to the researchers was bent at the knee, possessing four anklebones but no foot or toe bones. The high tech imaging further showed that the internal architecture of the leg bones strongly resembled that of modern terrestrial lizard legs.
Houssaye said "the legs were very regressed" in this snake, which she added is not the world's oldest snake, but it comes pretty close.
"The oldest snake remains are dated to 112 to 94 million years ago, and this snake is dated to around 90 million years ago," she explained.
Yet another snake from the same time period, Najash rionegrina, is also thought to have had two small rear legs, strengthening the theory that snakes once had legs and evolved from a lizard with limbs. Hussam Zaher of the University of Sao Paolo in Brazil, and a colleague found Najash (which means "snake" in Hebrew) at the Rio Negro province of Argentina.
Najash retained a sacrum, a bony feature that supported the pelvis. Zaher believes this feature was lost as snakes evolved from lizards. The fossil snake from Argentina is also thought to have lived on land, since it was found in what was once a terrestrial environment. Zaher said its anatomy suggests this snake lived in burrows.
Houssaye, however, does not think the case is yet closed as to whether or not snakes evolved from a marine or land-based lizard.
"The question of snake origin should not be resolved in the next 10 years," Houssaye said.
She is, however, hopeful that all of the separate teams working on this puzzle can one day pinpoint what species was the common ancestor of all snakes.