November 23, 2016

At a recent convention of paleontologists (scientists who study animals and plants that lived in prehistoric times), things got a bit venomous. A group of researchers claimed that a fossil recently identified as an early snake was not a snake at all. Furthermore, they stated that the specimen should not have been studied in the first place. The presentation was the most recent shot fired in the battle over the evolution (a process of change over time) of snakes.

This artist’s impression shows the four-footed tetrapodophis amplectus snatching its prey, an unlucky salamander. Credit: © James Brown, University of Portsmouth

In 2015, Dave Martill and his colleagues at the University of Portsmouth in England reported that they had discovered a new type of primitive snake. They found the ancient animal’s fossilized imprint (which came from Brazil) among the collections of a German museum. The British researchers named their discovery Tetrapodophis amplectus and published their findings in the journal Science. Tetrapodophis means “four-footed snake.” The animal was about 6 inches (15 centimeters) long and possessed four tiny limbs. It lived in an ocean environment some 110 million years ago.

This month, however, at the annual Society of Vertebrate Paleontology conference in Salt Lake City, Utah, Michael Caldwell of the University of Alberta in Edmonton, Canada, gave a presentation refuting Martill’s “four-footed snake” diagnosis. In the creature’s skull, for instance, Caldwell noted “every single character that was identified in the original manuscript as being diagnostic of a snake was either not the case or not observable.” Instead, Caldwell’s group contended that Tetrapodophis is not a snake at all, but rather a member of a group of unrelated marine reptiles.

The fossilized imprint of Tetrapodophis reveals small, specialized feet—or perhaps flippers. Credit: © Dave Martill, University of Portsmouth

This dispute is merely the latest spat among paleontologists on snake origins. Paleontologists agree that snakes likely evolved in the Jurassic Period some 150 million years ago. Some people (like Martill) think that snakes evolved from aquatic reptiles. Over million of years, four-legged reptiles would have spent more and more time in the water, eventually losing their limbs in favor of a long body good for swimming. Later, snakes made their way onto land, with some (sea snakes) remaining in their ancestral habitat. Martill’s group contends that snakes were closely related to mosasaurs, giant marine reptiles that prowled the oceans some 100 million years ago. Most paleontologists, however, think that snakes evolved from burrowing, terrestrial reptiles. As these aimals dug deeper and more complex burrows with their strong heads, their limbs vanished over millions of years. Later, snakes moved into different habitats, including the sea. In this scenario, snakes’ closest relatives would be monitor lizards such as the Komodo dragon. So far, a lack of ancient snake fossils has prevented either hypothesis from being proven.

Further muddying the water, Caldwell—of the “land snake” faction—reported that when he went to study the fossil in the German museum, the fossil was no longer there. Apparently, it had been a loan to the museum from a private collector. The collector had retrieved it from the museum because it had been damaged during an earlier study. Most paleontologists will not study privately owned fossils for this exact reason: an owner may take back the fossil at any time. Science must be repeatable, so a description of a specimen that is no longer available for study is not science at all. Since Tetrapodophis was revealed to be a privately owned specimen, many experts have vowed to ignore it while conducting future studies on snake evolution. We will have to wait for more fossils—in the permanent collections of museums and universities—to determine if snakes started out on land or in the water—with four legs or, perhaps, four flippers.

September 26, 2016

Large snakes have a well-established reputation as monsters in legend and folklore throughout the world. Monstrous snakes and serpents are common themes in the myths and iconography of many ancient cultures. Because snakes are sometimes poisonous and deadly, it is only natural that many people suffer from a general fear of snakes—so many, in fact, that the fear has a name: ophidiophobia. Small and slithery and creepy snakes can make people jump, but what about the monstrous anaconda, a snake so large it can swallow a small cow?

A giant anaconda is shown to a group of tourists in Los Llanos, Venezuela. Credit: © Vadim Petrakov, Shutterstock

Anaconda is the common name of a group of large snakes found in tropical South America. Anacondas (also called water boas) have greenish, yellowish, or brownish skin, often with many black rings or spots. The green anaconda (Eunectes murinas) may grow as long as 30 feet (9 meters) and weigh nearly 450 pounds (205 kilograms). Anacondas live near water, often swimming in rivers. Their main food is fish, but they also will eat birds, small mammals, and other reptiles. Anacondas kill by wrapping their coils tightly around prey and constricting (squeezing) it to keep it from breathing and to stop its heart.

Anacondas are top predators in their habitat, and they often prey on large animals, including capybaras, white-tailed deer, and even large caimans (reptiles closely related to the alligator). Anacondas are capable of eating such large prey because the skin and ligaments around their jaws easily stretch to fit around large objects. The two sides of an anaconda’s lower jaw are also joined by an elastic ligament, creating a mobile joint that allows the snake to move and stretch its jaws well beyond the size of its own head.

Large anacondas can be dangerous to people because of their size and strength. Fortunately, anacondas live in swampy habitats where people are unlikely to encounter them. Despite sensational stories that often circulate on the Internet, there are no known instances of anacondas eating people. In fact, there are only a couple of documented anaconda attacks on humans at all. Both were attacks on researchers trying to study the gigantic snakes. Fortunately, the scientists were rescued and the anaconda’s record remained clean. Like other snakes, anacondas defend themselves from enemies by retreating or, if cornered, by biting. Their bite is not poisonous, but their many teeth can inflict deep wounds.

July 4, 2016

The black mamba shows its ominous black smile. Credit: © NickEvansKZN, Shutterstock

Widely regarded as one of the world’s deadliest snakes, the monstrous reputation of the black mamba (Dendroaspis polylepis) is well deserved. A deep-seated fear of this snake is found throughout Africa, where local folktales attribute almost magical powers to it. The fear stems from the mamba’s aggressive disposition, lightning-quick speed, and lethal venom—and, because it lives in densely populated regions, the snake kills hundreds of people every year. Among locals in South Africa, a bite from this sleek and beautiful snake is referred to as “the kiss of death.” Once bitten, victims are said to take only two steps before they die.

The black mamba is not black, as the name implies, but actually gray, brown, or olive in color. The name comes from the dark black lining of the snake’s mouth which it displays with a wide gape when threatened. If the warning is not heeded, the aggressive mamba may strike. An adult mamba can reach 8 feet (2.5 meters) in length. Its body is long and slender, with smooth scales and a narrow head. The black mamba is also one of the fastest snakes in the world. Many tales describe its speed and aggressive nature—so aggressive that it is often said to chase after people. These serpents move faster than many people can run—about 12 miles per hour (19 kilometers per hour) over short distances—another reason for their fearsome reputation.

According to legend, the black mamba will bite its own tail to make a hoop and roll down a hill to gain speed. As the mamba gets to the bottom, it unwinds and flings itself like a high-speed missile towards its victim. Another popular myth claims that the mamba can balance its entire body on the tip of its tail to strike at a person’s face. One folktale claims that the black mamba is so intelligent that it actually plans its attacks on people. The snake is said to lurk at roadsides, where it waits to coil around the axle of an automobile. It then strikes the first foot out of the vehicle.

As with most legends, the reality of the black mamba is much less sensational. The snake is an active diurnal (daytime) predator, so it is often seen. That does not mean it is waiting to spring a trap, however. It hunts warm-blooded prey, but the black mamba does not pursue humans. In fact, the snake will usually flee human contact unless it is cornered. If that happens, the mamba will aggressively defend itself by rearing up, lifting two-thirds of its body off the ground, and striking with such force that it seems to shoot through the air.

There is no debating the black mamba’s lethal potential. It can strike repeatedly—up to 12 times in rapid succession. Short fangs at the front of the snake’s mouth efficiently inject its extremely potent venom. The neurotoxic venom, which is poisonous to nerve cells, immediately disrupts nerve transmissions in the body, rapidly affecting heart rate, vision, and breathing. Just two drops of black mamba venom can kill a human. If a person is bitten, death follows within 20 minutes unless antivenin (snakebite serum) is administered promptly. This perishable serum, however, is not widely available in the black mamba’s habitat in rural southern and eastern Africa.

February 22

The Florida Fish and Wildlife Commission announced this week that 68 Burmese pythons had been captured in the Florida Everglades in its 2013 Python Challenge. The Burmese python, the target of the hunt, is an invasive species–that is, it is not native to Florida. Most of the pythons in the wild in Florida are either snakes that escaped from captivity or pets that were deliberately released into the wild when owners could no longer care for them. Because the Burmese python is not native, it has no predators itself. Thus, the python has spread quickly throughout the Everglades, causing harm to the ecosystem and to native species in the region. According to a 2012 study, sightings of bobcats, opossums, rabbits, raccoons, and other mammals in the Everglades are down as much as 99% in areas where pythons live.

The Burmese python, a subspecies of the Indian python shown, has spread quickly through the Florida Everglades, threatening the ecosystem and the animals native to the area. (J. H. Robinson, Animals Animals)

Florida’s Fish and Wildlife Commission held its first python hunt from January 12 to February 10 in 2013. Any adult who wanted to try to harvest the nonvenomous snake was encouraged to do so, and nearly 1,000 people, mostly amateurs, signed on. Given how well camouflaged the snake is in the Everglades environment, experts were surprised that the hunt had found 68 pythons in the wild by the end date.

Most of the captured snakes were humanely euthanized. However, several snakes–including the longest, at 11 feet (3.3 meters)–were fitted with transmitters and released back into the wild. Scientists planned to track these snakes, hoping that they would lead to nests of breeding females, who could also then be captured before their young went into the wild.

Additional World Book articles:

• ecology
• environment
• Everglades
• python

Feb. 6, 2012

Pythons are battling alligators for the position of top predator in Everglades National Park in Florida, and native mammals are paying the price, according to a new study by two Florida university researchers. The study is the first to provide evidence linking a sharp decline in populations of medium- and large-sized mammals in the park to an explosion in the number and range of the large snakes.

Native to Southeast Asia, the python is classified as an invasive species in North America. From 1999 to 2004, pet exporters met a growing American demand for Burmese pythons by shipping more than 144,000 baby snakes to the United States. However, new owners were frequently unprepared or unwilling to care for the grown snakes, which can measure 23 feet (7 meters) in length and weigh 200 pounds (91 kilograms). Many owners dumped their snakes into the wild. Pythons released into the Florida Everglades, a region with a climate similar to that of the snakes’ native habitat, flourished. Pythons also have escaped into the wild during hurricanes.

The study’s researchers surveyed native mammal populations over 313 nights during an eight-year period by counting live and dead animals along a road that runs to the southern tip of the park. They then compared their tallies to population surveys done in 1996 and 1997. In areas of the Everglades where pythons have lived the longest, populations of raccoons had fallen by 99.3 percent. The number of opossums had dropped by 98.9 percent, and bobcat populations had fallen by 88.5 percent. The researchers were unable to find any rabbits or foxes. Populations of native animals were larger in areas more recently or not yet invaded by the snakes.

The U.S. Association of Reptile Keepers disputed the findings of the study. The organization contended that mercury pollution in the Everglades has played a major role in the disappearance of the mammals.

Young Indian pythons hatch from eggs outside the mother's body. The leathery shells of snake eggs expand as the young snakes grow inside. When they are ready to hatch, young snakes slash their shells with a special tooth that grows on the upper jaw. AP/Wide World

Wildlife experts agree that eliminating the secretive and hard-to-hunt snakes from the park would be impossible. They are unsure if the spread of the snakes, which have no natural predators in North America, can be halted. In January, the administration of President Barack Obama outlawed the import and interstate commerce of Burmese pythons, two other pythons, and the yellow anaconda. Reptile importers are still allowed to trade in reticulated pythons and boa constrictors.

Additional World Book articles:

• Ecology
• Invasive Species (A Special Report)
• Reptile