An American alligator successfully lures a snowy egret with a stick, and then eats it, at St. Augustine Alligator Farm Zoological Park in Florida.
Aug. 30, 2011 --
Evolution and natural selection have played a role in the ever-changing landscape of plants, animals, bacteria and fungi. Although species evolve as they find their niche and adapt to new opportunities, some animals have remained relatively unchanged over the course of history. These animals are known as living fossils. Compared to the animals on this list, humans are relative newcomers to this planet. Homo sapiens emerged out of Africa a mere 200,000 years ago. Many living fossils are considerably older than humans and other mammals; some have even outlasted the dinosaurs. In this slideshow, take an up-close look at animals that have persevered virtually unchanged through the ages and continue to thrive today. We begin with the platypus, an unusual egg-laying animal with fur, a bill and a venomous bite. Charles Darwin himself coined the term "living fossil" while observing the platypus. Native to eastern Australia, the animal is the only surviving example of its family, Ornithorhynchidae. This group of animals is believed to have split from mammals some 166 million years ago.
The horseshoe crab could hold the distinction of being the oldest animal species still in existence. Dating back to the Paleozoic era, the horseshoe crab existed on Earth before the dinosaurs and soldiered on through several mass extinction events. In 2008, a horseshoe crab fossil, the oldest in existence found so far, dated back to around 445 million years ago, according to a report by LiveScience.
The tadpole shrimp, Triops cancriformis, is another contender for the title of oldest living animal species. This shrimp is related to the horseshoe crab so its longevity should come as no surprise. According to a report by The Telegraph, the tadpole shrimp as it appears today is virtually identical to a fossil of a specimen that lived some 200 million years ago just as dinosaurs rose to prominence. Despite the animal's remarkable endurance, the tadpole shrimp is currently listed as an endangered species.
Once thought to be extinct in the same event that killed off the dinosaurs some 65 million years ago, the coelacanth is a lobe-finned fish that sparked a debate over whether this species represented a missing link between aquatic animals and four-legged terrestrial creatures, according to National Geographic. The animal was rediscovered in 1938 and only two species of coelacanth still exist today. In 2007, a fossilized coelacanth fin was found dating back roughly 400 million years.
Snapping turtles as we know them first walked the earth some 40 million years ago, but they have been virtually unchanged over the past 215 million years of their evolution, according to Tortoise Trust. Although not among the most endangered tortoises and turtles according to the Turtle Conservation Coalition, the snapping turtle is listed as threatened.
The more than 20 species of alligators and crocodiles living today have evolved beyond their more primitive ancestors. But the basic physical design of these reptiles has remained essentially the same for the past 320 million years or so. Alligators and crocodiles share a common ancestry, though the two groups separated from each other some 60 million years ago.
The nautilus is the most primitive cephalopod in existence, a group that includes the most complex squid and octopus. Dating back to more than half a billion years ago, the nautilus reached the high point in its evolution during the Paleozoic era about 505 million to 408 million years ago. Several species of nautilus still survive today -- relatively unchanged from their ancestral counterparts.
Goblin sharks are rare, deep-sea dwellers with a unique elongated nose that distinguishes them from other sharks. They're also ancient, and are between 112 million to 124 million years old as a species. Around 2,000 different species of fossil sharks have been discovered, according to the ReefQuest Centre for Shark Research. The earliest sharks predate the dinosaurs by more than 200 million years.
The cockroach is famous for being a survivor. These insects can survive for weeks without their heads and even withstand the fallout following a nuclear blast. Cockroaches are also an especially long-surviving animal. Roaches have thrived on Earth for some 320 million years, with an estimated 5 million to 10 million individual species ranging in shape, size and habitat. This photo shows Blaberus giganteus, one of the largest species of cockroach on Earth.
Hagfish may have had to endure a less-than-flattering name since scientists first described them in the 18th century. However, these famously ugly marine animals have existed for about half a billion years. The hagfish also represents an important evolutionary step in the development of vision. These ancient fish may have been among the earliest animals to evolve more complex, camera-like eyes as opposed to the strictly photosensitive vision possessed by more primitive species. As such, the hagfish represents a kind of missing link in the evolution of the eye.
It's official: Reptiles can use tools to help them hunt.
New research shows that alligators and crocodiles can use small sticks to attract birds looking for nesting materials. If the birds get too close, they become a meal. The behavior has so far been observed among American alligators in Louisiana, as well as mugger crocodiles (also known as marsh crocodiles) in India.
Alligators only engaged in this trickery during the nesting season and in areas where birds nested, said Vladimir Dinets, a behavioral ecologist at the University of Tennessee Knoxville. During nesting season, there's often a shortage of sticks in marshy areas where these reptiles and birds overlap, and birds sometimes even fight amongst themselves to procure sticks to build nests. The study, which Dinets co-authored and which was published in late November in the journal Ethology Ecology & Evolution, suggests that there is no other explanation for this behavior than as one of tool use.
"What's really remarkable — they are not only using lures, but they are timing it to just when the birds they want to capture are nesting and looking for sticks to use," said Gordon Burghardt, an ethologist (animal behaviorist) and comparative psychologist specializing in reptiles at UT-Knoxville. "They are making some assessment of the birds themselves."
"This is indeed the first convincing evidence of tool use in any reptile," said Burghardt, who wasn't involved in the study. (Alligator Alley: Pictures of Monster Reptiles)
The finding, along with other recent work, suggests reptiles are much more intelligent than generally acknowledged, Dinets said. As anybody who studies the beasts can attest, they are quite smart, he added. Crocodiles, for example, have complex communication systems, can hunt in coordination and ambush prey, and both parents may help raise young, he said.
Relatively less is known about crocodiles and alligators than many animals, because, as large predators, they are difficult to raise in the lab and study up close in the wild. Their cold-bloodedness also makes them slow.
"They operate on a different time scale; they do things more slowly," Burghardt said. "Sometimes we don't have the patience to let them strut their stuff, as it were … so this kind of study is important."
Wading birds like snowy egrets have been known to nest in wooded islands near areas with high levels of alligators, for example in Florida. Scientists think the birds nest near such scaly enemies because the alligators keep at bay predators like snakes. Apparently, the occasional loss of adult birds to the hungry alligators, or nestlings that fall into the water, is worth the lowered risk of being eaten by something else, according to the study.
More from LiveScience:
Photos: Giant Pythons Invade Everglades
Creative Creatures: 10 Animals That Use Tools
Album: Bizarre Frogs, Lizards, and Salamanders
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