One of the 46 ichthyosaur fossils discovered near a glacier in southern Chile.
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.
Dozens of nearly complete skeletons of prehistoric marine reptiles have been uncovered near a melting glacier in southern Chile.
Scientists found 46 specimens from four different species of extinct ichthyosaurs. These creatures, whose Greek name means "fish lizards," were a group of large, fast-swimming marine reptiles that lived during the Mesozoic Era, about 245 million to 90 million years ago.
The newly discovered skeletons are from both embryos and adults. The creatures, likely killed during a series of catastrophic mudslides, were preserved in deep-sea sediments that were later exposed by the melting glacier, the researchers said in the study, published May 22 in the journal Geological Society of America Bulletin. [See Photos of the Ichthyosaur Graveyard Found in Chile]
Ichthyosaurs had torpedo-shaped bodies with vertical flippers, and long snouts with teeth.
"They look a lot like dolphins today," said Wolfgang Stinnesbeck, a paleontologist at the University of Heidelberg in Germany and the leader of the study.
Stinnesbeck and his team found the Early Cretaceous (150 million to 100 million years old) specimens near the Tyndall Glacier in the Torres del Paine National Park in Chile. As the glacier melted, the rock containing the fossils became exposed, Stinnesbeck told Live Science.
Very few of the ancient reptiles have been found in South America before; only a few remnants of rib cages and vertebrae had been found.
The largest ichthyosaur skeleton unearthed in Chile measures more than 16 feet (5 meters) long. The skeletons were extremely well preserved — some even retained soft tissues. The researchers also found fossil embryos inside a female specimen. They assigned the fossils to the family Ophthalmosauridae.
These "fish lizards" probably hunted in an underwater canyon near the coastline, pursuing a diet of squidlike animals and fish, the researchers said. Occasionally, there would have been mudflows that cascaded into the water like an avalanche, and the researchers think these mudflows killed the ichthyosaurs. The animals likely became disoriented and drowned, getting sucked into the deep sea, where their bodies were entombed in the sediment, the researchers said.
Ichthyosaurs swam the seas at the same time as dinosaurs roamed the Earth and pterosaurs reigned the skies, but they may have died out before their land- and air-dwelling brethren, Stinnesbeck said. A global depletion of oxygen in the oceans, possibly due to volcanism, may have caused the extinction of these seagoing reptiles, he said.
The discovery of these creatures establishes the Chilean glacier as one of the prime sites for Early Cretaceous marine reptiles worldwide, the researchers said. But getting to the fossil site is half the battle. To reach it, the team had to drive for five hours, hike for 10 to 12 hours to camp and then hike another two hours, sometimes in heavy rain, hail or snow.
"This has been one of the toughest field camps I ever had," Stinnesbeck said.
More From LiveScience:
Image Gallery: Photos Reveal Prehistoric Sea Monster
Alligator Alley: Pictures of Monster Reptiles
Image Gallery: 25 Amazing Ancient Beasts