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.
Humans were in the Arctic at least 45,000 years ago, according to a new study that describes a brutal man versus mammoth event from that time.
The discovery, reported in the journal Science, extends the earliest presence of humans in the Arctic by 10,000 years. It also opens up the possibility that humans entered North America much earlier than previously thought, given that they were close to the Bering land bridge entry point.
At the center of it all were wooly mammoths, which hunters chased to the literal ends of the earth.
"Mammoth tusks were the main target for them, providing raw materials to produce long points and full-size spears, becoming a substitute for wood that equipped spears with shafts," lead author Vladimir Pitulko of the Russian Academy of Sciences' Institute for the History of Material Culture told Discovery News.
He added, "This is especially important for questions related to the peopling of the New World, because now we know that eastern Siberia up to its Arctic limits was populated starting at roughly 50,000 years ago."
Pitulko and his colleagues analyzed the frozen remains of a dead mammoth found in the central Siberian Arctic at what is now Yenisei Bay. The mammoth was a 15-year-old male in good physical condition before human hunters at close range killed him, the researchers believe.
At first it appears that the hunters threw spears at the mammoth, hitting his shoulders and going through muscle tissue. Other injuries reveal that the hunters missed their desired wound points several times while frantically stabbing the beast at closer range. Their goal was to cut major arteries to cause mortal bleeding, the scientists suspect. Glancing blows inflicted by the hunters bashed the mammoth's left and right ribs, suggesting that the men were also trying to damage the large animal's internal organs.
After multiple stabs with weapons that were ironically likely made of mammoth tusks, the hunters finally succeeding in killing their prey. They butchered the beast, including removing the tongue. It was probably eaten on site as a ritual food or delicacy.
A mammoth was one-stop shopping for humans then.
"It was a source of food, but also of fuel (dung, fat, bones) and raw materials for constructing tools," Pitulko explained.
Mammoth remains excavated in Arctic Siberia are shown.Pitulko et al., Science (2016)
Evidence for human habitation was also found at an eastern Siberian Arctic site called Bunge-Toll. It yielded remains of a mammoth, but also bison, rhinoceros, reindeer, red deer, and even a wolf killed with a sharp weapon.
"They were hunting everything that was available," Pitulko said, adding that the wolf might have been killed in self-defense or because it was going after the hunters' food.
The Arctic landscape at the time was vast and open, dominated by low-growing vegetation that attracted numerous large herbivores, the researchers indicated. They added that temperatures and precipitation were similar to those in the region today, although the summer climate might have been slightly warmer.
When informed of the butchered mammoth discovery, William Fitzhugh, director of the Smithsonian's Arctic Studies Center, told Discovery News: "This is a very remarkable find of a frozen mammoth with clear evidence of weapon impacts and partial butchery. It demonstrates human occupations in Arctic Eurasia 10,000 years earlier than previously known. A spectacular find and an exceptional case of archaeological sleuthing!"
Leonid Vishnyatsky of the Institute for the History of Material Culture agreed that "the authors have certainly made a very strong case that humans were present in the Arctic at least as early as 45,000 years ago."
Vishnyatsky, however, pointed out that it is not yet confirmed that the hunters were Homo sapiens. The early date, and the big game hunting practices of Neanderthals, means that this other human species cannot yet be fully ruled out as being the brave Arctic hunters, whose descendants might have first colonized the Americas.
Intriguingly, several studies show that East Asians and Native Americans have about 20 percent more Neanderthal DNA in their genomes than other populations.
More research is needed, however, to determine more about the Arctic hunters and their possible connection to the first settlement of North America.