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.
As if crocodiles and their kin needed further testament to their ferocity, now comes word that they may even know how to hunt together to take down their prey.
New research out of the University of Tennessee took advantage of the reach of social media to gather eyewitness accounts worldwide of crocodile and alligator predatory behavior. A research assistant in the university's psychology department, Vladimir Dinets, took that unusual course thanks to the crocodile's natural tendency to work the night shift, in out of the way places, eating infrequently -- all of which make it difficult for any behavioral research to be performed on it in the wild.
Dinets used Facebook and other social media outlets to collect the firsthand accounts, combining them with other science diaries -- some dating back to the 1800s -- and more than 3,000 hours of his own observations.
From Dinets' analysis of the accounts, a picture emerged -- consistent across accounts and the span of centuries -- of the giant-jawed creatures coordinating and collaborating on their attacks.
For example, alligators, Dinets found, arranged a sort of hunting party, teaming to drive fish into shallower waters where other alligators were ready to keep them from escaping. In another account, a crocodile frightened a pig into running headlong into a lagoon -- right into the maws of two smaller crocodiles waiting to pounce on a meal delivered to their home like a call-out pizza.
"All these observations indicate that crocodilians might belong to a very select club of hunters -— just 20 or so species of animals, including humans —- capable of coordinating their actions in sophisticated ways and assuming different roles according to each individual’s abilities," said Dinets in a release. "In fact, they might be second only to humans in their hunting prowess," he added.
One cautionary note from the researcher is that all of those social media accounts and thousands of hours of independent research produced just a handful of useful eyewitness accounts. More accounts are needed in order to firm up our understanding of these hunting teamwork behaviors. "And these observations don’t come easily," Dinets said.
Dinets' research has been published in the journal Ethology Ecology and Evolution.