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'Living Fossil' Coelacanth Has an Obsolete Lung

The deep-sea dweller, long thought extinct, has a vestigial lung lurking in its abdomen.

The coelacanth, an elusive deep-sea dweller long thought extinct, had another item added Tuesday to an already-long list of unusual physical traits: an obsolete lung lurking in its abdomen.

Similar to the human appendix, the organ was likely rendered defunct by evolution, researchers noted in the journal Nature Communications.

Like all fish, today's coelacanths -- referred to as "living fossils" -- use gills to extract oxygen from the water they live in.

Living Fossils: Animals From Another Time: Photos

But millions of years ago, coelacanth ancestors probably breathed using the lung, the team concluded.

"By the Mesozoic Era, adaptation of some coelacanths to deep marine water, an environment with very low variations of oxygen pressure, may have triggered the total loss of pulmonary respiration," co-author Paulo Brito of the Rio de Janeiro State University told AFP.

This could explain how it survived the extinction event 66 million years ago that wiped all non-avian dinosaurs and most other life from Earth -- and probably those coelacanths inhabiting shallow waters, he said.

'Fishimal' Was Part Fish, Part Limbed Animal

It would also account for "the marked reduction" of the lung into its shrivelled, present-day form, Brito said by email.

Coelacanth fossils have been dated to about 400 million years ago, and the fish was thought to have died out towards the end of the Mesozoic era, which stretched from about 250 to 66 million years ago.

But then one was caught off the South African coast in 1938, earning the coelacanth the title of "Lazarus taxon" -- a group of animals "resurrected" from extinction.

A few other individuals have been found since, as well as members of a cousin species off the coast of Indonesia, but the coelacanth is considered endangered.

These Fish Were Made For Walking: Photos

It is a queer fish in many ways.

Key among its quirks, it has paired, "lobe-shaped" fins which move in an alternating pattern similar to a four-limbed land animal -- sparking speculation that it may have been a member of a group of fish that first crawled onto land to evolve into animals with legs.

The grey-brown fish can grow up to two metres (6.5 feet) in length, weigh as much as 91 kilos (200 pounds), and may live up to 60 years.

It has a hollow, liquid-filled spine, enamel-capped teeth, and a hinged jaw that allows it to open its mouth wide to swallow larger prey.

Biofluorescent Fish Light Up The Deep: Photos

Little is known about how they live, what they eat, how they reproduce, or how many of them are left.

The new discovery was based on dissections and scans of infant and adult coelacanth samples, as well as 3D reconstructions, said Brito.

The team found that the disfunctional lung is proportionally much larger in the coelacanth embryo than the adult, meaning that growth of the organ slows as the fish gets older.

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.

Compared to other animals on this list, the mouse deer, better known as a chevrotain, is a relative newcomer. For a large mammal, however, it's relatively old. This animal is among the only survivors of a group of hoofed mammals that lived some 35 million years ago.