In 1938, men fishing off the east coast of South Africa caught a peculiar fish that was identified as a coelacanth (“SEE-la-canth”). This find shocked the paleontological world, because the coelacanth was a fish thought to have died out with the dinosaurs at the end of the Cretaceous Period 65 million years ago. Additional specimens of coelacanth have since been found in the waters of the Comoros, Kenya, Tanzania, Mozambique, and Madagascar. It is one of many “Lazarus taxa” – creatures once thought to be extinct, only to be “resurrected” by appearing as real living, breathing organisms long after having disappeared from the fossil record.

Darwinian evolution depends on the idea that life on earth has changed over the years due to natural selection and the survival of the fittest species. When the environment changes, those species that are best able to adapt to the new climate or habitat do so, and the rest die out. Darwin presented evolutionary change as a gradual series of steps in which one set of creatures slowly changed into another set of creatures, leaving millions of extinct things streaming behind.

There turned out to be a problem with Darwin’s phyletic gradualism, though; it wasn’t supported by the fossil record. Darwin expected that as paleontologists dug up more fossils, they would find a lineup of gradually changing forms to support his theory. The thousands of gradual intermediate forms were not found, though. Even the horse series and whale series, pointed to as evidence for the evolution of these creatures, have serious weaknesses.

To deal with the massive gaps in the evolutionary fossil record, in 1972 Stephen Jay Gould and Niles Eldredge proposed the punctuated equilibria theory. They argued that evolution didn’t occur gradually the way Darwin thought it did, but in spurts. Gould and Eldredge made the case that species remained unchanged for long periods of time, but evolved rapidly when some stress in the environment forced adaptation. Rather than presenting a smooth, continuous, gradual change over millions of years, which the fossil record did not support, they argued evolution had occurred in spurts of change, with species splitting up to form new species. Since these changes were rare and since fossilization was a relatively rare phenomenon, evolutionists should expect gaps in the fossil record, they said.

Regardless of whether Gould and Eldredge’s argument withstands scrutiny, these two contrasting views of the way that evolution works have something in common; they expect species to change.  When certain creatures show up, looking basically the same as their ancient fossilized ancestors allegedly buried millions of years ago, it causes puzzlement. First, if these species did not die out, why do they not appear in the more recent fossil record? Also, if they were the successful versions of the species, why do they look so much like their petrified grandparents, who notably did not survive?

Coelocanth is an oddity. These bizarre, oily, foul-tasting fish look much as they did when they were buried in rock layers eons ago. They are not alone, either. Other living fossils include the Monoplacophora, a class of mollusks that were found off of Costa Rica in 1952 after having been thought extinct for the past 380 million years. The Laotian Rock Rat was found in 1996 after having been thought “dead” for 11 million years. The ant genus Gracilidris was found in Paraguay, Brazil and Argentina even though it had been allegedly extinct for more than 15 million years. And if you want to purchase your very own living fossil, Beds & Borders Nursery in Parrish, Florida has Wollemi pines for sale. A hiker named David Noble found a stand of these of trees in Wollemi National Park near Sydney, Australia in 1994. In the wild they are still one of the rarest plants in the world.

Fossils like this, as well as the Metasequoia, the Nightcap Oak, the Chacoan Peccary (a pig) or Mountain Pygmy Possum were all once thought to have died out millions of years ago, only to be “surprise!” found alive and well after all, relatively unchanged from the way their family members looked before they were locked in stone.

The coelocanth also demonstrates the danger of paleontologists’ making assumptions about the internal organs or DNA of creatures based on their skeletons.  Prior to its being found alive, the coelocanth had been considered a link between fish and land animals. Paleontologists had suggested that the swim bladder of the coelocanth had turned into a lung which allowed it to breathe when it crawled out onto land.  When a living coelocanth swim bladder was examined, though, it ruined that idea.  The swim bladder was thin and filled with fat and in no position to act like a lung, no matter how much the paleontologists wanted the coelocanth’s lobed fins to act like crawling arms.

Have certain species changed over time? Certainly they have. There were once marmot-like gophers with horns and giant sloths as large as VW busses. Yet, the gophers were still gophers and the sloths were still sloths, and on the whole were not so different from the same creatures we see today. Rather than showing a convenient series of evolutionary steps, the fossil record continually shows specific groups of creatures that display wide variety within their groupings, but do not demonstrate much evidence of having changed into something else.

http://www.khouse.org/enews_article/2010/1607/print/

Categories: Articole de interes general, Uncategorized