Friday, March 20, 2009

The Coelacanth

On page 118, it states that the ceolacanth was "a member of a group of fish with paired fins thought to be closely related to the first four-legged vertebrates and believed to be extinct since the end of the Cretaceous period 65 million years ago."  Therefore how was it discovered in 1938, about 70 years ago in the Cape Province of South Africa when it hasn't been seen for 65 million years?  Carroll describes it as a "living fossil," but how can a creature go extinct for so long and then appear so recently?  Can fossils preserve the DNA that is needed for it to reproduce again, or was this simply a lucky day when they found this fish?  Are there any other organisms that have been said to be extinct, but have recently been discovered again?  Why does this occur?

2 comments:

  1. Extinction is a status that, unless there is absolute certainty that no more of a species exists on the planet, can only be measured by speculation. The coelacanth is a fish that, until 1938 had had no documented appearances besides that of its fossilized relatives. Therefore, it was speculated that, along with the dinosaurs, the coelacanth had gone extinct at the end of the Cretaceous period, as Carroll has already told us. This is probably because Coelacanths live in hidden environments, mainly deep underwater caves, where there are not many opportunities to catch or sight them. Also, they stay hidden due to the fact that they only go hunting at night, a time when the local fishermen would be less likely to see them. Thirdly, the coelacanth's veiled existence can be attributed to the fact that only less than 200 fish are believed to be alive today. Although this number was probably higher a century ago, it was still low enough that the chances of any one spotting AND recognizing a specimen were very slim. This evidence suggests that the coelacanth never went extinct in the first place, and comparisons between the DNA records of coelacanth fossils and extant species show that it has merely evolved. This is the very reason why this fish is such an appropriate story for Carroll’s book. *

    A species that has been labeled as “extinct” and then found living again is called a lazarus taxon. Lazarus taxa are species that appear to be extinct because of observational errors that are a result of local extinctions which were later resupplied or as a result of some error in population samplings. For instance, in the case with the coelacanth, scientists had had a running record of the animal’s fossil history, and this fossil history ended indefinitely at a certain period in time. When this occured, the animal, if no living species exist, was said to be extinct. For the coelacanth, the problem was that the fish had become inclined to live at depths too deep for fossil evidence to surface regularly or even to surface at all. So because the fossils were too deep, scientists were not finding them, and the fossils from this period of time remained absent from the coelacanth time line. Being that there were too few living coelacanth to be seen and identified, this fish was inaccurately labeled as extinct. Its rediscovery in 1938 made it a lazarus taxon. These specimen have been coined so because they have theoretically “risen from the dead” like the character Lazarus from the New Testament. There are numerous lazarus taxon, in fact, this list includes both animals and plants. Some lazarus taxon of note are the Night Parrot (Pezoporus occidentalis) which is a bird that only comes out at night and was thought to have gone extinct in the 1800s; the Monoplacothora, which is a mollusk with only one shell that was thought to have gone extinct 400 million years ago but was rediscovered deep in the Middle American Trench in 1957; and the Wollemi Pine, a species of evergreen tree that was thought to have stopped being a snack of herbivores more than 2 million years ago, but was rediscovered in 1994. ^

    It seems that survival really is the core theme behind all of evolutionary biology. Genes work to survive in DNA (some have even become “immortal”) by resisting deletion. Traits survive by being a selective advantage. Species survive by using those selective advantages to become “the fittest”. Now it seems that living creatures, even when multiple records of sound evidence prove that they have died off, can survive extinction and come back from the dead. As Lazarus will attest, rising from the dead is most definitely a selective advantage of the fittest.



    *information retrieved from dinofish.com, a website devoted to informing the public about the coelacanth and also to raising awareness about its endangerment.

    ^wikipedia.com

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  2. We refer to the coelacanth as a living "fossil" as it belongs to a taxon (a clade, class, order, genus, or something along those lines) of organisms that have all gone extinct. Fossil classes, like superorder Dinosauria, have long passed from this earth, and we assume the same of other classes, loosing out to more fit organisms. Living fossils, by contrast, are species that are the sole representative of their clade or class or order, and to be quite frank, there are more of them than one might think. The Koala is a living fossil, as is the aardvark, the opossum, the monotremes, such as the platypus and the echidna, or the Red Panda, all the sole surviving members of a certain group.
    What makes the coelacanth unique, is that their taxon only existed in fossils- these hollow-boned fishes were deemed extinct by whatever mysterious shadowy governing body, in this cast the ICUN, decided. These lazarus taxon, as Jack stated, mimic the Biblical story of Lazarus being raised from the dead, but most often are commonly known to locals- the Paraguayans knew of the Chacoan peccary, an animal that had only been described through fossils, a long time before scientists ever rediscovered the animal. In the case of the Coelacanth, fishermen in the Comoros long knew of the beast- an inedible fish (due to the oil that soaks its tissues), that occasionally turned up in the day’s catch- it was incredible to them that anyone would be offering such a reward for the animal.
    The coelacanth could avoid capture by scientists for millennia due to both where it lived, deep in the water, and how it hunted. The coelacanth is what one would call an opportunistic hunter- when a cuttlefish, or a small shark, enters the habitat, the coelacanth will strike quickly, then retreat. Their eyes are incredibly sensitive, due to the layer of tissue in its eyes that reflects light, boosting visibility in low light conditions, such as that of the deep sea. This is commonly called eyeshine- the effect one sees in a picture of a dog where the flash of the camera goes off. Because of the eyeshine, coelacanths can’t be caught at day-they avoid light to protect their eyes, when most fisherman fish, and only something like a trawler on a night of the new moon, or at least not a full moon, could possibly catch the coelacanth. Furthermore, they can slow their metabolism at will- which means a state of hibernation, making it extremely rare that a person could catch this fish. Its habitat, off from the ‘civilized’ world of England and France, further aided its avoidance of the public eye.
    Recently, news has been made about organisms, such as the Lord God bird, or Ivory-billed woodpecker, coming back from what was thought to be extinction. Pygmy tarsiers were thought to be dead 85 years ago, but were recently found. Okapi, a relative to the quagga, was seen for the first time in 50 years, and the cloud rat was seen for the first time in 112. It goes to show that there are a lot of things that scientists write off for dead, but in the end, turn out to be doing relatively fine.

    http://wikipedia.org/wiki/coelacanth
    http://news.aol.com/article/photos-spark-fear-of-borneo-monster/351853 (to get the info from this one, click on the pictures, click on menu, than go to the rare creatures gallery.

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