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Natural Science Forum / Biology / Paleontology / July 2005How can we know when prehistoric sealife died out?
A question: how do we know when say Megalodon became extinct? Discovery channel had a documentary in which it was speculated Megalodon could have lived as recently as ancient seafaring civilzations and might account for some of the early sea monster sightings..any thought? >A question: how do we know when say Megalodon became extinct? Discovery > channel had a documentary in which it was speculated Megalodon could > have lived as recently as ancient seafaring civilzations and might > account for some of the early sea monster sightings..any thought? Megalodon is known primarily from fossil teeth found in Miocene and Pliocene deposits. No megalodon fossils of younger age have been found. That is strong evidence that this animal is extinct, but by no means completely rules out the possibility that this animal still exists. Having said that, such an animal would have a voracious apetite and would require a large amount of food. As such, there would be evidence for its existence today if it still existed, such as huge and distinctive shark bites found on dead whales. And even more provocative, there would likely have been carcuses of these animals washing up on shore somewhere. We haven't seen such evidence, as far as I am aware. >>A question: how do we know when say Megalodon became extinct? Discovery >>channel had a documentary in which it was speculated Megalodon could [quoted text clipped - 11 lines] > carcuses of these animals washing up on shore somewhere. We haven't seen > such evidence, as far as I am aware. Then again, anyone can point to all manner of Lazarus groups, notably including coelacanths. And new species of sharks are still being discovered today, some of them quite large, like the megamouth. It's not completely out of the question that Carcharodon megalodon could still be around. All we can say is that it's unlikely based on the evidence we have now. All those dead whales with the shark bites could be at the bottom of the ocean, and the evidence down there is both hard to find and ephemeral. If they stick to waters far from shore, we might have trouble finding them or evidence of them. I don't mean in modern times, just how do we know it or other prehistoric sealife long thought extinct did not survive up until the emergence of early man? >I don't mean in modern times, just how do we know it or other > prehistoric sealife long thought extinct did not survive up until the > emergence of early man? An absolute and total lack of evidence in the fossil record strongly suggests it wasn't around. A few species show up that live in out of the way and remote locations. That would always have been true. A single grove of trees of named after Franklin were found on the East coast of colonial America. I think they still exist but only because the guy that found them collected a few specimens. No other stand of that tree was ever reported found. A type of tree found in Australia that dates back to the time of the dinosaurs was located a few years back as a few plants in a deep narrow canyon in a desert. I think every plant found was hundreds of years old. Once things get very rare they tend to eventually vanish but the may not show up in the fossil record for a very long time before the last one dies. >A question: how do we know when say Megalodon became extinct? Discovery >channel had a documentary in which it was speculated Megalodon could >have lived as recently as ancient seafaring civilzations and might >account for some of the early sea monster sightings..any thought? It's really difficult to identify when critters appear or disappear from the fossil record. Some really stunning examples of mistaken guesses can be cited. Among them, the discovery a few years ago of undeniable bony fishes in Lower Cambrian rocks in China, and the discovery of live Coelacanth fish in the mid 20th Century (and a second population of them in Indonesia a decade ago). Previously, bony fish were thought to have originated in the Ordovician and Coelacanths were thought to have died out in the Cretaceous. However, most sharks shed lots teeth of during their lifetime. The teeth are pretty sturdy, and big shark teeth are not easy to overlook. They fossilize well. As far as I know, no one has found either Megaladon style teeth or lamnid teeth bigger than about 6cm (2.5 inches) in Pleistocene or recent deposits. In the Miocene and Pliocene, the teeth of other large lamnid sharks -- Carcharias and Isurus -- with lifestyles presumably similar to Megaladon are found intermixed with Megaladon teeth. In Pleistocene/recent deposits Charcharias and Isurus are still there, but Megaladon is missing. it seems likely that Megaladon either died out or stopped visiting shallow water adjacent to the big continents, sometime in the Pliocene. I suppose that there could be a population of Megaladon living in deep water or in some fairly remote region. But it's not very likely. |
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