Trilobites is the name given to a class of arthropdswhich were the dominant formof sea life, millions of years ago. You can find their fossils on every continent,but they died out on the Cretaceous Period. I am struch by how similar they seem to be to modern horse shoe crabsm, and there are other inscts today that resemble them. My question: why was such a well-adapted species wiped out? Are biologists sure that some distant descendents aren’t still walking around somewhere?
Another question: I have a ginko tree in my yard-this species is said to be one of the oldest ones still extent…how didthe ginko survive so long, into the age of moderen trees?
If I remember my college instructor correctly, these shore-dwelling creatures lost much of their habitat when the continents merged into a giant continent (Gondwanaland or Pangea?)
The trilobites died off at the end of the Cretaceous period, coincident with the end of the dinosaurs (and flying reptiles like pteranodon, and sea-going reptiles like plesiosaur), so it’s hard not to think that there was some relationship between the demise of the dinosaurs and the end of the trilobites. If the strike of a huge meteorite was responsible for the dinos biting the dust, the, it seems likely that it was responsible for the trilobites, too.
How this happened, though, I have never heard a good theory for. Note also that there were a lot of other extinctions of sea creatures at the same time – an awful lot of the Ammonites died out at that time (shell-bearing cephalopods, similiar to the modern Nautilus), along with a lot of brachiopods (clam-like creatures with shells).
Much as I hate to contradict CalMeacham, when the dinosaurs (and their friends and relations) died out at the K-T, the only trilobites around were fossils.
Trilobites are common in the Cambrian and Ordovician Periods at the beginning of the Paleozoic Era; they declined abruptly during the mass extinction that ended the Ordovician, but a few families survived during the remainder of the Paleozoic, one family surviving into the Permian period which ended the Paleozoic. There is some debate about whether it lived right up until the 90%+ mass extinction that nded the Permian or died out during the period, but in any case, no trilobites survived past the Permian into the Mesozoic.
I’ve gotta disagree with Polycarp, here. All the books I’ve read had trilobites extending into the Mesozoic, and buying it with the dinosaurs. I haven’t got any references here, but I’ve seen plenty of charts showing the trilobite’d family tree anding at the K-T. And I know I’ve read about the bizarre forms trilobites started assuming in the Cretaceous.
OK, I’ve just checked some sites, and they all agree with Polycarp.
What’s wrong with my brain that I distinctly recall trilobites extending to the end of the Cretaceous? Did this used to be the common belief, and I just haven’t kept up?
As a weird last note, look at the photoshopped picture at the end of this page:
http://www.nctimes.net/~tyra-rex/tf.html
This time line supports my contention of early-Paleozoic diversity followed by a limited survival until the Permian. A reference to the Proetida indicates them as living from Ordovician times until the end of the Permian.
Your mention of their developing aberrant forms just prior to their extinction in the Cretaceous makes me think that you may have the (arthropod) Trilobites confused with the (cephalopod) Ammonites, which did live throughout the Mesozoic and developed aberrant forms just before their extinction at the K-T event. This abstract notes that aberrant forms were the most common ammonites of the Upper Cretaceous.
I think the answer is “Just about everything died at the end of the Permian.” There were very few survivors on land or sea. Luckily for us, one of the winning tickets in life’s lottery tickets was held by Lystrosaurus.
The question is not so much why the Trilobites died, but why did damn near everything die.
It seems to me the recent evidence is favoring yet another impact theory. Due to sublimation and erosion, however, it is quite unlikely that a crater would still exist. At any rate, the jury is still very much out.
This is one of the great mysteries of our world. Strangely, I rarely hear it talked about.
IIRC the Permian extinction event coincided with the eruption of the Siberian traps.
Considering the much smaller(but still absolutely immense) Deccan Traps eruptions which are a serious candidate for the K-T extinctions(or a serious contributor), it seems very likely that this could have produced this event.
One theory has it that the Siberian Traps raised world temperatures by around 5[sup]o[/sup]C, and that this in turn might have then released billions of tons of methane trapped in the seabed.
The additional effect of methane is to contribute to the greenhouse effect started by the Siberian Traps which released massive amounts of CO2.
The total rise in world temperature could have then risen by a further 10[sup]o[/sup]C.
Apparently this would have been more than enough to turn the world into virtual desert on land, and yet blocked out the sunlight to severly inhibit the growth of plankton.
Here was an excellent program on the subject:
http://www.bbc.co.uk/science/horizon/2002/dayearthdied.shtml
Another intersting site:
http://www.washington.edu/newsroom/news/2001archive/02-01archive/k022201.html
I’ve heard plenty of other theories as well. Glaciation, a nearby nova, continental drift, changing sea levels and and a massive increase in the acidity of the oceans have all been proposed. It seems quite likely there was a big impact and massive volcanism going on at the same time. Maybe this is why the Permian extinction was so much worse than the K/T extinction.
Whatever the cause, it’s spooky to think how close we came to never existing because of this.
And why DID Lystrosaurus survive? I think it may have been a burrower and that may have helped in the face of an unstable climate, but it’s still remarkable.
I thought that the Permian mass extinction was attributed to the formation of Pangaea? A lot of inland areas (very deep inland, mind you) would have become deserts, and the ocean current patterns would have changed drastically.
Pangaea was a hundred-million-year-long coalescence of continents. It certainly contributed to the evolution of exclusively-land plants and animals, but would not in and of itself been the cause of the Permian mass extinction, which was “geologically instantaneous” (i.e., within a million or two years). There is no question that the Siberian Traps were a major contributing cause; the only argument is whether they were the only main cause. And AFAIK there has been no impact event associated with the Permian extinction. (BTW, there was glaciation, but it preceded the mass extinction.)
One thought I have had and maybe someone here knows gthe answer, is that mass extinctions are not as complete as they think because of the fuzziness of our vision over geologic time. The 1-2 million years that constitutes “geologically instantaneous” could conceal a lot of events. Frex, a meteor strike wipes out trilobites over most of their habitat. The surviving trilobites slowly expand to fill the vacated habitats as things become more normalized, but because the ecological balance has been severely disrupted, it takes a lot of time. In the meantime other species are evolving to fill the niche. Some of these species are much more efficient than trilobites at exploiting their niche, and wherever there’s competition the new species wins and the trilobites disappear. They spread to cover the world, wiping out the trilobites they compete with, and in 1-2 million years we have the appearance of an instantaneous extinction caused by a meteor, even though it is in fact an opportunisitic expansion of a new species into territory where a species is weakened but not extinct.
I don’t have any actual data to support my theory, it’s more a MPSIMS than an actual theory, but I have wondered abuot it.
If I were a trilobite and saw a horseshoe crab I’d say “Got any plans for later? I hear this place rocks at night!”
The site is most interesting. I note that the Crinoids are still with us…you can find them in the deep oceans…why did they survive?
Maybe the trilobites became obsolete and were merely discontinued? Have you seen any in a closeout store?
Typically things like crinoids and ginkgos survive because they’re well adapted to their environment, there’s no evolutionary pressure forcing them to change, and there’s no competitor strong enough to drive them to extinction.
BTW, what dates from dinosaur times is the Family Ginkgoaceae, not the specific species Ginkgo biloba of today (which is, IIRC, extinct in the wild, with present ginkgo trees descended from ones raised as ornamental/shade trees in China). There’s no real difference here from conifers, which were around in the Cretaceous and survive today, yet nobody thinks of a pine tree as a living fossil.
Crinoids, BTW, are an entire class of echinoderm; their survival is really no more peculiar than the survival of snails or bony fish (both being at the class level).
“Living fossils” are simply species, genera, etc., that found an econiche, occupied it, and held it against all comers for a longer-than-normal time. The living Sumatran rhinoceros (endangered, to be sure) is the same genus as the common rhino of the Miocene, Diceratherium; the opossum family, Didelphidae, dates from the Cretaceous (and genus Didelphis, IIRC, from the Eocene). But the all-time winner in the survival race would go to the inarticulate brachiopod Lingula, of which living forms are indistinguishable from fossils from the Ordovician, over 400 million years back.