Prehistoric mass extinctions

This topic was created by LeeE .

  1. Anonymous Coward
    Anonymous Coward

    Prehistoric mass extinctions

    The article about the part that the Deccan Traps may have played in the extinction of the dinosaurs reminded me of a thought I had some time ago concerning mass extinctions: pandemics.

    The wikipedia article on mass extinctions mentions diseases in the 'Other hypotheses' section: "Many other hypotheses have been proposed, such as the spread of a new disease, or simple out-competition following an especially successful biological innovation. But all have been rejected, usually for one of the following reasons: they require events or processes for which there is no evidence; they assume mechanisms which are contrary to the available evidence; they are based on other theories which have been rejected or superseded."

    However, I can't see how diseases can be excluded for the reasons given there.

    For example, with regard to the lack of evidence, the number of complete fossilised animals found across all species is pretty small whereas we'd really need a large number of complete specimens from a single species to spot health differences due to disease in that species, and that's assuming that the disease leaves traces on the bits of the animal that do get fossilised. And then we must remember that many dinos are only known from partial fossil remains. In view of this I find it difficult to see how disease could be ruled out on the grounds of lack of evidence when the totality of the evidence we do have barely amounts to confirmation that the animal actually existed. Indeed, I think it's a pretty sure bet to say that we don't have fossil evidence of every creature that has existed, or even what percentage of all the creatures that have existed and become extinct that we are aware of.

    I also can't see how a pandemic disease would necessarily be dependent upon other events or processes; diseases would have been evolving alongside everything else and wouldn't need special events or processes to result in a pandemic.

    It seems to me that unless we postulate that there were no diseases in prehistory (which would mean that disease is a relatively new phenomenon) then diseases in dinosaurs must have been a certainty, and if diseases were a certainty then pandemics must have been a possibility.

    What I do find interesting, and which might support a pandemic hypotheses for some mass extinctions, is the degree of selectivity when these mass extinctions occurred; they seem to have affected only a limited number of families/genera and whilst this may reflect the susceptibility of those particular families/genera to the environmental phenomena that is usually blamed for mass extinctions it may equally reflect their susceptibility to a particular disease.

  2. Qwertius

    Diseases should be considered; but they are not what delivered the final coupe de grace.

    Question.

    Do you know of any disease in the modern world that has killed off 100% of its host ?

    Yes : diseases kill : but I somehow doubt diseases can bring about a complete collapse of an order of living creatures such as dinosauria.

  3. allthecoolshortnamesweretaken

    I'd say that when only a limited number of families/genera are wiped out a pandemic disease could have been the reason (or at least a strong factor). A disease doesn't have to kill 100% of its host. It has to kill enough hosts to mess up the reproduction mechanisms for good, that should do it. The disease initially thins out the population to a tipping point after which reproduction breaks down.

    Or a disease that renders its hosts infertile. There are a lot of possible scenarios. Like a disease that wipes out the mein food source, a real problem for specialized herbivores. Modern day examples are Pandas and Koalas.

    The black plague wiped out circa one third of the population of Europe, it took decades for the population to reach pre-disease levels. The spanish flu right after WW I killed more people than the war. It also was unusual as its 'targeting' was sort of reversed - children and old persons usually had better chances than the young and fit. Humans have developed technology to cope with stuff like that. Dinosaurs didn't.

    1. Swarthy

      Timeline

      The problem with the disease/pandemic idea is the timeline. Yes, a disease could wipe out a chunk of population, and a pandemic could wipe out a large section of a species; the pandemic could then mutate and take out other species. But, given natural infection vectors, some would have survived, and resistances or immunities would be developed before the bug could travel. Some geographically remote locations would have not have been exposed.

      But to take out all of the species that were wiped out, across the world, without time for a resistance/immunity to develop the Dinosaurs (or the small mammals that took 'em out) would have needed intercontinental travel and a military-grade superbug.

  4. Anonymous Coward
    Anonymous Coward

    Just a thought

    Could some sort of extraterrestrial nanoplague have been responsible?

    Evidence:

    Exhibit A:- A widespread iridium layer present in the K-T boundary worldwide

    Exhibit B:- Evidence of OOParts such as apparent screws embedded in >100MY old coal

    Exhibit C:- Lots of apparently unrelated extinctions in both oceanic and terrestrial life

    Exhibit D:- Weird spikes in certain rare metals not usually found in meteorites

    I theorize that some sort of self replicating alien probe turned up and due to a massive miscalculation it entered the Earth's atmosphere and dumped its nanotechnological self repair mechanism when it burned up along with the controls and failsafes.

    If iridium ions are essential then perhaps the replicators spread worldwide and ended up nearly destroying the biosphere before using all the native iridium up and running out of raw materials.

    As it happens some of the material might have survived and be buried tens of miles underground or in deep caverns, yet to be discovered.

  5. Anonymous Coward
    Anonymous Coward

    Also

    The antimatter containment breaching might account for the signs of impact, a nuclear detonation at ground level (or just above) looks exactly like an asteroid impact and all the strange isotopes would have long since decayed into stable lead and/or uranium.

    This was actually suggested as an alternative explanation for the Tunguska blast, perhaps a smaller version of the same probe?

    I did wonder if primordial plutonium could be signs of an extraterrestrial impact, Pu is found in some natural nuclear reactors but not in large quantities.

    1. allthecoolshortnamesweretaken

      Re: Also

      "This was actually suggested as an alternative explanation for the Tunguska blast, ..."

      For example in this movie.

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