Insects May Have Had a Hand In Dinosaur Extinction

eldavojohn writes "Everyone's got their favorite theories of Dinosaur extinction, but new speculation is rampant in a book that gives cause to believe it may have been disease-carrying insects. Due to the length of their slow and eventual extinction (the 'K-T Boundary'), it is argued that this would more likely be attributed to the spread of disease and the rise of parasitic insects like ticks or biting flies. Are our immune systems the only reason any animals survived?"

Comments

Co-evolution of animals and diseases

[PhilHibbs]

Any disease that wipes out its host will have to evolve to be less deadly, or it will run out of hosts. So it's not really right to say that it's our immune systems that allowed animals to survive - the evolution of an immune system and the diseases that it fights go hand-in-hand. There is some competition, with diseases finding new ways to get around immune responses, but also some co-operation, as an overly-effective disease will destroy its own ecosystem and thus die out.

Re:Co-evolution of animals and diseases

[MaxEmerika]

Diseases that are transmitted directly from host to host tend to evolve to be less deadly for the exact reasons you describe. Diseases that are transmitted through an intermediary (like insects) can afford to be much more aggressive against their final hosts. That said, this theory still sounds fishy to me. These diseases were so devastating that they managed to drive two orders of animals to total extinction?

Re:Co-evolution of animals and diseases

[jandrese]

Ebola isn't exactly as common as a cold you know. In fact it's a great example of a disease that wipes out its own hosts too quickly to spread very well. The only saving grace of Ebola is that it's extremely infectious, so over small and tightly knit populations it is devastating. It's the kind of diesease where the traders will come to a village for the next month's trade and find it dead, not the kind where you wipe out 3/4 of Europe.

Re:Co-evolution of animals and diseases

[hey!]

There is also some evidence that disease agents may confer a kind of symbiotic advantage on their hosts.

Hantavirus, for example, is relatively harmless rodent populations that harbor it. However it can be deadly to immunologically naive populations that might move in and displace them. So it is possible that infectious agents may help their hosts guard their ecological niche. We can see something of the opposite effect in the introduction of European diseases to North American populations living in what were more hygienic conditions.

The idea that alterations in insect populations and the geographic range of diseases may have played a role in a mass extinction event is a sobering one. Ecological disruption tends to cause geographically isolated infectious agents to spill out, especially in a world connected by global commerce. And we are in the middle of the mother of all ecological disruptions: global climate change.

Take Malaria, a constant presence in the tropics for as long as can be remembered. Malaria is special among vector transmitted diseases in that it does not have a significant animal reservoir: malaria pathogens specialize in one closely related group of species, say monkeys but not apes. So human malaria species specialize in humans, which potentially makes them eradicable.

This is important, because with climate change, the boundaries of Malaria carrying mosquitoes is shifting, not only away from the tropics, but to higher altitudes. Mexico city is in a malarial latitude; it is altitude of nearly 13,000 feet that keeps the Anopheles mosquito genus in check. Perturb the climate slightly, and the third largest metropolitan area in the world will provide over twenty million new hosts for Malaria protozoan. As a capital city, it has air links world wide.

I will give another example of how ecological disruption is tied to diseases. A friend of mine married into a family that lived on an island. Everyone in that family had contracted Lyme disease at some point in their life. The problem was the ecosystem needed a top-level predator, but humans had wiped out wolves over a century earlier. This disturbed the ecosystem, because without a top level predator, the only thing keeping the rodent population in check was how much food there was available, and disease. That disease spilled over into the human population.

Now a few decades ago, a small population of Western Coyotes swam out the island and established itself. They took down most of the deer herd, then turned to the rats, voles and other small mammals. Ticks have gone from being a plague of almost unimaginable proportions to being relatively rare. Imagine the amount of biomass in even a small coyote. Now imagine the ecosystem is using that biomass to generate ticks.

Of course, there aren't as many deer, and they make a hell of a racket at night, but on the plus side Lyme disease seems to have become much more rare. Attempts to eradicate the coyotes failed, because while they fill the wolf niche in the environment, they're much, much more adapted to living alongside humans. So overall, the coyotes have restored the disrupted ecology humans had "improved" by eliminating the wolves.

Re:Three questions

[Chris Burke]

Why wouldn't this also affect mammals? Is there an implication that dinosaurs had more primitive immune systems? Is any of this more than mere speculation?

Well this is mere speculation, but the implication isn't necessarily that dinosaurs had a more primitive immune system, it could simply be that it was different. Different diseases infect different animals. It makes sense that if a virulent and deadly disease borne by insects arose in one species of dinosaur, it would have an easier time adapting to others than the newly arisen mammals.

Disease, Insects, and Extension...

[Zymergy]

Short answer: Maybe... But if so, it is a small part of what let them survive...
Don't diseases and insects ALMOST ALWAYS follow other natural disasters where there are numerous dead and dying creatures on the land and in the water?
Besides, sharks have awesome immune systems (some scientists say they actually have the BEST immune systems) and many varieties of sharks also went extinct at the same extension period as well numerous species of plants...
Does the author mean to imply that plants also survived the insects and diseases because of their 'immune systems'? I did not realize that plants had immune systems??...
Guess I'll go RTFA...

Re:Three questions

[fbjon]

It would make an interesting anaolgy with computers and the Internet, though. First, everyone is assumed to play by the rules, then suddenly all manner of viruses start to flourish.

nah

[circletimessquare]

parasites and disease don't generally lead to the extinction of their hosts, as you tend to go extinct yourself

after an initial population decimation, in which the hosts suffer, then the parasite/ disease suffers a dramatic population decrease. more resistant strains of host emerge, and then more benign strains of parasite disease emerge. the parasite/ disease can't afford to threaten its own existence by being too virulent and deadly

however, i am willing to bet we, us mammals, killed off the dinosaurs. nothing like a few little rodents chewing on the slowly reproducing eggs of nesting dinosaurs to decimate the population

in fact, the only surviving dinosaurs of the egg-chewing rodent crisis were the ones who could nest in trees, offering some protection from the ground dwelling egg chewers. of course, we call these dinosaurs birds today

Re:Three questions

[zappepcs]

Sorry no link, but yesterday there was a story I read that about 8% of human DNA is made up of junk left behind by retrovirus infections. That is to say, we survived those. HIV is a retrovirus. It is not far fetched to believe that Dinosaurs also suffered from disease and virus infections, and that insects could carry these from one animal to another. The general panic over H5N1 should tell you just how serious such a thing can be. If the KT boundary event weakened many dinosaurs, leaving them vulnerable, diseases that were not typically a threat could have become one.

It's also possible that the combination of several things, including climate change after the KT boundary event, worked together to cause depopulation.

Um, why only dinosaurs?

[BobMcD]

"We can't say for certain that insects are the smoking gun, but we believe they were an extremely significant force in the decline of the dinosaurs," Poinar said. "Our research with amber shows that there were evolving, disease-carrying vectors in the Cretaceous, and that at least some of the pathogens they carried infected reptiles. This clearly fills in some gaps regarding dinosaur extinctions."

I'm failing to see any link between the rise of insects and the decline of dinosaurs. I accept that insects and their diseases were on the rise, and that plant life probably changed because of this. Still, though, we have a gap:

What about all the other life on earth?

I seem to recall being bitten by a tick once or twice in my lifetime. They're not dinosaur-exclusive.

Likewise, large animals other than dino's depended on that plant life, and many existed in astonishing numbers until the industrial revolution and gunpowder, etc.

For me to understand this, there really needs to be more explanation as to what fundamental differences killed off the dino's while mammals thrived under this same plague of insects.

A Book?

[whisper_jeff]

"...speculation is rampant in a book that gives cause to believe..."

Speculation? In a book? Get back to me when there's evidence in multiple books and scientific journals. Speculation in one book isn't cause to believe squat.

(Could biting insects have caused deaths? Of course but extinction? Highly doubtful and, as I said, until it's discussed more widely than speculation in one book, I'll file that theory away as nothing more than what it is - speculation in one book.)

Re:Reptile immune systems

[MozeeToby]

And what, exactly, do modern reptiles have to do with ancient dinosaurs? Almost all modern theories of dinosaur evolution state that they are more related to modern birds than modern reptiles. Furthurmore, most modern research (3 decades or more) indicates that at least the majority of dinosaurs were warm blooded.

Not necessarily that simple

[Moraelin]

Well, I don't think it's necessarily that simple. There are plenty of diseases that outright kill.

Probably the most obvious example is the bubonic plague, a.k.a., the Black Death. It eventually killed all 3 types of hosts involved in plague outbreaks:

- the rats (which were eventually replaced by a different and more robust species of rat, as, yes, the old one almost went extinct),

- the flea (the bacteria essentially plug its stomach, so it ends up perpetually hungry, sucking blood until it barfs it right back and infests a new host. Eventually it starves to death.)

- the humans

Early outbreaks of the Black Death killed 80% of the infected people and massively depopulated Europe. Nowadays you'd only have about 50% chance to die of it. Our immune system did evolve somewhat.

But if you combine it with other factors, e.g., a changing climate or whatever, and it could have driven a less resourceful species extinct. As I was saying, the black rats that were the co-hosts in those outbreaks did go pretty much extinct.

The bacterium itself, well, essentially the immense majority of those which caused such an outbreak, eventually died together with its hosts. You'd think that would be a very strong evolutionary pressure to evolve into something less suicidal. Essentially each outbreak ended up in a near wipe-out of the bacteria population. You have an advantage if you don't do that, no? But said evolution towards more benign versions just didn't happen. The humans evolved to have better chances of survival, but the bacterium seems to have stayed just as nasty as ever.

Basically what I'm saying is that there is no divine plan to save you, so to speak. The bacterium doesn't know whether it's heading towards extinction together with its hosts. As long as there are still _some_ available hosts, it didn't go extinct yet, and it can continue just as well.

Additionally, some bacteria can infect more than one host, or can survive decently in the ground without a host. For the latter, even killing all hosts immediately, still isn't really a problem. The former killing one of the hosts isn't much of an impediment either, as long as other hosts can survive (or breed faster than they're killed.)

So for example a hypothetical disease which could infest both dinosaurs and mammals, but only killed dinosaurs, could jolly well keep doing so ad infinitum.

Now I'm not saying that this is necessarily how the dinosaurs died out. Just that evolution works in perverse and mysterious ways.

Reptiles have great immune systems

[Comboman]

Reptiles actually have great immune systems. Crocodiles are frequently injured in territorial fights, yet their open wounds do not get infected in the less-than-antiseptic environments they live in. Scientist are currently studying them to try to figure out why their immune systems work so much better than ours. Then again, they are one of the few families of reptiles that survived the extinction, so maybe that had something to do with it.

Re:Three questions

[GargamelSpaceman]

Here's a wild ass guess that could explain it, but for which I have no evidence.

Meteor impacts and lava flows alter the earth's climate. In general this favors warm blooded creatures.

It also shakes things up in the plant world perhaps *causing* the explosion in flowering plants ( which actually happened first, meteors and volcano disasters or flowering plants, I don't know, this is just a wild ass guess with no supporting research )

The explosion in flowering plants and their insect symbiotes, also stimulates insect evolution. Sexual reproduction in plants creates a huge new set of insect poisons and insect niches, kicking insect evolution into overdrive as they adapt and change over ( a fairly short ) time. For a time there seemed to be a new disease carrying or food destroying insect evolving every (insert short period of time here).

Relative to Megafauna that typically lives long, insect and plant evolution can happen in a flash. The megafauna ( ie the large dinos ) die. Better able to evolve fast are small dinosaurs and mammals, however the mammals mostly win out because of their warm bloodedness which gives them the edge as temperatures fluxuate wildly because of the volcano eruptions..

I think even today long lived megafauna would adapt more slowly to a rapidly changing environment than small animals like rats and cockroaches. They may go extinct leaving empty niches for the remaining small life forms to evolve ( quickly since they are small and short lived ) to fill.

I don't think reptiles are inherently more primitive or less able to adapt than mammals. Immune systems evolve faster if each generation lives for a shorter timespan. If you are smaller, then your population can be bigger on a given landmass giving you more chances to evolve. That's what did the dinos in. Their size.

Insects resistance in mammals and birds

[DrYak]

Why wouldn't this also affect mammals? Is there an implication that dinosaurs had more primitive immune systems? Is any of this more than mere speculation?

Yes, indeed, Immunoglobuline E which are responsible for combating parasites are only found in mammals. Not in birds (the other groupe of dinosaurs' descendants). Thus we could speculate that dinosaurs laked them.
That's one less way to combat them.

As a side note, IgE are also responsible for allergic reaction in modern humans. Probably we aren't exposed to lots of parasites in the developed world - in most people the IgE system just stays idle, but in a few individual who had the misfortune to inherit the wrong genes, this system gets overzealous and tries to functions against things that are supposedly inoffensive.

I also would have thought dinosaurs had thicker skin, if for no other reason than having a lot more meat to hold together than the puny mammals of the time. Is this not a factor? Do modern day elephants and rhinoceroses suffer from insect infestations even tho they have thick skins?

Well that's a different factor but for an unobvious reason.
As modern birds and mammals aren't naked (for most of them. although a few evolved back to naked skin), they need to groom their fur (or feathers) and had evolved flexible backbones. (Which enable them to reach almost any surface with some member or another - even if it's a tail-used-as-a-fly-swater or a trunk). That also help them to bite and remove potential parasites, and made them more suited to survive to parasites.

Spines of dinosaurs seems a lot less flexible (don't need any when your skin doesn't require any maintenance).
Some species have even quite baroque decoration on their back (see Stegosaurus) that make them probably even less flexible than a modern day aligator, more like a turtle.

At least the turtle has a solid shell. But lots of dinosaurs would probably be left much more vulnerable to insects bites.

And lastly, I thought recent research had shown that the slow dying theory was just an artifact of the skimpy fossil record, that they did indeed die out very abruptly at the K-T layer. Is my memory wrong here?

Well, seems that every now and then a statistician comes up with a different interpretation of the few data we have available from that time. I really don't know which is currently the most popular

Re:birds

[MightyYar]

But an elephant can't reach it's back... and neither can many other large mammals. Of course, there are birds that love to ride around on them and eat any insect stupid enough to latch on. I guess there wasn't yet an equivalent?

Re:Three questions

[Convector]

It's more an issue of oxygen than gravity. Insects have a very primitive respiratory system. They basically just diffuse gases through their exoskeleton, so their size is limited by the oxygen content of the atmosphere. This was high during the Devonian, hence the 70 cm dragonflies mentioned by another poster. I also recall hearing about spiders that predated on those dragonflies, but I don't have any sources to back that up.

Re:Three questions

[jollyreaper]

Dragonfly fossils with 70 cm wingspans have been found.

Would they require just a higher oxygen content or also a thicker atmosphere to fly?

Re:Stupidity

[Anonymous Coward]

Dinosaurs were essentially restricted to megafauna, meaning they were much more susceptible to extinction than mammals and birds. Rather, they were probably as susceptible to extinction as recent mammalian megafauna. And look at how well they have been doing: in North America, South America, Australia, Europe, and most of Oceania almost all megafauna not introduced with humans has gone extinct. (Animals like bison, wolves, and bears have counterparts in Asia and may have migrated along with the humans.) The end of the Cretaceous had numerous land bridges, meaning species (and their diseases) probably mixed and may have weakened the populations enough that something like the Yucatan impact might have finished them off.

while treecroc is particularly frightening

[circletimessquare]

mother nature provided something far worse to have nightmares about:

sarcosuchus imperator

the crocodile the size of a city bus

eek

dinosaurs != humans (duh)

[gosand]

Uh, the species of rat which carried the Black Death did very nearly go extinct, and it wiped out one third of the population of Europe in just two years, in some areas as much as 60-75%. If that had been combined that with other pressures occurring simultaneously, like extreme changes in the environment, then yes, even two of evolution's greatest generalists could have been brought low.

I can't say I believe it, but I also don't find it inherently implausible.

Not to mention that dinosaurs wouldn't have been able to figure out what was causing their deaths the way humans did with the plague. If it were over an evolutionarily "short" period of time, their immune systems wouldn't have had time to evolve and protect them as a species.

Although, to say "dinosaur immune system" is kind of funny, since there are so many different kinds of dinosaurs spread out over such a long period of time.

Re:Three questions

[SpiderClan]

I thought the answer to the Parent's rhetorical was the dinosaur.

A bug the size of a Turkey wouldn't bite a mouse, it would either eat it or leave it alone. If it eats it, disease in the bug is a non-issue since the mouse is dead either way and this is simply the food chain to which both species have adapted.

If the turkeybug feeds on dino blood, though, the dinosaurs would not be adapted to death by mosquito on a large scale and would not have any defenses prepared should bug bites suddenly become deadly. This means that the advent of a disease being carried by these bugs is dangerous only to animals large enough that the bug can feed from it without killing it - dinosaurs in this case - even if the disease is deadly to reptiles and mammals. Small reptiles, of course, would be in the same situation as the mouse and wouldn't be bothered by the disease unless a brontosaurus fell on them.

Re:Yes

[b4upoo]

Can you visualize a skeeter with a snout fierce enough to puncture the hide of a dinosaur? Those skeeters must have been the size of blackbirds.

Re:Different effects

[Anonymous Coward]

Well, actually, yes. I you have a virus that targets a specific form of Windows, it would be fairly easy to mutate the virus so that it would that other forms of Windows as well.

Since the entire structure of Linux differs from all Windows species, a virus that could wipe out all of Windows would very probably have only a secondary effect on all other species. Of course, in a global ecology, all those other species would still suffer from collateral damage / fallout resulting from the destruction of 90% of the total population.

Now, where's that car analogy?