Did insect bites hasten demise of dinosaurs?

Did insect bites hasten demise of dinosaurs?
James Randerson, London
January 8, 2008

THEY were the most imposing and terrifying creatures to walk the earth, but according to a new theory the dinosaurs might have been pushed towards extinction 65 million years ago by insects.

During the later part of the dinosaurs' dominion over the land, insects underwent an explosion in diversity, dealing a double whammy to the lumbering giants — they spread disease and contributed to a change of vegetation to which the plant-eating reptiles failed to adapt.

The hypothesis is made in a new book by entomologists George and Roberta Poinar. The former is a professor of zoology at Oregon State University.

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

In the gut of one biting insect preserved in amber — fossilised tree sap — from that era, the team has found the pathogen that causes the parasitic disease leishmaniasis and in another a type of malaria parasite that infects birds and lizards. By inspecting fossilised dinosaur faeces, the team also found parasitic microbes carried by insects.

Apart from spreading disease, the insects were busy pollinating flowering plants. These gradually supplanted seed ferns, cycads and gingkoes. If herbivorous dinosaurs could not adapt to this new diet they would have starved.

Ms Poinar believes the most popular theory for the dinosaurs' demise — that a meteorite impact changed the global climate — falls short because the extinction took too long.

"Other geologic and catastrophic events certainly played a role. But, by themselves, such events do not explain a process that in reality took a very, very long time, perhaps millions of years. Insects and diseases do provide that explanation."

This could be a fun story to discuss. I'm just wondering though:

1. "at least some of the pathogens affected reptiles" - yep, and maybe others affected the proto-mammals, who survived. As did smaller reptiles (yet the tiny dinosauria didn't?) and birds. I'm no extinction expert, but this seems a bit simplistic. Mind you, the insects changing the environment bit makes some more sense - might have been a bit too much for the bigger guys to bear (shades of megafaunal extinction in Australia? There's an argument in Quaternary circles suggesting that the big mammals which became extinct around the same time as humans first arriving on the continent might have been "encouraged" towards extinction by alteration of habitat through human use of fire - among other things such as hunting and climatic change...).

2. "Other geologic and catastrophic events certainly played a role. But, by themselves, such events do not explain a process that in reality took a very, very long time, perhaps millions of years..." - um, as far as I know (and I'm speaking as a geochronologist here - this is my job!), we don't have the chronological resolution to know whether the extinction took millions or thousands of years, or even days - we're talking about something that happened 65 MILLION years ago and the best we can do is date that to plus or minus 10%. So we can't pin it down. Palaeontologists may have more to say about dinosaur diversity towards the end of the Cretaceous - perhaps we should check up to see whether it was in decline, but that's not something I recall from my first year geology. I still reckon a monstrous meteorite wholloping the Earth is going to cause some severe climate and habitat change, regardless of what the bugs had been doing for tens of millions of years prior to that.

Happy presenting!
Kat F

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