I’m an ornithologist by trade (and birds are dinos after all). But I was first turned on to biology by seeing T. rex at the American Museum in NY when I was five. I still read a lot about dinos and paleontology in general.
Bakker, along with most other paleo folks who actually handle fossils, does not think much of the asteroid hypothesis. He pointed out that the creatures that went extinct were more mobile/migratory. He pointed out that land bridge formations between previously isolated areas are also precursors to extinction events. The idea is that introduced predators and (much, much, much more effective) pathogens carried by migrants would preferential extinctify the larger, migratory animals and leave the smaller, stay- around-the-pond type animals alone.
I prefer this theory for the late Pleistocene North America Extinction event. (How long before somebody comes up with an impact crater for that?) A nasty little pathogen like brucellosis (sp?) is more likely a cause of extinctions than a few Clovis people stabbing every mega fauna creature they could find.
While I often find Bakker interesting, his idea of his about disease playing a major role in the K/T extinction event has to be one of the least plausible things in The Dinosaur Heresies.
A few counter arguments:
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The late Cretaceous continents were in the process of becoming less connected, not more. Gondwanaland was in the middle of its breakup; Africa, Madagascar, and India had already split off from the South America/Antarctica/Australia land mass. IIRC, Europe was still isolated from east Asia. All these places had dinosaurs, so the “increased contact” idea cannot apply to them. Bakker makes much of the migration between east Asia and western North America, which did occur at this time, but this is only one small part of the whole picture. It’s almost impossible to look at a map of the Late Cretaceous world and give Bakker’s idea any credence as a general explanation for the extinction of dinosaurs or other terrestrial forms.
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Of course, Bakker’s idea of migration cannot apply to extinctions in marine life at this time, including sea reptiles, ammonites, reef ecosystems, and some forms of plankton. Bakker contends that these extinctions were due to the draining of shallow epi-continental seas at this time, ignoring the fact that many areas of shallow seas remained and that the extinctions also affected deep-water forms.
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There is relatively little evidence of introduced disease actually causing extinction of individual animal species, let alone a diverse fauna including many taxonomic groups. No matter what the disease, usually at least a few individuals are resistant and survive to restore the former population. Even with massive human introductions of plants and animals around the world since 1492, there are few actual cases of disease producing extinctions. (Possibly avian malaria in the Hawaiian Islands, and a few others. Yes, human populations in the New World were decimated by smallpox and other European diseases, but they did not become extinct.)
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A more recent case of faunal interchange occurred when the Central American land bridge was formed about 3 million years ago. Giant Ground Sloths etc. moved north and Mammoths and many others moved south. While some forms did become extinct in the course of the interchange (e.g. South American marsupial carnivores) many members of the two faunas existed side by side for several millions of years. Most of those that are now extinct died out at the end of the Pleistocene, not during the initial phase of interchange, as would be expected if disease were involved.
In short, Bakker’s discussion of the K/T event in The Dinosaur Heresies is extremely misleading and inaccurate. He picks out a few examples of periods when migration and extinctions may have coincided, but ignores many others (e.g. the Ordovician, Devonian, and Triassic mass-extinctions). I’m not sure about the background of Bakker himself, but I find that many paleontologists have an extremely poor grasp of ecology, perhaps because many of them are trained as geologists rather than biologists.
Regarding the late Pleistocene extinctions, neither faunal interchange nor climate changes alone can explain the pattern. The northern icecaps came and went several times, and previous periods of intercontinental migration across Beringia and of rapid climate change failed to produce massive extinctions. And of course, such migrations cannot explain the extinction of the Australian megafauna either. The best explanation for most of the Pleistocene extinctions seems to be climate change in combination with the migrations of super-predator called Homo sapiens. This seems a lot more likely than a super-disease that would wipe out giant ground sloths, glyptodonts, mammoths, horses, toxodonts, liptoterns and artiodactyls at the same time.
I just wanted to add that Professor Stephen Falken once remarked that “no animal weighing more than 50 pounds survived thru the Great Extinction 65M years ago.”
Do you mean “land animals”? What about the crocodiles (and kin)? Or sharks?