At least 50 percent of the world's species, including the dinosaurs, perished 65 million years ago. A large meteorite struck Mexico's Yucatan Peninsula around the same time, and most scientists blame this impact for the mass extinction.

Yet there is nothing that directly links meteorite impacts with the extinction of entire species. Scientists can recite a long list of the devastating environmental consequences of a large meteorite impact, but they cannot prove these effects have led to the simultaneous loss of life around the globe. Answering the question of how and why such a large variety of species died out at the same time is one of the greatest mysteries in paleontology.

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It’s encouraging that more voices are questioning the single-bullet theory of the mass K-T extinction. One thing I see not included in the article is the belief that Dinosaurs were “rib-breathers” rather than diaphragm breathers. Unlike mammals, it is believed (by study of fossils) that the Dinosaurs drew air into their lungs by autonomic articulation of their ribs and not a diaphragm. This method of respiration is less efficient. A large drop in the oxygen content or an increase in other gases could have slowly killed off many of the plants of the period, not to mention the extinction of the Dinosaurs. Smaller relatives of the dinosaurs and even animals that had alternative sources of oxygen may not have been threatened or not threatened to the same degree.

We can't know how similar dinosaurs were to current reptiles, but it's not unreasonable to assume they may not have been too different. The sex of reptiles is not determined by chromosomes, but by the temperature during the gestation of the eggs. A two degree Fahrenheit difference in the average temperature can make the vast majority of the offspring the same sex. Crocodilians date back to the dinosaurs and are subject to temperature sensitivity.

Twenty or thirty years of cold weather could be enough to cause the extinction of a species. Such a temperature change would also affect the oceans, with the same results for the ocean-dwellers. Colder waters also hold more oxygen, perhaps enough to add to the impact on the land dwellers (pure speculation on my part).

There doesn't need to be a single direct cause of the mass extinction. A large impact would cause numerous changes to the global environment, and it usually doesn't require a lot of change to destroy an ecology.

If dinosaurs' sex determination was sensitive to temperature, the cold would reduce the density of populations. A lower oxygen availability combined with the lethargy likely from the lower temperature would reduce their ability to migrate and hunt. Even if some of the dinosaurs were partially warm-blooded, the colder temperature would still have a deleterious effect, by requiring more energy to maintain their temperature.

The cold would also provide a tremendous evolutionary advantage to the mammals, some of which must have been ovivorous, causing even more pressure.

Could an increase in background radiation also add to the problem? Meteors that fall to Earth often deposit large amounts of platimun group metals of which iridium is a member. Such an increase may be nominal to most life forms.



I could not agree with you more. Considering the dinosaur population was already in decline, their extinction is not a case of one simple cause.

Of equal importance to the fact that cataclismic events can cause mass extinction, is the fact that they also cause big shifts in the direction of evolution for many of the species which go on to survive. I would be interested in finding out what evolutionary effects were initiated by that 64 million-year-ago event?
There have been many cataclismic events leading to extinctions and evolutionary shifts over the millions of years of history of life on earth. Of particular note is the more recent event which apparently took place sometime around 8 million-years-ago. That event led to mass extinctions, and may also have sparked the evolution of early man-- i.e. the development of upright posture, and the subsequent use of our free hands to manipulate tools, and selecting also for increased brain size, and so on.... Interesting how these "chance" cataclismic events, when they happen at just the right time, and place, can lead to tremendous changes in the constitution and development of life on a planet.
I believe we owe our own existence, and our ultimate development towards self-awareness, to chance events such as these. One thing leads to another, as it just so happens. We are largely a result of chance events, where probability coexists with time.

While off topic, I'm most curious about slightly recent reports of certain dinosaurs in africa, and south america. I believe there were sighting of Pterodactyls digging up graves, and Brachiosaur in swamps, supposedly tipping over boats. Anyone heard anything of the subject?