Pterosaurs are the flying reptiles of the Mesozoic. They are closely related to dinosaurs and part of the archosaurs, along with dinosaurs, and crocodilians.

My hypothesis is that smaller pterosaurs carried diseases which killed the larger pterosaurs. This is normal in closely related groups of animals. But, in the cretaceous the birds out competed the smaller pterosaurs and drove them into extinction. With the disease carrying smaller pterosaurs out of the way the larger pterosaurs were able to grow larger. So the pterosaurs evolved larger and larger species until the last of them, quetzalcoatlus reached enormous size. Their wingspans have been estimated at between 12 and 18 meters, or 40 to 59 feet. It is widely believed that Quetzalcoatlus was the largest organism ever to fly.

The birds could not compete with the pterosaurs at the very large sizes because very large birds would have had to deal with the diseases carried by the smaller birds.

Diseases Caught From Close Relatives A Common Problem

If you live in Europe remember we Americans use the word moose for what you call an elk. What we call elk are a close relative to your red deer.

Particularly for Americans the case of the white tailed deer is close to home, but our closest relatives, the great apes, provide another example that is close to home for everyone. The great apes are suffering from our diseases, and in danger of extinction. We are not necessarily smaller than they, but we are very common, which makes us a prime target for parasites. Once the parasites have adapted to us that also makes them well adapted to our close relatives, which is one reason that the great apes are in danger of extinction.

What the above examples illustrate is that this is not a small or obscure phenomena. It is a common and very powerful phenomena that profoundly shapes the biological world, particularly the larger organisms.

Living Fossils Often Live Large

The giant red wood tree and the sequoia are living fossils, their closest smaller relatives live in China, safely removed from California where the giant red woods live.

Similarly, the largest freshwater fish in North America is the Alligator Gar another living fossil. The gars as a group are large predatory living fossils.

In South America we find much the same story. The largest freshwater fish is the Arapaima, a large predatory living fossil. The Arapaima has no real close relatives, but its closest relatives in South America are also large predatory living fossils the arowanas.

The sturgeon is similar, it is not predatory, but sturgeons are large to very large living fossils, and among the largest fresh water fish.

In the ocean the large and predatory roles for fish are often held by another group of living fossils, the sharks.

One could give many more examples.

The Bigger Picture

Wanted Professor or Graduate Student to Co-publish This

Several of the biology professors at the University of California at Davis said I should try to publish the idea that is at the center of the above. They even suggested a particular academic journal.

Currently I am a substitute teacher and staff member for the local public schools. Formerly, I was a full time economics instructor for seven semesters in New York City at St. John's University. I have a B.A., M.A. and Ph.C. in Economics from the University of California. A Ph.C. means I was advanced to candidacy on a PhD, in more common terms all but dissertation, A.B.D. You can read more about my qualifications on my biology index page.

If you are not a biologist, well you may be able to experience the thrill of knowing that you knew about about a major advance in biology before the biologists. Link here and contribute to a major break through.

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