Dinosaurs are reported to be extinct by the climatic consequences of an asteroid impact on Earth, some 60 million years ago. Of course this extinction did not happen suddenly and not all reptiles were affected in the same way. Some even did survive - as we still can see today - although they already were highly sophisticated, like turtles, lizards, crocodiles, etc. At the same time the warm-blooded species began their raise in the kingdom of animals. Would there be a coincidence and, if yes, what could it be?
From laboratory experiments with reptile eggs that were exposed to different incubation temperatures, we know now that their sex determination depends on the temperature level at incubation. There are several patterns, but to keep it simple one could say that at higher temperature females are formed, and at lower ones males. Or vice versa, depending on the species. Turtle females come out at higher temperatures, and the Leopard Gecko, the Lizard, the Crocodile and Alligator females at lower temperatures. Some reptiles are indifferent, like the Wall Lizards (Podarcis muralis) and the Iguana from Galapagos (Conolophus Subcristatus).
And now comes the hypothesis: Imagine a significantly cooler climate for a couple of centuries (or millennia?) due to the asteroid impact which would result in less abundance of food for the ubiquitous and high-consumer reptiles, the massive vegetarians and carnivores. Additionally, the relative lack of female hatchlings due to lower incubation temperatures would in turn result in less eggs produced in the next generation to compensate for the increased mortality rate due to higher competition for food and worse general conditions of life. Enough males to compete with, but lack of females to mate with and thus lack of offspring. The survivors that we can see today - like the Leopard Gecko, the Lizard and the Crocodile types - do make females at lower temperatures; however, the turtles do not... but weren't they migratory anyway and couldn't they move and hide away relatively fast(er) to warmer regions? Some other reptilians survived because they were indifferent to the changing temperatures. An intriguing hypothesis, maybe one day somebody will shed light on it.
At the same time the warm-blooded animals were feeling well at these cooler temperatures. They started to fill up the open areas, proliferated and developed to higher species... as we know.
Michel
Sources:
- Warner DA, Shine R (2008). "The adaptive significance of temperature-dependent sex determination in a reptile". Nature 451: 566-568. doi:10.1038/nature06519. PMID 18204437.
- Temperature-Dependent Sex Determination in the Leopard Gecko, Eublepharis macularius (BRIAN E. VIETS, ALAN TOUSIGNANT, MICHAEL A. EWERT, CRAIG E. NELSON, AND DAVID CREWS Indiana University, Bloomington, Indianu 47405 (B.E.V., M.A.E., C.E.N.);
University of Texas, Austin, Texas (A.T., D.C.))
- The Mechanism of Temperature Dependent Sex Determination in Crocodilians: A Hypothesis (DENIS C. DEEMING and MARK W. J. FERGUSON Department of Cell and Structural Biology, The University of Manchester Coupland III Building, Manchester, M13 9PL, England)
- Bull, J. J. (1980). Sex determination in reptiles. Quart. Review of Biology 55: 3-21.
- Wikipedia