Tuesday, August 14, 2012

Tectonics and dinosaur evolution?

Recently, a group of paleontologists published a fascinating paper entitled "Mountain Building Triggered Late Cretaceous North American Megaherbivore Dinosaur Radiation."  You can read the entire text of that analysis by Terry A. Gates, Albert Prieto-Marquez, and Lindsay E. Zanno by by following the link in the upper-right portion of the screen at the site above.

Their thesis proposes accelerated speciation among certain herbivorous dinosaurs in North America (duck-billed saurolophines and horned ceratopsids) caused by increased geographic isolation brought on by the rise of mountain ranges and inland sea-barriers caused by tectonic forces.

The paper's authors argue that "Late Cretaceous orogenesis commenced weather patterns" which changed "annual temperatures and rainfall patterns" that would then change "local plant composition"  (6).  At the same time, these changes created isolated regions as "orogenic uplift and basin segregation" prevented plants and animals from migrating along with the changes in geography and weather.  They conclude that: "Modified plant communities may have acted in combination with potential geographic barriers (such as the Castelgate river / delta system and Wind River Mountains) to spur ecological barriers to herbivorous dinosaurs, preventing gene flow, and creating endemic centers of megaherbivorous dinosaur evolution."

The scientists provide fossil evidence to back up their thesis, arguing that various species evolved into other species in a certain progression that shows greater "radiation" or speciation in areas that were isolated by the tectonic uplift proposed by their geological timeline (see chart below, from page 6 of the paper).

While the paper displays a well-argued thesis with supporting evidence, it is argued within a specific geological paradigm that may in fact be completely incorrect. 

There is a tremendous amount of evidence suggesting that the tectonic theory is wrong.  The tectonic theory was an important step forward, because it was better than the theories that came before it, and it opened our eyes to the fact that the plates did at one time slide, but it is quite possible that instead of sliding gradually and continuously, they slid catastrophically just one time, and created most of the geology we see today during that one catastrophic event.

This radically different geological paradigm, proposed by Dr. Walt Brown and called the hydroplate theory, may be ridiculed or ignored, but so was Alfred Wegener's theory of continental drift during his lifetime.  If the tectonic theory as it is understood today is incorrect, then the careful logical progression of the authors of the above paper, while not incorrect in and of itself, is built upon a flawed foundation.  It is a way of explaining the evidence, but there are other ways to explain the evidence as well.

If the hydroplate theory is correct, then the mountain ranges we see today were all thrust upwards rapidly and violently, while the earth was still covered with mud-laden water.  When the mountain ranges rose and water drained powerfully away, many large animals were trapped (see the discussion of the numerous fossil whales of the Atacama desert, on the Pacific side of the Andes Mountains).   It is quite possible that the number and variety of species is indeed influenced by geology and mountain ranges, but that their number and prevalence is influenced by the way that water flowed off of those ranges and buried large animals, not by increased speciation caused by imagined evolutionary mechanisms in isolated areas.

This type of discussion, however, is exactly what science should be all about -- looking at the evidence and proposing different explanations that appear to fit the evidence that is available, and then arguing the merits of the various theories.  Pointing out that different geological paradigms will lead to very different conclusions is not intended to be in any way derogatory -- to the contrary, I believe it is very important to acknowledge the impact of different geological theories and to argue about which ones appear to best fit the evidence.

Therefore, I applaud the work of the paper cited, even though I believe that the geological assumptions underpinning its arguments will one day be found to be in need of correction.

For more discussion of this recent paper, see this article entitled "Dinosaur boom linked to rise of Rocky Mountains," which contains some great additional quotations from the paper's authors describing their theory.