Wednesday, 26 August 2015

Oh Heck! A Fossil Out Of Place!

Life reconstruction of Gueragama sulamericana in its palaeohabitat.*
Reconstruction created by J. Csotonyi.
Fossil remains of Old World lizard discovered in the New World overturn long-held hypothesis of lizard evolution -- ScienceDaily

Normally, a headline about a long-held hypothesis about evolution being overturned would gladden the heart of any creationist more used to a constant stream of scientific papers showing creationism to be nothing more than an infantile fairy tale based on scientific ignorance. Is this J. B. S. Haldane's Cretaceous rabbit?

Well, no! But it is a Cretaceous lizard in the 'wrong' continent.

But there are a couple of small problems with this one; firstly it clears up something of a mystery in lizard evolution, and secondly, to try to make much of it, a creationist will need to accept a very old Earth, plate tectonics and the fundamental principle of evolution from a common ancestors. Well, either that, or revert to denialism and God did it! assertions as usual.

In contrast to religion, where new findings have to be fitted into old ideas or simply waved aside and discarded, and where the response to having them raised is more often than not, abuse, condescension and avoidance strategies, you can positively feel the thrill of excitement in the comments of the scientists involved, as they realise the discovery raises lots more questions to be answered.

As with many other scientific findings, this one raises a number of questions we haven't previously considered. This finding raises a number of biogeographic and faunal turnover questions of great interest to both paleontologists and herpetologists that we hope to answer in the future.

Tiago R. Simões, one of the authors.
This contrast if, of course because, unlike religions, which have sacred conclusions that cannot be challenged let alone revised, science is all about challenging ideas and revising earlier conclusions. There are few things more intellectually satisfying to a rational mind than changing it because the evidence has changed. That's the joy of finding things out.

This discovery is of a 80 million year old fossil of a stem acrodontan lizard in the 'wrong' geographical location. Gueragama sulamericana was found in Brazil in Late Cretaceous rock. The largest group of lizards, the iguanians, are divided into the acrodontan lizards that includes the chameleons and bearded dragons which dominate the Old world, and the non-acrodontan lizards, which includes iguanas, of the New World. The name 'acrodontan' comes from the way their teeth are fused to their upper jaws.

Iguanians are one of the most diverse groups of extant lizards (>1,700 species) with acrodontan iguanians dominating in the Old World, and non-acrodontans in the New World. A new lizard species presented herein is the first acrodontan from South America, indicating acrodontans radiated throughout Gondwana much earlier than previously thought, and that some of the first South American lizards were more closely related to their counterparts in Africa and Asia than to the modern fauna of South America. This suggests both groups of iguanians achieved a worldwide distribution before the final breakup of Pangaea. At some point, non-acrodontans replaced acrodontans and became the only iguanians in the Americas, contrary to what happened on most of the Old World. This discovery also expands the diversity of Cretaceous lizards in South America, which with recent findings, suggests sphenodontians were not the dominant lepidosaurs in that continent as previously hypothesized.*

Copyright © 2015, Rights Managed by Nature Publishing Group. Published under Creative Commons CC-BY license.

So, classical lizard evolutionary theory explained this distribution by assuming the two groups diverged when Gondwana split into Africa and South America, so, according to this theory, there should not have been acrodontan lizards in South America. Now that theory is having to be revised and it may be that iguanians of both groups had radiated before the breakup of Gondwana and that at least one early acrodontan became isolated on the South American continent. This then would mean the South American lizards evolved from two groups, not one.

South America remained isolated from the rest of the world for about 100 million years, until the Isthmus of Panama arose only about 5 million years ago and united it with North America and so, via an Alaskan-Siberian land bridge, with the Old World again.

Creationist often present these sorts of findings as a problem for science, even using them to try to discredit the entirety of science, especially geology, palaeontology and palaeobiology that they find most threatening. In reality, of course, they are not a problem at all for science because science has no precious dogmas. If the evidence forces science to revise and revisit its theories, then science has progressed and added to the sum total of human knowledge and our understanding of the world. No one is interested in holding wrong opinions or clinging on to refuted theories. This sort of finding is merely fine-tuning of our existing understanding.

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  1. I knew a genuine creationist a few years back and if he reads that story about the lizard fossil being on the wrong continent it will make his day. We would debate evolution and the mental gymnastics he would use to "prove" his point was frankly amazing. I hate to sound this way but in a wiser world people like him wouldn't be allowed to vote.

    1. I find it hard to believe that people who knowingly lie, even to themselves, to guard a sacred conclusion, are genuine. It certainly takes a special sort of arrogance to believe your opinions trump evidence and that evidence can be dismissed simply because it doesn't fit what you believe.


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