"transitional" turtle found

We're Sorry - Scientific AmericanPictures of one of the fossils and an artist rendition, plus:

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Researchers report in Nature today that the fossil indicates shells evolved as an extension of turtles' backbones and ribs.

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They conclude that the bones belonged to a Triassic turtle ancestor, which they named Odontochelys semitestacea, meaning "toothed turtle with a half shell."

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The newly discovered species sported a shelled belly and a little extra bone on its spine, supporting the theory that turtles' shells formed over eons as their backbones and ribs grew.

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Once again, adaptation of existing hardwareEnjoy.

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Rebel American Zen Deist
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Welcome to the fray, Cluim, Probably because creationists have asked for years for fossils of organisms with partially formed features, thinking that this is a necessary element of transitional development of what they conceive to be macroevolution.This is an organism with a partially formed feature - it only has the bottom shell and the center of the top shell.This not only fills the bill for a fossil with a partially formed feature, it actually demonstrates that evolution works by incremental steps with fully functional living organisms at every stage, and it shows that "macroevolution" is nothing more than "microrevolution" carried out over many generations. There is also no different mechanism, no different process, for "macroevolution" than we see, observe, document and agree about being involved in "microevolution" -- it is just the same evolution carried out over generations.The only reason you have different organisms, rather than all one kind of organism, is because of speciation -- where isolated populations evolve on different lines due to (a) different mutations within their subpopulations (b) no mechanism to share new mutations with the other population (c) different environment for each population means different selection operating on mutations -- until a point is reached where they do not see the other population as potential mates. Note that:

1. the evolution involved in each subpopulation is still "microevolution" and
2. once they have diverged into reproductively isolated subpopulations there is no mechanism to keep them from diverging further by additional variation and selection as they adapt to new and constantly changing environments, and finally,
3. by this process, repeated in every population of organisms as one generation follows the previous, every population of living organisms undergoes evolution ...

It is an ongoing process, and because variation is inevitable (mutations constantly occur), because isolation of subpopulations is inevitable (no species can cover the earth and still interbreed), and because environmental change is inevitable (long term climate changes), and because selection is inevitable (more young are produced every year than are needed to replace the parent population) ... evolution - the change in hereditary traits in populations from generation to generation - and speciation - the increased diversity of non-interbreeding populations - are inevitable. Unfortunately for you, nature is completely unimpressed with your opinion, nor is it restricted in any way from continuing to behave according to the natural laws of life, regardless of what you - or anyone - believe to occur or have occurred.Enjoy.

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Hello again Cluim, Excellent start. Pardon me if I quibble, but I don't see what your definition of "macroevolution" involves. What is "large" change compared to "small" change? Does it occur in one generation or over many?As a guide I would point to university definitions, such as this one from Berkeley University:

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The Definition:
Biological evolution, simply put, is descent with modification. This definition encompasses small-scale evolution (changes in gene frequency in a population from one generation to the next) and large-scale evolution (the descent of different species from a common ancestor over many generations). Evolution helps us to understand the history of life.

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The Explanation:
The central idea of biological evolution is that all life on Earth shares a common ancestor, just as you and your cousins share a common grandmother.

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Note that they divide small scale change as being within a breeding population, and that "large-scale evolution" occurs via speciation where subpopulations diversify from a parent "common ancestor" population.and this one from the University of Michigan:

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Definitions of Biological Evolution
We begin with two working definitions of biological evolution, which capture these two facets of genetics and differences among life forms. Then we will ask what is a species, and how does a species arise?

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Definition 1: Changes in the genetic composition of a population with the passage of each generation

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Definition 2: The gradual change of living things from one form into another over the course of time, the origin of species and lineages by descent of living forms from ancestral forms, and the generation of diversity

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Note that the first definition emphasizes genetic change. It commonly is referred to as microevolution. The second definition emphasizes the appearance of new, physically distinct life forms that can be grouped with similar appearing life forms in a taxonomic hierarchy. It commonly is referred to as macroevolution.

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So what we see is that "large scale change" occurs by "small scale change" within populations as they diverge from other populations. Within those millions of years you have genetic changes that are not as distinct. Often the early fossils of one "species" are not that different from the later fossils of a previous "species" - it is just that humans have drawn an arbitrary line to divide the fossils for ease of reference. In addition, evolution is not a steady state process, but occurs in fits and spurts, especially in response to environmental changes.Thus we see a fossil of an organism that is intermediate in form from a non shelled toothed creature to a shelled and toothless early turtle, an organism that demonstrates the accumulation of hereditary changes over time, or what evolutionary biologists define as macroevolution. Enjoy.Edited by RAZD, : hide off topic portion on human evolutionEdited by RAZD, : space

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Good stuff Cluim, Consider that an open-minded skeptic does not accept any position without reason, and is willing to discard any concept that is contradicted by evidence. We can always start a new topic on whatever interests you. If you want to discuss the issue of how much change is "large" change for instance, we could go through a review of the Dogs will be Dogs will be ??? thread.Enjoy.

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No problem Cluim, looks like we are crossing posts. Just remember that the way evolutionary biologists study evolutionary biology is with the terms defined within the field of evolutionary biology. If anyone tries to use a different definition for a term, then they are really talking about a different concept, and this leads to confusion. Using a wrong definition, then can lead to logically invalid conclusions, when mixed into a discussion.Enjoy.

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Rebel American Zen Deist
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