Morphology: The Quest To Explain A Turtle’s Shell

Turtle evolution has been the focus of this week’s Journal of Science and like always origins makes an interesting discussion. Among evolutionary biologists, there are two different views: the transformationists and the emergentists.

Now transformationists believes there is a “morphological evolution as a result of natural selection working on variation.” On the other hand, emergentists, believe in looking for developmental stages of turtles to look for clues about their evolutionary history.

When it came to explain Odontochelys researchers took the “emergentists” approach…

“Nagashima et al. observed that during early development of the Chinese soft-shelled turtle Pelodiscus sinensis (see the figure), translocation of the ribs to a position outside the shoulder blade involves folding of the lateral body wall along a line that defines the later formation of the carapacial ridge.  This folding restricts rib growth to the horizontal plane of the carapacial disk and also maintains the shoulder blade in its superficial position relative to the folded body wall.”

“This organization is thought to characterize ancestral turtles.  Some muscles that develop from the muscle plate that is associated with the folding body wall even retain their “ancestral connectivities” in the adult.”

“Nagashima et al. hypothesize that in this ancestral turtle, the carapacial ridge was differentiated only along the side of the trunk, remaining incomplete anteriorly and posteriorly.  Only later during the evolution of turtles would the carapacial ridge be completed, causing the anteriormost trunk rib to grow across the shoulder blade and localizing the latter inside the ribcage.”

Not surprisingly, the researchers in this paper already were focused on Odontochelys being a ‘missing link’ rather than a specialized form. More glory in ‘missing links’ than specialized forms. They on with their explanation which turns out to be a very confusing statement…

“Odontochelys reconstructed by Li et al. resembles the embryonic modern turtles in some respects (Fig. 2, A and E, and Fig. 4), and this animal may represent an ancestral state.  The Odontochelys-like, ancestral pattern is still retained in the first rib in modern turtles (Fig. 4, right).”

“Although it remains to be seen whether latissimus dorsi of Odontochelys was shifted rostrally (Fig. 4, middle), its pectoralis would have established a new attachment to the dorsal aspect of the plastron (Fig. 4, middle).”

“Thus, the developmental sequence of P. sinensis may not wholly recapitulate the suggested evolutionary sequence of turtles.  Nevertheless, the above suggests that the dorsal arrest of ribs can now be assumed to have taken place by the common ancestor of Odontochelys and modern turtles, and in the latter, the completed CR would have allowed for emergence of the carapace (Fig. 4, bottom).”

“The modern turtles have acquired their unique body plan by passing through an Odontochelys-like ancestral state during embryonic development.  Our embryological study may help to explain the developmental changes involved in both the pre- and post-Odontochelys steps of turtle evolution, from an evolutionary developmental perspective.”

This is like having your cake and eating too. They explain away their Biogenetic-Law, while using it to explain turtle evolution! This is so bad, I believe even Stephen Jay Gould would have been appalled when reading Haeckelian logic.

The funny part is, Recapitulation was rejected by Darwinists long ago, because even they realized there is no physical evidence that shows embryos having the ability to retain any memory of their assumed evolutionary past. But here it is being published in Science!

It’s like trying to explain chickens and turtles are sisters despite their radically different skeletons. However, there is one thing clear, observations are not matching up with claims evolutionary biologists are making on turtle evolution!

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2 thoughts on “Morphology: The Quest To Explain A Turtle’s Shell

  1. Michael: “Turtle evolution has been the focus of this week’s Journal of Science.”

    Hm. First sentence, two errors. First, the name of the publication is “Science,” not “Journal of Science.” Second, the entire issue contains only one research report, along with a summary of that report, which is a common practice in “Science.” This is not a focus. Oh, sorry—all you saw was the cover of the magazine.

    Michael: “Now transformationists believes [sic] there is a “morphological evolution as a result of natural selection working on variation.” On the other hand, emergentists, believe in looking for developmental stages of turtles to look for clues about their evolutionary history.”

    If you are attempting to use this report as evidence against evolution, you fail. It’s like saying, “This airplane crash could have happened when the altimeter quit, or when a hydraulic line ruptured. Because we don’t know which alternative is true, the crash did not happen at all.”

    The question, which is not yet resolved, is, what is the nature of the unit upon which natural selection operates? The older view was adult morphological structures, entirely. Evo-devo came along a couple decades ago, and posited developmental processes as a subject of selection. Either, neither, or both may turn out to be the case. None of these cases, however, casts any doubt upon whether evolution occurred.

    Michael: “They explain away their Biogenetic-Law, while using it to explain turtle evolution! This is so bad, I believe even Stephen Jay Gould would have been appalled when reading Haeckelian logic. The funny part is, Recapitulation was rejected by Darwinists long ago, because even they realized there is no physical evidence that shows embryos having the ability to retain any memory of their assumed evolutionary past. But here it is being published in Science!”

    Here, the ICR—probably deliberately—misunderstands the now discredited Haeckelian “recapitulation” or “biogenetic” law. This stated that embryos recapitulate the adult forms of their ancestors. What is still true, however, and has been confirmed by observations over the past 20 years, is that embryos go through many of the features of the _embryos_ of their ancestors, then modify them at later stages of development. For example, a creationist would predict that the human embryonic heart forms and functions like a tiny human heart, then merely grows to the proper size. Yet this is not how it develops. The human embryonic heart first forms with a single chamber, like that of an embryonic worm. Later, it grows a second chamber, like the heart of an embryonic fish. In a third stage, it adds a third chamber, a la reptiles. Finally, it generates the fourth chamber of the adult human heart. As another example, a human embryo forms a yolk sac like those of their egg-laying ancestors, but then fails to switch on genes for producing the nutritive content of the yolk. A human embryo devotes considerable time and energy generating the long tail of its ancestor mammals, and then spends more time and effort to destroy it before birth. Stephen Jay Gould understood this; you do not.

    Michael: “They [sic] on with their explanation which turns out to be a very confusing statement”

    Only because it was written for readers who have some qualifications in biology. The article was in “Science,” not in “Biology for Dummies.” And, again, this post follows the pattern of third-hand accounts—from primary source to review article to ICR apologetic to Michael. Calls up an image of rabbits eating their droppings.

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