Turtle Evolution

Explore Evolution pitches turtle evolution as a topic that has no settled answers in eovlutionary science. Along the way, they deploy a quote from Scott Gilbert and cite another paper to make the point that scientists are researching the issue; they don't have a current complete answer.

Commenter "JAM" points out that the second citation is misused.

Quote (JAM @ July 18 2007,18:21)

Re quotation #24,

The second and third quotations aren't in the cited paper. In fact, this very cool paper supports a hypothesis that provides an explanation for the rapid evolution of the turtle's shell, directly contradicting the apparently manufactured quote:

"The recognition of a simple developmental mechanism, namely an epithelial-mesenchymal interaction, at the initiation of carapace development provides a basis for hypotheses about the rapid evolution of this body plan (Burke 1989b).

Burke, A. C. 1989b. Development of the turtle carapace: implications for
the evolution of a novel bauplan. J. Morphol. 199: 363–378.

Note also that the authors hypothesize which proteins are involved, which inductive relationships between tissues are involved, etc.

Clearly, this is another lie by omission, possibly compounded by lies of commission.

Wesley,

You should update your description of the turtle quotations from page 24, because it doesn't include the second paper that they quote-mined:

How the Turtle Forms its Shell: A Paracrine Hypothesis of Carapace Formation
JUDITH CEBRA-THOMAS et al. JOURNAL OF EXPERIMENTAL ZOOLOGY (MOL DEV EVOL) 304B:558–569 (2005)

They are still being completely dishonest, however. Here are the partial quotes from that second paper:

Quote

Because "the distinctive morphology of the turtle appears to have arisen suddenly," Gilbert and his colleagues argue that evolution needs "to explain the rapid origin of the turtle carapace [shell]."

The first in context:

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This reptile [Proganochelys] had the characteristic derived trunk morphology now associated with turtles. Thus, the distinctive morphology of the turtle appears to have arisen suddenly. We can propose a hypothesis that may explain at least part of how this might happen. The key innovation is to getting the ribs into the dermis. Once there, variation in the population might enable some individuals to use this heterotopic placement of ribs to form a shell. If they could form a positive feedback loop between the rib and the CR (e.g., through Fgf10 and Fgf8), they could co-ordinate rib and carapace growth. When the ribs undergo normal endochodral ossification, the BMPs would induce the costal bones that form the plate of the carapace. (This may involve overpowering natural inhibitors of BMPs that are secreted by the dermis.) This mechanism, wherein the displacement of a tissue allows it to induce structures at new locations, has been proposed by Brylski and Hall (’88) to account for the rapid emergence of the fur-lined cheek pouches of pocket gophers. The compatibility of our findings with those of the
turtle fossil record has been noted by paleontologists (Rieppel, ’01).

The second in context:

Quote

These observations indicate that the ribs act as initiation centers for the dermal ossification of costal bones. The ossifying regions of the dermis extend towards one another to eventually fuse. The data reported in the present report confirm and extend these observations and permit us to frame a hypothesis to explain the rapid origin of the turtle carapace.