November 29, 2008 | David F. Coppedge

An Evolutionary Fly in the Turtle Soup

A new fossil turtle was found.  Is it a missing link?  That depends on whether you believe the popular press or the scientists.
    National Geographic News and Science Daily both led off with the missing link angle, complete with an artist reconstruction of the fossil turtle found in China named Odontochelys.  “Since the age of dinosaurs, turtles have looked pretty much as they do now with their shells intact, and scientists lacked conclusive evidence to support competing evolutionary theories,” Science Daily announced, leading up to the tour de force: “Now with the discovery in China of the oldest known turtle fossil, estimated at 220-million-years-old, scientists have a clearer picture of how the turtle got its shell.”  Little in the way of controversy was reported to alter this statement.  It’s another evolutionary success story.
    Nature,1 however, titled its piece, “Turtle origins out to sea.”  This isn’t a missing link, argued Robert J. Reisz and Jason J. Head: it’s a challenge to evolutionary theory.  “The evolutionary relationships and ecology of turtles through time, and the developmental and evolutionary origins of the shell,” they said, “are major controversies in studies of vertebrate evolution” and this fossil does not resolve them.  It apparently has an undershell but not a top shell.  It has a full set of teeth instead of a beak.  Like many fossils of extinct animals, it has some features that appear primitive and others that appear derived (evolved).  The discoverers put forth one evolutionary interpretation: “The authors infer, therefore, that the plastron evolved before the carapace, reflecting the timing of shell ossification during embryonic development in living turtles.”  Reisz and Head, however, had a different take:

Although this evolutionary scenario is plausible, we are particularly excited by an alternative interpretation and its evolutionary consequences.  We interpret the condition seen in Odontochelys differently � that a carapace was present, but some of its dermal components were not ossified.  The carapace forms during embryonic development when the dorsal ribs grow laterally into a structure called the carapacial ridge, a thickened ectodermal layer unique to turtles.  The presence of long, expanded ribs, a component of the carapace of all turtles, indicates that the controlling developmental tissue responsible for the formation of the turtle carapace was already present in Odontochelys.  The expanded lateral bridge that connects the plastron to the carapace in other turtles is also present, implying that the plastron was connected to the laterally expanded carapace.  Thus, an alternative interpretation is that the apparent reduction of the carapace in Odontochelys resulted from lack of ossification of some of its dermal components, but that a carapace was indeed present.
    This interpretation of Odontochelys leads us to the possibility that its shell morphology is not primitive, but is instead a specialized adaptation.  Reduction of dermal components of the shell in aquatic turtles is common: soft-shelled turtles have a greatly reduced bony shell and have lost the dermal peripheral elements of the carapace.  Sea turtles and snapping turtles have greatly reduced ossification of the dermal components of the carapace, a condition similar to that seen in Odontochelys.

If Reisz and Head are right, then, this is an advanced, specialized turtle.  The absence of the carapace is a secondary loss – not a turtle on the half shell evolving into a fully-housed modern turtle.  “Given the similarities between its shell morphology and early growth stages in living turtles, a simple truncation of carapace ossification, in which the adults retained juvenile features (paedomorphosis), could have been a developmental mechanism in the evolution of the reduced carapace.”  Loss of a feature is not the kind of evolution Darwin envisioned.  Somehow, they found a way to put a positive spin for Darwin on this fossil anyway:

Regardless of the primitive or derived nature of its shell, Odontochelys is in evolutionary terms the most ‘basal’ turtle yet found.  Its discovery opens a new chapter in the study of the origins and early history of these fascinating reptiles.  Both interpretations alter our views of turtle evolution: Odontochelys either represents the primitive ecology for turtles, consistent with the hypothesis that the turtles’ shell evolved in aquatic environments, or it represents the earliest turtle radiation from terrestrial environments into marine habitats.  Either way, these ancient turtles demonstrate yet again the value of new fossil discoveries in changing our understanding of vertebrate history.

Both interpretations may alter their views of evolution, therefore, but evolution itself was never subject to falsification – no matter how opposite the two interpretations.

1.  Robert J. Reisz and Jason J. Head, “Paleontology: Turtle origins out to sea,” Nature 456, 450-451 (27 November 2008) | doi:10.1038/456450a.
2.  Li et al, “An ancestral turtle from the Late Triassic of southwestern China,” Nature 456, 497-501 (27 November 2008) | doi:10.1038/nature07533.

Aren’t animals with a full set of teeth more advanced than those with just a beak?  Teeth are extremely complicated structures that must develop according to a strict timeline and fit on the top and bottom.  The beak on most turtles works well for them, but how can they say that this is evolution?  Look at all the problems that remain: they don’t know if turtles evolved as land animals or aquatic animals (see the 11/22/2008 story last week).  They don’t know if this fossil was primitive or advanced.  And they wonder why turtles have not changed significantly since the age of dinosaurs.  Where is the evolution?
    They confess, as the authors of the original paper stated, that “The origin of the turtle body plan remains one of the great mysteries of reptile evolution.”  One proposed intermediate that is subject to multiple interpretations is not going to help.  The fossil record should be filled with intermediates.  This species was apparently happily playing in the water, fully adapted to its habitat, not evolving like the evolutionary story you just heard.
    Evolutionists arrange their scientific explanations so that they can’t lose.  Why do they always get their explanations published?  Their controversies can consist of opposite stories: It’s a transitional form!  No it isn’t – it’s an advanced, specially adapted animal!.  No matter what, alternative explanations are never even heard.  Why do they always shut out their critics?  Because they have mastered the art of Calvinball: change the rules dynamically so that Charlie always wins.  Gag if you think this is a bad way to do science.

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Categories: Fossils, Marine Biology

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