Ker Than
for National Geographic News
July 9, 2009
Turtles develop their upper shells thanks to a unique feat of "origami" with their muscles and bones that occurs while the reptiles are still in their eggs, a new study has found.
In most other animals with backbones, the shoulder blade lies outside the ribs, explained study team leader Shigeru Kuratani of Japan's RIKEN Center for Developmental Biology.
But in turtles, the ribs grow over the shoulder blades and fuse to form the upper shell.
To figure out when exactly turtles start to develop differently, Kuratani and his team examined various stages of embryos of Chinese soft-shelled turtles, chickens, and mice.
Initially, turtle embryos develop like the birds and mammals do, the team found.
But as turtles mature, their bodies undergo an unusual folding process during which certain portions of their skeletons and muscles tuck in on themselves.
This folding causes some bones and muscles to connect in ways that they don't in other animals.
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Read more here/Leia mais aqui.
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Science 10 July 2009:
Vol. 325. no. 5937, pp. 154 - 155
DOI: 10.1126/science.1177446
PERSPECTIVES
EVOLUTION:
How Did the Turtle Get Its Shell?
Olivier Rieppel
In On the Origin of Species, Darwin asserted: "Monstrosities cannot be separated by any clear line of distinction from mere variations" (1). But encased in its shell, the turtle appears to be just such a monstrosity. No other animal, living or extinct, has its body enclosed within a bony shell that is similarly constructed in its entirety. Over the last few years, developmental biologists have started to tackle the question of how the turtle shell evolved. On page 193 of this issue, Nagashima et al. (2) provide a detailed account of muscular and skeletal changes during the embryogenesis of the modern turtle, and in drawing parallels between these early developmental changes and what is seen in ancestral turtles, provide insights into how turtle shell evolution might have occurred.
Rowe Family Curator of Evolutionary Biology, Department of Geology, The Field Museum, 1400 South Lake Shore Drive, Chicago, IL 60605–2496, USA.
E-mail: orieppel@fieldmuseum.org
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Science 10 July 2009:
Vol. 325. no. 5937, pp. 193 - 196
DOI: 10.1126/science.1173826
REPORTS
Evolution of the Turtle Body Plan by the Folding and Creation of New Muscle Connections
Hiroshi Nagashima,1 Fumiaki Sugahara,1,2 Masaki Takechi,1 Rolf Ericsson,1,* Yoshie Kawashima-Ohya,1,Yuichi Narita,1, Shigeru Kuratani1,
The turtle shell offers a fascinating case study of vertebrate evolution, based on the modification of a common body plan. The carapace is formed from ribs, which encapsulate the scapula; this stands in contrast to the typical amniote body plan and serves as a key to understanding turtle evolution. Comparative analyses of musculoskeletal development between the Chinese soft-shelled turtle and other amniotes revealed that initial turtle development conforms to the amniote pattern; however, during embryogenesis, lateral rib growth results in a shift of elements. In addition, some limb muscles establish new turtle-specific attachments associated with carapace formation. We propose that the evolutionary origin of the turtle body plan results from heterotopy based on folding and novel connectivities.
1 Laboratory for Evolutionary Morphology, RIKEN Center for Developmental Biology, 2-2-3 Minatojima-minami, Kobe 650-0047, Japan.
2 Graduate School of Science, Kobe University, Kobe 657-8501, Japan.
* Present address: Department of Biological Sciences, Macquarie University, 2109 Sydney, Australia.
Present address: Laboratory of Immunology, Department of Health Pharmacy, Yokohama College of Pharmacy, 601 Matano-cho, Yokohama 245-0066, Japan.
Present address: Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, CH-4058 Basel, Switzerland.
To whom correspondence should be addressed. E-mail: saizo@cdb.riken.jp
