Literaturdatenbank
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Scheyer, T. M., Sander, M. P., Joyce, W. G., Böhme, W., & Witzel, U. (2007). A plywood structure in the shell of fossil and living soft-shelled turtles (trionychidae) and its evolutionary implications. Organisms Diversity & Evolution, 7(2), 136–144.
Added by: Admin (01 Feb 2009 18:31:02 UTC) |
| Resource type: Journal Article BibTeX citation key: Scheyer2007 View all bibliographic details  |
Categories: General Keywords: Schildkröten = turtles + tortoises, Systematik = taxonomy Creators: Böhme, Joyce, Sander, Scheyer, Witzel Collection: Organisms Diversity & Evolution |
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| Abstract |
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The shell of soft-shelled turtles (Cryptodira: Trionychidae) can be characterised by a flexible bridge region, the loss of peripherals and a flattened carapace that is covered not with keratinous shields but with a leathery dermis. Here, we give a detailed description of the bone histology of this natural body armour that is unique not only among turtles but also among all known vertebrates. The flat bone elements have a sandwich-like morphology, with an internal and external compact bone layer framing inner cancellous bone. The external cortex is subdivided into two separate zones. The outer zone of the external cortex, which encompasses the ornamentation pattern typical for trionychid turtle shell bones, is comprised of lamellar bone. Similarly, the whole of the internal cortex is comprised of lamellar bone. The inner zone of the external cortex, however, consists of a highly ordered, plywood-like arrangement of structural collagen fibre bundles within the bone and skin of the shell. The orientation of the collagenous fibres also prescribes the orientation of the mineral phase of the bone, the hydroxyl-apatite crystallites. Strikingly, this peculiar fibre bundle arrangement strongly resembles artificial reinforced fibre-strengthened polymeric materials that combine superior mechanical strength with low weight. We hypothesise that the evolutionary success of soft-shelled turtles is tied to this plywood-like structure of the skin and bone. It may have been the key adaptation that allowed trionychids to greatly reduce and flatten their protective shell, resulting in decreased mineral needs for hard tissues, improved camouflage and hunting performance, biomechanical stability of the shell, as well as overall increased agility and short-term swimming boosts. Significantly, it also may have enabled more efficient cutaneous breathing while still retaining effective armour in both the fossil and Recent trionychid turtles.
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