MECHANICAL PROPERTIES OF THE CHITIN-CALCIUM-PHOSPHATE "CLAM SHRIMP" CARAPACE (BRANCHIOPODA: SPINICAUDATA): IMPLICATIONS FOR TAPHONOMY AND FOSSILIZATION

• Published in: Journal of crustacean biology 2015-03, Vol.35 (2), p.123-131
• Main Authors: Astrop, Timothy I., Sahni, Vasav, Blackledge, Todd A., Stark, Alyssa Y.
• Format: Article
• Language: English
• Subjects: Anatomy; Arthropoda; Branchiopoda; Decapoda; Spinicaudata
• ISSN: 0278-0372; 1937-240X
• DOI: 10.1163/1937240X-00002332

Spinicaudata (colloquially 'the clam shrimp') are freshwater branchiopod crustaceans that occur worldwide in lakes and temporary pools. The spinicaudatans are easily recognizable by their bivalved carapace which is unusual among arthropods in that it is subject to only partial molting. During ecdysis (molting), the outer surface of the carapace is not shed, resulting in the retention of the ontogenetic record of an individual through distinct growth-rings representing each molt. When this unusual feature is considered alongside the interesting chemical properties of the carapace, "clam shrimp" present an interesting biological material not seen anywhere else: a multi-laminar calcium-phosphate-chitin composite. In addition, the carapace survives numerous destructive taphonomic processes (including transport, decay, compaction, and desiccation) to become the dominant body component of Spinicaudata preserved in their 380 million year fossil record. Understanding the mechanical properties and chemical composition of this structure may not only aid in a better understanding of the evolutionary history of this group but also facilitate efforts to develop novel materials that retain functional material properties even in harsh aquatic conditions. Therefore, this study aims to provide quantitative information about the composition and mechanics of this unique and interesting biological material and help predict possible biases in the fossilization of different species of Spinicaudata to aid future palaeontological research.