30 D5. Paleontology (Posters)

Tuesday, 17 April 2018
8:00 AM - 5:30 PM
First Floor Lobby

RAMAN SPECTROSCOPIC ANALYSIS OF THE COMPOSITION OF CLAM SHRIMP (LAEVICAUDATA, SPINICAUDATA, CYCLESTHERIDA) CARAPACES: IMPLICATIONS FOR THE FOSSIL RECORD

Paper number: 30-7
Program: Technical Sessions
Time: 8:00 AM – 5:30 PM

Authors

Abstract

Clam shrimp are a paraphyletic group of bivalved branchiopod crustaceans including the Laevicaudata, Spinicaudata, and the Cyclestherida. In the published literature, the mineral content of the unique carapace (formed by molt retention in Spinicaudata and Cyclestherida) is variously ascribed to calcite or calcium phosphate. To better understand the mineral composition of clam shrimp carapaces, we analyzed the composition of the modern carpaces of one species of laevicaudatan, thirteen species of spinicaudatan (including both cyzicids, leptestheriids, and limnadiids), one species of cyclestherid, and two species of the notostracan Triops (as an outgroup comparison within Branchiopoda) via Raman spectroscopy.

The results were surprisingly variable. The outgroups species of Triops varied in either having no mineral content to having a slight amount of calcium phosphate in their carpaces. The laevicaudatan, Lynceus planifascia, likewise had a minor calcium phosphate peak. The leptestheriid, Leptestheria compleximanus, had a strong calcium phosphate peak and a strong calcium carbonate peak. The seven limnadiids were variable; varying from no mineral content to strong dual calcium carbonate and calcium phosphate peaks. The five cyzicids tended to have strong calcium phosphate peaks and some amount of calcium carbonate as well. The cyclestherid, Cylcestheria sp., had no mineral content. The results support the conclusion that spinicaudatans primitively have a unique dual mineralization system in their carapace that utilizes both calcium phosphate and calcium carbonate, with the calcium phosphate ability being primitive. Better understanding of the distribution of the phosphate vs. carbonate amongst modern spinicaudatans will help us better understand the evolution of biomineralization in the group. This, in turn, will help us to better understand the fossilization potential of different lineages of fossil clam shrimp.

Geological Society of America Abstracts with Programs. Vol. 50, No. 4

doi: 10.1130/abs/2018NC-312253

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