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Preservation of soft tissues in Silurian graptolites from Latvia
David K. Loydell, Patrick J. Orr and Stuart Kearns
PALAEONTOLOGY 2004, 47, 3, 503-513

Abstract of the paper:

"The contractile stalks of graptoloid zooids are preserved as organic carbon residues in thecae of the middle Llandovery
graptoloid graptolites
Rastrites geinitzii and Neolagarograptus ? sp. from the Aizpute-41 core, Latvia. The contractile
stalks are surrounded by equant pyrite crystals, resulting in three-dimensional preservation of the graptolite
rhabdosomes, and are associated with sediment of similar composition to, and derived from, the adjacent matrix. Matrix
entered the thecae after pyrite crystal growth and filled some of the space left by collapse of the contractile stalks
and some intercrystalline cavities; other space is partially infilled by diagenetic minerals. The contractile stalks are
parallel-sided and occupy up to one-half the metathecal width, which is not inconsistent, assuming post-mortem
shrinkage, with the suggestion that graptoloid zooids filled their tubes in life. The location of the preserved soft
tissues, towards the distal ends of the metathecae, is very different from that predicted by decay experiments on the
extant pterobranch hemichordate
Rhabdopleura, the latter's soft tissues may thus not be a reliable analogue for those
of these Silurian graptoloids."
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Dr Piotr Mierzejewski, Count of Calmont
since 2002