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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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