Walcott-Rust trilobite fossil calcite composition data

Trilobites with appendages from the Rust Formation of New York State were
discovered in the 1870s and represent one of the earliest known cases of
exceptional preservation of non- biomineralized tissues. The Rust
Formation trilobites feature three-dimensionally preserved walking legs
and delicate respiratory lamellae, but the mechanism behind their
fossilization remains unknown. Here we show that after burial, carcass
decay produced framboidal pyrite, while fibrous calcite precipitated on
the visceral side of the body, followed by the widespread formation of
sparry calcite crystal replicating non-biomineralized morphological
features. Trilobites and co-occurring calcite veins show no chemical or
petrographic differences, rejecting the hypothesis that exceptional
preservation was caused by a local microenviron- ment within enrolled
trilobites. These results suggest that fine-grained sediment provided
support for the appendages and facilitated their fossilization through
calcite replacement. Our findings carry broader implications for
understanding the exceptional three-dimensional preservation of animal
Paleozoic body fossils through calcite casts.