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 repla..., Studied specimens of Ceraurus pleurexanthemus and Flexicalymene senaria are housed at the Museum of Comparative Zoology, Harvard University. Historic samples were collected from the Walcott-Rust Quarry by Charles Walcott in the 1870s, prepared as thin sections by hand and affixed to glass slides using balsam sap (Yochelson, 1998; Fig. 1–2). Over 180 kg of rock from Layers 3 and 8 were collected from the Walcott-Rust Quarry based on the presence of trilobites preserved at the surface and donated to the MCZ by Mr. Dan Cooper (Covington, Kentucky, USA) (Supplementary Fig. 1). Three new specimens from Layer 8 (Spillway Member, Rust Formation) were imaged as they showed evidence of calcite within the glabella and doublure (Supplementary Fig. 1–2). Three trilobite specimens and three calcite veins from Layer 3 (Supplementary Fig. 1) were selected for chemical analyses (Figs. 3a, e, 4a–d) based on the presence of observable sparry calcite either in the hand sample or during grinding of the spe..., R and RStudio, # Walcott-Rust trilobite fossil calcite composition data [https://doi.org/10.5061/dryad.1jwstqk16](https://doi.org/10.5061/dryad.1jwstqk16) SEM spot analyses of Walcott-Rust fossils and veins and Raman spectra showing barite within one specimen. ## Description of the data and file structure Describe relationships between data files, missing data codes, other abbreviations used. Be as descriptive as possible. One Excel file with two sheets, one dedicated to the SEM spot analyses and the other to the Raman spectra. Empty cells within SEM spot analyses indicate that the element was not detected. ## Code/Software All graphs were made in R.