a MCZ:IP:111710 prone Flexicalymene senaria. b MCZ:IP:111708 prone Ceraurus pleurexanthemus. c Photomicrograph of transverse thin section through cephalon of MCZ:IP:104973 with preserved exopodite and lamellae. d Photomicrograph of sagittal thin section along axial lobe of MCZ:IP:158215 with preserved protopodites. e Photomicrograph of sagittal thin section of MCZ:IP:104956 with preserved protopodites. f Magnification of exopodite of MCZ:IP:104973 showing calcite crystals within lamellae. g Magnification of protopodites in MCZ:IP:104956 showing pyrite, fibrous and sparry calcite. Abbreviations: ax, axial lobe; cep, cephalon; ey, eye; ex, exoskeleton; exo, exopodite; fib, fibrous calcite; gl, glabella; L1, lobe 1; pt, protopodite; pyg, pygidium; pyr, pyrite; sp, sparry calcite; th, thorax.
Nature's journal communication Earth & environment has a paper about the preservation of trilobites in the Wolcott-Rust quarry. The Walcott-Rust quarry was discovered by Charles Wolcott in the 1870's. It dates to the Ordovician Period and yielded the first known trilobite appendages. This paper details research into the mechanism of the delicate, three dimensional preservation.
Abstract
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 microenvironment 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.
