215-1 Surprising Preservation of Herbivorous Dinosaur Gut Contents Through Replacement With Clay

Session: Coprolite Happens: Insights into Geobiology

Presenting Author:

Karen Chin

Authors:

Chin, Karen¹, Mahon, Elizabeth², Tosolini, Anne-Marie P.³, Korasidis, Vera A.⁴, Pfister, Craig⁵, Gale, Seth⁶, Fitzgerald, Erich⁷

(1) Geological Sciences & Museum of Natural History, University of Colorado Boulder, Boulder, CO, USA, (2) Department of Geology & Geophysics, University of Utah, Salt Lake City, UT, USA, (3) School of Geography, Earth and Atmospheric Sciences, The University of Melbourne, Melbourne, VIC, Australia, (4) School of Geography, Earth and Atmospheric Sciences, The University of Melbourne, Melbourne, Victoria, Australia, (5) Great Plains Paleontology, Madison, WI, USA, (6) SWCA Environmental Consultants, Sheridan, Wyoming, USA, (7) Museums Victoria, Melbourne, Victoria, Australia,

Abstract:

Fossilized digestive residues from ancient herbivores are notoriously rare.  Because plant tissues contain little phosphorus, lithification of herbivore coprolites and cololites generally requires exposure to allocthonous fluids containing minerals such as silica or calcite.  However, we report here the unexpected preservation of herbivorous dinosaur gut contents through replacement with clay rather than through permineralization.  This unusual preservation was recognized in the gut cavity of a nearly intact Triceratops skeleton (Museums Victoria specimen P256878) from the Upper Cretaceous Hell Creek Formation of Montana.  The carcass was entombed in a channel sandstone and the gut contents formed an unusual ~3.5 cm thick layer of comminuted plant tissues constrained to the bottom of the gut cavity.  Multiple lines of evidence indicate that the gut cavity plant tissues represent vegetation consumed by the Triceratops.

Microprobe, X-ray diffraction, and thin section analyses of the cololite reveal that some vegetative tissues were replaced by weakly lithified clay.  These fossil casts thus preserve external plant morphology, but show no histological detail.  Clays are known to play key roles in some fossilization processes, and clay replacement in this study resembles rare three-dimensional preservation of invertebrate soft tissues in the Ordovician Soom Shale Lagerstätte.  Yet these taphonomic settings are quite different; invertebrate soft tissues in the Soom Shale were preserved in marine siltstone and mudstone whereas plant tissues in the Hell Creek Formation were fossilized in the gut cavity of a dinosaur buried in fluvial sands.  It is particularly intriguing that this discovery appears to represent the second example of herbivorous dinosaur gut contents preserved with clay; previously-described brachylophosaur gut contents from the Cretaceous Judith River Formation also contain considerable clay.  In both cases, the cololites contain abundant clay even though the dinosaur carcasses were buried in sand.  Several studies have demonstrated that bacteria can facilitate clay authigenesis with access to appropriate cations.  Vertebrate guts host high bacterial populations that could have facilitated authigenesis of the amorphous clay in both cololites.  Even so, the occurrence of detrital clay- to silt-sized particles within the authigenic clay suggests that some sedimentary particles could have been introduced by water or possibly contributed by geophagy.  Additional examples of similar cololites may be discovered if conditions within herbivore guts promoted clay authigenesis or some dinosaurs engaged in geophagy.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9430

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.