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215-3 Community ecology from the Upper Triassic Chinle Formation, southwestern USA: insights from coprolite 𝛿13Corg and 𝛿15N stable isotope geochemistry

Session: Coprolite Happens: Insights into Geobiology

Presenting Author:

Morrison Nolan

Authors:

Nolan, Morrison R.¹, Kligman, Ben T.², Scher, Mason³, Marsh, Adam D.⁴, Reid, Rachel⁵, Gill, Benjamin C.⁶

(1) Independent, Stone Mountain, USA, (2) Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA, (3) Department of Geosciences, Princeton University, Princeton, NJ, USA, (4) Department of Science and Resource Management, Petrified Forest National Park, Petrified Forest, USA, (5) Department of Geosciences, Virginia Tech, Blacksburg, USA, (6) Department of Geosciences, Virginia Tech, Blacksburg, USA,

Abstract:

Coprolites represent important evidence of trophic interactions in the fossil record. The organic carbon (𝛿¹³C_org) and nitrogen (𝛿¹⁵N) stable isotope compositions of excrement from extant animals provide evidence for reconstructing ecological interactions, but the application of stable isotopes for reconstructing ancient trophic dynamics from the coprolite record has been limited. In this project, we investigate external and internal coprolite anatomy along with 𝛿¹³C_org and 𝛿¹⁵N compositions of an assemblage of coprolites collected from a sequence of fossiliferous horizons in the Upper Triassic Chinle Formation of northeastern Arizona. This succession represents marginal fluviolacustrine paleoenvironments in the humid equatorial paleotropics of continental Pangaea approximately 225 – 205 million years ago. Here, we present coprolite anatomy and isotopic data from four localities and use this data to infer trophic structure (i.e. we focus on the relative contribution of terrestrial versus aquatic food sources) of the coprolite producers. The data occupy a broad isotopic space, with 𝛿¹⁵N values ranging from 8.7‰ to -2.8‰ and 𝛿¹³C_org ranging from -26.6‰ to -5.0‰, with the values separating in two distinct spaces, reflecting different trophic relationships. Additionally, we use the well resolved temporal and paleoclimatic constraints of these Chinle Formation localities to potentially link changes in trophic structure over time to the drying of the climate during the Late Triassic in central Pangea. Our results also test the fidelity of trophic data sourced from coprolite assemblages to the osseus vertebrate record derived from the same horizons, and this suggests biases towards preservation of coprolites from aquatic and carnivorous groups. These findings denote a significant development in the use of coprolite-derived stable isotopes from the Mesozoic Era to study trophic interactions and provide further details of ecological changes during the Late Triassic.

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

doi: 10.1130/abs/2025AM-8462

Community ecology from the Upper Triassic Chinle Formation, southwestern USA: insights from coprolite 𝛿13Corg and 𝛿15N stable isotope geochemistry

Description

Session Format: Oral

Presentation Date: 10/21/2025

Presentation Start Time: 02:10 PM

Presentation Room: HBGCC, 304B

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