63 D25. Paleontology: Recent Developments in Paleoecology and Taphonomy (Posters)

Sunday, 9 October 2022
2:00 PM - 6:00 PM
Exhibit Hall F

NICHE PARTITIONING AND PALEOHYDROLOGY: MULTI-TAXA OXYGEN ISOTOPIC ANALYSIS OF VERTEBRATE PHOSPHATES, CRETACEOUS CLOVERLY FORMATION, MONTANA, USA

Paper number: 63-13
Program: Technical Sessions
Time: 2:00 PM – 6:00 PM

Authors

Abstract

The Cretaceous Cloverly Formation of Wyoming and Montana has produced one of the most complete continental vertebrate faunas known from the Early Cretaceous of North America, yet regional paleoclimatic and paleoecological conditions under which the Cloverly fauna evolved are poorly understood. Here we present some preliminary oxygen isotope data derived from phosphate of some fossil reptiles and fish from a single microfossil bonebed (OMNH V1075) in the Cloverly of Bighorn County, Montana. We calculated a δ18Ometeoric_water value of -7.2‰ (VSMOW) from pleurosternid turtle plastron and carapace fragments (δ18Ophosphate = 14.9‰, σ = 1.5‰), and a similar δ18Ometeoric_water value of -6.2‰ from enamel of button-like crocodylomorph teeth (δ18Ophosphate = 16.7‰, σ = 1.9‰). These meteoric water values both generally agree with a previously established δ18O-latitude gradient calculated for the Early Cretaceous based on δ18Opedogenic_carbonate and plant proxies. Our preliminary estimate of habitat water temperature (16.1°C) from pleurosternid turtle δ18Ophosphate is consistent with previous independent analyses of δ18Ophosphate in Cloverly aquatic turtles. Our data shows insignificant (p > 0.05) variation between most taxa and between ecophysiological groups, but this is likely due to under sampling of most groups analyzed. However, due to the exceptional abundance of crocodylomorph teeth at the V1075 site, crocodylomorph tooth morphotypes were well sampled. Analysis of variance reveals that δ18Ophosphate of atoposaurid-like teeth (cf. Wannchampsus sp., δ18Ophosphate = 17.4‰, σ = 2.5‰, p = 0.018) and button-like teeth (cf. Bernissartiidae, δ18Ophosphate = 16.7‰, σ = 1.9‰, p = 0.053) differ from conical teeth (cf. Goniopholidae, δ18Ophosphate = 14.2‰, σ = 2.8‰), which we interpret as evidence of niche partitioning. Further sampling within some taxonomic and ecophysiological groups across time and space is required to draw more conclusive paleobiological and paleohydrological interpretations. Still, these preliminary results further suggest that oxygen isotopes from fossil vertebrate phosphates can offer insight into regional climates and evolution of terrestrial ecosystems of Early Cretaceous North America.

Geological Society of America Abstracts with Programs. Vol. 54, No. 6

doi: 10.1130/abs/2022AM-382377

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