[dinosaur] Standing Rock Hadrosaur Site geochemical taphonomy and soft tissue preservation

Ben Creisler
[email protected]

A paper not yet mentioned:

Paul V. Ullmann, David E. Grandstaff, Richard D. Ash & Kenneth J. Lacovara
(2019)
Geochemical taphonomy of the Standing Rock Hadrosaur Site: Exploring links
between rare earth elements and cellular and soft tissue preservation.
Geochimica et Cosmochimica Acta (advance online publication)
doi: https://urldefense.proofpoint.com/v2/url?u=https-3A__doi.org_10.1016_j.gca.2019.10.030&d=DwIBaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=JNel9b6493UxrLQmu7a2gmq3yn3yeSA2UbHkAXeBAoI&s=oqmPFXJ0lHK1nTJmBHyp3LstOFpX_MfB5qbUJ3vKJ6k&e= 
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The Standing Rock Hadrosaur Site (SRHS) in South Dakota preserves a
mass-death assemblage of the hadrosaurine dinosaur Edmontosaurus annectens
in the Upper Cretaceous Hell Creek Formation. A previous study of SRHS
bones found many of them to yield microstructures morphologically
consistent with vertebrate osteocytes, blood vessels, and proteinaceous
matrix upon demineralization with weak acid. To examine the geochemical
history of these specimens in detail, we herein document the intra-bone
distribution of rare earth elements (REE) within nine of these
previously-examined Edmontosaurus limb bones from SRHS. Laser
ablation-inductively coupled plasma mass spectrometry was used to determine
the trace element composition of the specimens, which revealed the bones to
possess unusually low REE concentrations for bones of Mesozoic age,
consistent and steep declines in light REE concentrations with increasing
cortical depth, and uniformly low concentrations of middle REE and elements
with moderate and low diffusivities through the middle cortex. These
attributes imply: 1) at least partial preservation of early-diagenetic
trace element signatures; 2) that trace element uptake occurred primarily
during a single, early-diagenetic phase, and; 3) that the duration of trace
element diffusion was brief in these bones. As we previously reported, low
permeability of the fine-grain host matrix and early-diagenetic cementation
of portions of the host matrix by precipitation of siderite concretions
impeded pore fluid replenishment; this partial hindrance of fluid flow was
also likely responsible for the minimal trace element uptake observed in
the nine SRHS specimens further studied herein. From a paleontological
perspective, minimal trace element uptake reflects minimal chemical
alteration, meaning bones from this site are predicted to be ideal
candidates for preservation of original organics according to hypotheses
previously advanced by geochemical studies. Because low REE concentrations
reflect limited interaction with groundwaters during diagenesis, we propose
that late-diagenetic overprinting of early-diagenetic REE profiles was
minimal and that hydrolytic degradation of soft tissues was limited in the
burial environment at SRHS. Mitigation of biomolecular decay by hydrolysis
would favor ultrastructure stabilization and is therefore advanced as a
partial explanation for the preservation of cells and soft tissue
microstructures in these fossil bones.


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