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Neosauropod Nesting Site from Sanagasta in La Rioja, Argentina



From: Ben Creisler
bcreisler@gmail.com

A recent article not yet mentioned on the DML:

Lucas Ernesto Fiorelli, Gerald Grellet-Tinner, Eloisa Argañaraz &
Leonardo Salgado (2013)
Taphonomy of the Neosauropod Nesting Site from Sanagasta (La Rioja,
Argentina): Exceptional Preservation in a Cretaceous Hydrothermal
Paleoenvironment.
Ameghiniana 50(4) : 389 – 406
http://www.ameghiniana.org.ar/index.php/ameghiniana/article/view/523



The Cretaceous Sanagasta nesting site, La Rioja Province, Argentina,
has shed insights on the reproductive behavior of neosauropods,
documenting colonial behavior, phylopatry, and an opportunistic
environment-dependent-reproduction relationship with their
paleoenvironment. The taphonomy of this monotypic nesting site is
described in order to assess its biostratinomy and fossil diagenesis.
The 3D spatial egg-clutch arrangement is well preserved and suggests
the presence of autochthonous associations with in-situ ovipositions,
without nesting trace. The egg-bearing level presents a
matrix-supported packed biofabric and an “intrinsic” biogenic
accumulation that implies a gregarious behavior through their
preferential colonization of a specific paleohydrothermal nesting
site. The biocenosis of biogenically deposited eggs, with eggshell
mineralization is altered by hydrothermal activity, and extremophile
microorganisms. The thanatocenosis and time-averaging were virtually
null because the eggs buried in the substrate immediately after being
laid. In contrast, the taphocenosis represents the most important
taphonomic feature. The eggshells display several synchronous
taphonomic alterations produced by acidic hot spring solutions, while
re-calcification and silicification are the most common eggshell
recrystallizations. The presence of microchert, chalcedony, ~10
μm-diamteer opal-A microspheres, epidote aggregates, several
macro-structures, and fibrous clay minerals replacing parts of the
eggshell and egg membranes, indicates an extreme hydrothermal
alteration under exceptional conditions. The presence of fossil
stromatolites, cyanobacterians, and diatoms, coupled with sedimentary
tructures (microfacies and hydrothermal microfabrics), and with eggs
taphonomy imply that the Sanagasta nesting site represents a
particular instance of taphocenosis and a Lagerstätte. The Sanagasta
dinosaur nesting site is the first documented case of
environment-dependent reproduction amongst neosauropods.