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Titanosaur fossil egg preservation affected by soil movement processes



From: Ben Creisler
bcreisler@gmail.com


A new online paper:

Frankie D. Jackson,  James G. Schmitt &, Sara E. Oser (2013)
Influence of Vertisol development on sauropod egg taphonomy and
distribution at the Auca Mahuevo locality, Patagonia Argentina.
Palaeogeography, Palaeoclimatology, Palaeoecology (advance online publication)
doi: http://dx.doi.org/10.1016/j.palaeo.2013.05.031
http://www.sciencedirect.com/science/article/pii/S0031018213002733

At the Auca Mahuevo locality in the Upper Cretaceous Anacleto
Formation in Patagonia, Argentina pedogenic processes associated with
Vertisol development affected changes in both individual titanosaur
egg morphology and three-dimensional egg distribution. These changes
resulted primarily from vertical and lateral movement within fluvial
overbank sediments due to clay mineral expansion and contraction in
alternating wet and dry seasonal conditions. At the scale of
individual sauropod eggs, pedogenic sediment movement produced egg
shearing, eggshell fracture and displacement, mechanical abrasion of
egg ornamentation, and alteration of egg size and shape. Movement of
either individual eggs or subsets of eggs along slickensided surfaces
(1) modified the number and relative position of eggs within
individual clutches, (2) combined eggs of one of more clutches
produced by different females, and (3) combined eggs from one or more
nesting horizons, producing a time-averaged fossil assemblage. These
mechanisms of egg rearrangement suggest that accurate interpretation
of dinosaur reproductive behavior using fossil egg assemblages
preserved in fine-grained fluvial overbank deposits require careful
assessment of pedogenic processes.