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Aristonectes (plesiosaur) gastroliths



From: Ben Creisler
bcreisler@gmail.com

A new paper:


José Patricio O'Gorman, Eduardo Bernardo Olivero, Sergio Santillana,
Michael J. Everhart & Marcelo Reguero (2014)
Gastroliths associated with an Aristonectes specimen (Plesiosauria,
Elasmosauridae), López de Bertodano Formation (upper Maastrichtian)
Seymour Island (Is. Marambio), Antarctic Peninsula.
Cretaceous Research 50: 228–237
doi: http://dx.doi.org/10.1016/j.cretres.2014.03.011
http://www.sciencedirect.com/science/article/pii/S0195667114000512

The occurrence of a large gastrolith set associated with a specimen
referred to Aristonectes sp. is reported here for the first time. The
specimen MLP 89-III-3-1 comes from Seymour Island (Is. Marambio),
Antarctic Peninsula, López de Bertodano Formation (upper
Maastrichtian). The gastrolith cluster is composed of 793 elements
(534 in their presumed original state and about 259 that are broken).
The gastroliths are described using sedimentological indices. The mean
major axis of the gastroliths is 21 mm, the mean Maximum Projection
Sphericity is 0.71 and the standard deviation is 0.11. According to
Krumbein's classification, 43.3% are spheroidal (equant), 14.9% are
cylindrical (prolate), 34.7% are discoidal and 7.1% are bladed
(laminar). Following Powers' roundness categories, 10.1% are very
rounded, 29.2% are rounded and 60.7% are subrounded. The mean Maximum
Projection Sphericity value indicates a fluvial origin for the
gastroliths. Petrographically, the gastroliths comprise rhyolitic
volcanites (56.2%), quartz vein material (27.8%), subarkose arenites
(14.5%) and laminated, radiolarian-rich mudstones and tuffs (1.5%).
The potential geological sources are several formations from the
Antarctic Peninsula, such as the Upper Jurassic Antarctic Peninsula
Volcanic Group (rhyolitic volcanites), the Permian–Triassic Trinity
Peninsula Group (subarkose arenites), and the Kimmeridgian–Berriasian
Ameghino Formation (radiolarian-rich mudstones and tuffs). All these
formations crop out within about 100 km of the locality where the
specimen was collected. We also discuss how gastroliths were ingested,
concluding that the ingestion was not done individually. Finally, this
record of gastroliths provides evidence against the hypothesis of
their use for buoyancy control.