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Taphonomy and Paleoecology of Shonisaurus popularis (Reptilia: Ichthyosauria)

Jennifer A. Hogler
PALAIOS
Vol. 7, No. 1 (Feb., 1992), pp. 108-117
DOI: 10.2307/3514800
Stable URL: http://www.jstor.org/stable/3514800
Page Count: 10
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Taphonomy and Paleoecology of Shonisaurus popularis (Reptilia: Ichthyosauria)
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Abstract

Remains of the ichthyosaur Shonisaurus popularis are sufficiently abundant and well preserved in the Upper Triassic Luning Formation of Nevada to allow paleobiologic inferences to be drawn from taphonomic data. In Berlin-Ichthyosaur State Park, Shonisaurus popularis fossils define both a scattered-element taphofacies and an articulated-skeleton taphofacies. Because these taphofacies reflect disparate depositional environments, each provides unique paleoecologic information. The scattered-element taphofacies consists of fragmentary skeletons and disassociated bones that accumulated in relatively energetic carbonate platform settings. The paleogeographic and temporal extent of this taphofacies indicates that Shonisaurus popularis favored tropical to subtropical, deeper shelf and basinal waters throughout upper Carnian and lower Norian time. The articulated-skeleton taphofacies is composed of comparatively whole skeletons, found in low-energy, poorly oxygenated basin sediments. Because these specimens are not reworked, they afford detailed paleoecological insights. Ichthyosaur occurrences include both isolated individuals, and multiple skeletons clustered upon a single bedding plane, suggesting that Shonisaurus popularis was subject to both attritional and catastrophic mortality. The abundance and distribution of attritional deaths indicates that these animals lived in persistent, fairly high-density populations. Evidence from a single, upper Carnian mass-death suggests that adults of the species, at least occasionally, engaged in group activity. There are no data to support previous hypotheses that Shonisaurus popularis frequented intertidal waters or was prone to stranding.

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