Taphonomy and whale-fall analysis of the Tortonian baleen whales from the Stirone River, Emilia Romagna (northern Italy)

Michelangelo Bisconti ^1* Paola Monegatti ² Gianluca Raineri ³ Giandonato Tartarelli ⁴ Giorgio Carnevale ¹

• ¹ Department of Earth Sciences, School of Nature Sciences, University of Turin, Turin, Italy
• ² Dipartimento di Scienze della Terra, Università degli Studi di Parma, Parma, Italy, Parma, Italy
• ³ Museo 'Mare antico e biodiversità', San Nicomede, Salsomaggiore Terme, Italy
• ⁴ Normal School of Pisa, Pisa, Tuscany, Italy

The taphonomy of three balaenopterid skeletons is examined in order to describe the traces left by whale fall communities. The whale specimens include two partial skeletons and an isolated periotic; one of the partial skeletons is the holotype of Plesiobalaenoptera quarantellii, while the other two specimens represent two indeterminate balaenopterid species. The partially articulated skeletons were affected by intense bioerosion and disarticulation that displaced several bones before the final burials. Trace fossils found on the whale bones include shark bite traces, Trypanites, Gastrochaenolites, ?Meandropolydora and Gnatulichnus ichnogenera documenting an intense 2 exploitation of the energy reservoir represented by these carcasses. The biostratigraphic analysis of the site supports a Late Miocene (Upper Tortonian) age and shows presence of post-depositional processes. These included micro-faulting that acted on the whale bones and, in one case, provided forces able to deform a lumbar vertebra. Fish otoliths, mollusc shells and microfossils are consistent in supporting a c. 100 m deep inner shelf deposit. Absence of chemoautothrophic molluscs from the present whale falls confirm that water depth may be the main determinant of the presence of these highly specialized species, that flourish in anoxic environments, because decomposition at shallow depths may still occur in presence of high Oxygen concentrations. Those described herein are the most dense ensembles of traces documenting whale falls communities in the Late Miocene described up to now.