AN ICHTHYOSAUR CARCASS-FALL COMMUNITY from the POSIDONIA SHALE (TOARCIAN) of GERMANY Author(S): DANIEL G

AN ICHTHYOSAUR CARCASS-FALL COMMUNITY FROM THE POSIDONIA SHALE (TOARCIAN) OF GERMANY Author(s): DANIEL G. DICK Source: PALAIOS, Vol. 30, No. 5/6 (May–June 2015), pp. 353-361 Published by: SEPM Society for Sedimentary Geology Stable URL: https://www.jstor.org/stable/43683927 Accessed: 08-07-2021 11:50 UTC JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at https://about.jstor.org/terms SEPM Society for Sedimentary Geology is collaborating with JSTOR to digitize, preserve and extend access to PALAIOS This content downloaded from 86.59.13.237 on Thu, 08 Jul 2021 11:50:49 UTC All use subject to https://about.jstor.org/terms Г92' SEPM PALAIOS, 2015, 30, 353-361 " ^ Research Article | W ШВЯшёЛшшЛшЁ^Ш DOI: http://dx.doi.org/10.2110/palo.2014.095 K * K Emphasizing the impact of life on K * K Earth's history AN ICHTHYOSAUR CARCASS-FALL COMMUNITY FROM THE POSIDONIA SHALE (TO ARCI AN) OF GERMANY DANIEL G. DICK1'2 Staatliches Museum für Naturkunde Stuttgart, Rosenstein 1, 70191 Stuttgart, Germany 2 Eberhard-Karls-Universität Tübingen, Fachbereichs Geowissenschaften, Hölderlinstr. 12, 72074 Tübingen, Germany email: [email protected] Abstract: The possibility that large marine reptiles and other Mesozoic vertebrates produced nekton-fall communities similar to those of modern cetaceans is presently receiving increased attention in the literature. The author describes a rare ichthyosaur carcass-fall community from the Posidonia Shale (lower Toarcian) of Germany, which provides insights into the role played by large marine vertebrates in determining regional benthic ecology during this period. It is demonstrated here that, while more important than previously thought, there is little evidence to suggest that ichthyosaur carcasses played a substantial role in structuring the benthic ecology of the European Toarcian epeiric sea. In general, within the shallow waters of the Posidonia Shale, conditions conducive to the creation of carcass-fall communities were rare, and when present, resulted in localized magnification of background taxa and higher local biodiversity, rather than a unique community of epibiont organisms. The community which developed is ecologically similar to modern whale-fall communities, but differs in important ways, particularly with regard to the presence/absence of the chemosynthetic faunas which are most intensively described in the literature. INTRODUCTION discuss the degree to which the observed ecological succession represents the sort predicted by Hogler (1994) and others. The results suggest that, Following the discovery that sunken whale carcasses and other nekton in the shallower waters of the early Toarcian European epeiric sea, falls produced diverse macrofaunal communities similar to those found ichthyosaur carcasses were only colonized in a manner similar to around hydrocarbon seeps and hydrothermal vents, it has been predicted contemporary nekton falls under rare conditions (temporary increases in that similar communities should be found in association with Mesozoic benthic oxygen levels), and when this occurred they developed a fauna marine reptiles- particularly the ichthyosaurs (Martill et al. 1991; Hogler which was ecologically similar to contemporary whale-fall faunas, but 1994). Martill (1987) provided the first description of an ichthyosaur lacking the unique sulphophilic stage found among nekton falls in carcass-fall community, in his description of Middle Jurassic Ophthal - contemporary oceans. The specimen described in this article contains mosaurus bones with encrusted oysters and serpulid worms. Martill evidence et foral. a number of benthic biotic interactions which have not been (1991) and Hogler (1994) published speculative accounts on the role that previously described for the Early Jurassic. This has important large Mesozoic marine reptiles (including ichthyosaurs) may have played implications for our understanding of the structure and development of in deep-sea benthic ecology, and this was followed by a small number of the benthic ecosystem of the European Toarcian epeiric sea. studies which validated some of these predictions. Hogler (1992) described Shonisaurus popularis bones with encrusted bivalves from the CARCASS FALLS AND ECOLOGY Luning Formation in Nevada, which were embedded in sediments showing high benthic biodiversity. Kaim et al. (2008) produced The the benthic first zone of the open ocean is a region characterized by low description of a Mesozoic marine reptile-based chemosynthetic resource commu- availability, and consequentially low biomass and diversity nity (micrograzing provannid gastropods and ataphrid-like (Lundsten vetigastro- et al. 2010). The majority of biodiversity in the region occurs pods typical of coeval seep faunas; see Kaim et al. 2009, 2014), around which the was hydrothermal vents and cold hydrocarbon seeps, which found in association with Cretaceous plesiosaurid remains. provide Most chemical material of use to chemosynthetic organisms collec- recently, Danise et al. (2014) described a shallow-water ichthyosaur-fall tively referred to as the vent and seep biota (Kiel and Tyler 2010). community from the Late Jurassic (consisting mainly ofOccasionally, fossilized the remains of a large organism (usually a cetacean in serpulid worms, epifaunal suspension feeders including thecontemporary ostraeid oceans) will sink to the seafloor, dramatically altering the Deltoideum delta , as well as trace fossils of the species Gnathichnus surrounding ecological conditions. These events, known as whale, pentax , interpreted to have been caused by grazing echinoids); nekton, however, or carcass falls, alter the local benthic ecology in a number of they noted an absence of evidence for the chemosynthetic stageways, whichwhich can be described in four stages (Bennett et al. 1994; Smith had been previously predicted. This was suggested to have and been Baco 2003).due The first stage occurs when the soft tissues of the newly either to the shallow-water nature of the fall or to the small introduced size of the organism are rapidly consumed by mobile scavenging specimen (Danise et al. 2014). In the present article I provide a organismsdescription (the so-called mobile scavenger stage) (Smith and Baco of a shallow-water (~ 100 m; Röhl et al. 2001) ichthyosaur 2003). carcass Following fall this, the carcass tends to become dominated by what are from the Posidonia Shale (Toarcian) from Holzmaden, Germany, referred and to as enrichment opportunists; polychaete worms, echinoids, Published Online: May 2015 Copyright © 2015, SEPM (Society for Sedimentary Geology) 0883- 1351/1 5/030-353/$03.00 This content downloaded from 86.59.13.237 on Thu, 08 Jul 2021 11:50:49 UTC All use subject to https://about.jstor.org/terms 354 crustaceans, levels begin to decrease (to as low as 3.5%), and benthic anddiversity other small organisms which proliferate off the consumption increases (Röhl and Schmid-Röhl 2005). The specimen discussed hereof the material produced by bacterial breakdown of remaining comes from the horizon known as the Schieferklotzsoft (s II 6, Fig. 1), and is tissue (Bennett et al. 1994). The third stage in this generalized found within one of many known thin modelgray bioturbated marls within the has received the majority of attention in the literature; the sulphophilic Harpoceras falciferum zone, H. elegans subzone, representing times when stage, wherein the remains are colonized by chemosynthetic oxygenbivalves levels (and consequent benthic biodiversity) were temporarily and bacteria (Bennett et al. 1994). Following this, the protruding increased (Urlichs et al. 1994; Röhl and Schmid-Röhl skeletal 2005). elements provide a hard substrate which can be colonized Fluctuating benthic oxygenby levels which increased benthicorganisms scavenging which rely on increased water flow for feeding. This final will necessarily lower the quality stageof preservation in fossil material. Here, has been referred to in the literature as the reef stage (Smith this is suggestedand as an explanation for why fewBaco ichthyosaur carcass-fall 2003). In this communities article, are known from the Posidonia Shale, as they would only I describe a nearly complete but slightly disarticulated ichthyosaur become preserved under rare conditions; relatively highand benthic oxygen its associated carcass-fall faunai community from the Early Jurassic levels, with a sedimentation rate high enough to promote fossilization, (Toarcian) of Germany. This particular carcass fall has potential but low enough to allowto development of a contributecarcass-fall community prior immensely to our understanding of the role played by ichthyosaur to burial. The vast majority of ichthyosaur remains are found within carcasses in the benthic ecology of the Toarcian European epeiric faciessea wherein nekton-fall communitiesfor could not develop (due toa low number of reasons. First, the specimen represents a rare definitive oxygen levels, which increase example preservation), and this biases the record of prolonged exposure of an ichthyosaur carcass above the sediment-water from the Posidonia Shale toward preserving complete, uncolonized interface

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