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

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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

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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,

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 from the Posidonia Shale (German Posidonienschiefer vertebrate fossils, and makes carcass falls appear rare. However, this does ), a conservation Lagerstätte famous for its exceptional preservation not mean that carcass-fall communities were necessarily ofrare in the complete, undisturbed fossil organisms. Second, this study oxygenatedprovides geologically younger strata; merely that they are unlikely to an example of a relatively large event community preserved be preserved. Carcass falls werefrom almost certainly rare or nonexistent one of the many temporary oxygenation events that occurred during the highly anoxic periods,in i.e., the Fleins. the European epeiric sea throughout the early Toarcian, which contributes to efforts to increase the resolution of our understanding of the benthic paleoecology of this region. And finally, this A Note on the Possibility of Secondary Deposition study builds upon Danise et al. (2014) which demonstrated that of Faunai Remains ichthyosaurs (and possibly other marine reptiles) appear to have The possibility that the macroinvertebrate carcass-fall fauna described developed similar but ecologically unique carcass-fall faunas from the below does not represent an in situ community but rather a secondary cetaceans, which has important implications for our understanding of accumulation is refuted by the taphonomic and sedimentological history of Mesozoic benthic ecology in general. the assemblage. The possibility that the disarticulated nature of the remains was caused by current action rather than scavenging is unlikely due to the GEOLOGICAL SETTING preservation of both the ichthyosaur specimen's stomach contents (hundreds of cephalopod hooklets, Fig. 2), as well as small, distally The specimen described below comes from the Posidonia Shale positioned, and easily dispersed skeletal elements (i.e., terminal phalanges deposits exposed in the Kirschmann quarry, near the town of Holzmaden and posteriormost fluke vertebrae). Cephalopod hooklets and other tiny, in southern Germany (Fig. 1). The Posidonia Shale is a series of organic- lightweight stomach contents would be unlikely to remain in place in rich black shales deposited in the Southwest German Basin (SWGB) a region with sufficient currents to disarticulate the skeletal material to the during the early Toarcian (Röhl and Schmid-Röhl 2005). The SWGB was degree that is seen. Secondly, the depositional history of the Posidonia one of many basins which existed in central Europe during the early Shale is well documented, and is interpreted to have been a generally calm Toarcian, collectively referred to as the Central European epicontinental and consistent depositional environment (Röhl et al. 2001). Basins (CEBs) (Röhl and Schmid-Röhl 2005). The early Toarcian CEBs Lastly, the unusual apparent pattern seen below wherein the majority of are generally described as a shallow transcontinental shelf sea, generally epibionts are situated around the remains of SMNS 81841 (as opposed to less than 150 m in depth, which periodically connected the Proto-North directly encrusting) is due to the way in which the specimen was prepared. Atlantic region to the north and the Tethys to the south (Röhl et al. 2001; Like the majority of specimens from the Posidonia Shale, SMNS 81841 Röhl and Schmid-Röhl 2005). The high total organic content (TOC) and was prepared from the bottom up (due to the better preservation of the exceptional preservation of complete fossils within the Posidonia Shale undersurface) and as such, the pattern is as would be expected from an in has been long interpreted as indicating anoxic bottom conditions within situ community prepared in this manner; the convex sides of the bivalve the SWGB during the early Toarcian (Kauffman 1978; Röhl and Schmid- shells are exposed, and bone overlays many of the epibionts (as opposed to Röhl 2005). However, high resolution analyses of facies distribution the arrangement in life, which would have been the opposite). Secondly, within the Posidonia Shale have revealed a more complex and variable this pattern produces a natural bias against preserving epibionts and benthic environment (Röhl et al. 2001; Röhl and Schmid-Röhl 2005). taphonomic communities, as they would be mostly preserved on the The onset of the anoxic conditions and consequent black superior shale (and unprepared) surface of the specimen. As a result, the deposition occurred following the end of the late Pliensbachian numbersregression provided below are likely underestimating the true level of (Röhl and Schmid-Röhl 2005). During this initial transgressive period, diversity within the described community. Additionally, many lines of the first of the black shales (the Tafelfleins and Seegrasschiefer) evidence were conventionally used to support identification of fossil nekton-fall deposited (Fig. 1) (Urlichs et al. 1994; Röhl and Schmid-Röhl communities 2005). (i.e., ichnofossils related to scavenging found on the bone Short-term increases in benthic oxygen levels at this period surface) are are obscured due to the method of preparation. represented by thin, bioturbated marls with high benthic diversity found between the black shale horizons; these are predicted to have resulted MATERIALS AND METHODS from wind and/or wave action increasing mixing in the water column (Röhl and Schmid-Röhl 2005). Long-term anoxia became prevalent The specimen by described here, SMNS 81841, on display at the the end of the Dactylioceras tenuicostatum zone, into Staatlichesthe early Museum für Naturkunde Stuttgart (SMNS), was analyzed Harpoceras falciferum zone (i.e., the Fleins and Unterer Schiefer),in order to determine the taxonomie identification, number, and resulting in black shale deposition with high TOC (> 10%) proportion (Fig. 1) of associated carcass-fall faunai material. The ichthyosaur (Urlichs et al. 1994; Röhl and Schmid-Röhl 2005). Following remains this, TOC themselves were assigned to the species* Stenopterygius

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Fig. 1 A) Relevnt stratigraphie intervals and ammonite zones discussed here. The stratigraphie position indicated for SMNS 81841 is an estimate based on the associated benthic fauna and sedimentary characteristics. B) Oxygen curve showing relative oxygen levels for the intervals discussed here. C) Map showing the location of the Kirschmann quarry, where SMNS 81841 was found. Modified from Riegraf et al. (1984), Urlichs et al. (1994), and Röhl and Schmid-Röhl (2005). TOC = Total Organic Content. quadriscissus , using theGiven criteria the specimen's established nature in Maxwell as a permanent (2012). Identifi- display item, histological cation of the associated analyses, faunai while community desirable, were was unattainable. made based In on order the to assess the extent descriptions in Urlichs of etthe al. changes (1994), inas benthicwell as biodiversityby comparison represented with the by SMNS 81841, other collections housed at large the SMNS.vertebrates Following (> 1 m the in methodlength) houseddescribed at thein SMNS (n = 61) were Danise et al. (2014), anyassessed macroinvertebrates to determine iffound comparable either (a) faunai directly assemblages could be encrusting the bones, identified. or (b) within 10 cm of the remains were considered to be associated. Following this characterization, the proportions of macroinvertebrates and scavenging RESULTS vertebrates in association with other ichthyosaur remains from the same region (from the same, or geologically younger/older deposits) Figures 2, 3, and 4were provide a graphical assessed and quantitative representation to of determine the degree of similarity to the diversity the associated faunai represented remains. The faunai assemblage is dominatedin association by with SMNS 81841.

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Fig. 2. - Image showing the distribution and taxonomie identification of the macroinvertebrates found in association with SMNS 81841. bivalves, particularlycarcass-fall community, fossils of the hundreds inoceramid of cephalopod Pseudomytiloides arm hooklets dubius are preserved (n = 62, 46% as stomachof the assemblage), contents associated the pectinoids with the Oxytoma ventral inaequivalvis surface of the (n =vertebral 47, 36% of column the assemblage), of SMNS 81841and Parvamussium (Fig. 2). pumilus (n = 6), as well as a single specimen Overall, of the Bositra total buchibenthic (Figs. biodiversity 2-4). Two ammonitesrepresented assigned by SMNS to 81841 is the species greater Harpoceras than eleganswhat is , seenas well on asaverage a single within specimen the Schieferklotzof the genus of the Dactylioceras Posidonia were identified,Shale. As described along with in Schmid-Röhlthe fragmentary et al. remains (2002), oxygenof level a crinoid (a3 clearin the identification Posidonia Shale was (which not possible, a majority but givenof the the Schieferklotz nature of the falls into, deposit it issee possibly Fig. 1, Pentacrinus), above) can be and characterized the fragmentary by its remains low, monospecific(a single arm diversity and a portion (generally of the densebody) accumulationsof an ophiuroid of (brittle Pseudomytiloides star, identified dubius). as Data in Sinosura br Urlichs odiei, from et al. a description(1994) demonstrates in Hess 1991), that which comparable together represent levels of benthic the nonbivalve diversity macroinvertebrate to those seen diversity in SMNS (Figs. 81841 2-4). In (i.e., addition co-occurrence to the of ammonite Pseudomytiloides shells, a number dubius of ammonite , Parvamussium aptychi pumilus(n = 11) ,were and Oxytomafound in inaequi- association valvis) with the do remains, not occur but untila specific a much identification later interval was not (e possible. III- the Wilder The ophiuroid Schiefer; remains bifrons represent zone), the when first benthic examples oxygen of these levels organisms have remained described elevatedin association for a consistentlywith the remains longer ofperiod. an ichthyosaur, During the 8 andIII interval, this is oxygen discussed levelsin more consistently detail below. reached While thenot same considered level (level to be 3, a partFig. 1)of as the those seen

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Fig. 3. - Examples of the macroinvertebrates discussed here, from SMNS 81841. A) P = Pseudomytiloides dubius. B) S = Sinosura brodiei (arm), О = Oxytoma inaequivalvis. C) Harpoceras elegans. D) P = Parvamussium pumilus, A = Ammonite aptychus (unidentified).

during the peak oxygenated (in terms of number of taxa) nor periodsabsolute number of macroinvertebrates of the Schieferklotz (Röhl and Schmid-Röhl 2005). The was found. similar Only a small number ofrange specimens had any of macroinvertebrates diversity occurring during both these times supports in association the (n = 9, association suggestion was measured as described above), made and here that SMNS 81841 represents an event community these were mainly restricted to a few isolated from examples of Pseudomytiloides a short-term oxygenation event, which temporarily increased dubius and ammonites (Harpoceras benthic sp. and Dactylioceras biodiversity sp.) found near in the SWGB. Of the 61 comparative the remains large (Table 1). Of particularvertebrate importance were two additional specimens from the Posidonia Shale examined, no specimen Sinosura brodiei ophiuroids featuring found near the highly disarticulated a remainscomparable of amount of diversity another Stenopterygius quadriscissus from the same region (SMNS 80234) (Table 1). A specimen assigned to Stenopterygius sp. from the Braunjura a (SMNS 52112), a geologically later deposit (Aalenian) from the nearby Swabian Alps, was found with a number of complete gastropod shells (n = 7) assigned to the species Toarctocera subpunctata , as well as a single Leioceras opalinum ammonite (Dietl 1977; Griindel et al. 2009). While not directly relevant to discussion of the Posidonia Shale, this association is included here as it is relatively close geologically/ geographically, and has not been described elsewhere. Vertebrate remains embedded in Bositra valve pavements were excluded from this analysis, as it is accepted that the embedded vertebrate remains were not involved in the distribution of Bositra (Kauffman 1978). As can be seen in Table 1, the number and diversity of epibionts found in association with other large vertebrate falls from the Posidonia Shale is substantially lower than that seen in SMNS 81841. Additionally, contrary to what was predicted by the oxygen levels discussed above, a single, unusual specimen from the Fleins stratum (e II 3) was found Fig. 4.- SMNS 81841 faunai counts (total number of specimens) consisting of two large Liostrea sp. oysters directly encrusting a large and associations. fragmentary ichthyosaur basicranium (see Martill 1993 for an earlier

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Table 1. - Additional specimens examined and associated faunai remains.

Specimen ID Species Stratigraphie interval Associated fauna SMNS 51957 Steneosaurus hollensis e II 6 (Schieferklotz) Pseudomytiloides dubius (n = -25), fragmentary Harpoceras sp. (n = 4) SMNS 55748 Stenopterygius quadriscissus e II 4 (Unterer Schiefer) Harpoceras sp. (n = 2) SMNS 52460 Hybodus hauffìanus e II 6 (Schieferklotz) Pseudomytiloides dubius (n = 2), Dactylioceras sp. (n = 1) SMNS 51946 Stenopterygius triscissus e II 6 (Schieferklotz) Pseudomytiloides dubius (n = 2), Dactylioceras sp. (n = 1) SMNS 58876 Steneosaurus hollensis e II 12 (Schlacken) Harpoceras sp. (n = 3) SMNS 80234 Stenopterygius quadriscissus e II 4 (Unterer Schiefer) Sinosura br odiei (n = 2), Harpoceras sp. (n = 1), Ammonite aptychi (n = 1) SMNS 80113 Stenopterygius quadriscissus e II 4 (Unterer Schiefer) Pseudomytiloides dubius (n = 2), Harpoceras sp. (n = 1) SMNS 52112 Stenopterygius sp. Braunjura a Toarctocera subpunctata (n = 7), Leioceras opalinum (n = 1) SMNS 53363 Temnodontosaurus sp. (fragmentary) e II 3 (Fleins) Liostrea sp. (n = 2)

description/discussion). This is unusual for two reasons; first, because ofcarcass falls, and this supports the prediction that SMNS 81841 was the predicted extremely low or absent benthic fauna during these deposited under temporarily ameliorated conditions in an already depositional events (Röhl et al. 2001), and second, as this is the largest improving benthic environment (see Röhl and Schmid-Röhl 2005). known specimen of ichthyosaur (assigned to Temnodontosaurus sp.) from the Fleins, a strata wherein the ichthyosaur diversity is known to be DISCUSSION almost entirely composed of Stenopterygius quadriscissus (Urlichs et al. 1994). Three of the specimens included in Table 1 come from the same Figure 5 provides a graphical representation of the generalized ichthyosaur-fall community development model discussed in this paper deposit as SMNS 81841 (the Schieferklotz), but have a far less diverse (Smith and Baco 2003). Figure 5A represents the initial sinking action, and absolutely lower number of epibionts. This seemingly unusual wherein the remains are largely untouched (this assumes that the carcass pattern is explained by the substantially darker color of the associated did not float at the surface for an extended period of time; see Reisdorf et sediment (although this could be due to differences in preparation al. 2012 for discussion). The interpretation that the remains of SMNS method) and lack of bioturbation, which suggests that they were 81841 did not float at the surface for an extended period of time comes deposited during one of the lower-oxygen periods from this interval from the completeness of the specimen; as was demonstrated by Schäfer (Fig. 1). Despite the lower oxygen availability implied to have been (1972), extensive surface floating by cetaceans results in slow disarticulation associated with the deposition of these specimens, they still maintain of the remains over large sections of the seafloor. Additionally, Reisdorf et a relatively higher diversity of benthic fauna than geologically earlier al. (2012) demonstrated that ichthyosaur carcasses would have initially sunk upon death, and would only attain sufficient internal gas buildup to return to the surface postmortem in shallow-water situations with low scavenging activity, which is unlikely due to the large amount of evidence for scavenging seen above. Overall, SMNS 81841 is argued here to be too complete to have floated at the surface for an extended period of time. Figure 5B represents the mobile scavenger stage, wherein nektonic scavengers (here represented as Hybodus hauffìanus , based on previous work suggesting a scavenger role for this species (Martill et al. 1994a), as well as complete H. hauffìanus specimens found from the same stratigraphie unit [s II 6]) first encounter the carcass and consume the majority of the soft tissue. It is possible that the disarticulation of the ribs and gastralia, which is depicted in Figure 4 as being due to scavenging by H. hauffìanus , occurred instead due to (or in conjunction with) a corpse explosion following the build-up of gases in the body cavity of the ichthyosaur (see Reisdorf et al. 2012 for discussion). However, as mentioned above, the depositional history of SMNS 81841 indicates that scavenging activity was too high to have allowed the necessary amount of gas build-up to cause a carcass explosion. Without direct evidence in the form of fossil teeth or ichnofossils, it is difficult to definitively indicate that H. hauffìanus was involved in the scavenging of SMNS 81841. However, fossil evidence demonstrates that this shark was present in the region at the time, and their generalized dentition suggests a variable diet, which likely included scavenging (Martill et al. 1994a; Duffin 1997). Following the mobile scavenger phase, as represented in Figure 5C, bacterial breakdown of the carcass attracts smaller benthic and epibenthic saprovoric organisms (the enrichment opportunist stage). Both of the ammonite species found in association with SMNS 81841 (Dactylioceras sp. and Harpoceras elegans) have previously been identified as benthic scavengers, and they are depicted as such in Figure 5C (Kauffman 1978; Jäger and Fraaye 1997). Ophiuroids make up a large portion of the enrichment opportunist fauna in contemporary whale falls (Pavlyuk et al. 2009; Lundsten et al. 2010), Fig. 5. - Graphic representation of the taphonomic and ecological history of SMNS 81841 as inferred from the skeletal orientation and associated benthic and the presence of ophiuroid remains in association with SMNS 81841 fauna. A) initial sinking stage. B) mobile scavenger stage. C) enrichment suggests they have played a role in nekton-fall scavenging since as early as opportunist stage. D) reef stage. Image by author, based on Martill, 1987. the Mesozoic. Figure 5D represents the final stage in the ecological

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Fig. 6- Left image shows the fragmentary ophiuroid arm from SMNS 81841. The image on the right shows a less fragmentary ophiuroid (Sinosura brodiei ) from a different ichthyosaur specimen from the same region, shown in aboral (abactinal) view (SMNS 80234). А, В = Arm showing lateral (1) and dorsal (2) shields. С = Disk (body). D = Radial shield (three are visible). Both scale bars = 1 cm. history of SMNS 81841, 1.8 andm in depicts length), the this colonization could be ofa confounding the remaining variable regarding the hard skeletal elements. specimen's ability to develop a sulphophilic stage (as suggested in Danise et al. 2014; see also Smith 2006). However, Pyenson and Haasl (2007) The Role of Ichthyosaur demonstrated Carcasses that in body Posidoma size may not have been an important factor in the Shale Benthic developmentEcology of the sulphophilic stage in fossil whale falls (by documenting the presence of chemosynthetic communities on small-sized cetacean There are two main ways carcasses); that an as ichthyosaursuch, the absence carcass of could a chemosynthetic produce the community cannot be increased diversity seen definitively in association demonstrated with SMNS to 81841 be size (in related. addition to its role in the mobile scavenger As a result, and enrichmentit is suggested opportunist here that, stages):in general, (1) byichthyosaur carcasses introducing lipids whichplayed cana small be consumedrole in the bybenthic bacteria, ecology producing of the SWGB, primarily by hydrogen sulfide (H2S) creating allowing temporary for colonization event communities by chemosynthetic during brief periods of increased organisms (as in contemporary benthic diversity.whale falls); This (2) by is providingdue in part a large, to the hard generally inhospitable substrate for colonization conditions by filter in feedingthe benthic organisms zone of (Lundsten the early et Toarcian al. 2010; SWGB (either due to Danise et al. 2014). As wasa lack noted of bysuitable Gaillard substrate et al. (1992), or chemosyntheticanoxic conditions) preventing the bivalves (i.e., lucinids) colonization are known of from ichthyosaur the Jurassic carcasses (from in depositsmost cases. However, when interpreted to have been ichthyosaur hydrocarbon carcasses cold seeps), did enter and yet the they benthic are absentecosystem (as in the above from the few ichthyosaur example), carcass they falls appear previously to have described magnified (as well the aspresence from of background taxa, the present specimen) by (Daniseproviding et al.nutrients 2014). Despite for mobile the hundredsscavengers, of material for bacterial excavated Early Jurassic decomposition ichthyosaur (with specimens, secondary including products veryof this large increasing the presence of species (i.e., Temnodontosaurus benthic scavengersplatyodon, including~ 12 meters Dactylioceras in length), noammonites, clear Sinosura ophiur- evidence of a chemosynthetic oids, and community possibly other has been presently found inunidentified association taxa), and lastly by with an Early Jurassic providing ichthyosaur a hard (McGowan substrate and for Motani colonization 2003). by suspension feeders. The The continued failure high of effortsnumber toof documentPseudomytiloides such a dubiuscommunity remains may supports this claim, as the suggest that either: (1) presence ichthyosaur of strong skeletons pedalbyssal were, in muscles general, and too an small anterior or byssal slit strongly too deficient in bone suggest lipids that to thisproduce species sufficient was a filter H2S feeder to supportwhich attached itself to hard a sulphophilic fauna (however,substrates see(Kauffinan Pyenson 1978; and HaaslRöhl et2007), al. 2001). or; (2) Consequently, the P. dubius has marine environments been represented suggested by tothe have deposits lived from a facultative which the benthic/pseudoplanktonic vast majority of ichthyosaurs lifestyle, are knownwhich is(i.e., supported the Posidonia by the findingsShale, the suggested Blue above (Röhl et al. Lias, the Oxford Clay) 2001). were The not unusual of sufficient specimen depth mentioned to support above the (SMNS 53363, the large development of a sulphophilic fragmentary stage. ichthyosaur The role of basicranium depth in contemporary with encrusted Liostrea , Table 1) whale-fall ecological foundsuccession within was the demonstrated (presumably) byhighly Lundsten anoxic/soupy et al. Fleins strata (s II 3; (2010), and this supports Fig. the1) suggests possibility that that larger the specimens lack of evidence of ichthyosaur for (i.e., Temnodonto- chemosynthetic ichthyosaur-fall saurus sp.) communitiesmay have provided may be sufficient due to the hard scarcity substrate of to influence local deep-water (> 200 m) fossilbenthic specimens. ecology, Carcasses even in in times shallower of extreme shelf settings anoxia or extensive soupy (between 300 and 600 msediment-water depth) are liable substrate to disturbance extent (Martillby turbidity 1993). flows and high sedimentation The rates, final and stagethis could (the reducereef stage) their abilityrepresents to produce the greatest difference and maintain sufficient between H2S levels Mesozoic to produce fall communitiesa chemosynthetic and communitycontemporary whale falls. The (Lundsten et al. 2010). difference As SMNS is81841 due tois thecomparatively evolution of smallthe bone-eating (roughly worm Osedax greatly

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 360 reducing the REFERENCES ability of nekton falls to produce a reef stage, due to the rapid decomposition of whale bones by this organism (Vrijenhoek et al. Bennett, B.A., Smith, C.R., Glaser, В., and Maybaum, H.L., 1994, Faunai 2009; Lundsten community structure of a chemoautotrophic assemblage on whale bones in the deep et al. 2010). Molecular evidence suggests a Late Cretaceous northeast Pacific Ocean: Marine Ecology Progressor Series, v. 108, p. 205-223.early Paleogene origin for Osedax , which reduced the importance Danise, S., Twitchett, R.J., and Matts, К., 2014,of Ecological succession of thea Jurassic reef stage from this period onward (Vrijenhoek et al. shallow- water ichthyosaur fall: Nature Communications, v. 5, no. 4789, p. 1-8, doi: 2009; Lundsten 10.1038/ncomms5789. et al. 2010). Collectively, the carcass-fall community described Dietl, G., 1977, The Braunjurahere (Brown Jurassic) in Southwest Germany: differsStuttgarter from the contemporary role of large nekton falls, wherein Beiträge zur theyNaturkunde, Series В, v. 25, p. 1-41. produce a unique environment (high in hydrogen sulfide) for colonization Duffin, С. J., 1997, The dentition of Hybodus hauffianus FRAAS, 1895 (Toarcian, Early by chemosynthetic taxa which are otherwise restricted in Jurassic): Stuttgarter Beitrage zur Naturkunde, Series В, v. 256, p. 1-20. the surrounding Friedman, M., Shimada, К., Martin, L., Everhart, M., Liston, J., Maltese, A., and region (due to lack of nutrients/hard substrate). 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As was described Kauffman, E.G., 1978, Benthicabove, environments and paleoecology of the Posidonienschiefer the presence of Dactylioceras ammonites and Sinosura (Toarcian): Neues Jahrbuch für Geologie und Paläontologie Abhandlungen, v. 157, brodiei p. 18-36.ophiuroids (Fig. 6) suggest a well-developed enrichment opportunist stage. Kiel, S., 2008, Fossil evidence for micro- and macrofaunal utilization ofSecondly, large nekton- the high diversity of bivalves (compared to the surrounding falls: examples from early Cenozoic deep-water sediments in Washington State,matrix USA: and other stratigraphie units) suggests that the Palaeogeography, Palaeoclimatology, Palaeoecology, v. 267, p. 161-174, doi: 10.1016/ carcass of SMNS 81841 influenced and altered the local biodiversity by j.palaeo.2008.06.016. acting as Kiel, S., and Tyler, P., 2010,a Chemosynthetically-dnven hard ecosystems m the deep sea, in substrate for colonization. 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CONCLUSIONS York, Springer, p. 1-14. Lundsten, L., Schlining, K, Frasier, K, Johnson, S., Kuhnz, L., Harvey, J., Clague, G., and Vrijehoek, R., 2010, Time-series analysis of six whale-fall Overall, an analysis of SMNS 81841 suggests that the communities event in Monterey Canyon, California, USA: Deep-Sea Research Part I, v. communities (particularly ichthyosaur falls) of the early 57,Toarcian p. 1573-1584. Southwest German Basin, while rare, were of a higher diversity Martill, D.M.,than 1987, A taphonomic and diagenetic case study of a partially articulated ichthyosaur: Palaeontology, v. 30, no. 3, p. 543-555. conventionally predicted, with ichthyosaur carcasses producing Martill, D.M., large 1993, Soupy substrates: a medium for the exceptional preservation of aggregations of preexisting background taxa. However, this appearsichthyosaurs to of the Posidonia Shale (Lower Jurassic) of Germany: Darmstädter occur only when favorable conditions on the sea floor (either Beiträgeincreased zur Naturgeschichte, v. 2, p. 77-97. Martill, D.M., Cruickshank, A.R., and Taylor, M.A., 1991, Dispersal via whale oxygen levels or increased substrate availability) produce a preexisting bones: Nature, v. 351, no. 6323, p. 171-250, doi: 10.1 038/351 193a0. increase in benthic biodiversity. In most examples examined, ichthyosaur Martill, D.M., Taylor, M.A., Duff, K.L., Riding, J.B., and Bown, P.R., 1994a, The carcasses showed little evidence of having been scavenged or trophiccolonized structure of the biota of the Peterborough Member, Oxford Clay Formation postmortem. Given this, it is suggested here that ichthyosaur (Jurassic), carcasses UK: Journal of the Geological Society, London, v. 151, p. 173 - 194. Martill, D.M., Cruickshank, A.R., and Taylor, M.A., 1994b, Speculations on the appear to have played a minimal role in the SWGB benthic role ecology. of marine reptile deadfalls in Mesozoic deep-sea paleoecology: comment and There is also currently no evidence to suggest that ichthyosaur reply: carcasses PALAIOS, v. 10, p. 96-97. produced chemosynthetic communities, which is in contrast Maxwell, to E., 2012,the New metrics to differentiate species of Stenopterygius (Reptilia: Ichthyosauria) from the Lower Jurassic of southwestern Germany: Journal of situation in fossil and contemporary whale falls. This raises a Paleontology,number of v. 86, no. 1, p. 105-115, doi: 10.1666/11-038.1. questions regarding the ecology of the Mesozoic vent and seep McGowan, biota, C., and and Motaní, R., 2003, Ichthyopterygia, in Sues, H.-D., ed., Handbook their relationship to nekton falls. Further research (particularly of of Paleoherpetology: deep- München, Verlag Dr. Friedrich Pfeil, 175 p. Pavlyuk, O.N., Trebukhova, Y.A., and Tarasov, V.G., 2009, The impact of implanted water fossil specimens) is necessary to better understand this relationship. whale carcass on Nematode communities in shallow water area of Peter the Great Bay (East Sea): Ocean Science Journal, v. 44, p. 181-188, doi: 10.1 007/s 1 260 1 -009-00 16-1.9. ACKNOWLEDGMENTS Pyenson, N., and Haasl, D., 2007, Miocene whale-fall from California demonstrates that cetacean size did not determine the evolution of modern whale-fall communities: Biology Letters, v. 3, p. 709-711, doi: 10.1 098/rsbl.2007.0342. The author would like to thank Dr. Erin Maxwell for help with specimen Reisdorf, A., Bux, R., Wyler, D., Benecke, M., Klug, С., Maisch, M., Fornaro, P., access and early feedback on this manuscript. The author is also deeply and Wetzel, A., 2012, Float, explode or sink: postmortem fate of lung-breathing indebted to Dr. Andrzej Kaim and a second anonymous reviewer marinefor their vertebrates: Palaeobiodiversity and Paleoenvironments, v. 92, p. 67-81. comments, which greatly improved this manuscript. Lastly, while Riegraf, not W., in Werner, G., and Lörcher, F., 1984, Der Posidonienschiefer: direct support of this project, the author was funded by the StaatlichesBiostratigraphie, Fauna und Fazies des südwestdeutschen Untertoarciums (Lias e): Museum für Naturkunde Stuttgart while completing this manuscript. Ferdinand Enke Verlag, Stuttgart, p. 207.

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