Pliocene Stratigraphic Paleobiology in Tuscany and the Fossil Record Of
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FLORE Repository istituzionale dell'Università degli Studi di Firenze Pliocene stratigraphic paleobiology in Tuscany and the fossil record of marine megafauna Questa è la Versione finale referata (Post print/Accepted manuscript) della seguente pubblicazione: Original Citation: Pliocene stratigraphic paleobiology in Tuscany and the fossil record of marine megafauna / Dominici, Stefano; Danise, Silvia; Benvenuti, Marco. - In: EARTH-SCIENCE REVIEWS. - ISSN 0012-8252. - ELETTRONICO. - 176(2018), pp. 277- 310. [10.1016/j.earscirev.2017.09.018] Availability: This version is available at: 2158/1139176 since: 2020-12-18T15:37:43Z Published version: DOI: 10.1016/j.earscirev.2017.09.018 Terms of use: Open Access La pubblicazione è resa disponibile sotto le norme e i termini della licenza di deposito, secondo quanto stabilito dalla Policy per l'accesso aperto dell'Università degli Studi di Firenze (https://www.sba.unifi.it/upload/policy-oa-2016-1.pdf) Publisher copyright claim: (Article begins on next page) 10 October 2021 Earth-Science Reviews 176 (2018) xxx–xxx Contents lists available at ScienceDirect Earth-Science Reviews journal homepage: www.elsevier.com/locate/earscirev Pliocene stratigraphic paleobiology in Tuscany and the fossil record of MARK marine megafauna ⁎ Stefano Dominicia, , Silvia Daniseb, Marco Benvenutic a Università degli Studi di Firenze, Museo di Storia Naturale, Firenze, Italy b Plymouth University, School of Geography, Earth and Environmental Sciences, Plymouth, United Kingdom c Università degli Studi di Firenze, Dipartimento di Scienze della Terra, Firenze, Italy ABSTRACT Tuscany has a rich Pliocene record of marine megafauna (MM), including mysticetes, odontocetes, sirenians and seals among the mammals, and six orders of sharks among the elasmobranchs. This is reviewed with respect to paleogeography and sequence-stratigraphy in six different basins. Conditions at the ancient seafloor are explored by means of sedimentary facies analysis, taphonomy and multivariate techniques applied to a large quantitative dataset of benthic molluscs. MM is rare or absent in most basins during the Zanclean, except in one basin, and most abundant in Piacenzian deposits in all six basins. MM occurs preferentially in fine-grained, shelfal high- stand-deposits of small-scale depositional sequences, or at condensed horizons of the maximum flooding in- terval. It is rare in shallow marine paleonvironments and nearly absent in bathyal paleosettings. Paleogeographic and paleoecological evidence and a comparison with modern patterns of marine upwelling suggest that a wedge of nutrient-rich waters sustained in the offshore during the Pliocene a high biomass of primary producers and a community of apex consumers and mesopredators, similarly to the modern northwestern Mediterranean Sea, with a species-richness higher than the modern and a more complex trophic structure. The highest MM diversity coincides with the mid-Piacenzian warm period, suggesting that facies control does not obscure a link between climate and diversity. We underline however that not all marine environments were suitable for marine mammal preservation. Buoyant carcasses were preferentially dismembered and destroyed in high-energy shallow waters, with the possible exception of delta front deposits, where sudden sediment input occasionally buried pristine carcasses. We hypothesise that carcasses sunken on the seafloor below the shelf break underwent destruction through the activity of a whale-fall biota of modern type, specialised in the consumption of decomposing tissues, both soft and mineralised. A taphonomic window was left between storm wave base and the shelf break. Here water pressure is high enough to prevent the formation of decomposing gases and the resurfacing of carcasses, while the lack of a specialised whale-fall biota slows down bone degradation with respect to deeper settings. Sedimentation rate was high enough to cover skeletal material before its complete destruction. An estimate of paleobathymetries based on multivariate techniques suggests that the preferential depth for the inclusion of MM in the fossil record was 30–300 m. The results are compared with major Mesozoic and Cenozoic MM records worldwide. Available evidence suggests that the late Neogene radiation of large whales, true ecosystem engi- neers, and their size increase, triggered the radiation of a bone-eating fauna that hampered, and hampers, MM preservation in the deep sea. Stratigraphic paleobiology and an ecosystem-level approach deliver useful insights to the nature of the fossil record. 1. Introduction macroevolutionary scale, predation pressure has shaped the evolution of marine preys, with feedbacks on predators, setting the stage for the The modern marine megafauna (MM) includes all marine mammals, Mesozoic marine revolution (Vermeij, 1977; Chen and Benton, 2012; seabirds, sea turtles and sharks, apex consumers that influence their Benton et al., 2013). The new ecosystem structure started in the Early associated ecosystems (Lewison et al., 2004), both pelagic and near- and Middle Triassic with several lineages of actinopterygian fishes shore, through top-down forcing and trophic cascades, and now se- (Chen and Benton, 2012), continuing with marine reptiles possessing verely affected by human impact (Estes et al., 1998, 2011, 2016). On a feeding styles (Fröbisch et al., 2013; Motani et al., 2015; but see also ⁎ Corresponding author. E-mail address: stefano.dominici@unifi.it (S. Dominici). http://dx.doi.org/10.1016/j.earscirev.2017.09.018 Received 23 May 2017; Received in revised form 21 September 2017; Accepted 22 September 2017 Available online 28 September 2017 0012-8252/ © 2017 Elsevier B.V. All rights reserved. S. Dominici et al. Earth-Science Reviews 176 (2018) xxx–xxx Motani et al., 2013) and reproductive adaptations (Motani et al., 2014) holistic approach that includes functional diversity and embraces as of modern type. Triassic and Jurassic novelties underwent a prolonged many ecosystem components as possible (Dineen et al., 2014). By crisis during the Cretaceous, with the gradual extinction of plesio- analogy with ecologists who shift focus from models based on single saurians, mosasaurs (Benson et al., 2010) and ichthyosaurs (Fischer groups (e.g., Steeman et al., 2009) to an all-embracing vision of marine et al., 2016), and a diversity drop of sharks (Guinot et al., 2012). A life (Lawton, 1994; Sergio et al., 2014), connecting food web ecology marine megafauna of comparable size returned in the Paleogene, with with landscape ecology (Polis et al., 1997; Estes et al., 2011), strati- the new diversification of neoselachian elasmobranchs (Kriwet and graphic paleobiology can draw from the fossil record and offer multi- Benton, 2004) and the evolution of large marine mammals: Eocene dimensional insights on the complex geological history of modern archaeocetes (Uhen, 2008; Gingerich et al., 2009) and Oligocene marine ecosystems. odontocetes and mysticetes (Gingerich, 2005; Marx and Uhen, 2010; After revising fossil MM hosted in major museums of Tuscany, both Berta, 2012; Marx et al., 2016) empowered by high metabolic rates and isolated and articulated remains, we focus on all fossil bones that can be new anatomic features (Armfield et al., 2013). Among the largest ver- stratigraphically (e.g., Bianucci, 1995; Bianucci et al., 1998, 2001; tebrates of all times, after a dramatic size increase at the outset of Tinelli, 2013) and taphonomically framed (e.g., Dominici et al., 2009; glacial age (Marx et al., 2016; Bisconti et al., 2017; Slater et al., 2017), Bianucci et al., 2010; Danise and Dominici, 2014). MM lists for the baleen and sperm whales are among today's ocean's ecosystem en- Mediterranean Pliocene have been recently updated (marine mammals: gineers (Roman et al., 2014) with which to compare their Mesozoic Landini et al., 2005; Bianucci et al., 2009a; Sorbi et al., 2012; Bianucci analogues (Smith et al., 2016). Notwithstanding a crucial role in and Vomero, 2014; sharks: Marsili, 2006). Species-level ecological data ecology and evolution, the nature and distribution of the MM fossil are available on modern apex consumers and mesocarnivores (Pauly record has been less explored, compared to that of marine invertebrates et al., 1998; Cortés, 1999), with detailed information made available and terrestrial vertebrates. Available data suggest a strong correlation for Mediterranean species following conservation concerns (marine between taxic diversity and the number of marine fossiliferous forma- mammals: Notarbartolo di Sciara et al., 2016a; sharks: Cavanagh and tions, resulting in megabiases in the fossil record (e.g., Cretaceous: Gibson, 2007), allowing for a detailed paleoecological evaluation of the Benson et al., 2010). Within its vast history, studies on the geologically Tuscan fossil record. The actualistic approach is also viable for species recent marine megafauna offer important insights, considering our of benthic molluscs, about half of which are still extant in modern better knowledge of: (1) geological setting, in terms of outcrop extent Mediterranean bottoms (55% of extant species of Mediterranean and and high-resolution stratigraphy; (2) ecologic role played by individual North Sea bivalves, excluding strictly brackish and bathyal forms, i.e., species, whether extant or extinct, in terms of habitat, trophic role, life 202 out of 367 species, survive from the Zanclean: Raffi et al., 1985). histories and population structure, thanks to a comparison with extant The regional