PALAIOS, 2009, v. 24, p. 723–725 Spotlight DOI: 10.2110/palo.2009.S06 SPOTLIGHT TAPHONOMY OF VERTEBRATE MICROFOSSIL ASSEMBLAGES IN COASTAL ENVIRONMENTS: IN SEARCH OF A MODERN ANALOGOUS MODEL ROMAIN VULLO Universite´ de Rennes 1, UMR CNRS 6118, 263 Avenue du Ge´ne´ral Leclerc, 35042 Rennes, France e-mail: romain.vullo @ gmail.com Coastal environments, located halfway between continental and marine realms, are peculiar settings that concentrate and preserve diverse assemblages of mixed autochthonous and allochthonous organisms (Fig. 1). Vertebrate microfossil assemblages are regularly described from Cretaceous coastal deposits, but taphonomic and stratinomic processes involved in the formation of such accumulations often remain unclear. Actuotaphonomic studies dealing with the composition, distribution, and preservation of a specific group (i.e., ecological fidelity) within a modern coastal thanatocoenosis mainly concern such invertebrates as mollusks (Bosence, 1979; Cumins et al., 1986; Henderson and Frey, 1986; Kidwell, 2008) and echinoderms (Greenstein, 1989). For vertebrates, burial experiments have been conducted using large carcasses of marine turtles (Meyer, 1991), but actuotaphonomic analyses have never been performed on microremains. Peculiar detrital beds, with a calcareous bioclastic facies called falun in French, from the Late Cretaceous (early Cenomanian) of south- western France (Charentes region) have yielded a rich and diverse assemblage of vertebrate microremains (Vullo et al., 2003; Vullo, 2007) (Fig. 1H–J). A faunal analysis revealed that the association is largely dominated by small selachians, especially the primitive nurse-shark Cantioscyllium. It can be inferred from the small size, size distribution, and abrasion of the teeth that juveniles may have inhabited the depositional environment. Such selachians probably used this shallow coastal area as a nursery, like that observed in the extant nurse shark Ginglymostoma cirratum and various other species (Pratt and Carrier, 2007; Nagelkerken et al., 2008). Co-occurring vertebrates are repre- sented by small bony fishes (e.g., pycnodontids), frogs, turtles, crocodiles, pterosaurs, theropod dinosaurs, snakes, and marsupial-like mammals. Most of the tetrapods (terrestrial or amphibious) may have lived in or near a mangrove-type forest (Vullo et al., 2003; Girard et al., 2008). Their remains can be considered as subautochthonous elements that were deposited in a shallow marine lagoon after short-distance transport. In order to test this paleoecological and paleoenvironmental interpretation, I decided to sample recent sediments in a modern setting that displays features analogous with the early Cenomanian biota of Charentes. The selected area included the small islands of Bimini (western Great Bahama Bank, Bahamas). At Bimini, the shallow-marine inner lagoon and the Rhizophora–Avicennia mangrove forest developing along channels and shorelines provides feeding, mating, and nursery habitats for many species, including the lemon shark (Negaprion brevirostris) (Morrisey and Gruber, 1993) (Fig. 1A– F). Marine sediment consists mainly of coarse, calcareous sand dominated by bioclasts (bivalves, gastropods, calcareous algae, foraminifera) (Fig. 1G), which are also found on other Great Bahama Bank sites (Welle et al., 2004). Bimini, being located on an isolated carbonate platform, has no terrigenous, siliciclastic sediment input. In various intertidal and shallow subtidal sites (,1 m deep) characterized by a low to moderate energy, 11 sediment samples were collected in the superficial layer (0–20 cm) and then sieved through 2 mm and 0.5 mm screens. For all samples, the dry residue was sorted under binocular microscope, but no vertebrate remains were found. This result is rather unexpected, particularly for the sediment sample coming from a shark- holding pen (Fig. 1F). Several combined factors can be proposed to explain the apparent absence or perhaps the extreme rarity of vertebrate remains in the sediments of Bimini. Although the fish population density is high at Bimini, the relatively high sedimentation rate due to the intensive calcareous bioclast production may obscure any tooth or bone accumulations, which is likely similar to conditions that formed Cenomanian bioclast-dominated facies. In addition, vertebrate remains such as teeth can be transported from shallow areas of the lagoon to deeper settings. Greenstein (1989) noted that echinoderm material from a Caribbean reefal setting undergoes limited transport and accumulates at the base of the reef slope. He concluded that the distribution of echinoderm skeletal elements does not reflect that of the living echinoid fauna. This hypothesis, however, should be rejected because most of sediment samples collected at Bimini come from low-energy, confined Romain Vullo received his Licence degree in biology from the University of La Rochelle. He earned his Master’s and Ph.D. degrees in biology at the University of Rennes, where he is currently an Assistant Professor in paleontology working on Cretaceous vertebrate assemblages. He spent one year at the Autonomous University of Madrid working with A ´ ngela D. Buscalioni studying material from the Cretaceous of the Iberian Peninsula. His Ph.D. research (advised by Didier Ne´raudeau, Rennes, and Henri Cappetta, Montpellier) dealt with the systematic, taphonomic, and paleoecological analysis of vertebrate assemblages from the Late Cretaceous paralic deposits of southwestern France. Questioning stratinomic processes that led to such assemblages, he also spent one month at the Bimini Biological Field Station (BBFS Sharklab, operated by Samuel H. Gruber, Miami) in the Bahamas to test the fidelity of death assemblages against the local living vertebrate community in modern sediments, using an actuotaphonomic approach. Copyright G 2009, SEPM (Society for Sedimentary Geology) 0883-1351/09/0024-0723/$3.00