A new taphonomic bioerosion in a Miocene lakeshore environment M. Dolores Pesquero a,b, ⁎, Carmen Ascaso c , Luis Alcalá a , Yolanda Fernández-Jalvo b a Fundación Conjunto Paleontológico de Teruel-Dinópolis, Avda. Sagunto s/n, 44002 Teruel, Spain b Museo Nacional de Ciencias Naturales (CSIC), C/José Gutiérrez Abascal 2, 28006 Madrid, Spain c Instituto de Recursos Naturales, Centro de Ciencias Medioambientales (CSIC), C/Serrano 115-bis, 28006 Madrid Spain abstract article info Article history: Received 14 October 2009 Received in revised form 7 May 2010 Accepted 28 May 2010 Available online 9 June 2010 Keywords: Miocene Microboring Bacteria Aquatic ecosystems Concud Teruel Spain This study describes a new type of taphonomic alteration of fossil bone that occurred in a continental carbonate palaeolake environment at the reference Spanish Miocene site of Cerro de la Garita (Concud, Teruel). Scanning electron microscopy showed this type of alteration to be characterized by microtunnels that penetrate inward from the bone surface and by a branching-meandering arrangement of microchannels on the bone surface. These microtunnels had a highly electron dense inner wall, seen as a characteristic rim in transverse section. Microspheres were seen inside the microtunnels. Both this electron dense layer and these microspheres were found to be composed of calcium phosphate. These taphonomic modifications bear some similarities to, but also differs from, those caused by bacterial attack on bone and enamel in marine and terrestrial environments, suggesting the present process to be a new type of bioerosion. The microspheres inside the microtunnels were similar in size, shape and composition to the fossilized bacteria covering fossils from Fossil-Lagersttäten palaeolake sites, such as Libros (Teruel, Spain) and Messel (Germany). Under the transmission electron microscope these structures showed an apparent cell wall, suggesting them to be fossilized coccoid bacteria. © 2010 Elsevier B.V. All rights reserved. 1. Introduction 1.1. Microboring and activity of microorganisms Wedl (1864) was the first to describe microboring affecting the bone structure, a phenomenon he attributed to fungal attack. Hackett (1981) distinguished four types of microscopic focal destruction (MFD) of such bone which he divided into three non-Wedl-types (linear longitudinal, lamellate and budded foci) and one Wedl-type. Hackett (1981) attributed the first three types to bacterial activity and described the areas so attacked to be surrounded by zones of remineralization. Hedges et al. (1995) proposed an index of histolog- ical destruction (the Oxford Histology Index, OHI) for describing the overall extent to which the histological integrity of post-mortem bone attacked in this way is lost, from stage 0 (with no original histological features identifiable other than Haversian canals) to stage 5 (with less than 5% of bone affected by bacterial attack). The distribution of modifications affecting the bone matrix made by indigenous bacteria during decay is conditioned by the histological microstructure of the bone in question (Bell, 1990; Jans et al., 2002, 2004; Turner-Walker and Jans, 2008). However, the marks left by bacteria in non-Wedl alteration may appear dispersed, independent of the vascular or cell network; such bacterial activity is post-depositional or post-skeleto- nization (i.e., appearing after the soft tissues have disappeared) (Bell and Elkerton, 2008; Fernández-Jalvo et al., 2010). The most commonly observed type of non-Wedl microbial bone deterioration in terrestrial environments involves discrete zones that in backscattered scanning electron microscopy (BSE-SEM) are seen to contain small pores and thin channels 0.1–1.0 μm in diameter (Hackett, 1981; Bell, 1990; Bell et al., 1991, 1996; Turner-Walker et al., 2002; Jans, 2005). These zones are often surrounded by an electron dense region marking the limit of the affected area. Jackes (1990) hypothesized that this was due to coccoid bacteria removing collagen from the solubilized compactum and then reprecipitating bone mineral in a more dense form. Using the scanning electron microscope (SEM), Jackes et al. (2001) showed a rim surrounding the destructive foci to be much more electron dense than unaltered bone. These authors indicated these rims to contain more mineral (a higher percentage of Ca + P) and less organic matter (collagen) than the surrounding unaltered bone. The remaining type of microscopic focal destruction in post-mortem bones (i.e., Wedl microscopic focal destruction) involves microboring similar to that seen by Wedl (1864). Roux (1887) agreed with Wedl that this bioerosion was the product of fungal activity and assigned such microborings to the ichnogenus Mycelites ossifragus. Arnaud et al. (1978) sectioned medieval human bones from a shipwreck and observed microboring similar to this Wedl type alteration. However, these authors were unable to find any microorganism inside the microtunnels that might have given rise to them. Ascenzi and Silvestrini (1984) extended the study to experimental work and analysed both medieval and modern human bones collected from sea water using the Palaeogeography, Palaeoclimatology, Palaeoecology 295 (2010) 192–198 ⁎ Corresponding author. Fundación Conjunto Paleontológico de Teruel-Dinópolis, Avda. Sagunto s/n, 44002 Teruel, Spain. Fax: +34 978 617 638. E-mail address: pesquero@fundaciondinopolis.org (M.D. Pesquero). 0031-0182/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2010.05.037 Contents lists available at ScienceDirect Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo