Palaeogeography, Palaeoclimatology, Palaeoecology 537 (2020) 109372 Contents lists available at ScienceDirect Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo Diagenetic changes on bone histology of Quaternary mammals from a T tropical cave deposit in southeastern Brazil ∗ Elver Luiz Mayera,b, , Alex Hubbec,d, Jennifer Botha-Brinke,f, Ana Maria Ribeirob,g, Paulo Miguel Haddad-Martimh, Walter Nevesi a Instituto de Estudos do Xingu, Rua Constantino Ferreira Viana, Quadra 8, Centro, São Félix do Xingu, PA, 68380-000, Brazil b Programa de Pós-Graduação em Geociências, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves 9500, Porto Alegre, RS, 91501-970, Brazil c Departamento de Oceanografia, Instituto de Geociências, Universidade Federal da Bahia, Salvador, BA, 40170-020, Brazil d Instituto do Carste. Rua Barcelona, 240/302, Belo Horizonte, MG, 30360-260, Brazil e Karoo Palaeontology, National Museum, Box 266, Bloemfontein, 9300, South Africa f Department of Zoology and Entomology, University of the Free State, Bloemfontein, 9300, South Africa g Setor de Paleontologia, Museu de Ciências Naturais, Secretaria de Meio Ambiente do Rio Grande Do Sul, Av. Salvador França, 1427, Porto Alegre, RS, 90690-000, Brazil h Instituto de Geociências, Universidade Estadual de Campinas, Campinas, SP, 13083-855, Brazil i Instituto de Estudos Avançados da Universidade de São Paulo, Rua da Praça Do Relógio, 109, São Paulo, SP, 05508-050, Brazil ARTICLE INFO ABSTRACT Keywords: Karst caves are suitable environments for the accumulation and preservation of fossils. Cave deposits are often Diagenesis complex and the environmental conditions within cave sites result from intricate interactions between various Bone preservation biological, physical and chemical factors. However, it is not fully understood how the complexity of the en- Cervidae vironmental conditions of caves influences bone diagenesis. The study of the initial stages of bone diagenesis Tayassuidae depends to a large extent on understanding the changes in the bone histology. To contribute to this issue, we Karst examine a set of postmortem changes affecting the bone histology of Quaternary mammals that accumulated Microstructure naturally in Locus 2, a pitfall site in Cuvieri Cave, located in the tropical region of Brazil. Our analyses show that bones deposited in caves may be subject to a peculiar set of environmental conditions that in tropical regions may prevent the preservation of bone histological structure. The effect of diagenetic processes on the bones differs depending on the taphonomic stage of the bone and the diagenetic alterations appear to haveinfluenced each other. The deposition of bioclasts following the entrapment of individuals in Locus 2 favours the pro- liferation of bacteria on bones and appears to be important in directing the diagenetic alteration. The hydro- logical regime of the cave, that is recharge with potential phases of higher humidity, also is important in di- recting the diagenetic alteration and further decreased the preservation potential of the bone microstructure. The formation of macroscopic and microscopic cracks related to bone weathering in caves shows that the ta- phonomic processes peculiar to these environments are poorly understood, highlighting the need for more re- search to be conducted on cave taphonomy. 1. Introduction decomposition and involving UV radiation, moisture and temperature, among others factors; Behrensmeyer, 1978; Trueman et al., 2004; Bone diagenesis consists of processes by which, after an individual's Pfretzschner, 2000; Pfretzschner and Tütken, 2011) and microbial de- death, bones are altered in the depositional environment. The under- composition (degradation of organic and inorganic elements of bone by standing of the diagenetic processes is important because this phe- direct and indirect effects of microorganisms; Hackett, 1981; Jans et al., nomenon determines if a bone deteriorates until it is completely dis- 2002; see also Kendall et al., 2017). The consequences of both processes integrated or if it is preserved as a fossil. Abiotic and biotic factors can be observed as macroscopic changes, such as weathering cracks on acting on bones influence diagenetic processes, such as bone weath- the external surface of bone (Behrensmeyer et al., 1978; Dirks et al., ering (physical and chemical destruction of bone enabling further 2015; Pokines et al., 2018) and microscopic changes, such as ∗ Corresponding author. Instituto de Estudos do Xingu, Rua Constantino Ferreira Viana, Quadra 8, Centro, São Félix do Xingu, PA, 68380-000, Brazil E-mail addresses: [email protected] (E.L. Mayer), [email protected] (A. Hubbe), [email protected] (J. Botha-Brink), [email protected] (A.M. Ribeiro), [email protected] (P.M. Haddad-Martim), [email protected] (W. Neves). https://doi.org/10.1016/j.palaeo.2019.109372 Received 27 September 2018; Received in revised form 23 July 2019; Accepted 11 September 2019 Available online 03 October 2019 0031-0182/ © 2019 Elsevier B.V. All rights reserved. E.L. Mayer, et al. Palaeogeography, Palaeoclimatology, Palaeoecology 537 (2020) 109372 Fig. 1. Geographic location of the study area and of Cuvieri Cave showing the position of Locus 2 (map courtesy of Laboratório de Estudos Evolutivos Humanos and Grupo Bambuí de Pesquisas Espeleológicas). microcracks on bone histological structure (Pfretzschner, 2000, 2004; paleontological (e.g. Pfretzschner and Tütken, 2011; Trueman et al., Pfretzschner and Tütken, 2011), and tunnels formed by bacteria 2003; Tomassini et al., 2015) and archaeological contexts (e.g. Hollund (Hackett, 1981; Jans et al., 2004). et al., 2012; Jans et al., 2002; Dal Sasso et al., 2014) formed within The diagenetic processes are related to some extent to the hydro- different environmental settings. However, as pointed outby Kendall logical regime of a given environment. Moisture is one of the main et al. (2017), the range of climates and environments explored during elements of bone weathering. It facilitates microbial metabolism and the study of bone diagenesis should be expanded. This is especially the groundwater is the means by which chemical exchanges occur be- important for cave environments, which are known to preserve many tween bones and the environment (Behrensmeyer, 1978; Fernandez- fossils around the world (Lundelius, 2006; Klein, 2009), and for which Jalvo et al., 2010; Hedges et al., 1995; Hedges and Millard, 1995; investigations include uneven research efforts in different climatic Pokines et al., 2018; Trueman et al., 2004; Turner-Walker, 2008). Thus, zones (North Temperate Zone, Bocherens et al., 2008; Hedges et al., hydrology is a major factor that influences the preservation of bone 1995; Quattropani et al., 1999; Nielsen-Marsh and Hedges, 2000a, histology in different depositional environments. Diffusion, hydraulic 2000b; Rogóz et al., 2009; Farre et al., 2014; Monge et al., 2014; Marín- flow and recharge are categories used as reference models to under- Arroyo, 2015; North Tropical Zone, Robles et al., 2002; South Tropical stand how hydrology influences bone diagenesis (Hedges and Millard, Zone, Sillen and Parkington, 1996; Hanson and Cain, 2007). To con- 1995). The diffusion regime is typical of soaked soils, where there isno tribute to broadening the spectrum of conditions investigated for bone gradient in the hydraulic potential neither in time nor in space, whereas diagenesis, this study aims to examine a set of postmortem changes in the hydraulic flow regime the quantity of water is more orless affecting the bone histology of Quaternary mammals that naturally constant in time, but variable in space. In the recharge regime the hy- accumulated in a pitfall deposit in Cuvieri Cave, located in the tropical draulic potential is more or less constant in space, but variable in time region of Brazil. Our findings provide important information on the (Hedges and Millard, 1995). Fluctuations in the recharge regime are influence of depositional environments on skeletal remains preserved in considered to be the most harmful for the microscopic integrity of karst caves. skeletal tissues (Hedges and Millard, 1995; Nielsen-Marsh and Hedges, 2000a; Kendall et al., 2017). In contrast, the diffusion regime seems to 1.1. Study site: Cuvieri Cave cause relatively little microscopic change (Hedges and Millard, 1995; Nielsen-Marsh, 2000a; Kendall et al., 2017). The Cuvieri Cave is situated within the Lagoa Santa Karst, in the Among terrestrial ecosystems, karst caves are suitable environments state of Minas Gerais, eastern Brazil (Fig. 1; entrance coordinates: UTM for the accumulation and preservation of fossils because the interior 7846105 N and 0603756 E; fuse 23K; Corrego Alegre Datum). The generally consists of protected areas, presenting less variable conditions current entrance of Cuvieri Cave (around 1.5 m × 1 m) is at the base of than its surroundings (i.e. temperature and humidity) and sediments a doline. After the entrance the cave develops into a sub-horizontal with pH levels that can buffer the dissolution of bones (Lundelius, 2006; passage that ends in three vertical pits, with no noticeable connection Simms, 1994). Deposits in karst caves preserve fossils of many verte- between them. The pits have been named Loci 1, 2 and 3, and ap- brate groups from the Paleozoic, Mesozoic, and Cenozoic, from fish to proximate depths of 16 m, 4 m and 8 m, respectively (Fig. 1) (see humans (Lundelius, 2006