Taphonomic aspects of the Pleistocene vertebrate assemblage of Itaboraí, state of Rio de Janeiro, southeastern Brazil

Journal of South American Earth Sciences 46 (2013) 26e34

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Taphonomic aspects of the Pleistocene vertebrate assemblage of Itaboraí, state of Rio de Janeiro, southeastern Brazil Hermínio Ismael de Araújo Júnior a, *, Victor Hugo Dominato a, Cristina Bertoni-Machado b, Leonardo dos Santos Avilla c a

Universidade Federal do Rio de Janeiro, Programa de Pós-Graduação em Geologia, Instituto de Geociências, CCMN, Cidade Universitária, Ilha do Fundão, Av. Athos da Silveira Ramos, 274, Bloco G, 21941-916 Rio de Janeiro, RJ, Brazil Universidade Federal do Rio Grande do Sul, Instituto de Geociências, Laboratório de Modelagem de Bacias, Av. Bento Gonçalves 9500, Prédio 43130, Campus do Vale, 91501-970, Brazil c Universidade Federal do Estado do Rio de Janeiro (UNIRIO), Departamento de Zoologia, Laboratório de Mastozoologia, Av. Pasteur, 458, sala 501, Urca, 222290-240 Rio de Janeiro, RJ, Brazil b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 25 October 2012 Accepted 2 May 2013

Pleistocene vertebrates from Itaboraí Basin have not been taphonomically studied prior to this work, limiting the understanding of the deposition and preservation of the only Pleistocene vertebrate accumulation known for the state of Rio de Janeiro. In this work, the taphonomic signatures of the Pleistocene vertebrate assemblage of Itaboraí are identified and interpreted in order to increase the knowledge about the formation of this fossil association and the paleoecology of the region of Rio de Janeiro during the late Pleistocene. Our analysis shows that the thanatocoenosis was exposed to the biostratinomic processes during a small time span; that it is parautochthonous; and experienced short transport distances by normal fluvial streams and floods. Subsequently, the fossiliferous horizon was quickly covered by the superjacent soil. Yet, the skeletal elements were fractured and deformed during the sedimentary compaction. The differential preservation of megamammal bones is associated to the bone resistance against those destructive processes and to the specific anatomical features. Comparison between Itaboraí and other Brazilian Pleistocene vertebrate accumulations shows that the Itaboraí fossil accumulation was less affected by taphonomic processes, although it is also a time-averaged fossil concentration. Finally, some of the taphonomic features indicate an arid paleoclimate. Ó 2013 Elsevier Ltd. All rights reserved.

Keywords: Taphonomy Vertebrates Late Pleistocene Itaboraí State of Rio de Janeiro

1. Introduction The Brazilian vertebrate fossil accumulations are commonly studied in terms of their taxonomic and paleoecological aspects, whereas there are few taphonomic approaches for these associations (Holz and Barberena, 1989; Bertoni-Machado and Holz, 2006; Bertoni-Machado et al., 2008; Araújo-Júnior and Porpino, 2011; Dominato et al., 2011; Araújo-Júnior et al., 2013; Avilla et al., 2013). The identification and interpretation of taphonomic signatures of fossil vertebrates allow the recognition of physical, chemical and biological processes that control the genesis of fossil concentrations. In addition, Taphonomy is also a tool for understanding the modifications that acted upon a biocoenosis and transformed it into a * Corresponding author. Tel.: þ55 2180153603. E-mail addresses: [email protected] (H.I.de Araújo Júnior), [email protected] (V.H. Dominato), [email protected] (C. Bertoni-Machado), [email protected] (L.dosS. Avilla). 0895-9811/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jsames.2013.05.001

taphocoenosis (Damuth, 1982; Behrensmeyer et al., 2000; Paw1owska, 2010); and to make paleoenvironmental inferences (Dominato et al., 2011). Among the few vertebrate fossil assemblages known for the state of Rio de Janeiro, southeastern Brazil, the São José de Itaboraí Basin (or only Itaboraí Basin; Itaboraí municipality) is the most noteworthy one. The basin has Paleocene age and contains a rich record of mammals, birds, crocodiles and amphibians (Paula-Couto, 1949; Bergqvist, 1996, 2005). Its geology was well studied (Medeiros and Bergqvist, 1999) and there are also some previous taphonomic studies made with Paleocene fossils (Bergqvist et al., 2011). However, the Itaboraí municipality also has a Pleistocene vertebrate fossil record, collected nearby the São José de Itaboraí Basin in 1969 by geologists and paleontologists of Divisão de Geologia e Mineralogia do Departamento Nacional de Produção Mineral do Rio de Janeiro (DNPM/RJ; Price and Campos, 1970). Studies related to Pleistocene of Itaboraí are scarce, and the work of Price and Campos (1970) stands out. They described

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previously collected bones and provided assignments to Eremotherium sp. (Pilosa: Megatheriidae), Haplomastodon sp. (Proboscidea: Gomphotheriidae), Testudo sp. (Cryptodira: Testudinidae) and Testudinidae nec Testudo. Furthermore, those authors also described the lithology of the deposit and, based on both the lithology and faunal record, made paleoclimatic inferences for the locality. Recently, Oliveira et al. (2010) analyzed the dental wear of Gomphotheriidae and recognized at least two adult individuals for the fossil accumulation of Itaboraí. Considering the few works regarding the Pleistocene fossils of Itaboraí and the scarcity of taphonomic studies on fossil vertebrate assemblages of the region of Rio de Janeiro, this study aims to identify and interpret the taphonomic signatures observed on the Pleistocene vertebrate assemblage of Itaboraí. As a result, this study will increase our understanding of the depositional environment and the preservational aspects of this material and their bearing on the paleoecology of the Itaboraí region during the late Pleistocene. 2. Study area and geologic setting The Pleistocene deposit containing these fossils overlies a gneiss basement. The site is situated 100 m south of the southern margin of Itaboraí Basin (22 500 2000 S, 42 520 3000 W), at the Itaboraí municipality, state of Rio de Janeiro (Figs. 1 and 2A). The total area of the fossiliferous unit is still unknown.

Fig. 2. Geological aspects of the Pleistocene deposit of Itaboraí; A. South edge of the Itaboraí Basin, emphasizing area where the Pleistocene fossils of Itaboraí were collected; B. Stratigraphy of the deposit (after Price and Campos, 1970).

Currently, the exact place where the fossils were collected is unknown because the remains of calcareous explored from Itaboraí Basin is overlying the area. According to Price and Campos (1970), the excavated area of the deposit was 6 m of length and 1.3 m of depth, and is overlain by a reddish soil of varied thickness. The fossiliferous layer (Fig. 2B) consists in a conglomerate with framework formed by boulders, cobbles and angular pebbles, but with the predominance of quartz cobbles and silex (Price and Campos, 1970). The matrix is composed of coarse sand and a high percentage of clay. There are sand lenses within the conglomerate. Price and Campos (1970) observed two distinct layers in the deposit. The lower one is 70 cm thick, dominating the large skeletal elements and the less developed coarse-sandy lenses, indicating the occurrence of fluvial stream on the genesis of this layer. The upper layer has approximately 60 cm thick and consists in a conglomerate composed of small cobbles and pebbles and with the coarser sandy lenses. The authors also observed that between the sequences there is a small yellow layer of ferruginous sand. The specimens analyzed here were found indistinctly in all layers (Price and Campos, 1970). 3. Material and methods Fig. 1. Location map of the Pleistocene deposit of Itaboraí, state of Rio de Janeiro, Brazil (modified from Bergqvist et al., 2011).

The analyzed material comprises 28 specimens, including remains assigned to Eremotherium, Notiomastodon, Testudo and

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Mammalia incertae sedis. The material is housed at the Seção de Paleontologia do Departamento Nacional de Produção Mineral do Rio de Janeiro (DNPM/RJ). Bone modification criteria provided by Hill (1980), Shipman (1981), Behrensmeyer (1991) and Lyman (1994, 2008), such as bone representativeness, fractures, abrasion marks, desiccation marks, deformations, color pattern, teeth marks, trampling, rooting and invertebrate modifications, are applied here. Bone representativeness includes the integrity of the skeletal remains and the identification of the representativeness of skeletal portions. It is expected that rapidly buried accumulations have a large amount of complete bones (Shipman, 1981; Lyman, 1994). Usually, bones are broken by natural processes such as weathering, abrasion, predation, trampling, transport, and during the fossildiagenesis. Based on the bone representativeness, the Number of Identifiable Skeletal Parts (NISP), Minimum Number of Individuals (MNI), and Minimum Number of Elements (MNE) were calculated according to descriptions of Shipman (1981), Badgley (1986) and Lyman (1994). Afterwards, the Relative Abundance for each taxon (%Ri) was calculated applying the Andrews’ formule (Andrews, 1990):

Ri ¼ MNEi=ðMNI  EiÞ  100 where Ri is the relative abundance of the i element, MNEi is the minimal number of the i element in the sample, MNI is the minimal number of individuals of the taxon of interest, and Ei is the number of times which the i element appears in a complete skeleton. The Ei values were based onPaula-Couto (1979) for mammals and Blob (1997) for turtles. The %Ri of bones of Mammalia incertae sedis were not calculated to avoid the inclusion of analytical biases. Although the degree of fragmentation of a fossil accumulation is not diagnostic for taphonomic processes, it can reveal the duration of the time span of subaerial exposure of bioclasts during the biostratinomic phase and the intensity of the agents that modified the bones (Shipman, 1981). In order to classify the fossils analyzed here, they were separated in groups according to three main stages of fragmentation: (A) complete, when more than 90% of the bone is present; (B) partial, when 50e90% of the bone is present; and (C) fragment, when the bone is represented by less than 50% of its total (Behrensmeyer, 1991). Regarding the breakage patterns, only the long bones (femurs, humeri and phalanges) were considered in the analysis because the types of fractures are more easily diagnosed on these elements. The fracture patterns were based on Shipman et al. (1981). Multiple fractures were also analyzed for all elements (Cladera et al., 2004). Desiccation marks are features produced by weathering on bones and the most common ones are fractures along the long bone axis and mosaic fractures on the bone articular surfaces. Generally, desiccation marks can be used to infer the time of subaerial exposure of the thanatocoenosis prior to burial (Behrensmeyer, 1978; Shipman, 1981). Based on the size and depth of these fractures, the specimens can be positioned on the Behrensmeyer’s weathering scale (Behrensmeyer, 1978), which ranges from 0 (zero) to 5 (five), where 0 comprises the elements without desiccation marks and 5 comprises the extremely weathered elements. Abrasion marks are produced by the collision of particles carried by wind or water upon the bone surface. During the abrasion, edges, anatomic crests and fractures tend to get rounded. In extreme cases, the bone surface can be totally removed by abrasion (Shipman, 1981). The teeth marks allow the identification of carnivore and/or scavenger activities on bones during the biostratinomy (Shipman, 1981; Lyman, 1994). On the other hand, marks produced by invertebrates reveal necrophagy during the necrolysis (Behrensmeyer, 1991; Kaiser, 2000). Usually, teeth and invertebrate marks provide

information related to time-averaging of skeletal remains before burial (Shipman, 1981; Behrensmeyer, 1991; Lyman, 1994; Rogers et al., 2007). Root marks are commonly found on fossils from deposits that allowed the rooting of vascular plants or in layers that were not rapidly covered by other layers (Behrensmeyer et al., 1995; Montalvo, 2002). Deformations are physical alterations caused by the pressure of the overlying sediment. These features usually modify the anatomical details of bones and can mislead the taxonomic identification of fossils. In addition, the progressive deposition of minerals in the cancellous bone can also deform the bone tissue by expansion (Medeiros, 2010; Sinibaldi, 2010). 4. Results 4.1. Taxonomic remarks and bone representativeness Among the 28 specimens of the fossil assemblage of Itaboraí, there are elements of the mammalian megafauna and one small turtle (Fig. 3A). The fossils assigned to Eremotherium sp. by Price and Campos (1970) are considered here as Eremotherium laurillardi because the morphological characters of the specimens (mainly teeth, femur and phalanges) are according to descriptions of Cartelle (1992) for this species. The Brazilian species of gomphotheres was once considered as Stegomastodon waringi (Alberdi et al., 2002; Prado et al., 2005), however, the species was revised and Notiomastodon platensis is now considered the valid taxon for Itaboraí (Mothé et al., 2012, 2013). For the reason that E. laurillardi and N. platensis have been recorded in this assemblage, the Itaboraí deposit was assigned to the late Pleistocene (Cione and Tonni, 1999, 2005). However, an absolute dating is ongoing in order to elucidate the age of the deposit more decisively. Among the seven specimens listed by Price and Campos (1970) as Testudo sp. and Testudinidae nec Testudo (DGM-548-R, DGM-549-R, DGM-552-R, DGM-553-R, DGM-554-R, DGM-555-R and DGM-556-R), only DGM-552-R (assigned to Testudo sp.) was found in the collection. For DGM552-R we opt for maintaining the original assignment of Price and Campos (1970). Eremotherium laurillardi is the most abundant taxon in the fossil assemblage, followed by N. platensis and Testudo sp., respectively. Some specimens could not be identified because they are poorly preserved and very fragmented. All bones are disarticulated and have distinct degrees of fragmentation. The partially preserved bones (50e90% of bone) are the most frequent, followed by fragments (less than 50% of bone preserved; Fig. 3B). The complete fossils are the less common in the taphocoenosis. Long and short bones are the most abundant, followed by flat ones (Fig. 3C). Table 1 shows the absolute values of bone representativeness (MNI, MNE and %Ri) for each type of skeletal element. The most representative specimens are vertebrae, isolated teeth and podials. The humeri found are represented only by their ends e two distal ends and one proximal end. Femurs are more complete, but all specimens have some degree of fragmentation. The podials are well preserved, but they are more fractured and weathered than phalanges, which are the most complete elements of the assemblage. The only scapula encountered in the assemblage has only its glenoid cavity preserved. The abundance and preservation are better for specimens measuring 15 cm (width)  15 cm (length), but fossils measuring 25 cm (width)  30 cm (length) are also abundant and well preserved. Large elements are also present but in smaller quantities, and measure approximately 40 cm (width)  70 cm (length; Fig. 3D). Mandibles and axis have the highest %Ri (100%) among the skeletal elements, followed by humeri, femurs, podials and maxillae.

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Fig. 3. Analysis of bone representativeness; A. Percentage of skeletal elements according to the taxa recorded; B. Percentage of bones according to the different states of physical integrity; C. Percentage of bones forms present in the fossil concentration; D. Size of the bioclasts (largest width  largest length; in cm).

Phalanges have the lowest %Ri, followed by teeth and vertebrae (excepting axis). E. laurillardi is the taxon with the highest %Ri, followed by N. platensis and Testudo sp., respectively. 4.2. Fractures About 75% of the fossils show at least one type of fracture. The long bones have only irregular fractures perpendicular to the long bone axis. Smooth fractures perpendicular to the long bone axis and jagged and columnar fractures are not present in the specimens. Short and flat bones, such as vertebrae and parts of maxillae

and jaws, have multiple fractures. This kind of fracture on vertebrae was caused by deformations (see Section 4.5). Sandy and clayey sediments are found filling all multiple fractures (Fig. 4). The unbroken fossils comprise phalanges and podials, which are the smaller elements found in the assemblage. 4.3. Desiccation marks About 96.4% of the fossils show desiccation marks (Fig. 5A). Specimens classified in the stages 2 and 1 of Behrensmeyer (1978) are the most abundant in the accumulation. Specimens belonging

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Table 1 Number of skeletal elements in the fossil vertebrate accumulation of Itaboraí with the values for the Number of Identifiable Skeletal Parts (NISP), Minimal Number of Individuals (MNI), Minimal Number of Elements (MNE) and the percentage of Relative Abundance (%Ri). Taxa

Skeletal element

Eremotherium laurillardi

Mandible Isolated tooth Axis Cervical vertebra Lumbar vertebra Caudal vertebra Scapula Femur Astragalus (podial) Scaphoid-trapezoid (podial) Lunar (podial) Phalanx Maxilla

Isolated tooth Humerus

3 3

Testudo sp. Mammalia incertae sedis

Femur Unciform (podial) Phalanx Dorsal scute Cranial fragment Rib Indeterminated

1 1 1 1 1 1 1

Total



Notiomastodon platensis

a

NISP

Position

MNI

1 1 1 1 1 2 1 1 1 1

e e e e e e e Left Left Left

1

1 1 2

Right e Left and right fragments e Two rights and one left Left Left e e e e e

28

e

2

1 a

4

MNE

Ri

1 1 1 1 1 2 1 1 1 1

100% 5.5% 100% 20% 11.1% 14.3% 50% 50% 50% 50%

1 1 1

50% 3.1% 50%

3 2

12.5% 50%

1 1 1 1 1 1 1

25% 25% 1% 7.1%

26

a a a

e

Without MNI and MNE values.

to stage 3 were also identified. Specimens belonging to the stage 4 and 5 (which indicate long time span of subaerial exposure before burial) are absent. The bones that showed the highest degree of desiccation were the caudal vertebrae of E. laurillardi, and only one lumbar vertebra of this species do not presents desiccation. Among the specimens in the stage 2, there are teeth, femurs and humeri of N. platensis, and femurs, vertebrae, teeth, astragalus and lower jaw of E. laurillardi (Fig. 5B). The fragment of plastron assigned to Testudo sp.; maxillae, humeri, carpals and phalanges of N. platensis; and carpals, scapulae, phalanges and axis of E. laurillardi were classified in the stage 1.

Fig. 5. Desiccation marks on the fossils; A. Percentage of fossils in accordance to the weathering stages of the Behrensmeyer’s scale; B. Mandible of Eremotherium laurillardi (DGM-732-M) displaying the stage 2. Arrows indicate desiccation marks. Scale bar ¼ 20 mm.

4.4. Abrasion marks All specimens have wear marks caused by abrasion. Around 92.8% of the fossils present moderated degree of abrasion (Fig. 6A), whereas only 7.2% of bones are very damaged (Fig. 6B). The most

Fig. 4. Articular surface of the humerus of Notiomastodon platensis (DGM-723-M) displaying the multiple fractures filled by sediments. Scale bar ¼ 20 mm.

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damaged specimens are vertebrae and isolated teeth. Among the long bones, phalanges are the smallest skeletal elements found in Itaboraí and they present the lowest degree of abrasion in the assemblage. 4.5. Deformations The deformations occur on three vertebrae of E. laurillardi. Two vertebrae have a deviation of the prezygapophysis to the left side (in cranial view; Fig. 7A). In one vertebra, the vertebral centrum is displaced SEeNW relative to the rest of the vertebral body (according to the position of the neural arch) and, in ventral view, there is a deeper depression on the right size when compared to the left side (Fig. 7B). Yet, the two vertebrae (in lateral view) have a ventral displacement of the cranial portion of the vertebral centrum relative to the caudal portion (Fig. 7C). The third vertebra, represented only by its spinal apophysis, presents a small deformation next to its apical portion and is associated with multiple fractures all over its surface. We discard the possibility that these features are ante-mortem bone alterations because there are no evidences of bone remodeling on both fractures and deformations observed in the vertebrae (Waldron, 2008; Sinibaldi, 2010). 4.6. Other taphonomic features Teeth and trample marks are absent on this assemblage. Other taphonomic features, such as rooting and invertebrate marks, are also absent. Two main colors were observed on bone surface: (A) white (92.8% of the fossils); and (B) reddish (7.2% of the fossils). Reddish bones (one axis and one lumbar vertebra) also have low degree of abrasion and few desiccation marks, whereas white bones are the most damaged. 5. Discussion The most representative bones in the Pleistocene vertebrate assemblage of Itaboraí (vertebrae, isolated teeth and podials) are the most numerous ones in a mammalian skeleton (Moore, 1994). This characteristic probably allowed the high amount of these elements in the deposit. However, the %Ri values show that, although the aforementioned pattern has been occurred, there was a

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remarkable reduction on the number of vertebrae, isolated teeth and podials during the taphonomic history if compared to the elements less abundant in the mammalian skeleton. This fact can be related to the facility that ribs, phalanges and vertebrae have to be scattered (Behrensmeyer, 1975; Voorhies, 1969; Frison and Todd, 1986) or how easily these elements can be destroyed soon after burial (Behrensmeyer et al., 1979; Behrensmeyer, 1991; Lyman, 1994). The large amount of distal ends of humeri can be associated with the higher density of the cancellous tissue of the distal end (Getty, 1981; Lyman, 1994) and with the greater thickness of the compact bone in the same portion (Brain, 1976; Getty, 1981). The small amount of cranial bones can be related to the rapid dissociation of these elements after death (Toots, 1965; Hill, 1979), facilitating their scattering and fragmentation. The presence of a only glenoid cavity of scapula can be assigned to the greater resistance of this portion (Moore, 1994). The phalanges and podials are better preserved because they are the smaller bones and their reduced surfaces are less susceptible to impacts (Bergqvist et al., 2011). The presence of complete and almost complete femurs can reflect transport of these elements from a nearby area (Frison and Todd, 1986; Araújo-Júnior et al., 2012). This corroborates the idea of Price and Campos (1970) that these elements were not transported from more distant areas, but probably closer to their final depositional area. The degree of abrasion suggests the occurrence of a moderate transportation, and possibly indicates a spacial-mixing on this fossil assemblage (Shipman, 1981; Kidwell et al., 1986). The high amount of megamammalian specimens can be related to the large-sized bones of megamammals, once they are more resistant to destruction than skeletal elements of smaller species (Behrensmeyer et al., 1979; Araújo-Júnior and Porpino, 2011; Araújo-Júnior et al., 2011). Furthermore, it is likely that the absence of the medullar channel (Bergqvist et al., 2004) and, hence, a higher bone density in E. laurillardi remains, could have facilitated its differential preservation. This observation concurs with similar conclusions furnished by Santos et al. (2002), Araújo-Júnior and Porpino (2011) and Araújo-Júnior et al. (2013) for Pleistocene deposits from the states of Rio Grande do Norte State and Ceará, in northeastern Brazil. The MNI counting showed the presence at least of four individuals in Itaboraí. For N. platensis, the MNI value (¼2) is similar to the conclusion of Oliveira et al. (2010; based on dental wear).

Fig. 6. Skeletal elements with wear marks; A. Carpal of Eremotherium laurillardi (DGM-735-M) with moderate degree of abrasion; B. Carpal of Notiomastodon platensis (DGM-734M) with high degree of abrasion. Arrows indicate wear marks. Scale bar ¼ 20 mm.

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Fig. 7. Caudal vertebra of Eremotherium laurillardi (DGM-731-M) displaying deformations; A. Prezygapophysis with deformation; B. Vertebral centrum with deformation, in cranial view; C. Vertebral centrum with deformation, in lateral view. Arrows indicate the deformations. Scale bar ¼ 50 mm.

The presence of fossils assigned to the stage 3 of the Behrensmeyer’s weathering scale (Behrensmeyer, 1978) indicates that the fossil accumulation was exposed prior to burial. However, the absence of teeth marks, trampling and invertebrate modifications suggests a short exposure of the thanatocoenosis (Behrensmeyer et al., 1986; Fiorillo, 1984, 1987, 1989; Behrensmeyer, 1991; Kaiser, 2000; Sinibaldi, 2010). This idea is reinforced by the absence of columnar and jagged fractures which are consensually assigned to the biostratinomic phase (Shipman, 1981; Shipman et al., 1981). It is noteworthy to observe that wear marks found on teeth surface are related to biostratinomic processes and not to chewing, once they show distinct patterns. Regarding the color pattern, it is likely that the reddish fossils acquired this color because they were stratigraphically positioned at the uppermost layer of the deposit and, therefore, closer to the reddish soil. Furthermore, it is also likely that these bones were the last ones to be inputted into the taphonomic cycle, since they show a better preservation than the white specimens. The absence of clast and bioclast sorting (Price and Campos, 1970) in the fossil layer suggests that a high-energy agent deposited the bones inside their burial environment. The taphonomic signatures of the uppermost reddish specimens (low degrees of fragmentation, abrasion and weathering) and granulometric analysis (framework with granulometry smaller than the lowermost layer) may indicate a deposition unleashed by fluvial stream. Thus, the hypothesis of Price and Campos (1970) that the uppermost layer was originated by fluvial processes is plausible. On the other hand, it seems probable that the lowermost layer has been

deposited by a more energetic agent than a fluvial stream (e.g., debris-flows). Moreover, another important characteristic is the predominance of less dense fossils, such as vertebrae, phalanges and fragments of humerus (Price and Campos, 1970). However, heavier specimens are also present, such as teeth and femurs. This peculiar type of sorting allows the assumption that at least two events of transport occurred: (A) an agent with less intensity carrying lighter elements, possibly by a normal fluvial stream; and (B) another one, with higher intensity, such as a debris-flow, capable of transporting teeth and long bones (Shipman, 1981; Holz and Simões, 2002; Araújo-Júnior et al., 2013). Regarding the fractures, Shipman et al. (1981) proposed that irregular fractures perpendicular to the diaphysis can be produced during the fossildiagenesis. Badam et al. (1986) disagree, claiming that this type of fracture can be produced by weathering or trampling on bones during the biostratinomic phase. For Cladera et al. (2004) and Bergqvist et al. (2011) these fractures obey the processes that take place after the fossilization. For Lyman (1994), Medeiros (2010) and Sinibaldi (2010), the main factors capable of fracturing bones during the fossildiagenesis are the compression forces induced by sedimentary overloads. According to Cladera et al. (2004), the multiple fractures are also produced after the fossilization, due the compression made by the sediment supply. It is likely that the deposition of sand and clay into the fractures were also responsible for fragmenting the fossils. These fractures filled by sediments were produced prior to burial. However, it seems more plausible that the fossils acquired those fractures after burial and being percolated by minerals afterwards. The deformation

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observed on some fossils corroborates the hypothesis that some of the fractures were produced by the overload of the uppermost layers on the bones (Medeiros, 2010; Sinibaldi, 2010). Gangloff and Fiorillo (2010) have also associated multiple fractures and bone deformation on vertebrate fossils from the Late Cretaceous of Alaska (EUA) to the overload of the superior layers acting upon the fossiliferous layer. Price and Campos (1970) recognized a more arid paleoenvironment for Itaboraí during the late Pleistocene based on the faunal composition and the lithology of the deposit. The high degree of disarticulation and the presence of desiccation marks on bones are also suggestive of aridity, adding support for the conclusions of those authors. It is likely that an arid climate operated on a wide area of Brazil during the late Pleistocene (Avilla et al., 2013), mainly for the Brazilian Intertropical Region (Bergqvist et al., 1997; Cartelle, 1999; Ribeiro, 2010; Araújo-Júnior et al., 2013; this work). 6. Conclusion The Pleistocene vertebrate assemblage of Itaboraí is a timeaverage accumulation and experienced short transport distances. The main taphonomic processes operating on the Pleistocene vertebrate accumulation of Itaboraí were the weathering, transport and deformations. There was a short time span of subaerial exposure of the specimens prior to burial. Possibly transportation occurs in two distinct events: (A) a normal fluvial stream; and (B) debrisflow. After the deposition, the fossils were fractured and deformed by lithostatic compression. The fossiliferous layer was rapidly covered by a red soil, giving a reddish color to some bones. The large amount of megafaunal remains and the skeletal completeness show that both paleobiological signatures and taphonomic biases were the main responsible for the patterns observed in the final fossil accumulation. The taphonomic features are clearly suggestive of an arid paleoclimate. Acknowledgments The authors would like to thank to the Setor de Paleontologia do Departamento Nacional de Produção Mineral do Rio de Janeiro (DNPM/RJ) for allowing the access to the Pleistocene fossils collected in Itaboraí and to C. Cartelle (PUC-MG) for allowing access to the collection of specimens of E. laurillardi under his care; to C. Bernardes (Laboratório de Mastozoologia, UNIRIO) and A.O. Braga for reviewing the English language; to L.P. Bergqvist for furnishing the Fig. 2A; we extend our gratitude to the Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ) for the APQ1-Auxílio à pesquisa básica 2010/02 given to the author LSA under the title “O parque quaternário: a paleoecologia de mamíferos pleistocênicos no sudeste do Brasil” (E-26/110.591/2011); to the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for the post-graduation scholarships given to HIAJr and VHD, respectively; to the anonymous reviewers by the criticisms and suggestions for improving this manuscript. References Alberdi, M.T., Prado, J.L., Cartelle, C., 2002. El registro de Stegomastodon (Mammalia: Gomphotheriidae) en el Pleistoceno Superior de Brasil. Revista Espanhola de Paleontologia 2, 217e235. Andrews, P., 1990. Owls, Caves and Fossils. The Natural History Museum, London. Araújo-Júnior, H.I., Porpino, K.O., Ximenes, C.L., Bergqvist, L.P., 2013. Unveiling the taphonomy of elusive natural tank deposits: a study case in the Pleistocene of northeastern Brazil. Palaeogeography, Palaeoclimatology, Palaeoecology 378, 52e74. Araújo-Júnior, H.I., Porpino, K.O., 2011. Assembleias fossilíferas de mamíferos do Quaternário do Estado do Rio Grande do Norte, Nordeste do Brasil: diversidade e aspectos tafonômicos e paleoecológicos. Pesquisas Em Geociências 38, 67e83.

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