Palaeogeography, Palaeoclimatology, Palaeoecology 378 (2013) 52–74

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Palaeogeography, Palaeoclimatology, Palaeoecology

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Unveiling the taphonomy of elusive natural tank deposits: A study case in the of northeastern

Hermínio Ismael de Araújo-Júnior a,⁎, Kleberson de Oliveira Porpino b, Celso Lira Ximenes c,d, Lílian Paglarelli Bergqvist a a Programa de Pós-graduação em Geologia, Departamento de Geologia, Instituto de Geociências, Universidade Federal do Rio de Janeiro, Av. Athos da Silveira Ramos, 274, 21.941-916, Cidade Universitária, Ilha do Fundão, Rio de Janeiro, RJ, Brazil b Departamento de Ciências Biológicas, Universidade do Estado do Rio Grande do Norte, Av. Professor Antônio Campos, s/n, 59.610-090, Costa e Silva, Mossoró, RN, Brazil c Museu de Pré-história de Itapipoca, Av. Anastácio Braga, 349, 62.500-000, Centro, Itapipoca, CE, Brazil d Programa de Pós-graduação em Geologia, Departamento de Geologia, Universidade Federal do Ceará, Campus do Pici, Av. Humberto Monte, s/n, 60.455-760, Fortaleza, CE, Brazil article info abstract

Article history: Fossiliferous natural tanks are a singular type of sedimentary deposit restricted to northeastern Brazil, which usually Received 22 June 2012 preserves a diversified late Pleistocene vertebrate fauna. Their fossil assemblages are taxonomically well known, but Received in revised form 27 March 2013 their taphonomy is poorly understood. This work presents a detailed taphonomic analysis of a tank deposit from Accepted 1 April 2013 Jirau site (Ceará State, Northeastern Brazil) to improve understanding of the processes that influenced fossil depo- Available online 8 April 2013 sition and preservation in natural tanks and to shed light on paleoecological and paleoenvironmental aspects related to the late Pleistocene vertebrate fauna from Northeastern Brazil. Tank deposits from different localities were also Keywords: fi Taphonomy compared to gure out potential taphonomic patterns among them. Additionally, comparisons with other Brazilian Natural tanks Pleistocene deposits and other debris-flow deposits bearing vertebrates were undertaken. Pleistocene vertebrates The study revealed the predominance of the megamammal Eremotherium laurillardi in the deposit, which we attrib- Northeastern Brazil uted to its abundance in late Pleistocene biocoenosis as well as bone resistance. Scarcity of non-mammalian verte- Debris flow brates is likely related to their paucity in late Pleistocene biocoenosis. Time-averaging was evidenced by the co-occurrence of different weathering, petrographic and color patterns, and may have affected the ontogenetic profile of the accumulation relative to the original biocoenosis. Analyses of weathering stages, tooth and trample marks, indicate wide exposition of the thanatocoenosis before burial. Abrasion and petrographic patterns allow reworking in the assemblage to be inferred. Permineralization and substitution are the fossilization processes observed. Taphonomy indicates that floods deposited clasts and bioclasts in the tank under an arid or semiarid climate in a debris-flow regime. Comparison with other tank deposits revealed several similar taphonomic features and differences related to sedi- mentology and stratigraphy. Taphonomic similarities suggest rather homogeneous environmental conditions in the northeastern Brazil during the late Pleistocene, as previously suggested by taxonomic studies. Comparison with other Brazilian Pleistocene deposits shows that tanks have more temporal fidelity than caves, coastal and some flu- vial deposits. The Jirau vertebrate accumulation was produced by the reworking and transport of skeletal elements accumulated in a nearby thanatocoenosis and is similar to other better known debris-flow hosted vertebrate accumulations. © 2013 Elsevier B.V. All rights reserved.

1. Introduction barely understood, despite some analyses on Paleocene (Bergqvist et al., 2011) and Pleistocene deposits (Bergqvist et al., 1997; Santos et al., Taphonomic analyses of Brazilian vertebrate fossil accumulations are 2002a; Auler et al., 2006; Alves et al., 2007; Dantas and Tasso, 2007; scarce and most studies were carried out on taphocoenoses Araújo-Júnior and Porpino, 2011; Araújo-Júnior et al., 2012). Most of (Holz and Soares, 1995; Holz and Souto-Ribeiro, 2000; Bertoni-Machado these taphonomic studies on Pleistocene vertebrates were superficial and Holz, 2006; Bertoni-Machado, 2008; Bertoni-Machado et al., 2008). and based on little evidence. The taphonomy of fossil concentrations of Cenozoic vertebrates is still Late Pleistocene outcrops are more common in northeastern Brazil, beingmostlyrepresentedbykarst(cavesandfissures), alluvial deposits, lakes and natural tanks (Cabral-de-Carvalho et al., 1966; Santos et al., ⁎ Corresponding author. Tel.: +55 21 80153603. 2002b; Bergqvist and Almeida, 2004; Porpino et al., 2004; Dantas et al., E-mail addresses: [email protected] (H.I. Araújo-Júnior), [email protected] (K.O. Porpino), [email protected] (C.L. Ximenes), 2005; Ribeiro and Carvalho, 2009; Araújo-Júnior and Porpino, 2011). [email protected] (L.P. Bergqvist). Those assemblages are characterized by a well-known and diversified

0031-0182/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.palaeo.2013.04.001 H.I. Araújo-Júnior et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 378 (2013) 52–74 53 vertebrate fauna, which include , reptiles, avians and amphib- sediments probably were not deposited by fluvial streams, but generat- ians (Paula-Couto, 1980; Cartelle, 1999; Bergqvist and Almeida, 2004; ed in the surrounding areas by the weathering of the basement rocks Dantas et al., 2005; Silva et al., 2006). Mammalian remains are the most and transported by floods and wind action during wet and dry periods, common fossils in all aforementioned kinds of deposits. respectively (Paula-Couto, 1980; Oliveira and Hackspacher, 1989; The taphonomy of natural tanks is perhaps the most elusive of all Santos, 2001). Pleistocene vertebrate deposits from Brazil (see Porpino and Santos, The basement rock outcrop where the tank of Jirau lies is a 2002). Tanks are natural depressions formed by physico-chemical Neoprotherozoic granodiorite belonging to the Borborema Province weathering in fractures on basement rock outcrops that seasonally geomorphological unity (Nascimento, 2006). This unity is an exten- accumulate rainwater producing small lag deposits (Paula-Couto, sive region of Pre- rock outcrops that encompass an area of 1980; Rolim, 1981; Oliveira and Hackspacher, 1989; Santos, 2001). 405,000 km2 in northeastern Brazil. The tank has an ellipsoid outline, Most of them have ellipsoid outline and occurs in small inselbergs 22 m along its main axis, a width of 3.5 m, a depth of 4 m and (Santos, 2001; Araújo-Júnior and Porpino, 2011). According to Oliveira 308,000 liters minimum volume. It was classified by Ximenes (2003) and Hackspacher (1989) and Oliveira et al. (1989), tanks originated dur- as a semi-open tank (i.e., it has open edges). ing the early Pleistocene and were filled by clasts and bioclasts through Three sedimentary layers can be recognized inside the tank (Fig. 2). hydraulic and aeolian agents during the late Pleistocene/early Holocene. From bottom to top they are: (A) a basal one (1.5 m thick) quartz coarse From paleoenvironmental studies carried out during the last decades sandstone with rock fragments likely resulting from the weathering of (e.g. Galindo et al., 1994; Silva, 2001, 2008) the tank deposits have been basement rocks which comprise the tank walls; (B) an intermediary clearly interpreted as generated under debris-flow regimes. In Australia, layer (about 1 m thick), characterized by debris flow sedimentation, USA and Portugal, analogous depressions occur and are named consisting of conglomerate supported by feldspatic clayey-sandy ma- gnammas. Like tanks, gnammas were formed by physico-chemical trix, with fossils, rounded quartz pebbles and rock fragments from weathering on basement rock outcrops and their geneses are associ- tank walls; (C) and an upper layer composed of clayey and silty sedi- ated with arid climates during the Holocene (Twidale and Corbin, ments, rich in organic remains. The upper layer shows thickness varia- 1963; Dominguez-Villar and Jennegins, 2008; Dominguez-Villar et tion along its bedding plane, being about 1 m thick in proximal part of al., 2009). However, there are no references to vertebrate remains inside the tank (open edge) and 1.5 m thick in the distal part. gnammas up to now. Mabesoone et al. (1990) was the first to propose a stratigraphic Two main hypotheses have been suggested to explain the accu- modelfornaturaltanksbasedonhisstudiesontanksofRioGrandedo mulation and preservation of fossils inside the tanks: (A) Norte State: (A) a lower layer composed of sediments resulting from fell into and died in the tanks when they were searching for water weathering of basement rocks (conglomerate sandstone); (B) an inter- (Branner, 1902; Moreira et al., 1971; Paula-Couto, 1980); (B) animals mediary layer, a conglomerate with fossils; and (C) an upper layer com- died around the tanks and were transported to these depressions by posed of mudstone. This stratigraphic arrangement is similar with that floods (Bergqvist, 1993; Bergqvist et al., 1997; Santos et al., 2002a,b). observed in Jirau as described above. Nonetheless, later studies have During last decade, new tanks have been carefully excavated (Alves found stratigraphic patterns in tanks that are clearly at odds with et al., 2007; Ribeiro and Carvalho, 2009; Ximenes, 2009), allowing the Mabesoone et al. (1990), including tanks with only two discernible discovery of new local faunas and the preliminary decoding of taph- layers (Paula-Couto, 1980; Bergqvist, 1989) and tanks with more than onomic information through field and laboratory investigations. In two fossiliferous layers, showing distinct sedimentological features, addition, several researchers noted, based on dating or fragmentary such as angular quartz grains and poor granulometric sorting (Alves, evidences, that tank deposits are time-averaged accumulations 2007). Although this may be simply due to differences in the criteria (Silva, 2001; Santos et al., 2002a; Silva, 2008; Araújo-Júnior and used in layers recognition among authors, if we take the available data Porpino, 2011). However, none of the previous studies were sup- for granted, it seems likely that the stratigraphic settings of tanks are ported by detailed biostratinomic and diagenetic analyses. variedly influenced by the sedimentary input and energy of the trans- In this work, we carried out a taphonomic analysis of Pleistocene port agent resulting in distinct numbers of layers. vertebrates from the Tank of Jirau, Itapipoca, Ceará State, northeast- The presence of quartz sands associated with rock fragments and the ern Brazil. Our aim was to improve knowledge on biostratinomic and absence of unstable minerals (e.g. feldspar) in the basal layer in the tank fossildiagenetic processes that operated during deposition and pres- of Jirau suggest reworking during early stages of clastic deposition. ervation of bones in natural tanks and shed light on the vertebrate Probably, rainwaters reworked the few sediments deposited in the paleoecology of the late Pleistocene of northeastern Brazil. Addition- tank, during its initial expansion, eliminating the more unstable min- ally, we compare our results with other tanks in order to highlight erals. The fossiliferous layer shows poor granulometric sorting. This potential general preservation patterns among these deposits. We suggests that a high-energy agent acted during the sediment deposition compare the tank of Jirau with: (A) other Brazilian Pleistocene deposits and taphocoenosis formation. However, the abundance of feldspar indi- to figure out common taphonomic patterns and evaluate time resolu- cates low reworking rates inside the tank in comparison to the lower tion; and (B) with other debris-flow deposits bearing vertebrates to layer (Suguio, 2003). Rounded quartz pebbles were not generated shed light on the phenomena involved in the taphonomic histories of from tank walls, but carried out to the tank by earlier floods or rivers accumulations generated by this depositional agent. from distant areas. Decreasing grain size toward the upper layer, which is composed of clayey and silty sediments, suggests decreasing 2. Location, geology and stratigraphy influence of tractive processes and increase of deposition by decanta- tion (Suguio, 2003). Such variations in depositional processes common- The natural tank of Jirau (03°21′23.1″ S 39°42′20.2″ W; Fig. 1A) is ly result from changes in the climate or geomorphology (Bishop, 1980; located in the Jirau Paleontological Site, located 35 km northwest of Suguio, 2003). There is now compelling evidence of geomorphologic Itapipoca City, in the north of Ceará State (Fig. 1B). changes in Ceará State area during the Quaternary period (Cavalcante, According to Ximenes (2003), the tanks of Itapipoca display varied 2006), so we attribute the inferred depositional variations to climate sizes and dominantly ellipsoid outline, though circular or irregular out- changes. lines are also observed. In several localities of Itapipoca, they are associ- ated with small inselbergs. They are filled with clastic sediments and 3. Material and methods bioclasts. The bioclasts are represented by late Pleistocene vertebrate remains, chiefly large mammals collectively referred to as Pleistocene The tank of Jirau was excavated and its fossils were prepared from megafauna (Ximenes, 2003). According to previous studies, the clastic 2003 to 2008. The studied fossils are housed in the paleontological 54 H.I. Araújo-Júnior et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 378 (2013) 52–74 H.I. Araújo-Júnior et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 378 (2013) 52–74 55

Fig. 2. Stratigraphic diagram of the deposit of Jirau. collection of Museu de Pré-história de Itapipoca (MUPHI; Fig. 3). A The collection of taphonomic data followed methods suggested stratigraphic section of the deposit was produced based on a trench, by Dodson et al. (1980), Hill (1980), Shipman (1981), Badgley which allowed general view of the sedimentary layers within the (1986), Behrensmeyer (1991), Lyman (1994, 2008), Holz and tank. Taxonomic identification was based on comparable material of Simões (2002), Rogers (1994), Eberth et al. (2007a) and Simões the paleomammalogy collection from the Pontifícia Universidade Católica et al. (2010a, 2010b), which have been widely employed in taphonomic de Minas Gerais (PUC-MG) and on the relevant literature. analyses (e.g. Turnbull and Martill, 1988; Rogers, 1990; Varricchio, 1995; The dataset we used comprises 1405 skeletal specimens collect- Cassiliano, 1997; Coombs and Coombs, 1997; Ryan et al., 2001; Myers ed in the tank of Jirau. The taphonomic behavior of some types of and Storrs, 2007; Britt et al., 2009; Fiorillo et al., 2010). The following skeletal elements, such as horns, teeth, and xenarthran osteoderms, macroscopical features were considered: (A) taxonomic composition is largely unknown compared to the skeletal elements previously and ontogenetic stages; (B) articulation and fragmentation; (C) bone rep- evaluated in classic neotaphonomic/actuopaleontological studies resentation; (D) hydraulic equivalence; (E) breakage; (F) weathering; (e.g. Voorhies, 1969; Dodson, 1973; Behrensmeyer, 1975, 1978; Frison (G) abrasion; (H) trampling; (I) tooth marks; (J) invertebrate modifica- and Todd, 1986; Hutson, 2012), and for this reason, they were excluded tions; (K) rooting; and (L) color patterns. For each registered color pat- from this analysis. Besides, xenarthran osteoderms are overrepresented tern, we made petrographic thin sections across transversal cuts in long in the assemblage and could introduce an analytical bias. bones in order to diagnose preservational stages of bone microstructure

Fig. 1. General view and location of the tank of Jirau; A. view of the tank; B. location map of Jirau Paleontological Site at Itapipoca, Ceará State, northeastern Brazil. AL = Alagoas State; BA = Bahia State; CE = Ceará State; MA = Maranhão State; PB = Paraíba State; PE = Pernambuco State; PI = Piauí State; RN = Rio Grande do Norte State; SE = Sergipe State. 56 H.I. Araújo-Júnior et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 378 (2013) 52–74

Fig. 3. Field images of the tank of Jirau highlighting fossils that are evident in the fossiliferous layer; arrows indicate the fossils. H.I. Araújo-Júnior et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 378 (2013) 52–74 57 and fossilization processes and stages. In addition, ante-mortem bone al- dominated by megamammals, but large and midsized mammals are terations were identified and interpreted. Finally, a taphogram (Fig. 13) also present in significant amounts. Semi-aquatic vertebrates, such as was constructed to illustrate the hypothetical sequence and relative dura- crocodilians and turtles, are also preserved in the taphocoenosis. For tion of taphonomic processes inferred for the fossil accumulation from faunal list, ontogenetic stages, Number of Identifiable Skeletal Parts Jirau. (NISP) and Minimum Number of Individuals (MNI) values see Table 1. For counting of specimens, we used the Number of Identifiable Skel- etal Parts (NISP). For each taxon, Minimum Number of Individuals 4.1. Mammals (MNI) was calculated following the method described in Badgley (1986) and Lyman (1994, 2008). MNI values were calculated from the NISP and MNI for mammals are 1399 and 45, respectively. The Jirau most abundant skeletal element from either the left or right side of fossil assemblage is multitaxic and monodominant (sensu Eberth et al., the (Lyman, 1994). Ontogenetic stages (subadult and adult) 2007b). Megamammal Eremotherium laurillardi (Pilosa, Megatheriidae; for mammals were determinated based on the interpretation of epiph- Fig. 4B and E) is the dominant species in the accumulation (NISP = ysis–diaphysis fusion grade (to long bones) and centrum–disk fusion 1143; MNI = 19), representing 81.35% of the total NISP and 42.2% of grade (to vertebrae). We assume that totally fused elements pertain total MNI for mammals. Palaeolama major (Artiodactyla, Camelidae) a to adult individuals and incomplete fusion to subadults. Similarly, onto- large , is the second taxon with highest MNI value (=5), but genetic stages of non-mammalian vertebrates were defined on the ob- with lower NISP (=47) than Tayassu pecari (=67), a midsized mammal servation of fusion grade of sutures. Distinctions between adult and (Artiodactyla, Tayassuidae). Taxa with the lowest NISP values (=1) are subadult individuals were also taken into consideration in establishing Equus (Amerhippus) neogaeus (large mammal; Perissodactyla, Equidae), MNI values. Catonyx cuvieri (megamammal; Pilosa, Mylodontidae) and Holmesina We conducted comparative analysis of the long bones portion fre- paulacoutoi (megamammal; , Pampatheriidae). Mazama sp., a quency (proximal and distal) proposed by Richardson (1980);(seealso small-sized mammal, has NISP equal to 5, higher than the values for Todd and Rapson, 1988) and an analysis of skeletal elements according some large mammals and megamammals (e.g. Notiomastodon platensis— to the Fluvial Transport Index (FTI; Frison and Todd, 1986). The former al- Proboscidea, Gomphotheriidae; Hippidion principale—Perissodactyla, lows evaluation of the influence of carnivores in the accumulation of ver- Equidae). tebrate thanatocoenoses. High values of long bones, especially tibia and Other mammal taxa are include: Tolypeutes tricinctus (small mammal; humerus, indicate sorting by carnivores during the biostratinomic stage, Cingulata, Dasypodidae), Pachyarmatherium brasiliense (midsized mam- whereas low values indicate its absence (Todd and Rapson, 1988). The mal; Cingulata incertae sedis;seePorpino et al., 2009), Ocnotherium FTI allows assessment of the level of transport in the fossil accumulation. giganteum (megamammal; Pilosa, Mylodontidae), Panochthus greslebini We follow Lyman (1994) in the use of the terms specimen and skeletal and Glyptotherium sp. (megamammals; Cingulata, Glyptodontidae). How- element. The former corresponds to an “observational unity” whether a ever, those animals were excluded from our taphonomic analysis because complete bone (skeletal element) or a simple bone fragment. Skeletal they are represented only by teeth and osteoderms (see Section 3). element corresponds to a “discrete, natural anatomical unit of a skeleton, such as a humerus, a tibia, or a tooth” (Lyman, 1994, p. 100). The terms biocoenosis, thanatocoenosis and taphocoenosis also follow Lyman 4.2. Non-mammalian vertebrates (1994): (A) biocoenosis, life assemblage; (B) thanatocoenosis, death assemblage, derived from the biocoenosis and subsequently modified Three non-mammalian taxa are recorded. Among those, Caimaninae by biostratinomic processes; and (C) taphocoenosis, buried and pre- (Alligatoridae, Crocodylia) is the best represented taxon (NISP = 4; served assemblage. Terms megamammals, large mammals, mid- sized mammals and small mammals follow Araújo-Júnior and Porpino (2011): (A) megamammals, >1000 kg; (B) large mam- mals, between 100 and 1000 kg; (C) midsized mammals, between Table 1 10 and 100 kg; and (D) small mammals, b10 kg. The estimated Taxa found in the Jirau vertebrate assemblage with NISP, MNI and ontogenetic stages; *Taxa present in Jirau, but not considered in the taphonomic analysis because are mass for each species was taken from previous studies (e.g. Fariña recorded by osteoderms or teeth only. et al., 1998; Giuseppe, 2002; Prevosti and Vizcaíno, 2006). Terms autochthonous, parautochthonous and allochthonous are according Group Taxa NISP MNI (Subadult/adult) to Behrensmeyer and Hook (1992): (A) autochthonous, a non- Mammals Eremotherium laurillardi 1143 19 (4/15) transported fossil assemblage; (B) parautochthonous, a transported Catonyx cuvieri 1 1 (0/1) Glossotherium sp. 14 1 (0/1) fossil assemblage, but preserved within habitat area; and (C) allochtho- Holmesina paulacoutoi 1 1 (0/1) nous, fossil assemblage transported and preserved outside the habitat Pampatherium humboldti 7 2 (0/2) area. Finally, terms monotaxic, paucitaxic and multitaxic were used Notiomastodon platensis 5 2 (1/1) according to Eberth et al. (2007b): (A) monotaxic, a fossil assemblage Toxodon platensis 9 2 (1/1) formed only by a single species; (B) paucitaxic, between two and nine Xenorhinotherium bahiense 10 3 (0/3) populator 10 2 (0/2) species; and (C) multitaxic, more than nine species. Palaeolama major 47 5 (0/5) Fossils from Jirau are here attributed to the late Pleistocene based on Mazama sp. 5 1 (0/1) previous datings of specimens from other tanks from northeastern Brazil Tayassu pecari 67 2 (1/1) which yielded ages compatible with this interval (see Kinoshita et al., Equus (Amerhippus) neogaeus 1 1 (0/1) Hippidion principale 2 1 (0/1) 2005, 2008; Oliveira et al., 2009; Dantas et al., 2011), although recent geo- Equidae indet. 45 1 (0/1) chronological studies indicate a late Pleistocene/early Holocene age for Mammalia incertae sedis 32 1 (0/1) some tank deposits (Silva, 2008; Ribeiro et al., in press). “Non-mammals” Caimaninae indet. 4 1 (0/1) Testudines indet. 1 1 (0/1) 4. Taxonomic composition and ontogenetic stages Aves incertae sedis 1 1 (0/1) Total 1405 48 (7/41) * Tolypeutes tricinctus From the 1405 specimens considered in this analysis, 1303 were an- Pachyarmatherium brasiliense atomically and taxonomically identified to species level. Some hard to Panochthus greslebini identify fragmented bones were assigned to genus (19), sub-family Glyptotherium sp. Ocnotherium giganteum (4), family (45) order (1) or class (33). The Jirau assemblage is 58 H.I. Araújo-Júnior et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 378 (2013) 52–74

Fig. 4. Mammal skeletal elements from Jirau; A. incomplete tibia of Cervidae indet. (Artiodactyla); B. incomplete mandible of Eremotherium laurillardi (Megatheriidae, Pilosa); C. lumbar vertebra of Smilodon populator (Felidae, Carnivora); D. distal end of humerus of S. populator; E. complete metapodial of E. laurillardi.Scalebars=2cm.

MNI = 1), encompassing three fragment of vertebral centrum and one Couto, 1980). Only a single fragment of plastron was found and attribut- small skull fragment. Crocodiles are the more common group among ed to Testudines indet. Until now, turtle remains were found only in a the non-mammalian vertebrates in tank deposits (Vidal, 1946; Paula- tank at Sergipe State (Dantas et al., 2005). Besides fossil reptiles, one H.I. Araújo-Júnior et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 378 (2013) 52–74 59 fragment of long bone was attributed to a large avian. In natural tanks, abundance of humeri is unusual, as they have been scarcely reported only Rhea sp. (Reiformes, Rheidae) was previously recorded (tanks of among the skeletal elements found in other tanks (e.g. Bergqvist, 1989; João Cativo town, Itapipoca; Paula-Couto, 1980). Probably, crocodiles Gomide, 1989; Dantas et al., 2005; Araújo-Júnior and Porpino, 2011). In- and turtles lived in nearby rivers, and their remains were transported terestingly, almost 80% of the humeri belong to E. laurillardi,inwhichMNI to tanks during overflow events. However, we cannot discard that, is much higher than the other mammals present in the assemblage (see due to their small size, turtles also could eventually have used the Section 4.1). Its large and dense humerus (Santos et al., 2002a, 2002b) tank as habitat. This would also account for their poor representation is highly resistant to destructive processes, and this can explain its high in the assemblage. In fact, we have eventually observed some compara- abundance in the fossil accumulation. Scarcity of turtle shells might be bly sized turtles currently living in small lags formed inside other natu- due to the rarity of turtles in the vicinity of the tank, while the rarefaction ral tanks at Ceará State. of the scapula and clavicle may be related to the greater fragility of these bones (Moore, 1994). 4.3. Ontogenetic stages Metapodials and phalanges are the most complete bones found in Jirau. As suggested for other deposits (Almeida, 2005; Bergqvist et al., Among the skeletal elements identified, 52 specimens are attribut- 2011; Araújo-Júnior et al., 2012), this may be related to size, as able to sub-adults, and 1353 to adults. Among the sub-adult specimens, small-sized bones have reduced surface impact. Symptomatically, in 43 belong to Eremotherium laurillardi,fourtoNotiomastodon platensis, the tank of Jirau, ribs, vertebrae, femora, humeri, skulls and jaws – three to Toxodon platensis,andtwotoTayassu pecari. With respect to which have great surface area – are the most fragmented bones. the MNI, only seven individuals were classified in the sub-adult stage Long bones are the most common in Jirau (68%), followed by short and 41 into adult stage. E. laurillardi is represented by four sub-adult in- (22%) and flat ones (10%). It is likely that the greater proportion of dividuals while the others aforementioned species are represented by long bones in Jirau is not due to sorting, but the result of the preserva- one individual each. All non-mammalian bones were assigned to adult tion of bones which are abundant in vertebrate skeletons, such as ribs, because their sutures are closed. humeri, femurs and radii (Moore, 1994). However, the pervasive frag- The dominance of adults in relation to sub-adults in the Jirau accumu- mentation observed in these skeletal elements can have inflated long lation is compatible with a catastrophic death scenario for the biocoenosis bone frequencies. existing around this deposit during the late Pleistocene (Voorhies, 1969; Specimens with size between 51 and 100 mm are the most abun- Shipman, 1981; Holz and Simões, 2002). Yet, senility signs observed in dant in Jirau (52.59%), while specimens with size above 301 mm are some fossils (see Section 6) suggest, in contrast, an attritional assemblage. less common (4.98%). This size-related preservation pattern is not con- The likely occurrence of time-averaging in this accumulation, as argued sidered here the result of sorting during the depositional history of the below (see Section 7), prevents more accurate conclusions, as this phe- assemblage, but of the high degree of fragmentation of skeletal ele- nomenon affects dramatically the ontogenetic frequency distribution ments likely due to wide exposure time before burial and/or reworking that would be expected for fossil associations generated by catastrophic (see Sections 7 and 10). death, due to the collapse of several generations in a single accumulation The values found for tibia (0.22) and humerus (0.53) bones in the (Behrensmeyer, 1982; Bertoni-Machado, 2008). analysis of the long bones portions frequency are low and suggest the ab- sence of carnivore influence on the accumulation of vertebrate remains 5. Taphonomy (Table 2). Tooth marks identified on some fossils (1.85% of NISP) can in- dicate scavenging (see Section 5.8), however, it is unlikely that most 5.1. Articulation and physical integrity bones were accumulated inside the tank by scavengers, otherwise, a large number of bones with these features should be found (Hutson, All skeletal elements found in the fossil accumulation are 2012). disarticulated suggesting extensiveexposuretimebeforeburial In Jirau the less transportable bones are relatively abundant (19.72%), (Holz and Simões, 2002). With respect to physical integrity, 82% of while more transportable bones are less common (0.7%). The bones with the analyzed specimens correspond to bone fragments (b50% of the intermediate FTI values (between 50 and 74) are the most abundant bone), but complete (100% of the bone preserved) and partial (between (79.58%). The prevalence of less transportable elements points to a 50 and 95% of the bone) elements also occur, representing 4% and 14% short transport of the bones to the tank. On the other hand, the low of skeletal elements, respectively (Fig. 5A). Among these classes (frag- amount of more transportable elements is intriguing. It is likely that ments, partial and complete), those with area up to 15 × 15 cm the strength of the transport agent had been so high, that the more (Fig. 5B) are better represented. Specimens with length between 5 dense bones were deposited into the tank while the less dense ones and 10 cm are the most abundant (Fig. 5C). It is widely known that remained outside of the depression and were not incorporated into fragmentation can be generated by various processes, ranging from the taphocoenosis. The relatively few astragali and calcanei, which is physical (e.g. transport, reworking and lithostatic pressure; Voorhies, also unusual for tank deposits, can be related to high energy of floods, 1969; Shipman, 1981; Holz and Simões, 2002; Pawłowska, 2010)tobi- since these elements are less dense (Moore, 1994)and,consequently, ological (e.g. trampling, scavenging and rooting; Toots, 1965; Hill, 1979; more transportable. Weigelt, 1989). This renders it difficult to attribute the high degree of fragmentation observed to one of the processes mentioned. In the stud- ied case, other features (e.g. diagenetic patterns and tooth and trample 5.3. Hydraulic equivalence marks) may be more diagnostic for the processes operating in the taph- onomic history of the Jirau assemblage. As described above (see Section 2), the fossiliferous layer of the stud- ied deposit is a conglomerate, with quartz pebbles and granules imbed- 5.2. Bone representation ded in a matrix of coarse sand and clay. Most bioclasts range between 50 and 100 mm, which is equivalent to gravel size (Behrensmeyer, The most abundant skeletal elements in Jirau fossil assemblage are 1975). This hydraulic equivalence suggests strong influence of high- ribs (37.39%), vertebrae (17.72%) and humeri (15.30%). Turtle shells energy hydraulic transport in the deposition of the thanatocoenosis (0.07%), calcaneum (0.21%), scapulae (0.28%), clavicles (0.8%) and astrag- (Behrensmeyer, 1975). Tooth marks are rare in Jirau (see Section 5.8), alus (0.49%) are poorly represented. Ribs and vertebrae are the most so we discard the hypothesis of biological transport. Finally, the transport abundant elements in postcranial skeleton of vertebrates (Moore, 1994) of whole carcasses is unlikely due to the absence of articulated fossils, but and this could explain their abundance in Jirau. On the other hand, the this may be also due to reworking (see Section 7). 60 H.I. Araújo-Júnior et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 378 (2013) 52–74

Fig. 5. Physical integrity and size patterns observed in the Jirau fossil accumulation;A.boneintegrity;B.measuresofbones (biggest width versus biggest length); C. bioclast length frequency.

5.4. Breakage humeri, tibiae and femurs. Smooth breaks, perpendicular to the shaft (Fig. 6B), were observed in 34.7% of the bones, especially ribs, Irregular breaks, perpendicular to the shaft (Fig. 6A), are the most humeri and femurs. Columnar breaks are also observed, correspond- common breakage pattern (61.2%) and are more frequent in ribs, ing to 4.1% of the breaks (Fig. 6C). Consensually, smooth breaks are H.I. Araújo-Júnior et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 378 (2013) 52–74 61

Table 2 and scavenging were observed in our analysis (see Sections 5.7 and 5.8, Number of complete bones, bones represented only by proximal ends, only by distal respectively), however, the higher amount of trample marks, when ends, only by diaphyses and values of the Difference in the Amount of Long Bone compared to tooth ones, is evidence in favor of trampling as responsible Ends (DALBE value). for most of the fragmentation. Bone Proximal Distal Complete Diaphysis DALBE value In some specimens, the edges of the breaks are predominantly Humerus 22 6 1 186 0.53 perpendicular and angular, and the innermost part of the bone Radius 15 0 1 7 0.88 shows different colors relative to the external surface, suggesting Ulna 11 0 0 3 1.00 that these breaks were produced after fossilization (Shipman, 1981; Femur 11 6 0 44 0.29 Tibia 6 10 1 3 0.22 Behrensmeyer, 1991). Interestingly, we also noted the presence of broken Metapodial 3 11 6 0 0.30 fossils with rounded to sub-rounded edges which have counterparts lo- Phalanx 21 7 26 8 0.17 cated in relatively distant positions within the tank. This likely implies Total 69 40 35 251 0.16 that these breaks observed in the fossil accumulation from Jirau occurred not only during fossildiagenesis, but also during biostratinomic phase or by reworking as well. Moreover, during excavations and collecting we interpreted as generated after fossilization, when bones have lost also observed the presence of skeletalelementsbrokeninsitu,someof their original elasticity (Shipman et al., 1981; Cladera et al., 2004; which were overlain by granite blocks collapsed from the tank walls Bergqvist et al., 2011). According to Shipman et al. (1981) irregular (Fig. 6D) and quartz pebbles (Fig. 6E). breaks perpendicular to the shaft and columnar breaks are related to biostratinomic processes, such as trampling, scavenging and/or trans- 5.5. Weathering port. A short transportation was interpreted for the Jirau accumulation (Araújo-Júnior et al., 2012; this work, see Sections 5.2 and 7), ruling The degree of weathering of the fossils shows a polymodal pattern out the hypothesis of transport breaking bones. Evidences for trampling (Fig. 7A). Specimens with noticeable drying fissures (stages 4 and 5)

Fig. 6. Breakage observed in Jirau fossil accumulation; A. radius with irregular break, perpendicular to the shaft; B. radius with smooth break, perpendicular to the shaft; C. tibia with columnar break; D. mammal long bone fragmented by a boulder; E. mammal flat bones fragmented by quartz pebbles. Arrows indicate fractures. Scale bar = 2 cm. 62 H.I. Araújo-Júnior et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 378 (2013) 52–74 are well represented, but skeletal elements without these features are unaffected bone surface. In addition, all specimens show desiccation also common (Fig. 7B). The specimens with intermediate degrees of marks, resulting from the exposure of thanatocoenosis to weathering weathering (i.e. stage 3) are best represented in the accumulation. Verte- (sensu Behrensmeyer, 1978;seeSection 5.5), and grooves, possibly gen- brae, phalanges, metapodials, ribs and humeri are slightly weathered erated by trampling before burial (sensu Behrensmeyer et al., 1986; (stages 1 and 2), whereas ribs and vertebrae are strongly weathered Brittetal.,2009;seeSection 5.7), that overlap the putative tooth marks, (stages 4 and 5). Bones belonging to E. laurillardi and Equidae indet. implying that the these marks were not produced during collection are the most affected by desiccation marks, while the majority of skele- and/or preparation. tal elements without these features belong to E. laurillardi, P. major, The aforementioned marks occur in fossils assigned to N. platensis, P. humboldti and T. pecari. The presence of bones attributable to E. laurillardi and Glossotherium sp., all herbivore megamammals, and E. laurillardi encompassing all weathering stages may indicate that were observed on four tibiae (E. laurillardi), seven humeri (one—N. this species had the widest temporal range among the vertebrates platensis;six—E. laurillardi), two femora (E. laurillardi), four ribs found in Jirau. The presence of fossils showing advanced weathering (E. laurillardi), four vertebrae (E. laurillardi), one ulna (E. laurillardi), stage suggests that the Jirau's thanatocoenosis had undergone episodes one astragalus (Glossotherium sp.), two phalanges (E. laurillardi)and in which it was widely exposed before burial (Behrensmeyer, 1978). one fragment of indeterminate bone. Overall, the grooves on bones such as femur, humerus, tibia and vertebrae are about 50 mm (length) 5.6. Abrasion and 3 mm (width), while the grooves on ulna and ribs vary from 25 to 30 mm (length) and 3 mm (width). They occur mainly in the medial Bone abrasion results from the interaction with the substrate and and lateral sides of the shaft and are perpendicular to the long axis of suspended sediment. The wear marks generated by this process are in- the bone. Scratch-like teeth marks, perpendicular to the long axis of dicative of the time and intensity of interaction between bone and sed- bones, are generated chiefly by medium-sized canids, which have the iment, but not necessarily a function of the distance of the transport, as habit of gnawing on bones, dragging their teeth on the surface, produc- some skeletal elements can be easily transported without rounding and ing linear marks (Haynes, 1983; Lyman, 1994). A more detailed analysis can also be reworked inside the deposit (Shipman, 1981; Argast et al., of these very marks is presented in Araújo-Júnior et al. (2011a). 1987; Lopes, 2009; Simões et al., 2010a; Lopes and Buchmann, 2011). Similar tooth marks were identified by Dominato et al. (2011) on In the tank of Jirau, 75% of the bones are moderately abraded (Fig. 8A), remains of Notiomastodon platensis from Araxá, Minas Gerais State, 21.1% are heavily abraded (Fig. 8B) and 3.9% do not show signs of abra- Southeastern Brazil. These authors concluded that these features were sion. The heavily abraded bones also fall among those with high degree produced at the early stages of necrolysis, but according to Haynes of weathering and fragmentation. Fossil reworking or transport of the (1983) scratches are generated in skeletal elements in the final stage of bones can be inferred from such a pattern. However, considering the re- decomposition. This latter hypothesis seems more feasible for the fossils sults obtained through the application of FTI (Section 5.2), the incidence from Jirau, because in megamammals only the final stage of necrolysis al- of extensive transport is unlikely. On the other hand, the color variation lows the canid teeth to penetrate through the soft tissues as they become and the diagenetic pattern observed in the material (see Section 5.11) thinner due to decomposition. suggest that several cycles of reworking occurred during the formation of the assemblage. 5.9. Invertebrate modifications The reworking of fossil-bearing assemblages in natural tanks was originally hypothesized by Paula-Couto (1980), based on the analysis Invertebrate bioerosion traces have been reported for Pleistocene fos- of fossils from the tanks of João Cativo town, at Itapipoca. He argued sil vertebrates from Brazil and attributed to the action of Dermestidae in- that this phenomenon would arrange the fossils in tanks according to sects (Dominato et al., 2009). In Jirau, these features were not observed. their density, placing the densest at the bottom of the fossiliferous sed- Absence of these modifications indicates short exposition of the imentary layer and the less dense at the top. Such a gradation, however, thanatocoenosis before burial (Kaiser, 2000) or that these features was not observed in the tank of Jirau. have been blurred by other taphonomic processes (e.g. abrasion, weathering). The presence of desiccation and abrasion marks and the 5.7. Trampling high fragmentation support the latter scenario.

Sub-parallel linear and shallow depressions are the main evidence of 5.10. Rooting trampling on bones. These features are generated when large animals press sandy grains against the bone surface (Fiorillo, 1984, 1987, 1988, Evidence of rooting was not observed. Absence of these features, 1989, 1991) and not by direct abrasion of hooves and nails. These features according to Behrensmeyer et al. (1995) and Montalvo (2002),canindi- have been diagnosed and illustrated in several studies (Fiorillo, 1984; cate that the fossiliferous layer was shortly exposited before final burial Behrensmeyer et al., 1986; Olsen and Shipman, 1988; Fiorillo, 1989, or that its superficial or sub-superficial conditions did not allow growth 1991; Britt et al., 2009). of vascular plants. Trample marks were identified in 224 bones from Jirau, accounting for 15.94% of total NISP (Fig. 9). These features occur mainly in ribs, humeri, 5.11. Color and other diagenetic patterns femora and mandibles. However, spiral fractures, also attributable to trampling (Gangloff and Fiorillo, 2010), are absent in the assemblage. Five distinct colors were observed in the fossils from Jirau: white Like teeth (see below) and desiccation marks, trample marks are also (60.64%), black and white (17.72%), beige (14.23%), red (6.97%) and evidence of exposure of the material before burial (Bertoni-Machado, blue (0.44%). Blue and red fossils are more fragmented if compared to 2008). other colors. Moreover, the number of taxa showing the more abundant colors is greater than blue and red colors. Accumulations with fossils 5.8. Tooth marks bearing different colors result from bone concentrations that suffered distinct impregnation processes; thus, the color pattern can be evidence Among the specimens collected in Jirau, scratch-like teeth marks of: (A) reworking of pre-buried bones inside the tanks; or (B) reworking were identified (Fig. 10) in 26 bones (1.85% of NISP) and are here attrib- of pre-buried bones in nearby areas and subsequent deposition inside the uted to the action of scavengers. It is very unlikely that these features tanks. have been produced during collection or preparation of fossils, other- Through the analysis of petrographic thin sections of the five colors, wise the resulting marks would present different colors relative to the we observed that: (A) white fossils are partially filled by iron carbonate H.I. Araújo-Júnior et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 378 (2013) 52–74 63

Fig. 7. Desiccation marks observed in the bones of Jirau fossil accumulation; A. percentage of bone with desiccation marks according to Behrensmeyer's Weathering Scale; B. long bone with desiccation marks parallel to the shaft. Arrows indicate desiccation marks. Scale bars = 2 cm. 64 H.I. Araújo-Júnior et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 378 (2013) 52–74

Fig. 8. Fossils with wear marks; A. moderate abrasion; B. heavy abrasion. Arrows indicate wear marks. Scale bars = 2 cm. and, in lesser amount, by opaque mineral and partially substituted by bone. Finally, the iron carbonate may have originated from the associa- calcite (CaCO3; Fig. 11A); (B) black and white bones are slightly tion between dissolved calcium and iron oxide. Bone permineralization permineralized, dominantly by opaque mineral and iron carbonate by opaque minerals was previously identified by Santos et al. (2002a) (Fig. 11B); (C) beige fossils are totally substituted by calcite, the com- for Pleistocene mammalian fossils in Northeastern Brazil, but in ele- pact bone is permineralized by an opaque mineral and the cancellous ments collected in a karst deposit, so that this represents the first occur- bone by iron carbonate and opaque mineral matter (Fig. 11C); (D) red rence in fossils collected in tank deposits. bones are completely permineralized by opaque mineral and iron car- Concerning the original microstructure, we verified that the ana- bonate and shows slight signs of substitution by calcite (Fig. 11D); final- lyzed specimens are not significantly altered in their volume and/or ly, (E) blue bones are filled by calcite and opaque mineral and are not morphology, except the substituted fossils, which have cracked trabec- substituted (Fig. 11E). ular bone. In the non-substituted bones, Havers's channels and trabecu- The opaque mineral is likely to be iron oxide, which is common in lar bone are unaltered. Quaternary lacustrine environments (Soubiès et al., 1991; Suguio, 2003). In the present case, the likely source of iron oxide was the Cam- 6. Ante-mortem bone alterations brian basement rocks forming the tank walls. On the other hand, the calcite observed in some petrographic sections likely derived from the We observed ante-mortem bone alterations only in 10 fossils from dissolution of bone calcium, which later precipitated within cancellous Jirau (=0.71%). These features are present mainly in articular surfaces

Fig. 9. Mammal long bone with trample marks. Arrows indicate marks. Scale bar = 2 cm. H.I. Araújo-Júnior et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 378 (2013) 52–74 65

Fig. 10. Rib of Eremotherium laurillardi with teeth marks. Arrows indicate marks. Scale bars = 2 cm.

of two vertebrae (Fig. 12), five phalanges, two tibiae and one humerus, all 7. Taphonomic history and time-averaging in the Jirau fossil belonging to Eremotherium laurillardi. One vertebra, probably from the accumulation lumbar region, shows irregular bone growth at its center bordered by a well-defined rounded depression on the vertebral centrum, which is The taphonomic processes that acted on Jirau fossil accumulation asymmetrical in cranial view and shows signs of osteophytosis dorsally. and their relative timing are summarized in Fig. 13. In short, mamma- The other vertebra shows a bone callus located at the dorsal portion of lian remains were exposed subaerially for a long time span in the the vertebral centrum. We observed signs of bone remodelation on all thanatocoenosis accumulated around the tank, where they were sides of the proximal portion of tibiae, phalanges and humerus, which disarticulated and the skeletal elements modified by physico-chemical can be associated with trauma and microtrauma. Osteophytosis and and biogenic factors, such as weathering, trampling and scavenging bone remodelation are commonly due to overload on the vertebral col- under an arid or semiarid climate. Several episodes of debris-flow umn and senility (Halstead, 1990; Waldron, 2008; Sinibaldi, 2010). unleashed by floods shortly transported at least some of the skeletal 66 H.I. Araújo-Júnior et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 378 (2013) 52–74

Fig. 11. Petrographic thin sections of bones from the Jirau; A. white bone; B. black and white bone; C. beige bone; D. red bone; E. blue bone; B—bone; IC—iron carbonate; OM—opaque mineral; PC—permineralization by calcite; SC—substitution by calcite. Scale bars = 500 μm.

elements from the surrounding thanatocoenosis together with rounded reworked skeletal elements previously buried outside the tank, to in- pebbles originated in more distant areas to inside the tank, while bury- side the tank. It is also possible that, during these debris-flow epi- ing other skeletal elements outside the tank. In the course of time, there sodes, some of the specimens forming the taphocoenosis inside the were new carcass inputs into the thanatocoenosis followed by other tank had also been reworked, though, this seems unlikely due to episodes of debris-flow, that transported these new carcasses and the geometry of the deposit and the presence of unstable minerals H.I. Araújo-Júnior et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 378 (2013) 52–74 67

Fig. 12. Ante-mortem bone alterations in the fossils from Jirau; A. vertebral centrum of Eremotherium laurillardi with irregular bone growth; B. bone callus in vertebral centrum of E. laurillardi; Arrows indicate ante-mortem bone alterations. Scale bar = 2 cm.

in the fossiliferous layer. Taphonomic processes such as weathering, The cyclic input of carcasses, together with the transporta- transport and reworking have altered the compositional fidelity of the tion and reworking events resulted in the mixture of non- assemblage in relation to the original biocoenosis (e.g. ontogenetic stage contemporaneous bioclasts producing a time-averaged fossil as- profile), although some of the original paleobiological patterns seems to semblage. The co-occurrence of several taphonomic features provides have been preserved (e.g. relative abundance of Xenarthra Pilosa). Finally, evidence for this time-averaging, including: (A) noteworthy taxonomic the final taphocoenosis was affected by permineralization by opaque diversity, which, in fossil accumulations, increases when time-averaging minerals and calcite and substitution by calcite. Probably, these minerals increases (Peterson, 1977; Fürsich and Aberhan, 1990); (B) expressive originated from the weathering of basement rocks around the tank and fragmentation (Behrensmeyer, 1991;seealsoBown and Kraus, 1981; dissolution–precipitation of bone calcium. Badgley, 1986; Wood et al., 1988; Schröder-Adams et al., 2001 for similar 68 H.I. Araújo-Júnior et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 378 (2013) 52–74

Fig. 13. Taphogram for Jirau fossil accumulation showing hypothesized sequence and duration of the events.

conclusion); (C) dominance of adults relative to sub-adults, which is more 8. Comparison with other natural tanks indicative of temporal-mixed accumulations than assemblages generated by catastrophic death; (D) the association between very weathered skel- Thefossilvertebrateaccumulations of natural tanks known so far dif- etal elements and non-weathered specimens (Behrensmeyer, 1978; fer in relation to taxonomic composition, encompassing both paucitaxic Simões et al., 2010a); (E) finally, diagenetic differences between speci- and multitaxic assemblages (sensu Eberth et al., 2007b). The former are mens, which are the most consistent evidence for interpreting time- morecommonintanksfromthesouthernportionofnortheasternBrazil, averaging as they suggest that bones suffered mineralization in different such as those from Alagoas (Dias-Neto et al., 2008; Silva, 2008), Bahia time spans. However, only absolute dating of fossils could quantify the (Dantas and Tasso, 2007; Dantas and Zucon, 2007; Ribeiro and degree of time-averaging involved in the formation of the Jirau fossil Carvalho, 2009) and Sergipe States (Dantas et al., 2005), while the latter accumulation. are observed in tanks of more northern states, such as Rio Grande do H.I. Araújo-Júnior et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 378 (2013) 52–74 69

Norte (Cabral-de-Carvalho et al., 1966; Santos et al., 2002a; Araújo-Júnior suffered further fragmentation after the burial (Myers et al.;, 1980; and Porpino, 2011), Ceará (Paula-Couto, 1980; Bergqvist et al., 1997;this Shipman, 1981; Lyman, 1994; Cladera et al., 2004; Bergqvist et al., work), Paraíba (Bergqvist et al., 1997) and Pernambuco States (Vidal, 2011). Unfortunately, analyses of breakage patterns have not been 1946; Silva et al., 2006). Among all these, the tank of Jirau is the performed for other tank assemblages. most diversified deposit known so far. If vertebrate accumulations Our results related to weathering are consistent with similar with high indices of taxonomic diversity are also the ones most se- studies carried out on tanks from the Rio Grande do Norte (Santos verely time-averaged (see Peterson, 1977; Staff et al., 1986; Fürsich et al., 2002a) and Bahia (Ribeiro, 2010) States. These studies con- and Aberhan, 1990; Behrensmeyer, 1991; Kidwell and Bosence, cluded that the bioclasts were exposed before burial. In addition, 1991; Behrensmeyer et al., 2000; Lockwood and Chastant, 2006), it the extensive weathering and disarticulation observed in fossils is possible that tanks located in the north of northeastern Brazil from Jirau and other tanks from northeastern Brazil (Rio Grande do have higher ratios of time-averaging, while the southern ones are Norte and Bahia States; Santos et al., 2002a; Ribeiro, 2010)indicate less time-averaged. This would have serious implications for the often an arid or semiarid climate during the formation of their associated commonly held assumption that the fossil assemblages of tanks and thanatocoenoses (Shipman, 1981). caves of northeastern Brazil are synchronous (e.g. Cartelle, 1999), a Regarding fossildiagenesis, the processes of fossilization observed in view already criticized in recent dating studies of both tanks (Kinoshita Jirau are strikingly similar to those observed by Santos et al. (2002a) for et al., 2008; Silva, 2008; Oliveira et al., 2009; Dantas et al., 2011; Ribeiro fossils from Rio Grande do Norte State where permineralization pre- et al., in press)andcaves(Auler et al., 2006). However, only additional ab- dominates with substitution occurring simultaneously in some cases. solute datings of materials from deposits of different latitudes, including As in Jirau, Santos et al. (2002a) noted the contribution of opaque min- Jirau's assemblage, will answer this question more decisively. erals, probably iron oxides, in the substitution process. According to Like in Jirau's assemblage, fossils of E. laurillardi are abundant in Santos et al. (2002a) and Araújo-Júnior and Porpino (2011), the substi- other known tank deposits from northeastern Brazil (Santos et al., tution can have contributed to the better preservation in Pleistocene 2002a; Alves, 2007; Dantas and Tasso, 2007; Dantas and Zucon, 2007; fossils found in Rio Grande do Norte. However, in Jirau we observed Ribeiro and Carvalho, 2009; Araújo-Júnior and Porpino, 2011). We be- that the fossils bearing evidence of this process are not necessarily the lieve that the dominance of this species in Jirau may be due at least in better preserved. With respect to bone microstructure, we obtained part to the resistance of its skeletal elements to biostratinomic process- results identical to those reported by Ribeiro (2010): the material es compared to other species with less powerfully built bones, as appears slightly altered due to the absence of post-depositional evidenced by the impressive amount of preserved humeri of this spe- deformations. cies (see Section 5.2).Thesemayalsobethereasonfortheabundance Regarding colors, we observed that, although colors can be very dis- of this species in other tanks, but this should be more carefully evaluated. tinct among the preserved elements, the minerals involved in the fossil- Amphibian, crocodilian, turtle and bird remains have been reported, ization (calcium, iron oxides and iron carbonates) are well-represented so far, only for tanks in the States of Ceará (Paula-Couto, 1980; this on thin sections of almost all colors. This suggests that the external work, Section 4.2), Pernambuco (Vidal, 1946)andSergipe(Dantas et al., colors were acquired outside the tank, in a pre-fossilized stage, and 2005). One of the reasons that can explain the scarcity of their re- that internal fossilization processes occurred after the final burial into mains in those deposits is the assumption that they visited tanks as the tank. Carbonate cementation was identified by Alves et al. (2007) occasional foragers. Birds and amphibians bones are very fragile and Oliveira et al. (2009) in a tank at Fazenda Nova, Brejo da Madre de and easily fragmented by taphonomic processes (Lyman, 1994). Deus, Pernambuco State, however, these authors did not discuss origin The turtle and crocodilian fossils found in the tank of Jirau show signs of of carbonates in the fossiliferous layer. Silva (2008) identified carbonate abrasion and are represented by more transportable skeletal elements, cementation in a tank deposit at Alagoas State and attributed this feature such as osteoderms and vertebrae (Voorhies, 1969; Behrensmeyer, to chemical sedimentation during gaps in the terrigenous sedimentation.

1975; Hanson, 1980; Behrensmeyer, 1990; Blob, 1997). This pattern In the present case, the origin of CaCO3 is likely related to partial dis- is suggestive that the remains of these animals were more likely solution of bone calcium and its subsequent deposition inside the transported to the interior of the tank from more distant areas than bones, for we did not identify carbonate cementation between clasts – mammals. suggesting external provenance of the CaCO3 – but only permineralizing In relation to transport, Santos et al. (2002a), Alves (2007), Dantas and substituting bones internally. and Tasso (2007), Ribeiro (2010) and Araújo-Júnior and Porpino Previous paleontological studies on tank deposits in the States of (2011), based on an analysis of the degree of abrasion and Voorhies Paraíba (Bergqvist et al., 1997)Ceará(Bergqvist et al., 1997), Alagoas groups (Voorhies, 1969), have inferred short transport to vertebrate (Silva, 2008) and Bahia (Ribeiro and Carvalho, 2009) revealed that these thanatocoenoses of natural tanks from the Rio Grande do Norte, deposits share sedimentological features, suchasthepresenceofcoarse Pernambuco and Bahia States. We extend this inference to the tank sandstones or conglomerates, rich in feldspar, rock fragments (gneiss of Jirau based on the results obtained in our FTI analysis. Bergqvist and/or granite) and mica flakes within a silty-clayey matrix. According et al. (1997), Cartelle (1999), Santos (2001) and Ximenes (2003) to Bergqvist et al. (1997), these features suggest that the sediments argued that the tanks served as the last water sources in drought were barely or not transported, likely generated by weathering of rocks periods, and that the preserved individuals probably would have from the tank walls, as here inferred for Jirau. Concerning stratigraphy, died in the surrounding area. The short transport inferred for tank like in Jirau, Bergqvistetal.(1997), Silva (2008) and Ribeiro and thanatocoenoses supports this hypothesis. Santos et al. (2002a) and Carvalho (2009) also reported the presence of coarse sediments in Alves et al. (2007) pointed out, based on the high degree of abrasion, the basal layers grading toward silt and clay in the uppermost layers, the influence of high-energy agents in the deposition of mammalian suggesting energy decreasing toward the top of the sequence (Suguio, bones within three tanks from the Rio Grande do Norte and one from 2003) in several tank deposits. However, at least in one case (Pernam- Pernambuco States. The abrasion marks observed in the bones of Jirau buco State; Alves et al., 2007), there is evidence of constancy of concur with the scenario proposed by those authors and offers addition- high-energy events through time, which is suggested by the presence al support for the hypothesis of flood deposition of bioclasts in natural of coarse sediments in all layers. Therefore, though architectural dif- tanks during the late Pleistocene (Paula-Couto, 1980; Bergqvist et al., ferences can be observed, the similarities related to textural aspects 1997). of sediments observed in all aforementioned tanks suggest that the Regarding breakage pattern, Ribeiro (2010) observed, in a tank from deposition inside the tanks was strongly influenced by non-sorting the Bahia State, the prevalence of breaks perpendicular to the shaft in processes (floods) and not by sedimentary fluvial contributions, as fragments of long bones, which suggests that these skeletal elements suggested in early works (e.g. Paula-Couto, 1953; Santos, 1982). 70 H.I. Araújo-Júnior et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 378 (2013) 52–74

9. Comparison with other Brazilian Pleistocene deposits paleoecological studies than all other Brazilian Pleistocene deposits, including tanks. Fluvial deposits from Rondônia State belong to the Rio Besides tanks, Brazilian Pleistocene vertebrate deposits include caves, Madeira Formation (Abunã Basin) and contain highly diversified late lakes, fluvial and coastal deposits (Cartelle, 1992; Ranzi, 1999; Bergqvist Pleistocene vertebrate concentrations (Nascimento, 2008). Santos et al. and Almeida, 2004; Auler et al., 2006; Ribeiro and Scherer, 2009; (2011) and Araújo-Júnior et al. (2012) carried out a taphonomic analysis Araújo-Júnior and Porpino, 2011; Aires and Lopes, 2012). on the material collected in conglomerate lithofacies of this unit and The fossiliferous natural tanks are exclusive to northeastern Brazil, but noted features typical of fluvial channel concentrations, including sorting other deposits also occur in this region, such as caves (Cartelle, 1992; of more dense skeletal elements, disarticulated bones and heavy abrasion. Auler et al., 2006; Dantas, 2009). For these deposits few high-resolution These taphonomic signatures are also observed in the tanks of northeast- taphonomic studies have been undertaken, however, datings are increas- ern Brazil (including tank of Jirau), and although both tanks and fluvial ingly abundant (Guérin et al., 1996; Baffa et al., 2000; Neves and Piló, channels can hold very distinct deposits, they share similarities related 2003; Piló et al., 2004; Auler et al., 2006). Overall, fossils from Brazilian to the energy of their depositional agents. caves are better preserved than fossils collected in tank deposits (Auler et al., 2006; Araújo-Júnior et al., 2011b), but cave bone concentrations 10. Comparison with other debris-flow deposits bearing vertebrates are much more time-averaged. Auler et al. (2006), for instance, found a wide range of time-averaging in the vertebrate accumulations of caves As previously suggested, tank deposits are formed by floods in Bahia State (~94,000 years and ~280,000 years in Toca da Boa Vista (Bergqvist, 1993; Galindo et al., 1994; Bergqvist et al., 1997; Silva, andTocadaBarrigudacaves,respectively). In contrast, tanks display 2001, 2008), a classic type of debris-flow sedimentation (Dasgupta, lower rates of time-averaging than caves (~5300 years, ~12,000 years, 2003; Suguio, 2003). Reports of skeletal accumulations formed by de- ~12,100 years and ~41,000 years in Puxinanã, Poço Redondo, Brejo da bris flows have increased during the last 30 years (e.g. Andrews and Madre de Deus and Baixa Grande, respectively; Kinoshita et al., Alpagut, 1990; Andrews and Ersoy, 1990; Fastovsky et al., 1995; 2005; Alves et al., 2007; Kinoshita et al., 2008; Silva, 2008; Dantas Eberth et al., 2000, 2006; Rossetti et al., 2004; Rogers, 2005; et al., 2011; Ribeiro et al., in press). In comparison, the highest rate of Lauters et al., 2008; Britt et al., 2009; Mazza and Ventra, 2011). A time-averaging in tank deposits (~41,000 years in Baixa Grande; Ribeiro review of the more detailed studies shows that debris-flow deposits et al., in press) is considerably lower than the lowest values of time- bearing vertebrate accumulations may have originated during: averaging in caves (~94,000, Toca da Boa Vista; Auler et al., 2006). Thus, (A) debris-flow reworking and burial of pre-existing thanatocoenoses even if tank deposits have not the better preserved fossils, they seem (Andrews and Ersoy, 1990; Fastovsky et al., 1995; Eberth et al., 2006; more valuable than caves at least for some kinds of paleoecological anal- Lauters et al., 2008; Britt et al., 2009); (B) in situ burial of a pre-existing yses because they bear less time-averaged vertebrate accumulations. thanatocoenosis by a debris flow (Eberth et al., 2000; Rogers, 2005; Concerning taphonomic features, Brazilian cave accumulations have Mazza and Ventra, 2011); (C) death and burial of the biocoenosis by very complex taphonomic settings, because they can accumulate both debris flow (obrution; Eberth et al., 2000; Rossetti et al., 2004); and in situ and ex situ fossils (Auler et al., 2006). This contrast with tanks, (D) combinations of A–C(Fastovsky et al., 1995; Eberth et al., 2000). which are believed to comprise mainly in situ assemblages (Cartelle, Among the aforementioned studies, the Dalton Wells bonebeds of the 1999;ourinterpretationsinSection 8). Furthermore, Araújo-Júnior Lower Cedar Mountain Formation, in USA (Britt et al., 2009)is et al. (2011b) observed that taxonomic composition of individual cave the most similar to the tank of Jirau. They share the following features: assemblages is very distinct as they show greater variations in their (A) most elements are broken; (B) large vertebrate remains are overrep- large and small-sized vertebrate composition relative to tanks, which resented; (C) wide range of weathering stages; (D) trample and tooth seem more homogeneous in this regard. marks on bones; and (E) semi-aquatic vertebrates are rare. Another Brazilian coastal Pleistocene deposits are located in Rio Grande do Sul debris-flow deposit, the Upper Cretaceous Udurchukan Formation in State (Southern Brazil; Ribeiro and Scherer, 2009). These accumulations Russia (Lauters et al., 2008), also shares several features with Jirau accu- are also more time-averaged than tanks, encompassing a time span mulation, including dominance of broken bones, overrepresentation of of.700,000 years (Lopes et al., 2010). Thus, it would be comparatively large vertebrates, tooth marks (although underrepresented) and scarcity much more difficult to extract more detailed paleoecological information of semi-aquatic vertebrates. Lauters et al. (2008) and Britt et al. (2009) from Brazilian coastal deposits than from tank accumulations. In terms of interpreted those fossil assemblages as lag deposits that gathered skeletal taphonomic signatures, fossils collected at Rio Grande do Sul exhibit elements reworked and shortly transported during debris-flow events similarities with tank fossils, such as: (A) they have moderate to highly from nearby areas of accumulation, which is a similar scenario to abraded bones; and (B) more massive skeletal remains that are more that we can infer for the Jirau assemblage (see Section 7). In the fragmented (Lopes et al., 2008; Aires and Lopes, 2012). Lopes et al. case of Jirau, the different colors observed (not mentioned by Lauters (2008) and Aires and Lopes (2012) attributed these bone modifications et al., 2008 and Britt et al., 2009) furnish additional support to infer ep- to reworking on old deposits by waves and storms. In fact, it seems that isodes of reworking during the formation of Jirau's assemblage. Further- reworking is a broad process operating on Brazilian vertebrate deposits more, the assumption that the Jirau accumulation represents a lag during the late Pleistocene and its origin can be associated with diverse deposit formed by debris-flow under similar conditions to that of the factors depending on local features, such as the nature of the deposit, its Cedar Mountain and Udurchukan formations, could explain the com- depositional environment and the nature of the transport agent involved plexity of taphonomic signatures observed in our analysis (i.e. high di- in the formation of the taphocoenosis. versity of taphonomic signatures and high variation of parameters The better known Brazilian fluvial deposits bearing late Pleistocene within signatures) because debris flows hosted vertebrate accumula- vertebrates are located in Rio Grande do Sul and Rondônia States tions are, overall, very taphonomically complex (Eberth et al., 2000; (Kerber and Oliveira, 2008; Ribeiro and Scherer, 2009; Santos et al., Rogers, 2005; Britt et al., 2009). 2011). These fossil concentrations bear several taphonomic signatures Yet, some differences can be observed in the assemblage data and directly related to their surrounding depositional systems (Kerber and element modification data in the studies cited above (including Oliveira, 2008). Floodplain accumulations preserved in Touro Passo Jirau). As mentioned by Britt et al. (2009), this is not surprising Formation outcrops at Rio Grande do Sul State bear articulated and given that debris flows last only a very short time (minutes to semi-articulated skeletal elements and do not present bioclast sorting, hours) and there are temporally-limited opportunities to impart ev- representing a low-energy environment (Kerber and Oliveira, 2008). idence of the debris-flow event onto the elements being transported Reworking cannot be inferred for that fossil concentration and it repre- and reworked. Behrensmeyer (1988) and Aslan and Behrensmeyer sents a low time-averaged assemblage, being more useful to detailed (1996) showed that, in general, a great deal of time and reworking H.I. Araújo-Júnior et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 378 (2013) 52–74 71 in these settings are required to modify element surfaces, and that 11.2. Biostratinomy element breakage in these settings is infrequent, especially where collagen is still present in bones. Thus, differences in the assemblage The ontogenetic stage frequencies observed in the bone concentra- and bone modification data among debris flows bearing vertebrates tions of tanks were likely biased by time-averaging, rather than reflecting likely reflect variations in a wide range of biostratinomic histories. a catastrophic death. After death, the skeletons were disarticulated and In the Pleistocene of central Italy, Mazza and Ventra (2011) rec- damaged by scavengers and trampling, which may also have caused ognized a debris-flow deposit bearing mammals based on tapho- their fragmentation. Probably, the thanatocoenosis was widely exposed, nomic and sedimentological analyses. In contrast to Jirau, this fossil comprising a mix of young and older bones. A short transport caused by accumulation was interpreted as resulting from an in situ burial of episodic debris flows unleashed by floods deposited the remains inside the thanatocoenosis. Accordingly, it differs from Jirau in the absence the tank, along with clasts from more distant sources. Non-mammalian of weathering, scavenging, trampling and sorting due to the rapid burial vertebrates remains were probably more transported than mammals. (Mazza and Ventra, 2011). Yet, there are some similarities between Thus, the accumulation of Jirau can be classified as parautochthonous Jirau's fossil assemblage and this Italian site, such as: (A) short transport (sensu Lyman, 1994). Other taphonomic features that would have been of the thanatocoenoses to the final site of accumulation; (B) both are previously reported for other tank accumulations (e.g. rooting and inver- monodominant assemblages (sensu Eberth et al., 2007b); (C) preserved tebrate modifications) may have been obscured by processes such as mainly large-sized mammals; and (D) were enclosed in conglomeratic abrasion and weathering. lithofacies. The similarities in transport and lithofacies are clearly reflec- tive of a similar depositional context (debris-flow sedimentation), 11.3. Reworking while similarities “B” and “C” are interpreted for both sites as reflecting non-biased past biocenotic patterns (Mazza and Ventra, 2011). These It is likely that the skeletal elements forming the assemblage of the are interesting agreements as they suggest that, though debris-flow tank of Jirau underwent several cycles of reworking, resulting in the deposits bearing vertebrates (including Jirau) have intricate taphonomic fragmentation of the material and mixing of old and younger bones. histories, at least in some cases, they can preserve essential paleoecolog- Moreover, based on the results of FTI analysis, we conclude that the ical information. abrasion observed in the fossils is due to reworking rather than to ex- In Brazil, besides natural tanks, another debris-flow deposit bearing tensive transport. Pleistocene vertebrates (megatheriid ground sloths and mastodonts) is reported from the Itaituba area, Pará State, central Amazonia, in the Am- 11.4. Fossildiagenesis azonian Basin (Rossetti et al., 2004). This deposit shares a few similari- ties with Jirau, such as the mixture of both broken and complete bones The diagenetic features observed indicate permineralization as the and the low amount of bones found when compared to what would predominant fossilization process and substitution as a process with be expected based on MNI. The aforementioned features are sugges- minor incidence. In addition, the mineralogical and color differences tive of thanatocoenoses suffering subaerial exposure prior to burial observed in the material reinforce the time-averaging inference for (Behrensmeyer, 1978, 1991; Rogers and Kidwell, 2007). These pat- the studied assemblage. terns are at odds with interpretations given by Rossetti et al. (2004) that “An event such as flash flooding might have promoted slope instability, 11.5. Paleoclimate death of the ground sloths, and their transportation into the basin together with the other debris” (Rossetti et al., 2004; page 295, lines 2–5). Thus, it The accumulation from Jirau shows biostratinomic features indica- is more likely that the Pleistocene accumulation of central Amazonia tive of an arid to semiarid climate. The diagenetic patterns identified is an attritional accumulation (like tanks) rather than a catastrophic also support this inference. The analysis of sedimentary facies indicates burial. However, though the central Amazonia debris-flow assem- the occurrence of environmental shifts after the final burial, as the fos- blagemaybeanattritionalassemblage,itislikelythatitwasargu- siliferous layer and the overlying strata were likely generated by differ- ably formed under a taphonomic regime distinct from that of tanks ent depositional processes. due to the absence of several taphonomic features observed in the latter (e.g. desiccation, teeth and trample marks and diversified tax- 11.6. Comparative taphonomy onomic composition). Although tank deposits other than Jirau have not been subject to A comparison between the tank of Jirau and other analogous deposits equally detailed study with regard to taphonomy, they (Paraíba, Pernam- from northeastern Brazil revealed common taphonomic and sedimento- buco, Alagoas, Sergipe and Bahia States) show general preservational pat- logical patterns, although there is an exception related to sedimentologi- terns very similar to those described for Jirau, Udurchukan assemblage cal aspects. Based on the assumption that taphonomic signatures and Cedar Mountain accumulations (Bergqvist et al., 1997; Dantas et al., reflect environmental conditions (Brett and Baird, 1986; Brett and 2005; Silva et al., 2006; Silva, 2008; Ribeiro, 2010). Therefore, we suggest Speyer, 1990), the observed patterns suggest a rather homogeneous that they also underwent similar taphonomic histories and share similar environment for the northeastern Brazil during the late Pleistocene. depositional contexts, representing a peculiar case of debris-flow hosted Comparison with other Brazilian Pleistocene deposits reveals that tank fossil accumulations. deposits are more informative for paleoecological analyses than caves, coastal and some fluvial deposits and that reworking operated widely on Pleistocene Brazilian deposits, including tanks. Tank deposits seem 11. Conclusions similar to other debris-flow vertebrate accumulations in several general aspects. Furthermore, such comparisons reveal that the taphonomic 11.1. Biocoenosis and relative abundance complexity of Jirau is likely resulting from reworking and, consequently, from time-averaging. The abundance of megamammals compared to small vertebrates is likely due to both greater bone resistance and abundance of these animals Acknowledgments inthebiocoenosisassociatedwiththetankofJirauthelatePleistocene. This study provides evidence that E. laurillardi was very abundant in the Authors are grateful to A.S.T. Santos, Director of the MUPHI, for region of Itapipoca during the late Pleistocene, while non-mammalian allowing the study of the fossils collected at Jirau; Drs. J.C. Mendes vertebrates were scarcely present. (UFRJ) and A.M. Rios-Netto (UFRJ) for helping with petrographic 72 H.I. Araújo-Júnior et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 378 (2013) 52–74 analysis; Dr. M.G. Simões (UNESP/Botucatu) and R.C. Ribeiro (UFRJ) for Bergqvist, L.P., 1993. Jazimentos pleistocênicos do Estado da Paraíba e seus fósseis. Revista Nordestina de Biologia 8, 143–158. suggestions, which contributed to the improvement this analysis; Dr. G. Bergqvist, L.P., Almeida, E.B., 2004. Biodiversidade de mamíferos fósseis brasileiros. Haynes (University of Nevada, USA) for helping with identification of Geociências 9, 54–68. the teeth marks; F.H.S. Barbosa (UFPE) for helping with ante-mortem Bergqvist, L.P., Gomide, M., Cartelle, C., Capilla, R., 1997. Faunas-locais de mamíferos pleistocênicos de Itapipoca/Ceará, Taperoá/Paraíba e Campina Grande/Paraíba. bone alterations; Coordenação para Aperfeiçoamento de Pessoal de Estudo comparativo, bioestratinômico e paleoambiental. Geociências 2, 23–32. Ensino Superior (CAPES) and Fundação Carlos Chagas Filho de Amparo Bergqvist, L.P., Almeida, E.B., Araújo-Júnior, H.I., 2011. Tafonomia da assembleia à Pesquisa do Estado do Rio de Janeiro (FAPERJ) for financial support; fossilífera de mamíferos da “Fenda 1968”, Bacia de São José de Itaboraí, Estado do – the editor and two anonymous reviewers for presenting valorous criti- Rio de Janeiro, Brasil. 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