lable at ScienceDirect Journal of South American Earth Sciences 31 (2011) 17e27 Contents lists avai Journal of South American Earth Sciences journal homepage: www.elsevier .com/locate/ jsames Pleistocene mammals from the southern Brazilian continental shelf Renato Pereira Lopes a,*, Francisco Sekiguchi Buchmann b a Programa de Pós-graduação em Geociências (UFRGS)/Universidade Federal do Rio Grande (FURG), Instituto de Oceanografia, Laboratório de Oceanografia Geológica - Setor de Paleontologia, Av. Itália, km 8, CEP 96201-900 Rio Grande, RS, Brazil bUniversidade Estadual de São Paulo (UNESP), Campus São Vicente, Praça Infante D, Henrique, s/no. CEP 11330-900, São Vicente, SP, Brazil a r t i c l e i n f o Article history: Received 18 May 2010 Accepted 8 November 2010 Keywords: Megafauna Pleistocene Eustasy Continental shelf Konzentrat-lagerstätte Rio Grande do Sul Abbreviations: LGP, Laboratório de Geologia e Pal Toxodontidae; G, Proboscidea: Gomphotheriidae. * Corresponding author. E-mail addresses: paleonto_furg@yahoo.com.br yahoo.com.br (F.S. Buchmann). 0895-9811/$ e see front matter � 2010 Elsevier Ltd. doi:10.1016/j.jsames.2010.11.003 a b s t r a c t Fossils of terrestrial mammals preserved in submarine environment have been recorded in several places around the world. In Brazil such fossils are rather abundant in the southernmost portion of the coast, associated to fossiliferous concentrations at depths up to 10 m. Here is presented a review of such occurrences and the first record of fossils in deeper areas of the continental shelf. The fossils encompass several groups of both extinct and extant mammals, and exhibit several distinct taphonomic features, related to the marine environment. Those from the inner continental shelf are removed and transported from the submarine deposits to the coast during storm events, thus forming large konzentrat-lagerstätte on the beach, called “Concheiros”. The only fossils from deeper zones of the shelf known so far are a portion of a skull, a left humerus and of a femur of Toxodon sp. and a lower right molar of a Steg- omastodon waringi, all collected by fishermen at depths around 20 m. The presence of fossils at great depths and distances from the present coastline, without signs of abrasion and far from areas of fluvial discharges does indicate that these remains have not been transported from the continent to the shelf, but have been preserved directly on the area that today correspond to the continental shelf. These remains indicate the existence of large fossiliferous deposits that have developed during periods of sea- level lowstand (glacial maxima) and have been submerged and reworked by the sea-level rise at the end of the last glaciation. � 2010 Elsevier Ltd. All rights reserved. 1. Introduction Fossils of terrestrial mammals have been recorded on conti- nental shelves of the Sea of Japan, the northeastern coast of North America (Whitmore et al., 1967; Hoyle et al., 2004), the North Sea (Van Kolfschoten and Laban, 1995; Mol et al., 2006), in the Argen- tinean continental shelf (Tonni and Cione, 1999; Cione et al., 2005) and the northeastern coast of Uruguay (Rinderknecht, 2006). The presence of such remains in submarine environment is attributed to fossiliferous deposits that were formed on areas of the continental shelf that have been under subaerial exposure due to sea-level oscillations during the Quaternary (glacio-eustasy). This exposition is correlated to glacial maxima, when sea-level dropped 120 m below the present level all around the globe (Villwock,1984; Corrêa et al., 1996; Bridgland, 2002). In the Brazilian continental shelf, such eontologia; E, Notoungulata: (R.P. Lopes), paleonchico@ All rights reserved. fossils have been recovered so far only from its southernmost portion, in the coast of the Rio Grande do Sul State, mostly on the beach but also from deeper locations, such as the Parcel do Car- pinteiro, a submarine rocky structure located at 32�160S� 051�470W at a depth of 25m (Buchmann,1994; Buchmann et al., 2001). Here is presented a review of the presence of fossils of terrestrial mammals in nearshore environments, and some specimens collected from deeper areas far from the coast are described for the first time in the Brazilian coast. 2. Geological setting The Coastal Plain of the of Rio Grande do Sul State (RSCP, Fig.1) is a 620 km-long geomorphological unit located between the lati- tudes 29�1803100S and 33�4301700S, and constitutes the area of the coastal province of Rio Grande do Sul that remains above sea-level. It corresponds to the upper portion of the Pelotas Basin, the southernmost Brazilian marginal sedimentary basin. This basin has a maximum thickness of 10 km and was formed by the accumula- tion of sediments eroded from Paleozoic and Mesozoic rocks of the continental geological units after the split between South America and Africa in the Late Cretaceous (Closs, 1970). After the opening of mailto:paleonto_furg@yahoo.com.br mailto:paleonchico@yahoo.com.br mailto:paleonchico@yahoo.com.br www.sciencedirect.com/science/journal/08959811 http://www.elsevier.com/locate/jsames http://dx.doi.org/10.1016/j.jsames.2010.11.003 http://dx.doi.org/10.1016/j.jsames.2010.11.003 http://dx.doi.org/10.1016/j.jsames.2010.11.003 Fig. 1. Map of the State of Rio Grande do Sul showing the structure of the coastal plain (modified from Tomazelli et al., 2000), plus bathymetric lines and places where the specimens LGP-E0024 and G0032 were collected. The area of the “Concheiros” is indicated by the stippled rectangle on the south. A e Patos Lagoon; B e Mirim Lake. R.P. Lopes, F.S. Buchmann / Journal of South American Earth Sciences 31 (2011) 17e2718 the Atlantic Ocean, the Brazilian continental margin was subject to deposition of sediments eroded from continental areas and trans- ported to the coastal areas by fluvial systems. In the Pelotas basin, Albian sediments mark the transition from continental to marine transgressive enviroments (Bueno et al., 2007). Between the Tertiary and Quaternary the morphology of the RSCP was influ- enced by eustatic oscillations correlated to the glacialeinterglacial cycles, represented by facies changes and microfossil assemblages recovered from drilling holes (Closs, 1970; Carreño et al., 1999). As a result of these oscillations, two major depositional systems were formed parallel to the coastline: the Tertiary Alluvial Fans System and the Quaternary Complex Multiple Barrier system (Villwock, 1984; Villwock et al., 1986). The Complex Multiple Barrier System is subdivided into four major barrier-lagoon depositional systems and associated features. Each system was formed in response to a major sea-level trans- gression during interglacial episodes. The exact ages of such deposits is still undetermined, but are correlated to the interglacialmaxima at 400 ky (Barrier-Lagoon System I), 325 ky, (Barrier-Lagoon System II), 123 ky (Barrier-Lagoon System III) and 6 ky (Barrier-Lagoon System IV) (Villwock and Tomazelli, 1995; Tomazelli et al., 2000). The sedi- ments that constitute these systems are essentially terrigenous sicliciclastic, well-selected and mature, with small fractions of organic matter, biogenic carbonate and diagenetic clays, with some expressive concentrations of heavy minerals (Villwock and Tomazelli, 1995). In the southen portion of the coast, large concen- trations of Pleistocene marine bioclasts, composed mostly by rounded shell fragments, are found (Buchmann et al., 2009; see below). Figueiredo (1975) obtained 14C ages between 16 ka and more than 30 ka for fossil marine shells collected from the conti- nental shelf. These bioclasts can be classified as palimpsests, i.e., relict sediments (deposited during and/or right after the last glacial maximum) that are being reworked by dynamic processes of today (Pilkey and Frankenberg, 1964; Swift et al., 1971). Some 70% of the sediments from continental shelves around the world can be clas- sified as relicts (Emery, 1968). The continental shelf, which constitutes the submarine portion of the coastal province, has a low topographic gradient (a 1:1.000 average ratio) and the shelf break is located at depths between 80 and 170 m. The shelf is broad and was subject to extensive reworking and contains submerged paleo-fluvial channels and sand banks (Corrêa et al., 1996). During the Holocene sea trans- gression, around 6e7 ky, variations in the rates of sea-level rise resulted in the reworking and concentration of terrigenous clastic sediments of the shelf, and erosive terraces were formed in response to episodes of sea-level stabilization (Kowsmann and Costa, 1974; Martins et al., 1996). Sediments that constitute the upper portion of the shelf are clastic terrigenous, originated in the older geomorphologic units, and were deposited by several fluvial systems during the sea-level lowstands, including the La Plata river (Tomazelli, 1978; Martins, 1983). The fossils described here come from two distinct areas of the shelf: the inner shelf (from the surf zone up to depths of 10 m, roughly the zone affected by wave action), and the outer shelf (at depths of 20 m andmore, where the action of waves does not reach the ocean bottom). Although the presence of fossils from the nearshore has been recorded all along the coast of Rio Grande do Sul, such remains are more conspicuous in the southernmost portion (Buchmann, 1994). Fossils from the outer continental shelf are described here for the first time for the Brazilian coast. 3. Fossils from the inner continental shelf The presence of fossils of terrestrial mammals on the coast of Rio Grande do SulState, in southernmost Brazil, has been known since the late XIX century, when German naturalist Herman von Ihering described in a letter to the Argentinean paleontologist Florentino Ameghino some remains of glyptodonts that he had collected on the beach (Von Ihering, 1891). Throughout the XX century, the fossils have been subject of several studies, focusing mostly on its systematics (e.g. Cunha, 1959 47 p.; Paula Couto and Cunha, 1965; Oliveira, 1992, 1996; Rodrigues et al., 2004; Scherer, 2005; Marcon, 2007). Other studies have described the distribu- tion of these remains along the shoreline (Buchmann, 1994) and its taphonomy (Lopes et al., 2008). These fossils are found associated to large concentrations of fossil shellfish and othermarine organisms found on the inner continental shelf (Figueiredo (1975)). During autumn and winter, storm waves erode these deposits, removing the fossils and throwing it onto the beach. The fossil shellfish accumulated throughout the years along Table 1 Terrestrial mammals found in fossiliferous deposits of the southern Brazilian continental shelf (following the classification of McKenna and Bell, 1997). Phyllum CHORDATA Bateson, 1885 Class MAMMALIA Linnaeus, 1758 Superorder XENARTHRA Cope, 1889 Order PILOSA Flower, 1883 Family MEGATHERIIDAE Owen, 1843 Megatherium Cuvier, 1796 Family MYLODONTIDAE Gill, 1872 Glossotherium Gervais, 1855 Lestodon Gervais, 1855 Mylodon Owen, 1839 Catonyx Ameghino, 1891 Order CINGULATA Illiger, 1881 Family DASYPODIDAE Bonaparte, 1838 Propraopus Ameghino, 1881 Family PAMPATHERIIDAE Paula Couto, 1954 Holmesina Simpson, 1930 Pampatherium Ameghino, 1875 Family GLYPTODONTIDAE Burmeister, 1879 Doedicurus Burmeister, 1874 Glyptodon Owen, 1845 Panochthus Burmeister, 1872 Neuryurus Ameghino, 1889 Pachyarmatherium Downing & White, 1995 Order LITOPTERNA Ameghino, 1889 Family MACRAUCHENIIDAE Gervais, 1855 Macrauchenia Owen, 1838 Family Proterotheriidae Ameghino, 1887 Neolicaphrium Frenguelli, 1921 Order NOTOUNGULATA Roth, 1903 Family TOXODONTIDAE Owen, 1845 Toxodon Owen, 1838 Order CARNIVORA Bowdich, 1821 Family FELIDAE Gray, 1821 Smilodon Lund, 1842 Family CANIDAE Fischer de Waldheim, 1817 Protocyon Lund, 1842 Dusicyon Hamilton-Smith, 1839 Theriodictis Mercerat, 1891 Order RODENTIA Bowdich, 1821 Family CAVIIDAE Fischer de Waldheim, 1817 cf. Cavia Pallas, 1766 Dolichotinae (indet.) Pocock, 1922 Family HYDROCHOERIIDAE Brisson, 1762 Hydrochoerus Brisson, 1762 Family OCTODONTIDAE Waterhouse, 1839 cf. Ctenomys Blainville, 1826 Family MURIDAE (¼CRICETIDAE) Illiger, 1811 Reithrodon Waterhouse, 1837 R.P. Lopes, F.S. Buchmann / Journal of South American Earth Sciences 31 (2011) 17e27 19 the beach constitutes a large konzentrat-lagarstätte called “Con- cheiros” along the southernmost portion of the coast. Such lager- stätte did not exist on the beach until the early 1970s (Luiz Rota, pers. comm.); Figueiredo (1975) described it as patches of fossil shellfishmeasuring few kilometers in length, some 5m inwidth and 3 cm in thickness. Today the “Concheiros” are large fossil concen- trations extending continuously for some 40 km, measuring up to 2 m in thickness, and have been expanding northwards and southwards throughout the years (Buchmann, 2002). The origin and evolution of such concentrations is probably related to the marine erosive processes that have been affecting this portion of the coast in the last decades (Dillenburg et al., 2004) and remove the recent sedimentary cover, exposing the underlying Pleistocene sediments. The shellfish fossils encompass both taxa that live in the surf zone and others that live in deeper areas (Lopes and Buchmann, 2008), thus these concentrations do not represent a community, but instead are a result of sedimentological processes. The fossils are founddisarticulated and scattered along the beach. Although remains of several marine organisms such as teleost and elasmobranch fishes (Richter, 1987; Buchmann and Rincón Filho, 1997), shellfish (Figueiredo (1975); Lopes and Buchmann, 2008), echinoderms, crustaceans (Buchmann, 1994; Lopes, 2009), pinni- peds (Oliveira and Drehmer, 1997), cetaceans (Cunha, 1982; Ribeiro et al., 1998) and seabirds (Lopes et al., 2006) are found in these concentrations, the most remarkable are the fossils of terrestrial mammals (Fig. 2). Several taxa are represented among these remains, most of them extinct (Table 1). Some Pleistocene taxa are recorded in Rio Grande do Sul State only by fossils collected in the “Concheiros” (Rodrigues et al., 2004; Rodrigues and Ferigolo, 2004; Bostelmann, 2008; Ribeiro et al., 2008; Scherer et al., 2009), and an alligatorid fossil has also been recorded (Hsiou and Fortier, 2007). Because these fossils are found removed from its deposits they do not have a precise stratigraphic context, and this has led to several misconceptions regarding the geological origin of these remains. In the first systematic geological mapping of the coast of Rio Grande do Sul (Delaney,1965), the remains were associated toTertiary deposits of the “Graxaim Formation” (now recognized as the Alluvial Fans Systems) that presumably extended in subsurface from the conti- nent to the continental shelf. Later, this assumption was challenged because no vertebrate fossil was ever recovered from the “Graxaim Formation” (Paula Couto and Cunha, 1965). Soliani (1973) described the stratigraphy of the Chuí Creek, a fossiliferous continental deposit in the southernportion of theRSCP containing the same fossils found along the beach, thus he concluded that both deposits had the same age andwere part of the “SantaVitória Formation”, a scheme that has Fig. 2. A detail of the “Concheiros”, with a fossil of terrestrial mammal (distal portion of the caudal tube of the glyptodont Panochthus) (the scale measures 50 mm). Family ECHIMIYDAE Gray, 1825 Myocastor Kerr, 1792 Heteromysopinae (indet.) Anthony, 1917 Order URANOTHERIA McKenna & Bell, 1997 Family GOMPHOTHERIIDAE Hay, 1922 Stegomastodon Pohlig, 1912 Order PERISSODACTYLA Owen, 1848 Family EQUIDAE Gray, 1821 Equus Linnaeus, 1758 Hippidion Owen, 1869 Family TAPIRIDAE Gray, 1821 Tapirus Brunnich, 1772 Order ARTIODACTYLA Owen, 1848 Family CAMELIDAE Gray, 1821 Lama Cuvier, 1800 Hemiauchenia Gervais & Ameghino, 1880 Family CERVIDAE Goldfuss, 1820 Antifer Ameghino, 1889 Morenelaphus Carette, 1922 Family TAYASSUIDAE Palmer, 1897 Tayassuidae indet. Fig. 4. A molariform of a mylodontid ground sloth (indicated by arrow) embedded in a coquina (scale bar 20 mm). R.P. Lopes, F.S. Buchmann / Journal of South American Earth Sciences 31 (2011) 17e2720 been adopted throughout the years (Oliveira,1992,1996; Lopes et al., 2005). However, datings by electron spin resonance (ESR) in enamel samples extracted from teeth, obtained ages between 650 � 100 ka and 18� 3 ka for the fossils from the nearshore and between 34� 7 ka and 42 � 3 ka for those from the Chuí Creek (Lopes et al., 2010), thus indicating that both deposits are distinct units, formed at different epochs. The vertebrate fossils exhibit remarkable taphonomic features, related to its preservation inmarine environment. All specimens are heavily mineralized and exhibit dark colors, ranging from reddish to black, probable due to the influence of elements such as iron and manganese. Most of the fossils are broken and abraded due to erosion and transportation by waves (Lopes et al., 2008). Although unidentifiable, broken and very abraded bone fragments are the most common (Fig. 3), sometimes larger and even complete speci- mens are found. Some fossils are either embedded in coquina blocks (Fig. 4) or have cavities filled with sand or mud that was lithified by precipitation of calcium carbonate, features related to the Taphofa- cies II of Lopes et al. (2008) (Table 2). The precipitation of carbonate cement under a warmer climate regime during the Pleistocene was responsible by the formation of lithified paleo-beachlines that are found in the near continental shelf and are the source of the blocks of coquinas found thrown onto the beach by storms (Asp, 1999; Buchmann et al., 2001; Buchmann, 2002). These fossils are subject to two major environmental processes: exposure in the wateresediment interface due to removal of Holocene sediments by long-term erosion of the shelf, related to shoreface retreatment, and removal and transportation to the beach bywaves. Two types of waves affect the fossil remains: storm waves, which remove and transport large amounts of fossils and redeposit it onto the beach, and “normal” waves, which continu- ously rework smaller remains in the surf zone. These physical processes are the main cause of biostratinomic alteration on these remains, although some features are probably related to preser- vation on continental environment, prior to its exposure to marine environment (Lopes et al., 2008). In a biostratigraphic sense, Paula Couto and Cunha (1965) correlated these mammalian fossils to the “Pampeano Superior” (Bonaerean) of Argentina. Later, Bombin (1975) correlated these remains to the Lujanian Land-Mammal Age of the Pampean Region of Argentina based on the presence of fossils of Equus (Amerhippus) Fig. 3. Unidentified fossil fragments (scale bar 20 mm). neogaeus, and this has been accepted throughout the years. More recently, Cione and Tonni (1995) have replaced the South American “Land-Mammal Age” concept for the chronostratigraphic Stage/Age scheme, placing the Lujanian Stage/Age between 130 and 8,5 ka AP. However, the ESR ages indicate that the fossils from the continental shelf are not only of Lujanian bus also of Ensenadan and Bonaerean Stage/Ages (Lopes et al., 2010). Although these fossils do not have a precise stratigraphic context, the ages are correlated to marine isotope stages (MIS) 16, 12, 8, 6, 4 and 2, indicating that the organisms occupied the area during the glacial maxima. According to Rabassa et al. (2005), during these maxima the Pampean fauna would have extended its distribution area farther to the north, following the northward migration of the climatic belt. The northern distribution of certain mammalian taxa, such as Mega- therium americanum and Doedicurus clavicaudatus is restricted to southern Brazil, probably reflecting the maximum reach of the climatic belt during glaciations. During interglacials, on the other hand, elements of the Brazilian fauna such as Tapirus and Holochilus reached the Pampean area of Argentina, reflecting the southward migration of the climatic belts. A survey among 1819 fossils from the paleontological collection of Universidade Federal do Rio Grande (FURG), all collected along the 226 km-long shoreline between Rio Grande and Chuí during the last 15 years, has shown that the most common remains are teeth (Fig. 5), followed by osteoderms and cranial elements (Table 3). The osteoderms belong to cingulates, mostly glypto- dontids. The glyptodontid osteoderms occur mostly isolated, but partial carapaces, formed by several osteoderms fused together, can also be found (Fig. 6). Osteoderms of pampatheriids and dasypodids are also common, found only as isolated elements. The osteoderms are found mostly complete, but sometimes it is difficult to see morphological details because of abrasion. The cranial remains are representedmostly by cervid antlers, but some jaw and skull fragments of other taxa are also found. The most conspicuous autopodial elements are astragali of artiodactyls and mylodontid sloths; phalanges of ground sloths are also common (Fig. 7). These smaller elements are foundmostly complete, although Table 2 Taphofacies recognized among the fossils from the continental shelf (Lopes et al., 2008). Taphofacies Features Depositional context I Very fragmented and abraded fossils, without colonization or carbonate cement Remains that were covered by sediments, now exposed by erosive processes and continuously under influence of waves. II Fossils fragmented and very abraded; associated to coquinas Remains that were reworked and redeposited on beach environments in the past, when climatic conditions allowed the formation of coquinas. Currently associated to rocky structures representing paleo-beachlines that are being eroded. III Fossils with better preservation, mostly incomplete, but with few or no signs of abrasion. Colonization by epi- and endoskeletozoans Remains currently exposed on the sedimentewater interface, below the zone influenced by waves. Probably reworked in the past during a sea-level transgression R.P. Lopes, F.S. Buchmann / Journal of South American Earth Sciences 31 (2011) 17e27 21 some are much abraded. Most of the limb bones belong to large- bodied taxa such as toxodontids and sloths, but bones of smaller organisms, although less common, can also be found. Limb bones exhibit the largest range of taphonomic variation, from specimens nearly unrecognizable due to abrasion and/or fragmentation to complete or nearly complete specimens. The transport of larger limb fossils to the beach requires extremely strong waves, thus these are not verycommon, but once thrownonto thebeach suchboneswould not be reworked or transported again until the next extreme storm surge. On the other hand, limbs of smaller specimens aremore easily transported and removed, thus are more likely to be destroyed by mechanical action of the waves in the surf zone. Vertebral elements occur mostly as broken neural arches or centra. Complete or near complete vertebrae are mostly smaller ones that belong to Fig. 5. Isolated teeth collected in the “Concheiros”. A: artiodactyls artiodactyls. Other elements, found as fragments, include scapulae, ribs and caudal tubes of glyptodontids (Fig. 8). Very few of the fossils that are transported to the beach exhibit signs of boring or fouling by marine organisms, such as barnacles, pelecypods, corals or bryozoans. The remains that do not exhibit bioerosion are either being constantly subject to moving by waves and currents, or are coveredwith sediments until being exhumed and transported to the beach (Lopes et al., 2008). The recorded taxa are mostly large-bodied herbivores such as toxodonts, mastodonts, glyptodonts, horses and cervids. A remarkable fact is that in comparison to other Pleistocene fossil localities in Brazil the record of cervids is much more abundant. Other organisms such as macrau- cheniids, proterotheriids and rodents, although scarce, can also be found (Rodrigues and Ferigolo, 2004; Scherer et al., 2009). The latter ; B: equids; C: Stegomastodon; D: Toxodon (scale bar 50 mm). Table 3 Relative proportions of fossil specimens from the neashore in the paleontological collection of FURG. Skeletal parts N Teeth (isolated) 659 Osteoderms 466 Skull elements (including jaws) 255 Autopodial elements (carpal, metacarpals, tarsals, metatarsals, phalanges) 180 Limb bones (humeri, ulnae, radii, femora, tibiae) 135 Vertebrae 102 Scapulae 19 Ribs 3 TOTAL 1819 Fig. 7. A) fragment of a mylodontid sloth dentary; B) fragment of a Toxodon dentary; C) antler of Morenelaphus; D) antler of Antifer; E) mylodontid sloth ungueal phalange; F) megatheriid sloth ungueal phalange; G) artiodactyl astragalus; H) astragalus of Smi- lodon; I) equid metatarsal (scale bars 50 mm). R.P. Lopes, F.S. Buchmann / Journal of South American Earth Sciences 31 (2011) 17e2722 are represented mostly by isolated teeth, and the absence of other skeletal elements isprobablydue tomechanical destructionbywaves. 4. Fossils from the outer continental shelf The presence of fossils of large vertebrates found on the conti- nental shelf of Rio Grande do Sul at depths up to 46 m have been cited on the literature (Villwock, 1984; Buchmann, 1994), but because no detailed description of such fossils was ever published, it is not possible to evaluate whether these were from marine or terrestrial taxa. Here is presented the first detailed description of fossils unambiguously identified as extinct terrestrial mammals found in the outer continental shelf. The fossils are part of the paleontological collection of the Universidade Federal do Rio Grande (FURG), and consist of a partial skull (catalog number LGP-E0020), a left humerus (LGP-E0021) and a distal fragment of a right femur (LGP-E0024), all belonging to Toxodon sp. Owen, 1838. The other fossil is a lower right m3 (LGP- G0032) of a Stegomastodon waringi Holland, 1920. These specimens (Fig. 9) were brought to FURG in the early 1990s by fishermen who caught it in bottom trawlers between the central and southern sectors of the coast. However, because the fishing technique requires the fishing net to be dragged for long distances, and the fossils have been collected before the adoption of GPS, only two have the exact location described. One of these (LGP-E0024) was collected at depths around 20 m, some 100 km to the north of the city of Rio Grande and some 20 km offshore. The other (LGP-G0032) was collected some 16 km to the south of the city, some 36 km offshore, in an area known by the fishermen as “graveyard” due to the presence of several bones (mostly cetaceans) on the bottom, that are brought to the surface by the fishing nets. Fig. 6. Osteoderms of cingulates: fused osteoderms of Glyptodon (A); isolated osteo- derms of Panochthus (B) and Doedicurus (C) (scale bar 50 mm). The specimen LGP-E0020 (Fig. 9a) is an occipital portion of the skull of a Toxodon sp. The dorsal margin of the skull is partially broken, but the sagittal crest and the caudal portion of the zygo- matic arches are preserved. The specimen LGP-E0021 (Fig. 9b) is a left humerus of Toxodon, originally mentioned by Buchmann (2002). This fossil is fractured on its proximal end. The internal cavity of the bone is hollow and has some fine sediment within. The shaft was damaged right above the distal articular surface during the recovery from the bottom of the sea, and part of the bone above the entepicondyle was lost. The specimen LGP-E0024 (Fig. 9c) is the lower portion of a right femur of a Toxodon sp. This fossil exhibits little colonization by organisms. The medial side of the patellar surface is the only portion with significant colonization; few other organisms are found isolated along the specimen. The medullar cavity is hollow, and contains vestiges of mud. Longitudinal crackings are visible long the axis of the bone, and both articular condyles are covered by reticulate crackings. These features may be result of the exposition to weathering for some time before the final burial (Lopes et al., 2008). The molar of Stegomastodon (Fig. 10d) was originally described by Marcon (2007). This fossil consists of the crown of a right lower m3, without the roots. The protolophid and metal- ophid exhibit wearing due to mastication, while the 3rd, 4th and 5th lophids are partially fractured, but exhibit no signs of wear. This specimen does also exhibit little colonization by episkeletozoans, encrusted on the labial side of the caudal end. The skull and humerus are almost entirely colonized by encrusting (episkeletozoans, sensu Taylor andWilson, 2002) marine organisms such as ostreids (Ostrea cf. equestris), barnacles (Toracica Fig. 8. A) distal portion of the humerus of a mylodontid sloth; B) ulna, and C) radius of Toxodon; D) unidentified vertebra; E) proximal end of a rib (scale bars 50 mm). R.P. Lopes, F.S. Buchmann / Journal of South American Earth Sciences 31 (2011) 17e27 23 balanus), galleries of polychaets (Spirolis sp.), corals (Astrangia rathbuni) and an unidentified coelenterate. The humerus does also exhibit colonization by a boring (endoskeletozoan) pelecypod (Litophaga sp.) (Fig. 10). The colonizing organisms are recent, as indicated by the presence of soft tissues associated. Some valves of Ostrea do also exhibit small (about 1 mm in diameter) circular borings identical to those present on fossil shellfish from the coastal plain (Lopes and Buchmann, 2008) and attributed to the ichnogenus Entobia sp. The age of these remains is uncertain, but probably encom- passes the time interval between 650 and 18 ka at least, by extrapolating the ages of the fossils dated by Lopes et al. (2010). 5. Discussion The main difference between the fossils collected along the shoreline and those from the outer continental shelf is the presence of colonizing organisms on the latter. This feature allows a correla- tion of these remains to the Taphofacies III of Lopes et al. (2008), characterized by relatively well-preserved remains exhibiting endo- and episkeletozoans, indicating that these fossils remain total or partially exposed for long periods on the wateresediment interface, at depths below the influence of the waves (Table 2). Other preser- vation features include the absence of abrasion and the longitudinal fractures along the axis of the specimen LGP-E0024. The pattern of plain fractures does indicate that the remains were subject to some post-fossilization reworking. This could only have occurred in the past, probably by sea-level oscillations, because the fossils are currently preserved at depths below the influence area of thewaves, thus are not moved. The m3 of Stegomastodon and the humerus of Toxodon were fractured during its retrieval from the bottom of the sea, and had to be restored in laboratory. The recent fractures exhibit different color in comparison to the rest of the bone. Cunha (1959, 47 p.) described several dental and postcranial isolated remains attributed to Toxodon platensis, plus a distal end of a right femur classified as Toxodontidae indet., all collected along the beach. However, the wide time span obtained by Lopes et al. (2010) for the fossils from the continental shelf, encompassing from Ensenadan to Lujanian, imply that other species of Toxodon may be represented among the specimens from the continental shelf. The specimens MOT0035 and MOT0027, with ages of 650100 ka and 480 30 ka, respectively, were classified as T. platensis, but now should be considered Toxodon sp. and the same should be applied to all toxodontid remains from the continental shelf. According to Bond (1999), T. ensenadensis is a valid Ensenadan taxa, while T. platensis, T. burmeisteri, T. darwinii, T. paradoxus, T. bilobi- dens, T. gracilis and T. gezi are valid Lujanian taxa found in Argentina, although only T. platensis and T. burmeisteri survived into the upper Lujanian. Because the systematics of these taxa is based mostly on dental features and body size, a revision of the southern Brazilian toxodontid remains is necessary in order to clarify the taxonomic status of the toxodontid remains from the continental shelf. From the Holocene onwards, the formation of the Barrier- Lagoon System IV blocked all significant fluvial discharges that would reach the coastline of Rio Grande do Sul, thus the fossils could not have been transported to the shelf during post-Pleisto- cene times. Besides, after the formation of the MirimLake and Patos Lagoon, between 325 and 120 ka AP, most of the fluvial discharge became retained in these bodies and could not reach the sea anymore. Nevertheless, several seismic studies have demonstrated that during sea-level lowstands related to glacial maxima, the then exposed continental shelf was cut by the Guaíba, Camaquã, Piratini, Jaguarão, Tacuari and Cebollati rivers (Corrêa, 1990; Abreu and Calliari, 2005; Weschenfelder et al., 2008; Silva, 2009). These rivers have transported and distributed clastic terrigenous sedi- ments that today cover the continental shelf (Tomazelli, 1978; Martins, 1983). The available seismic studies, however, focus on the central and northern portions of the continental shelf; the only seismic survey on the southern portion of the shelf was aimed at mapping Mesozoic and Tertiary paleo-fluvial channels deep in the sedimentary sequences, thus have not the necessary resolution to reveal details on the Pleistocene paleodrainages (Silva, 2009). According to Corrêa (1990) the Jaguarão, Tacuari and Cebollati rivers converged to form a single channel that passed trough a gap in the Pleistocene barriers II and III. This gap is found in the area of a negative gravimetric anomaly (Taim Anomaly) related to a series of E-W-oriented fault and dyke systems of the underlying Precambrian bedrock (Rosa, 2009) (Fig. 11). Vertebrate remains could have been transported to the continental shelf by these paleo-fluvial systems but the largest fossiliferous area of the coast, the “Concheiros”, is far from the area that could have been influ- enced by these systems. Besides, the absence of abrasion on the fossils from the outer shelf suggests that transportation of these remains, if happened, was minimal. On the other hand, the spec- imen LGP-E0024 was collected in an area of the shelf that was cut by the paleo-channel of the Camaquã river during sea-level low- stands (Toldo et al., 1991; Weschenfelder et al., 2008). It seems probable that the fossiliferous deposits on the shelf do represent continental environments that were covered by the sea advance at the end of the major Late Pleistocene glaciations. Several features found along the continental shelf do indicate the presence of continental environments in the past, such as paleo-beachlines (Asp,1999; Buchmann et al., 2001), concentrations of heavyminerals (Corrêa and Ade, 1987) and terrigenous sediments (Kowsmann and Costa, 1974), as well as channels that represent paleo-fluvial Fig. 10. Marine organisms found associated to the fossils from the outer continental shelf: A) coral Astrangia rathbuni; B) unidentified coelenterates; C) barnacles Toracica balanus; D) galleries of Spirolis sp. polychaets; E) a boring pelecypod Litophaga sp. (indicated by arrow); F) ostreids Ostrea cf. equestris, showing bioerosion (ichnogenus Entobia sp.) caused by clionid sponges (scale bars 10 mm). Fig. 9. Fossils of terrestrial mammals from the outer continental shelf: A) LGP-E0020 in caudal and dorsal views; B) LGP-E0021 in anterior and posterior views; LGP-E0024 in anterior and posterior views; D) LGP-G0032 in occlusal and labial views (scale bars 50 mm). R.P. Lopes, F.S. Buchmann / Journal of South American Earth Sciences 31 (2011) 17e2724 Fig. 11. Paleo-drainages recorded on the RS continental shelf during pre-Holocene sea- level lowstands, associated to the Patos Lagoon (a) and Mirim Lake (b): A - Guaíba River, B - Camaquã River, C e PiratiniRiver, D e Jaguarão, Tacuari and Cebollati rivers. Modified from Weschenfelder (2005) and Silva (2009). R.P. Lopes, F.S. Buchmann / Journal of South American Earth Sciences 31 (2011) 17e27 25 drainages (Abreu and Calliari, 2005; Weschenfelder, 2005; Weschenfelder et al., 2008). Due to the low slope, any sea-level oscillationwould have affected large portions of the shelf; during the glacial maxima, when the sea-level reached some 120 m below the present (Corrêa et al., 1996; Martins et al., 1996), the coastline would have been located some 100 km to the east. As a result, during sea- level lowstands the emergent area of the coastal province was twice that of the present. During sea-level transgressions these continental deposits would have been eroded, reworking and redepositing the fossils in submarine environments. The association of terrestrial fossils with lithified beach sediments (coquinas) is also an indicator that older continental fossiliferous deposits have been reworked by eustatic oscillations in the past. By modeling the influence of a sea- level transgression over the northern coast of Rio Grande do Sul, Dillenburg (1994) concluded that such an event would erode at least 10 m of the sediment cover of the shelf. This erosion would rework older fossils and redeposit them together with younger remains. The presence of large herbivores in areas far from the present coastline does not only indicate that large areas of the continental shelf have been exposed during sea-level lowstands, but also that these areas have been occupied by terrestrial environments suit- able for these organisms. Paleofloristic reconstructions have demonstrated that the lowlands of southern and southeastern Brazil, to latitudes of at least 20� S, have been covered by grasslands during the glacial maxima (Behling, 2002). Because of the sea-level lowstands related to the glacial maxima, such environments would have expanded not only latitudinally, but also farther to the east, thus the organisms would have also extended its distribution. The Brazilian continental shelf is wider between 22� and 33� S, thus this is potentially a large fossiliferous area. The concentration of marine and terrestrial fossils at the “Con- cheiros” seems to be the result of the exhumation of the large fossiliferous concentrations located on the inner continental shelf that today are being reworked by erosion and shoreline retreat- ment that have been affecting some 80% of the coast of Rio Grande do Sul for the last 5 ka (Esteves et al., 2002; Dillenburg et al., 2004). This process is more visible during autumn andwinter, when storm surges caused by polar fronts affect the coast (Calliari et al., 1998a). During these events large areas of the beach can be covered by shell fragments in a matter of hours. In the “Concheiros” the beach presents a steeper slope and coarser sediment, which affect the coastal dynamics in the area (Calliari and Klein, 1993). The erosive processes that affect this area, related to sediment starvation (Dillenburg et al., 2004) and wave dynamics (Calliari et al., 1998b) are probably the responsible for the exhumation of the Pleistocene deposits of the inner shelf, while the storm surges are responsible for transporting the fossils from these deposits to the beach. 6. Conclusions The fossil remains of terrestrial mammals found along the coast of Rio Grande do Sul State were originally preserved in continental environments on areas of the continental shelf that have been exposed in the Pleistocene because of the sea-level regressions during the glacial maxima. Although some large fluvial systems did cut the exposed continental shelf during sea-level lowstands, there is no conclusive correlation between the presence of paleo-fluvial channels and terrestrial vertebrate fossils, save possibly for the specimen LGP-E0024 collected in the area near the paleo-channel of the Camaquã river. Detailed seismic and geological surveys in the southern portion of the coast should reveal if the largest concen- tration of mammalian fossils at the “Concheiros” is related to paleo- fluvial discharges. The presence along the beach of fossils from the inner shelf is probably a combination of two processes: a) the long-term erosion that have been affecting the coast for the last 5 ka, removing the Holocene sediment cover and exposing the underlying fossiliferous Pleistocene sediments; b) removal and transportation by storm waves. This characterizes these fossils as palimpsest sediments (Pleistocene sediments that are being reworked by revcent processes). The fossils collected on the continental shelf off the coast of Rio Grande do Sul are currently below the depth influenced by waves, thus its partial or total exposure on the wateresediment interface is a result of past erosive processes, probably related to sea- level advances at the end of glaciations. Although these remains could have been transported from the continent to the shelf by paleo-fluvial systems during sea-level lowstands, preservation of these remains indicates that such transport, if it happened, was minimal, thus the fossils were preserved on the then exposed shelf. Its presence in areas much farther from the coast than those collected on the beach does indicate that the fossiliferous area of the shelf is much larger than previously known. Moreover, it does indi- cate that the terrestrial environments suitable for these organisms (open grasslands) occupied large (if not all) areas of the shelf that remained above the sea-level during glacial maxima. The wide geographic distribution of fossils of terrestrial mammals along the South American coast suggests that all the continental shelf has R.P. Lopes, F.S. Buchmann / Journal of South American Earth Sciences 31 (2011) 17e2726 a great potential for paleontological surveys, mostly on the southern and southeastern Brazilian coast, where the shelf is wider. The fossiliferous deposits of the continental shelf were formed during episodes of sea-level lowstand related to glacial cycles. The intervening sea-level transgressions eroded the deposits and reworked the fossils, resulting in a mixture of remains of different ages. Despite its broad age range, the fossils of terrestrial mammals do not constitute “true” time-averaged assemblages, because the accumulation of these remains was not a continuous process. Although there is a taxonomic correlation of the fossils from the submarine deposits with those from the Chuí Creek, both fossilif- erous concentrations have distinct origins, and the former encom- pass a much wider time span. The presence of fossils of terrestrial mammals on marine envi- ronment opens newperspectives for studies on thepaleogeography, paleoclimates and paleoenvironments of the eastern South Amer- ican continental shelf during glacial episodes, not only in southern and southeastern Brazil, but also in Uruguay and Argentina as well. The submarine nature of these fossiliferous concentrations demands a multidisciplinary approach, congregating paleontolo- gists, marine geologists geophysicists and oceanographers, using different study techniques such as shallow high-resolution seismic profiling, side scan profiling, piston corers, bottom trawling and scuba diving in order to understand the Quaternary evolution of the continental shelf. Acknowledgements The authors would like to thank CNPq for the finantial support (Doctorship grant for the first author), and to Carlos Emilio Bem- venuti and Leonir Colling from the Laboratório de Ecologia de Comunidades Bentônicas (FURG) for identifying the colonizing organisms on the fossils. References Abreu, J.G.N., Calliari, L.J., 2005. Paleocanais na plataforma interna do Rio Grande do Sul: evidências de uma drenagem fluvial pretérita. Revista Brasileira de Geo- física 23 (2), 123e132. Asp, N.E., 1999. Evidence of pleistocenic and holocenic barriers on the inner continental shelf of Rio Grande do Sul state. Brazil. Anais da Academia Brasileira de Ciências 71 (4), 832e833. Behling, H., 2002. South and southeast Brazilian grasslands during Late Quaternary: a synthesis. Palaeogeography, Palaeoclimatology, Palaeoecology 177, 19e27. Bombin, M., 1975. 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Pleistocene mammals from the southern Brazilian continental shelf Introduction Geological setting Fossils from the inner continental shelf Fossils from the outer continental shelf Discussion Conclusions Acknowledgements References