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Quaternary Research 61 (2004) 289–300

Reconstructing habitats in central Amazonia using megafauna,

sedimentology, radiocarbon, and isotope analyses

Dilce de Fatima Rossetti,a,* Peter Mann de Toledo,a

Heloısa Maria Moraes-Santos,a and Antonio Emıdio de Araujo Santos, Jr.b

aMuseu Paraense Emılio Goeldi, Av. Perimetral, 1901, CP 399, CEP 66710-530 Belem, PA, BrazilbUniversidade Federal do Para, Centro de Geociencias, Campus do Guama S/N, Belem, PA, Brazil

Received 14 November 2002

Available online 30 April 2004

Abstract

A paleomegafauna site from central Amazonia with exceptional preservation of mastodons and ground sloths allows for the first time a

precise age control based on 14C analysis, which, together with sedimentological and y13C isotope data, provided the basis to discuss habitat

evolution within the context of climate change during the past 15,000 yr. The fossil-bearing deposits, trapped within a depression in the

Paleozoic basement, record three episodes of sedimentation formed on floodplains, with an intermediate unit recording a catastrophic

deposition through debris flows, probably favored during fast floodings. The integrated approach presented herein supports a change in

humidity in central Amazonia through the past 15,000 yr, with a shift from drier to arboreal savanna at 11,340 (F50) 14C yr B.P. and then to a

dense forest like we see today at 4620 (F60) 14C yr B.P.

D 2004 University of Washington. All rights reserved.

Keywords: Amazonia; Pleistocene; Paleontology; Mammals; Sedimentology; Radiocarbon dating; Landscape evolution

Introduction

Deciphering the origin of the Amazon biodiversity has

been a challenge to the scientific community with special

interest in issues related to natural history and conservation

of communities and ecosystems. An important aspect of this

multidisciplinary field is the understanding of the main

historical factors relating physical and biological phenome-

na that acted upon the shaping of the modern biome as we

see today. In order to reconstruct the origin and the historical

events of the main ecological processes that took place to

form the rain forest, an analysis and organization of a series

of multidisciplinary data related to geology and climate and

a reasonable control of the fossil history are needed. So far,

geological and paleontological data are relatively scarce,

considering the continental dimensions of the Amazon

region, and the information available furnishes only a broad

view on the evolutionary patterns. The building of historical

datasets is an important contribution to the understanding of

0033-5894/$ - see front matter D 2004 University of Washington. All rights rese

doi:10.1016/j.yqres.2004.02.010

* Corresponding author. Fax: (091) 249-0466.

E-mail address: rossetti@museu-goeldi.br (D. de Fatima Rossetti).

such a large and complex natural system. Although the

entire history back to at least the Early Tertiary is relevant to

these studies, the Pleistocene should be particularly

addressed, as it bears the closest relationship with the

modern ecosystem. Only a broad picture of what happened

in the Amazon region during the major ecological shifts

between ice-age aridity and more humid interglacial periods

has been provided so far (reviewed by Latrubesse, 2000).

This is mainly due to the following reasons: (1) geological,

palynological, and vertebrate paleontological data are still

scarce and spotty; (2) information refers only to some areas

located in southeastern and southwestern Amazonia; and (3)

the best information is related to times before 24,000 yr ago

(Latrubesse, 2000). The incomplete information has moti-

vated many debates, with the arid Amazonia refugia model

(Haffer, 1969; Prance, 1982) on one side against stability of

the forest throughout the Cenozoic on the other side

(Colinvaux et al., 2000; Colinvaux and Oliveira, 2001).

This paper reports a new fossil quarry bearing two

megafauna elements consisting of Haplomastodon waringi

and Eremotherium laurillardi from the locality of Itaituba,

State of Para, northern Brazil (Fig. 1), in Central Amazonia,

rved.

Fig. 1. Location and geologic map of the Itaituba area in the state of Para, northern Brazil, with the location of the fossil quarry bearing the megafauna of

mastodon (Haplomastodon waringi) and giant ground sloth (Eremotherium laurillardi).

D. de Fatima Rossetti et al. / Quaternary Research 61 (2004) 289–300290

which allowed precise age control. Integration of paleontol-

ogy and sedimentology, as well as radiocarbon and isotope

data, provides the basis for discussing the possible changes

in this landscape through the past 15,000 yr.

Geological framework and physiography

The Itaituba area is located in the southern margin of the

Amazonas Basin, which is a large (i.e., nearly 500,000 km2)

depression located in the middle and low Amazonas. This

basin is bounded by the Guianas Shield to the north, Brazil-

ian Shield to the south, Purus Arch to the west, and Gurupa

Arch to the east. The origin of the Amazonas Basin is related

to rifting associated with intraplate stretching during the

Paleozoic, which took place in three stages and gave rise to a

6500-m-thick sedimentary package represented by three

megasequences formed in the Ordovician–early Devonian,

middle/late Devonian–early Carboniferous and middle Car-

boniferous–Permian. The opening of the South Atlantic

Ocean and rise of the Andean Cordillera resulted in the

tectonic reactivation of the area during the Cretaceous–

Cenozoic and deposition of a fourth megasequence up to

500 m thick. This later phase of tectonism continued even in

more recent times in the late Quaternary, having a strong

effect in the development of the modern drainage system

(e.g., Costa and Hasui, 1997; Bemerguy, 1997).

The fossil-bearing sedimentary deposits emphasized in

this study rest in the left margin of the middle Tapajos River

and occur overlying limestone of the upper Carboniferous

Fig. 2. A view of the Itaituba fossil quarry, illustrating the sharp, erosional

contact between the Pleistocene deposits and the underlying Paleozoic

Itaituba Formation. Note the karstic structures at the bounding surface

(arrows) and the ragged, straight vertical segments of the basement,

probably resulting from fault displacement.

D. de Fatima Rossetti et al. / Quaternary Research 61 (2004) 289–300 291

Itaituba Formation (Fig. 1). The Tapajos River runs through

a NE/SW-oriented normal fault zone, which is part of a

triple junction formed by strike–slip reactivation of Meso-

zoic structures during the Quaternary (Costa and Hasui,

1996). This river is in general straight but it becomes highly

meandering in the Itaituba region, with large coarse-grained,

sandy point bars. The fossil quarry is located in the flood-

plains, which at this locality reach up to 7 km wide and

extend through an area with relief <20 m. A hilly area with

Paleozoic rocks displaying altitudes up to 300 m occurs

surrounding the floodplains.

Fig. 3. Stratigraphy of the Itaituba fossil site, displaying the main characteristic

basement with Paleozoic rocks.

Today, the central Amazonia is characterized by a humid

to subhumid, equatorial climate, with well-defined dry (June

to November) and rainy (December to May) seasons. The

registered mean annual precipitation is 2000 mm and the

mean temperature is 35j. Vegetation pattern is complex,

ranging from dense to open tropical forests, as well as areas

of cerrado.

Sedimentology of the fossil beds

Facies description

The Itaituba megafauna occurs within a thin (<2 m thick)

sedimentary package that directly overlies Carboniferous

limestone of the Itaituba Formation. A sharp erosional

contact occurs between these deposits, forming an uncon-

formity locally marked by a surface with erosional relief of a

few meters and with microkarstic structures that form

dissolution holes up to 15 cm deep (Fig. 2). The succession

with the megafauna also occurs laterally at the same

horizontal level as the limestone. In this case, the edge of

the Itaituba limestone is defined by a ragged, sharp surface

displaying straight, vertical segments (Fig. 2), which sug-

gest fault displacement. Although detailed tectonic studies

in the Itaituba area are still unavailable, regional works attest

that the Amazon area from Manaus to Belem displays a

variety of faults formed by a relatively young strike–slip

tectonism, which took place during the Miocene/Pliocene

and even more recently during the late Pleistocene/Holocene

(Bemerguy, 1997; Costa and Hasui, 1996).

Three sedimentary successions were distinguished in the

Itaituba fossil quarry (Fig. 3). The lowermost unit (unit I) is

up to 30 cm thick and rests directly on the basal unconfor-

megafauna-bearing sedimentary units formed from late Pleistocene upon a

Table 1

List of bone elements of Haplomaston waringi and Eremotherium

laurillardi collected from the Itaituba site

Cranial elements Post cranial elements

H. waringi Isolated molars

and fragments of

mandible skull

Not preserved

E. laurillardi Partial skull and

jaw fragments of

three adult specimens

and one newborn

individual

Incomplete acropodial,

stylopodial, pectoral,

and pelvic girdle elements

plus several isolated vertebrae

and ribs belonging to four

individuals (3 adults and

1 newborn). Complete and

broken bones are identified as

the following: femur, humerus,

tibia, fibula, ulna, radius,

scapula, pelvis, calcaneum,

astragalus, and other bones of

the manus and pes.

D. de Fatima Rossetti et al. / Quaternary Research 61 (2004) 289–300292

mity. It consists of a sandy and a light-colored clay facies

with a very low content in plant debris. The sandy facies is

white to yellowish and comprises well-sorted, fine-grained,

massive sands. The overlying clay facies is light gray to

greenish and has no observable sedimentary structures.

Disarticulated bone fragments of the mastodon H. waringi

(Table 1; Fig. 4) were found concentrated at the base of this

clay facies. The top of unit I is sharp and defined by vertical,

wedge-shaped holes that average 10 cm deep. These cavities

were filled with sediments derived from the overlying bed.

Grain size analysis shows that the contents of clay and silt

fractions in unit I reach up to 86%. Analysis of X-ray

diffraction of the clay minerals revealed the presence of

smectite, illite, and kaolinite, with the first being by far the

dominant one (Figs. 5A and 6).

The intermediate unit II averages 1 m thick and consists

also of two facies. The lowermost one is represented by

poorly sorted, massive conglomerate characterized by quartz

and, subordinately, limestone pebbles. Pebbles vary in size,

but are usually <3 cm in diameter, and they are sub- to well-

rounded. The matrix is composed of mud and a high volume

of plant debris, which gives a black color to this facies.

Granules and fine- to medium-grained quartz sands are

Fig. 4. Fossils of H. waringi found at the base of unit I in the Itaituba fossil quarry

tooth. Scale bar, 5 cm.

mixed with the carbonaceous matrix. Ground sloth bones,

including several parts of four incomplete E. laurillardi (one

newborn and three adults; Fig. 7; Table 1), occur within this

facies, being particularly concentrated at its base (Fig. 8).

The fossiliferous bed of unit II contains a large amount of

wood fragments, with individual logs reaching up to 15 cm

long and 3 to 4 cm in diameter. The amounts of both fossils

and pebbles decrease upward, which is followed by an

increase in the amount of matrix, thus characterizing an

overall normal grading. The upper facies in unit II consists

of massive, carbonaceous mudstone bearing disperse quartz

pebbles and shells, the later sourced from the basement,

represented by Paleozoic rocks of the Itaituba Formation.

The mudstone displays a lighter color relative to the lower

facies of this unit, due to a lower content of carbonaceous

debris. Fine-grained quartz sands are dispersed in the

mudstone. The contact between the conglomerate and the

mudstone in unit II is gradational, and the clay minerals

consist of kaolinite and illite, with only minor amounts of

smectite (Figs. 5B and 6).

The uppermost unit III averages 20–25 cm thick and

consists of black, highly organic mudstone. This unit con-

trasts with the underlying ones, as it does not contain neither

vertebrate fossils nor quartz pebbles, and it is characterized

by a high content of organic matter. The clay content is the

highest of the whole succession, being represented by up to

95% of the grain sizes. Similar to the underlying units, this

succession also shows smectite, illite, and kaolinite, but it is

interesting to notice that the relative proportions among

these minerals are lower compared to unit I, where smectite

clearly dominates (Figs. 5C and 6).

Depositional history

The Itaituba fossil quarry is located in the central intra-

cratonic Amazon Basin (Fig. 1). It records an area of great

stability, without significant sediment preservation since the

Paleozoic, when the Itaituba Formation was formed in a

shallow marine setting. It is possible that after this time,

sedimentation returned to this area only at the end of the

Pleistocene, when the sedimentary succession described

here was formed. The sharp boundary between these depos-

, illustrating (A) a lateral view of a mandible and (B) an occlusal view of a

Fig. 5. Results of X-ray analysis of clays from sedimentary units (A) I, (B) II, and (C) III in the Itaituba fossil quarry (I, illite; S, smectite; K, kaolinite).

D. de Fatima Rossetti et al. / Quaternary Research 61 (2004) 289–300 293

its and the underlying Paleozoic rocks, forming vertical

straight segments, as well as the record of numerous fault

traces in the area as indicated by regional studies, suggest

that sedimentation might have been renewed due to fault

reactivation associated with the late Pleistocene/Holocene

phase of strike–slip deformation (Costa and Hasui, 1997).

Fault processes would have created traps in the limestone,

where the deposits and the megafauna of mammals accu-

mulated. Initially, the rate of fault displacement might have

been reduced, creating a shallow depression, where low-

energy sediment deposition took place. During this time

(Figs. 9A and 9B), a thin sedimentary succession, repre-

sented by unit I, was formed most likely through streams

(sandy facies) and then a small lake or pond (clay facies).

The low-energy conditions prevailing in the latter would

have been ideal for preservation of the H. waringi remains.

The abundance of smectite and illite relative to kaolinite in

these beds is suggestive of deposition under climates rela-

tively drier than for the upper units.

After lake formation, there was a period of nondeposi-

tion, when the lake surface was exposed to a period of

subaerial exposure (Fig. 9C), as interpreted from the vertical

wedge-shaped holes at the top of unit I, attributed to root

development. A renewed period of sediment accumulation

took place, forming a thicker succession, represented by unit

II. This unit formed under high-flow energy conditions, as

indicated by its high volume in quartz pebbles. The lower

facies records maximum flow energy when, together with

Fig. 6. Relative proportions in clay minerals comparing the three

sedimentary successions of the study area, based on peak intensity as

indicated by the X-ray diffractometers.

Fig. 8. A detail of the base of unit II, with remains of E. laurillardi. Note

also abundant quartz pebbles, which decrease in size upward, forming

normal grading.

D. de Fatima Rossetti et al. / Quaternary Research 61 (2004) 289–300294

the pebbles, a huge amount of vertebrate bones and plant

fragments, as well as quartz sands and muds, were all

brought together and deposited into the basin as debris

flows (Fig. 9D). As flow energy decreased, normal grading

was developed. Debris flows occur in most climatic regimes

but they are usually initiated in slope areas after heavy

rainfall (Leeder, 2001). The four incomplete skeletons of

ground sloths, including three adults and a juvenile, mixed

with a high volume of other disarticulated bones, suggest

accidental death as the most likely, which together with the

Fig. 7. Examples of fossils of E. laurillardi found in unit II of the Itaituba fossil quarry, illustrating (A) a calcaneum, (B) a dorsal view of a skull from an adult,

and frontal views of skulls from (C) an adult and (D) a newborn. Scale bar, 5 cm.

Fig. 9. Proposed reconstruction of landscapes for the Itaituba area, as

indicated by the depositional units described in this paper. (See text for

explanations).

D. de Fatima Rossetti et al. / Quaternary Research 61 (2004) 289–300 295

occurrence in the debris flow deposits, is consistent with a

catastrophic event. An event such as a flash flooding might

have promoted slope instability, death of the ground sloths,

and their transportation into the basin together with the other

debris. Considering the proposed fault displacement as the

origin for this Pleistocene basin, an alternative explanation

would be that these debris flows were favored by a combi-

nation of fast flooding and fault reactivation, which created

space to accommodate the three described sedimentary

units. Holocene clay–pebbly conglomerate beds rich in

reworked Tertiary fossil vertebrates extensively exposed in

western Amazonia have been attributed to a catastrophic

flooding resulting from the sudden draining of glacial Lake

Titicaca (Campbell and Frayley, 1984; Campbell et al.,

1985). Although we do not have evidence to support their

model, it is interesting to note that coarse-grained deposits

would be expected in such a flooding event and the high

amount of quartz pebbles associated with the debris flow

deposits from the base of unit II could be a record of such a

large-scale phenomenon. However, the data presented in

this study are local and allow only speculation about the

origin of the flooding event.

The upper facies in unit II is also attributed to debris

flows, but this deposit differs from the underlying one as it

bears a higher amount of matrix, has only dispersed verte-

brate fossils, and shows a high content of shell fragments

eroded from the Paleozoic basement. These characteristics

point to a genesis related to waning flows as the most likely.

The high content in plant debris supports a vegetated area,

and the prevalence of kaolinite relative to the other clay

minerals suggests deposition during a period of higher

humidity compared to the underlying stratigraphic unit.

The sharp, undulating surface at the top of unit II

suggests another period of nondeposition. This was fol-

lowed by the accumulation of a thin succession, represented

by the black clay in unit III. This deposit records the return

to basin stability and sediment accumulation in low energy

areas of the floodplain, which was then densely vegetated

(Fig. 9E). The high amount of organic matter and clay

minerals (up to 96%) is consistent with this interpretation.

The low proportional difference between smectite and illite

relative to kaolinite and the high content in plant debris

point to an environment developed under high humidity

(e.g., Tucker, 1981; Chanley, 1989).

Radiocarbon dating

Four samples were dated at the Beta Analytic Radiocar-

bon Dating Laboratory (Table 2). Carbon from samples 1

and 2, corresponding to the Haplomastodon and Eremothe-

rium derived from depositional units I and II, respectively,

was extracted from collagen using alkali (NaOH) washes,

reduced to graphite (100%C), and dated by accelerator mass

spectrometer (AMS). The first sample might include some

exogenous carbon within the collected organics due to

degradation of bone protein, but sample 2 provided accurate

measurement. Samples 2 and 3, corresponding to wood and

organic sediments derived from depositional units II and III,

respectively, were dated by scintillation spectrometer. The

first sample was pretreated with acid to remove carbonates

and weaken organic bonds, washed with alkali to remove

Table 2

Conventional and AMS radiocarbon dates of the Itaituba quarry samples.

Sample Dep.

unit

Type of

material

14C yr B.P. 13C/12C

(x)

Cal year B.P.

4 III Wood 4620 (F60) �29.6 5570–5540;

5470–5270;

5170–5070

3 II Wood 37,700 (F540) �31.3 Outside the

calibration range

2 II Bone

collagen

11,340 (F50) �26.9 13,760–13,700;

13,470–13,140

1 I Bone

collagen

15,290 (F70) �28.5 18,730–17,860

D. de Fatima Rossetti et al. / Quaternary Research 61 (2004) 289–300296

secondary organic acids, and then combined with acid again

to provide more accurate dating. Sample 4 was repeatedly

washed with acid (HCl) to ensure the absence of carbonates.

The 14C results confirm that, during the past 15,000 yr,

sedimentation in the Itaituba quarry did not take place as a

continuum, but through different episodes of deposition

alternated with erosion. The bone fragment of H. waringi

collected from unit I was preserved within mud deposits

formed in a low-energy setting (i.e., lake or pond) and does

not show any evidence for reworking. The age obtained by

AMS indicates 15,290 (F70) 14C yr B.P. Despite the

possibility that some exogenous carbon might have been

added to this sample, given some degradation of the bone

protein attributed to subaerial exposure during formation of

a discontinuity surface at the top of unit I, the indicated age

is consistent with the stratigraphic position of this sample.

The two samples from unit II provided very distinctive

radiocarbon ages. Hence, sample 2, corresponding to bone

material of E. laurillardi, indicated 11,340 (F50) 14C yr

B.P, while the wood fragment was dated at 37,700 (F540)14C yr B.P. Because the analyzed ground sloth bone came

from an articulated specimen, and bone protein was excep-

tionally well preserved, it is concluded that deposition of

unit II took place at 11,340 (F50) 14C yr B.P. The wood

sample indicating a much older age was clearly reworked

from older deposits underlying the studied sedimentary

succession, or from nearby depositional sites, during mass

failure through debris flows. Unfortunately, the small pieces

of this material did not allow further studies concerning the

type of vegetation.

Unit III was deposited much more recently, as revealed

by radiocarbon analysis of its organic content, indicative of

4620 (F60) 14C yr B.P. These data are consistent with the

presence of a discontinuity surface at its base, which is

attributed to another period of nondeposition and/or erosion.

y13C isotope data

y13C data have been increasingly used as an important

tool for reconstructing ancient landscapes regarding C3- and

C4-dominated plants. This is possible because, in general

the y13C values of C3 and C4 plants range from �26 to

�28x and from 12 to �28x, respectively (Merwe, 1982;

Tieszen, 1991). This allows making a distinction from

forest- to grass-dominated vegetation, an approach that has

been used to characterize modern and ancient vegetation

patterns (e.g., Merwe and Medina, 1991; Bird et al., 1992;

Magnusson et al., 2002; Kastner and Goni, 2003). However,

empiric studies have shown a broader range of values, and

even overlaps, within plant groups (Medina et al., 1986).

For the particular case of Amazonia, depleted values as low

as �37x have been recorded for the undergrowth vegeta-

tion and �31.5x for the upper canopy (Merwe and Medina,

1991).

Stable carbon isotope was measured in materials derived

from the three stratigraphic units of the Itaituba site (Table

1). Collagen from H. waringi collected in unit I indicates

y13C value of �28.5x. Unit II shows values of �26.9 and

�31.3x for collagen from E. laurillardi and the reworked

wood fragment, respectively. Organic debris derived from

unit III gave a y13C value of �29.6x. Before interpreting

these data, the collagen–diet spacing must be considered. In

general, the ratio in bulk plants is transferred to higher

trophic levels, but the absorption of carbon by the collagen

may vary according to metabolic rates, food preferences,

body size, and, possibly, phylogenetic distances (e.g.,

Merwe, 1982; Merwe and Medina, 1991; Tieszen, 1991).

The collagen–diet relationship of extinct megafauna can be

only estimated. Considering the enrichment of collagen

relative to diet for large size browsers of +5.3x (Merwe

and Medina, 1991), the isotope data obtained from the

Haplomastodon and Eremotherium of the Itaituba site

indicate a C3 vegetation corresponding to �33.8 and

�32.2x, respectively. Considering these corrections, the

y13C values of the Itaituba site, ranging from �28 to

�33.8x, indicate the prevalence of C3 plant types in this

central Amazonian area at least for some of the past 37,700

yr. That is not to say, however, that a dense forest vegetation

would have dominated through this time, as arboreal sav-

annas with more than 40% of tree cover might display y13Cvalues that are undistinguishable from forest values (Merwe,

1982; Magnusson et al., 2002). Taking this into account, the

y13C isotope results must be used in integration with

geological and paleontological data in order to provide a

full discussion of paleolandscapes in the study area, as

presented below.

The use of megafauna as a paleoecological indicator

Two major points must be taken into account regarding

the usefulness of megafauna as past environmental indica-

tors. The first is related to definition of paleoecological

variables, such as of broad or specific preferences for open

and/or closed habitats. The second is related to the historical

control of events, which poses the major restriction in

efforts of timing correlation between the different megafau-

na sites.

D. de Fatima Rossetti et al. / Quaternary Research 61 (2004) 289–300 297

The megafauna association, mostly including large mas-

todons (Haplomastodon) and ground sloths (Eremothe-

erium), is common in several Brazilian sites and has been

used to support changes from closed to more open habitats

during the late Cenozoic in northern South America (Rancy,

1991). Studies based on the analysis of body design led to

relate mastodon with a savanna-like environment and Ere-

motherium with a forest edge (Webb and Rancy, 1996;

Rancy, 2000). Based on this information, it has been

proposed that such mammals are reliable indicators for

reconstructing past Amazon landscapes. However, four

main problems must be considered: (1) most of the studies

have solely reported the occurrence of taxa, without precise

dating; (2) the data available have included only transported

fossils along riverbanks, which do not allow one to test the

hypotheses on the timing and mode of environmental

changes in northern South America; (3) the findings of

Pleistocene mammals in the Brazilian Amazon, especially

mastodons and ground sloths, are concentrated in the

western and southern marginal areas, leaving a void of

information about the advance and retreat of open-environ-

ment/savanna-like habitats in the central and northern por-

tions of the basin; and (4) findings regarding the combined

association of Haplomastodon and Eremotherium have been

regarded as a stratigraphical marker for the late Pleistocene/

Holocene (Rancy et al., 1984), which has led interpretations

of regional geographical correlation to be so far highly

speculative.

Furthermore, the use of megafauna elements as habitat

indicators (Owen-Smith, 1988) has been questioned on the

basis of the statement that large mammals, like tapirs,

may develop adaptive capability to different types of

landscapes (Colinvaux et al., 2000). In fact, some modern

African proboscideans, which are modern counterparts of

mastodons, occupy a variety of habitats, including open

savanna, wet marsh, thorn bush, semidesert scrub, and

even deep forest, and the Asiatic elephant, which also

shows large body size, varies in habitat from grassy plains

to thick jungles (Nowak, 1999). The wide distribution for

such large-size animals, and mostly their record in deep

forest habitats, leads us to review the overall assumption

that mastodons were actually restricted to savanna-like

habitats.

However, one must take into account the large differ-

ence in sizes among the megafauna associated with the

Pleistocene deposits throughout the Amazon, such as

ground sloths, mastodons, glyptodonts, pampatheres, tox-

odons, camelids, large-sized capybaras, and litopterns,

which is in great contrast to the small size range of

the modern mammals that inhabit the dense Amazon

forest, like tapirs and artiodactyls (Webb, 1991; Webb

and Rancy, 1996; Rancy, 2000; Croft, 2001). This

strongly supports the presence of relatively more arid

climate regimes and the existence of large areas with

more open, though not necessarily grass-dominated, Pleis-

tocene environments.

A similar approach is provided in the case of terrestrial

sloths. As opposed to mastodons, there is no modern

analog for these animals, thus any effort toward ecological

reconstructions must rely on its geographical distribution,

fauna associations, and inferences from biomechanical

information. Eremotherium displays, with the modern

puma (Felis concolor), one of the largest latitudinal

distributions of a mammalian species in America (Hoff-

stetter, 1982; Toledo, 1986; Cartelle and de Iullis, 1995).

Pleistocene occurrences of this terrestrial sloth are known

from southeastern North America to southern Brazil. The

other sister taxon, Megatherium, was restricted to southern

South America with northern limits at the central portions

of the Andean valleys. There is a consensus among most

of the authors (e.g., Toledo, 1986; Cartelle, 1999; Webb,

1999) that the large herbivores were mixed feeders and

that the pan-American megafauna taxa inhabited a mosaic

of savanna with forest patches. The broad latitudinal and

altitudinal biogeographic distribution suggests that Eremo-

therium occupied a wide range of ecological habitats and

might have fed on a variety of plant types sourced from

gallery forests, open woodlands, and shrub-covered areas.

This is particularly suggested on the basis of morpholog-

ical features of dental patterns and postcrania, which

resulted in a combination of a unique body design and

large size (up to 6 m in length). Such adaptations include

a doubled parallel chisel-like tooth wear pattern adapted

for cutting/crushing of foliage, twigs, and possibly fruits;

long anterior limbs and large-clawed manus, which were

very efficient for branch reaching while displaying a

bipedal stance and particularly for defense, avoiding

predators in open environments (a frequent incursion in

dense forests would increase the vulnerability against

ambush predators such as large cats); and long tongues

frequently used in the process of food gathering. The

hairy and thick skin was adapted for protection against

plant structures such as thorns and needles. Such charac-

teristics suggest that these ground sloths were better

adapted to open vegetation communities than to dense

forests.

In addition, paleontological data support that megatheres

displayed a gregarious social behavior. This is shown by the

Itaituba ground sloths and other findings, such as the one

from the Toca dos Ossos in the State of Bahia, central

Brazil, where a large number of complete skeletons were

recovered from a natural trap cave (Cartelle and Bohorquez,

1982). These characteristics are strong evidence to discard a

closed canopy forest as the preferential habitat of these

animals, since group behavior among large mammals in

modern habitats is more frequently observed in open

habitats.

Finally, it has been demonstrated that Eremotherium

had a high browser adaptation (Toledo, 1998), as sug-

gested by its giant size, the large claws of the upper

members, and the possibility of standing in the upright

position.

D. de Fatima Rossetti et al. / Quaternary Research 61 (2004) 289–300298

Habitat evolution in central Amazonia: an integrated

approach

Evolutionary models relating to the Amazonian biodi-

versity are based on the assumption that global climate

during the Quaternary was the major driving force of

habitat modification, which affected and, at the same time,

enhanced the changes in precipitation, depositional/ero-

sional levels, and, ultimately, the geomorphologic frame-

work. Despite a recent proposal favoring a continuous

forest cover throughout most of the Amazon region since

the mid-Cenozoic (Colinvaux and Oliveira, 2001), a mul-

titude of scientific fields, coming mainly from geology,

palynology, genetics, and biogeography, has led to the

general acceptance that the Amazonian ecosystem experi-

enced several alternating wet and dry periods, which

resulted in forest and savanna expansion, respectively

(Morner et al., 2001; van der Hammen, 2001; Haffer,

2001). Among these data, pollen analysis has been so far

the only reliable source from the fossil record, providing

information about Pleistocene paleoenvironmental changes

in the Amazonia with precise age control (Absy et al.,

1991; Sifeddine et al., 2001). However, the pollen record

is still scarce and spotty, providing only a broad picture of

what happened during the major ecological shifts of glacial

and interglacial periods.

There are few studies of the Amazonian megafauna with

precise stratigraphic control (e.g., Rancy, 1991; Latrubesse

and Rancy, 1998). These works have been crucial to support

dry periods, with savanna expansion in the western Ama-

zonia. This paper represents the first documentation based

on an integrated approach using paleontology, sedimentol-

ogy, and radiocarbon and isotope data that allow insights

into past habitats from the latest Pleistocene in a central

Amazonian area. This time was characterized by a world-

wide drop in sea surface temperature of 1–4j, with the

proposed impact in low-latitudinal areas, such as the Ama-

zonia, being represented by several periods of dry climate,

with changes in river discharge and sedimentation and

development of savanna vegetation (van der Hammen,

2001).

The data collected from the Itaituba site do not appear to

indicate any drastic landscape changes at least during the

past 15,000 yr, although slight variation in vegetation

density seems to have taken place through this time. The

y13C data, as discussed above, unequivocally discard any

significant contribution of tropical grassland savanna vege-

tation, recording instead a landscape dominated by C3

plants. However, the low content in plant debris observed

in the muddy unit I is more consistent with scarce vegetation

15,000 yr ago, suggesting a period with a tendency to

aridity. It is interesting to notice that the abundance of

smectite relative to the other clay minerals is consistent

with an area undergone to low humidity. In addition,

although probably not exclusively, Haplomastodon has been

preferentially found in association with open paleohabitats.

Based on the combination of these data, we envisage a

landscape with arboreal savannas for the study area 15,000

yr ago.

It is appropriate to include a brief discussion on the

potential paleoenvironmental significance of the wood as-

sociated with the fossil sloths. This is because the obtained

age of 37,700 14C yr B.P. is close to those from many other

Amazonian sites, which have been related to open habitats

(e.g., Rasanen et al., 1990; van der Hammen et al., 1992;

Latrubesse and Rancy, 1998). As previously mentioned, the

wood fragment dated here was reworked from older depos-

its, being derived either from underlying beds or from

nearby depositional sites. In either case, it records a period

of sedimentation taking place before deposition of the

studied deposits. The y13C value of �31x could suggest

a dense forest rather than open habitats in this central

Amazon area at 37,700 14C yr B.P., but this interpretation

is biased considering the reworking nature of this material

and the absence of any further information related to this

depositional time.

At 11,340 (F50) 14C yr B.P., the landscape seems to

have remained similar, though the humidity might have

been slightly enhanced. This is suggested by the relative

increase in kaolinite relative to other clay minerals in unit II.

The high content of logs and plant debris in this unit could

also be a further support for the proposed increased humid-

ity. However, the deposits with abundant quartz pebbles

attributed to debris flows conform to the presence of open

land areas. This information suggests an environment with

arboreal savannas similar to the one that occurred at 15,000

yr ago. The presence of E. laurillardi in unit II is consistent

with a landscape with abundant trees, as this ground sloth

genus had a high browser nature. The possibility of a diet

including upper canopy leaves could explain the slightly

heavier y13C values of the giant sloths, as in a same area the

undergrowth vegetation is usually depleted in y13C relative

to the upper canopy (Merwe and Medina, 1991). Finally, as

shown in the foregoing discussion, the presence of Eremo-

therium in these deposits is in itself highly suggestive that a

dense forest was not present yet in the Itaituba area around

11,000 yr ago, when open woodlands seem to have domi-

nated the habitat.

At 4620 (F60) 14C yr B.P. even moister conditions seem

to have prevailed, with the establishment of a forest vege-

tation similar to that seen today in the Itaituba area. The

y13C value of �29.6x for organic soils indicates a C3 tree

cover (values obtained from modern Amazon soils are

usually less than 27x according to Magnusson et al.,

2002). However, the high amount of organic matter and

clay minerals, the latter with low proportional difference

between smectite and illite relative to kaolinite, is consistent

with an environment developed under higher humidity than

those recorded for the underlying units. Hence, it is pro-

posed that after sediment deposition through debris flows

(unit II), there was a return to low-energy deposition, with

development of ponds and/or marshes along floodplains in a

D. de Fatima Rossetti et al. / Quaternary Research 61 (2004) 289–300 299

forested area undergoing higher humidity than in the previ-

ous time intervals recorded here.

While pollen data from deep-sea fan hemipelagic and

continental shelf sediments through the past 50,000 yr

support that the Amazon Basin forests were not extensively

replaced by savanna vegetation during the glacial period

(Heberle and Maslin, 1999; Kastner and Goni, 2003), other

sources of information led to the proposal of drastic changes

in environmental conditions during this time interval. A

wide array of data from different fields of biology and

geology has pointed out successive periods of dry and wet

climate throughout the Pleistocene and on, which resulted in

changes from savanna to rain-forest vegetation. For in-

stance, in a seminal work revising the hypotheses to explain

the origin of species in Amazonia, Haffer (2001) has

eloquently put strong arguments for drastic changes in

climate pattern supported by a large body of hard evidence.

In addition, pollen data from the Carajas area shows a period

of dry climate with savanna vegetation between 25,000–

10,000 yr ago (Absy et al., 1991) and 22,000–13,000 yr ago

(Sifeddine et al., 2001). According to these authors, heavy

rainfall and high sediment inflow with variable lake levels

and low organic carbon seem to have prevailed between

13,000 and 10,000 yr ago, as a result of climates transition-

ing from arid to humid. From 10,000 to 8000 yr ago there

was a relative increase in humidity, which was followed by

drier conditions up to 4000 yr ago, when humidity returned,

giving rise to development of rain forests (Sifeddine et al.,

2001). Studies along the Rio Negro record abundant sus-

pended load, with formation of white water between 14,000

and 4000 yr ago, attributed to increased erosion during

relatively more arid conditions (Latrubesse and Franzinelli,

1998). Only after this time there was a change to black

waters, characterized by low suspension load and high

organic content as we see today.

Our integrated analysis supports a progressively in-

creased humidity in the Itaituba area through the past

15,000 yr, which was directly reflected by a simultaneous

change in vegetation cover from arboreal savanna to dense

rain forest as we see today. These data add new insights to

the discussion of Amazonian climate and landscape during

the Quaternary, an issue still largely controversial.

Final remarks

The available historical data related to climate evolution

throughout the Pleistocene and Recent in the Amazon

region are still insufficient to provide a detailed character-

ization of all shifting episodes. There seems to be an overall

fairly good agreement on the major climatic patterns when

data from the study area are compared with those from other

places located thousands of kilometers apart throughout

northern South America, with a change from arid to rela-

tively more humid conditions in the past 15,000 yr. How-

ever, the data from the Itaituba area do not reveal any drastic

change in landscape in central Amazonia. Instead, integra-

tion of geological, paleontological, and isotope data

revealed only a slight change in humidity and, as a result,

vegetation density, with a shift from arboreal savanna to

forest. Such interpretation can be easily accommodated with

the data obtained from Amazon deep sea fan sediments

(e.g., Heberle and Maslin, 1999; Kastner and Goni, 2003),

as arboreal savanna would show y13C values that might be

indistinguishable from those of forest vegetation. The in-

formation provided in this paper should be taken as an

additional source of data in the design of large-scale climatic

scenarios, but a word of caution must be considered in the

interpretations, as the modern landscape in the Central

Amazonia area is complex, with open and dense forest

and even areas with savannas.

Acknowledgments

We acknowledge the support given by Dr. Ima Celia

Vieira as the chair-in-charge of the Goeldi Museum during

the initial fieldwork. We thank Mr. Antonio Anildo Aguiar

and Mr. Joelson Aguiar, who first reported the fossil

occurrence on their farm, geologists Every Aquino (DNPM)

and Elias Leao Moraes (SEMMA) for field assistance, and

to Dr. Walter Neves (USP) for payment for one 14C analysis.

Finally, we thank two anonymous reviewers for comments

that improved this paper significantly.

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