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The youngest record of phorusrhacid birds (Aves, Phorusrhacidae) from the late Pleistocene of Uruguay

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We report the youngest record of a phorusrhacid bird based on a distal portion of a right tarsometatarsus. This fossil comes from late Pleistocene sediments of Uruguay. The age determination was based on lithological features, biostratigraphical studies and absolute dating. The evidence indicates that these groundbirds co-occurred with the typical Pleistocene South American megafaunal mammals. The so far youngest fossils of phorusrhacids stem from the Pliocene or lower Pleistocene of South and North America.
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The youngest record of phorusrhacid birds
(Aves, Phorusrhacidae) from the late Pleistocene of Uruguay
Herculano Alvarenga, Taubaté, Washington Jones, Montevideo
and Andrés Rinderknecht, Montevideo
With 2 figures
A
LVARENGA
, H., J
ONES
, W. & R
INDERKNECHT
, A. (2010): The youngest record of phorusrhacid birds
(Aves, Phorusrhacidae) from the late Pleistocene of Uruguay. – Neues Jahrbuch für Geologie and
Paläont. Abh., 256: 229234; Stuttgart.
Abstract: We report the youngest record of a phorusrhacid bird based on a distal portion of a
right tarsometatarsus. This fossil comes from late Pleistocene sediments of Uruguay. The age
determination was based on lithological features, biostratigraphical studies and absolute dating. The
evidence indicates that these groundbirds co-occurred with the typical Pleistocene South American
megafaunal mammals. The so far youngest fossils of phorusrhacids stem from the Pliocene or lower
Pleistocene of South and North America.
Key words: Giant groundbird, Phorusrhacidae, late Pleistocene, youngest record, South America,
Uruguay
1. Introduction
The phorusrhacids, also called “terror-birds”, were
carnivorous groundbirds that lived mainly in Ceno-
zoic environments of South America. Probably,
evolved to giant sizes due the geographic isolation of
South American continent. These birds are amongst
the largest birds that have ever existed on the planet,
ranging in height from approximately 1 to 3 meters
(M
ARSHALL
1994; A
LVARENGA
& H
ÖFLING
2003).
Phorusrhacid birds apparently shared with borhyaenid
marsupials the predator niche of grassland eco -
systems, and perhaps open areas in dry forest.
Because its huge skull with a powerful hooked beak,
large curved claws and considerable running abilities
(B
LANCO
& J
ONES
2005), are generally considered as
swift cursorial predators. About 13 genera, and 18
species are known for this family, and these are
distributed over five subfamilies (A
LVARENGA
&
H
ÖFLING
2003; B
ERTELLI
et al. 2007). The oldest
record of this family is from the Paleocene of Brazil
(A
LVARENGA
1985), and the youngest to date may
either be a large tibiotarsus assigned to Pliocene or
lower Pleistocene of the Raigón Formation in
Uruguay (T
AMBUSSI
et al. 1999) or the various
remains of another gigantic species, Titanis walleri ,
from the Pliocene (late Hemphillian to late Blancan),
of Texas and Florida, USA (B
RODKORB
1963; C
HAN
-
DLER
1994; B
ASKIN
1995; G
OULD
&Q
UITMEYR
2005;
M
AC
F
ADDEN
et al. 2006). These latter discoveries
show phorusrhacids to have been part of the Great
American Biotic Interchange, and they were the only
carnivorous group of South American animals to dis-
perse northward (M
ARSHALL
1988, 1994). The present
note documents the occurrence of a specimen of terror
bird from the late Pleistocene of Uruguay that consti-
tutes the latest geologic occurrence of the Phorus-
rhacidae.
© 2010 Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany www.schweizerbart.de
DOI: 10.1127/0077-7749/2010/0052 0077-7749/2010/0052 $ 1.50
N. Jb. Geol. Paläont. Abh. 256/2, 229 234 Article
Stuttgart, published online April 2010
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eschweizerbart_xxxx
2. Locality and geological setting
The material described in this study was collected
by Luis Castiglioni in Casil Quarry, Department of
Montevideo, about 2.4 km west from the town of
La Paz (34º45’24S, 56º15’53W), Uruguay (Fig. 1). It
comes from sediment belonging to the Dolores
Formation, usually considered to be of middle-late
Pleistocene age (A
NTÓN
& G
OSO
1974). This litho -
logical unit is characterized by siltstones, pelites,
sandy to gravely pelites, and sandstones with argil -
laceous matrix. Calcium carbonate is abundant in
various forms (B
OSSI
& N
AVARRO
1991; G
UTIÉRREZ
et
al. 2005). The tarsometatarsus comes from a bone bed
in greenish clayish siltstone with sand and gravel
clasts. Its color, texture, and degree of abrasion are
consistent with those of other fossils from the same
bone bed. Taphonomic information, sedimentological
features, and mineralogical studies suggest that the
depositional event was a high energy deposit such as
a mud flow (C
ORONA
et al. 2005, 2007). The asso -
ciated fauna includes several genera of cingulates
(Glyptodon sp., Panochthus sp., Doedicurus sp., Neu -
ryurus sp., Propraopus sp.); ground sloths (Lestodon
armatus and Megatheriinae gen. et. sp. indet.); several
ungulates (Macrauchenia patachonica, Toxodon cf. T.
platensis, Hemiauchenia sp., Ozotocerus cf. bezo -
articus, Hippidion sp., and Stegomastodon waringi); a
rodent (Myocastor sp.), and some indeterminate bird
bones. This faunal association, especially the taxa
230 H. Avarenga
Fig. 1. Map of Uruguay with solid circle indicating the locality where the specimen. MNHN-1736 was collected.
0052_Alvarenga.Fast.qxd:Grundlayout 06.05.2010 11:31 Uhr Seite 230
eschweizerbart_xxxx
Phorusrhacid birds from the late Pleistocene of Uruguay 231
Macrauchenia patachonica , Lestodon armatus and
Stegomastodon waringi, restricts the age of this fauna
to middle or late Pleistocene (P
EREA
et al. 2001;
M
ARCHESANO
et al. 2002; C
ORONA
et al. 2005). A
sample of enamel from a proboscidean molar from the
same stratigraphic level was dated to 17620 ± 100
years BP by AMS 14C (see G
UTIÉRREZ
et al. 2005).
Thus, various lines of evidence confirm a late
Pleistocene age for this quarry.
3. Material and methods
The specimen consists of the distal portion of a right
tarsometatarsus (Fig. 2), lacking the trochlea meta -
tarsi IV. The texture of the periosteum indicates an
adult individual. The specimen was compared with
the homologous bone of all orders and almost all
families of extant non-passerine birds in the osteolog-
ical collections of the Museu de Historia Natural de
Taubaté, Brazil, and the Museo Nacional de Historia
Natural y Antropología de Montevideo, Uruguay.
Comparisons were also made with published illustra-
tions of extinct families such as Teratornithidae,
Diatrymidae, Plotopteridae, Odontopterygidae, and
Pseudodontornithidae (M
ILLER
1909, 1910; M
ATTHEW
& G
RANGER
1917; O
LSON
& H
ASEGAWA
1979;
H
ARRISON
& W
ALKER
1976). Comparisons were also
made with tarsometatarsi attributed to the Phorus-
rhacidae, using the original data from A
LVARENGA
&
H
ÖFLING
(2003). Anatomical terminology follows
B
AUMEL
and W
ITMER
(1993). The material described
here is deposited in the Museo Nacional de Historia
Natural y Antropología, Montevideo (MNHN-1736).
4. Description and comparisons
Compared with extant birds of South America, the
specimen (MNHN-1736) is smaller than the tarso -
metatarsus of rheas (Rheidae) but larger than that of all
other terrestrial birds, including storks. Among the
phorusrhacids the specimen is smaller than Mesembri-
ornis incertus (the smallest Mesembriornithinae) but is
of similar size to that of Procariama simplex, the largest
of the Psilopterinae (the subfamily that includes the
smallest species of Phorusrhacidae). The bone lacks
the trochlea metatarsi IV, but the remainder is well
preserved and shows some important features. On the
lateral side, across the damaged area (Fig. 2D), it is
possible to observe the longitudinal section of the
canalis interosseus distalis and its ventral branch, which
conducts the tendon of Musculus extensor brevis digiti
IV and blood vessels into the lateral intertrochlear
incisure (B
AUMEL
& W
ITMER
1993). In dorsal view it is
possible to see the foramen vasculare distale located
more proximally than the proximal rim of the middle
trochlea (Fig. 2A). We can conclude that the specimen
came from a large, cursorial bird characterized by:
(1) a large and distally expanded trochea metatarsi III
(middle trochlea); (2) a very narrow trochlea metatarsi
II (inner trochlea,) with the articular surface trans -
versally convex and without a longitudinal sulcus (in
dorsal and distal view); (3) the trochlea metatarsi II in
dorsal view is not turned mediad, being almost parallel
and much shorter than the middle trochlea, and forming
a narrow notch between trochleae II and III. It is im -
portant to note that in most extant birds, including some
cursorial ones such as Rheidae, Tinamidae, Caria -
midae, and Otididae, the trochlea metatarsi II is de -
flected medially; in Teratornithidae, Vulturidae and
Ciconiidae, the trochlea II is much wider and reaches
almost the same distal size as the trochlea III.
The three features outlined above identify the
specimen as a phorusrhacid bird. In addition, the
morphology of trochleae II and III in medial view,
including the very deep foveae ligamentum col -
lateralium, is very typical of the Phorusrhacidae.
Among the terror birds, MNHN-1736 differs from
the Psilopterinae in most representatives of which the
trochlea metatarsi II is wider and its inner edge is
considerably expanded (S
INCLAIR
& F
ARR
1932). It
also differs from the Brontornithinae, the largest of the
Phorusrhacidae, in lacking the expansion of the dorso-
medial extremity of the articular surface of trochleae
III (A
LVARENGA
& H
ÖFLING
2003). Some features of
this specimen are shared with Titanis walleri (see
B
RODKORB
1963 and Fig. 2) of North America, such
as the distally expanded trochlea metatarsi III (dorsal
view), which is unlike that in Phorusrhacos or
Devincenzia. Likewise, the morphology of the plantar
supratrochlear surface and of trochleae II and III in
medial view resembles that of Titanis.
5. Discussion
Fossils of Titanis are from temporally mixed faunas
associated with Hemphillian (5 Mya) and late
Blancan (2.4 to 2.0 Mya) ages in North America
(M
AC
F
ADDEN
et al. 2006). T
AMBUSSI
et al. (1999)
identified a large tibiotarsus of the Phorusrhacinae
(MNHN-1563) from Uruguay, to the Pliocene or early
Pleistocene of Raigón Formation (Uruguay). Thus the
new fossil described here is the youngest occurrence
0052_Alvarenga.Fast.qxd:Grundlayout 06.05.2010 11:31 Uhr Seite 231
eschweizerbart_xxxx
232 H. Avarenga
of the Phorusrhacidae and extends the family into the
late Pleistocene of South America.
The three other Phorusrhacidae specimens pre -
viously described from Uruguay – a tarsometatarsus
MNHN-189 (type of Devincenzia pozzi), a distal
portion of tarsometarsus assigned to Devincenzia sp.
(Museo Municipal “Bautista Rebuffo”, Uruguay,
MR-1215) described by P
EREA
and A
LFARO
(2004),
and a tibiotarsus MNHN-1563 (T
AMBUSSI
et al. 1999)
– are all from the Pliocene or lower Pleistocene. All
these fossils belong to very large species, different
from the smaller and more recent fossil described
here. Although the present specimen (MNHN-1736) is
insufficient for generic determination, some features
(the distally expanded trochlea metatarsi III and a
narrow trochlea metatarsi II) are shared with Titanis
walleri from North America, and other features (as the
trochlea metatarsi II not turned mediad, and almost
parallel to the middle trochlea and also the absence of
a dorsomedial expansion of the trochlea III) preclude
a close relationship with the subfamilies Bronto -
rnithinae and Psilopterinae suggesting that the last
representative of the terror birds may belong to one of
the subfamilies Phorusrhacinae, Patagornithinae, or
Mesembriornithinae. The extinction of phorusrhacids
was presumably due to the invasion into South
America of North America flesh-eating placental
mammals (see M
ARSHALL
1988, 1994; W
OODBURNE
et al. 2006). This hypothesis could be precluded be -
cause the presence of at least one phorusrhacid
Fig. 2. Distal end of right tarsometatarsus of a Phorusrhacidae from the late Pleistocene of Uruguay (MNHN-1736)
(top) and Titanis walleri (holotype, University of Florida, UF-4108) (below). A, dorsal, B, medial, C, planar, D, lateral
and E, distal views.
0052_Alvarenga.Fast.qxd:Grundlayout 06.05.2010 11:31 Uhr Seite 232
eschweizerbart_xxxx
representative in the South American late Pleistocene,
coexisting with many predators, even actual species.
For these reasons, the extinction causes should be
reevaluated in function of this fossil finding.
Acknowledgements
We thank L
UIS
C
ASTIGLIONI
who collected the specimen
described here, permitted our study of it, and provided
additional information. G
USTAVO
L
ECUONA
prepared the
map and figure. S
TORRS
L. O
LSON
critically reviewed a
preliminary version and greatly improved this paper. Also
we thank C
ECILÈ
M
OURER
-C
HAUVIRÉ
and G
ERALD
M
AYR
for their final reviews that greatly improved this paper.
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Addresses of the authors:
H. A
LVARENGA
, Museu de História Natural de Taubaté. Rua
Juvenal Dias de Carvalho, 111. Taubaté, SP, 12070-640
Brazil;
e-mail: halvarenga@uol.com.br
W. J
ONES
, Museo Nacional de Historia Natural y Antro -
pología. 25 de Mayo 582. Montevideo, 11300 Uruguay;
e-mail: wawijo@yahoo.com.ar
A. R
INDERKNECHT
, Museo Nacional de Historia Natural
y Antropología. 25 de Mayo 582. Montevideo, 11300
Uruguay;
e-mail: rinderk@adinet.com.uy
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... Among Phorusrhacidae, members of Mesembriornithinae have been considered traditionally as middle to very large forms, whereas the cursorial bird Procariama simplex was considered as a Psilopterinae (Alvarenga & Höhfling, 2003;Vezzosi, 2012), i.e., the subfamily that includes all the small phorusrhacids (Agnolin, 2009;Alvarenga, et al. 2010). However, a recent phylogenetic analysis included Procariama simplex into the Mesembriornithinae clade, being considered as the sister taxon of Llallawavis scagliai, and this clade as sister-taxon to both Mesembriornis species (Degrange et al., 2015). ...
... If this evidence, among other Pleistocene specimens under study (see Jones et al., 2016), confirms the assignment to Procariama simplex, the mesembriornithines would have survived until the Late Quaternary. Thus, two subfamilies of Phorusrhacidae would have persisted until the Quaternary in America: the North American Phorusrhacinae represented by Titanis walleri from the late Pliocene to the early Pleistocene and, probably, the South American Mesembriornithinae with only the small Procariama-relative from the Late Pleistocene deposits of Uruguay (Baskin, 1995;Alvarenga et al., 2010;Vezzosi, 2012). Although the occurrence of Titanis in the early Pleistocene has been reported previously, Gould and Quitmyer (2005) refer all the material from Florida to the Pliocene (Blancan NALMA) and conclude that the specimen coming from Texas likely belongs to the Pliocene. ...
... The distal section of the right tarsometarsus preserves only the trochlea metatarsi II (entotrochlea) and III (mesotrochlea) (Fig. 5) and, medially, the area corresponding to the foramen vasculare distale shows a large and deep channel (Fig. 5.3). The trochlea metatarsi II is slightly turned as in Mesembriornis incertus and M. milneedwardsi (Alvarenga & Höfling, 2003;Alvarenga et al., 2010), and shows a caudomedial crest (i.e. ppm) that is clearly identified in Llallawavis, Procariama and Mesembriornis incertus. ...
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The giant carnivorous phorusrhacid bird Phorusrhacos longissimus (Aves, Cariamiformes) was first described in 1887 by Florentino Ameghino on the basis of a jaw fragment. The majority of a skull of the species still encased in crumbling rock was preserved only long enough for illustrations to be made by Carlos Ameghino in the field and for a brief description to be written. Skull remains of this species have remained scarce, and few postcranial remains have been figured. Here, we reassess the cranial anatomy of this outstanding 'terror bird' species taking into account data from a newly discovered skull. An additional specimen of a well-preserved dorsal vertebra referable to Phor-usrhacinae is also described from a separate locality within the Miocene Santa Cruz Formation (late early Miocene) from Santa Cruz Province in Argentina. The skull includes most of the rostrum, skull roof, and mandible and is compared with material from other members of the Phorusrhacinae. The new data from the skull and vertebra provide morphological features of this clade that benefit future taxonomic and phylogenetic analyses of this iconic group of birds.
... The latest records with reliable stratigraphic data are from the Chapadmalalan , but material from putative Pleistocene beds have been found in Uruguay (Tambussi et al. 1999;Agnolin 2009). The most recent of these seemingly include a phorusrhacid from the Late Pleistocene (Lujanian) (Alvarenga et al. 2009;Jones et al. 2016). The relevance of environmental changes and their impact on terrestrial mammalian communities in connection with the demise of sparassodonts occasionally has been addressed (see also Marshall 1977Marshall , 1978 Marshall and Cifelli 1990, partim;Forasiepi et al. 2007;. ...
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The Earth experienced dramatic transformations during the Cenozoic, with changing sea levels, climate, and tectonic events having major influences on the global biota. In South America, loss of the connection between Patagonia and Antarctica, Andean orogeny, and formation of the Isthmus of Panama defined the continent, as we know it today. These events had enormous effects on local faunas, with major consequences for their evolution and extinction. The Great American Biotic Interchange (GABI), a major natural experiment in biotic reorganization, was either enabled or at least greatly enhanced by land connections between North and South America during the late Neogene. The outcome of the meeting of previously separated biotas was a drastic change, both for the composition of South American faunas and the terrestrial ecosystems they inhabited.
... The latest records with reliable stratigraphic data are from the Chapadmalalan , but material from putative Pleistocene beds have been found in Uruguay (Tambussi et al. 1999;Agnolin 2009). The most recent of these seemingly include a phorusrhacid from the Late Pleistocene (Lujanian) (Alvarenga et al. 2009;Jones et al. 2016). The relevance of environmental changes and their impact on terrestrial mammalian communities in connection with the demise of sparassodonts occasionally has been addressed (see also Marshall 1977Marshall , 1978 Marshall and Cifelli 1990, partim;Forasiepi et al. 2007;. ...
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South America has a rich fossil record that allows the reconstruction of the continental communities during the Cenozoic. Florentino Ameghino was one of the earliest advocates of a temporal sequence of faunas and biogeographic events, later refined by several authors (e.g., George G. Simpson, Rosendo Pascual, Bryan Patterson). This scheme is continually revised and improved by new faunal, systematic, and chronological studies. The fossil record is always incomplete, and many biases are recognized, some of them—the megabiases affect the interpretation of the global fossil record. For example, in South America, a megabias exists with respect to tropical areas, particularly before the Late Pleistocene. The SA fossil record contains large hiatuses between ages, with some ages being unconstrained by geochronological dates, while others are poorly sampled in terms of fossil recovery, faunal diversity, and identified localities. This form of bias which together with the differential duration of the South American Ages affects interpretation of the evolution of the continental fauna. In this chapter, we examine the spatial distribution of South American fossil localities, their frequency per age in the Cenozoic, and discuss the effect biases in the fossil record by means of a statistical approach.
... The latest records with reliable stratigraphic data are from the Chapadmalalan , but material from putative Pleistocene beds have been found in Uruguay (Tambussi et al. 1999;Agnolin 2009). The most recent of these seemingly include a phorusrhacid from the Late Pleistocene (Lujanian) (Alvarenga et al. 2009;Jones et al. 2016). The relevance of environmental changes and their impact on terrestrial mammalian communities in connection with the demise of sparassodonts occasionally has been addressed (see also Marshall 1977Marshall , 1978 Marshall and Cifelli 1990, partim;Forasiepi et al. 2007;. ...
Chapter
Carnivora is a clade of mammalian predators that evolved in northern continents during the Paleocene, and since the Miocene have invaded the southern continents (i.e., Africa and South America). They evolved a large diversity and disparity of body forms and size, which allowed the occupation of many ecological niches. Carnivorans arrived in South America in the late Miocene, when Central America provided a land bridge, or an island chain that facilitated migration of initial mammalian groups including carnivorans. The first carnivorans in South America were procyonids, followed by mustelids and canids in the late Pliocene, and felids, mephitids, and ursids in the Pleistocene. Their high diversity and morphological disparity can be explained through a combination of repeated immigrations and radiations into empty ecological zones. Here we present a synthesis of the systematics, distribution, and paleocology of fossil terrestrial carnivorans of South America.
... The latest records with reliable stratigraphic data are from the Chapadmalalan , but material from putative Pleistocene beds have been found in Uruguay (Tambussi et al. 1999;Agnolin 2009). The most recent of these seemingly include a phorusrhacid from the Late Pleistocene (Lujanian) (Alvarenga et al. 2009;Jones et al. 2016). The relevance of environmental changes and their impact on terrestrial mammalian communities in connection with the demise of sparassodonts occasionally has been addressed (see also Marshall 1977Marshall , 1978 Marshall and Cifelli 1990, partim;Forasiepi et al. 2007;. ...
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The process by which successive groups using the same resources occupy the same geographic area through time is frequently attributed to competition. Several authors have argued that competitive displacement was the cause of the decline and extinction of Sparassodonta, due to the introduction of carnivorans into South America about 8–7 Ma, although this view has been recently criticized. The diversity of Sparassodonta was low relative to that of Carnivora throughout the Cenozoic. The greatest peak in sparassodontan diversity was during the early Miocene (Santacrucian), with 11 species. After the late Miocene (Huayquerian), sparassodont diversity decreased and the group became extinct in the mid-Pliocene (~3 Ma, Chapadmalalan). In the late Miocene–mid Pliocene (Huayquerian–Chapadmalalan), the fossil record shows that sparassodonts and carnivorans overlapped. During this time, carnivoran diversity consisted of four or fewer species; thereafter, it expanded to more than 20 species in the early–Middle Pleistocene (Ensenadan). Initially, Carnivora was represented by middle-sized, omnivorous species, with large omnivores first represented in the mid-Pliocene (Chapadmalalan). By contrast, over this period, Sparassodonta was represented by both large and small hypercarnivores and a single large omnivorous species. We review hypotheses of replacement using the available information and perform new analyses to test the effect of sampling bias, ecological overlap between clades, and the relevance of environmental and faunistic changes for the evolution of sparassodonts. From this review of the fossil record, it is suggested that stochastic mechanisms other than competitive displacement may have caused the decline and extinction of Sparassodonta, possibly as part of a larger faunistic turnover related to multicausal biological and physical factors. Similarly, at the Pleistocene/Holocene boundary, an extinction event affected large mammals in South America, including large carnivorans, in the context of a multicausal event that involved human presence as well as collateral factors.
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Coastal exposures of the Santa Cruz Formation in southern Patagonia have been a fertile ground for recovery of Early Miocene vertebrates for more than 100 years. This volume presents a comprehensive compilation of important mammalian groups which continue to thrive today. It includes the most recent fossil finds as well as important new interpretations based on 10 years of fieldwork by the authors. A key focus is placed on the paleoclimate and paleoenvironment during the time of deposition in the Middle Miocene Climatic Optimum (MMCO) between 20 and 15 million years ago. The authors present the first reconstruction of what climatic conditions were like and present important new evidence of the geochronological age, habits and community structures of fossil bird and mammal species. Academic researchers and graduate students in paleontology, paleobiology, paleoecology, stratigraphy, climatology and geochronology will find this a valuable source of information about this fascinating geological formation.
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The extinction of the Quaternary megafauna stands out among the evolutionary history of Cenozoic mammals. In South America, nearly 80% of the megamammals went extinct, including the native un-gulates Macrauchenia patachonica and Xenorhinotherium bahiense. Little is known about the causes of the macraucheniids' extinction and their paleobiology. Here, we have reconstructed the dietary habits of M. patachonica and X. bahiense using enamel microwear and occlusal enamel index analyses, and also inferred their niches using species distribution modeling and stable isotope paleoecology, in addition to enamel microwear and occlusal enamel index data. We found that both macraucheniids had grazer-feeding habits, although their environmental requirements were different. M. patachonica could live in colder temperatures and arid, subtropical/temperate ecosystems, while X. bahiense was adapted to warmer temperatures and more humid, semi-arid tropical environments. Thus, despite similar feeding habits, these macraucheniids had distinct environmental requirements and ecological niches, which might explain the disjunction in the South American records.
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The Great American Biotic Interchange (GABI) is one of the biggest biogeographical events, which has shaped the modern South American fauna. It refers to several migratory pulses of continental fauna between North and South America, beginning during the Miocene and continuing to the present day. It intensified during the Pliocene with the closure of the Isthmus of Panama and has been fundamental in the settling of the Neotropical and Nearctic realms as we know them today. However, this is far from being the only time that South America has been colonized or being part of a biotic exchange with other continental masses. During approximately 400 million years South America was part of the ancient supercontinent Gondwana, being connected with the other large land masses of the Southern Hemisphere. The later break-up of this supercontinent paid an enormous impact in the composition of faunas across the whole hemisphere, and the resulting extended period of South American isolation gives birth to a unique assemblage of animals and plants. This chapter aims to offer an introduction to the biogeographical events and processes that shaped the South American fauna during the Cenozoic, with an emphasis on those that took place before the GABI. It provides a broad context to understand the processes at work during the Late Pleistocene when the Pilauco site was formed and the origin of the animals that inhabited it.
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The Pilauco site is located in north-western Chilean Patagonia, Region de Los Lagos (40°34′12″S, 73°06′12″W). The stratigraphy of the site comprises of two distinct Pleistocene units. The lower unit corresponds to the sequence San Pablo of MIS5e age and consists of clastic and volcanoclastic sediments (PB-1 to PB-5). The upper unit includes the strata PB-6 to PB-9 with age constraints between 17,370 and 4,340 cal. year BP. The strata bearing fossil mammals and archaeological evidence (PB-7 and PB-8; 16,400–12,800 cal. year BP) correspond to layers of sand derived by means of colluvial transport from the nearby hills to the north of the site, in a fine-grained matrix of organic anoxic material and dispersed gravel clasts deposited in a seasonal wetland. The contact between the layers PB-8 and PB-9 is characterized by an erosional unconformity, a drastic increase in charcoal particles coeval with the nearly complete disappearance of pollen and other plant remains. Moreover, layer PB-9 lacks paleontological and archaeological remains. The discordance has been dated on ~12,800 cal. year BP, which coincides with the Younger Dryas Northern Hemisphere climatic oscillation. The local geological characteristics are concordant with regional geomorphological interpretations that have identified several terraces formed during the last glaciation and the Holocene.
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Fossil Proboscidea remains from the Dolores Formation, Montevideo, Uruguay, are described and taxonomically identified. We compared these remains with those of Stegomastodon waringi and Stegomastodon platensis from several localities in Brazil and Argentina using multivariate analysis. The results indicate that Stegomastodon waringi (HOLLAND, 1920) is represented in the quarry. Enamel tooth sample of gomphothere was dated to 17,620 ± 100 BP by AMS 14C so we confirm the late Pleistocene age for this fauna. To reconstruct the paleodiet and habitat preference we measured the carbon and oxygen isotope composition of the teeth dentine. Of the two different adaptations attributed to Stegomastodon waringi, we found that at this latitude they were mixed-C3 feeders, closely related with the Brazil population.
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Describes a group of large flightless, flesh-eating birds known as phorusrhacoids, which lived from 62 million years to about 2.5 million years ago, and which became the dominant carnivores of South America. The history of their discovery and taxonomic classification, the reconstruction of their appearance from fossil remains, their mode of life, and their nearest living relatives, are described. The creatures ranged in height from one to three metres, and were able to kill and eat animals the size of small horses. By about five million years ago phorusrhacoids had completely replaced their nearest competitors, the doglike borhyaenoids, on the savannas of South America. However, their decline came soon after, following the emergence of the Panamanian land bridge, and the dispersion into South America of new competitors in the form of placental dogs and cats. -G.E.Hodgson