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Evaluating Habitats and Feeding Habits Through Ecomorphological Features in Glyptodonts (Mammalia, Xenarthra)

Authors:
  • Museo Argentino de Ciencias Naturales "Bernardino Rivadavia" - División Mastozoología
  • Museo de La Plata-Universidad Nacional de La Plata

Abstract and Figures

The goal of this study is to evaluate ecomorphological variables in glyptodonts from different ages (Miocene to early Holocene), clades, and sizes, with the purpose of inferring their habitats and feeding habits. The analyses included estimation of body masses and three variables: relative muzzle width (RMW), hypsodonty index (HI), and dental occlusal surface area (OSA). RMW allows the distinction of two main groups: the small-sized early Miocene propalaehoplophorids were selective feeders, while the larger post-Miocene forms were more bulk feeders. The Pleistocene Glyptodon appears as an exception, implying a reversion to a selective feeding behavior. The relation between RMW and HI allows discriminating feeding niche partitioning in glyptodonts. Among the early Miocene propalaehoplophorids, Eucinepeltus would have been a highly selective feeder in relatively closed environments, Propalaehoplophorus a highly selective feeder in moderately open habitats, and Cochlops a less selective feeder in moderately open habitats. Among the large Pliocene and Pleistocene taxa, cf. Neuryurus and Neosclerocalyptus were probably bulk feeders in relatively open environments, while Panochthus and Doedicurus were bulk feeders in open environments. Alternative interpretations can be assessed for Glyptodon: it was a more selective feeder in closer habitats, or had a different feeding behavior, browsing on specific plants at higher levels from the ground, and/or a specialized physiology. The late Miocene and Pliocene forms (Hoplophractus, Eosclerocalyptus, and Urotherium) were probably intermediate between the Miocene and the Pleistocene ones.
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305
EVALUATING HABITATS AND FEEDING HABITS
THROUGH ECOMORPHOLOGICAL FEATURES
IN GLYPTODONTS MAMMALIA, XENARTHRA
1
División Paleontología Vertebrados, Museo de La Plata, Paseo del Bosque s/n, B1900FWA, La Plata, Argentina. CONICET - CIC. vizcaino@fcnym.unlp.edu.ar,
msbargo@fcnym.unlp.edu.ar, gcassini@fcnym.unlp.edu.ar
2
División Paleontología, Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”, Av. Ángel Gallardo 470, C1450DJR Buenos Aires, Argentina. jctano@macn.gov.ar
3
Universidad Nacional de Luján, Departamento de Ciencias Básicas, Ruta Nacional 5 y Av. Constitución, 6700 Luján, Argentina.
AMEGHINIANA, Tomo 48 (3): 305 - 319 ISSN 0002-7014
SERGIO F. VIZCAÍNO
1
, GUILLERMO H. CASSINI
1,3
, JUAN C. FERNICOLA
2,3
 M. SUSANA BARGO
1
AMGHB2-0002-7014/11$00.00+.50
Abstract. e goal of this study is to evaluate ecomorphological variables in glyptodonts from dierent ages (Miocene to early Holocene),
clades, and sizes, with the purpose of inferring their habitats and feeding habits. e analyses included estimation of body masses and three
variables: relative muzzle width (RMW), hypsodonty index (HI), and dental occlusal surface area (OSA). RMW allows the distinction of
two main groups: the small-sized early Miocene propalaehoplophorids were selective feeders, while the larger post-Miocene forms were more
bulk feeders. e Pleistocene Glyptodon appears as an exception, implying a reversion to a selective feeding behavior. e relation between
RMW and HI allows discriminating feeding niche partitioning in glyptodonts. Among the early Miocene propalaehoplophorids, Eucinepel-
tus would have been a highly selective feeder in relatively closed environments, Propalaehoplophorus a highly selective feeder in moderately
open habitats, and Cochlops a less selective feeder in moderately open habitats. Among the large Pliocene and Pleistocene taxa, cf. Neuryurus
and Neosclerocalyptus were probably bulk feeders in relatively open environments, while Panochthus and Doedicurus were bulk feeders in
open environments. Alternative interpretations can be assessed for Glyptodon: it was a more selective feeder in closer habitats, or had a dif-
ferent feeding behavior, browsing on specic plants at higher levels from the ground, and/or a specialized physiology. e late Miocene and
Pliocene forms (Hoplophractus, Eosclerocalyptus, and Urotherium) were probably intermediate between the Miocene and the Pleistocene ones.
Keywords. Mammalia. Cingulata. Masticatory apparatus. Paleoecology.
Resumen: EVALUANDO HÁBITAT Y HÁBITOS ALIMENTARIOS EN GLIPTODONTES (MAMMALIA, XENARTHRA) A
TRAVÉS DE VARIABLES ECOMORFOLÓGICAS. El objetivo de este estudio es evaluar variables ecomorfológicas en gliptodontes de
diferentes edades (Mioceno al Holoceno temprano), clados y tamaños, con el propósito de inferir sus hábitats y hábitos alimentario. El
análisis incluyó una estimación de las masas corporales y tres variables: ancho relativo del hocico (RMW), índice de hipsodoncia (HI) y área
de la supercie oclusal dentaria (OSA). RMW permite distinguir dos grupos principales: los pequeños propalaehoplofóridos del Mioceno
temprano se alimentaban de forma selectiva, mientras que las formas más grandes post-miocenas se alimentaban al bulto. Glyptodon del
Pleistoceno aparece como una excepción, que implica una reversión a una conducta de alimentación selectiva. La relación entre RMW y HI
permite discriminar la partición del nicho alimentario en gliptodontes. Entre los propaleoplofóridos del Mioceno temprano, Eucinepeltus
habría tenido una alimentación altamente selectiva en ambientes relativamente cerrados, Propalaehoplophorus una alimentación muy selectiva
en hábitats moderadamente abiertos y Cochlops una alimentación menos selectiva en hábitats moderadamente abiertos. Entre los taxones
grandes del Plioceno y Pleistoceno, cf. Neuryurus y Neosclerocalyptus probablemente se alimentaban al bulto en ambientes relativamente abi-
ertos, mientras que Panochthus y Doedicurus se alimentaban al bulto en entornos abiertos. Se pueden proponer interpretaciones alternativas
para Glyptodon: tenía una alimentación más selectiva en hábitats más cerrados o una conducta de alimentación diferente, alimentándose de
plantas especícas en los niveles más superiores, y/o una siología especializada. Las formas del Mioceno tardío y del Plioceno (Hoplophractus,
Eosclerocalyptus y Urotherium) probablemente tuvieron hábitos intermedios entre las del Mioceno temprano y las del Pleistoceno.
Palabras clave. Mammalia. Cingulata. Aparato masticatorio. Paleoecología.
 are very peculiar extinct mammals of the New
World that vanished as part of the great end-Pleistocene ex-
tinction of continental mammals. ey comprise some 65
named genera, according to the last all-inclusive revision of
the fossil mammals (McKenna and Bell, 1997), and more
than 150 named species according to Mones (1986).
In recent years several authors have either synonymized
several names (e.g., Perea, 2005; Zurita et al., 2008, 2009),
excluded taxa (e.g., Porpino et al., 2009), named new spe-
cies, or validated previously abandoned names (e.g., Carlini
et al., 2008; Fernicola, 2008; Porpino and Bergqvist, 2002;
Porpino et al., 2010; Zurita and Ferrero, 2009; Zurita et al.,
2008). However, the taxonomic status of numerous genera
and species is still in ux.
e bony carapace of glyptodonts clearly relates them to
the armadillos (including dasypodids —extant armadillos—
and extinct pampatheres; see Hostetter, 1958, 1982; Pat-
terson and Pascual, 1968, 1972; Engelmann, 1985; Gaudin
306
AMEGHINIANA, Tomo 48 (3): 305 - 319
and Wible, 2006). Glyptodonts and armadillos together
constitute the clade Cingulata within the Xenarthra, but
glyptodont evolutionary history has been independent from
that of armadillos at least since the middle Eocene Mustersan
Age (Scillato-Yané, 1986), i.e., about 45–48 million years
ago (Flynn and Swisher, 1995). Although phylogenetic re-
lationships among cingulates have not been fully resolved,
it is clear that glyptodonts represent the most derived forms
among them (e.g., Gaudin and Wible, 2006).
Recent phylogenetic analyses (Fig. 1) by Fernicola (2008)
and Porpino et al. (2010) focused on cranial and postcra-
nial characters of the endoskeleton, while previous analy-
ses on the subject relied mostly on features of the exoskel-
eton (e.g., Ameghino, 1889; Castellanos, 1932; Hostetter,
1958). Since endoskeletal remains are much rarer than the
osteoderms constituting the exoskeleton (carapace, cephal-
ic shield, and caudal sheath), the phylogenies of Fernicola
(2008) and Porpino et al. (2010) used a limited number of
Figure 1. Phylogeny and chronological distribution (thick line) of the
genera of Glyptodontia (based on Fernicola, 2008 and Porpino et al.,
2010) / logenia y distribución cronológica (línea gruesa) de los géneros
de Glyptodontia (basadas en Fernicola, 2008 y Porpino et al., 2010)
taxa, although this sample represented several of the main
groups considered by earlier authors.
Fernicola (2008) and Porpino et al. (2010) strongly sup-
ported the monophyly of Glyptodontia, rejecting several
of the historical groupings (Ameghino, 1889; Castellanos,
1931, 1932; Hostetter, 1958; Paula Couto, 1979) and
reinstated other groups that had been proposed previously,
and subsequently ignored. While these previous phyloge-
netic proposals had implied Propalaehoplophorus Ameghino,
1887a, and allied genera were paraphyletic, Fernicola (2008)
and Porpino et al. (2010) supported the existence of a basal
dichotomy with Propalaehoplophoridae as the sister group
of Glyptodontoinei including the remaining glyptodonts.
Following these authors, Hoplophorinae (sensu Hostetter,
1958), Hoplophorini, and Plohophorini are considered to be
paraphyletic. e late Miocene “Plohophorini” Stromaphorus
Castellanos, 1926, and Pseudoplohophorus Castellanos, 1926,
and the early and late Pleistocene “Hoplophorini Hoplo-
phractus Cabrera, 1939, and Eosclerocalyptus C. Ameghino,
1919, were placed basally in a successive and intercalated ar-
rangement (Fig. 1). e monophyly of the last two tribes, as
well as the Hoplophorinae, was contradicted by the derived
allocation of the “Hoplophorini Neosclerocalyptus Paula
Couto, 1957, and Hoplophorus Lund, 1839, which form a
monophyletic group with the Panochthinae. is monophy-
letic group is named Panochthidae (sensu Fernicola, 2008).
Also the “Plohophorini Plohophorus Ameghino, 1887b,
is in a derived position and forms a monophyletic group
with the Glyptodontinae (sensu Fernicola, 2008) Doedicu-
rus Burmeister, 1874, and Glyptodon Owen, 1839. Finally,
the “HoplophorinaeLomaphorini Urotherium Castellanos,
1926, was interpreted by Porpino et al. (2010) as the sister
group of the clade including Plohophorus, Doedicurus, and
Glyptodon. e Neuryurini (sensu Hostetter, 1958), with
the genus Neuryurus Ameghino, 1889, were not included in
the phylogentic analysis by Fernicola (2008) and Porpino et
al. (2010), and were considered only as Glyptodontia incer-
tae sedis (Fernicola, 2008).
e morphology of the glyptodont skull (Fig. 2) in gen-
eral, and the masticatory apparatus in particular, is probably
more bizarre than even the carapace. Fariña and Vizcaíno
(2001) provided a basic description that we summarize here.
Compared with that of dasypodid armadillos, a shorten-
ing of the snout is apparent, along with a reduction in the
premaxillae. Fariña and Vizcaíno (2001) conrmed a previ-
ous hypothesis by Fariña and Parietti (1983) on its unique
geometry among mammals. It suggested that the skull of
307
VIZCAÍNO et al.: ECOMORPHOLOGY OF GLYPTODONTS
of processing, and that these dierences in capacity might
reect competitive exclusion by niche partitioning among
sympatric species. Further observations by Fariña and Viz-
caíno (2001) on the stout architecture of the masticatory
apparatus and the very hypsodont teeth with occlusal ridges
of hard dentine indicated that glyptodonts were probably
grazers. However, in that study glyptodonts were treated as
a whole and no comparisons among them were provided.
One persistent problem when inferring dietary habits in
extinct xenarthrans is that dietary labels tend to be vague
and ambiguous. For example, Bargo and Vizcaíno (2008)
considered many uses of the terms “browserand grazer”
to be ambiguous. eir review of the literature available on
living herbivores demonstrates that the terms have been used
to refer to the mode of food acquisition as well as the type of
food ingested, i.e., “browsing” may refer to selective feeding
of any food type and/or to eating dicotyledonous material.
Moreover, grazing” denotes grass eating, but is also used to
mean consuming forbs. Consequently, when applied to ex-
tinct species it is not always clear whether the terms refer
to a mode of food acquisition where food is selected by size
and shape (thus, independent of the plant taxonomy), to the
selection of specic taxa (independent of the size and shape),
or to some unspecied combination of both selection crite-
ria. ese authors indicated that the problem with trying to
classify mammals as either browsers or grazers is that these
terms are based on dierent criteria. While browsing reects
capacity for searching on a variety of vegetation independent
of plant taxonomy, grazing implies taxonomic and structural
constraints. After further considerations, Bargo and Vizcaí-
no (2008) advocated analyzing morphology based on how it
deals with physical properties (hardness, resistance to wear,
size) and using dietary categories based on the main physical
properties of the food, inferred from the morphology of the
feeding apparatus.
e goal of this study is to apply some ecomorphologi-
cal variables from recent studies of other fossil xenarthrans
(particularly the Pleistocene ground sloths; Bargo and Viz-
caíno, 2008) to glyptodonts from dierent ages (Miocene
to Holocene), clades, and sizes, for the inference of feeding
habits. Ultimately, this will lead us to specic paleoecological
interpretations for these enigmatic glyptodonts.
MATERIALS AND METHODS
Acronyms
MACN A, Museo Argentino de Ciencias Naturales “Ber-
nardino Rivadavia”, Colección Nacional Florentino Ameghi-
glyptodonts has undergone a very peculiar process of tele-
scoping, in which the braincase is positioned dorsal to the
posterior half of the tooth row. Another conspicuous feature
is the huge descending process of the anterior portion of the
zygomatic arch, formed by the maxillary and jugal bones.
e glenoid fossa —bordered posteriorly by the paraoccipi-
tal process— is transversely elliptical and rather at, directed
backward, and slightly downward and outward, lying well
above the tooth row.
e jaw also has the distinctive feature of a highly devel-
oped angle. In general, the mandibular symphysis is com-
pletely fused. e mandibular condyle is transversely elon-
gated and dorsoventrally convex. Its articular facet is directed
forward, nearly at a right angle respect of the arrangement
normally observed in mammalian herbivores. Each hemi-
mandible possesses a row of eight cheek-teeth that lies almost
perfectly parallel to the sagittal plane and that is sinusoid in
lateral view. e teeth (Fig. 3) have a curious morphology
lacking the tribosphenic pattern generally present in other
mammals (see Vizcaíno et al., 2004; Vizcaíno, 2009, and
references therein). ey are three-lobed, with the exception
of some groups (e.g., propalaehoplophorids), in which the
rst two teeth are usually reduced and oval shaped. Teeth
are hypselodont (ever-growing and open-rooted), and true
enamel is entirely absent in glyptodont teeth (and in most,
if not all, other xenarthrans). Glyptodonts show a three-lay-
ered tooth construction with an inner, often branching core
of vascularized osteodentine, and an outer layer of ortho-
dentine of which the outermost part is especially hardened
(Ferigolo, 1985; Kaltho, 2011).
Despite that the last thirty years —but especially the last
fteen— have seen an increasing number of studies on the
masticatory apparatus and its relationships with feeding hab-
its in other xenarthrans such as armadillos, pampatheres, and
sloths (for overviews see Vizcaíno et al., 2004; Bargo and
Vizcaíno, 2008; Vizcaíno et al., 2008; Vizcaíno, 2009), yet
glyptodonts remain much less understood. Gillette and Ray
(1981) proposed that they were probably browsers belong-
ing to Turnbull’s (1970) rodent-gnawing” type. However,
an analysis of the craniomandibular joint (CMJ) by Fariña
and Vizcaíno (2001) indicated that the vertical articular sur-
face of the CMJ implies mostly vertical sliding, while in ro-
dents sliding is mostly horizontal. e CMJ of glyptodonts
also allowed —albeit limited— side-to-side movements of
the jaw. In a preliminary study Vizcaíno (2000) proposed
that the main dietary dierences among cingulates lied in
the degree of coarseness of the vegetation they were capable
308
no, Buenos Aires, Argentina; MACN Pv, Museo Argentino
de Ciencias Naturales “Bernardino Rivadavia”, Colección
Nacional de Paleovertebrados, Buenos Aires, Argentina;
MLP, Museo de La Plata, La Plata, Argentina; MPM-PV,
Museo Regional Provincial “Padre M. J. Molina”, Paleon-
tología Vertebrados, Río Gallegos, Argentina.
Materials
Propalaehoplophoridae cf. Asterostemma depressa Ame-
ghino, 1889. MACN A-7663, partial cranium; locality: Ca-
ñadón Jack Harvey, Santa Cruz Province, Argentina; stratig-
raphy: Santa Cruz Formation (latest Early Miocene).
Cochlops muricatus Ameghino, 1889. MPM-PV 3420,
cranium, partial skeleton, and carapace; locality: Puesto Es-
tancia La Costa (= Corriguen Aike), Santa Cruz Province,
Argentina; stratigraphy: Fossiliferous Level (FL) 5.3 (Tauber,
1997), Santa Cruz Formation (latest Early Miocene). MPM-
PV 3432, partial cranium (including maxilla with dentition,
and left hemimandible), fragment of carapace; locality: An-
teatro, Santa Cruz Province, Argentina; stratigraphy: Santa
Cruz Formation (latest Early Miocene).
Eucinepeltus petesatus Ameghino, 1891. MACN A-4758,
complete cranium and mandible; locality: Monte Observa-
ción, Santa Cruz Province, Argentina; stratigraphy: Santa
Cruz Formation (latest Early Miocene). MACN A-4760:
left hemimandible; locality: Monte Observación, Santa Cruz
Province, Argentina; stratigraphy: Santa Cruz Formation
(latest Early Miocene).
Propaleohoplophorus incisivus Ameghino, 1887a. MACN
A-7655, cranium; locality: Corriguen Aike, Santa Cruz
Province, Argentina; stratigraphy: Santa Cruz Formation
(latest Early Miocene). MACN A-7656: partial cranium;
locality: Corriguen Aike, Santa Cruz Province, Argentina;
stratigraphy: Santa Cruz Formation (latest Early Miocene).
Propalaehoplophorus minus Ameghino, 1891. MACN
A-4757, right hemimandible; locality: Corriguen Aike, San-
ta Cruz Province, Argentina; stratigraphy: Santa Cruz For-
mation (latest Early Miocene).
Propalaehoplophorus australis Ameghino, 1887a. MLP
16-15, cranium, mandible, and skeleton; locality: Santa
Cruz Province, Argentina; stratigraphy: Santa Cruz Forma-
tion (latest Early Miocene); gured in Lydekker (1894, 3,
Pl. 32).
Propalaehoplophorus sp. MACN-A 4754, cranium; lo-
cality: Corriguen Aike, Santa Cruz Province, Argentina;
stratigraphy: Santa Cruz Formation (latest Early Miocene).
AMEGHINIANA, Tomo 48 (3): 305 - 319
Figure 2. Skulls in lateral and frontal views of some specimens of the glyptodonts studied/ cráneos en vista lateral y frontal de algunos especimenes
de los gliptodontes estudiados. 1, MLP 16-15 Propalaehoplophorus australis. 2, MLP 24 Neosclerocalyptus sp. 3, MLP 16-29 Panochthus tuberculatus. 4,
MLP 16-24 Doedicurus clavicaudatus. 5, MLP 16-41 Glyptodon sp. (taken from Lydekker, 1894). Escala/scale bar: 200 mm
1 2 3 4 5
309
MPM-PV 3419, complete mandible and partial carapace;
locality: Puesto Estancia La Costa (= Corriguen Aike), Santa
Cruz Province, Argentina; stratigraphy: Fossiliferous Level
(FL) 6 (Tauber, 1997), Santa Cruz Formation (latest early
Miocene). MPM-PV 3422, partial cranium (anterior part)
with dentition and complete right mandible, humerus, par-
tial scapula, other fragments of skeleton, and isolated os-
teoderms; locality: Puesto Estancia La Costa (= Corriguen
Aike), Santa Cruz Province, Argentina; stratigraphy: Fossil-
iferous Level (FL) 5.3 (Tauber, 1997), Santa Cruz Formation
(latest early Miocene).
Glyptodon reticulatus Owen, 1845. MACN-Pv 10153,
cranium and mandible of a sub-adult specimen; locality:
Río Luján, Buenos Aires Province; stratigraphy: “Pampeano
Formation (Pleistocene).
Glyptodon munizi Ameghino, 1881. MACN-Pv 8706,
complete cranium and mandible; locality: Cauce del Río de
La Plata, Vicente López, Buenos Aires Province, Argentina;
stratigraphy: Ensenada Formation (early Pleistocene).
Glyptodon sp. MACN Pv-2908, complete cranium and
mandible; locality: unknown; stratigraphy: “Pampeano
Formation (Pleistocene). MLP 16-41, cranium, mandible,
and skeleton; locality: Olivera, Buenos Aires Province; stra-
tigraphy: “Pampeano Formation (Pleistocene); gured in
Lydekker (1894, 3, Pl. 5).
Eosclerocalyptus planus (Rovereto, 1914). MACN-Pv
4853, cranium; locality: La Hoyada, Catamarca Province, Ar-
gentina; stratigraphy:Araucanian” (late Miocene–Pliocene).
Urotherium antiquum Castellanos, 1926. MACN A-229,
partial cranium and partial mandible; locality: Monte Her-
moso clis, Buenos Aires Province, Argentina; stratigraphy:
Monte Hermoso Formation (early Pliocene).
Hoplophractus proximus (Moreno and Mercerat 1891).
MLP 31-X-12-19, cranium; locality: Corral Quemado,
Catamarca Province, Argentina; stratigraphy: “Araucanian”
(late Miocene–Pliocene).
Figure 3. Upper tooth series of glyptodonts / series molares superiores de gliptodontes. 1, Cochlops muricatus (MPM-PV 3432). 2, Neosclerocalyptus
sp. MACN Pv-8579. 3, Glyptodon reticulatus (MACN-Pv 10153).
1 2 3
VIZCAÍNO et al.: ECOMORPHOLOGY OF GLYPTODONTS
310
Neosclerocalyptus paskoensis Zurita 2002. MACN
18107, cranium and mandible; locality: Carhué, Buenos Ai-
res Province, Argentina; stratigraphy: “Pleistocene”.
Neosclerocalyptus sp. MACN Pv-8579, complete cranium;
locality: Toscas” del Río de la Plata, Olivos, Buenos Aires
Province, Argentina; stratigraphy: Ensenada Formation (ear-
ly Pleistocene). MACN Pv-8091, complete cranium; local-
ity: Mar del Plata, Buenos Aires Province, Argentina; stra-
tigraphy: Ensenadan (early Pleistocene). MACN Pv-15151,
cranium; locality: unknown; stratigraphy: unknown.
Doedicurus sp. MACN Pv-2762, complete cranium and
mandible; locality: Río Salado, Buenos Aires Province, Ar-
gentina; stratigraphy: Lujanian (late Pleistocene–early Ho-
locene). MACN Pv-15153, complete cranium; locality: Ar-
royo Tapalqué, Olavarría, Buenos Aires Province, Argentina;
stratigraphy: “Pampeano” Formation (Pleistocene).
Panochthus tuberculatus Owen, 1839. MLP 16-29, cra-
nium and mandible, skeleton, carapace, and caudal tube;
locality: Tapalqué, Buenos Aires Province, Argentina; stra-
tigraphy: “Pampeano Formation (Pleistocene); gured in
Lydekker (1894, 3, pls. 22–23).
Panochthus intermedius Lydekker, 1894. MLP 16-37,
cranium, mandible, skeleton and caudal tube; locality: un-
known; stratigraphy: unknown.
Panochthus sp. MLP P-1, cranium and mandible; locality:
unknown; stratigraphy: unknown.
Neuryurini cf. Neuryurus sp. MLP 16-151, cranium and
mandible; locality: Monte Hermoso, Buenos Aires Province,
Argentina; stratigraphy: Monte Hermoso Formation (early
Pliocene); gured in Lydekker (1894, 3, pl. 8, g. 2).
is sample represents a wide size and temporal range of
glyptodonts, at least with respect to the skull and mandible.
METHODS
Following previous research in Pleistocene ground sloths
(Bargo et al., 2006a, b; Vizcaíno et al., 2006; Bargo and
Vizcaíno, 2008), the ecomorphological analyses performed
here include estimation of body mass, relative muzzle-width
index (RMW), hypsodonty index (HI), and dental occlusal
surface area (OSA).
Body masses (BM) were assigned by the following crite-
ria. For each specimen, a published estimate was preferred
when available. When published estimates were not available
for a particular specimen, a body size estimate was obtained
assuming a geometric similarity among dierent sizes, where
overall size was based on the total length of the upper tooth
row. However, if there was a published body mass estimate
for a close relative (either at the species or genus level), geo-
metric similarity was calculated in comparison with the spec-
imen used for the published mass estimations. For specimens
where there is no body mass estimation published even for
close relatives (Urotherium, Hoplopractus and Eosclerocalyp-
tus), we used an average mass value obtained by assuming
geometric similarity among specimens belonging to every
genus with published mass estimations (Tab. 1).
e RMW was calculated following Janis and Ehrhardt
(1988) for ungulates, as palatal width (PW) divided by max-
imum muzzle width (MMW). Following these authors, the
width of the palate is correlated with the rate of food inges-
tion. High values of this ratio indicate selective feeders with
narrow muzzles. In ungulates, MMW was measured at the
premaxillo-maxillary suture and PW is the distance between
the M2 protocones (Janis and Ehrhardt, 1988; Janis, 1990).
Because the premaxillae are reduced in glyptodonts, as in
ground sloths, MMW is generally on the maxilla only, and
this variable was measured following Bargo et al. (2006b) as
the distance between labial alveolar margins of rst molari-
forms. PW was measured between the lingual alveolar mar-
gins of central lobe of the fourth molariform, where the pal-
ate is narrowest in glyptodonts. e values obtained cannot
be compared directly with those for ungulates, because the
obviously dierent phylogenetic constraints in each group
and the lack of clear homology in the landmarks used; how-
ever, they provide a framework for comparison among xen-
arthrans, especially glyptodonts.
e HI was calculated as depth of mandible (DM) di-
vided by length of molariform tooth row (LTR), as used by
Bargo et al. (2006a) for ground sloths. Xenarthran specialists
have agreed that the relative increase in depth of the jaw in
sloths reects increased hypsodonty (Bargo et al., 2006a and
references therein); the same applies for glyptodonts. In this
case, depth of the mandible was measured at the sixth molari-
form, where this variable presents its maximum value, instead
of at the third molariform as used by Bargo et al. (2006a).
e OSA was evaluated following Vizcaíno et al. (2006)
as the total cheek-tooth occlusal surface area, considering the
infolding contour of the tooth. Vizcaíno et al. (2006) ap-
proached this problem considering OSA as the two-dimen-
sional projection of a three-dimensional structure, using dig-
ital photos of the occlusal surfaces of the upper cheek-tooth
rows. Herein we use a Microscribe G2 to digitize the three-
dimensional contour and inner osteodentine crests of each
upper molariform. e data-points obtained were converted
to a mesh-surface to calculate the area with Rhinoceros 4.0
AMEGHINIANA, Tomo 48 (3): 305 - 319
311
VIZCAÍNO et al.: ECOMORPHOLOGY OF GLYPTODONTS
Catalogue number Taxa RMW HI OSA Body mass Source body mass
MACN-A 7663 cf. Asterostemma depressa 0.726 375.9335 78.13 Vizcaíno et al., 2006
MPM-PV 3420 Cochlops muricatus 0.655 340.3753 79.27 GS- MLP 16-15
MPM-PV 3432 Cochlops muricatus 0.655 0.434 303.4343 86.71 GS-MLP 16-15
MACN-A 4758 Eucinepeltus petesatus 0.710 0.362 457.4104 115.00 Croft, 2000
MACN-A 4760 Eucinepeltus petesatus 0.362
MPM-PV 3419 Propalaehoplophorus sp. 0.398
MPM-PV 3422* Propalaehoplophorus sp. 0.778 0.403
MACN-A 7655 Propalaehoplophorus incisivus 0.752 314.1836 74.49 GS-MLP 16-15
MACN-A 7656 Propalaehoplophorus sp. 0.820 332.1412 77.98 GS-MLP 16-15
MACN-A 4757 Propalaehoplophorus minus 0.361
MACN-A 4754 Propalaehoplophorus australis 365.0685 93.48 GS-MLP 16-15
MLP 16-15 Propalaehoplophorus australis 0.745 0.427 330.1710 81.10 De Esteban-Trivigno et al., 2008
MACN-A 10153 Glyptodon reticulatus 0.714 0.415 1590.3930 819.04 GS-MACN 200**
MACN-A 8706 Glyptodon munizi 0.664 0.438 1950.1597 1150.05 GS-MACN 200
MACN-A 2908 Glyptodon sp. 0.631 0.384 1886.9831 968.03 GS-MACN 200
MLP 16-41 Glyptodon sp. 0.656 0.406 1590.5900 831.90 GS-MACN 200
MACN-A 4853 Eosclerocalyptus lilloi 0.540 621.6683 185.73 Mean GS
MACN-A 229 Urotherium antiquus 0.564 833.2613 326.41 Mean GS
MLP 31-X-12-19 Hoplophractus proximus 0.577 769.9640 221.83 Mean GS
MACN-A 18107 Neosclerocalyptus paskoensis 0.491 0.422 1302.1728 574.53 GS-MLP 16-28
MACN-A 8579 Neosclerocalyptus sp. 0.583 859.8465 383.99 GS-MLP 16-28
MACN-A 8091 Neosclerocalyptus sp. 0.485 1092.6327 485.40 GS-MLP 16-28
MACN-A 15151 Neosclerocalyptus sp. 1292.6393 507.44 GS-MLP 16-28
MLP 16-28 Neosclerocalyptus ornatus 1276.1900 598.30 Vizcaíno et al., 2006
MACN-A 2762 Doedicurus sp. 0.522 0.530 1812.2203 1547.20 GS-MLP 16-24***
MACN-A 15153 Doedicurus sp. 0.509 1759.2136 1215.54 GS-MLP 16-24
MLP P-1 Panochthus sp. 0.538 0.428 1101.63 GS-MLP 16-29
MLP 16-29 Panochthus tuberculatus 0.527 0.488 2578.5900 1061.00 Fariña et al., 1998
MLP 16-37 Panochthus intermedius 0.488 0.427 1157.40 GS-MLP 16-29
MLP 16-151 cf. Neuryurus sp. 0.484 0.447 1119.1010 311.00 Vizcaíno et al., 2006
* Some specimens do not have body mass estimate because the upper dentition is incomplete or they are only mandibles / Algunos especímenes
no poseen estimaciones de masa corporal porque la dentición superior está incompleta o son solo mandíbulas.
**MACN-A 200 Glyptodon reticulatus (862.00 kg, Fariña et al., 1998).
*** MLP 16-24 Doedicurus clavicaudatus (1468.00 kg, Fariña et al., 1998).
GS-catalogue number: geometric similarity with a fossil taxon with body mass estimate /similitud geométrica con un taxón fósil que posee esti-
mación de masa corporal.
Mean-GS: mean of body mass, obtained assuming geometric similarity to specimens belonging to every genus with published mass estimates /
media de la masa corporal obtenida asumiendo similitud geométrica con especímenes de cada género con estimación de masa édita.
Table 1. Relative muzzle width index (RMW), hypsodonty index (HI), tooth occlusal surface area (OSA), and body mass estimates and their
sources / índice del ancho relativo del hocico (RMW), índice de hipsodoncia (HI), área de la supercie oclusal dentaria (OSA) y estimaciones
de masa corporal y sus fuentes.
312
AMEGHINIANA, Tomo 48 (3): 305 - 319
software. When OSA values obtained with this method are
contrasted with those obtained on the same specimens by
Vizcaíno et al. (2006), the absolute value (modulus) of the
mean dierence obtained is of only 38 mm
2
(i.e., less than
5%). us, we consider our results to be comparable with
those of Vizcaíno et al. (2006).
e allometric relationship between OSA and BM was
assessed following Vizcaíno et al. (2006), calculating the re-
gression lines by the least-squares method, using log trans-
formed OSA as the dependent variable and log transformed
BM as the independent variable. Deviation of the observed
slope from the predicted slope of isometry and from the pre-
dicted slope given by Kleibers (1932) law (0.66 and 0.75
respectively) was tested by two-tailed Student’s t statistic.
Residuals from the regression (size independent OSA) was
plotted against both HI and RMW.
RESULTS
Body mass estimates RMW, HI, and OSA values are
summarized in Table 1. Figure 4 shows RMW and HI for
the specimens studied. Values of RMW close to 1 or 0 indi-
cate more selective-feeding or more bulk-feeding specializa-
tion respectively. Using 0.6 as a threshold value of RMW,
two main groups can be dened. Propalaehoplophorids plus
Glyptodon have values above 0.6, with Propalaehoplophorus
showing the highest values. e remaining genera all fall be-
low 0.6, with cf. Neuryurus and two Neosclerocalyptus speci-
mens showing the lowest values. Higher values of HI indicate
greater hypsodonty. Although there is no clear threshold,
0.44 is a tentative boundary between high and low hypso-
donty. In our sample there were no mandibles of cf. Aster-
ostemma, Urotherium, and Hoplophractus complete enough
to obtain HI. For the remaining genera there was only one
mandible for each, except for Glyptodon. While this fact lim-
its the extent of the predictions to be made, some facts can
be addressed. Propalaehoplophorids, Glyptodon, and Neo-
sclerocalyptus show values lower than 0.44, with Eucinepeltus
showing the lowest and Glyptodon values ranging from 0.38
to 0.44. Among the high values of cf. Neuryurus, Doedicu-
rus, and Panocthus, the highest are those of Doedicurus (0.53).
HI discards by itself a potential size-eect on the degree of
hypsodonty, a detail readily evident by the fact that the large
Glyptodon again clusters with the propalaehoplophorids.
When RMW was plotted against HI (Fig. 5), a general
pattern emerges: glyptodonts with low RMW have high
values of HI and vice versa. Among the glyptodonts with
RMW below 0.6, Doedicurus has the highest HI followed
by one specimen of Panochthus. e remaining specimens of
the latter show moderate HI (between 0.42 and 0.44), over-
lapping with some narrow-muzzled glyptodonts (Glyptodon,
Cochlops, and Propalaehoplophorus). Among the narrow-
muzzled glyptodonts, Eucinepeltus has the lowest HI.
Figure 6 shows the distribution of taxa around the re-
gression line of OSA against body mass and the residuals of
regression analysis plotted against RMW and HI. Statistical
parameters for the new regression equation for log OSA and
body mass are shown in Table 2. e observed slope is not
signicantly dierent from the isometry slope, but it is dif-
ferent from that expected based on Kleiber’s (1932) law of
metabolism. Most taxa fall on or close the regression line.
Panochthus and cf. Neuryurus lie above the regression line
Figure 4. Graphic distribution of relative muzzle width index (RMW)
and hypsodonty index (HI) of the specimens studied /distribución
gráca del índice del ancho relativo del hocico (RMW) y el índice de hip-
sodoncia (HI) de los especímenes estudiados.
313
whereas Doedicurus lies below, indicating higher and lower
values than expected for their body masses respectively. e
residuals show that the genera that depart from expected val-
ues of OSA (i.e., those for which the residual modulus is
greater than 0.06) have the lowest RMW and the highest
HI. e only exception is Cochlops, which has intermediate
values.
DISCUSSION
is ecomorphological approach, previously applied to
other xenarthrans (Bargo and Vizcaíno, 2008), allows eluci-
dating of paleobiological hypotheses and provides a interest-
ing preliminary insight to the evolution of the masticatory
apparatus in glyptodonts.
It seems quite evident that the RMW by itself allows
distinguishing two main groups of glyptodonts based on
their inferred feeding behavior. In general, the small-sized
early Miocene propalaehoplophorids are narrow-muzzled
forms, while the larger post-Miocene forms developed wider
muzzles. e fact that smaller glyptodonts have lower RMW
than larger ones relies on the allometric relationships between
the two variables (MMW and PW) involved in the index
and body mass. On the one hand, decimal log-transformed
PW shows a positive correlation with log transformed body
mass (R
2
=0.89, F(1, 19)= 152.67), , with an isometric trend
(slope=0.2994) not signicantly dierent from theoretical
0.333 for isometry (t(19)=1.3992 p=0.089). On the other
hand, log-transformed MMW shows signicant positive
correlation with log-transformed body mass (R2=0.97, F(1,
19)=649.41), with a positive allometric trend (slope=0.38397)
signicantly higher than the theoretical 0.333 (t(19)=3.3605,
p=0.0016).
Even more, considering only MMW, the positive allo-
metric trend indicates that larger glyptodonts have propor-
VIZCAÍNO et al.: ECOMORPHOLOGY OF GLYPTODONTS
Figure 5. Plot of relative muzzle width index (RMW) against hypsodonty index (HI) / gráca de índice del ancho relativo del hocico (RMW) y el índice
de hipsodoncia (HI)
314
tionately wider muzzles than the smaller ones. Consequently,
propalaehoplophorids were probably more selective-feeders
while the larger post-Miocene forms were bulk-feeders to a
greater degree. A remarkable exception is the large Pleistocene
Glyptodon, whose muzzle is relatively as narrow as in propal-
aehoplophorids. Propalaehoplophorids are considered a basal
clade and Glyptodon a more derived taxon (Fernicola, 2008;
Porpino et al., 2010); this implies a reversion to selective feed-
ing behavior.
e validity of HI as an indicator of feeding habits has
been discussed recently, especially for ungulates, and there
seems to be a consensus that hypsodonty correlates to forag-
ing in open habitats more than indicating the sort of food
items eaten (Mendoza and Palmqvist, 2008, and references
therein). An increase in total masticatory eort has been also
evoked as a cause for increasing tooth wear (and increasing
hypsodonty) in hypsodont mammals (Williams and Kay,
2001; Billet et al., 2009), associated not only with the inges-
tion of abrasive elements, but also with food of low nutri-
tive value that must be ingested in large quantities (Williams
and Kay, 2001; Sanson, 2006; Strömberg, 2006) and tougher
plants or plant parts that require investing more energy in
chewing (Pérez-Barbería and Gordon, 1998). Janis (1988)
and Mendoza and Palmqvist (2008) demonstrated that high-
crowned teeth in ungulates represent an adaptation to resist
tooth wear resulting from the airborne grit and dust accumu-
lated on herbaceous plants in open environments.
Regarding xenarthrans, the use of HI was applied by Mc-
Donald (1995) for North American mylodontine ground
sloths and more recently to South American ground sloths by
Bargo et al. (2006a). e latter extensively discussed the sub-
ject and suggested that dierences in crown height in fossil
sloths may be explained by a combination of variables (rather
than any single one), including dietary preferences (e.g., food
quality), habitat (closed or open, temperate or tropical) and
behavior (feeding at ground level or higher, digging). In the
case of glyptodonts, it is also dicult to interpret the indi-
vidual dierences in HI.
e relation between RMW and HI allows us to infer
feeding niche-partitioning among glyptodonts. is method
improves upon the preliminary hypothesis proposed by Viz-
caíno (2000) for Pleistocene cingulates. Interestingly, these
variables also allowed us to discriminate feeding niches be-
tween Pleistocene ground sloths although in a dierent way:
bulk-feeders (Lestodon Gervais, 1855, and Glossotherium
Owen, 1839) are less hypsodont than the selective-feeders
(Megatherium Cuvier, 1796, and Scelidotherium Owen, 1839)
(Bargo and Vizcaíno, 2008). is is probably related to dier-
ences in feeding physiology (see below).
When RMW and HI are interpreted together in our
analysis (Fig. 5), a general relationship between these traits
becomes apparent. is suggests that selective-feeders and
bulk-feeders have a lesser and a greater degree of hypsodonty
respectively. e small latest early Miocene propalaehoplo-
phorids would have been selective feeders that required a
moderate chewing eort; among them, Eucinepeltus and
Propalaehoplophorus are inferred to have been more selective
in their feeding behavior than Cochlops was. e latter two
genera likely preferred more open environments than the rst
one. Consequently, Eucinepeltus would have been a highly
selective-feeder in relatively closed environments, Propalae-
hoplophorus a highly selective-feeder in moderately open habi-
Table 2. Results of simple linear regression of OSA vs body mass. Coecient of determination (R
2
) and estimators of regression coecients are
in bold. Dierences between the observed slopes and the predicted slope of isometry (2/3) were not signicant in both regressions (p < 0.05).
Dierences between the observed slopes and the predicted slope given by Kleiber´s law (0.75) were signicant except in the regression tagged
by an asterisk (p = 0.05) / Resultados de las regresiones lineales simples de OSA vs. masa corproral. Coeciente de determinación (R
2
) y
estimadores de los coecientes de regresión indicados en negrita. Las diferencias entre las pendientes observadas y la esperada para
isometría (2/3) fueron no signicativas en ambas regresiones (p < 0.05). Las diferencias entre las pendientes observadas y las esperadas a
partir de la ley de Kleiber (0.75) fueron signicativas, excepto en la regresión marcada por un asterisco (p = 0.05).
Taxa Range of n Nº of R2 Std. error Intercept Std. error Slope Std. error Isometry Kleibers
W (kg) genera estimate at W=1 kg t(n-2) law t(n-2)
Glyptodontia
Vizcaíno et al., 73.40 - 1061 10 7 0.955 0.0788 1.182 0.14276 0.729 0.05626 1.1116 -0.3697
(2006) ± 0.1113
Glyptodontia
This article 74.49 - 1547 24 12 0.966 0.058 1.291 0.06606 0.6563 0.02611 -0.3966 -3.5887*
± 0.0541
AMEGHINIANA, Tomo 48 (3): 305 - 319
315
tats, and Cochlops a less selective-feeder in moderately open
habitats. Pliocene and Pleistocene forms seem to reverse this
pattern, the smallest forms like cf. Neuryurus and Neosclero-
calyptus having narrower muzzles and being less hypsodont
than the largest forms, suggesting bulk-feeding in relatively
open environments. e largest forms Panochthus and Doedi-
curus are more hypsodont, suggesting bulk-feeding in open
environments, and probably required a high masticatory ef-
fort. e narrow muzzle and low hypsodonty of Glyptodon
suggest more selective-feeding and a better performance in
closed habitats. Interestingly, with the exception of Glypto-
therium Osborn 1903, recently recorded in Venezuela as a
possible migrant from North America (Carlini et al., 2008),
Glyptodon is the only large South American glyptodont rep-
resented in northern South America (see Carlini et al., 2008,
and references therein). erefore, it is possible to hypoth-
esize that the extensive closed environments present during
the Plio-Pleistocene in at least a great part of northern South
America (Clapperton, 1993; Cione et al., 2003) did not act
as a geographical barrier for its dispersal. However, because
Glyptodon is frequently recorded in the same formations as
the others, an alternative interpretation is that it had a dif-
ferent feeding behavior, browsing on specic plants or plant
parts higher o the ground; perhaps it had a more specialized
physiology. We could not calculate HI for the late Miocene
and Pliocene glyptodonts in our sample, Hoplophractus, Eo-
sclerocalyptus and Urotherium. However, assuming the above
mentioned relationship between RMW and HI, these forms
are interpreted as bulk-feeding inhabitants of moderately
open habitats —occupying a position intermediate between
the groups constituted by cf. Neuryurus, Neosclerocalyptus,
Panochthus, and Doedicurus, on the one hand, and the propa-
laehoplophorids and Glyptodon on the other.
Phylogeny is ambiguous (see Fig. 1) in establishing the
ancestral habitat of the studied glyptodonts. However, it
seems plausible to assume that it was not frankly open, if the
habitat inferred for the oldest forms —the propalaehoplo-
phorids— is considered. If our assumption about the habitat
of Hoplophractus, Eosclerocalyptus, and Urotherium is correct,
it would lead us to reconstruct the ancestral habitat for
Panochthus and Doedicurus as a moderately open one. How-
ever, as they do not share a close phylogenetic relationship, we
must infer “habitat convergence” in the ancestors of Doedi-
curus and Panochthus. e previous assumption also implies
a moderately open ancestral habitatfor Glyptodon, which
leads us to infer for this genus a “habitat reversionto more
closed conditions similar to the habitat of the propalaehoplo-
phorids. Alternatively, as mentioned above, it may have had
specic dierent feeding behavior or physiology.
ese conclusions about glyptodont habitats are consis-
tent with the general picture of environmental evolution dur-
ing the Cenozoic in South America. For instance, Pascual and
Ortiz-Jaureguizar (1990) stated that during the latest Ceno-
zoic, many xenarthrans (in addition to ungulates and various
gigantic native rodents) followed a similar dental modica-
tion pattern, from low-crowned to high-crowned teeth. is
instance of dental evolution was likely a response to a shift
from predominantly closed-forested, warm and wet habitats
to open temperate grasslands, followed by a shift toward hot
deserts or cold habitats. More recently, Ortiz-Jaureguizar and
Cladera (2006) summarized paleoenvironmental changes in
southern South America (SSA) during the Cenozoic. ese
changes were inferred mainly from dental adaptations in
mammalian faunas, but also from evidence drawn from oral
VIZCAÍNO et al.: ECOMORPHOLOGY OF GLYPTODONTS
Figure 6. Regression of occlusal surface area (OSA) against body mass,
and the residuals of regression analysis plotted against RMW and HI /
regresión del área de la supercie oclusal (OSA) contra la masa corporal y
residuos del análisis de regresión gracado contra RMW y HI.
316
successions, diastrophism, and sedimentology. ey pointed
out that the record of land-mammals in SSA suggests a large-
scale succession of climates: from the early Paleocene to the late
Pleistocene, the overall trend of environmental change moved
from more equable to less equable conditions. In other words,
climates changed from warm, wet, and non-seasonal, to cold,
dry, and seasonal. Concomitantly, biomes transformed from
tropical forests to steppes, with the following intermediate
stages: subtropical forest, woodland-savanna, park-savanna,
and grassland-savanna. During the Quaternary, glacial cycles
caused cold, dry climates interrupted by warmer and wetter
intervals. Accordingly, several pulses of expansion and retrac-
tion of steppes (and, concomitantly, advances and retreats of
the northern tropical forests) have been recorded. is cyclic
pattern of changes produced the provincialism that character-
ized the South American biota from the early Pleistocene to
the present day.
Another aspect to consider is that despite some ability
to adopt bipedal postures proposed for glyptodonts (Fariña,
1995; Vizcaíno et al., 2011), all glyptodonts would have need-
ed to forage mostly near the ground because of their body
form and fusion of the cervical vertebrate. Hence, they may
have been conned to a very narrow feeding-zone regarding
access to vegetation. is would result in greater competition
among glyptodonts than among other xenarthrans such as
ground sloths. e latter would have had access to a greater
variety of vegetation at dierent levels o the ground. Also,
it may explain glyptodont diversity in a fauna with only one
type of glyptodont per ecological niche.
e relation between OSA and body mass agrees in gen-
eral with the results of Vizcaíno et al. (2006) stating that
glyptodonts, like other xenarthrans, have less OSA avail-
able for triturating food than other placentals of similar size.
However, probably because of the small sample available in
Vizcaíno et al. (2006), slope values for both dasypodids and
glyptodontids had a wide 95% condence interval that in-
cludes the predicted slopes of isometry (0.67) or of Kleiber´s
law (0.75). The results of our more inclusive sample allow us
to reject a slope of 0.75 for glyptodonts. Vizcaíno et al. (2006)
related the smaller OSA to the low basal metabolic rates char-
acteristic of living xenarthrans, which fall between 40 and 60
percent of the rates expected from mass in Kleiber’s (1932)
relation for placental mammals (McNab, 1985). is sug-
gests that xenarthrans have lower energetic requirements than
other placental mammals and, therefore fewer requirements
for a specic type of food; they can survive with lower intake
rates than other placental herbivorous mammals of similar
body mass. Vizcaíno et al. (2006) also found that, within xen-
arthrans, cingulates have higher OSA values than some tardi-
grades, suggesting a greater food processing in the oral cavity.
Particularly, the extremely low OSA of mylodontid ground
sloths was interpreted as indicating low eciency in oral food
processing, probably compensated by high fermentation in
the digestive tract (Vizcaíno et al., 2006). is may explain
the lower HI of wide-muzzled sloths mentioned above.
e major deviations from the correlation between OSA
and body mass are recorded in post-Miocene glyptodonts,
particularly the Pleistocene mega-mammals (i.e., adult body
mass above 1000 kg., see discussion in Vizcaíno et al., in
press). While Glyptodon specimens fall on the regression line,
meaning that they have the OSA expected for glyptodonts of
their size, Panochthus lies well above the regression line and
Doedicurus lies well below, indicating higher and lower values
than expected for their body masses respectively. is sug-
gests that these two forms followed divergent evolutionary
pathways.
Vizcaíno et al. (2006) suggested that a reduction in OSA
can be compensated by an increase in tooth lobation or
the extension of hard osteodentine crests. In general, pam-
patheres seem to have higher OSAs, less complex lobation,
fewer ridges, and less shearing surfaces than glyptodonts. e
relationships among these three variables among glyptodonts
remain to be tested.
CONCLUSIONS
e results provided by this ecomorphological approach
allow us to infer habitat and dietary habits of several taxa
of glyptodonts, improving the preliminary hypothesis pro-
posed by Vizcaíno (2000). Additionally, it is possible to infer
possible niche dierentiation among the taxa that lived in
the same general habitat.
e Relative Muzzle Width Index (RMW) allows distin-
guishing two main groups among glyptodonts based on their
feeding behavior, i.e., the small-sized early Miocene propa-
laehoplophorids were selective-feeders, whereas the larger
post-Miocene forms were more like bulk-feeders. e large
Pleistocene Glyptodon, with a relatively narrow muzzle as in
propalaehoplophorids, appears to be an exception implying
—from a phylogenetic point of view— a reversion to a selec-
tive feeding behavior.
e dierences recorded in the Hypsodonty Index (HI)
between the studied specimens are dicult to interpret when
the index is considered alone. However, together with RMW
it did allow us to infer feeding niche partitioning. Among
AMEGHINIANA, Tomo 48 (3): 305 - 319
317
the early Miocene propalaehoplophorids, Eucinepeltus would
have been a highly selective-feeder of relatively closed en-
vironments, Propalaehoplophorus a highly selective-feeder in
moderately open habitats, and Cochlops a less selective-feeder
in moderately open habitats. Among the larger Pliocene and
Pleistocene taxa, the smallest forms (cf. Neuryurus and Neo-
sclerocalyptus) were probably bulk-feeders in relatively open
environments, while the largest (Panochthus and Doedicurus)
were clearly bulk-feeders in open environments.
Two alternative interpretations can be oered in the
case of Glyptodon, i.e., it was a more selective-feeder in more
closed habitats, or it had a dierent feeding behavior, brows-
ing on specic plants or plant parts higher above the ground,
or perhaps it had unknown physiological specializations. e
late Miocene and Pliocene forms (Hoplophractus, Eoscleroca-
lyptus, and Urotherium) were probably intermediate between
the Miocene and the Pleistocene ones.
Finally, the relation between tooth Occlusal Surface Area
(OSA) and body mass agrees with the results of Vizcaíno et
al. (2006) stating that glyptodonts, like other xenarthrans,
have lower energetic requirements than other placental
mammals and, therefore, can survive with lower intake rates
than other placental herbivores of similar body mass.
ACKNOWLEDGMENTS
e authors acknowledge the following persons for access to collections: M.
Reguero (Museo de La Plata), A. Kramarz (Museo Argentino de Ciencias
Naturales “Bernardino Rivadavia”, Buenos Aires), and A. Tauber (Museo
Regional Provincial P.M.J. Molina, Río Gallegos). To J. M. Perry for a criti-
cal review of the manuscript. To the reviewers, Greg McDonald and Rich-
ard Fariña, for their interesting suggestions that enriched the discussion.
is is a contribution to projects PIP-CONICET 1054, PICT 0143, and
UNLP N 647.
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doi: 10.5710/AMGH.v48i2(364)
Recibido: 23 de febrero de 2010
Aceptado: 26 de noviembre de 2010
... However, glyptodonts can present a set of unique traits that makes them stand out from all other mammals, including defensive tail weaponry, large size, and, specifically, a highly modified skull. The glyptodont skull has undergone a particular process of telescoping in which the rostrum is ventrally expanded, and the tooth row is posteriorly extended, resulting in a structure with unprecedented biomechanical proprieties among mammals [12,13]. Because of this unique morphology, glyptodonts' phylogenetic position has been historically uncertain. ...
... Because Cingulata shows a proportionally shorter generation time than the linear trend for all mammals, we subtracted a constant to correct for that difference (electronic supplementary material, figure S2). Given that Glyptodon body mass estimates can vary, ranging from 819 kg to 2000 kg [13,22], we calculated generation times for these extreme values. This resulted in generation times estimates ranging from 3.8 to 4.6 years, consistent with generation times for large ungulates [21,23]. ...
... The most straightforward explanation for this is that glyptodonts invaded a new adaptive zone fuelled by a drastic change in ecology. Glyptodonts are thought to be highly specialized herbivores, a diet with strong functional demands [13]. These demands were then responsible for imposing a strong directional selection, leading to radical morphological change and functional innovation seen in this group [12]. ...
Article
The prevalence of stasis on macroevolution has been classically taken as evidence of the strong role of stabilizing selection in constraining morphological change. Rates of evolution calculated over longer timescales tend to fall below the expected under genetic drift, suggesting that directional selection signals are erased at longer timescales. Here, we investigated the rates of morphological evolution of the skull in a fossil lineage that underwent extreme morphological modification, the glyptodonts. Contrary to what was expected, we show here that directional selection was the primary process during the evolution of glyptodonts. Furthermore, the reconstruction of selection patterns shows that traits selected to generate a glyptodont morphology are markedly different from those operating on extant armadillos. Changes in both direction and magnitude of selection are probably tied to glyptodonts' invasion of a specialist-herbivore adaptive zone. These results suggest that directional selection might have played a more critical role in the evolution of extreme morphologies than previously imagined.
... This group includes medium to very large forms, some of them approaching ca. two tons (i.e., Doedicurus; Vizcaíno et al. 2011;Soibelzon et al. 2012). Records of Pliocene and Pleistocene Glyptodontidae extend into Central and North America, demonstrating that the group successfully participated in the Great American Biotic Interchange (Woodburne 2010;Gillette et al. 2016;Zurita et al. 2018). ...
... This lack of fossils during the earliest stages has been interpreted as evidence of a possible rapid evolution from an "armadillo-like" ancestor (see Mitchell et al. 2016). Coincident with this possible early radiation, southern South America experienced a progressive tendency towards more open biomes during the late Eocene-Oligocene (Iglesias et al. 2011), concordant with the interpretation of glyptodonts as grazing herbivores (Vizcaíno et al. 2011). More precisely, the late Oligocene-early Miocene period was characterized by the presence of shrub-herbaceous elements, which began to give a modern appearance to vegetation communities (Barreda and Palazzesi 2007). ...
... Anatomical evidence suggests the existence of some kind of niche partitioning among early to middle Miocene "Propalaehoplophorinae", with Cochlops more adapted to open paleoenvironments than Propalaehoplophorus and Eucinepeltus (see Vizcaíno et al. 2011). In this framework, it is interesting to note that the length of the caudal tube of Mayoan middle Miocene "Palaehoplophorini" (Mayoan SALMA) resembles that of more modern taxa but retains some primitive characteristics, such as an absence of ornamentation. ...
Article
Full-text available
Glyptodonts (Xenarthra, Cingulata) are one of the most amazing Cenozoic South American mammals, with some terminal forms reaching ca. two tons. The Paleogene record of glyptodonts is still poorly known, although some of their diversification is observable in Patagonian Argentina. Since the early and middle Miocene (ca. 19–13 Ma), two large clades can be recognized in South America. One probably has a northern origin (Glyptodontinae), while the other one, called the “austral clade”, is interpreted to have had an austral origin, with the oldest records represented by the “Propalaehoplophorinae” from the late early Miocene of Patagonian Argentina. In this scenario, the extra-Patagonian radiations are still poorly known, despite their importance for understanding the late Miocene and Pliocene diversity. Here, we carry out a comprehensive revision of late Miocene (Chasicoan Stage/Age) glyptodonts of central Argentina (Buenos Aires and San Juan provinces). Our results show that, contrary to what is traditionally assumed, it was a period of very low diversity, with only one species recognized in this region, Kelenkura castroi gen et sp. nov. Our phylogenetic analysis shows that this species represents the sister taxon of the remaining species of the “austral clade”, representing the first branch of the extra-Patagonian radiation. Additionally, K. castroi is the first taxon showing a “fully modern” morphology of the caudal tube.
... Within this diversity, glyptodonts (late Eocene-latest Pleistocene/earliest Holocene) are a clade composed of large to very large grazing armored herbivores, with body masses ranging between 100 kg to ca. 2000 kg (Vizcaíno et al. 2011;Soibelzon et al. 2012;Quiñones et al. 2020). In a phylogenetic framewok, there is consensus that pampatheres (Pampatheriidae) is the sister group of glyptodonts (Gaudin and Wible 2006;Gaudin and Lyon 2017;Fernicola et al. 2018; but see Delsuc et al. 2016;Mitchell et al. 2016 for an alternative view). ...
... Likewise, these deposits coincide with the period in which C4 becomes an important component in the diet of large herbivores (Hynek 2011), before becoming dominant after 4 Ma (Latorre et al. 1997). As stated above, the general morphology of the mandible and teeth of E. solidus is almost identical to that of Doedicurus, which has the highest hypsodonty index among glyptodonts (Vizcaíno et al. 2011). These anatomical features can be interpreted as a way of increasing the mechanical capacity in relation to accidental consumption of abrasive particles (i.e., sand, dust, volcanic glass) adhering to the surface of plants (Janis 1988;Candela and Bonini 2017) or the ingestion of large amounts of food with low nutritive value (Vizcaíno et al. 2011;see Fig. 9). ...
... As stated above, the general morphology of the mandible and teeth of E. solidus is almost identical to that of Doedicurus, which has the highest hypsodonty index among glyptodonts (Vizcaíno et al. 2011). These anatomical features can be interpreted as a way of increasing the mechanical capacity in relation to accidental consumption of abrasive particles (i.e., sand, dust, volcanic glass) adhering to the surface of plants (Janis 1988;Candela and Bonini 2017) or the ingestion of large amounts of food with low nutritive value (Vizcaíno et al. 2011;see Fig. 9). ...
Article
Full-text available
Glyptodonts (Mammalia, Xenarthra, Glyptodontidae) represent a diversified radiation of large armored herbivores, mainly related to open biomes in South America, with an extensive fossil history since the late Eocene (ca. 33 Ma) until their extinction in the latest Pleistocene–earliest Holocene. During the Pliocene and Pleistocene, glyptodonts arrived in Central and North America as part of the Great American Biotic Interchange. Within glyptodont diversity, one of the most enigmatic groups (and also one of the least known) are the Doedicurinae, mainly recognized by the enormous Pleistocene Doedicurus, with some specimens reaching ca. two tons. Almost nothing is known about the Neogene evolutionary history of this lineage. Some very complete specimens of the previously scarcely known Eleutherocercus solidus, which in turn becomes the most complete Neogene Doedicurinae, are here described in detail and compared to related taxa. The materials come from the Andalhuala and Corral Quemado formations (north-western Argentina), specifically from stratigraphic levels correlated to the Messinian–Piacenzian interval (latest Miocene–Pliocene). The comparative study and the cladistic analysis support the hypothesis that Doedicurinae forms a well supported monophyletic group, located within a large and diversified clade mostly restricted to southern South America. Within Doedicurinae, the genus Eleutherocercus (E. antiquus + E. solidus) is the sister group of the Pleistocene Doedicurus. Unlike most of the late Neogene and Pleistocene lineages of glyptodonts, doedicurins show along its evolutionary history a latitudinal retraction since the Pleistocene, ending with the giant Doedicurus restricted to the Pampean region of Argentina, southernmost Brazil, and southern Uruguay. This hypothetic relationship between body mass and latitudinal distribution suggests that climate could have played an active role in the evolution of the subfamily.
... El ancho relativo del hocico también permitió distinguir dos formas principales de alimentación en el linaje de los gliptodontes (Vizcaíno et al., 2011b): los relativamente pequeños propalaehoplofóridos (masas corporales entre 80 y 100 kg) del Mioceno temprano, de hocico angosto, se alimentarían de forma selectiva, mientras que las formas grandes postmiocenas, de una tonelada o más y hocico ancho, lo harían al bulto. Con su hocico angosto, Glyptodon del Pleistoceno aparece como una excepción, que implica una reversión a una conducta de alimentación selectiva. ...
... Vizcaíno et al. (2006b) volvieron a abordar el tema midiendo OSA como la proyección bidimensional de una estructura tridimensional, usando fotografías digitales de las superficies oclusales de las filas de dientes yugales superiores (Figura VIII.23). Posteriormente Vizcaíno et al. (2011b) refinaron el enfoque midiendo OSA como el área total de la superficie oclusal de los dientes de mejilla, teniendo en cuenta las invaginaciones del contorno del diente. Figura VIII.23. ...
... Esto implica que los xenartros tienen requisitos energéticos menores que otros terios y, por lo tanto, para un tipo específico de alimento, requieren consumir menos que otros terios de masas corporales similares. Vizcaíno et al. (2006b;2011b) investigaron las relaciones entre OSA de los molariformes, la masa corporal, la dieta inferida y otros factores biológicos en diferentes xenartros extinguidos. Además de tener OSA menores que otros terios, encontraron que, entre los xenartros, los perezosos milodóntidos del Pleistoceno (la mayoría de más de una tonelada) mostraron OSAs extremadamente bajas (Figura VIII.25), lo que se interpretó como una indicación de pobre eficiencia en el procesamiento de alimentos en la cavidad oral, probablemente compensada por una alta fermentación en el tracto digestivo (Vizcaíno et al., 2006b). ...
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Nuestra formación en el estudio de la forma y función ha tenido y tiene gran parte de prueba y error. Hay mucho material para estudiar, muchas problemáticas que abordar y mucho de marco conceptual y metodología que aprender. O desarrollar… En este proceso ha sido y es crucial el aporte de los editores y revisores de nuestros trabajos. Los manuscritos enviados a las revistas retornaron y retornan con correcciones y sugerencias o perspectivas que no habíamos considerado y que nos enriquecen intelectualmente. La interacción dentro del grupo y con otros interesados en el tema nos permite incrementar las temáticas a tratar y metodologías a utilizar y generar una masa crítica para la exploración de nuevas metodologías y la discusión del marco conceptual. Así, creemos que estamos aportando al desarrollo y la innovación de la dimensión funcional de las expectativas de Reig y Pascual. Con este libro esperamos ayudar a tomar un atajo a quienes buscan iniciarse en el estudio de la forma y función de vertebrados fósiles. De ninguna manera pensamos que es un texto definitivo; solo es una apretada síntesis de los trayectos que recorrimos, dónde nos encontramos y dónde creemos que podemos llegar. Nuestro relato transita por los caminos más firmes que conocemos. Por ello, nos referimos mayormente a nuestros propios trabajos, resumiendo las discusiones metodológicas, conceptuales y epistemológicas que se nos han ido planteando y señalando alternativas. Nuestra perspectiva es que, desde la singularidad de las faunas extintas de vertebrados de América del Sur, los estudios funcionales ayudarán a descifrar procesos a nivel de organismos que aportarán a enfoques supraorganísmicos (incluyendo el ambiental) en los análisis evolutivos. (del prólogo de los autores)</i
... The data were reconstructed using phoenix datos|x 2.0 reconstruction software, then exported into a 16-bit TIFF image stack and segmented with Mimics Innovation Suite 18 (Materialise), and exported with 3D object rendering. The hypsodonty index was calculated, following Vizcaíno et al. (2011), as the depth (dorsoventral diameter) of mandible at mf6 divided by the length (anteroposterior diameter) of the tooth row (here, from mf1 to mf7). ...
... Eucinepeltus has been interpreted by Vizcaíno et al. (2011), on the basis of the hypsodonty index and the relative muzzle width index, as highly selective feeder in relatively closed habitats, living within the flora of the Santa Cruz Formation (late early Miocene) on the Atlantic coast represented by a mixture of open, semiarid temperate forests and humid warm-temperate forests (Brea et al., 2012(Brea et al., , 2013. Unfortunately, the relative muzzle width could not be calculated for cf. ...
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The earliest complete glyptodonts (Glyptodontidae, Cingulata) found belong to the Propalaehoplophorinae from Santa Cruz Formation (late early Miocene, Burdigalian) in Patagonia, Argentina. Although several skulls and mandibles have been described from this formation, and assigned to five genera (Propalaehoplophorus Ameghino, Cochlops Ameghino, Asterostemma Ameghino, Eucinepeltus Ameghino, and Metopotoxus Ameghino), the fossil record and knowledge of juvenile specimens of glyptodonts are still poor. Here, we provide a detailed morphological description of a mandible of a juvenile propalaehoplophorinae glyptodont from the Santa Cruz Formation, using micro-computed tomography and scanning electron microscopy images. We compare the juvenile mandible with adult specimens and discuss the taxonomic assignment, the juvenile and adult mandibular and dental characters, and dental eruption and tooth wear.
... The Xenarthra teeth are morphologically simple and do not provide unambiguous information about their diet (Bargo and Vizcaíno, 2008). However, skull and jaw morphology differences among these taxa yielded evidence for possible feeding mechanisms and therefore food composition (Vizcaíno et al., 2011). Recently, an isotopic study on bulk collagen showed that xenarthrans were exclusively herbivorous (Bocherens et al., 2017). ...
Article
Stable isotopes are a powerful tool for reconstructing the past. However, environmental factors not previously considered can lead to misinterpretations. Our study presents a novel analysis of the feeding behavior of the megafauna that inhabited the Pilauco ecosystem in south-central Chile during the last glacial termination. We analyzed a suite of modern plant and animal samples from closed-canopy forests to establish an isotopic baseline with which to compare stable isotope results from fossil megafauna. Using the modern samples as a reference, the δ ¹³ C results from the Pilauco megafauna indicate feeding behaviors in forested areas. These results were then calibrated with dental calculus samples and coprolites, which suggest the coexistence of graze- and grass-dominated mixed-feeder diets. The δ ¹⁵ N values found in Pilauco megafauna are not consistent with modern reference data sets or with the low δ ¹⁵ N values of extinct proboscideans from other contemporaneous and nearby sites. Probably, the δ ¹⁵ N values of the Pilauco ecosystem were not primarily affected by climate, but rather by disturbance factors (e.g., grazing effect). Our results indicate that the Pilauco megafauna fed mainly on arboreal vegetation; however, non-isotopic proxies indicate that they were also eating open vegetation (e.g., herbs and grasses).
... Chorobates has also been recorded in the 'Araucanense' of Catamarca province (Esteban et al. 2014). The glyptodontid Hoplophractus has been described as a bulkfeeding inhabitant of moderately open habitats (Vizcaíno et al. 2011). Typotheriopsis (Notoungulata) is considered as an inhabitant of open, dry areas, with fossorial abilities and masticatory specialisations for the consumption of hard food items (Fernández-Monescillo et al. 2018;Ercoli & Armella 2021). ...
Article
Echimyidae is the most widely diversified family among hystricognath rodents, both in the number of species and variety of lifestyles. In the Patagonian Subregion of southern South America, extinct echimyids related to living arboreal species (Echimyini) are recorded up to the middle Miocene, whereas all the known southern fossils since the late Miocene are linked to terrestrial and fossorial lineages currently inhabiting the Chacoan open biome in eastern South America. In this work, we describe a new genus of echimyid rodent, Paralonchothrix gen. nov., from the late Miocene of northwestern Argentina and western Brazil. Its single recognised species, Paralonchothrix ponderosus comb. nov., is represented by two hemimandibles. One of them comes from a level of Loma de Las Tapias Formation, underlying a tuff dated at 7.0 ± 0.9 Ma (Huayquerian age, late Miocene); the other specimen comes from the 'Araucanense' of Valle de Santa María (type locality, Huayquerian age, late Miocene). A phylogenetic analysis linked Paralonchothrix to Lonchothrix, both being the sister group to Mesomys. Thereby, for the first time, an echimyid linked to living Amazonian arboreal clades is recognised for the late Miocene of southern South America. Paralonchothrix gen. nov. thus represents an exceptional record that raises the need to review the postulated evolutionary pattern for echimyids recorded at high latitudes since the late Miocene. The new genus provides a minimum age (ca.7 Ma) in the fossil record for the divergence between Mesomys and Lonchothrix. The palaeoenvironmental conditions inferred for the late Miocene in western and northwestern Argentina suggest savanna-type environments, with areas with more closed woodlands in peri-Andean valleys. The record of Paralonchothrix gen. nov. supports the hypothesis that this area would have maintained connections with tropical biomes of northern South America during the late Miocene.
... The absence of Propalaehoplophorus in our collections but present in the old collections at RSC may be an artifact due to the lack of diagnostic features in the specimens we collected . Santacrucian glyptodonts are moderately large (up to 120 kg) and ambulatory selective feeders in relatively closed to strictly closed habitats (Vizcaíno et al., 2011(Vizcaíno et al., , 2012c. ...
Article
The continental early-middle Miocene Santa Cruz Formation (SCF) and its fossils in Austral Patagonia represent the best record of South American mammalian faunas prior to the Great American Biotic Interchange (GABI) and is of particular interest because it is the best preserved high-latitude continental biotic record in the Southern Hemisphere spanning the mid-Miocene Climatic Optimum. Through intensive fieldwork we recovered numerous fossil vertebrates, mostly mammals, from the SCF along the Río Santa Cruz (RSC), the type area for the formation and its fauna. We examine whether the SCF fauna differed among three distinct temporal intervals of the SCF spanning, from the oldest to youngest, the Atlantic coastal suite of localities Fossil Levels (FL) 1–7, at about 17.4 Ma, through localities in the RSC Barrancas Blancas (BB), between ∼17.2 and ∼16.3 Ma, and Segundas Barrancas Blancas (SBB), between ∼16.5 and ∼15.6 Ma. With the objective of reconstructing paleoenvironmental and community structure of these RSC faunas, we compared them with 55 extant lowland mammalian localities across South America from 8° N to ∼55° S latitude representing a wide range of seasonality and annual rainfall and temperature, as well as canopy height and net primary productivity, sampling communities ranging from tropical rainforest to semi-arid steppe. Extant nonvolant mammalian genera at each locality were assigned a body size interval and niche parameters reflecting diet and substrate use, from behavioral data in the literature. Extinct genera were assigned similar niche metrics on the basis of their morphology. From the generic niche parameters, we compiled indices and ratios that express vectors of the community structure of each fauna, including the total number of genera, the pervasiveness of arboreality, frugivory, and browsing, and the relative richness of predators to their prey. The community structure variables were used to model community structure of the fossil localities based on uniformitarian principles. The fossil sample includes 44 genera of mammals from FL 1–7, 38 genera from BB, and 44 genera from SBB. The Simpson Coefficients of faunal similarity among the fossil localities are no greater than expected on the basis of the geographic distances among them, and do not suggest any apparent climatic differences. Based on the models we obtained no significant differences in MAP (Mean Annual Precipitation) for FL 1–7, BB and SBB, with mean estimates of 1635 mm, 1451 mm, and 1504 mm, with the confidence intervals for the estimates overlapping widely. MAT (Mean Annual Temperature) estimates are between ∼21 °C and ∼22 °C for FL 1–7 and SBB, possibly lower at 16 °C for BB, but with a wide and overlapping range of estimates. Temperature seasonality is modest (3 °C to 4 °C) and similar for all localities. Canopy heights exceed 20 m for all sites. Despite these geographic and inferred climatic similarities, the presence of certain key taxa (e.g., the caviomorph rodent Prolagostomus and the typothere Pachyrukhos) together with an increased overall abundance and richness of rodents with ever-growing cheek teeth suggests a trend to aridification in the upper part of the SCF at SBB compared with FL 1–7 and BB. Taken together, we propose that the SCF paleoenvironment consisted largely of semi-deciduous forests ranging into savannas with gallery-forest components. This range of habitats occurs today where the mesic inland Atlantic forests of Southern Brazil, northeastern Argentina and eastern Paraguay give way northwestward into the more xeric Paraguayan Gran Chaco. This interpretations are in general agreement with the other sources of evidence from sedimentology, paleosols, isotopes, paleobotany and other faunal elements. We highlight the value of focusing paleoenvironmental and paleocological studies of the SFC on stratigraphically and geographically controlled samples instead of on the entire temporal and geographic distribution of the formation based on historical collections with limited provenance. The Santacrucian can be considered a model to the study of South American faunas after the arrival of hystricomorph rodents and anthropoid primates but before GABI.
... Nevertheless, many extinct mammalian groups lack much dental information due mainly to the scarcity of complete and well-preserved dental remains. Historically, the dental characteristics have been used to erect, describe, and contrast mammalian species, as well as to infer different aspects of their way of life, such as their habitat and feeding preferences (e.g., Patterson and Pascual, 1968;Fortelius, 1985;Janis, 1988Janis, , 1990Janis, , 1995Janis and Constable, 1993;Solounias et al., 1994;Pérez-Barbería and Gordon, 1998;Vizcaíno et al., 2006Vizcaíno et al., , 2011Townsend and Croft, 2008;Reguero et al., 2010;Cassini et al., 2012aCassini et al., , b, 2017Candela et al., 2013;Famoso et al., 2013Famoso et al., , 2016. In recent years, these works have been strongly enriched by the publication of other studies focused on deciduous dentition, reconstruction and description of the ontogenetic series, and tooth eruption/replacement patterns of fossil mammals, whose adaptive, taxonomic, and phylogenetic weight is recognized (Smith, 2000). ...
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Studies focused on deciduous dentition, ontogenetic series, and tooth eruption and replacement patterns in fossil mammals have lately increased due to the recognized taxonomic and phylogenetic weight of these aspects. A study of the deciduous and permanent dentition of Interatherium and Protypotherium (Interatheriinae) is presented, based mainly on unpublished materials. Deciduous cheek teeth are brachydont and placed covering the apex of the respective permanent tooth; in addition, some morphological and metrical differences are observed along the crown height. Five dental ontogenetic stages are distinguished among the juvenile specimens on the basis of the degree of wear, the replacement of the deciduous premolars, and the eruption of the molars. The crown height and the wear degree of different Interatheriinae taxa show: (1) eruption pattern of molars in an anterior–posterior direction (M/m1 to M/m3); (2) pattern of replacement of deciduous premolars and eruption of permanent premolars in a posterior–anterior direction (dP/dp4 to dP/dp2 and P/p4 to P/p2); and (3) eruption of M/m3 before the replacement of dP/dp4. Results allow evaluating the diagnostic dental characteristics used to describe some interatheriines, as well as reinterpreting some taxonomic assumptions: the holotype of Protypotherium diversidens Ameghino, 1891 is recognized as a juvenile of another species of the genus, and the species is not validated, considering it as Protypotherium sp.; the holotype of Eudiastatus lingulatus Ameghino, 1891 falls in the variability of Protypotherium , becoming P. lingulatus new combination, tentatively maintaining the species and implying the synonymy between Eudiastatus and Protypotherium ; and the holotype of Eopachyrucos ranchoverdensis Reguero, Ubilla, and Perea, 2003 is reinterpreted as bearing deciduous premolars.
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Prehistoric and recent extinctions of large-bodied terrestrial herbivores had significant and lasting impacts on Earth’s ecosystems due to the loss of their distinct trait combinations. The world’s surviving large-bodied avian and mammalian herbivores remain among the most threatened taxa. As such, a greater understanding of the ecological impacts of large herbivore losses is increasingly important. However, comprehensive and ecologically-relevant trait datasets for extinct and extant herbivores are lacking. Here, we present HerbiTraits , a comprehensive functional trait dataset for all late Quaternary terrestrial avian and mammalian herbivores ≥10 kg (545 species). HerbiTraits includes key traits that influence how herbivores interact with ecosystems, namely body mass, diet, fermentation type, habitat use, and limb morphology. Trait data were compiled from 557 sources and comprise the best available knowledge on late Quaternary large-bodied herbivores. HerbiTraits provides a tool for the analysis of herbivore functional diversity both past and present and its effects on Earth’s ecosystems.
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A species of glyptodontid, Pseudoplohophorus absolutus n. sp. from the Upper Miocene of Uruguay is described. The holotype is represented by skull, mandible, great part of dorsal and cephalic carapace, caudal tube, humerus, hand bones, some vertebrae, and fragmentary pelvis and caudal ring plates. These materials were compared with very complete specimens of Neogene Sclerocalyptinae from Argentina and Uruguay. On the basis of these comparisons the partial synonymy between Pseudoplohophorus Castellanos and Stromaphoropsis Kraglievich, and the inclusion of genus Hoplophractus Cabrera within Eosclerocalyptyus C. Ameghino are proposed. A bio-zone characterized by Pseudoplohophorus, included in Camacho Formation deposits, is redefined.
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This chapter examines how mammal body mass maxima and ranges have changed over the past 40 Ma. The study demonstrates that different taxonomic groups have occupied the role of largest herbivore during this interval, and indicates that the greatest diversity of large species was present in South America only 10,000 BP. This latter observation has important implications for the functioning of modern ecosystems and suggests that these paleocommunities were structured quite differently than those of today, a finding that echoes results of similar studies of other time intervals. The chapter adds to an expanding body of literature on diet, locomotion, body mass, and community structure that together have created a much more detailed picture of the life and times of extinct South American mammals. The absence of carnivorans (i.e., members of the order Carnivora) is a characteristic and intriguing feature of most South American paleocommunities. In their absence, the role of large, terrestrial, warm-blooded meat-eater (carnivore) was filled by metatherian mammals—specifically sparassodonts (borhyaenids and relatives)—as well as phorusrhacids, also known as terror birds, which were large to giant flightless birds with oversized heads and hooked beaks.