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ARTICLES
ISSN 0002-7014
NOTHROTHERIOPS SHASTENSIS (SINCLAIR) FROM ACTUN LAK: FIRST RECORD OF NOTHROTHERIIDAE (MAMMALIA, XENARTHRA, PILOSA) FROM BELIZE GERARDO DE IULIIS1, H. GREGORY McDONALD2, NORBERT STANCHLY3, JON SPENARD4 AND TERRY G. POWIS5 1
Department of Ecology and Evolutionary Biology, University of Toronto, 25 Harbord Street, Toronto, ON M5S 3G5, Canada and Section of Palaeobiology, Department
of Natural History, Royal Ontario Museum, 100 Queen’s Park Crescent, Toronto, ON, M5S 2C6 Canada.
[email protected] 2
Museum Management Program, National Park Service, 1201 Oakridge Drive, Fort Collins, CO 80525, USA.
[email protected]
3
AS&G Archaeological Consulting, 34 Leith Hill Road, Suite 306, Toronto, ON M2J 1Z4, Canada.
[email protected]
4
Department of Anthropology, University of California, Riverside, Riverside, CA 92521-0418, USA.
[email protected]
5
Department of Geography and Anthropology, Kennesaw State University, 1000 Chastain Road, Kennesaw, GA 30144-5591, USA.
[email protected]
Abstract. Sloth remains recovered from Actun Lak, Cayo District, Belize, during archaeological excavations by the Pacbitun Regional Archaeological Project include numerous though mainly fragmentary elements. Among the identifiable remains are a lower molariform tooth and several elements of the manus and pes. Although no complete cranial and long bone postcranial remains are available, the sloth is confidently assigned to the nothrotheriid species Nothrotheriops shastensis (Sinclair). This is the most southern certain record of the North American genus Nothrotheriops Hoffstetter and the first record of a nothrotheriid from Central America. Based on our knowledge of the species’ diet and habitat preference from dry caves in the southwestern United States, its presence in Belize has paleoecological and biogeographic implications. The Belize remains clearly indicate that sloth diversity in northern Central America was greater than previously suspected. They also suggest that a greater variety of habitats existed in this region during the Pleistocene, and that vegetation communities underwent more dramatic changes during this interval than previously thought. Key words. Extinct sloth. Nothrotheriid. Paleobiology. Paleoecology.
Resumen. NOTHROTHERIOPS SHASTENSIS (SINCLAIR) DE ACTUN LAK: PRIMER REGISTRO DE NOTHROTHERIIDAE (MAMMALIA, XENARTHRA, PILOSA) DE BELICE. Los restos de perezosos recuperados durante las excavaciones arqueológicas realizadas por el Proyecto Arqueológico Regional Pacbitun en Actun Lak, Distrito de Cayo, Belice, incluyen numerosos elementos, aunque mayormente fragmentarios. Entre los restos identificables hay un diente molariforme inferior y varios elementos de la mano y el pie. Aunque no hay restos craneales ni huesos largos postcraneanos completos, el ejemplar es asignado con confianza a la especie de notrotérido Nothrotheriops shastensis Sinclair. Este es el registro más austral del género norteamericano Nothrotheriops Hoffstetter y el primer registro de un notrotérido en América Central. Sobre la base de nuestro conocimiento de la dieta y de la preferencia de hábitat de la especie de cuevas secas en el suroeste de Estados Unidos, su presencia en Belice tiene implicancias paleoecológicas y biogeográficas. Los restos de Belice indican claramente que la diversidad de perezosos en el norte de América Central era mayor que lo sospechado previamente. También, sugieren que una mayor variedad de hábitats existía en esta región durante el Pleistoceno, y que las comunidades vegetales sufrían cambios más dramáticos durante este intervalo que lo pensado anteriormente. Palabras clave. Perezoso extinguido fósil. Notrotérido. Paleobiología. Paleoecología.
THE placental clade Xenarthra includes the armadillos and
dith et al., 2011; O’Leary et al., 2013). Modern xenarthrans
their extinct kin (Cingulata), and Pilosa, comprised of sloths
are not particularly diverse compared to their fossil record,
or Tardigrada (= Phyllophaga= Folivora; see Delsuc et al.,
with 31 species, mostly armadillos, typically recognized and
2001; Fariña and Vizcaíno, 2003) and the South American
distributed mainly in Central and South America; one taxon,
anteaters or Vermilingua. Although consensus on patterns
a species of Dasypus Linnaeus, 1758, is present in North
of relationships of xenarthrans to other placentals has not
America (Aguiar and Fonseca, 2008; Vizcaíno and Loughry,
been achieved, they are considered one of four main pla-
2008). However, they were among the more important and
cental clades or the sister group to all other placentals, a
characteristic mammals in the Cenozoic of South America,
clade termed Epitheria (e.g., Asher and Helgen, 2010; Mere-
a history documented by a diverse and extraordinarily
AMGHB2-0002-7014/12$00.00+.50
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abundant fossil record (McDonald and De Iuliis, 2008). Xe-
al., 2011). Nothrotheriops was the last ground sloth to enter
narthrans dispersed into North America at different times
North America, with the earliest records in the middle Irving-
during the Great American Biotic Interchange (GABI) (Mc-
tonian (McDonald, 1995; McDonald and Jefferson, 2008;
Donald, 2005). A profound exchange of faunal elements
McDonald et al., 2013).
occurred between North and South America during both the
The sloth remains described in this report are from
early stages and after the complete emergence of the Pana-
Actun Lak (Yucatec Mayan for Pottery Sherd Cave), a cave
manian Isthmus approximately 3 Ma, and also to the West
in western Belize (Figs. 1–2), and are the first published
Indies, by way of a separate migration route and episode
records of a nothrotheriid from Central America. They are
(McDonald and De Iuliis, 2008). They established them-
assigned to the species Nothrotheriops shastensis (Sinclair,
selves as important faunal elements in both of these re-
1905).
gions. The living Tardigrada, the tree sloths, are highly special-
LOCALITY AND GEOLOGY
ized arboreal mammals relying almost exclusively on a fo-
Actun Lak has been under active investigation by the
livorous diet, but fossil sloths display considerable diversity
Pacbitun Regional Archaeological Project (PRAP) since
in terms of body sizes, dietary habits, and modes of loco-
2010 under the direction of Dr. Terry Powis (Spenard, 2011,
motion (e.g., Bargo and Vizcaíno, 2008; Bargo et al., 2012;
2012a,b, 2013a,b, 2014; Spenard et al., 2013; Stanchly et
Pujos et al., 2012; Toledo et al., 2013; Amson et al., 2014).
al., 2013; Spenard and Powis, 2014). It is one of the primary
Four main sloth clades, represented primarily by fossil
foci of a regional archaeological cave study by PRAP mem-
taxa, are usually recognized: Megatheriidae, Megalonychi-
ber and junior author (JS) for his dissertation at the Univer-
dae, Mylodontidae, and Nothrotheriidae; a fifth clade is also
sity of California, Riverside, on the ritual use of limestone
recognized, Bradypodidae, which includes only the living
karst features by the pre-Hispanic Maya (300 B.C. to A.D.
tree sloth Bradypus Linnaeus, 1758, whose phylogenetic
900) (Spenard, 2014). PRAP’s investigations in the cave
affinity to the other clades remains to be resolved (Gaudin,
have resulted in the recovery of three groups of sloth re-
2004). The nothrotheriids, the main focus of this paper,
mains (see below). These remains include numerous frag-
have been considered closely allied to either megatheriids or
ments, but several elements are sufficiently preserved to
megalonychids (De Iuliis et al., 2011). Although nearly a
allow confident assignment to Nothrotheriops shastensis.
dozen genera of nothrotheriids have been erected, several
Actun Lak, in the Cayo District of western Belize, Central
are based on fragmentary material and are thus poorly
America (Fig. 1), was named after ubiquitous surface de-
diagnosed. Those that are well represented as fossils and
posits of ancient Maya (300 BC to AD 900) ritual ceramics
for which the major portion of the skeleton is known include
found within. The region around the cave is naturally di-
the South American Mionothropus De Iuliis, Gaudin and Vi-
vided into two distinct geographic zones. Gently rolling
cars, 2011, Nothrotherium Lydekker, 1889, Pronothrotherium
Late Jurassic to early Paleogene (155 Ma to 50 Ma) period
Ameghino, 1907, and Thalassocnus Muizon and McDonald,
limestone and dolomite hills, interspersed with alluvial
1995, and the North American Nothrotheriops Hoffstetter,
valleys, lie to the north and west. The zone to the south and
1954 (see De Iuliis et al., 2011). While Nothrotherium and
east is defined by the geologically complex Maya Mountains
Nothrotheriops are considered sister taxa (McDonald and
that rise rapidly from the low-lying terrain to an average
Muizon, 2002), the degree of relationship amongst many of
elevation of 750 masl (Bateson and Hall, 1977; Miller, 1996,
the other taxa still needs to be resolved, although there
p. 104; Martens et al., 2010: fig. 2) and extend into the
have been some initial efforts in this direction (De Iuliis et
eastern Peten, Guatemala, as part of the anticlinal La Liber-
Figure 1. Map of Belize indicating the location of Actun Lak, from which remains of Nothrotheriops shastensis were recovered. Sources: Esri, DeLorme, NAVTEQ, TomTom, Intermap, increment P Corp., GEBCO, USGS, FAO, NPS, NRCAN, GeoBase, IGN, Kadaster NL, Ordnance Survey, Esri Japan, METI, Esri China (Hong Kong), swisstopo, and the GIS User Community: Esri, USGS, NOAA. Map drawn by Peter Spenard and Jon Spenard.
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DE IULIIS ET AL.: FIRST NOTHROTHERIID RECORD FROM CENTRAL AMERICA
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AMEGHINIANA - 2015 - Volume 52 (1): 153 – 171
tad Arch structure (Weyl, 1980, p. 155). They are composed
Spenard, 2011). Subsequent examination of the material
of an uplifted, karstified fault block of the Jurassic–Paleo-
indicated that the remains belonged to a large non-human
gene limestone and dolomite and several exposed Cambrian
mammal (Spenard, 2012a, p. 147). Furthermore, they were
to Early Devonian period (517 Ma to 406 Ma) and possible
disarticulated and covered in soil of a significantly different
Permian–Triassic (250 Ma to 225 Ma) and Precambrian
color than the current cave surface, suggesting that the
(613 Ma to 565 Ma) batholiths (Bateson and Hall, 1977;
bones were in a disturbed context, and likely originated at
Miller, 1996; Steiner and Walker, 1996; Martens et al., 2010:
the bottom of one of many pits dug by the illicit activities of
fig. 2). The tectonic Northern and Southern Boundary Faults,
pot hunters in the eastern side of Chamber 2. The second
and one unnamed each to the east and west, the latter of
group of bones comprised a disarticulated pile encountered
which is buried by deep sediment, demarcate the extent of
adjacent to a small alcove in the eastern wall of the cham-
the mountains (Miller, 1996).
ber named the “Sloth Alcove”. Among these remains were
Actun Lak is located halfway up a hill in the initial range
large unguals that were preliminarily identified as belonging
of foothills in the northern Maya Mountains along the
to an extinct ground sloth (Spenard, 2011, p. 147). The pot
Northern Boundary Fault, approximately 1.5 km north of the
hunters had tossed the dirt from their illicit digging back
Mountain Pine Ridge, the largest batholith cluster. It is
into the Sloth Alcove, and the color of that matrix matched
considered a fossil chamber stratum cave because its floor
that on the bones of both groups, indicating that the re-
is composed of soil-covered large ceiling collapse boulders
mains were likely initially recovered from those disturbed
and has a high roof reaching up to 12 m (e.g., Miller, 1996;
areas. These soils were screened and additional sloth re-
Palmer, 2007; Spenard, 2014). It is a relatively straight 43 m
mains were recovered, which prompted formal excavations
long passage that terminates at a small, muddy choke but
in the alcove in hopes of unearthing in situ animal remains
undulates vertically due to a series of natural drops and con-
and associated evidence of early human use of the cave
strictions formed from the ceiling breakdown boulders. Four
(Stanchly et al., 2013). The excavation of a single 1.75 m by
main areas (Entrance Passage and Chambers 1, 2, and 3) and
1 m unit (designated Unit 13) in 2012 and two 1 m by 0.5 m
ledges (labelled Ledges 1 through 4) are recognized (Fig. 2).
units (designated Units 19 and 20) in 2013. These findings
Chamber 2 and Ledge 1 are located approximately 30 m
suggest that the matrix of the entire “Sloth Alcove” had
into the cave. All of the sloth remains were recovered in
been disturbed by the illicit pot hunting. Furthermore, no
Chamber 2, and Ledge 1 contains evidence of a possible
pre-Maya artifacts were recovered nor did the bones
ancient entrance. The ledge is located above the western
demonstrate any signs of having been butchered. A total of
side of Chamber 2 and is only accessible by climbing up a
863 sloth remains were recovered from the Actun Lak in-
series of natural, narrow, step-like formations protruding
vestigations and all were exported for analysis.
from the cave wall. A small cluster of unidentified and dis-
One long bone specimen, designated as Sample 49,
articulated medium to large-sized mammal bones had been
was submitted to Beta Analytic, Inc. (Miami, FL) for radio-
naturally cemented in calcium carbonate to the floor at the
carbon dating. This specimen and three others were re-
edge of the ledge, supporting the possibility of a collapsed
moved from the alcove on June 15, 2013, and exported by
second entrance.
junior (TGP) to the Department of Geography and Anthro-
As noted in the Introduction, PRAP’s investigations have
pology at Kennesaw State University in Kennesaw, Georgia.
recovered three groups of sloth bones. The first group was
Sample 49 was sent to Beta Analytic Inc. for radiocarbon
noted during reconnaissance of the cave but was initially
dating while the remaining three bones were sent to the
believed to represent human remains because it had been
first author (GDI) at the ROM (see below for institutional
placed on a large limestone slab on the floor of a small, ar-
abbreviations) for detailed analysis.
tificially sealed alcove (Spenard, 2011). The pre-Hispanic
Unfortunately, Actun Lak Sample 49 (Beta 357264) did
Maya commonly buried the deceased and sacrificed indi-
not yield any separable collagen and thus could not be
viduals in such subterranean settings (e.g., Thompson, 1959,
dated. Possible reasons for the degradation or removal of
1975; Brady, 1989; Owen, 2005; Scott and Brady, 2005;
collagen include but are not limited to bleaching by the sun,
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DE IULIIS ET AL.: FIRST NOTHROTHERIID RECORD FROM CENTRAL AMERICA
Figure 2. Plan view drawing of Actun Lak, Belize, from which remains of Nothrotheriops shastensis were recovered.
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AMEGHINIANA - 2015 - Volume 52 (1): 153 – 171
leaching by water, partial heating, burning or cooking, mi-
and pieces. However, there are several complete or nearly
crobial activities, replacement by other mineral species
complete identifiable and diagnostic elements, mainly
(typically SiO2 or CaCO3), and natural degradation due to extreme age (typically greater than 20,000 years unless
from the manus (Fig. 3.3–3.11) and pes (Fig. 4.4–4.16), as
burial conditions are optimal) (Chris Patrick, Beta Analytics
diagnostic remains are a L m3, middle and ungual phalanges
Inc., pers. comm., 2013). Being exposed on the cave floor is
of R manual digits 2 and 3, a portion of the R astragalus, a
unlikely to have caused much change in Actun Lak Sample
R navicular, partial R metatarsals IV and V, and a complete
49 since its time there was short compared to its actual age.
R metatarsal II.
From an archaeological perspective, it seems more likely
List of material. L m3 (missing basal portion and part of
that leaching or degradation of the collagen occurred while
crown); carpals, L pisiform (missing posterior and pos-
the bone was buried in the cave soil.
terodistal surfaces), R pisiform (missing posterodistal sur-
well as a molariform tooth (Fig. 3.2–3). Among the more
In terms of relative dating, the sloth bones were mixed
face); manual digit 1, probable R ungual phalanx (missing
with cultural material associated with Late Classic Maya
sheath and portion of dorsal surface of ungual process);
civilization (ca. AD 700–900). This vertical mixing of cultural
manual digit 2, nearly complete R middle and ungual pha-
material and sloth remains was secondary and the result of
langes (with ungual phalanx missing only sheath and distal
recent pot hunting in the cave. Of note, the bones, in one or
tip of ungual process); manual digit 3, distal end of R middle
two instances, were found to be stratigraphically sealed
phalanx and nearly complete ungual phalanx (missing
beneath the Maya artifacts. No pre-Maya artifacts were
sheath), small portion of proximodorsal ungual process and
recovered, as noted above, which might help date the sloth
articular facet; manual digit 4, complete R middle phalanx;
bones or at least provide a minimum age. One piece of
distal end of R Mc V; R and L lunulae; distal end of femur;
unidentified and partially burned wood recovered from ex-
probable R ossified meniscus; proximal end of fibula; tarsals,
cavation Unit 2 adjacent to the Maya altar was processed
incomplete R astragalus (missing distomedial portion but
by Beta Analytic (Beta-313731). The assay returned a date
preserving nearly completely the odontoid, discoid, and
of 1180 + 30 cal. years BP (AD 770–940), which provides a
fibular articular facets); incomplete L astragalus (preserving
time-range for when the ancient Maya used the cave but is
proximomedial surface with portion of odontoid and discoid
much younger than any published dates for fossil sloths in
facets); nearly complete R navicular; nearly complete L ecto-
North, Central or South America and even the youngest
cuneiform; complete fused L entocuneiform and Mt I; nearly
dates for Caribbean sloths (Steadman et al., 2005).
complete R Mt II (missing small portion of distal articular
Institutional abbreviations. IOA, Belize Institute of Archeology,
keel); R Mt IV (missing distal end); R Mt V (missing proximo-
Belmopan, Belize; LACM, Los Angeles County Museum of
lateral flange); pedal digit 2, complete R middle phalanx and
Natural History, Los Angeles, USA; OMNH, Oklahoma Mu-
ungual phalanx (missing sheath and distal end of ungual
seum of Natural History, Norman, USA; ROM, Royal Ontario
process).
Museum, Toronto, Canada; UALP, University of Arizona Laboratory for Paleontology, Tucson, USA; ZMUC, Zoologisk Museum Universitat Copenhagen, Copenhagen, Denmark.
Methods Taxonomic assignment is based on morphological and
Anatomical abbreviations. L, left; m3, lower third molariform;
metric comparisons with Nothrotheriops shastensis and
Mc, metacarpal; Mt, metatarsal; R, right.
Megalonyx jeffersonii Harlan, 1825 material at the ROM and descriptions and figures of the skeletal elements of these
MATERIALS AND METHODS Materials
two taxa in Leidy (1855), Stock (1925), Lull (1929), and
Nothrotheriops specimens. The sloth remains from Actun
prises mainly casts, including isolated manus elements
Lak are cataloged as IOA 27.189.003:0255. The remains in-
(catalogued under as a single number, CIT 192, of the LACM
clude many fragments of fossilized bone, largely portions of
collection, but as separate ROM numbers, as noted below,
vertebrae and ribs, as well as numerous unidentifiable bits
due to the likelihood that they do not pertain to a single
158
Paula Couto (1974). The ROM N. shastensis material com-
DE IULIIS ET AL.: FIRST NOTHROTHERIID RECORD FROM CENTRAL AMERICA
individual), an articulated manus (ROM 44928, cast of
those of Nothrotheriops shastensis in form and size.
LACM HC418; likely a composite but not comprised of the
The partial tooth of IOA 27.189.003:0255 is a L m3 (Fig.
isolated ROM elements), and an articulated pes (ROM
3.1–2). It is slightly longer vestibulolingually than mesiodis-
13077, cast of LACM 192/15187). The molariform tooth
tally (17.0 and 14.1 mm, respectively). Its lingual surface
was compared with the dentition of the skulls ROM 44927
bears a deep and well-defined apicobasal sulcus, charac-
(cast of LACM HC634) and ROM 55675 and mandible ROM
teristic of nothrotheriids, whereas its vestibular surface is
55677 (the last two are LACM specimens, but no further in-
regularly rounded in section. The other molariforms in
formation is available). Although Nothrotherium is regarded
nothrotheriids are square in cross section, with similar di-
as the sister taxon to Nothrotheriops, it was not compared
mensions both mesiodistally and vestibulolingually and
to the Belize remains because Nothrotherium has never
have an apicobasal sulcus on the midline of both the
been reported near North America and is much smaller. For
vestibular and lingual surfaces. The rounded lingual margin
example, the greatest length of the femur of Nothrotherium
and a single vestibular sulcus are present only in m3. Oc-
maquinense (Lund, 1839) is 247 mm (ZMUC 5711, the type
clusally, the preserved periphery of the tooth is raised as a
of this species), whereas a series of Nothrotheriops shas-
narrow crest-like ridge, enclosing a gently concave central
tensis femora ranges from 347.6 mm (LACM 21744) to
portion.
398.1 mm (LACM HC 428).
The pisiform of Nothrotheriops shastensis was described by Paula Couto (1974) and illustrated by Lull (1929: pl. 4;
SYSTEMATIC PALEONTOLOGY
figs. B, D). The articular surface bears a large facet for the ulna contiguous with a smaller facet for the cuneiform. The
XENARTHRA Cope, 1889
pisiform resembles but is less rounded than the pisiform
TARDIGRADA Latham and Davies in Forster, 1795
of Mionothropus cartellei De Iuliis, Gaudin, and Vicars, 2011.
(=PHYLLOPHAGA Owen, 1842)
Although that of IOA 27.189.003:0255 (Fig. 3.10–11) has
NOTHROTHERIIDAE Gaudin, 1994
some breakage, it preserves the base of what appears to
NOTHROTHERIINAE Ameghino, 1920
have been a large protuberance, absent in M. cartellei. Only the distal end of Mc V is preserved, but the articu-
Definition (from De Iuliis et al., 2011). Least inclusive clade
lar facet and form of the distal end of the diaphysis and the
including Mionothropus, Pronothrotherium, Nothrotheriops,
articular facet on its distal surface are like those of ROM
and Nothrotherium (= Nothrotheriidae of Gaudin, 2004).
44928 and ROM 36005. Stock (1925) noted the presence
Remarks. A revised diagnosis of Nothrotheriops was provided
of only a single Mc V of Nothrotheriops shastensis, but as it
by De Iuliis et al. (2011). However, as no cranial material was
lacked the distal epiphysis, this author could not report on
recovered we have focused only on the part of the diagno-
its form or the presence of phalanges for manual digit 5.
sis pertinent to the recovered parts of the skeleton that
The remains available to us indicate at least rudimentary
permits us to assign the sloth remains to Nothrotheriops.
phalanges were certainly present, as the distal end of Mc V bears a distinct, approximately B-shaped (with notch
Genus Nothrotheriops Hoffstetter, 1954
lateral) articular facet. Lull’s (1929: pl. 5) illustration indicates the presence of two somewhat nodular phalanges
Diagnosis. See Paula Couto (1971) and De Iuliis et al. (2011).
for this digit. Mc V of IOA 27.189.003:0255 is larger than
Type species. Nothrotheriops shastensis (Sinclair, 1905).
those of ROM specimens (dorsopalmar depth of distal end= 35.5 mm in IOA 27.189.003:0255, 33.7 mm in ROM 36005
Nothrotheriops shastensis (Sinclair, 1905) Figures 3–4
and 33.1 mm in ROM 44928). The ungual phalanx of manual digit 1 (Fig. 3.3) differs only in size from those of ROM 44928 and ROM 36013, and
Diagnosis. See McDonald (1995).
the specimen described by Lull (1929: pl. 5). Due to incom-
Description and comparison. The remains closely resemble
pleteness, direct measurements are not possible, but IOA
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AMEGHINIANA - 2015 - Volume 52 (1): 153 – 171
Figure 3. Nothrotheriops shastensis, IOA 27.189.003:0255, from Actun Lak, Belize. 1–2, L m3 in occlusal and lingual views, respectively; 3, ungual phalanx of R manual digit 1 in medial view; 4, middle phalanx of R manual digit 2 in dorsal view; 5, middle and ungual phalanges of R manual digit 2 in lateral view; 6, middle and ungual phalanges of R manual digit 3 in lateral view; 7–9, middle phalanx of R manual digit 4 in proximal, dorsal, and lateral views, respectively; 10–11, pisiform in side and dorsal views, respectively. Scale bar= 50 mm.
27.189.003:0255 is intermediate in size between the ROM
mm, compared with 72.5 mm in ROM 36016 and 66.5 mm
specimens, with ROM 44928 being the smallest of the three.
in ROM 64290. For the ungual phalanx, the dorsopalmar
The middle and ungual phalanges of manual digit 2 of
height of the phalanx just distal to the articular surface
IOA 27.189.003:0255 (Fig. 3.4–5) articulate perfectly with
(with the sheath missing) is 33.4 mm in IOA 27.189.003:0255
each other and differ only in being slightly larger than ROM
and 31.3 mm in ROM 36019.
36016 (middle phalanx), ROM 36019 (ungual phalanx), and
The middle and ungual phalanges of manual digit 3
LACM 1930-l-1 (Stock, 1925: figs. 24a, 25a). The greatest
(Fig. 3.6), articulate perfectly with one another and are
length of the middle phalanx of IOA 27.189.003:0255 is 73.2
nearly identical to those of ROM 44927, though in this
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DE IULIIS ET AL.: FIRST NOTHROTHERIID RECORD FROM CENTRAL AMERICA
case the latter are slightly larger. The only comparable
LACM 1891-R-1 (Stock, 1925: fig. 33A–C) and differs from
measurement possible is the dorsopalmar height of the
the latter only in that the facets for the cuboid and ecto-
distal trochlea (33.9 mm in IOA 27.189.003:0255; 34.1 mm
cuneiform share a less extensive contact. In size the navicu-
in ROM 44927).
lar of IOA 27.189.003:0255 falls within and toward the larger
The middle phalanx of manual digit 4 (Fig. 3.7–9) differs only in being larger than ROM 36014 and 1928-L-1 (Stock, 1925: fig. 24c). Proximal dorsopalmar depth is 41.9 mm in IOA 27.189.003:0255 and 32.5 mm in ROM 36014.
end of the range of a large sample of Nothrotheriops shastensis from several localities (Tab. 1). The morphology of the navicular of Megalonyx Harlan, 1825 and Nothrotheriops is different and the two genera
The lunula and ossified meniscus (Fig. 4.1–3) are two
can be readily distinguished utilizing this bone. The shape
ossicles between the femoro-tibial articulation. The lunula
of this bone in both genera is triangular when viewed proxi-
(Fig. 4.1) is approximately semicircular in outline; its poste-
mally (astragalar articular surface), but they differ in size and
rior margin is nearly rectilinear, wedge-shaped in section,
proportions. Among the differences are that the plantar
and has a thin posterior edge. Large, nearly flat articular
margin of the navicular is wide in Megalonyx and the bone
facets occupy the proximal and distal surfaces, whereas the
narrows towards the dorsal surface, so that its greatest
thickened anterior margin is rugose. It strongly resembles
mediolateral dimension is along the plantar edge; in Nothro-
morphologically that of Eremotherium laurillardi Lund, 1842
theriops the plantar edge of the navicular is narrower than
(sensu Cartelle and De Iuliis, 1995, 2006; e.g., ROM 27363)
the dorsal edge and the greatest mediolateral dimension of
and Megatherium urbinai Pujos and Salas, 2004 (Salas et
the bone is through the midline of the astragalar surface.
al., 2005: fig. 4B) and to a lesser degree of Scelidodon chilien-
The dimensions of the mammillary process of the astragalar
sis (Lydekker, 1886) (Salas et al., 2005: fig. 4C). That of Tha-
facet are similar so that the process is circular in Megalonyx
lassocnus natans Muizon and McDonald, 1995 is distinct,
while in Nothrotheriops it is elliptical with the dorsoplantar
being nearly trapezoidal in outline with a marked antero-
dimension narrower than the mediolateral dimension.
lateral expansion (Salas et al., 2005: fig. 4C). Salas et al. (2005)
Viewed laterally, the height of the plantar wall in Megalonyx
also reported a lunula in Eremotherium eomigrans De Iuliis
is the same as the mammillary process while in Nothrothe-
and Cartelle, 1999 but did not describe nor illustrate it.
riops the plantar wall extends higher, giving the bone a more
The ossified meniscus (Fig. 4.2–3) is crescentic in out-
angled appearance.
line and wedge-shaped in section, with a thin medial edge.
The ectocuneiform of IOA 27.189.003:0255 (Fig. 4.7–9)
The lateral margin is thickened and rugose. Its identifica-
is likewise entirely similar to those of ROM 13077 and LACM
tion as a R element is based on the nature of the articular
1943-L-2 (Stock, 1925: fig. 34A–B). Greatest length of this
facets, which occupy the proximal and distal surfaces. The
specimen= 54.4 mm, width= 36.3 mm, and thickness= 25.3
former is gently concave, presumably reflecting the slightly
mm; it compares closely with the range for the two speci-
convex lateral femoral condyle, and the distal articular facet
mens reported by Stock (1925: tab. 43; 50.5–51.4, 39.7–
is nearly flat, presumably reflecting the flattened lateral
43.3, and 18.5–25.2 mm, respectively).
tibial facet.
The entocuneiform and Mt I (Fig. 4.10–11) of IOA
The astragalus of IOA 27.189.003:0255 (Fig. 4.4) con-
27.189.003:0255 are fused into a single element, as also
forms entirely to the form of ROM 13077 and LACM 1875-
occurs in the specimens noted by Stock (1925). The ele-
R-1 (Stock, 1925: fig. 31A–B). It is slightly larger than that
ment is longer than that of ROM 13077 (greatest length is
of ROM 13077, with the only comparable measurement
58.3 mm vs 49.1 mm; in LACM 1880-R-1 and 1880-R-2,
being the length of the discoid facet (IOA 27.189.003:0255=
greatest length= 56.8 and 53.6 mm, respectively). It is also
79.6 mm; ROM 13077= 79.1 mm). Its morphology also
considerably more robust, with greatest width 26.3 vs 19.9
matches that of the astragalus described and illustrated for
mm. It strongly resembles LACM 1880-R-2 (Stock, 1925:
Nothrotheriops by McDonald (2012).
fig. 35), the main difference being that the facets for the
The form of the navicular of IOA 27.189.003:0255 (Fig. 4.5–6) is entirely consistent with those of ROM 13077 and
mesocuneiform are separated in the latter, but form a single contiguous surface in IOA 27.189.003:0255.
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AMEGHINIANA - 2015 - Volume 52 (1): 153 – 171
162
DE IULIIS ET AL.: FIRST NOTHROTHERIID RECORD FROM CENTRAL AMERICA
Mt II of IOA 27.189.003:0255 (Fig. 4.13–14) is not
gular, with a distinct plantar projection, in ROM 13077. The
fused to the mesocuneiform, which is apparently the more
distal surface bears a narrow, elongated and slightly
common condition in Nothrotheriops (Stock, 1925). That of
rounded facet, suggesting the presence of a rudimentary
IOA 27.189.003:0255 is nearly as long as the fused Mt II
digit, as postulated by Stock (1925), although Lull’s (1929:
and mesocuneiform of ROM 13077. It otherwise closely
pl. 6A) illustration appears to show two rudimentary and
resembles the homologous element, though it is more ro-
somewhat nodular phalanges for pedal digit 5. Comparable
bust, with midshaft width= 31.0 mm in IOA 27.189.003:0255
measurements are not possible, owing to incompleteness
and 26.7 mm in ROM 13077. The element also strongly re-
of IOA 27.189.003:0255, but the latter is slightly longer
sembles the Mt II illustrated by Stock (1925: fig. 36A–C),
than ROM 13077 based on visual inspection.
except that the facet for Mt I is elongated, forming an oval
The middle and ungual phalanges of pedal digit 2 of IOA
surface that reaches and becomes contiguous with the facet
27.189.003:0255 (Fig. 4.16) articulate perfectly with each
for the mesocuneiform on the proximal surface of Mt II,
other and do not differ from those of ROM 13077 and LACM
whereas in Stock’s specimen the facet is nearly circular
1887-R-1. As noted by Stock (1925), the middle phalanx of
and does not extend as far proximally. Greatest length of
pedal digit 2 is comparable in size to that of the middle
IOA 27.189.003:0255= 74.2 mm, compared with a range of
phalanx of manual digit 3. However, the two are easily dis-
71.4–76.6 mm given by Stock (1925: tab. 45).
tinguishable in that the manual element has a larger, more
Mt IV of IOA 27.189.003:0255 (Fig. 4.14) articulates
robust trochlea.
perfectly with Mt V (see below, Fig. 4.15) and is precisely of
Discussion. Remains of Nothrotheriops have been recovered
the same form as that of ROM 13077 and LACM 1883-R-1
from some 70 localities in the United States and Mexico. Al-
(Stock, 1925: fig. 42A–D). As with many of the other ele-
though they range in age from early Irvingtonian (ca. 1.7 Ma)
ments described here, the Mt IV of IOA 27.189.003:0255 is
to latest Rancholabrean (ca. 11 Ma), most records are late
larger than in ROM 13077, but easily comparable to the
Pleistocene (McDonald and Jefferson, 2008). Nothrotheriops
range of measurements given by Stock (1925: tab. 49). For
is represented by two species, Nothrotheriops texanus
IOA 27.189.003:0255 the greatest proximal mediolateral
(Hay, 1916), which is restricted to the Irvingtonian, and N.
width= 56.3 mm (range in Stock’s specimens= 49–58.2
shastensis, which is mainly Rancholabrean, although re-
mm) and greatest proximal dorsoplantar depth= 50.6 mm
mains described by McDonald et al. (2013) extend its age
(range in Stock’s specimens= 54–57.5 mm).
into the middle Irvingtonian. Of these two species, N. texanus
Mt V of IOA 27.189.003:0255 (Fig. 4.15) generally re-
is the more widespread, occurring from California to Flo-
sembles those of ROM 13077 and LACM 1884-R-1 (Stock,
rida and as far north as Oklahoma and south to Sonora (in
1925: fig. 43A–C) but its diaphyseal portion is more nearly
Mexico; McDonald, 2002; McDonald and Jefferson, 2008),
cylindrical, rather than the mediolaterally widened and dor-
though its remains are less abundant. N. shastensis, on the
soplantarly flattened form present in these other speci-
other hand is represented by numerous remains, mainly from
mens. In this respect IOA 27.189.003:0255 resembles more
the western United States and Mexico and is commonly
the form of Mt V illustrated in Lull (1929: pl. 6). The disto-
preserved in caves (McDonald, 2002; McDonald and Jeffer-
lateral surface bears a large rugose and oval protuberance
son, 2008; McDonald et al., 2013).
in IOA 27.189.003:0255. This region is less prominent but
Both species are known from Mexico (Fig. 5). N. texanus
of similar shape in LACM 1884-R-1, whereas it is more trian-
is known only from a single (and northern) Irvingtonian lo-
Figure 4. Nothrotheriops shastensis, IOA 27.189.003:0255, from Actun Lak, Belize. 1, probable R ossified meniscus in proximal view; 2–3, lunula in ?proximal or distal and posterior views, respectively; 4–5, R navicular in proximal and distal views, respectively; 6, R astragalus in dorsolateral view; 7–9, L ectocuneiform in proximal, distal, and lateral views, respectively; 10–11, fused L Mt I and entocuneiform in lateral and medial views, respectively; 12, middle and ungual phalanges of R pedal digit 2 in lateral view; 13–14, R Mt II in medial and dorsal views, respectively; 15–16, R Mts IV and V, respectively, in dorsal view. Scale bar= 50 mm.
163
AMEGHINIANA - 2015 - Volume 52 (1): 153 – 171 TABLE 1 - Measurements (in mm) of mediolateral width and dorsovolar height of the navicular of Nothrotheriops shastensis (many of the elements are included in a block number, so not all elements have an individual catalogue number). Specimen LACM 18855-L LACM 18860-R LACM 15186-R LACM 15186-R
LACM 15185
LACM 15185 LACM R, ucat LACM 18855-L LACM 3156-L OMNH 59273 UALP 3344 IOA 27.189.003:0255 LACM 1891-R-1 LACM 1891-R-2 LACM 1891-R-3 LACM 1891-R-4 LACM 1891-L-1 LACM 1891-L-2
164
Locality
Mediolateral Width
Dorsovolar Height
San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave San Josecito Cave Pyeatt Cave Pyeatt Cave Actun Lak Rancho La Brea Rancho La Brea Rancho La Brea Rancho La Brea Rancho La Brea Rancho La Brea
65.8 64.5 64 69.8 68 62.8 56.4 61.1 63.1 58.9 58.9 58 71.1 64.7 61 58.1 60.2 64.7 65 59.9 64.8 63 54.6 63 57.7 51 60.6 64.8 57 59.6 59.7 60 64.3 58.5 57.3 68 54.6 58.8 57 64.5 59.8 58.4 60.5 59.2 61.7 64.9 66.9 62.8 63.1 70.8 64 61.5 66.9 64.6 65.8 65.2
49.9 49.9 52 52.1 50.3 50.8 46.1 48 50.2 45.3 50.4 47.3 59.1 51 47.8 46.1 51 53.6 51.7 44.6 45.2 48.8 46.4 43.4 47.7 41.4 58.1 50.4 45.9 45 46.1 44.3 46.3 44.6 51.7 46.1 48.2 45.1 50.1 49.5 47.3 50.8 46.8 47.4 40.8 49.9 49.7 51.9 54.2 53.7 51.5 49.5 54.2 51 51.2 50
DE IULIIS ET AL.: FIRST NOTHROTHERIID RECORD FROM CENTRAL AMERICA
Figure 5. Map showing localities in Mexico and Belize from which Nothrotheriops remains have been recovered (modified from McDonald, 2002; see this author for details of Mexican localities). Sources: Esri, DeLorme, NAVTEQ. Map drawn by Jon Spenard and Peter Spenard.
cality of El Golfo, Sonora (Shaw, 1981), whereas N. shasten-
except in size. The Actun Lak remains are nearly indistin-
sis, known from 10 Rancholabrean localities, is much more
guishable morphologically from those of N. shastensis and
abundant, widely distributed, and had a range extending
seem to represent an individual near the higher end of the
much farther south (see McDonald, 2002). The most
size range reported for this species. This is clearly demon-
southern records in Mexico, and thus in North and Central
strated by the navicular, a commonly recovered element
America before this report, are from the Rancho de las Ollas,
(Tab. 1; Fig. 6).
Michoacán (Silva-Bárcenas, 1969) and the Valley of Mexico, México (Freudenberg, 1921) (see also McDonald, 2002).
Two elements, the lunula and ossified meniscus (Fig. 4.1–3), merit further discussion. These ossicles were noted
McDonald and Jefferson (2008) noted that the main
in the description as lying between the femoro-tibial ar-
differences between the two species are in size, with a
ticulation and are preserved in IAO 27.189.003:0255. As the
difference of about 30% between the smaller N. texanus (es-
terminology applied to ossifications associated with this
timated mean body mass= 332 kg) and N. shastensis (esti-
joint is not consistent in the literature, a short discussion is
mated mean body mass= 463 kg), and in cranial and dental
warranted. Vickaryous and Olson (2007, p. 324), in a com-
proportions, specifically in the ratio of alveolar length to
prehensive review of appendicular ossicles (nodular ossifi-
predental length of the maxilla in the skull and to spout
cations associated with joints in many vertebrates),
length in the mandible. Postcranial elements are similar
restricted the term intratendinous elements to ossicles
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AMEGHINIANA - 2015 - Volume 52 (1): 153 – 171
Figure 6. Bivariate plot of mediolateral length and dorsovolar height of navicular of Nothrotheriops shastensis (refer to Table 1 for measurements).
“that initially develop within a tendon or ligament” and in-
galus, following Lessertisseur and Saban (1967). The term
cluded sesamoids and mineralized tendons; they applied the
lunula has been applied more broadly in recent literature,
term periarticular elements to “those that develop adjacent
however, including ossifications between the femoro-tibial
to joints and articulations but not initially within a tendon
articulation.
or ligament” and included lunulae (meniscal ossicles) and
The ossified meniscus of IOA 27.189.003:0255 resem-
other such elements commonly associated with the au-
bles what would be expected to have been the main larger
topodium. Within the knee joint, ossification of meniscal
and lateral portion of the meniscus between the lateral
cartilage is variable, with only a single lunula or several
femoro-tibial articulation. Given that the proximal articular
being present (see, for example, Araújo et al., 2013, and
surface is concave and the distal nearly flat, it is likely that
Rahal et al., 2013). As noted by Araújo et al. (2013), lunulae
this represents the element between the lateral femoro-
are apparently true ossifications integrated with menisci
tibial articulation, as the proximolateral articular surface of
rather than ossified cartilages and occupy relatively small
the tibia is concave.
portions of an entire meniscus. In our observations among
Lull (1929) described the presence of two osseous ele-
sloths, the lunula is a semicircular, wedge-shaped element
ments between the femoro-tibial articulation of Nothrothe-
bearing flattened proximal and distal articular facets that
riops. One of these, positioned posterolaterally at the knee
lies anteriorly between the lateral femoro-tibial articulation.
joint, was considered the fabella (Stock, 1925, described the
Salas et al. (2002, 2005) noted the presence of this element
presence of the articular facet for this element in the tibia
in Thalassocnus natans but referred to it as an ossified
of Nothrotheriops). So far as can be discerned from Lull’s
meniscus because they restricted use of the term lunula to
(1929: pl. 2) illustration, it resembles in form and morphology
the plantar sesamoid of the pes adjacent to the astra-
the element reported for Thalassocnus natans by Salas et al.
166
DE IULIIS ET AL.: FIRST NOTHROTHERIID RECORD FROM CENTRAL AMERICA
(2005), who interpreted this element, following the opinion
Iuliis, 1995) from Belize (reported but undescribed by Stemp
of Lessertisseur and Saban (1967) for the condition in Cho-
and Awe, 2013), Honduras (Webb and Perrigo, 1984; Jack-
loepus Illiger, 1811, as a fusion of the cyamella and fabella,
son and Fernandez, 2005), El Salvador (Webb and Perrigo,
and thus recognized it as the cyamo-fabella. This element
1984, 1985; Cisneros, 2005), Panama (Gazin, 1957; Pear-
is not preserved among the Belize sloth remains. The
son, 2005), Costa Rica (Mead et al., 2006) and Guatemala
second osseous element noted by Lull (1929, p. 14) was
(McDonald, pers. observ.); the megalonychids Megalonyx
described as a flattened bone, “the outlines of which are
from El Salvador (Stirton and Gealey, 1949; Webb and Pe-
obscured by tissue”. This element is not discernable in Lull’s
rrigo, 1984; Cisneros, 2005) and Honduras (Webb and Pe-
(1929: pl. 2) illustration, but from his description and the
rrigo, 1984) and Meizonyx Webb and Perrigo, 1985 (see also
fact that it is not visible in his illustration suggests that it is
McDonald, 2014) from El Salvador; and mylodontids from
not a lunula (which should be recognizable in Lull’s x-ray
Guatemala, reported but undescribed by Woodburne (1969).
image), but rather an ossified meniscus, such as that of IOA
Remains of earlier taxa include the Miocene megalonychid
27.189.003:0255.
Pliometanastes Hirschfeld and Webb, 1968 from Costa Rica
The nearest geographic records of nothrotheriids are, as
(Laurito and Valerio, 2012).
noted above, of N. shastensis from Rancho de las Ollas,
The Belize nothrotheriid is a significant discovery, given
Michoacán, and the Valley of Mexico, México, but in reality
that it is the southernmost certain record for nothrotheriids
all the records from Mexico except that from the very north-
and raises interesting paleoecological and biogeographic
ern El Golfo, Sonora, locality are of this species. Despite this
questions. The diet of Nothrotheriops has been well docu-
morphological resemblance, the limited material available
mented based on the recovery of dung referred to this taxon
from Actun Lak might seem to preclude certain specific
from numerous caves in the southwestern United States.
assignment, as the postcranial remains of N. shastensis and
Confirmation that the dung was indeed produced by a sloth
N. texanus are morphologically similar to each other and
has come from the recovery of ancient DNA (Poinar et al.,
these species are distinguishable mainly on proportions of
1998). Over 72 genera of plants were identified in dung
the skull and mandible. On the other hand, the likely late
from Rampart Cave, Arizona (Martin et al., 1961; Hansen,
age of the Actun Lak material, the geographic proximity to
1978), which indicates that while its diet was dominated
other N. shastensis remains, and the very close similarity
by xeric vegetation, such as Atriplex Linnaeus, 1753, Ephedra
in size between the Actun Lak and other N. shastensis re-
Linnaeus, 1753 and Larrea Cavanilles, 1801, Nothrotheriops
mains (with the understanding that N. texanus is clearly con-
was quite eclectic in what it consumed and fed on what was
siderably smaller than N. shastensis) strongly suggest that
available, including the common reed Phragmites Adanson,
the Actun Lak nothrotheriid belongs to N. shastensis. Other
1763. Studies of the dung of Nothrotheriops from other
sloths have been previously reported from Central America
caves in the southwestern United States (such as Gypsum
(see below), but this is the first record of a nothrotheriid from
Cave, Nevada; Shelter Cave, New Mexico, and Upper and
Central America and the southernmost record of the North
Lower Sloth Cave in the Guadalupe Mountains in Texas)
American genus Nothrotheriops.
consistently show that the animal fed on desert vegeta-
In contrast to the abundant fossil sloths remains from
tion (Laudermilk and Munz, 1934, 1938; Thompson et al.,
North America, where they extend as far north as the Yukon
1980). The advent of DNA analysis has also expanded our
(Canada; McDonald et al., 2000) and Alaska (USA; Stock,
ability to identify plants in sloth dung beyond macroscopic
1942), and South America, as well as many Caribbean is-
identification and when combined with AMS radiocarbon
lands (see McDonald, 2002; McDonald and De Iuliis, 2008),
dating permits us to track changes in diet through time
very few fossil sloth remains have been reported from Cen-
(Hofreiter et al., 2000).
tral America. In addition to being numerically depauperate,
However, the widespread distribution of Nothrotheriops
their known remains suggest a much lower level of taxo-
and its presence in faunas that were clearly not xeric (such
nomic diversity. Included among these are Pleistocene re-
as Rancho La Brea in southern California and caves sites
mains of Eremotherium Spillmann, 1948 (Cartelle and De
such as Potter Creek and Hawver in northern California)
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AMEGHINIANA - 2015 - Volume 52 (1): 153 – 171
demonstrate that Nothrotheriops was not restricted to
Pleistocene or is merely a short term range expansion re-
desert environments and was capable of utilizing a much
flecting climate conditions that permitted the establishment
wider range of habitats. Unfortunately, we do not have
of more xeric adapted vegetation to which the genus was
dung from these other sites determine exactly what types
clearly adapted to utilize as a food source. Its discovery does
of plants were being consumed. We therefore need to
clearly indicate that the diversity of sloths in northern Cen-
recognize the highly biased sample that tends to guide our
tral America was much greater than had been previously
thinking about the diet and ecology of this genus.
suspected and indicates a greater variety of habitats and
If radiocarbon dates can eventually be obtained for
that there may have been more dramatic changes in the
Nothrotheriops specimens from Belize or as might be ex-
types of vegetation communities present in the region during
pected from other sites in the region now that its presence
the Pleistocene than previously thought.
has been documented, it may be that these records document times of decreased rainfall and a more arid environ-
ACKNOWLEDGMENTS
ment and perhaps communities of more xeric adapted
We would like to thank J. Awe and J. Morris of the Belize Institute of Archaeology for their continuing support of the research in and around Pacbitun. We would also like to thank the Alphawood Foundation, Petzl, and the University of California, Riverside Center for Ideas and Society for their generous financial support of our project. It is greatly appreciated and excavations like this would not have been possible without it. We thank R. McAfee and A. Zurita for reviewing the manuscript. Their comments and suggestions were helpful in improving this paper. M. Badillo of the Institute of Archaeology is thanked for her help and expertise with the exportation of the sloth bones. We appreciate the efforts of K. L. Seymour (ROM) for his help in temporarily curating the remains and accommodating our research at the ROM. C. Shaw shared with us his measurements of Nothrotheriops from Josecito Cave, and F. Pujos for help with the figures.. Thanks are also extended to A. Boileau, J. Griggs Burnette, A. McKinney, J. Weber, and P. Spenard. These excavations would have also not been possible without the local support and assistance of F. Bol, J. Mai, L. Mai, O. Mai, and S. Bol.
vegetation. Around the Last Glacial Maximum it appears that the modern summer precipitation regime in the Yucatan had collapsed (Metcalfe et al., 2000). Leyden (1984) and Leyden et al. (1993) documented that the Central American lowlands were cooler and more arid during Interstadial Stage 3 (~36 to 24 ka) and continued to cool with increasing aridity during Stage 2 (~24–13 ka), with the lowest lake levels at this time resulting in savanna and juniper scrub habitat, a habitat utilized by Nothrotheriops farther north. Given the essential absence of the present rainforest in the region during this time, the presence of Nothrotheriops is not all that unusual. Alternatively, it may be that its presence does not reflect simply a decrease in rainfall but
REFERENCES
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Adanson, M. 1763. Familles des Plantes. Vincent, Paris, 640 p. Aguiar, J.M., and Fonseca, J.A.B. 2008. Conservation status of the Xenarthra. In: S.F. Vizcaíno, and W.J. Loughry (Eds.), The Biology of the Xenarthra. University Press of Florida, Gainesville, p. 215–231. Akersten, W.A., and McDonald, H.G. 1991. Nothrotheriops (Xenarthra) from the Pleistocene of Oklahoma and paleogeography of the genus. The Southwestern Naturalist 36: 178–185. Ameghino, F. 1907. Notas sobre una pequeña colección de huesos de mamíferos procedentes de las grutas calcáreas de Iporanga en el estado de São Paulo, Brasil. Revista do Museu Paulista 7: 59–124. Ameghino, F. 1920. Sur les édentés fossiles de l’ Argentine. Examen critique, révision et correction de l’ ouvrage de M. R. Lydekker “The exinct edentates of Argentina”, etc. (Ouvrage à démi-inédite avec des notes additionelles sur quelques ongulés et carnassiers). In: A.J. Torcelli (Ed.), Obras Completas y Correspondencia Científica de Florentino Ameghino, Taller de Impresiones Oficiales del Gobierno de la Provincia de Buenos Aires, 11: 447–909. Amson, E., Muizon, C. de, Laurin, M., Argot, C., and de Buffrénil, V. 2014. Gradual adaptation of bone structure to aquatic lifestyle in extinct sloths from Peru. Proceedings of the Royal Society B: Biological Sciences. doi: 10.1098/rspb.2014.0192. Araújo, F.A.P., de Sesoko, N.F., Rahal, S.C., Teixeira, C.R., Müller, T.R., and Machado, M.R.F. 2013. Bone morphology of the hind limbs in two caviomorph rodents. Anatomia, Histologia, Embryologia 42: 114–123.
Nothrotheriops may have occurred during the Late Glacial Maximum when there was the maximum lowering of sea level and less surface water in the region. The drop in sea level would have effectively lowered the water table throughout the Yucatan Peninsula and surrounding limestone areas and reduced the amount of surface water available to plants as well as the fauna (Metcalfe et al., 2000). The use of caves by Nothrotheriops has been discussed by Akersten and McDonald (1991), but these previously proposed ideas might not be relevant in the current regional context. It is possible that the sloths’ use of the caves in Belize and the Yucatan was primarily to access water, which was no longer available on the surface. Based on the current geographically limited sample and the lack of a chronology we cannot determine whether Nothrotheriops was a long-term resident of the region dating back to its first appearance in North America in the middle
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doi: 10.5710/AMGH.05.11.2014.2821 Submitted: August 20th, 2014 Accepted: November 5th, 2014
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