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Journal of South American Earth Sciences 110 (2021) 103389
Available online 21 May 2021
0895-9811/© 2021 Elsevier Ltd. All rights reserved.
A new mammalian assemblage for Guanaco Formation (northwestern
Argentina), and the description of a new genus of New World porcupine
Marcos D. Ercoli
a
,
b
,
*
, Alicia ´
Alvarez
a
,
b
, Diego H. Verzi
c
, Juan Pablo Villalba Ulberich
a
,
b
,
Sofía I. Qui˜
nones
d
, Ornela E. Constantini
a
,
b
, Alfredo E. Zurita
d
a
Instituto de Ecorregiones Andinas (INECOA), Universidad Nacional de Jujuy, CONICET, Av. Bolivia 1661, CP 4600, San Salvador de Jujuy, Jujuy, Argentina
b
Instituto de Geología y Minería, UNJu, Av. Bolivia 1661, CP 4600, San Salvador de Jujuy, Jujuy, Argentina
c
CONICET, Secci´
on Mastozoología, Divisi´
on Zoología Vertebrados, Museo de La Plata, Paseo del Bosque S/Nº, CP B1900FWA, La Plata, Buenos Aires, Argentina
d
Laboratorio de Evoluci´
on de Vertebrados y Ambientes Cenozoicos-Centro de Ecología Aplicada del Litoral (CECOAL-CONICET) y Universidad Nacional del Nordeste,
Ruta 5, kil´
ometro 2,5, CP 3400, Corrientes Capital, Corrientes, Argentina
ARTICLE INFO
Keywords:
Caviomorpha
Glyptodontidae
Jujuy
Miocene-pliocene transition
Late neogene paleoenvironments
Río chico locality
ABSTRACT
The Guanaco Formation (Or´
an Group) is one of the Neogene units outcropping in the Subandean region of
northwestern Argentina. The fossil assemblage from the middle section was studied in a few contributions. Here
we present new remains for the middle section (~6.3 Ma) and the rst records for the upper section (<5.7 Ma) of
this unit, collected in the Río Chico locality of Jujuy Province. The remains from the middle section include very
well-preserved cranium, cephalic armor, and part of the carapace of a small glyptodontid assigned to Cra-
nithlastus xibiensis, representing the second specimen known for the species. The remains from upper section
represent the youngest mammalian association known for the Guanaco Formation, and include fragmentary
remains of ve caviomorph rodent taxa, including Lagostomus sp., Caviinae indet., Caviodon sp., Octodontoidea
indet., the latter three representing new taxa for the unit. The fth taxon of the upper section corresponds to a
new genus and species of porcupine (Erethizontidae), represented by a fragment of left maxilla with DP4-M1.
This and other recent paleontological studies, together with sedimentological and geochronological data of
Guanaco Formation, are contributing to the knowledge of the past diversity of the area, and the faunistic and
environmental evolution of the Central Andes ecoregions in northwestern Argentina. The preliminary charac-
terization of the youngest faunistic association reveals the presence of forest-dweller taxa with conservative
occlusal and postcranial morphologies, concurs with the context of local and regional progressive break-up of
basins, increasing of moisture supply, and development of powerful streams related to a stepper slopes landscape.
The evidence supports forested foothill environments, including subtropical components, for the upper levels of
the Guanaco Formation, giving clues regarding to the tempo and mode in which Chacoan-like communities were
replaced by subtropical mountain rain forests communities of Yungas.
1. Introduction
Guanaco Formation (Or´
an Group; late Miocene-early Pliocene;
Gebhard et al., 1974; Hain et al., 2011; Villalba Ulberich et al., 2021) is
one of the Neogene units outcropping in the Subandean and closer re-
gions of Jujuy and Salta provinces (northwestern Argentina). In a
regional context, the same span is also represented in fossiliferous lo-
calities of Puna and Eastern Cordillera of these provinces. In eastern
Puna, two new fossiliferous localities (Calahoyo and Casira) were
recently described (Zurita et al., 2017; Qui˜
nones et al., 2019), and, ac-
cording to the recorded palaeofauna, they correspond to middle-late
Miocene and Pliocene, respectively (see also Qui˜
nones, 2021). In
Eastern Cordillera two units roughly contemporaneous with the Gua-
naco Formation are exposed: Maimar´
a (late Miocene–early Pliocene; e.
g., Pingel et al., 2013; Abello et al., 2015; Bonini et al., 2017a), and Palo
Pintado formations (late Miocene), the latter intensively studied (e.g.,
Reguero et al., 2014; Zimicz et al., 2018; Robledo et al., 2020). These
recent studies are improving the knowledge about paleocommunities
* Corresponding author. Instituto de Geología y Minería, UNJu, Av. Bolivia 1661, 4600, San Salvador de Jujuy, Jujuy, Argentina.
E-mail addresses: marcosdarioercoli@hotmail.com, marcos.ercoli@conicet.gov.ar (M.D. Ercoli), alvarez.ali@gmail.com (A. ´
Alvarez), dverzi@fcnym.unlp.edu.ar
(D.H. Verzi), jpvillalbaulberich@gmail.com (J.P. Villalba Ulberich), soaiq9@gmail.com (S.I. Qui˜
nones), constantini.oe@gmail.com (O.E. Constantini),
aezurita74@yahoo.com.ar (A.E. Zurita).
Contents lists available at ScienceDirect
Journal of South American Earth Sciences
journal homepage: www.elsevier.com/locate/jsames
https://doi.org/10.1016/j.jsames.2021.103389
Received 16 February 2021; Received in revised form 29 April 2021; Accepted 17 May 2021
Journal of South American Earth Sciences 110 (2021) 103389
2
and paleoenvironmental changes during the Neogene, and the link with
tectonic evolution in Central Andes in northern Argentina.
In the territory of Jujuy Province, the most studied outcrops corre-
spond to the Río Chico locality, where fossils described here were found.
The Guanaco Formation is a coarsening upward sequence characterized
by coarse to ne-grained sandstones, with levels of conglomerates
interbedded corresponding to uvial and alluvial environments (Geb-
hard et al., 1974; Russo and Serraiotto, 1979; Gonz´
alez et al., 1996;
Villalba Ulberich et al., 2021). Different studies allowed to constraint
the age of deposition of the sedimentary column of this unit between
~10 Ma and ~5 Ma (Viramonte et al., 1994; Reynolds et al., 2000; Hain
et al., 2011; Coira et al., 2018; Villalba Ulberich et al., 2021).
As typical for the units of these subtropical latitudes located on the
eastern ank of Central Andes, it is extensively covered by the Yungas
jungles, a situation that limits the prospection and knowledge about its
fossil record. Nevertheless, early contributions (Arias et al., 1979) and
recent ones (Ercoli et al., 2017, 2019) revealed an interesting diversity
of fossil mammals so far exclusively coming from two localities: Río
Chico and Los Alisos (Arias et al., 1979; Ercoli et al., 2019; Salgado
Ahumada et al., 2020). These records, although mainly represented by
fragmentary materials, include several caviomorph rodents and xenar-
thrans. Among caviomorphs, teeth and some postcranial remains of
small taxa are recorded, which correspond to Lagostomus (“Lagosto-
mopsis”; Chinchillidae), Orthomyctera (Caviidae), and an indeterminate
octodontoid. Among xenarthrans, many isolated osteoderms of several
small-to medium-sized dasypodids are known, including several species
of euphractines and eutatines, and an isolated movable osteoderm of the
dasypodine Dasypus. Additionally, few medium to large taxa are recor-
ded by two well-preserved specimens of the glyptodontid Cranithlastus
xibiensis (“Plohophorini”; with preserved skull and different carapace
parts including the caudal tube), isolated glyptodontid and pampa-
theriid osteoderms, and an isolated mandibular remain of an indeter-
minate megatheriid (Pilosa). Finally, some plates of indeterminate
turtles (Testudines) are known as the only non-mammalian vertebrates
record (Arias et al., 1979; Starck and Vergani, 1996; Ercoli et al., 2017,
2019, 2019; Salgado Ahumada et al., 2020). All these specimens came
from middle levels of the Guanaco Formation, closer to a dated tuff of
6.3 Ma (Messinian stage; late Miocene; Coira et al., 2018 and cites
therein) and previously interpreted as corresponding to the Huay-
querian (Arias et al., 1979; Coira et al., 2018; Ercoli et al., 2019). Fossil
records from upper levels were not known until this study.
Here we present new mammalian fossil records for the middle and
upper sections of the Guanaco Formation outcropping at the Río Chico
locality, Jujuy Province, northwestern Argentina. Remains from the
upper section are the youngest records for the Guanaco Formation
represented by novel taxa for the area and a new genus and species of
erethizontid rodent. Based on recent depositional environments in-
ferences and well-constrained geochronological framework, the new
mammalian association is analyzed considering its relevance for the
knowledge of the faunal diversity of the Guanaco Formation, and evo-
lution of the Central Andes ecoregions.
2. Materials and methods
The studied specimens were collected in the middle and upper sec-
tions of the Guanaco Formation in the cliffs of the Chico river (Xibi-xibi
river) and nearer exposures on Provincial Route 2 (Fig. 1). In the case of
the fossils coming from the upper section, we took advantage of the
exposure of new and non-weathered outcrops related to the roadworks
on this route. The described specimens correspond to a glyptodontid and
Fig. 1. Map indicating the geographic locations of the outcrops of Río Chico locality (circles): Site 1- middle levels below Corte Blanco tuff (fossil described in this
contribution), Site 2-middle levels above Corte Blanco tuff (fossils described in Arias et al., 1979), and Site 3- upper levels above “4th tuff” of Villalba Ulberich et al.
(2021) (fossils described in this contribution).
M.D. Ercoli et al.
Journal of South American Earth Sciences 110 (2021) 103389
3
several rodents, all of them housed in the paleontological collection of
the Instituto de Geología y Minería (JUY-P, IdGyM, Universidad
Nacional de Jujuy, Jujuy Province, Argentina). Mentioned comparative
materials belong to the following collections: mammalogical collection
of Colecci´
on Miguel Lillo (CML-, Tucum´
an, Argentina); mammalogical
and paleontological collections of Field Museum of Natural History
(FMNH-, FMNH P-, Illinois, U.S.A); mammalogical and “Ameghino”
paleontological collections of the Museo Argentino de Ciencias Natu-
rales “Bernardino Rivadavia” (MACN Ma-, MACN A-, Ciudad Aut´
onoma
de Buenos Aires, Argentina); paleontological collection of the Museo de
Ciencias Naturales de Salta (CNS-, Universidad Nacional de Salta,
Province, Argentina); paleontological collection of the Museo Uni-
versitario Carlos y Florentino Ameghino (MUFyCA, Universidad
Nacional de Rosario, Santa Fe, Argentina); and mammalogical collection
of the Museu de Zoologia da Universidade de S˜
ao Paulo (MZUSP-,
Universidad de S˜
ao Paulo, S˜
ao Paulo, Brasil). For the case of the novel
porcupine taxon, an exhaustive list of specimens and sources of litera-
ture used during comparisons were enlisted on Appendix 1. Measure-
ments of the specimens were taken on scaled digital images.
Taxonomical assignments were performed considering the more recent
systematic contributions and limited by the fragmentary nature of
almost all the studied specimens.
The glyptodontid specimen was collected from a massive sandstone
level of the middle section of the Guanaco Formation on the cliffs of the
Chico river -site 1- (Figs. 1 and 2), which represents a sandy channel of a
braided uvial system (Villalba Ulberich et al., 2021). This level is few
meters below the Corte Blanco tuff level (Coira et al., 2018). The rst
glyptodontid remains collected by Arias et al. (1979) came from higher
Fig. 2. Stratigraphic prole of Río Chico locality
modied from Villalba Ulberich et al. (2021). Fossil-
iferous levels, limit between formations, and relevant
tuffs are indicated. In the zoom-in column, levels A, B,
C, and D are indicated, corresponding to upper
fossiliferous levels in which rodent fossil remains
were identied, while assignable remains correspond
to levels C (small rodents) and D (Caviodon sp.). First
tuff corresponds to Corte Blanco; second tuff corre-
sponds to “4th tuff” of Villalba Ulberich et al. (2021).
Scale in meters.
M.D. Ercoli et al.
Journal of South American Earth Sciences 110 (2021) 103389
4
levels of the middle section of Guanaco Formation (see Starck and
Vergani, 1996), above the Corte Blanco tuff level (Fig. 2). Rodents came
from four thin ne-grained levels (site 3, A-D levels; Figs. 1 and 2),
interbedded in the mainly conglomeratic upper section, which represent
low-energy episodes in alluvial fan environments. These levels,
outcropping in the Provincial Route 2, are located near to the top of
Guanaco Formation, above from the level corresponding to the “4th tuff”
(dated at 5.7 Ma) of Villalba Ulberich et al. (2021) (Fig. 2). Only the two
upper levels (C and D levels) provided fossil remains sufciently pre-
served to be determined (Fig. 2).
3. Results
3.1. Systematic paleontology
Class MAMMALIA Linnaeus, 1758
Order RODENTIA Bowdich, 1821
Suborder HYSTRICOMORPHA Brandt, 1855
Superfamily OCTODONTOIDEA Waterhouse, 1839
Gen. et sp. indet.
Referred material. JUY-P-157, incomplete left calcaneum (Fig. 3).
Occurrence. Site 3 of Río Chico Locality, Jujuy Province, north-
western Argentina; level C, upper section of the Guanaco Formation, late
Miocene and/or early Pliocene (<5.7 Ma).
Description. The proximodistal length of the fragment measures
9.12 mm. The astragalar platform is proximodistally short and wide. Its
lateral margin is convex. The tubercle for the quadratus plantae is absent
or restricted to the badly preserved distal aspect of this margin. The ectal
facet is proximodistally elongated, constantly convex, and its proximal
end is rounded. The preserved lateral aspect of the sustentacular facet is
separated from the ectal one by a narrow calcaneal canal. The distal end
of the ectal facet is at the level of the middle point of the sustentacular
facet. The sustentacular facet is separated from the cuboid facet by a
short distance, lesser than its own proximodistal length. The sustentac-
ular platform projects distally further beyond the sustentacular facet.
Although poorly preserved, the cuboidal facet and the distal facet for the
astragalus face are markedly tilted toward the medial direction, and
slightly tilted toward the anterior direction. The scar for the long plantar
ligament and contiguous region of the posterior aspect of the calcaneum
are markedly wide and at. The groove for the tendon of the m. exor
digitorum lateralis is shallow.
Comparisons and comments. In comparison with other similar-
sized mammals, the generalized morphology of JUY-P-157 is clearly
different from that of rodents with different modes of strictly terrestrial
locomotion (e.g., extant Octodontidae, Caviidae, Chinchillidae) or
fossorial taxa (e.g., Ctenomyidae, some Octodontidae), in which the
astragalar platform is long and the ectal and sustentacular surfaces
generate a well-interlocked joint for the talus, and are proximally
located in the former. The constantly convex prole of the ectal facet,
and non-protruding distal facet for the astragalus, differ from other
mammals of similar sizes, such as pachyrukhines (Notoungulata). The
wide distal portion, at posterior surface, markedly medially tilted
cuboid facet, and rounded aspect of the lateral margin of the astragalar
platform strongly resemble the conguration observed in some extant
echimyid rodents, particularly in representatives of the Myocastorini
tribe (sensu Fabre et al., 2017), such as Myocastor, and especially to some
species of Proechimys (e.g., Proechimys cuvieri), and the fossil aff.
Thrichomys MUFyCA 483 (Neogene of Catamarca Province). Other
octodontoid indeterminate remains are known for the middle levels of
the Guanaco Formation in Los Alisos locality (Ercoli et al., 2019).
Family ERETHIZONTIDAE Thomas, 1897
Genus Noamys nov.
Derivation of name. Noa, from the Spanish abbreviation NOA for
northwestern Argentina, -mys Greek-derived sufx for mouse or rat.
Type species. Noamys hypsodonta, the single species of the genus.
Occurrence. Site 3 of Río Chico Locality, Jujuy Province, north-
western Argentina; level C, upper section of the Guanaco Formation, late
Miocene and/or early Pliocene (<5.7 Ma).
Diagnosis. Small-sized erethizontid. Ventral zygomatic root anterior
to DP4. DP4-M1 unilaterally hypsodont, higher crowned than those of
other extinct and living erethizontids; tetralophodont and with oval-
shaped overall occlusal contour. Lophs and surrounding enamel very
thin. Paraexus and metafossette mesiodistally wide, not lingually
extended beyond the mure or only slightly so. Metaloph no distinct.
Paracone bulky and well-dened. Hypoexus short, wide and mesially
tilted, oriented towards and close to (DP4) or contacting with (M1) the
paraexus. Mure present. Hypocone at the level of (M1) or slightly
lingual to (DP4) the protocone.
Noamys hypsodonta sp. nov.
Holotype. JUY-P-153, fragment of left maxilla with DP4-M1 (Fig. 4).
Derivation of name. -hypso, high; -donta, teeth; because its higher
hypsodonty in molariforms compared to other erethizontids.
Diagnosis. As for the genus by monotypy.
Description. Noamys hypsodonta sp. nov. is described through a
single juvenile specimen, JUY-P-153, represented by a left maxillary
fragment with complete and scarcely worn DP4-M1. The anteroposterior
and transverse maximum lengths of DP4 are 2.97 mm and 1.84 mm,
respectively. The anteroposterior and transverse maximum lengths of
M1 are 3.04 mm and 2.24 mm, respectively. The preserved portion of
maxilla, restricted to a sector lateral and anterior to the molariforms,
includes the zygomatic root; which is wide and anterior respect to the
level of the DP4. The DP4-M1 are unilaterally hypsodont, with an oval-
shaped and tetralophodont occlusal design. The fully molarized DP4 is
similar in size and shape to the M1, but slightly narrower. The protocone
and hypocone areas, as well as the lophs, are narrow, and seem to be
maintained during ontogeny since the crown does not expand towards
the base or it does so only moderately. The protocone is at the level of
the protoloph. Both, protocone and hypocone are distolingually
directed; the hypocone locates at the same level (M1) or is slightly
lingual (DP4) to the protocone. The hypoexus is short, mesially tilted,
facing towards the lingual end of the paraexus. The mure is present,
separating the hypoexus from the mesoexus, and the posterior arm of
the protocone separates the hypoexus from the paraexus. The lophs
and surrounding enamel are thin. The protoloph, mesolophule, and
Fig. 3. Octodontoid calcaneum (JUY-P-157) in anterior view. Proximal sector
of calcaneal tubercle is not preserved. Scale bar =1 mm.
M.D. Ercoli et al.
Journal of South American Earth Sciences 110 (2021) 103389
5
posteroloph are slightly anterolabially directed. Both in the DP4 and M1,
the anteroloph is anteriorly extended and strongly curved, and conse-
quently the paraexus is wide. The anteroloph of DP4 is more curved
than that of M1. There is a constriction at the end of the anteroloph in
the DP4 that separates this loph from a presumed parastyle. On both the
DP4 and M1, this end curves posteriorly towards the paracone. The
paracone is the best dened labial cusp, which is located immediately
labial and anterolabial to the end of the protoloph. The paraexus and
metafossette are mesiodistally wide, not lingually extended beyond the
mure or only slightly so. The mesoexus is also wide, rectangular-
shaped, with the labial opening markedly shallower than the lingual
bottom. There is not a distinct metaloph, but it could be submerged into
the posteroloph expansion.
Comparisons and comments. Noamys shares similarities with ere-
thizontids and some rooted-molared octodontoids. It resembles the
octodontoids Acaremys and Cercomys in its small size, hypsodont and
tetralophodont molars with a deep mesoexus (see Arnal and Vucetich,
2015; Montalvo et al., 2019:Fig. 6). Nevertheless, Noamys shares more
similarities with erethizontids. We assign the new genus to Erethi-
zontidae based on the following evidence: 1) roughly similar amplitude
of paraexus, mesoexus and metafossette; the paraexus and meta-
fossette being anteroposteriorly wider than in octodontoids; 2) proto-
cone area anteroposteriorly elongate, this and the hypocone area being
nearly parallel to the sagittal axis; 3) anteroloph strongly curved back-
ward, with its labial end oriented towards the paracone; 4) well-dened
paracone, extended especially ahead of the end of the protoloph; pro-
toloph and mesolophule slightly divergent, not parallel.
Noamys and steiromines, except by Hypsosteiromys, share a ventral
zygomatic root located anterior to the DP4 (Candela, 1999, 2004; this
structure is not preserved in some fossil taxa, e.g., Branisamyopsis,
Microsteiromys; Walton, 1990; Kramarz, 2001, 2004), a feature consid-
ered relevant by its diagnostic and phylogenetic value (Candela, 1999,
2004; and cites therein). In erethizontines, the ventral zygomatic root is
placed at the level of DP4, except by some specimens of Chaetomys (e.g.,
MZUSP 32110). The oval-shaped and mesiodistally elongated DP4-M1,
with labiolingually narrower fossettes/exi are non-frequent features
in erethizontids, but they are recorded in Hypsosteiromys (Dozo et al.,
2004) and the smallest fossil erethizontids (e.g., Frailey, 1986:Fig. 11C;
Campbell et al., 2006:Fig. 15 E, here considered to represent an upper
molar; but see P4 of cf. Microsteiromys, Antoine et al., 2013). Although a
roughly oval occlusal contour is also present in Chaetomys, this genus
possesses a completely different occlusal design (e.g., MZUSP 32038;
MZUSP 32110). The remaining of the compared erethizontids show
equi-dimensional or labiolingually elongated DP4-M1 (e.g., Candela,
2003, 2004). The putative octodontoid Marisela (Vucetich et al., 2010)
also presents mesiodistally elongated teeth but they are sub-rectangular
in their occlusal contour. A not very frequent feature in erethizontids is
the presence of tetralophodont molariforms, without a distinct metal-
oph. This conguration is shared by Noamys and the smallest erethi-
zontids (cf. Microsteiromys and specimens from Madre de Dios
Formation, Acre river, Peru; Frailey, 1986; Campbell et al., 2006;
Antoine et al., 2013), and also recorded in the M1 of Hypsosteiromys
(Patterson, 1958; Candela, 1999; Dozo et al., 2004), some specimens of
Coendou spinosus (which present a tetralophodont pattern with an absent
or vestigial metaloph; MACN Ma 22839, MACN Ma 54–3; see also MACN
Ma 30–243), and a non-published species of Eosteiromys (see Candela,
2003:492). The same conguration is also recorded in Marisela (Vuce-
tich et al., 2010). With regards to the hypoexus conguration, Noamys
strongly resembles to Hypsosteiromys (Patterson, 1958:Fig. 1; Dozo et al.,
2004), some specimens of Protosteiromys (e.g., Wood and Patterson,
1959:Fig. 30B), and in their shortness and oblique orientation, facing
toward the protoloph or paraexus/parafossette. The hypoexus
conguration also resembles in these concerns isolated molars from Acre
river, Peru, illustrated by Frailey (1986:Fig. 11C) and Campbell et al.
(2006:Fig. 15E). The oblique orientation of the hypoexus of Marisela
also resembles to that observed in the DP4 and M1 of Noamys, but they
are deeper in the former. The hypocone located at a similar level with
that of the protocone, or slightly lingual to the latter, is a feature that
Noamys shares with several fossil taxa, including the erethizontids Par-
asteiromys, Protosteiromys, Hypsosteiromys, the small erethizontids from
Fig. 4. Fragment of left maxilla with DP4-M1 of Noamys hypsodonta (gen. et sp. nov., JUY-P-153) in occlusal view. Scale bar =1 mm.
M.D. Ercoli et al.
Journal of South American Earth Sciences 110 (2021) 103389
6
Acre river, Peru (Frailey, 1986:Fig. 11C; Campbell et al., 2006:Fig. 15D),
some specimens of Eosteiromys (e.g., Kramarz, 2001:Fig. 20B,C), and the
putative octodontoid Marisela (Vucetich et al., 2010). Regarding to
extant taxa, this conguration is only observed in Chaetomys and the
DP4 and M1 of some specimens of Coendou (e.g., DP4 and M1 of FMNH
61863, MACN Ma, 19050; DP4 of MACN Ma 54–3, MACN Ma 17918,
MACN Ma 31–237; M1 of FMNH 15611, FMNH 34993). In summary, the
analysis of the combined features of Noamys support that the new genus
differs from all extant and extinct erethizontids.
Noamys is the most hypsodont genus among both extinct and extant
erethizontids (see Candela and Vucetich, 2002; Dozo et al., 2004). It is
smaller in size than other extant and extinct erethizontids except by cf.
Microsteiromys (Antoine et al., 2013) and the small erethizontids from
Acre river reported by Campbell et al. (2006). Enamel layers are thin in
Noamys, and tend to be thicker in other erethizontids, especially in
Neosteiromys (Candela, 2004), although this comparison could be biased
by the juvenile condition of Noamys (see Candela, 2003). Noamys differs
from Coendou, Erethizon, Hypsosteiromys (Dozo et al., 2004), and some
specimens of Chaetomys in the advanced location (anterior to DP4) of the
ventral zygomatic root (see also Candela, 1999 and see above); this
feature is not known for Microsteiromys, Branisamyopsis, and Acre re-
mains. The new genus differs from most extant and extinct erethizontids
by: 1) rounded and mesiodistally elongated molar contours and nar-
rower exi/fossettes (except by Hypsosteiromys; see Dozo et al., 2004); 2)
tetralophodont DP4-M1 by the complete loss of the metaloph and
posterofossette [except for some Coendou specimens, especially
C. spinosus (see above), cf. Microsteiromys in Antoine et al. (2013), some
Acre remains in Campbell et al. (2006), the M1 of Hypsosteiromys (see
Patterson, 1958; Dozo et al., 2004), and Neosteiromys bombifrons (see
Candela, 2004); Steiromys detentus has a very reduced posterofossette
(see Kramarz, 2001)]; 3) shallower hypoexus (except for Proto-
steiromys; Patterson, 1958; Wood and Patterson, 1959; see also Candela,
1999; and Hypsosteiromys; Patterson, 1958; Dozo et al., 2004); 4) more
labially located protocone (except for Coendou, Parasteiromys, Proto-
steiromys, and Hypsosteiromys). In addition, Noamys differs from Para-
steiromys (Candela, 1999) and the M1 of N. bombifrons (Candela, 2004)
by the presence of mure; the DP4 differs from that of Hypsosteiromys by
the presence of mesolophule. DP4-M1 of Noamys differs from Branisa-
myopsis, Neosteiromys, Hypsosteiromys (in the case of DP4, Dozo et al.,
2004), and some specimens of Eosteiromys annectens (Kramarz, 2001:
Fig. 19; 2004:Fig. 6) by the paraexus disconnected from the hypoexus
(Candela, 2003, 2004, 2004; Dozo et al., 2004; Kramarz, 2001, 2004).
Finally, Noamys differs from Neosteiromys by the well-differentiated
labial cusps and later closing of lingual and labial exi (Candela,
2004), and from the putative octodontoid Marisela by the rounded
contour of its M1, non-sharp ends of protocone and hypocone, and
narrower exi/fossettes.
Although Noamys cannot be directly compared with Paradoxomys
and Microsteiromys, which are known only through lower molars (Wal-
ton, 1990, 1997, 1997; Vucetich and Candela, 2001), the latter taxa
have low-crowned molars. Paradoxomys is clearly larger than Noamys
(Vucetich and Candela, 2001; Candela, 2004), while Microsteiromys is
smaller than Noamys and presents thicker enamel layers (Walton, 1990,
1997).
Superfamily CAVIOIDEA Fischer de Waldheim, 1817
Family CAVIIDAE Fischer de Waldheim, 1817
Caviodon sp.
Referred material. JUY-P-156, right lower molar (Fig. 5).
Occurrence. Site 3 of Río Chico Locality, Jujuy Province, north-
western Argentina; level D, upper section of the Guanaco Formation, late
Miocene and/or early Pliocene (<5.7 Ma).
Description. The mesiodistal length is 7.72 mm. The length and
width of the anterior lobe are 3.52 and 5.54 mm, respectively. The
length and width of the posterior lobe are 4.22 and 5.52 mm,
respectively. The deepness of the ssures of the anterior and posterior
lobes are 1.84 and 1.76 mm, respectively. It is a bilobed tooth with two
heart-shaped prisms, not markedly mesiodistally compressed. Each lobe
presents an accessory internal ssure; in the case of the anterior one (hsi
sensu P´
erez et al., 2018), it is displaced distally from the middle line of
the prism, while the accessory ssure of the posterior lobe (hpi sensu
P´
erez et al., 2018) is located on the middle-line. These ssures present
irregular margins, and they are subequal in depth reaching a point near
to 30% of the labiolingual width of each prism. The hsi is mesiodistally
narrower than the hpi. The overall contour, relative mesiodistal width
with respect to the labiolingual width of both lobes, and the main di-
rection of prisms, mainly perpendicular to the inferred lingual margin
allow assigning the JUY-P-156 fossil to an inferior molar. With respect to
upper dentition, the only element that could eventually agrees with this
morphology is the P4 (Rovereto, 1914; Vucetich et al., 2010:Fig. 4),
which usually presents a similar mesiodistal and labiolingual pro-
portions, but the prisms direction tend to tilt mesially, which seems to
disagree with the described specimen.
Comparisons and comments. In literature, diagnostic traits for
Caviodon and Cardiomys are related mainly to skull features, number of
prisms in p4 and M3 (Pascual et al., 1966; P´
erez et al., 2018), which are
not comparable to JUY-P-156. However, overall teeth morphology can
be taken into account in comparisons. The similar extension and rela-
tively depth of both accessory ssures allow us assigning the analyzed
material to Caviodon, and not to Cardiomys or Procardiomys (see Pascual
et al., 1966; Vucetich et al., 2010; P´
erez et al., 2018). Although is not a
diagnostic trait, the irregular margins of the accessory ssures, are
present in several species of Caviodon such as C. andahualensis and
C. cuyano, differing from other Caviodon species and Cardiomys ones that
do not present this character (P´
erez et al., 2018:Figs. 4–5). In Caviodon,
the lobes tend to be more transversally elongated, and the accessory
ssures usually are near the middle line of each prism compared to
Cardiomys (P´
erez et al., 2018). Nevertheless, there are some variants in
these aspects for Caviodon species, and the conguration of JUY-P-156 is
similar to that described and illustrated for C. andalhualensis (e.g. P´
erez
et al., 2018:Fig. 5I). Despite this, we preferred to avoid a specic
assignment considering that only an isolated tooth was recovered, and
the previous contributions denoted intraspecic and ontogenetic vari-
ations (Vucetich et al., 2010; P´
erez et al., 2018). The material here
described represents the rst record of cardiomyines for Guanaco For-
mation and other Neogene units of Jujuy Province. The fossil record of
Caviodon spp. encompasses Huayquerian to Chapadmalalan (latest
Miocene-Pliocene) (P´
erez et al., 2018).
Fig. 5. Right lower molar of Caviodon sp. (JUY-P-156) in occlusal view. Scale
bar =2 mm.
M.D. Ercoli et al.
Journal of South American Earth Sciences 110 (2021) 103389
7
Subfamily CAVIINAE Fischer de Waldheim, 1817
Gen. et sp. indet.
Referred material. JUY-P-152, fragmentary left upper molariform
(Fig. 6).
Occurrence. Site 3 of Río Chico Locality, Jujuy Province, north-
western Argentina; level C, upper section of the Guanaco Formation, late
Miocene and/or early Pliocene (<5.7 Ma).
Description. The labiolingual width is 2.94 mm, and the mesiodistal
length of the anterior lobe is 1.34 mm. The general shape and marked
labial projection of the lobe immediately mesial to the secondary
external exus allowed us assigning the JUY-P-152 to an anterior prism
of an upper molariform. Small cordiform prism corresponding to the
anterior lobe; mesiodistally wider in its middle sector. Lingual tip
cramped nearly to its end. The contour is covered by enamel, including
the external secondary exus, except by the labiodistal extreme of the
prism. A transverse dentine crest is present near to the middle of the
lobe, slightly displaced distally. The preserved mesial sector of the
external secondary exus indicates that it is deep, reaching the same
level that the deepest part of the hypoexus, but posteriorly displaced
with respect to the latter. The labial end of the anterior lobe is markedly
projected labiodistally, and it is delimited distally by a transverse
enamel margin that corresponds with the mesial margin of the external
secondary exus, and mesially by a subtly sinuous enamel layer, that
corresponds to the transition with the anterior margin of the prism. The
external secondary exus and hypoexus are lled with cement.
Although partially broken, the connection area between the anterior and
posterior lophs is represented by a narrow dentine bridge surrounded by
the enamel layers of the deepest aspects of the external secondary exus
and hypoexus.
Comparisons and comments. The shape and position of the
external secondary exus, which is posterior to the hypoexus (instead
at the level of the hypoexus as occurs in Dolichotinae), allow us the
assignation to Caviinae (Ameghino, 1889; Pascual et al., 1966). The
absence of a very deep external secondary exus, a quadrangular shape
of the prism, and the absence of a primary external ssure in the labial
margin of the anterior prism, allowed discarding the assignation to Cavia
and Galea, respectively and their closer taxa. The rounded contours of
the prism in its wider sector, the relatively poor deepening of the
external secondary exus, and the absence of a primary external ssure
found in the JUY-P-152 material resemble to features present in upper
molariforms of the clade Neocavia +Microcavia +Dolicavia. Particularly,
the labial projection reaching the anterior margin of the posterior loph
(represented in JUY-P-152 by a small sector adjacent to the deepest part
of the hypoexus) is a diagnostic trait of this clade and useful to
distinguish among those genera (Madozzo-Ja´
en et al., 2018). Although
the state of preservation of the studied material precludes an accurate
comparison, a relatively sharp condition can be described, making the
studied remain more similar to Microcavia and Dolicavia though it has a
sharp projection but distally projected; Neocavia spp. were described as
presenting a rounded posterolabial projection (Madozzo-Ja´
en et al.,
2018). This fossil material represents the rst caviinae taxa for Guanaco
Formation and other Neogene units of Jujuy Province. The temporal
span of the caviine taxa included in the clade Neocavia +Microcavia +
Dolicavia encompasses Huayquerian to Marplatan (latest
Miocene-earliest Pleistocene) (Deschamps, 2005; Madozzo-Ja´
en et al.,
2018; Candela et al., 2019).
Superfamily CHINCHILLOIDEA Bennet, 1833
Family CHINCHILLIDAE Bennet, 1833
Subfamily LAGOSTOMINAE Wiegmann, 1835
Lagostomus sp.
Referred material. JUY-P-155, a lingual fragment of left lower
molariform.
Occurrence. Site 3 of Río Chico Locality, Jujuy Province, north-
western Argentina; level C, upper section of the Guanaco Formation, late
Miocene and/or early Pliocene (<5.7 Ma).
Description. It is composed of two long and compressed lophids.
The hypoexid, which presents a layer of cementum, is anteriorly
recurved suggesting that the element is a lower molariform.
Comparisons and comments. Although incomplete, the described
morphology shows is typical of all lagostomines, but the exact length of
lophids is unknown. The assignment to Lagostomus is based on the
presence of straight and long lophids and hypoexid (Rasia, 2016; Rasia
and Candela, 2016). Other remains of the genus were previously
described for middle levels of Guanaco Formation in Los Alisos locality
(Ercoli et al., 2019). The record of Lagostomus extends from Chasicoan to
recent times, being the smallest species recorded up to Chapadmalalan
(Rasia et al., 2020).
Fig. 6. Fragment of left upper molariform of caviine (JUY-P-152) in occlusal view. Scale bar =1 mm.
M.D. Ercoli et al.
Journal of South American Earth Sciences 110 (2021) 103389
8
Order XENARTHRA Cope, 1889.
Suborder CINGULATA Illiger, 1811
Family GLYPTODONTIDAE Gray, 1869
Genus Cranithlastus Arias, Alonso & Malanca, 1978
Cranithlastus xibiensis Arias, Alonso & Malanca, 1978
Referred material: JUY-P-118, almost complete skull and fragments
of the dorsal carapace (anterodorsal and middleventral regions) and
cephalic armor (Fig. 7).
Occurrence. Site 1 of Río Chico Locality, Jujuy Province, north-
western Argentina; middle section of the Guanaco Formation, late
Miocene (~6.3 Ma).
Description.
Skull. It measures 185 mm length and 84 mm of dorsoventral
diameter at the level of Mf8.
In lateral view (Fig. 7A), it is observed that the parieto-occipital re-
gion is located in a very high position, while the dorsal prole markedly
descends towards the rostral region behind the orbital notches. The
ventral end of the descending process of the zygomatic arch shows a
marked curvature toward posterior region. The dorsal margin of the
nasal opening is located at the level of the ventral-most borders of the
orbital notches. In dorsal view, there is a poorly developed sagittal crest,
which bifurcates, and reaches the postorbital process. In anterior view,
the nasal opening shows a subtrapezoidal contour, with the lateral
margins somewhat convex. In occlusal view (Fig. 7B), the infraorbitary
foramina are small and are located at the Mf3-Mf4 level, opening
cranially. The palate is narrow and concave. The molariform series
measures 116 mm length. Despite the Mf1 is not present, the preserved
alveolus shows in transversal section a clear sub-circular outline. In turn,
the Mf2 has an elliptical-oval and simple section. The remaining
molariforms (Mf3-Mf8) are trilobated, being their posterior margin
quite convex, while the anterior margins become at, especially for Mf4-
MF8.
Cephalic armor. This structure is almost complete, preserving seven
associated osteoderms (Fig. 7C) and various isolated osteoderms. The
largest osteoderm are located at the posterior center portion, while the
remaining become progressively smaller toward the anterior margin. In
general, they show a polygonal or circular contour. The exposed surface
is at and somewhat rugose, lacking any kind of ornamentation. Sur-
rounding each osteoderm there is a depressed and very rugose area.
Dorsal carapace. In the anterodorsal region (Fig. 7D) the exposed
surface of osteoderms is ornamented by a large sub-circular central
gure surrounded by 15–17 small peripheral gures. The osteoderms
conforming the dorsal margin of the cephalic notch have a quadrangular
shape, with subcircular and at central gure. The peripheral gures of
these osteoderms are scarce and poorly developed. In turn, in the ventral
margin of the border of the cephalic notch there are some irregular
osteoderms without ornamentation pattern. The osteoderms of the
middle ventral region (Fig. 7E) have a rectangular contour and become
smaller caudally. The central gure of these osteoderms tends to be
more circular compared to those of the anterodorsal region and are
displaced to the posterior margin. This central gure is surrounded by a
row of angular peripherical gures, which are more developed in the
anterior margin of the osteoderms. In turn, the posterior-most osteo-
derms of the carapace fragment (Fig. 7E) present a more quadrangular
contour, in which the central gure become larger and lacking periph-
eral gures.
Comparisons and comments. In general, no signicant differences
are observed with respect to the type material of Cranithlastus xibiensis
(CNS–V10014; Arias et al., 1979).
The overall shape of the skull JUY-P-118 and the holotype of Cra-
nithlastus xibiensis show some resemblance with Plohophorus guratus
Ameghino (see Zurita et al., 2017:Fig. 2). In lateral view (Fig. A), it is
observed that the dorsal prole shows the inection point of the pari-
etals at level of the temporal end of the zygomatic arch, being similar to
E. tapinocephalus (Zurita and Aramayo, 2007:Fig. 1), but different to
P. guratus in which this point appears at level of the postorbital process.
The distal end of the descending process of the zygomatic arch shows a
markedly curvature toward posterior (not preserved in the type material
of C. xibiensis), while this curvature is not observed in Plohophorus and
Eosclerocayptus (Zurita, 2007a). In anterior view, the nasal opening is
Fig. 7. Cranium (A, B; in lateral and ventral view, respectively), cephalic armor (C), and some main fragments of the carapace (D, E) of Cranitlhastus xibiensis (JUY-P-
118). Scale bars =20 mm.
M.D. Ercoli et al.
Journal of South American Earth Sciences 110 (2021) 103389
9
similar to that of the type of C. xibiensis (i.e. subtrapezoidal), resembling
the morphology observed in P. guratus and Plohophorus sp. In addition,
the position of the infraorbitary foramina is similar to those observed in
P. guratus and Plohophorus sp. (Zurita et al., 2017). In dorsal view, the
sagittal crest is less evident compared to the type material of C. xibiensis
and P. guratus. In oclusal view, the morphology of the molariform series
is almost similar to the type material of C. xibiensis.
The relative size of osteoderms that compose the cephalic armor
resembles those of Eosclerocalyptus proximus and Pseudoplohophorus
(Perea, 2005; Zurita, 2007b). The contour and morphology of the
exposed surface of the osteoderms are similar to Glyptodon (Cuadrelli
et al., 2020), Eosclerocalyptus proximus, Pseudoplohophorus sp. and the
“Propalaehoplophorinae” Eucinepeltus petesatus (Gonzalez, 2010), and
differ from Plohophorus (Ameghino, 1889).
In the dorsal carapace, the circular general shape of the central gure
of the osteoderms of the middleventral region, and the posterior position
of this central gure resemble that of “Glyptatelinae”, Boreostemma
acostae, and Parapropalaehoplophorus septentrionalis (see Croft et al.,
2007; Zurita et al., 2013). The ornamentation of the osteoderms of the
cephalic notch (quadrangular shapes, with subcircular and at central
gures, surrounded by few and rudimentary peripheral gures), and the
anterodorsal region (with 15–17 small peripheral gures) is almost
identical to that described for the holotype of C. xibiensis (Arias et al.,
1979, see above). The ornamentation of the anterodorsal region is
different to that of Eosclerocalyptus, which have only 13 to 15 peripheral
gures.
In summary, the features of JUY-P-118 and the type of C. xibiensis
agree with that expected for late Miocene-Pliocene glyptodonts, being
several characters very similar to those observed in late Neogene genera
such as Phlyctaenopyga (see Cabrera, 1944). This is in concordance with
the inferred age of the unit of provenance of these materials (Starck and
Vergani, 1996; see also, Starck and Anz´
otegui, 2001; Coira et al., 2018;
Villalba-Ulberich et al., 2021). Some of these features (not present in late
Pliocene and Pleistocene taxa) include: the small size of the skull, the
particular morphology of the molariforms, the high number and small
size of peripheral gures surrounding a large central gure on the
exposed surface of the osteoderms, lateral osteoderms showing a more
developed anterior peripheral gures and the central gure posteriorly
displaced, and the particular morphology of the exposed surface of the
osteoderms of the cephalic shield. Most of the Neogene lineages of
glyptodonts became extinct during the Pliocene, while in the Pleistocene
glyptodonts achieved much larger sizes and decreases in diversity
(Cuadrelli et al., 2020; Qui˜
nones et al., 2020).
4. Discussion and conclusions
The recent studies on chronostratigraphy and depositional environ-
ments of the Guanaco Formation (e.g., Hain et al., 2011), in particular in
Río Chico locality (e.g., Coira et al., 2018; Villalba Ulberich et al., 2021),
provided an adequate framework to constrain the age and assess the
paleoenvironmental meaning of the mammalian taxa here described.
The geological study of Villalba Ulberich et al. (2021) suggested that the
sequence thickness of Guanaco Formation in Río Chico is much higher
than previously recognized. Based on this new denition, we consider
that the fossils here described come from levels that correspond to the
upper section of Guanaco Formation instead the overlying Piquete
Formation. Additionally, that study indicated a wide temporal range for
the sequence of Guanaco Formation in this locality, encompassing at
least the lapse between two tuffs dated at 6.3 Ma and 5.7 Ma, respec-
tively (Coira et al., 2018; Villalba Ulberich et al., 2021). Two previous
contributions described fossils coming from levels close to the 6.3 Ma
tuff (Arias et al., 1979; Ercoli et al., 2019). The upper fossiliferous levels
here studied come from nearly 200 m above the 5.7 Ma tuff (Villalba
Ulberich et al., 2021), and nearly (level D) or more than (level C) 350 m
below the limit between Guanaco and Piquete formations (Fig. 2). The
sedimentary record of Piquete Formation was proposed as beginning at
~5 Ma (Reynolds et al., 2000; Hain et al., 2011; Villalba Ulberich et al.,
2021; see also García et al., 2017). In consequence, the rodent associa-
tion (C and D levels) here described could be constrained to an age
younger than those previously known for the Guanaco Formation, be-
tween the Miocene-Pliocene limit and the early Pliocene (considering
that those levels are well-above a 5.7 Ma tuff). In this case, these
fossiliferous levels, and their faunas, would be contemporaneous with
late Huayquerian (late Messinian, latest Miocene) or even Mon-
terhermosan (early Zanclean, earliest Pliocene) deposits and faunas
from central Argentina (Marshall et al., 1983; Deschamps, 2005; Verzi
et al., 2008; Tomassini et al., 2013); in any case, it brings a new temporal
window for the fossil record of the southern Subandean region in
northwestern Argentina. The known biochrons of the taxa identied
here (i.e., clade Neocavia +Microcavia +Dolicavia, Caviodon sp.,
Lagostomus sp.), and the morphology of Cranithlastus xibiensis, agree
with an expected late Miocene-early Pliocene age.
Since late Miocene, in northwestern Argentina, and particularly for
the Eastern Cordillera and Subandean region, predominant xeric vege-
tational communities and eolian and aquatic ephemeral environments of
middle Miocene were replaced by more humid and typically seasonal
vegetation communities and permanent uvial systems with wide ood
plains (Pascual and Odreman Rivas, 1973; Starck and Vergani, 1996;
Starck and Anz´
otegui, 2001; Anz´
otegui et al., 2017). A contrasting sit-
uation is recorded in Patagonia and Pampean plains of central Argentina
where open and arid biomes expanded during that time (Palazzesi and
Barreda, 2007; Domingo et al., 2020). The climatic change toward
warmer and wetter conditions during the transition between middle to
late Miocene recorded in northwestern Argentina is linked to changes in
the regional atmospheric circulation and the development of a moisture
barrier related to the uplifting of the western orogenic front triggering
higher rainfall, intensied in the foothills of the front (Starck and Ver-
gani, 1996; Reynolds et al., 2000; Starck and Anz´
otegui, 2001; Hain
et al., 2011; Anz´
otegui et al., 2017; Rohrmann et al., 2016; Robledo
et al., 2020). Close forested patches and humid seasonal conditions were
developed in some specic moments and localities, such is the case of
the base of Andalhuala Formation in Puerta de Corral Quemado, Cata-
marca Province (8.7–5.6 Ma; e.g., Nasif et al., 2019), and particularly
rainy, humid, warm condition prevailed during the deposition of the
upper levels of Palo Pintado Formation (10.3–5.3 Ma) in Calchaquí
Valleys, Salta Province, in which subtropical, rain-forests communities
are recorded (Starck and Anz´
otegui, 2001; Anz´
otegui et al., 2017;
Zimicz et al., 2018; Galli et al., 2019).
Subsequent Andean tectonism and related eastward displacement of
the orogenic front, mainly recorded between latest Miocene and Plio-
cene in the studied area and closer regions, implied the break-up of the
foreland and the generation of local basins and new ranges (Starck and
Vergani, 1996; Starck and Anz´
otegui, 2001; Hain et al., 2011; Pingel
et al., 2014; García et al., 2017). These new ranges uplifted between the
Eastern Cordillera and Subandean regions resulted in strong and
opposed environment changes in both regions. Eastern Cordillera areas
such as Calchaquí Valleys and Quebrada de Humahuaca basin, suffered
aridization by the rain shadow effect (Starck and Vergani, 1996; Pingel
et al., 2014; Strait et al., 2015; Rohrmann et al., 2016; Robledo et al.,
2020), nishing the record of diverse and forested communities (Starck
and Anz´
otegui, 2001; Reguero et al., 2007; Anz´
otegui et al., 2017;
Robledo et al., 2020), and a similar situation could eventually explain
the environmental turnover recorded in eastern Puna localities (e.g.,
Qui˜
nones et al., 2019). Conversely, this tectonic phase resulted in the
approaching of the orogenic front from the west, the establishment of
more humid environmental conditions in the southern Subandean re-
gion, and progressive sloping landscapes similar to those present in the
current southern Jujuy (Starck and Vergani, 1996), changing from
Chacoan’ (see Starck and Vergani, 1996) to Yungas’ environments.
These events of landscape structuring bring the framework to interpret
the fossil record of Guanaco Formation.
A rst sight interesting fact of the fossil record of Guanaco Formation
M.D. Ercoli et al.
Journal of South American Earth Sciences 110 (2021) 103389
10
is that xenarthrans, which are the most abundant mammals in middle
section, were not found among a dozen of fragmentary cranial and
postcranial remains of mammals collected in the upper levels. Middle
levels bear a large diversity and abundance of dasypodids, and various
larger xenarthrans, including pampatheriids, glyptodontids, and mega-
theriids (e.g., Arias et al., 1979; Ercoli et al., 2019; Salgado Ahumada
et al., 2020). The new record of Cranithlastus xibiensis for the middle
levels of this unit represents the second specimen known for the taxon
(Arias et al., 1979) and the third glyptodontid specimen known for this
section (Ercoli et al., 2019; Salgado Ahumada et al., 2020). This nding
is also important because C. xibiensis is currently the most complete
Neogene glyptodont known for the Subandean region. Unlike the late
Neogene glyptodonts from the Pampean region, which are relatively
well characterized (see Zurita et al., 2013, 2016a,b), little is known
about glyptodonts from northwestern Argentina (Cabrera, 1944),
despite the fact that a revision is currently carrying out (see
Nú˜
nez-Blasco et al., 2021). In this scenario, further comparative and
phylogenetic studies based on the type and referred material of
C. xibiensis will allow to better understand this poorly known glypto-
donts and its relationship with the Pampean taxa, having into account
that preliminary evidence suggest that both areas (Pampean and
Northwestern regions) had a different taxonomic composition of glyp-
todonts during the late Neogene (Zurita, 2007; Nú˜
nez-Blasco et al.,
2021).
Differently, rodent assemblages from the middle and upper levels of
the Guanaco Formation are similar at some extent, sharing some taxa as
well as the main ecomorphotypes. They include lagostomines (Lagosto-
mus in middle and upper levels), octodontoids (octodontoids indet. in
middle levels and upper ones), and small caviids (corresponding to
Orthomyctera in middle levels and Caviinae indet. in upper ones; Ercoli
et al., 2019; this contribution). The upper levels also include the record
of Caviodon sp. and the new erethizontid Noamys hypsodonta (see
below).
Villalba Ulberich et al. (2021) denoted depositional environmental
changes from base to top in the Guanaco formation, with the decreasing
of the extension of oodplains and open areas characterized by ne
deposits, and the progressive record of paleo-ows of higher energy and
rocky soils in relation to the increasing of the paleorelief of nearer areas,
folded, faulted, and uplifted by the oncoming orogenic front (Pingel
et al., 2014; Strait et al., 2015 and cites therein). Although taphonomic
biases should be analyzed, the absence, or at least the apparently
marked decrease in the record of the dasypodids, was probably related
to the fact that the frequent construction of burrows is hindered or
almost impossible for armadillos in rocky or ooded soils (e.g.,
Scillato-Yan´
e et al., 2013; Carlini et al., 2016). It is probable that these
environmental changes at this latitude of the Subandean region during
late Miocene-early Pliocene could be related to the mentioned faunal
turnover that apparently affected differentially to xenarthrans and ro-
dents ecomorphs, an issue that should be better explored in future
studies with more abundant and well-preserved records.
Two new caviomorph clades are recorded for Guanaco Formation in
the upper levels: the cardiomyine Caviodon and the erethizontid Noamys.
Cardiomyines are commonly recorded in other non-Patagonian late
Miocene-early Pliocene localities (e.g., P´
erez et al., 2018; Zimicz et al.,
2018), and would had have generalized life habits (e.g., Cardiomys; see
Candela et al., 2018). The record of an erethizontid is relevant from its
biogeographic and paleoenvironmental meaning because they are un-
commonly recorded in sub-tropical or southern localities of similar age
(Pascual and Odreman Rivas, 1973; Candela and Morrone, 2003). Only a
few previous records of erethizontids are known for fossiliferous units of
similar ages: Neosteiromys spp. from Valle de Santa María of Catamarca
Province (Andalhuala Formation; Rovereto, 1914; Pascual and Odreman
Rivas, 1973; Candela and Morrone, 2003; Candela, 2004) and Para-
doxomys cancrivorus from the “Mesopotamian” of Entre Ríos Province
(Ituzaing´
o Formation; Vucetich and Candela, 2001; Candela and Mor-
rone, 2003). In this context, Noamys is the rst late Miocene erethizontid
with precise stratigraphic provenance.
South American Erethizontidae is considered a family strictly related
to tropical or sub-tropical forests, being all its extant representatives and
studied fossil taxa considered as mainly or strictly arboreal (Candela and
Morrone, 2003; Candela and Picasso, 2008; Voss, 2011; Candela et al.,
2012; Patton et al., 2015; Barthelmess, 2016; Vezzosi and Kerber, 2018).
Only one fossil porcupine, Neosteiromys, was inferred as inhabiting more
open areas, in a landscape with patches of open and forested environ-
ments, instead woodlands or rainforest as those occupied by living taxa
(Candela, 2004). Following previous interpretations in the mentioned
studies, the presence of an erethizontid in the upper levels of Guanaco
Formation could strongly support the presence of tropical or sub-tropical
forested environments in southern Jujuy for the Miocene-Pliocene
transition. Regarding the tooth morphology of this rodent, the pres-
ence of unilateral hypsodont cheek teeth would suggest moderate
resistance to processing abrasive items or particles, although higher than
in other erethizontids. Abrasive particles would have been abundant in
southern Jujuy due to volcanic activity, as indicated by ash beds known
for this lapse. On the other hand, conservative, non-attened occlusal
morphology with well-differentiated cusps, and relatively thin enamel
layers would suggest poor grinding abilities and a diet mainly based on
soft items as in living erethizontids. This condition is more similar to that
of Coendou species (Patton et al., 2015; Vezzosi and Kerber, 2018) than
that of some extinct taxa such as Neosteiromys, which has a modied
dentition and masticatory apparatus capable to process harder and more
abrasive items (Candela, 2004).
Finally, the morphology of the isolated octodontoid calcaneum JUY-
P-157 also seems to be relevant from an environmental point of view. It
presents several traits expectable for generalized or climbing locomo-
tory habits, and a morphology only similar to some extinct and extant
small echimyids of forested environments (see above), which is in
concordance with the interpretation obtained with the remaining fossil
taxa and the sedimentology. Upper levels of the Guanaco Formation and
other late Miocene units of Catamarca and Salta provinces in north-
western Argentina share the presence of exclusively subtropical and
tropical mammals, including erethizontids (Pascual and Odreman Rivas,
1973; Candela, 2004), echimyids (e.g., aff. Thrichomys MUFyCA 483;
Candela et al., 2019) and octodontoids with conservative and rooted
cheek teeth (Octodontoidea indet. in Ercoli et al., 2019; aff. Acarechimys,
aff. Sciamys in Nasif et al., 2019).
In summary, available evidence makes it possible to distinguish
common features of northwestern localities from those of the contem-
poraneous southern ones (e.g., Cuyo and Pampean regions) in key
faunistic components that are informative from a paleoenvironmental
point of view, supporting the development of forested patches and
seasonally humid climatic conditions in different areas of the north-
western Argentina (Pascual and Odreman Rivas, 1973; Nasif et al.,
2019). The expansion of this northern forested environments along the
eastern ank of the Central Andean ranges, and the contemporaneous
replacement of forested habitats by open environments in southern lo-
calities, is evidenced by differences in the mammalian assemblages,
being the northwestern region appropriate areas for the arrival and
diversication of new Brazilian components or survival of lineages that
went extinct since late Neogene in southern South America (Pascual and
Odreman Rivas, 1971, 1973; Reguero et al., 2007; Nasif et al., 2019; see
also Verzi et al., 2016).
The features of the sedimentology and faunistic assemblage of the
Guanaco Formation in the upper section of Río Chico locality indicate
the presence of subtropical forested environments, as suggested for
other northwestern mammalian fossiliferous localities, but with the
particularity of representing foothills communities emplaced in alluvial
fans related to closer highs and sloping landscapes. The absence of
xenarthrans in the known fossil record and the reconstruction of high-
energy paleo-ows and rocky soils of the upper levels of Guanaco For-
mation (Villalba Ulberich et al., 2021) are associated to this recon-
structed foothill scenario. This situation would be the direct
M.D. Ercoli et al.
Journal of South American Earth Sciences 110 (2021) 103389
11
consequence of the concomitant migration and approaching of the
orogenic front from west, moving early atter landscapes recorded in
lower levels toward the east. Although mountain forests were inferred in
different late Miocene localities for different northwestern localities
through the palynological record, the vertebrate bearing units are
mainly restricted to distal environments with wide oodplains, calmest
rivers and even lacustrine lowland environments (Starck and Anz´
otegui,
2001; Bonini et al., 2017b; Anz´
otegui et al., 2017), highlighting the
importance of the faunistic association here presented.
The here described fossil record of the Guanaco Formation improves
the available information about the faunistic and environmental evo-
lution of a poorly studied area of northwestern Argentina, and increases
the knowledge of the mammalian past diversity of the Neogene of
middle-latitude of South America. Although more fossils are needed, the
environmental, landscape, and faunistic changes toward the Miocene-
Pliocene limit seem to indicate the replacement of oodplains and
Chacoan communities by foothills and sloping landscapes with high-
energy rivers in southern Subandean region. The record of arboreal
and generalized rodents would be the rst clues for the detecting the
beginning of the differentiation of the modern ecorregions of central
Andes, and the establishment of Yungas’ forested subtropical environ-
ments that predominate until the present.
Funding
This work was supported by Consejo Nacional de Investigaciones
Cientícas y T´
ecnicas CONICET (Argentina), INECOA-PUE 2017
22920170100027CO (Argentina), and the Percy Sladen Memorial Fund
2018 (United Kingdom).
Declaration of competing interest
The authors declare that they have no known competing nancia-
linterestsor personal relationships that could have appeared to inuence
the work reported in this paper.
Acknowledgments
Thanks to Marcos Vaira (Director of INECOA, UNJu-CONICET),
Natalia Solís (Director of IdGyM, UNJu), María In´
es Zamar (Director of
INBIAL, UNJu), for their support and help with logistic, access to insti-
tutional equipments, and/or supplies. To two anonymous reviewers for
their valuable comments and suggestions. To Emilia Silva de Cruz
(IdGyM), Myriam Boivin (INECOA), and Cynthia Jofre (INECOA), for
their help with bibliography, geological setting, and other data. To
Carlos Luna (CECOAL), Soledad Palomas (INECOA), Sonia Gonzalez
Patagua, Analía Rivero, and Emilia Vargas (IdGyM) for fossils prepara-
tion. To curators and technicians Josena Aris (CNS, UNSa), Silvia
Cornero (MUFyCA, UNR), Martín Ezcurra and Laura Chornogubsky,
Pablo Teta, Guillermo Cassini, and Sergio Lucero (MACN), Bruce Pat-
terson, William Simpson (FMNH), Juliana Gualda de Barros (MZUSP),
Rub´
en B´
arquez and M´
onica Díaz (CML). To Silvia Rosas (INECOA) and
Itatí Olivares for their help with gures. To Adriana Candela (MLP) for
their invaluable help for the assignation of the cardiomyine remain, and
talks about the erethizontid material. To La. Te. Andes for tuff dating
which gives the geochronological framework to the study of the Sub-
andean region. To María Camacho (IdGyM, UNJu), Gustavo Vergani
(Pluspetrol), and Ricardo Alonso (UNSa) for early discussions about eld
observations in the Subandean region. To Jumi S.R.L. building company
for help during eld works. We are very grateful with the Percy Sladen
Memorial Trustees and Gina Douglas for their invaluable support to
carry out this project, This work was supported by Consejo Nacional de
Investigaciones Cientícas y T´
ecnicas (CONICET, INECOA-PUE 2017
22920170100027CO), and Percy Sladen Memorial Fund grant (2018)
given by the Percy Sladen Memorial Trust administered by the Linnean
Society of London. To Federico Posadas (Minister of Cultura y Turismo,
Jujuy), Valentina Mill´
on, Juan Carlos Rodríguez, and Silvia Flores
(Direcci´
on Provincial de Cultura, Ministerio de Cultura y Turismo,
Jujuy) for granting paleontological permits (Exp. 1301–963/17,
1301–355/20).
Appendix
Erethizontid specimens and references analyzed for the comparative
description of Noamys hypsodonta.
Branisamyopsis spp.: Candela (2003); Kramarz (2001, 2004).
Chaetomys subspinosus: MZUSP 32108, MZUSP 32110. Coendou
bicolor: CML 591. Coendou mexicanus: FMNH 15611, FMNH 43993.
Coendou prehensilis: FMNH 61863, MACN Ma 19050. Coendou roth-
schildi: FMNH 30742, FMNH 121529. Coendou spinosus: CML 1543,
CML 1549, CML 1550, FMNH 65799, MACN Ma 54–3, MACN Ma 17918,
MACN Ma 22839, MACN Ma 22840, MACN Ma 31–237. Coendou sp.:
MACN Ma 30–243. Eosteiromys spp.: FMNH P 13588; Candela (1999,
2003), Kramarz (2001, 2004). Erethizon dorsatus: FMNH 20343, FMNH
20344, FMNH 38029, FMNH 124114. Hypsosteiromys spp.: Patterson
(1958); Candela (1999); Candela and Vucetich (2002); Dozo et al.
(2004). Microsteiromys jacobsi: Walton (1990, 1997). cf. Micro-
steiromys: Antoine et al., (2013). Neosteiromys spp.: Rovereto (1914);
Candela (1999, 2004). Parasteiromys spp.: Candela (1999, 2004);
Vucetich and Candela (2001). Protosteiromys spp.: Wood and Patterson
(1959); Candela (1999). Steiromys spp.: MACN A 10083-10085;
Candela (1999); Kramarz (2001, 2004). Steiromys duplicatus: MACN
A 1906, MACN A 10055–78. Non-assigned erethizontid remains:
Frailey (1986); Campbell et al. (2006).
Author contributions
Marcos D. Ercoli: Conceptualization, Investigation (data collection),
Writing- Original draft preparation, Writing- Reviewing and Editing,
Visualization, Funding acquisition, Alicia ´
Alvarez: Conceptualization,
Investigation (data collection), Writing- Original draft preparation,
Writing- Reviewing and Editing, Visualization, Funding acquisition,
Diego H. Verzi: Writing- Original draft preparation, Writing- Reviewing
and Editing, Visualization, Juan Pablo Villalba Ulberich: Conceptuali-
zation, Investigation (data collection), Writing- Reviewing and Editing,
Visualization, Sofía I. Qui˜
nones: Writing- Original draft preparation,
Writing- Reviewing and Editing, Visualization, Ornela E. Constantini:
Conceptualization, Investigation (data collection), Alfredo E. Zurita:
Writing- Original draft preparation, Writing- Reviewing and Editing,
Visualization.
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