New Middle Miocene Caviomorph Rodents from Quebrada Honda, Bolivia

Abstract

The rodents of the middle Miocene fauna of Quebrada Honda Bolivia are described. The most abundant rodent is the chinchillid
Prolagostomus sp. More precise identification of this species will require revision of early to middle Miocene lagostomines, taking into
account variation in modern populations. The next most common rodents are the tiny octodontoid Acarechimys, sp. nov.?, and the caviid Guiomys unica. The Acarechimys species may be unique to Quebrada Honda, but verification awaits revision of this geographically and temporally widespread
genus. Guiomys unica is a recently described species otherwise known only from two Patagonian localities, El Petiso and Río Chico. Two rodents
are unique to Quebrada Honda. Mesoprocta hypsodus, gen. et sp. nov., is a dasyproctid distinguished by its very hypsodont, cement-covered cheek teeth. Quebradahondomys potosiensis, gen. et sp. nov., is an adelphomyine echimyid distinguished by the less oblique lophids of its trilophodont cheek teeth,
among other features. The rodents of Quebrada Honda are more similar to those of Patagonia than those of northern South America,
paralleling patterns seen in other mammal groups from this fauna.

KeywordsEndemism–Laventan–Neogene–Neotropics–Provinciality–Rodentia–South America

Full text

ORIGINAL PAPER
New Middle Miocene Caviomorph Rodents from Quebrada
Honda, Bolivia
Darin A. Croft &Jennifer M. H. Chick &Federico Anaya
Published online: 5 July 2011
#Springer Science+Business Media, LLC 2011
Abstract The rodents of the middle Miocene fauna of
Quebrada Honda Bolivia are described. The most abundant
rodent is the chinchillid Prolagostomus sp. More precise
identification of this species will require revision of early to
middle Miocene lagostomines, taking into account variation
in modern populations. The next most common rodents are
the tiny octodontoid Acarechimys, sp. nov.?, and the caviid
Guiomys unica. The Acarechimys species may be unique to
Quebrada Honda, but verification awaits revision of this
geographically and temporally widespread genus. Guiomys
unica is a recently described species otherwise known only
from two Patagonian localities, El Petiso and Río Chico.
Two rodents are unique to Quebrada Honda. Mesoprocta
hypsodus, gen. et sp. nov., is a dasyproctid distinguished by
its very hypsodont, cement-covered cheek teeth. Quebra-
dahondomys potosiensis, gen. et sp. nov., is an adelpho-
myine echimyid distinguished by the less oblique lophids
of its trilophodont cheek teeth, among other features. The
rodents of Quebrada Honda are more similar to those of
Patagonia than those of northern South America, paralleling
patterns seen in other mammal groups from this fauna.
Keywords Endemism .Laventan .Neogene .Neotropics .
Provinciality .Rodentia .South America
Introduction
Rodents are conspicuous members of nearly all modern South
American terrestrial communities. The vast majority of the
species pertain to two groups, each of which underwent an
adaptive radiation in South America: cricetids (muroids) and
caviomorphs. The former includes far more species, but is a
geological newcomer in South America. There is no definitive
evidence for cricetids in South America prior to about five
million years ago (Pardiñas et al. 2002; Prevosti and Pardiñas
2009). Even if cricetids entered South America several
million years earlier than indicated by their fossil record,
their remarkable diversification into more than 350 species—
well over one third of all South American mammal species
(Wilson and Reeder 2005)—took place in a surprisingly short
period of time. They apparently dispersed to South America
from North America via the Panamanian land bridge along
with many other participants of the Great American Biotic
Interchange (see Webb 2006 for a recent review).
Caviomorph rodents, in contrast, have been in South
America for at least half of the Cenozoic, since at least the
early Oligocene (Wyss et al. 1993,1994; Vucetich et al. 1999,
2010b; Flynn et al. 2003). The fossil record of caviomorphs
may extend into the late Eocene (Frailey and Campbell
2004), though this locality has no independent temporal
constraints and could be as young as late Oligocene
(Shockey et al. 2004). The origin of caviomorphs has long
D. A. Croft (*)
Department of Anatomy,
Case Western Reserve University School of Medicine,
10900 Euclid Ave.,
Cleveland, OH 44106-4930, USA
e-mail: dcroft@case.edu
J. M. H. Chick
Department of Biology, Case Western Reserve University,
10900 Euclid Ave.,
Cleveland, OH 44106, USA
F. Anaya
Facultad de Ingeniería Geológica,
Universidad Autónoma Tomás Frías,
Av. Del Maestro s/n,
Potosí, Bolivia
F. Anaya
e-mail: fedanaya@hotmail.com
J Mammal Evol (2011) 18:245–268
DOI 10.1007/s10914-011-9164-z

been a matter of debate (reviewed by Wood 1985), but
several lines of evidence now all favor waif dispersal from
Africa during the late Eocene (Houle 1998;Huchonand
Douzery 2001; Sallam et al. 2009;Costeretal.2010;Rowe
et al. 2010). Platyrrhine primates likely also reached South
America in this manner, at approximately the same time
(Kay et al. 2008). Although caviomorphs are today
represented by fewer than 250 species (Woods and Kilpatrick
2005), the morphological diversity of the group far exceeds
that of cricetids. This distinctiveness is highlighted by
rodents such as the capybara (Hydrochoerus hydrochaeris),
the guinea pig (Cavia porcellus), the agouti (Dasyprocta
punctata), and the chinchilla (Chinchilla laniger), which are
among the most characteristic South American mammals.
The details of caviomorph diversification—such as the
timing of cladogenic events, relationship between morphologic
and taxonomic diversity, and biogeographic histories of
important clades—remain relatively poorly known despite
South America’s excellent fossil record.Thispartlystemsfrom
the disproportionately small amount of attention they have
received from researchers, at least for some time intervals and
some regions of the continent. Filling such gaps in knowledge
is essential to understanding the radiation of caviomorph
rodents and the development of South American mammal
communities as a whole. The present study contributes to this
effort by describing the caviomorph rodents of Quebrada
Honda, an assemblage from a sparsely sampled temporal
interval (the middle Miocene) and area of the continent (the
Neotropics).
Materials and Methods
The fossils described in this study derive from Quebrada
Honda in southern Bolivia (Fig. 1). Specifically, we focus
on: (1) new specimens collected in 2007 by DAC and FA
and colleagues (see Acknowledgments), which are housed
at the Universidad Autónoma Tomás Frías (Potosí, Bolivia);
and (2) previously undescribed specimens from the Florida
Museum of Natural History in Gainesville that were
collected in 1978 and 1981 by FA and B. MacFadden and
colleagues. We provisionally identify other Quebrada
Honda specimens that we were unable to study firsthand.
This is a much revised and updated version of our
preliminary report (Chick et al. 2008) and is based on
study of additional specimens and museum collections.
The Quebrada Honda Fauna is temporally well con-
strained to 13.5–11.8 Ma (MacFadden et al. 1990). It
pertains to the Laventan South American Land Mammal
“Age”(SALMA)(Madden et al. 1997; Croft 2007) (Figs. 1,
2). For additional details on the stratigraphy of the locality,
see MacFadden and Wolff (1981) and MacFadden et al.
(1990). Two local faunas have been recognized: the
Quebrada Honda Local Fauna, from exposures near the
town of the same name, and the Río Rosario Local Fauna,
from exposures near the town of Río Rosario, located ca.
6 km to the north of the town of Quebrada Honda. Outcrops
in both areas are mapped as the Honda Group (MacFadden
et al. 1990) and both local faunas appear to be of
approximately the same age. In this work, Quebrada Honda
refers to the assemblage as a whole unless noted otherwise.
Terminology Nomenclature of dental occlusal structures dis-
cussed in this work is presented in Fig. 3. We follow that used
in other recent studies of cavioids (Kramarz 1998; Pérez
2010), chinchilloids (Kramarz 2002), and octodontoids
(Vucetich and Ribeiro 2003; Vucetich et al. 2010b), all of
which are compatible with recent nomenclatural schemes for
hystricognaths as a whole (e.g., Marivaux et al. 2004).
Uppercase letters denote upper teeth and lowercase letters
denote lower teeth. All rodents described in this study possess
one pair of incisors (I/i), one pair of premolars (P4/p4), and
three molars (M1-3/m1-3). Deciduous premolars (DP4/dp4)
are maintained through adulthood in some octodontoids. The
suffix “–id”is used to denote structures of the lower dentition.
A flexus/flexid is a valley that remains open along the side of
the tooth crown. A fossette/fossettid is a flexus/flexid that has
become isolated (i.e., closed off from the side of the tooth
crown) due to wear. High- and low-crowned dentitions are
referred to as hypsodont and brachydont, respectively. Ever-
growing, rootless, and/or open-rooted teeth are hypselodont.
Other Notes Hypsodonty index (HI) follows Williams and
Kay (2001) and was calculated by dividing m1 height by the
square root of the occlusal area (mesiodistal × buccolingual
diameter). Diagnostic characters used to identify each species
are included in the systematic paleontology section below.
Unless otherwise noted, cheek tooth dental measurements
are length (= mesiodistal or anteroposterior diameter) ×
width (= buccolingual or transverse diameter).
Institutional Abbreviations AMNH, American Museum of
Natural History, New York; IGM, Instituto Nacional de
Investigaciones en Geociencias, Minería y Química
(INGEOMINAS), Colombia; MACN, Museo Argentino
de Ciencias Naturales, Buenos Aires, Argentina; MLP,
Museo de La Plata, Argentina; MPEF, Museo Paleontológico
Edigio Ferugulio, Trelew, Argentina; UATF, Universidad
Autónoma Tomás Frías, Potosí, Bolivia; UCMP, University
of California Museum of Paleontology; UF, Florida Museum
of Natural History, Gainesville, Florida; YPM-PU, Princeton
University Collection of Yale Peabody Museum, New Haven,
Connecticut. Specimens from these museums were studied
firsthand. Dental measurements were made to the nearest
0.1 mm using digital calipers. Published sources were used as
supplemental resources.
246 J Mammal Evol (2011) 18:245–268

Systematic Paleontology
Class Mammalia Linnaeus, 1758
Order Rodentia Bowdich, 1821
Suborder Hystricognathi Tullberg, 1899
Infraorder Caviomorpha Wood and Patterson, 1955
Comments: Caviomorph rodents are a monophyletic group
of New World hystricognaths that share numerous derived
craniodental and molecular character states (e.g., Wood and
Patterson 1959; Huchon and Douzery 2001;Marivauxetal.
2004;Roweetal.2010). More than 60 genera are extant or
have gone extinct in historical times, and more than twice
this number have been described from fossil deposits; they
are currently divided among 12 extant and five extinct
families (McKenna and Bell 1997; Vucetich et al. 1999;
Woods and Kilpatrick 2005). Phylogenies of extant families
based on nuclear and/or mitochondrial genes support
recognition of four main clades (superfamilies) within
Caviomorpha: Cavioidea (Caviidae, Cuniculidae, and Dasy-
proctidae), Chinchilloidea (Chinchillidae and Dinomyidae),
Erethizontoidea (Erethizontidae only), and Octodontoidea
(Abrocomidae, Capromyidae, Ctenomyidae, Echimyidae,
M
I
O
C
E
N
E
MA
M
I
D
D
L
E
L
A
T
E
E
A
R
L
Y
5
10
20
15
??
??
??
SALMA
Chasicoan
*Laventan*
Huayquerian
Mayoan
Colloncuran
Santacrucian
Colhuehuapian
Montehermosan
?Friasian s.s
Fig. 2 Miocene South American
Land Mammal “Ages”
(SALMAs). The age of Quebrada
Honda (the Laventan SALMA) is
indicated by asterisks. Light
shading denotes the Friasian
sensu lato (see discussion in
Croft et al. 2009). Modified from
Croft et al. (2009)
0° S
20° S
W °04W °06W °08
0° S
20° S
40° S
80° W 60° W 40° W
40° S
Fig. 1 Map of South America
indicating the location of Que-
brada Honda and other localities
discussed in the text. Argentine
Mayoan localities are grouped
together. Abbreviations: C, Cer-
das; N, Nazareno
J Mammal Evol (2011) 18:245–268 247

Myocastoridae, and Octodontidae) (Huchon and Douzery
2001; Opazo 2005; Sallam et al. 2009;Roweetal.2010). As
noted above, the caviomorph fossil record begins in the early
Oligocene, but they are not found in abundance until later in
the Oligocene (Vucetich et al. 1999,2010b).
Superfamily Cavioidea Fischer de Waldheim, 1817
Family Dasyproctidae Gray, 1825
Mesoprocta hypsodus, gen. et sp. nov.
Figs. 3b,4,5a
Holotype: UF 26915, right dentary bearing m1.
Etymology: The genus combines the common suffix for
dasyproctids (−procta) with reference to its provenance in
the middle latitudes of South America (Meso-); the species
name refers to its teeth (−odus), which are higher crowned
(hyps-) than some other members of the family.
Type Locality: Quebrada Honda Local Fauna, Unit 2 of
Section 1 of MacFadden and Wolff (1981).
Age and distribution: Unnamed formation (Honda
Group) of Quebrada Honda, southern Bolivia, middle
Miocene age, Laventan South American Land Mammal
“Age”(SALMA) (present study).
Diagnosis:Mesoprocta, like other Miocene and younger
dasyproctids, is a relatively large rodent with high-crowned,
lophate cheek teeth and thick enamel (Walton 1997)(Figs.4,
5). It resembles Neoreomys Ameghino, 1887 (Fig. 5e–f)but
clearly differs in its much greater hypsodonty and possession
of cement. It further differs in having less oblique crests
(especially the hypolophid), a less pronounced anterofosset-
tid, and a more persistent metaflexid (Kramarz 2006b). It
differs from “Neoreomys”huilensis (Fig. 5b–c) in the
characters noted above for Neoreomys (= N.australis)as
well as in its much larger size (40% larger than the holotype
based on AP length of m1), its large, triangular i1 (as
opposed to small and oval), and probably in its larger p4, as
estimated from the portion that is preserved (Fields 1957;
Walt on 1997). Mesoprocta is approximately 30% smaller
than poorly characterized Megastus Roth, 1898. Mesoprocta
differs from Australoprocta Kramarz, 1998 (Fig. 5d) and the
small dinomyid “Scleromys”(sensu Walton 1997)inpos-
sessing a metaflexid that does not join the hypoflexid.
Mesoprocta also has a smaller anterofossettid than Austral-
oprocta (Kramarz 1998), and its buccal flexids do not extend
as far lingually as in “Scleromys.”Mesoprocta differs from
Alloiomys Vucetich, 1977 (Fig . 5g) in having lophids that are
nearly perpendicular to the long axis of the tooth (as opposed
to markedly oblique) and a straighter lingual face. Meso-
procta superficially resembles some early Miocene eocar-
diids (e.g., Luantus Ameghino, 1899), but is about 30%
larger, has a much more robust mandible, and has a
metaflexid that persists after isolation of the mesoflexid
(see Kramarz 2006a).
Description: The holotype is the anterior portion of a
right dentary bearing m1 and the bases of i1 and p4 (Fig. 4).
Little mandibular morphology can be discerned due to the
state of preservation, though it is evident that the dentary is
quite robust (greatest depth is ca. 15 mm near m1) and
bears a large symphyseal region (ca. 19 × 6 mm). The lower
incisor is broken and partially obscured by broken bone,
but the exposed anterolabial surface is 5.0 mm wide. It is
triangular in cross section and has a nearly flat buccal
enamel face. The base of the incisor passes lingual to m1
and extends 6.4 mm past its distal surface. It cannot be
c
postero-
lophid
hypoconid
metaflexidentoconid
mesoflexid
metaconid
anterolophid
(metalophulid 1)
protoconid
ectolophid
hypolophid
anterior
arm of
hypoconid
h
y
poflexid
hypoconulid
spur
b
hypoconulid
entoconid
protoconid
hypoconid
anterofossettid
mesofossettid
metaflexid
metalophulid 1
posterolophid
hypolophid
ectolophid
metaconid
hypoflexid
metalophulid 2
anterolophid
(metalophulid 1)
d
metaconid
entoconid
protoconid
hypoconid
posterolophid
ectolophid
hypolophid
hypoflexid
mesoflexid
metaflexid
anterior
arm of
hypoconid
hypoconulid
a
posterior
prism
hypoflexus
anterior
prism
interprismatic furrow
anterior
projection
posterior projection
hypoflexid
posterior
sulcus
anterior
sulcus
interprismatic furrow
Fig. 3 Terminology used to
describe caviomorph premolar
and molar occlusal structure. a
right upper dentition (above,
UATF-V-001038) and right
lower dentition (below, UATF-
V-000971) of Guiomys unica
(Caviidae); bRm1 of
Mesoprocta hypsodus
(Dasyproctidae; holotype, UF
26915); cRdp4 of Acarechimys,
sp. nov.? (Octodontoidea;
UATF-V-000934); dRm3 of
Quebradahondomys potosiensis
(Echimyidae: Adelphomyinae;
holotype, UATF-V-001030).
Anterior is to the right in all
illustrations. Drawings
are not to scale
248 J Mammal Evol (2011) 18:245–268

determined if this is the actual base of the incisor or
whether it would have extended further in life.
Only the base of p4 is preserved. In superior view, it is
composed of two roots that are just beginning to diverge as
they pass into the body of the dentary. The posterior root is
triangular in cross section and is much larger than the elliptical
anterior root; they measure 5.0× 4.7 mm and 3.6× 2.8 mm,
respectively. The total length of the p4 alveolus is 8.8 mm. The
preserved portion of the diastema between p4 and i1 measures
8.3 mm, though this would be greater in a complete specimen.
The m1 is well preserved and its distal face is entirely
exposed. The tooth extends 5.5 mm above the alveolar
border and 14 mm below it. Its base lies just above the
inferior border of the dentary and its roots are not closed.
At a minimum, HI =3.6. Based on the exposed portion of
the tooth, it appears that its dimensions would have
changed little with additional wear. The surface of the
tooth is noticeably worn; relief is evident between the
enamel and dentin and the occlusal surface is trough-
shaped, highest lingually and buccally. It measures 6.1×
4.9 mm at its occlusal surface. Cement fills the lingual half
of the hypoflexid and the fossettids and likely would have
covered most of the tooth. A thin layer of cement covers the
buccal half of the mesial face, and fresh edges are evident
in cross section near the base of the tooth, apparently where
it was removed during preparation.
The molar is tetralophodont. The buccal conids are
thick and are separated by a hypoflexid that extends to
near the buccolingual midpoint of the tooth. The flexid is
oriented nearly perpendicular to the long axis of the
tooth. Two fossettids are present, the anterofossettid and
the mesofossettid. The metaflexid is open lingually but
would have become isolated with 1.1 mm of additional
wear, as judged by the lingual face. The anterofossettid is
small and circular and located near the buccolingual
midpoint of the tooth. It appears that it would be rapidly
lost with additional wear. The mesofossettid and meta-
flexid are parallel to each other and perpendicular to the
long axis of the tooth. Both extend buccally about
halfway across the occlusal surface. The entoconid is
separated from the metaconid by a small inflection of
enamel, possibly a remnant of the lingual opening of the
mesoflexid. Enamel is thickest along the mesial face of
the hypoflexid and the distal face of the posterolophid; it
is thinnest surrounding the anterofossettid, mesofossettid,
and metaflexid.
Discussion: Extant members of the Dasyproctidae
include more than a dozen species of Dasyprocta Illiger,
1811, and Myoprocta Thomas, 1903 (mainly the former;
Woods and Kilpatrick 2005). These species clearly are
closely related to each other, but their relationship to the
many extinct species referred to the family is unclear
Fig. 4 Mesoprocta hypsodus,
gen. et sp. nov., partial right
dentary bearing m1 (UF 26915,
holotype) in occlusal (above)
and buccal (below) views, ante-
rior to the right. Scale bar equals
5mm
J Mammal Evol (2011) 18:245–268 249

(Walton 1997; Vucetich and Verzi 2002). A phylogenetic
analysis of these species likely would help clarify the
situation, especially considering that good cranial material
exists for some species in addition to dentitions (e.g., N.
australis,“N.”huilensis, and Alloiomys pattersoni).
In an unpublished PhD thesis, Frailey (1981:61–62)
tentatively referred UF 26712 (a poorly preserved partial
right dentary bearing p4-m3) to Neoreomys. We have been
unable to study this specimen firsthand. Based on the
limited information provided by Frailey (1981), we cannot
assess whether this specimen pertains to Mesoprocta
hypsodus. We presently consider it as Dasyproctidae gen.
et sp. indet.
Family Caviidae Fischer de Waldheim, 1817
Diagnostic characters: Caviids have simple, hypselodont
cheek teeth with triangular lobes and deep sulci. Enamel is
reduced or absent on the lingual surfaces of lower cheek
teeth and on the buccal sides of upper cheek teeth, at least
in adults. In most cheek teeth, a narrow isthmus obliquely
connects the lobes. Caviids differ conspicuously from
“eocardiids”such as Eocardia and Luantus in their lack
of fossettes/fossettids in all ontogenetic stages, as well as in
the morphology of the external face of the mandible (Pérez
2010; Pérez et al. 2010; Pérez and Vucetich 2011).
Discussion: The family Caviidae traditionally has included
two subfamilies, Dolichotinae and Caviinae. Recent molecular
studies have indicated that capybaras (Hydrochoeridae) should
be included as a third subfamily (Rowe and Honeycutt 2002;
Rowe et al. 2010). Both of these arrangements are based on
modern representatives (Woods and Kilpatrick 2005), and
many extinct taxa do not unequivocally fit into this tripartite
scheme. Hydrochoerids (hydrochoerines) and their close
relatives are easily distinguished from other caviids by the
additional well-developed flexuses and flexids on their cheek
teeth (e.g., Vucetich et al. 2005; Deschamps et al. 2007). The
validity, contents, and distinguishing characters of the two
other subgroups are less clear (Quintana 1996,1998; Ubilla et
al. 1999; Ubilla and Rinderknecht 2003;Pérez2010). The
situation is further complicated by the many extinct species
known only from dental remains and/or small samples that
preclude adequate assessment of population variation.
Guiomys Pérez, 2010
Type species:Guiomys unica Pérez, 2010.
Included species: The type only.
Age and distribution: Unnamed formation of El Petiso
locality, Chubut, Argentina, middle? Miocene age, Laven-
tan? SALMA (Pérez 2010); Collón Curá Formation, Río
Negro, Argentina, middle Miocene age, Colloncuran
SALMA (Pérez 2010); unnamed formation (Honda Group)
of Quebrada Honda, southern Bolivia, middle Miocene age,
Laventan SALMA (present study).
Diagnostic characters:Guiomys is a small caviid (tooth-
row length similar to Orthomyctera rigens Ameghino,
1889) that is distinguished by its autapomorphic mandib-
ular morphology. On the external face of the mandible, the
shelf for the insertion of the masseter medialis pars infraorbi-
talis (mmpi) is distinct from and anterior to both the horizontal
crest and the masseteric crest. The shelf for the insertion of the
mmpi is horizontal relative to the inferior border of the
mandible, whereas the horizontal crest lies an angle of ca. 30°,
paralleling the superior border of the horizontal ramus. The p4
bears a distinct, wide buccal anterior sulcus between the
anterior prism and its anterior projection, but the shapes and
a
e
b
f
c
g
d
Fig. 5 Comparison of dasyproctid lower molars. am1 of Mesoprocta
hypsodus (UF 26915, holotype)1; bm1-2 of “Neoreomys”huilensis
(IGM 183327) from Walton (1997); cm2-3 of “N.”huilensis (IGM
183683) from Walton (1997); dm2 of Australoprocta fleaglei (MACN
CH 1784) from Kramarz (1998); em1 or m2 of Neoreomys pinturensis
(MACN Pv SC2211) from Kramarz (2006a,b); fm1 or m2 of N.
australis from Kramarz (2006a,b); gm2 of Alloiomys sp. (MLP 76-
VIII-30-4). Black indicates dentine and gray indicates enamel.
Anterior is to the right in all illustrations. Scale bar equals 2 mm
250 J Mammal Evol (2011) 18:245–268

sizes of these three structures apparently vary among
individuals. The teeth of Guiomys lack transverse dentine
crests, which characterize later-diverging members of the
family (Pérez and Vucetich 2011).
Guiomys unica Pérez, 2010
Figs. 6a, c-d,7
Holotype: MPEF-PV 3504, partial right dentary bearing
p4–m3.
Referred specimens: UATF-V-000962, UATF-V-000971,
UATF-V-000973, UATF-V-000981, UATF-V-001008, UATF-
V-001017, UATF-V-001038, UF 26914, UF 66003, UF
236852, UF 236853, UF 236854, UF 236858, UF 236859,
UF 236860 (Appendix 1).
Provisionally referred specimens: UF 26717, UF 26718,
UF 26719, UF 26720 (see below).
Localities: Quebrada Honda Local Fauna, Units 2 and 4,
and Río Rosario Local Fauna, levels equivalent to Units 2
and 4 of Quebrada Honda of MacFadden and Wolff (1981),
as well as unspecified lower levels.
Diagnostic characters: As for genus.
Description: The dentition and mandibular crests of G.
unica are described in detail by Pérez (2010). We therefore
focus our description on new information provided by the
more complete material from Quebrada Honda.
Fig. 6 Specimens of Guiomys
unica from Quebrada Honda
and other caviids. apartial
cranium of G. unica (UF
236852) in right lateral (above)
and palatal (below)views;
bholotype cranium of Ortho-
myctera andina (MACN 8350)
in right lateral (above)and
palatal (below)views;cpartial
cranium of G. unica (UF
236853) in right lateral (above)
and palatal (below)views;
dpartial mandible of G. unica
(UF 236854) in left lateral
(above, reversed) and occlusal
(below)views;eholotype of
Orthomyctera rigens (MACN
A 1661–62), cranium in palatal
view (left), left dentary in
lateral view (above right,
reversed), and close-up view
of left maxillary dentition in
occlusal view (below right).
Anterior is to the right in all
photos. Scale bar equals 1 cm
J Mammal Evol (2011) 18:245–268 251

UF 236852 is a nearly complete cranium in moderately
good condition (Fig. 6a). Much of the overall morphology
of the cranium is evident, but many details are not
preserved. All teeth except RP4 are present (though only
part of the base of LP4 remains) and about half are not fully
situated in their alveoli. The soft tissue anchoring the teeth
apparently decomposed prior to burial of the specimen,
permitting some teeth to partially slide out of their alveoli.
This suggests that the specimen was exposed for an
intermediate period of time prior to fossilization: long
enough to permit soft tissue decomposition but not long
enough to degrade the bone or dentition. Most of the skull
roof is missing (nasals, frontals, parietals), exposing a
natural endocast of the nasal passages, cranial cavity, and
other spaces. The small portion of the roof that is present is
fractured into small pieces, suggesting that the skull roof
was lost when the fossilized specimen was exposed through
erosion. Greatest skull length is 86.2 mm. The skull is
relatively narrow, measuring 28.6 mm across the para-
occipital processes, ca. 48 mm across the zygomatic arches
(only the right is preserved), and ca. 18 mm at the
premaxillary-maxillary suture (part of the right premaxilla
is missing). The zygomatic arch is straight in dorsal view,
and is directed slightly toward the midline anteriorly.
In lateral view, the skull has a slightly curved profile, and
the large auditory bullae lie below the level of the tooth
row. Among extant caviids, the profile of UF 236852 most
resembles Kerodon rupestris Weid, 1826 (Quintana 1998).
The incisive foramina are long and narrow in palatal
view (ca. 14×3.5 mm), unlike any extant caviine but
similar to the condition in Dolichotis Desmarest, 1820
(Campos et al. 2001). The dispositions of the upper tooth
rows are not evident in UF 236852, but can clearly be seen
to be straight and anteriorly convergent in another partial
cranium, UF 236853 (Fig. 6c). The palate of this specimen
is 11.0 mm wide at the posterior lobe of M3 and only
2.6 mm wide at the anterior lobe of P4. Toothrow lengths
for these and other specimens are provided in Appendix 1.
UF 236853 also preserves the posterior border of the palate
in G.unica (i.e., the anterior border of the mesopterygoid
fossa; see Carleton and Musser 1989:fig. 16). It sits
opposite the anterior or posterior lobe of M3 and is broadly
rounded with a slight midline tubercle. The area also is
preserved in UF 236860, UATF-V-001038 and, to a lesser
extent, in UATF-V-000962. This is more similar to the
condition present in most modern caviines (except K.
rupestris)thanitistothatofDolichotis and other
dolichotines. In K.rupestris and dolichotines, the meso-
pterygoid fossa extends farther anteriorly and is more
triangular, coming to a point anteriorly.
The left upper incisor of UF 236852 measures 4.3 ×
2.6 mm in section near its tip (anteroposterior × mesiodistal
diameter). This is the only specimen in which the upper
incisors are preserved. The upper cheek teeth of Quebrada
Honda specimens of G. unica generally resemble those
from El Petiso. The morphology of P4 cannot be discerned
clearly in UF 236852, but it is present on both sides in UF
236853 and UF 236859. In all specimens, P4-M2 each
consists of two subequal prisms separated by a hypoflexus
that is broad lingually and narrow buccally. Cement fills the
buccalmost portion of the hypoflexus. Enamel is present
along the lingual faces of the teeth. It is completely absent
on the buccal faces of some specimens (UF 236852, UATF-
V-000962, UATF-V-001038) and restricted to the shallow
interprismatic sulci in others (UF 236852, UF 236859).
This may represent ontogenetic variation.
The greatest variation in cheek tooth morphology is
evident in M3, which is preserved in several specimens.
The M3 of UF 236852 resembles MPEF-PV 3534 and 3535
(Pérez 2010:figs. 2, 6) in having a straight-sided posterior
(distal) projection that is lingually separated from the
posterior prism by a sulcus that forms an angle of 90°.
(The posterior projection is considered a distinct prism by
some authors, in which case this posterior sulcus separates
f
a
e
b
c
d
Fig. 7 Right lower dentitions of Guiomys unica from Quebrada
Honda. aUATF-V-000971, right p4-m3; bUATF-V-001017, left p4-
m2 (reversed); cUF 26914, left p4-m2 (reversed); dUF 236858, right
p4-m2; eUF 66003, right p4-m2; fUF 236854, right p4-m3. Anterior
is to the right in all illustrations, and specimens are aligned at the m2
hypoflexid. Scale bar equals 2 mm
252 J Mammal Evol (2011) 18:245–268

the second and third prisms; Ubilla and Rinderknecht
2003.) In other Quebrada Honda specimens (UATF-V-
001038, UF 236853; Fig. 3a), the posterior sulcus is
rounded and more similar to that of Orthomyctera
Ameghino, 1889 (Ubilla and Rinderknecht 2003:fig. 4).
Based on variation in extant caviids (Contreras 1964) and
the relatively limited data presently available for Ortho-
myctera and other extinct taxa, we provisionally interpret
this as intraspecific variation (see also discussion below).
The mandibular morphology of G.unica is best
preserved in UF 236854, which includes most of both
horizontal rami (Fig. 6d). On both sides, the diagnostic
morphology of G.unica is evident. The insertion of the
mmpi is a shelf that protrudes laterally from each side of
the mandible and is broadest from below the posterior
prism of m2 to the hypoflexid of m1. The horizontal crest is
superior to this shelf. Its anterior end lies below a point
between m2 and m3 and its posterior end extends well
posterior to the distal border of m3.
The most variable tooth of the lower dentition is p4. In
most Quebrada Honda specimens (Fig. 7a–d, f), it
resembles specimens from El Petiso in having a shallow
anterior sulcus on its buccal face that separates the anterior
prism from a rounded anterior projection. In UF 66003
(Fig. 7e), however, this sulcus is quite deep and parallels
the hypoflexid, creating two subequal divisions of the
anterior prism. This morphology is more similar to the
condition in Prodolichotis pridiana Fields, 1957, than other
G.unica. In the absence of unambiguous evidence to the
contrary, we interpret this as intraspecific variation rather
than as indicative of a second species.
The molars resemble those of G.unica from El Petiso,
though some variation is present. For example, in UATF-V-
000971, the m3 interprismatic furrow is broad and
posteriorly directed, unlike in most other specimens from
Quebrada Honda (Fig. 7a). This is a characteristic feature of
Microcardiodon williensis Pérez and Vucetich, 2011, and
Eocardia robusta Vucetich, 1984 (Pérez and Vucetich
2011), but is not evident in the other molars of this
specimen, suggesting it represents an example of dental
variation within G.unica. Such variation is expected in m3,
which tends to be quite variable in caviids, even within a
single species (M. Pérez, pers. comm., April 2011). The
first and second molars are subequal in size, whereas m3 is
slightly larger. A similar pattern is evident in the only
specimen of G. unica from El Petiso that preserves all
lower molars (Pérez 2010:table 2). This apparently differs
from the condition in M.williensis, in which the molars
increase in size posteriorly (distally), though no single
specimen from El Petiso that completely preserves all three
molars (Pérez and Vucetich 2011:table 2).
Discussion: UF 236854 clearly illustrates the autapo-
morphic structure of the external face of the mandible
characteristic of G.unica. Less complete dentaries from
Quebrada Honda appear to have a similar morphology. The
dentitions of Quebrada Honda specimens generally resem-
ble G. unica from El Petiso (with a few exceptions noted
above), and dimensions of individual teeth mainly fall
within the range of specimens from El Petiso (Pérez 2010:
table 2). Together, these provide clear evidence that G.
unica is present at Quebrada Honda. It is possible that
larger samples or more complete specimens from Quebrada
Honda and El Petiso could demonstrate that the two
populations represent distinct species or that more than
one species is present at Quebrada Honda. Nevertheless, we
think it is prudent at the present time to interpret differences
among Quebrada Honda specimens as intraspecific rather
than interspecific variation.
One issue that cannot be answered presently is how the
mandibular morphology of G.unica compares to that of
Orthomyctera Ameghino, 1889, another early caviid.
Orthomyctera is a rather poorly characterized genus despite
its broad geographic range. It has been reported from late
Miocene to early Pliocene faunas (Chasicoan to Monteher-
mosan SALMAs) from Bolivia to central Argentina
(Rovereto 1914; Bondesio et al. 1980a; Marshall and
Patterson 1981; Hoffstetter 1986; Marshall and Sempere
1991; Herbst et al. 2000; Tauber 2005; Verzi et al. 2008).
Fivespecieshavebeenreferredtothegenus:O. rigens
Ameghino, 1889;O. vaga Ameghino, 1889;O.chapalma-
lense Ameghino, 1889;O. lacunosa Ameghino, 1889;O.
andina Rovereto, 1914;andO.brocherense Castellanos,
1956. Of these, O.chapalmalense probably pertains to
Dolichotis (Kraglievich 1930a; Ubilla and Rinderknecht
2003)andO.lacunosa probably pertains to Prodolichotis
Kraglievich, 1932 (Kraglievich 1932). Orthomyctera vaga is
basedonafragmentarymaxillabearingM3andhasbeen
disregarded by most authors (e.g., Quintana 1998; Ubilla and
Rinderknecht 2003), though Kraglievich (1932)referreda
cranium to this species. The distinctiveness of O.brocherense
also is dubious. Only two species are based on adequate type
material: O.rigens (the type species) and O.andina.
The holotype of O.rigens, MACN A 1661–62,
includes a poorly preserved cranium bearing LP4-M3
and parts of RP4-M2, and a partial left dentary bearing i
and m1 (Fig. 6e). It appears to differ from G.unica
primarily in having more pronounced interprismatic
furrows in the upper dentition. The M3 morphology
differs from that of El Petiso G.unica in having a broad,
rounded posterior sulcus lingually separating the posterior
prism from its posterior projection. Based on specimens of
G.unica from Quebrada Honda, however, this may
represent intraspecific variation. It would be useful to test
this hypothesis with a larger sample of O.rigens.The
shape and position of the mesopterygoid fossa in O.rigens
resembles that of specimens of G.unica from Quebrada
J Mammal Evol (2011) 18:245–268 253

Honda. Size also is comparable; toothrow length of
MACN A 1661–62 is ca. 16 cm, within the range of
Quebrada Honda G.unica. The partial dentary of the
holotype of O.rigens unfortunately does not permit the
morphology of the external face of the mandible to be
assessed. Transverse dentine crests appear to be present on
the molars, which would distinguish this species from G.
unica and earlier-diverging caviids.
The holotype of O.andina, MACN 8350, is a fairly
well-preserved cranium (Fig. 6b). It is noticeably smaller
overall than both O.rigens and specimens referred to G.
unica from Quebrada Honda. Total skull length of MACN
8350 is ca. 60 mm, compared to 86.2 mm for UF 236852.
The unfused cranial sutures of MACN 8350 suggest that
the specimen is from a young individual, and this might
partly account for its smaller size. However, the dentition is
fully erupted. The shape of the skull in lateral view does not
closely resemble that of UF 236852. The postorbital portion
is proportionally smaller (anteroposteriorly) and more
rounded, similar to the condition in Dolichotis. As is the
case for O.rigens, the morphology of the external face of
the mandible in O.andina is not known. The dentition
appears to preserve transverse dentine crests, a feature
lacking in G. unica.
Pérez (2010; see also Pérez and Vucetich 2011)
performed an extensive phylogenetic analysis of caviids
(34 taxa, 83 characters) but only included O.chapalma-
lense among species of Orthomyctera. As noted above, this
species likely pertains to Dolichotis (Kraglievich 1930a;
Ubilla and Rinderknecht 2003). Thus, the degree to which
the mandibular morphology of G.unica differs from
species referred to Orthomyctera presently is not known,
because this character cannot be assessed in the holotypes
of O.rigens and O.andina. Such comparisons must await
recovery of more complete mandibular material of Ortho-
myctera. Larger sample sizes of relevant species also would
be useful for assessing intraspecific dental variation more
accurately.
Frailey (1981:66–74) referred three UF Quebrada Honda
specimens to Schistomys, sp. nov. (UF 26718, 26719,
26720), and one to Eocardia cf. montana Ameghino,
1887 (UF 26717). Frailey (1981) did not directly compare
these specimens to caviids, and although we have been
unable to study these specimens firsthand, there is no
evidence for referral of them to the Eocardiidae; fossettes/
fossettids apparently are absent, and there is little variation
in morphology among the teeth (Pérez 2010; Pérez and
Vucetich 2011). Dental measurements provided for these
specimens fall within the range of variation of G.unica
from Quebrada Honda, except for some measurements of
UF 26717. Length of p4-m3 of this specimen is given as
20.7 mm, but m3 appears to be incompletely preserved
(measured at 6.4 mm). Because measurements of other
teeth of this specimen fall within the range of G. unica,it
appears that the length of m3 (and the toothrow) is an
overestimate. All four of these specimens appear to pertain
to G. unica.
Superfamily Octodontoidea Simpson, 1945
Acarechimys Patterson, 1965 (in Kraglievich 1965)
Type species:Acarechimys minutus (Ameghino, 1887).
Included species: the type, A.constans (Ameghino,
1887), A.minutissimus (Ameghino, 1887), A.pulchellus
(Ameghino, 1902).
Age and distribution: Sarmiento Formation, Chubut,
Argentina, early Miocene age, Colhuehuapian and Santa-
crucian? SALMAs (Kramarz et al. 2010; Vucetich et al.
2010a); Chichinales Formation, Río Negro, Argentina,
early Miocene age, Colhuehuapian SALMA (Kramarz et
al. 2004); Chucal Formation, Region XV, Chile, late early
Miocene age, Santacrucian SALMA (Croft et al. 2007);
middle and upper sequences of Pinturas Formation, Santa
Cruz, Argentina, late early Miocene age, Santacrucian?
SALMA (Kramarz 2004; Kramarz and Bellosi 2005);
unnamed formation of Pampa Castillo, Region XI, Chile,
early Miocene age, Santacrucian SALMA (Flynn et al.
2002b); Santa Cruz Formation, Santa Cruz, Argentina, late
early Miocene age, Santacrucian SALMA (Ameghino
1887,1889; Scott 1905); Cura-Mallín Formation, Region
VIII, Chile, late early to middle Miocene age (Flynn et al.
2008); Collón Curá Formation, Neuquén, Argentina, early
middle Miocene age, Colloncuran SALMA (Vucetich et al.
1993); Honda Group, Colombia, middle Miocene age,
Laventan SALMA (Walton 1997); unnamed formation
(Honda Group) of Quebrada Honda, southern Bolivia,
middle Miocene age, Laventan SALMA (present study);
conglomerates of Fitzcarrald Arch, eastern Peru, middle
Miocene age, Laventan SALMA (Antoine et al. 2007;
Negri et al. 2010); questionably present in Madre de Dios
and other formations, eastern Peru, late Miocene age
(Campbell et al. 2006).
Diagnostic characters:Acarechimys includes very small,
brachydont rodents that retain DP4/dp4 (Patterson and
Wood 1982; Vucetich et al. 2010a). The lower molars have
three main transverse crests and upper molars have four
such crests. The labial flexi and lingual flexids are shallow
and form fossettes or fossettids after relatively little wear.
As is true of octodontids, the mesofossettid forms after the
metafossettid.
Acarechimys, sp. nov.?
Figs. 3c,8,9
Referred Specimens: UATF-V-000935, UATF-V-000896,
UATF-V-000897, UATF-V-000934, UATF-V-000940, UATF-
254 J Mammal Evol (2011) 18:245–268

Fig. 8 Dentitions of Acare-
chimys, sp. nov.? from Que-
brada Honda. aUATF-V-
000935, partial right dentary
bearing dp4-m3 in occlusal
(above) and buccal (below)
views. bUATF-V-000952, par-
tial right dentary bearing m1-3
(and roots of dp4) in occlusal
view. cUATF-V-001039, partial
right dentary bearing dp4-m2 in
occlusal view. dAMNH 107911
(= UF 26713), partial right
maxilla bearing M2-3. Anterior
is to the right in all photos. Scale
bar equals 2 mm
J Mammal Evol (2011) 18:245–268 255

V-000950, UATF-V-000952, UATF-V-000958, UATF-V-
000960, UATF-V-000974, UATF-V-000983, UATF-V-
001039, AMNH 107907 (= UF 26695), AMNH 107908
(= UF 26696), AMNH 107909 (= UF 26697), AMNH
107910 (= UF 26698 or 26699), AMNH 107912 (= UF
26698 or 26699) (Appendix 2).
Localities: Units 2, 3, and 6 of MacFadden and Wolff
(1981), Quebrada Honda Local Fauna; Río Rosario Local
Fauna, unspecified lower levels equivalent to Units 2–4of
Quebrada Honda Local Fauna.
Description: The most complete specimen, UATF-V-
000935, is a moderately worn partial right dentary bearing
dp4-m3 and the base of i1 (Figs. 8a,9d). A small scar for
the insertion of the masseter medialis pars infraorbitalis is
located just anterior to the masseteric crest, a feature that is
characteristic of octodontids and kin (Verzi et al. 1994; Verzi
1999,2002).
The total length of the toothrow is 7.1 mm. Based on
measurements by Scott (1905), this is larger than A.
minutissimus (5.0 mm) and within the lower part of the
range of A.minutus (7.0–8.0 mm). However, based on the
data of Walton (1990:fig. 8), m1s of Quebrada Honda
Acarechimys are much larger (in length and breadth) than
those of both A. minutissimus and A.minutus, presumably
closer to A.constans and A.pulchellus (Kramarz 2004,
Vucetich et al. 2010a). Ameghino notes a toothrow length
of 9.0 mm for A.constans (Ameghino 1889) and 8.0 mm
for A.pulchellus (Ameghino 1902). UATF-V-000935 is the
only Quebrada Honda specimen that preserves dp4-m3, but
many other specimens preserve three of the four cheek
teeth. All are at least as large as UATF-V-000935. Estimated
toothrow lengths for these specimens based on UATF-V-
000935 average 7.5 mm and range up to 8.3 mm
(Appendix 2). This overlaps the range of both A.minutus
and A.pulchellus.
The largest tooth in the dental series is m2, which tends
to be broader than all other teeth and longer than all others
except dp4. The smallest tooth is m3, which is 70–90% the
anteroposterior length of m2. In overall form, dp4 is
rectangular, m1 and m2 are quadrangular, and m3 is
triangular.
All cheek teeth of UATF-V-000935 are trilophodont. The
hypoflexid is the deepest flexid (i.e., the last to form a
fossettid). It is open externally in all teeth and extends
across ca. 40% of the buccolingual diameter of each tooth.
It is directed distolingually toward the metaflexid/metafos-
settid, but is separated from it by the anterior arm of the
hypoconid. The metaflexid has become isolated as a
metafossettid in all teeth of UATF-V-000935 except m3.
The mesoflexid, in contrast, is open lingually in all teeth
except dp4. The mesoflexid is slightly larger than the
metaflexid, as is the corresponding fossettid in teeth in
which it has become isolated. It is much larger than the
metaflexid in m3, but in moderately worn specimens (e.g.,
UATF-V-000950; Fig. 9e), the resulting fossettids are
subequal in size. The greater persistence of the mesofos-
settid is evident in the most heavily worn specimen, UATF-
V-000983. The metafossettid is absent in this specimen, but
both the mesofossettid and hypofossettid are present. The
latter is larger and has thicker enamel. The depth of these
structures evidently varies among individuals. In m1 of
UATF-V-000952 (Fig. 8b), both the meso- and metafosset-
tid are absent, but a hypoflexid has not yet formed a
hypofossettid.
Variation also is evident in dp4, as is typical for basal
octodontoids (Kramarz 2004). In UATF-V-000934 (Figs. 3c,
9c), dp4 has an expanded metaconid and a small spur on
the anterolophid (= metalophulid 1) in the region of the
protoconid. The spur is directed distolingually, resulting in
a mesoflexid that bifurcates buccally. The ectolophid is
slightly expanded near its juncture with the hypolophid.
The posterolophid joins the hypo- and ectolophid via the
anterior arm of the hypoconid, which is flanked by
subequal meta- and hypoflexids. In UATF-V-000960
(Fig. 9a), a specimen exhibiting very little wear, a trigonid
a
c
d
b
e
Fig. 9 Lower dentitions of Acarechimys, sp. nov.? aUATF-V-000960,
Rdp4-m1; bLdp4 of UATF-V-000974 (reversed); cUATF-V-000934,
Rdp4-m2; dUATF-V-000935, Rdp4-m3; eUATF-V-000950 Lm1-m3
(reversed ). Black indicates dentine and gray indicates enamel.
Anterior is to the right in all illustrations. Scale bar equals 1 mm
256 J Mammal Evol (2011) 18:245–268

fossettid (anterofossettid) is present between the metal-
ophulid 1 and another lophid. Unlike a typical metalophulid
2, this lophid does not extend transversely across the tooth
from the metaconid, however, but rather distolabially
toward the anterior arm of the hypoconid. The resulting
anterofossettid is quite large and the metaflexid is directed
more distally than in other specimens. UATF-V-000974 is
not well preserved, but it shows yet another variation
(Fig. 9b). Both an anterofossettid and mesoflexid are
present. The mesial and distal sides of the mesoflexid
approach each other near its buccolingual midpoint, nearly
creating a distinct fossettid. With additional wear, it is
possible that this specimen would have had an anterofos-
settid, a mesofossettid, and a mesoflexid. In UTAF-V-
000935 (Figs. 8,9d), most of the structure of dp4 has been
worn away. Only the bases of the anterofossettid and
metafossettid are present.
UATF-V-001039, a partial right dentary bearing dp4-m2,
is noteworthy among Quebrada Honda specimens in being
the only one with a more complex molar morphology, best
seen in m2 (Fig. 8c). Unlike other Quebrada Honda
specimens, the m2 of UATF-V-001039 bears a small,
anterolingually directed spur on the ectolophid and a small
mesolophid (metalophulid 2) that connects the posterior
(distal) edge of the metaconid to the midpoint of the
anterolophid (metalophulid 1), resulting in a lingually
positioned anterofossettid. The overall occlusal pattern is
more similar to that of a dp4 than a typical m2, though its
size and relative proportions are comparable to m2s of other
specimens (other than being slightly wider). The morphol-
ogy of m1 is much less clear due to greater wear, but the
presence of two tiny trigonid fossettids rather than a single
mesofossettid suggests that the unworn morphology was
similar to that of m2.
UF 26713, a moderately worn partial right maxillary
dentition preserving M2-3, may pertain to the same species
of Acarechimys. This specimen was referred to Acaremyi-
nae (= Acaremyidae) indet. by Frailey (1981). A cast in
AMNH collections (AMNH 107911) of a Quebrada Honda
specimen that was collected in 1978 matches the descrip-
tion of this specimen as well as its stratigraphic provenance
and therefore likely represents UF 26713 (Fig. 8d). M2 is
slightly broader anteriorly (mesially) than posteriorly and
bears four transverse lophs. Two flexuses are present, the
mesoflexus and the hypoflexus. The former is perpendic-
ular to the long axis of the tooth whereas the latter runs
anterolingually from the buccal face. They are separated by
the anterior arm of the hypoconid, which is as broad as the
four main lophs. Two small, oval fossettes are present, one
between the anteroloph and protoloph (parafossette) and the
other between the metaloph and posteroloph (metafossette).
Their long axis are parallel to the mesoflexus, and both are
narrower anteroposteriorly than the mesoflexus. The M3 is
slightly smaller than M2 and also is tetralophodont. A
hypoflexus is present, but the mesoflexus has become
isolated as a mesofossette. It and the parafossette are
subequal in size and both are larger than the metafossette. A
fifth fossette, slightly smaller than the metafossette, is
present just lingual to the parafossette and may represent a
separately isolated portion of the paraflexus. The tip of the
paracone lies just posterior to this accessory fossette.
Discussion: Five Quebrada Honda specimens (four
dentaries and one maxilla) are listed in the UF collections
database as pertaining to Echimyidae (UF 26695–26699).
The study of Frailey (1981) made no mention of them, and
we have not been able to study them firsthand. However,
these appear to be represented by five casts in AMNH
collections: AMNH 107907, 107908, 107909, 107910, and
107912. The accompanying labels read “Santacrucian,
Quebrada Honda, Tarija Prov., Bolivia, Frailey party,
1978,”but no field numbers or UF collections numbers
are associated with the specimens. The stratigraphic data
for each of these specimens precisely matches that for the
five echimyid specimens in the UF collections database.
They closely (but not precisely) match the brief descriptions
provided in the UF database; one specimen listed as a maxilla
actually is a dentary, and one preserves dp4-m1 rather than
dp4-m2. These discrepancies probably are due to initial
misinterpretations of the teeth represented. We therefore
interpret these casts as representing UF 26695–26699.
They match UATF specimens of Acarechimys in size and
morphology and clearly represent the same species.
Species and specimens of Acarechimys are clearly in
need of revision. The three Santacrucian species (A.
minutus,A.minutissimus,A.constans) are distinguished
primarily by size (Vucetich et al. 1993), but whether such
differences are valid for large samples sizes has not been
demonstrated. Acarechimys pulchellus was recently
transferred from Protacaremys to Acarechimys, but no
characters distinguishing this species from others in the
genus were provided (Vucetich et al. 2010a). As noted by
Vucetich et al. (2010a), no specimens referred to
Acarechimys from localities other than Santa Cruz have
been referred to a particular species, although resemblances
have been noted in some instances (e.g., Acarechimys cf. A.
minutus from Pampa Castillo and Acarechimys cf. A.
minutissimus from La Venta). Moderate metric and
morphological variation certainly is present among
specimens referred to Acarechimys, but no published
study other than the present one has described variation
among a reasonably large sample from a single locality. In
the absence of other such studies, the identity of the
Quebrada Honda species cannot be determined with
certainty. Its relatively large size, proportionately small
m3, and absence of metalophulid 2 (mesolophid) and other
accessory lophids in m1-3 of most individuals, among other
J Mammal Evol (2011) 18:245–268 257

characters, suggest that it may be distinct from early
Miocene species of Acarechimys.
Family Echimyidae Gray, 1825
Subfamily Adelphomyinae Patterson and Pascual, 1968
Diagnostic characters: Adelphomyines exhibit a tenden-
cy towards hypsodonty (Kramarz 2001) and m2 is often the
largest tooth in the molar series (Prostichomys,Stichomys).
Members of this subfamily possess trilophodont or tetralo-
phodont molars with oblique lophids that tend to form
plates. Adelphomyines such as Adelphomys,Stichomys,
Spaniomys, and Maruchito also possess shortened lower
incisors that do not extend posteriorly past m2 (Vucetich et
al. 1993). It apparently represents a monophyletic group
(Vucetich et al. 2010a).
Quebradahondomys potosiensis, gen. et sp. nov.
Figs. 3d,10,11a
Holotype: UATF-V-001030, right dentary bearing m1-m3.
Provisionally referred specimen: UF 26714, left dentary
bearing m1-2.
Etymology: The genus name combines reference to the
type locality with the common suffix for rodent genera
(−mys). The specific epithet honors Potosí, Bolivia, the
location of the Universidad Autónoma Tomás Frías, a
critical supporter of our investigations in Bolivia.
Type locality: Quebrada Honda Local Fauna, Unit 2 of
MacFadden and Wolff (1981).
Age and distribution: Unnamed formation (Honda
Group) of Quebrada Honda, southern Bolivia, middle
Miocene age, Laventan SALMA (present study).
Diagnosis:Quebradahondomys differs from Spaniomys
Ameghino, 1877, in having trilophodont molars (tetralo-
phodont in Spaniomys). It differs from Maruchito Vucetich
et al., 1993, in its straighter, less undulating lophids,
shallower and medially-directed hypoflexids, and narrower
buccal lophids. Quebradahondomys differs from Stichomys
Ameghino, 1887,Prostichomys Kramarz, 2001,Xylechimys
Patterson and Pascual, 1968, and Deseadomys Wood and
Patterson, 1959, in its lack of an anterofossettid and its
more transverse lophids. It further differs from Stichomys in
having a hypoflexid that is less penetrating and proportion-
ally wider lingually, and in m3 being the largest tooth in the
molar series (it is the smallest in Stichomys). Quebrada-
Fig. 10 Right dentary of
Quebradahondomys potosiensis,
gen. et sp. nov. (holotype,
UATF-V-001030) in occlusal
(above) and lateral (below)
views, anterior to the right.
Scale bar equals 2 mm
258 J Mammal Evol (2011) 18:245–268

hondomys resembles Adelphomys Ameghino, 1887,in
having the hypoflexid and metaflexid separated only by a
very narrow isthmus, but in Quebradahondomys the
hypoflexid is shallower, the lophids are more transverse,
and the posterolophid is anteroposteriorly thicker.
Quebradahondomys lacks the confluence of the hypoflexid
and mesoflexid present in Paradelphomys Patterson and
Pascual, 1968. The molars of Ricardomys Walt on, 1990,are
smaller, proportionately narrower, and have less penetrating
hypoflexids than Quebradahondomys (Fig. 11).
Description: The holotype is a right dentary bearing m1-
m3 and the base of the incisor. Its depth is 6 mm below the
first molar. The base of the incisor measures ca. 1.7×
1.3 mm in section at its mesial end, and the distal end does
not extend posterior to m2. The teeth are hypsodont. The
crowns extend ca. 2 mm above the alveolar border. The
molars are formed by a series of thin laminae with uniform,
thin enamel. They increase in anteroposterior diameter from
m1 to m3. Total molar row length is 9.2 mm. The individual
molars measure 2.4×2.1 mm (m1), 3.0 ×2.5 mm (m2), and
3.2×2.6 mm (m3). The premolar alveolus is 3.8 mm long.
All molars are generally similar in form. Each is composed
of three lophids that are relatively less oblique to the long
axis of the dentary than in most other adelphomyines. The
hypoconid and protoconid are large, and the ectolophid and
posterolophid are correspondingly thick (anteroposteriorly).
They are separated by a moderately deep hypoflexid that
extends less than halfway across the tooth. It is propor-
tionately deepest in m1 and forms an acute angle. It
approximates a right angle in m2-3. The hypoflexid is
separated from the metaflexid by a very narrow isthmus
connecting the hypoconid to the hypolophid. The hypo-
lophid is markedly narrower anteroposteriorly than the
posterolophid in m1, slightly narrower in m2, and roughly
equal in m3. The anterolophid (metalophulids 1 and 2)
bears no evidence of an anterofossettid. Its lingual portion
(metaconid) is expanded in m1-2 and only slightly
expanded in m3. Similarly, the connection to the protoconid
is thickest in m1, intermediate in m2, and very narrow in
m3. These primarily appear to be due to differences in wear
among the molars. The mesoflexid and metaflexid are
approximately equal in their buccolingual extend.
Discussion: Frailey (1981:44–47) tentatively identified
UF 26714 (a partial left dentary bearing m1-2) as a new
species of Spaniomys. We have been unable to study this
specimen firsthand, but based on the figures and measure-
ments in Frailey (1981), it closely matches UATF-V-001030
in both size (m1=2.7×2.1 mm, m2=3.1× 2.7 mm) and
morphology. It very likely pertains to Quebradahondomys
potosiensis.
Superfamily Chinchilloidea Bennett, 1833
Family Chinchillidae Bennett, 1833
Subfamily Lagostominae Wiegmann, 1832
Diagnostic characters: Chinchillids have very character-
istic hypsodont to hypselodont cheek teeth composed of
parallel laminae with reduced enamel between them. The
teeth of lagostomines are composed of only two laminae,
whereas those of chinchillines often have three laminae
(\Flynn et al. 2002a). Fossettids are present in the teeth of
basal chinchillids from the Oligocene (e.g., Vucetich 1989)
but are lacking in the adult teeth of later species.
a
b
c
d
f
e
Fig. 11 Lower dentition of adelphomyines. aQuebradahondomys
potosiensis, gen. et sp. nov. (holotype, UATF-V-001030) Rm1-m3; b
Ricardomys longidens (IGM 183847) Ldp4-m2 (reversed) from
Walton (1997); cParadelphomys fissus (MLP 125) Ldp4-m1
(reversed) from Patterson and Pascual (1968); dAdelphomys candidus
(YPM-PU 15090) L dp4-m2 (reversed); eStichomys sp. Rdp4-m3
from Kramarz (2001); fProstichomys bowni (MACN SC 3856) Ldp4-
m2 (reversed) from Kramarz (2001). Anterior is to the right in all
illustrations. Scale bar equals 2 mm
J Mammal Evol (2011) 18:245–268 259

Genus Prolagostomus Ameghino, 1887
Type species:Prolagostomus pusillus, Ameghino, 1887.
Included species:Thetype;Prolagostomus divisus
Ameghino, 1887;Prolagostomus profluens Ameghino,
1887;Prolagostomus imperialis Ameghino, 1887;Prola-
gostomus amplus Ameghino, 1889;Prolagostomus obliqui-
dens Scott, 1905;Prolagostomus rosendoi Vucetich, 1984.
Age and distribution: See Discussion.
Diagnostic characters:Prolagostomus resembles Pliola-
gostomus Ameghino, 1887, in having bilobed cheek teeth
with oblique laminae. However, Pliolagostomus possesses
molar laminae with relatively straight anterior and posterior
margins, whereas those of Prolagostomus are more rounded
(Vucetich 1984). Also, the M3 of Pliolagostomus has a
smaller, more triangular third prism that is more lingually
oriented than that of Prolagostomus.
Discussion: Prolagostomus is widespread throughout
middle and high latitude faunas from at least the late early
Miocene to the early late Miocene. The earliest occurrence
of the genus is in the Pinturas Formation of southern
Argentina (Santacrucian SALMA, though older than the
Santa Cruz Formation; Kramarz 2002). The latest occur-
rence is the Arroyo Chasicó Formation of east-central
Argentina (Chasicoan SALMA; Bondesio et al. 1980a).
The range of Prolagostomus extends as far north as Bolivia
(Nazareno, Quebrada Honda, possibly Cerdas; Marshall
and Sempere 1991; Oiso 1991; Croft 2007; Croft et al.
2009; present study) and as far west as south-central Chile
(Flynn et al. 2008) though it apparently is absent from the
late early Miocene of northern Chile (Flynn et al. 2002a;
Croft et al. 2007). Most of these reports do not include
species level identifications, and no study has assessed
whether early Miocene and late Miocene species referred to
Prolagostomus actually pertain to the same genus. The
temporal and geographic distribution of the genus therefore
should be considered provisional.
Prolagostomus sp.
Fig. 12
Referred specimens: UATF-V-000887, UATF-V-000888,
UATF-V-000898, UATF-V-000901, UATF-V-000902, UATF-
V-000903, UATF-V-000904, UATF-V-000905, UATF-V-
000906, UATF-V-000907, UATF-V-000908, UATF-V-
000910, UATF-V-000915, UATF-V-000927, UATF-V-
000929a, UATF-V-000929b, UATF-V-000929c, UATF-V-
000929d, UATF-V-000929e, UATF-V-000929f, UATF-V-
000933, UATF-V-000937, UATF-V-000938, UATF-V-
000939, UATF-V-000941, UATF-V-000942, UATF-V-
000943, UATF-V-000946, UATF-V-000947, UATF-V-
000948, UATF-V-000949, UATF-V-000954, UATF-V-
000955, UATF-V-000957, UATF-V-000963, UATF-V-
000965, UATF-V-000970, UATF-V-000972, UATF-V-
000977, UATF-V-000984, UATF-V-000985, UATF-V-
001004, UATF-V-001005, UATF-V-001009, UATF-V-
001021, UATF-V-001024, UATF-V-001025, UATF-V-
001026, UATF-V-001031, UATF-V-001032, UATF-V-
Fig. 12 Representative specimens of Prolagostomus sp. in occlusal
view aUATF-V-000887, rostrum; bUATF-V-001025, LP4-M3
(reversed); cUATF-V-000933, Rp4-m3; dUATF-V-000929d, Lp4-
m3; eUATF-V-001029, Rp4-m3. Anterior is to the right in all photos.
Scale bar equals 5 mm (a) or 2 mm (b–e)
260 J Mammal Evol (2011) 18:245–268

001034, UATF-V-001037, UATF-V-001040, UATF-V-
001041, UATF-V-001046, UATF-V-001050, UF 26912, UF
26916, UF 26917, UF 26919, UF 26920, UF 26924, UF
26927, UF 26932, UF 26935, UF 26940, UF 26942, UF
26943, UF 26944, UF 27897, UF 66001, UF 66002, UF
236855, UF 236856, UF 236857, UF 236861.
Provisionally referred specimens: UF 26682, UF 26683,
UF 26684, UF 26685, UF 26686, UF 26687, UF 26688,
UF 26689, UF 26690, UF 26691, UF 26692, UF 26693,
UF 26694, UF 26700, UF 26701, UF 26702, UF 26703,
UF 26704, UF 26705, UF 26706, UF 26707, UF 26708,
UF 26709, UF 26710, UF 26711 (see below).
Localities: Units 2–4 of Quebrada Honda Local Fauna as
well as unspecified lower levels; Río Rosario Local Fauna,
levels equivalent to Units 2 and 4 of Quebrada Honda
(MacFadden and Wolff 1981).
Discussion: The great quantity of lagostomine material
from Quebrada Honda shows much metric and morpholog-
ic variation. In the absence of studies of dental variation in
modern lagostomine populations (or fossil ones, for that
matter), it is not possible at this time to confidently
distinguish among ontogenetic, intraspecific, and interspe-
cific variation. Moreover, the species of Prolagostomus
have not been revised in more than a century. We therefore
do not attempt to provide specific identifications at this
time. Representative photos are presented in Fig. 12. The
material to which we have access is currently under study
by a CWRU graduate student whose thesis will integrate a
study of modern lagostomine dental variation with descrip-
tion of Quebrada Honda lagostomines.
Frailey (1981) referred 25 Quebrada Honda chinchillid
specimens from UF collections to the Santacrucian species
P.divisus,P.imperialis, and P.profluens. Illustrations and
measurements of these specimens (Frailey 1981:47–61)
suggest that these specimens do not differ significantly
from those currently under study by our research group.
Community Structure and Paleoecology
The Quebrada Honda rodent community is dominated by
lagostomine chinchillids (Prolagostomus sp.), which consti-
tute more than two-thirds (69.9%) of identified rodent
specimens (Fig. 13). Caviids (Guiomys unica) and incertae
sedis octodontoids (Acarechimys sp. nov.?) are the next most
abundant rodents (13.7% and 12.3%, respectively). Dasy-
proctids and adelphomyine echimyids are uncommon,
represented by only two specimens each. The same may be
true for cephalomyids, but we have been unable to verify the
presence of this group at Quebrada Honda in our recent
collections or through study of available UF specimens. The
possible occurrence of cephalomyids at Quebrada Honda is
based on the referral of two specimens (UF 26715 and UF
26716) to Cephalomys by Frailey (1981). The illustrations in
Frailey (1981) suggest that these specimens represent a
species distinct from those described here. If referral of
these specimens to Cephalomyidae is accurate, it extends
the temporal range of the family by more than 5 Ma.
Celphalomyids otherwise are unknown in faunas younger
than Colhuehuapian in age (upper boundary ca. 19 Ma;
Flynn and Swisher 1995;Kramarz2005;Réetal.2010).
Chinchillids are the most abundant rodents in both
local faunas of Quebrada Honda, though they comprise a
slightly smaller percentage of specimens in the Río
Rosario Local Fauna (RRLF; 62.5%) than in the
Quebrada Honda Local Fauna (QHLF; 72.6%). Caviids
are the next most abundant group in the RRLF,
accounting for nearly one third of rodent specimens
(30.0%), and octodontoids account for the remainder
(<8%). None of the rarer species have yet been collected
at Río Rosario. In the QHLF, the second and third most
abundant groups of rodents are reversed; octodontoids
account for just over 14% of specimens whereas caviids
account for <8% of specimens. The conspicuous differ-
ence in relative abundances of octodontoids and caviids
in the two local faunas probably is related to differences
in habitat and/or mode of accumulation at the two sites.
The rodents collected from the two sites do not differ in
any manner that would suggest that they represent
temporally distinct populations. All of the rarer species
come from the QHLF. This is not surprising given that
the QHLF accounts for nearly three times as many
rodent specimens as the RRLF, and therefore would be
more likely to sample rare species.
The abundances, taxonomic affinities, and presumed
dietary adaptations of the rodents of Quebrada Honda
indicate that a mixed vegetational structure likely was
present in the area in the middle Miocene, probably with a
greater proportion of open areas than forested ones. Modern
chinchillids are colonial and occur in the Andean highlands
Caviidae
Echimyidae
Chinchillidae
“Cephalomyidae”
Dasyproctidae
Octodontoidea i.c.
Fig. 13 Number of Identifiable Specimens (NISP) of rodents at
Quebrada Honda, coded by family. Data are from UATF and UF
specimens studied firsthand (N=112) as well as others noted in this
study (N=34)
J Mammal Evol (2011) 18:245–268 261

of Peru, Bolivia, and Chile (Chinchilla,Lagidium) as well
as the lowlands of Argentina, Bolivia, Paraguay, and
Uruguay (Lagostomus). They prefer open, arid habitats of
various types and are primarily folivorous (Redford and
Eisenberg 1992;Jacksonetal.1996). The abundant
chinchillids at Quebrada Honda suggest a colonial lifestyle
also characterized extinct species and implies that signifi-
cant open areas were present.
Modern caviids (excluding hydrochoerines) occupy a
wide variety of habitats. Some live in open and/or arid
habitats whereas others prefer more forested or riparian
areas (Redford and Eisenberg 1992; Eisenberg and
Redford 1999). They generally do not occur in areas of
tropical rainforest (Mares and Ojeda 1982), and their
presence at Quebrada Honda argues against a heavily
forested habitat. Modern dasyproctids, in contrast, are
frugivores characteristic of tropical forests (Emmons and
Feer 1997). Their presence at Quebrada Honda implies at
least some forested areas were present. The cheek teeth
of Mesoprocta are much higher crowned than those of
modern dasyproctids, however (HI ≥3.6 in Mesoprocta
vs. < 1.6 for modern dasyproctids; Williams and Kay
2001). This suggests that Mesoprocta may have had a
more abrasive diet than modern forms and perhaps
preferred more open habitats. The relative rarity of
dasyproctids at Quebrada Honda could reflect a relatively
small proportion of forested habitat and/or lower popu-
lation densities due to a non-social lifestyle.
Echimyids mostly inhabit rainforest habitats, and many
species are arboreal or semi-arboreal (Emmons and Feer
1997). The crown group therefore is a reliable indicator of
tropical forests. Adelphomyines are an extinct subgroup of
echimyids, and their relationships to extant echimyids are
unclear (Kramarz 2001). They tend to be more hypsodont
that most extant species and may represent a distinct
radiation (Kramarz and Bellosi 2005). Quebradahondomys
therefore probably is not a reliable habitat indicator.
Similarly, the closest extant relatives of Acarechimys are
unknown. Affinities with octodontids have been proposed
(Verzi 2002), and this might suggest that Acarechimys
occupied open habitats. Nevertheless, the brachydont cheek
teeth of Acarechimys contrast markedly with the hypsodont
ones of early octodontids such as Chasichimys, indicating
that Acarechimys may have been dissimilar ecologically. Its
broad geographic and temporal range in the fossil record
(see below) implies that it may have had broad habitat
tolerances.
Faunal Comparisons and Biogeography
The most apparent characteristic of the rodent fauna of
Quebrada Honda is the preponderance of chinchillids.
Modern chinchillids have been described as “by and large…
a temperate zone family that has colonized both montane and
lowland habitats”(Redford and Eisenberg 1992:348). As
illustrated by Quebrada Honda and other fossil localities, this
does not accurately describe the past distribution of the
group. Chinchillids have been present in central Chile since
the early Oligocene (Flynn et al. 2003; Croft et al. 2008)and
in the southern Neotropics and lowland Argentina since at
least the late Oligocene (Vucetich 1989). Most of the uplift
of the Andes post-dated the Oligocene and early Miocene
(Gregory-Wodzicki 2000; Bershaw et al. 2010), indicating
that chinchillids ancestrally occupied lowland areas in both
temperate and tropical latitudes. It is thus plausible that the
common ancestor of chinchillids originally occupied low-
land habitats, perhaps even in the tropics, only later
expanding to higher elevations and latitudes. Chinchillines
may have originated in a more montane habitat (Flynn et al.
2002a), but their fossil record is extremely sparse and nearly
all fossil occurrences for the family, including those at
Quebrada Honda, pertain to species more closely related to
modern Lagostomus.
Regardless of the precise area of origin of chinchillids,
they apparently have been restricted to the southern
Neotropics and more southerly latitudes for most of their
history. We are unaware of any Tertiary records of the
family north of central Bolivia (i.e., about 16° S, roughly
the latitude of Lake Titicaca). Chinchillids are nearly
ubiquitous in Miocene fossil localities south of this point,
though the fossil record is mainly limited to areas outside of
present-day tropical lowlands. Exceptions to the wide-
spread occurrence of chinchillids include a handful of
rather poorly characterized Mayoan SALMA faunas of
western Argentina from which chinchillids have not yet been
reported. These include localities in the Río Mayo Formation
(Cerro Guenguel and Arroyo Pedregoso), Laguna Blanca,
Río Fénix, and Río Huemules (Kraglievich 1930b;
Bondesio et al. 1980b). Interestingly, dinomyids are
present in all of these faunas and are absent from at least
some other middle Miocene faunas in which chinchillids
are present (e.g., Collón Curá, Río Senguerr). Dinomyids
have not yet been reported from any Miocene locality in
Bolivia or northern Chile, though they commonly occur in
lower latitude faunas of Peru (Antoine et al. 2007),
Ecuador (Madden et al. 1994), and Colombia (Fields
1957;Walton1997).
The middle Miocene fauna of La Venta, Colombia is the
only well-characterized fauna in South America that is at least
partially equivalent in age to Quebrada Honda (Madden et al.
1997;Croft2007). A preliminary comparison by Croft
(2007) of the fauna of Quebrada Honda with that of La Venta
and two faunas from Argentina (Collón Curá, which is
slightly older, and Arroyo Chasicó, which is slightly
younger) indicated that Quebrada Honda was most similar
262 J Mammal Evol (2011) 18:245–268

to Collón Curá. The two faunas had at least 23% of genera in
common. A minimum of 11.5% of genera were shared with
La Venta, despite its more similar age. This pattern indicates
that a more significant biogeographic barrier existed north of
Bolivia and Chile than south of the region. However, this
study relied on provisional rodent identifications for Que-
brada Honda as recorded in UF collections. The present
study has clarified the identities of Quebrada Honda rodents
(Table 1), thus permitting a more accurate analysis of faunal
resemblance among the rodents. These comparisons indicate
that the rodents exhibit a pattern similar to that of the
fauna as a whole. One-third (33%) of Quebrada Honda
rodent genera are shared with Collón Curá (Acarechimys
and Prolagostomus) whereas only 1/6 (17%) of genera
(Acarechimys) are shared with La Venta.
Several other faunas are potentially contemporaneous
with Quebrada Honda but have not yet been analyzed in
detail: El Petiso (Chubut, Argentina), Fitzcarrald (eastern
Peru), and the Girón Basin (Ecuador). Quebrada Honda
shares only one genus (Guiomys) with El Petiso, but only
two genera have been identified thus far (Pérez 2010;
Pérez and Vucetich 2011). A full analysis of resemblance
must await description of the remaining rodents, which
include representatives of Dasyproctidae, Chinchillidae
(Lagostominae), Echimyidae, Acaremyidae, and Octodon-
tidae (Villafañe et al. 2008). No genera are shared between
Quebrada Honda and Fitzcarrald (Antoine et al. 2007)nor
the Girón Basin (Madden et al. 1994), at least based on the
present state of knowledge.
Several early to middle Miocene faunas from northern
Chile and Bolivia are close to Quebrada Honda both
geographically and temporally (Fig. 1). The rodents of the
late early Miocene fauna of Chucal, Chile have not yet been
described, but preliminary studies indicate that at least one
new species of chinchilline chinchillid accounts for the vast
majority of recovered specimens (Flynn et al. 2002a;Croftet
al. 2004,2007). Other rodents include the dasyproctid
Neoreomys, the octodontoid Acarechimys, and possibly
another octodontoid (Croft et al. 2007). Chucal thus
generally parallels Quebrada Honda in ecological diversity;
most specimens pertain to medium-sized hypselodont spe-
cies, and a few pertain to small and brachydont or large and
very hypsodont species. Acarechimys is the only genus
potentially shared between the two faunas. The late early to
early middle Miocene fauna of Cerdas, Bolivia includes a
single rodent, an indeterminate lagostomine chinchillid
(Croft et al. 2009). The locality of Nazareno, Bolivia is
temporally unconstrained but may be of middle Miocene
age. Two rodents have been identified, Prolagostomus sp.
and Octodontidae gen. et sp. indet. (Oiso 1991). The former
is present at Quebrada Honda. The latter is larger than
Acarechimys, based on the measurements provided, but is
close in size to Quebradahondomys. Unfortunately, the
occlusal morphology is unclear in the published photo-
graphs, and we have been unable to study the specimens
firsthand.
Conclusions
The locality of Quebrada Honda has been known for more
than three decades (Hoffstetter 1977). A few taxonomic
studies were published not long thereafter (Frailey 1987,
1988), but it is only within the past decade or so that most
specimens and species have received detailed attention in the
scientific literature (e.g., Sánchez-Villagra et al. 2000;Goin
et al. 2003;CroftandAnaya2006; Forasiepi et al. 2006;
Croft 2007). Rodents have been conspicuously absent from
any of these treatments, though they were described early on
in an unpublished dissertation thesis (Frailey 1981). Our
identifications of the rodents of Quebrada Honda differ
substantially from those of Frailey (1981)(Table1). More-
over, we see no strong resemblance between the rodents of
Quebrada Honda and those of the early Miocene fauna of
Santa Cruz, Argentina, as advocated by Frailey (1981).
Instead, we observe much greater resemblance with faunas
that are closer in space (northern Chile, Bolivia) and/or
time (middle Miocene, Colloncuran and Laventan SAL-
MAs). We also find that some species are unique to
Quebrada Honda. Few Tertiary intervals in South America
Family Frailey (1981) Present Study
Dasyproctidae Neoreomys pachyrhynchus? Mesoprocta hypsodus, gen. et sp. nov.
Cephalomyidae Cephalomys, sp. nov. (unavailable for study)
Eocardiidae/Caviidae Eocardia cf. montana Guiomys unica
Schistomys, sp. nov.
Octodontidae (?) Acaremyinae indet. Acarechimys, sp. nov.?
Echimyidae Spaniomys?, sp. nov. Quebradahondomys potosiensis, gen. et sp. nov.
Chinchillidae Prolagostomus imperialis Prolagostomus sp.
Prolagostomus profluens
Prolagostomus divisus
Table 1 Rodents of Quebrada
Honda as identified by
Frailey (1981) and the present
study
J Mammal Evol (2011) 18:245–268 263

are represented by contemporaneous faunas at low,
intermediate, and high latitudes. The late middle Miocene
appears to be one such interval. Further study of Quebrada
Honda, La Venta, and El Petiso therefore will provide a
rare opportunity to assess latitudinal provinciality within
South America and to better understand the major factors
that resulted in the biogeographic patterns seen in South
American mammals today.
Acknowledgements We thank N. Czaplewski, A. Kramarz, M.
Pérez, S. Simpson, and J. Wertheim for very helpful discussions; M.
Jin (AMHN), A. Kramarz (MACN), S. McLaren and J.R. Wible
(Carnegie Museum), and D. Rubliar (Museo Nacional de Historia
Natural, Santiago, Chile) for access to specimens in their care; D.
Brinkman (YPM-PU), and R. Hulbert and B. MacFadden (UF), and
M. Jin (AMNH) for loans of specimens; D. Auerbach, R. Chavez, J.
Conrad, P. Higgins, C. Garzione, and J. Smith for assistance in the
field; J.R. Wible and anonymous reviewers for critical reviews of the
content of this paper; and D. Chapman, M. Ryan, A. Shinya, and L.
Yerian for assistance with fossil preparation and specimen curation. A
preliminary version of this research was submitted for J. Chick’s M.S.
thesis. Funding for this research was provided by the National
Geographic Society Committee for Research and Exploration (NGS
8115–06 to D. Croft) and the National Science Foundation (EAR
0958733 to D. Croft, EAR 0635678 to C. Garzione and T. Jordan).
Appendix 1
Dental measurements (in mm) for Guiomys unica
(Caviidae) from Quebrada Honda. Abbreviations: AP,
anteroposterior length; LF, local fauna; ML, mediolateral
width; QH, Quebrada Honda Local Fauna; RR,Río
Rosario Local Fauna; TTL, total toothrow length (only
included for specimens preserving three or four cheek
teeth). Measurements in parentheses are estimates.
P4 M1 M2 M3
Specimen LF Element Side TTL AP ML AP ML AP ML AP ML
UATF-V-000962 RR Palate R –3.3 2.8 3.3 3.3
UATF-V-000962 QH Palate L –3.5 3.3
UATF-V-000981 RR Maxilla R –3.1 3.0
UATF-V-001038 QH Palate R 15.8 3.3 3.3 3.4 3.0 3.5 2.8 4.5 3.2
UATF-V-001038 RR Palate L (16.1) (3.2) (2.9) 3.5 3.1 3.3 3.1 5.0 2.7
UF 236852 RR Cranium R 13.6 ––3.6 3.3 3.6 3.2 4.9 3.2
UF 236852 RR Cranium L 13.9 ––3.9 3.3 –3.3 5.1 3.1
UF 236853 RR Cranium R (16.0) 4.3 3.5 3.5 3.4 3.7 (3.0) ––
UF 236853 RR Cranium L 15.9 4.2 3.0 3.8 3.3 3.7 3.3 4.0 3.0
UF 236859 RR Rostrum R –3.1 –3.3 3.3
UF 236859 RR Rostrum L –3.3 2.8 3.1 3.0
UF 236860 RR Palate R (15.3) 3.5 3.1 3.1 3.5 3.4 3.3 –(3.5)
UF 236860 RR Palate L (15.5) –– 3.5 3.3 (4.5) (3.6)
p4 m1 m2 m3
Specimen LF Element Side TTL AP ML AP ML AP ML AP ML
UATF-V-000971 RR Dentary R 16.1 3.1 2.4 3.5 3.2 4.3 3.2 4.9 2.9
UATF-V-000973 RR Dentary R 13.3 (2.0) 2.4 3.4 2.7 3.5 3.0 4.3 2.8
UATF-V-001008 RR Dentary R 11.6 3.0 2.8 3.4 2.8 3.9 3.0
UATF-V-001017 RR Dentary L 10.9 3.0 2.5 3.5 3.3 4.1 3.2
UF 26914 QH Dentary L 10.1 3.0 2.2 3.4 3.0 3.7 2.8
UF 66003 RR? Dentary R 12.0 3.4 2.9 4.0 3.3 4.0 3.4
UF 236854 RR Mandible R 18.0 3.6 2.7 4.2 3.2 4.7 3.2 4.9 3.2
UF 236854 RR Mandible L 17.5 3.6 2.8 4.3 3.2 4.6 3.5 (5.0) 3.3
UF 236858 RR Dentary R 9.2 2.3 2.1 3.2 2.9 3.5 2.7
264 J Mammal Evol (2011) 18:245–268

Appendix 2
Dental measurements (in mm) for Acarechimys, sp. nov.?
(Octodontoidea) from Quebrada Honda. Abbreviations: AP,
anteroposterior length; ETL, estimated toothrow length
(based on UATF-V-000935); LF, local fauna; ML, medio-
lateral width; QH, Quebrada Honda Local Fauna; RR, Río
Rosario Local Fauna; TTL, total toothrow length. ETL and
TTL are only provided for specimens preserving at least
three cheek teeth.
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