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A PLIOCENE RECORD OF
ANTILOCAPRIDAE) IN MÉXICO
Author(s): E. JIMÉNEZ-HIDALGO, O. CARRANZA-CASTAÑEDA, M. MONTELLANO-
Source: Journal of Paleontology, 78(6):1179-1186. 2004.
Published By: The Paleontological Society
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J. Paleont., 78(6), 2004, pp. 1179–1186
Copyright q 2004, The Paleontological Society
A PLIOCENE RECORD OF CAPROMERYX (MAMMALIA: ANTILOCAPRIDAE)
Universidad del Mar, Campus Puerto Escondido, Km 3.5 Carretera Puerto Escondido-Oaxaca, Puerto Escondido, 71980 Oaxaca, Me´xico;
Centro de Geociencias, UNAM, Juriquilla, Quere´taro 76230, Me´xico; and
Instituto de Geologı´a, Universidad Nacional Auto´noma de Me´xico,
Ciudad Universitaria, Coyoaca´n 04510, D. F. Me´xico
—The Antilocapridae was a diverse artiodactyl family present in some late Tertiary faunas of North America. In Me´xico, its
Tertiary fossil record is poorly known. The antilocaprid material described in this paper was collected from the early Blancan ﬂuvial
deposits of the San Miguel de Allende Area, state of Guanajuato, Me´xico. It includes isolated upper and lower premolars and molars,
dental series, and some rami fragments. The material is assigned to Capromeryx tauntonensis. The presence of this species in the early
Pliocene of central Me´xico represents the oldest record in North America and extends its known geographic distribution from the
northwestern United States to central Me´xico.
is a North American endemic family of
ruminant artiodactyls that appeared in the fossil record in the
early Hemingfordian (early Miocene); it showed its greatest di-
versity during the middle and late Miocene, and its diversity de-
clined during the Pliocene (Blancan) and Pleistocene (Janis and
Manning, 1998). The only surviving species of the family is An-
tilocapra americana (Ord, 1815), the pronghorn antelope, which
lives in western North America. The group includes two subfam-
ilies, the paraphyletic ‘‘Merycodontinae,’’ which has a biochron-
ologic range from early Hemingfordian (early Miocene) to late
Clarendonian (late Miocene), and the Antilocaprinae, whose re-
cord extends from late Barstovian (middle Miocene) to Recent
(Janis and Manning, 1998).
In Me´xico, the fossil record of Antilocapridae spans from the
middle Miocene to the late Pleistocene. Known Mexican records
include the merycodont Merycodus Leidy, 1854 from the Barsto-
vian of Oaxaca, southeastern Me´xico (Jime´nez et al., 1999;
Jime´nez-Hidalgo, 2000); Hexobelomeryx Furlong, 1941, from the
Hemphillian of Chihuahua, Jalisco, Guanajuato, and Hidalgo
(Furlong, 1941; Carranza-Castan˜eda and Ferrusquı´a-Villafranca,
1978; Lindsay, 1984; Carranza-Castan˜eda, 1989, 1994; Miller and
Carranza-Castan˜eda, 1998, 2001; Castillo-Cero´n, 2000) and the
Blancan of Guanajuato (Carranza-Castan˜eda and Miller, 2000);
Capromeryx Matthew, 1902, from the Rancholabrean of Aguas-
calientes, Hidalgo, Estado de Me´xico, and Puebla (Furlong, 1925;
Mooser, 1958; Mooser and Dalquest, 1975; Miller and Carranza-
Castan˜eda, 1984; Cabral-Perdomo, 2000); Stockoceros Frick,
1937, from the Irvingtonian of Sonora and the Rancholabrean of
Nuevo Leo´n, Zacatecas, and Aguascalientes (Mooser and Da-
lquest, 1975; Lindsay, 1984; Arroyo-Cabrales and Johnson, 1998;
Guzma´n and Polaco, 2000); and Tetrameryx Lull, 1921, from the
Rancholabrean of Aguascalientes, Jalisco, and Puebla (Downs,
1958; Mooser, 1958; Dalquest, 1974; Mooser and Dalquest, 1975;
Miller and Carranza-Castan˜eda, 1984).
The small-sized pronghorn Capromeryx is represented in the
United States by four species: C. tauntonensis Morgan and Mor-
gan, 1995 from the early Blancan of Washington; C. arizonensis
Skinner, 1942 from the early Blancan of Nebraska, late Blancan
of Arizona, Florida, and Nebraska, as well as from several early
Irvingtonian localities; C. furcifer Matthew, 1902 from diverse
late Irvingtonian and early Rancholabrean localities; and C. minor
Taylor, 1911, collected in numerous Rancholabrean localities
(Skinner, 1942; Webb, 1974; Kurten and Anderson, 1980; Morgan
and Morgan, 1995; Janis and Manning, 1998). In Me´xico the only
recognized species, C. mexicanus Furlong, 1925, has been recov-
ered from sediments of late Pleistocene age in central and south-
As a result of the paleontological work carried out in the late
Tertiary continental sediments of central Me´xico, especially in the
San Miguel de Allende Graben, a large collection of mammals
has been acquired. Its importance is based on the strict strati-
graphic control exercised during the collecting.
Recent examination of the artiodactyl material from the San
Miguel de Allende Area revealed the presence of an unidentiﬁed
antilocaprid. Detailed study of this antilocaprid material supports
its referral to the genus Capromeryx. The purpose of this paper
is to describe the referred Capromeryx fossil material recovered
from several Blancan localities of the subject area.
Location.The San Miguel de Allende Area is located in the
northeastern part of the state of Guanajuato, central Me´xico, with-
in the northern limit of the Transmexican Volcanic Belt. The land-
scape of the study area is characterized by low hills and ﬂat lands
within the San Miguel de Allende Graben. The main access to
the area is by Highway 51, the road that connects the cities of
San Miguel de Allende and Dolores Hidalgo (Fig. 1).
Lithostratigraphy.Fluvial sediments of late Miocene to late
Pliocene age, informally named Rancho Viejo beds by Carranza-
Castan˜eda et al. (1994), bear an important mammalian fauna. The
Capromeryx material comes from yellow brown sandy and silty
clays with some lenses of volcanic ash and sand, which has been
interpreted as ﬂoodplain deposits (Fig. 2). The ash deposits were
dated by ﬁssion-track and
Ar, yielding ages of 3.60 and
3.36 Ma (Kowallis et al., 1986, 1998).
Biostratigraphy.Analysis of the mammalian fossil material
collected from the Rancho Viejo beds has allowed paleontologists
to deﬁne the presence of two superposed faunal associations that
represent two North American Land Mammal Ages: Hemphillian
(late Miocene) and Blancan (Pliocene). The fossil indexes that
characterize each mammal age were described in previous papers
(Miller and Carranza-Castan˜eda, 1984, 1998; Carranza-Castan˜e-
da, 1989; Carranza-Castan˜eda and Walton, 1992; Carranza-Cas-
tan˜eda and Miller, 1998, 2000).
The Rancho Viejo beds apparently represent the most contin-
uous sequence across the Hemphillian–Blancan boundary of any
area known in North America (Carranza-Castan˜eda et al., 1994;
Carranza-Castan˜eda and Miller, 1996).
Associated fauna.The mammalian taxa collected from the
same sediments where the Capromeryx specimens from Guana-
juato were recovered are: Glossotherium (P.) sp., Glyptotherium
1180 JOURNAL OF PALEONTOLOGY, V. 78, NO. 6, 2004
1—Index map showing the location of the San Miguel de Allende
Area and the localities from where the Capromeryx Matthew, 1902
material was recovered.
sp., Hypolagus mexicanus Miller and Carranza-Castan˜eda, 1982,
Paranotolagus complicatus Miller and Carranza-Castan˜eda, 1982,
Neochoerus sp., Spermophilus sp., Paenemarmota sp., Boropha-
gus diversidens Cope, 1892a, Trigonictis? sp., Felis cf. F. studeri
Savage, 1960, Platygonus cf. P. alemani Duge´s, 1887, Hemiauch-
enia blancoensis (Meade, 1945), Hexobelomeryx fricki Furlong,
1941, Equus (Dolichohippus) simplicidens Cope, 1892b, Nanni-
pus peninsulatus (Cope, 1885), and Rhynchotherium sp. (Miller
and Carranza-Castan˜eda, 1982, 1998, 2001; Carranza-Castan˜eda
and Miller, 1996, 1998, 2000; Jime´nez-Hidalgo and Carranza-
Castan˜eda, 2002). The ash dating (3.6–3.3 Ma) provides evidence
for assigning the age of the fauna to the early Blancan according
to Lundelius et al. (1987) and Janis and Manning (1998), or to
the middle Blancan (Blancan III) of Repenning (1987).
MATERIALS AND METHODS
The fossil material described in this paper was recovered from
localities Gto-4, Gto-6, Gto-18, and Gto-45, which are 12–15 km
north of the city of San Miguel de Allende (Fig. 1). It consists of
isolated upper and lower premolars and molars as well as upper
and lower dental series with good preservation. Most of the spec-
imens come from locality Gto-6. They were collected through
The preparation of the fossils was done at Instituto de Geologı´a
(IGM), Universidad Nacional Auto´noma de Me´xico (UNAM),
Me´xico City, using standard techniques. This institution is also
the repository of all the collected specimens under the IGM.
Comparisons of specimens were made with those at Instituto
de Geologı´a, Universidad Nacional Auto´noma de Me´xico (IGM),
Universidad Auto´noma del Estado de Hidalgo (UAHMP), Florida
Museum of Natural History at the University of Florida (UF),
with descriptions and illustrations of specimens housed at the Mu-
seum of Paleontology, University of California (UCMP); the
American Museum of Natural History (AMNH); the Frick Col-
lection, American Museum of Natural History (F:AM) and the
University of Kansas (KU); and calibrated photographs of fossil
specimens are housed at the Burke Museum, University of Wash-
The dental nomenclature used is that described in Gentry and
Hooker (1988); measurements of upper and lower dentition were
taken with a caliper as maximum lengths and widths at the oc-
clusal level (Janis, 1990; Morgan and Morgan, 1995) and are
expressed in millimeters (mm). Additional abbreviations used in
the text are: P, upper premolar; p, lower premolar; M, upper mo-
lar; m, lower molar; Gto, Guanajuato; USA, United States of
America; Ka, thousand years; Ma, million years.
Morgan and Morgan, 1995
Diagnosis.Large species of Capromeryx; differs from other
species of the genus in that horn core base is larger, unconstricted,
and centered over orbit; the horn cores are signiﬁcantly larger;
the p4 has a deep posterolingual inﬂection and the M3 has not
developed a posterior heel (Morgan and Morgan, 1995).
Material examined.From locality Gto-4: IGM 8385, jaw
fragment with p2–m3. From locality Gto-6: IGM 8379, right P4
and M1; IGM 8380, right M1; IGM 8381, right M2; IGM 8382,
right M2; IGM 8383, right M3; IGM 8384, right M3; IGM 8386,
right ramus fragment with p4–m2; IGM 8388, left p4; IGM 8391,
left m3; and IGM 8392, right m3. From locality Gto-18: IGM
8389, left p4; IGM 8390, left p4. From locality Gto-45: IGM
8377, right P3 and P4; IGM 8378, right M1; IGM 8387, right
and left dental series with p3–m3 of a single individual (together
with IGM 8377 and IGM 8378).
Occurrence.Taunton local fauna, early Blancan (Lundelius et
al., 1987; Janis and Manning, 1998), or middle Blancan (Blancan
IV) (Repenning, 1987) of southeastern Washington, USA (Mor-
gan and Morgan, 1995), and San Miguel de Allende Area, early
Blancan (Lundelius et al., 1987; Janis and Manning, 1998) or
middle Blancan (Blancan III) (Repenning, 1987) of Guanajuato
State, central Me´xico.
Upper dentition.The P3 has a half-moon outline, its parastyle
is moderately developed and the metastyle is very strongly de-
veloped; between the two styles there is a prominent rib all along
the crown height. The P4 has also a half-moon outline, its par-
astyle is moderately developed but disappears in an advanced
wear stage; the metastyle is moderately developed and increases
its anteroposterior length as the premolar wears. Between the two
styles there is a well-developed rib present all along the crown
height (Fig. 3).
The M1 has three roots. The lingual root is anteroposteriorly
elongated and the anterolabial and posterolabial ones are almost
NEZ-HIDALGO ET AL.—PLIOCENE CAPROMERYX FROM MEXICO
2—Generalized stratigraphic section of the late Hemphillian–
Blancan sediments of the Rancho Viejo beds, San Miguel de Allende,
Guanajuato, Me´xico. Modiﬁed from Carranza-Castan˜eda and Miller,
3—Upper dentition of Capromeryx tauntonensis Morgan and
Morgan, 1995 from Guanajuato. IGM 8377, right P3–P4 and IGM
8378, right M1, 1, occlusal view, 2, labial view. IGM 8379, right P4–
M1, 3, occlusal view, 4, labial view. Bar scale 5 10 mm.
4—Upper molars of Capromeryx tauntonensis from Guanajuato.
IGM 8381, right M2, 1, occlusal view, 2, labial view. IGM 8383, right
M3, 3, occlusal view, 4, labial view. IGM 8384, right M3, 5, occlusal
view, 6, labial view. Bar scales 5 10 mm, with upper right scale for
occlusal views and lower left scale for labial views.
cylindrical; the molar has a poorly developed parastyle and a
moderately developed mesostyle (Fig. 3). The labial border of the
anterior lobe is V-shaped and the posterior lobe is U-shaped. The
M2 has also three roots, and the parastyle, mesostyle, and the
anterior rib are prominent, while the metastyle is moderately de-
veloped; the styles and rib reduce their development toward the
base of the tooth (Fig. 4). The M3 has prominent styles and the
anterior rib is moderately developed. In an advanced wear stage
the parastyle is poorly developed, the anterior rib is moderately
developed, and the metastyle increases its anteroposterior length
but does not form a heel or third lobe (Fig. 4).
Lower dentition.The p2 is compressed transversely, with a
wide and moderately deep anterolingual fold that delimits a nar-
row paraconid slightly oriented lingually. The p3 has a deep and
wide anterolingual fold all along the crown height. Posterolin-
gually there is a deep narrow fold, which disappears in the ad-
vanced wear stage, leaving a narrow paraconid and a broad pos-
terior cuspid that occupies two-thirds of the premolar length (Fig.
5). The p4 has a triangular outline; it has a deep anterolingual
fold present all along the crown height. The paraconid, bracketed
by the anterolingual fold, has in its lingual side a small stylid in
a poorly (in IGM 8389 it measures 3.4 mm) or moderately worn
tooth (in the p4 of IGM 8386 it measures 2.5 mm); it disappears
with wear. In the posterolingual side of the premolar there is a
deep fold (Figs. 5, 6). In some moderately worn premolars this
fold tends to close or is completely closed by the fusion of the
metaconid and the entoconid, forming a deep circular-shaped fos-
settid (Figs. 5, 6). Only in the slightly worn premolar IGM 8389
is the posterolingual fold shallow and the fossettid deep. On the
posterolabial side of the premolar there is a moderately deep or
shallow fold present all along the crown height. In the posterior
part of the occlusal surface there is a re-entrant that forms a shal-
low depression that ﬁnally disappears as the wear of this region
The m1 has two roots and a poorly developed entostylid. The
m2 also has two roots and a moderately or slightly developed
parastylid and entostylid (Fig. 5). The m3 is a three-lobed tooth
with a poorly or moderately developed parastylid; it has three
roots, from which the middle and posterior are fused. On the
posterior margin of the third lobe there is a slightly developed
ridge or stylid that does not form any talonid (Figs. 5, 6). In
specimen IGM 8392, which is a moderately worn m3, there is a
little basal expansion of this stylid, but it does not form a talonid.
Measurements of upper and lower dentition are given in Table 1.
Mandible.A lower jaw and a ramus fragment are present in
the sample. IGM 8386 is a very damaged and fragmented right
ramus with p4–m2; a small fragment of diastema is seen in the
1182 JOURNAL OF PALEONTOLOGY, V. 78, NO. 6, 2004
5—Ramus fragment and lower dentition of Capromeryx tauntonensis from Guanajuato. IGM 8385, right ramus of lower jaw with p2–m3,
1, lingual view, 2, occlusal view of dental series. IGM 8387, right dental series with p3–m3, 3, occlusal view. Bar scales 5 10 mm.
specimen, which is broken behind the m2 on the lingual side and
behind the ﬁrst alveolus of the m3 on the labial one. IGM 8385
is an almost complete lower jaw broken at the diastema and the
most posterior end; it preserves a complete cheek tooth series.
The dorsal border of the diastema is acute, the ventral border
of the horizontal ramus is almost straight below the premolar
region and becomes convex below the second lobe of m1 back-
wardly; the depth of the mandible increases toward m3 (Fig. 5).
The depth of the ramus in IGM 8386 at the posterior border of
the p4 is 17.2 mm and below the ﬁrst lobe of m2 is 20.3 mm; in
the right ramus of IGM 8385 the depth is 17.0 mm and 21.0 mm,
respectively, and below the second lobe of m3 is 29.0 mm.
The Mexican material differs from C. arizonensis housed at UF
in that P3 and P4 are around 17 percent larger and their metastyle
stronger; M2 shows stronger anterior ribs and a mesostyle; and
the heel is absent in M3. The rami from San Miguel Allende are
about 17.1 percent deeper and stouter, and the lower premolars
are larger and the premolar series is not reduced (Table 2).
The p4s from Guanajuato have a deep posterolingual fold and
a posterior re-entrant, both not present in C. arizonensis. In three
p4s (the two of IGM 8387 and IGM 8389) the fold is closed to
form a fossettid, a character not seen in the Florida species. The
Mexican p4s are wedge-shaped, while those of UF are more rect-
angular, with similar middle and posterior width.
Compared with the specimen of Capromeryx mexicanus UCMP
26648, a cranial fragment with upper dentition (Furlong, 1925,
ﬁg. 9, table 1), the upper premolars from Guanajuato are signif-
icantly larger (around 40 percent) (Table 3), have better-developed
styles and ribs; the upper molars are about 30 percent larger (Ta-
ble 3); and the M3 lacks a well-developed heel.
In comparison with unpublished mandibular and lower dental
specimens of C. mexicanus housed at UAHMP, the lower pre-
molars and molars from San Miguel de Allende are larger (around
30 percent) and stouter; the p4s are triangular in shape, have a
posterolingual fold, while in C. mexicanus from Hidalgo they
have similar middle and posterior width and do not have a pos-
Mooser (1958) assigned a left mandibular fragment with p2–
m3 from the El Cedazo local fauna to Capromeryx cf. C. mexi-
canus. The comparative study of this specimen revealed that the
conﬁguration of the premolars and molars as well as their dimen-
sions do not correspond to that of Capromeryx. The specimen is
similar to F:AM 42592 and F:AM 42599, both assigned to Stock-
oceros (Skinner, 1942, ﬁg. 16); the shared characters include a
shallow mandible, a p3 with a deep anterolingual fold, and a
middle fossettid in its occlusal surface; the p4 is rectangular in
outline, there are no anterolingual or posterolingual folds, and in
its occlusal surface there is a deep anterior triangular fossettid, an
elongated middle fossettid, and a little circular posterior fossettid;
NEZ-HIDALGO ET AL.—PLIOCENE CAPROMERYX FROM MEXICO
6—Lower p4s and m3s of Capromeryx tauntonensis from Guanajuato. IGM 8380, left p4, 1, occlusal view, 2, lingual view. IGM 8390, left
p4, 3, occlusal view, 4, lingual view. IGM 8389, left p4, 5, occlusal view, 6, lingual view. IGM 8391, left m3, 7, occlusal view, 8, lingual view.
IGM 8392, right m3, 9, occlusal view, 10, lingual view. Bar scales 5 10 mm, with upper scale for occlusal views and lower scale for lingual
1—Measurements of upper and lower teeth of Capromeryx taunto-
nensis from San Miguel de Allende, Guanajuato, central Me´xico.
Tooth Dimension Number
and the molars have well-developed styles. These features allow
for referring IGM 5267 to Stockoceros.
In comparison to the specimens of Capromeryx furcifer AMNH
2771, a right ramus fragment with p2–m3 (Matthew, 1904), and
KU 7419, a right p2–m3 series (Hibbard and Taylor, 1960), the
lower premolars from San Miguel de Allende are larger and not
reduced (Tables 2, 3); and the p4s have a deep posterolingual fold
or fossettid. Neither character is present in the genotypic species.
The comparison of the Guanajuato material with upper and
lower teeth and a ramus fragment with incomplete dentition of C.
tauntonensis shows a close morphology between the specimens
of the two sets. The P3 has a moderately developed parastyle and
a strong rib and metastyle, as present in UWBM 78977. The M1s
from Guanajuato have a poorly developed parastyle and a mod-
erately developed mesostyle, as observed in UWBM 78975. The
M2s have a strongly developed parastyle, mesostyle, and anterior
rib, and a moderately developed metastyle, as present in UWBM
78968. Comparing the slightly worn M3 IGM 8384 and UWBM
78967, it is evident that both have moderately developed styles
and anterior rib and a posterior basal expansion. In the well worn
M3s IGM 8383 and UWBM 78966 the metastyle does not form
Regarding the lower dentition, the moderately worn p4s have
a deep posterolingual fold, as in the p4 of the mandibular frag-
ment UWBM 78979. It is important to note that in UWBM 78993
(Morgan and Morgan, 1995, ﬁg. 3) there is a small circular fos-
settid that also is present in some p4s from San Miguel de Allen-
de. The m1s have a poorly developed entostylid, as in the molar
UWBM 78979 of C. tauntonensis. The m2s have a moderately
developed parastylid and entostylid, as seen in UWBM 78986.
The m3 of specimen IGM 8385, the moderately worn m3 of spec-
imen IGM 8387, and the well-worn IGM 8391 show no evidence
of a talonid, as in UWBM 78982; in contrast, IGM 8392 has a
posterior basal expansion, as in UWBM 80700. As is the case of
the p3s from Guanajuato, Morgan and Morgan (1995) mentioned
that this premolar of C. tauntonensis has three inﬂections on the
lingual side of the tooth, and that with additional wear the pos-
terior one subsides.
As can be observed in Tables 1 and 3, some mean lengths of
the Capromeryx teeth from Guanajuato are slightly smaller than
the length range of those from Taunton. These are subtle differ-
ences that can be explained taking into account the age of the
organisms, the intraspeciﬁc variation, the sexual dimorphism, and
possibly geographic variation, since the observed range of the two
sets overlaps (Table 3).
1184 JOURNAL OF PALEONTOLOGY, V. 78, NO. 6, 2004
2—Comparison of p3-p4 mean length percent regarding m1-m3 mean length of different Capromeryx species.
IGM 8385 and IGM 8387
Morgan and Morgan, 1995
AMNH2771 KU 7419
40.42 41.2 34.0 36.7 33.5
Composite mean lengths dimensions from table 1.
3—Comparison of anteroposterior length range in upper and lower molariforms of different Capromeryx species.
(1995, table 1).
Taylor, 1960 (table 9, ﬁg. 17);
Matthew, 1904 (ﬁg. 20).
(1925, table 1).
The Mexican material shows the dental diagnostic features of
Capromeryx tauntonensis, such as a deep posterolingual fold on
p4 and an absence of a posterior heel on M3. Also the close
morphological similarity of the upper and lower dentition in sim-
ilar wear stage allow for conﬁdently assigning the specimens from
San Miguel de Allende to C. tauntonensis.
Although the systematics of the Antilocapridae is based pri-
marily on horn core characters, in the case of Capromeryx, due
to the progressive dwarﬁng observed in the genus (Morgan and
Morgan, 1995; Janis and Manning, 1998), the size of the teeth
(especially the length), as well as their morphology, are different
enough to allow species identiﬁcation.
Paleobiological considerations.Previous to this study, Cap-
romeryx tauntonensis was only known from the Taunton local
fauna of Washington and from a tentative referral from the Sand
Draw local fauna in Nebraska (Morgan and Morgan, 1995; Janis
and Manning, 1998).
The localities in Guanajuato and Washington where this species
unquestionably occurs are separated by more than 3,000 km, sug-
gesting that C. tauntonensis had a wide geographic distribution.
The recent pronghorn Antilocapra americana has a very extensive
distribution, occupying almost all of western North America and
historically ranging from central Canada to central Me´xico (Hall,
1981; Grubb, 1993). It is not surprising that C. tauntonensis
would have had a similarly broad geographic distribution.
The early Blancan (Lundelius et al., 1987; Janis and Manning,
1998) or middle Blancan (Blancan III) (Repenning, 1987) faunal
association of San Miguel de Allende suggests a savanna habitat,
with grazing species, such as the equids and lagomorphs, mixed-
feeders, the antilocaprids, mixed-feeders or browsers like Hem-
iauchenia Gervais and Ameghino, 1880, some browsing forms
such as Rhynchotherium Falconer, 1868, and carnivores of dif-
ferent sizes (Webb, 1977, 1983; Janis, 1982; Dompierre and
Churcher, 1996; Janis and Manning, 1998; MacFadden, 1998;
Lambert and Shoshani, 1998). Of the two antilocaprids present
(Capromeryx tauntonensis and Hexobelomeryx), the former is the
smaller and the one with a proportionally longer premolar row,
which probably reﬂect some kind of niche partitioning for a better
distribution of the resources.
Faunal and age comparison.The shared taxa with the Taun-
ton local fauna include Hypolagus Dice, 1917, Spermophilus Cu-
vier, 1825, Borophagus Cope, 1892a, Felis Linnaeus, 1758, Pla-
tygonus Le Conte, 1848, Hemiauchenia, Capromeryx and Equus
(Dolichohippus) Skinner and Hibbard, 1972. The paleomagnetic
studies carried out in that fauna establish an age of 2.85–2.95 Ma
(Morgan and Morgan, 1995). The radiometric dating of the fos-
siliferous sediments of San Miguel de Allende (3.3–3.6 Ma) in-
dicates that the fauna from Guanajuato is older by 350–600 Ka
than the one from Washington.
The Mexican fossil record of Antilocapridae is scarce and
strongly biased towards the late Pleistocene. Of the ﬁve genera
reported, only two (Merycodus and Hexobelomeryx) are of Ter-
tiary age, and of these only Hexobelomeryx has been extensively
described. Regarding central Me´xico, in many papers late Tertiary
antilocaprids have been mentioned but not described; so this study
represents the ﬁrst detailed description of an antilocaprid from
central Me´xico and the second of the country.
The record of Capromeryx tauntonensis in sediments of early
Blancan (Lundelius et al., 1987; Janis and Manning, 1998) or
middle Blancan (Blancan III) (Repenning, 1987) age from Gu-
anajuato extends the geochronological range of the species about
350–600 Ka and its geographic distribution from the northwestern
USA to central Me´xico; also it represents the oldest record of the
genus in North America.
We thank J. Rensberger of the Burke Museum University of
Washington for providing the calibrated photographs of C. taun-
tonensis, and to G. A
lvarez-Reyes and EarthWatch volunteers for
collecting part of the fossil material described in this paper. Thank
to C. Carranza who made the ﬁrst drafts of Figures 1 and 2 and
to A. Altamira who took the photographs of Figures 3–6. We
extend our thanks to reviewers J. K. Morgan and S. D. Webb for
their comments and suggestions, which improved this paper.
The senior author expresses special thanks to B. J. MacFadden,
S. D. Webb, and R. Hulbert for their kind hospitality and valuable
NEZ-HIDALGO ET AL.—PLIOCENE CAPROMERYX FROM MEXICO
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