New primate genus from the Miocene of Argentina
Marcelo F. Tejedor*†, Ada´n A. Tauber‡, Alfred L. Rosenberger§¶, Carl C. Swisher III
, and Marı´a E. Palacios**
*Consejo Nacional de Investigaciones Cientı´ficas y Te´cnicas, Laboratorio de Investigaciones en Evolucio´n y Biodiversidad, Facultad de Ciencias Naturales,
Sede Esquel, Universidad Nacional de la Patagonia ‘‘San Juan Bosco,’’ Sarmiento 849, 9200 Esquel, Argentina; ‡Facultad de Ciencias Exactas, Fı´sicas y
Naturales, Universidad Nacional de Co´rdoba, Avenida Velez Sarsfield 249, 5000 Co´rdoba, Argentina; §Department of Archaeology and Anthropology,
Brooklyn College, City University of New York, 2900 Bedford Avenue, Brooklyn, NY 11210; ¶Division of Vertebrate Zoology (Mammalogy), American
Museum of Natural History, Central Park West at 79th Street, New York, NY 11024;
Department of Geological Sciences, Rutgers University, Piscataway, NJ
08854; and **Museo Regional Provincial ‘‘Padre Manuel Jesu´s Molina,’’ Ramo´n y Cajal 51, 9400 Rı´o Gallegos, Argentina
Edited by Jeremy A. Sabloff, University of Pennsylvania Museum of Archaeology and Anthropology, Philadelphia, PA, and approved December 28, 2005
(received for review August 4, 2005)
Killikaike blakei is a new genus and species of anthropoid from the
late Early Miocene of southeastern Argentina based on the most
pristine fossil platyrrhine skull and dentition known so far. It is part
of the New World platyrrhine clade (Family Cebidae; Subfamily
Cebinae) including modern squirrel (Saimiri) and capuchin mon-
keys (Cebus) and their fossil relatives known from Early to Middle
Miocene and subrecent periods. Living cebines are relatively large-
brained, adroit predatory foragers and live within complex social
groups, and wild capuchins exhibit a wide range of behaviors
associated with enhanced intelligence. We show that K. blakei
lacks diagnostic derived characteristics of the lower face and
premolar dentition that are shared by modern cebines, but its
strongly vaulted frontal bone and capacious anterior cranial fossa
indicate the early evolution of an enlarged forebrain.
Miocene  Paleoprimatology  Patagonia  Platyrrhini  Cebinae
Intact craniodental remains of pre-Pleistocene fossil NewWorld anthropoids are exceedingly rare (1–3). Of the five
Miocene genera that are known from crania (Dolichocebus,
Tremacebus, Homunculus, Chilecebus, and Lagonimico), the first
three are essentially edentulous and all but one are broken
andor deformed. Chilecebus carracoensis from a site in the
western Andes of Chile (4) is an exception. It preserves an
unspoiled skull with teeth in situ, albeit heavily worn. Here we
report a fossil of a platyrrhine that preserves the entire face and
also an unworn, little damaged dentition that is the best ana-
tomical evidence of the maxillary teeth of any Santacrucian fossil
monkey. It also provides relatively complete and undistorted
evidence of the anterior braincase of a fossil platyrrhine. The two
specimens of this species come from the classic Santacrucian
sediments of Patagonian southeastern Argentina (5, 6), which
has produced a substantial primate fauna (1, 7, 8, ††). They are
the southernmost fossil platyrrhine primates ever described.
Systematic Paleontology. The classification of Killikaike blakei is as
follows: Order Primates (Linnaeus, 1758); Suborder Anthro-
poidea (Mivart, 1864); Superfamily Ateloidea (Gray, 1825);
Family Cebidae (Bonaparte, 1831); Subfamily Cebinae
(Bonaparte, 1831; Mivart, 1865); K. blakei, gen. et sp. nov.
Holotype. MPM-PV 5000 (Museo Regional Provincial ‘‘Padre
Manuel Jesu´s Molina’’ Padre Molina, Vertebrate Paleontology
Collection) is an intact, undistorted face of an adult individual
that preserves the forehead, orbits, snout, dental arcade, and
roots of the pterygoid processes. The dentition includes right C,
P2–3, root of P4, crowns of M1–3; left C, broken crowns of P2–3, and
roots of M1–3 (Fig. 1 A–E).
Hypodigm. Holotype and MPM-PV 1607, a right M1–3 associated
in a piece of maxilla (Fig. 1F).
Locality and age. MPM-PV 5000 was collected
25 years ago at the
locality Killik Aike Norte (formerly known as Estancia Felton)
(5, 6, 9), 50 km northwest of the city of Rı´o Gallegos, Santa
Cruz Province, Argentina (Fig. 2). MPM-PV 1607 was collected
in January of 2005 at the same locality. Killik Aike Norte is part
of the Santa Cruz Formation (10) exposed in the northern cliffs
of the estuary of the Rio Gallegos river. The stratigraphy is
divided into two members (6): Estancia La Costa (120 m thick
with 18 fossiliferous levels) and Estancia Angelina (103 m thick
with four fossiliferous levels). There are two types of volcanic ash
at the locality. The exact provenience of the MPM-PV 5000
specimen is not known, but the mineralogy and chemistry of the
rock that encased it are consistent with an origin in the lower
volcanic tuff, which is part of the Estancia La Costa member
(Fig. 3). MPM-PV 1607 was also collected from the lower tuff.
The level 6 tuff of the Estancia La Costa member at the locality
Estancia La Costa, northeast of Killik Aike Norte, previously
yielded a primate skull attributed to Homunculus patagonicus
(7). Correlation of the level 6 at La Costa with the tuff at Killik
Aike Norte is not confirmed yet.
We have determined the age of the MPM-PV 5000 through
40Ar39Ar laser incremental-heating analyses of plagioclase sep-
arated from the tuff level where the skull was found at Killik
Aike Norte. Three separate incremental-heating experiments
yielded reproducible plateau ages of 16.45 0.14, 16.5 0.2, and
16.5  0.3 mega-annum (Ma) (see Fig. 4, which is published as
supporting information on the PNAS web site).
The CaK ratio, derived from the 37Ar39Ar ratio obtained
during the 40Ar39Ar dating of the plagioclase, can be used to
delimit possible correlative Santa Cruz tuffs previously dated at
the coastal sites of Monte Observacio´n and Monte Leo´n, which
are 100 km north of Killik Aike Norte. These sites contain key
fossil mammal localities of the Santa Cruz Formation and have
yielded 40Ar39Ar ages similar to that reported here for Killik
Aike Norte. The low CaK ratios of the Killik Aike Norte
plagioclase compare best with Monte Observacio´n MO2, al-
though the variation in the CaK measurements does not
preclude possible correlation with MO64 or ML18 tuffs, and
further geochemical study is needed (11, ‡‡).
Our 40Ar39Ar age for Killik Aike Norte is appreciably
younger than the older age limit of 17.7 Ma for the Santa Cruz
Formation based on a K-Ar date from the same site (12). The
older age may be attributed to contaminant (detrital grains
incorporated into the bulk K-Ar sample). The younger age for
Killik Aike Norte reported here corroborates the assessment of
Fleagle et al. (10, 11) that the base of the Santacrucian at the
classic coastal localities between Rı´o Gallegos and Rı´o Coyle is
not older than 16.5 Ma. The older age limit for the Santacru-
cian based on the 17.7 Ma K-Ar date may be in error. The main
terrestrial fossiliferous units of the Santacrucian Land Mammal
Age appear to have been laid down over a relatively short time
Conflict of interest statement: No conflicts declared.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviation: Ma, mega-annum.
†To whom correspondence should be addressed. E-mail: mtejedor@lieb.org.ar.
††Fleagle, J. G., Buckley, G. A. & Schloeder, M. E. (1988) J. Vert. Paleontol. 8, 14a (abstr.).
‡‡Fleagle, J. G. Perkins, M., Bown, T. M., Tauber, A. A. & Dozo, M. T. (2004) J. Vert. Paleont.
24, Suppl. 3, 58A (abstr.).
© 2006 by The National Academy of Sciences of the USA
www.pnas.orgcgidoi10.1073pnas.0506126103 PNAS  April 4, 2006  vol. 103  no. 14  5437–5441
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period of 400,000 years, approximately between 16.1 and
16.5 Ma.
Etymology. Killikaike, after Killik Aike Norte, the name of the
ranch and fossil site; blakei, in honor of the Blake family, who
donated the fossil to the Padre Molina museum.
Diagnosis. Killikaike is unique among platyrrhines in the following
combination of craniodental characters: relatively short face that
is not wide anteriorly, narrow interorbital region, deep recessed
orbits that lack an imperforate medial orbital wall, high arched
frontal bone conforming to an enlarged anterior cranial fossa,
and nonbunodont cheek teeth with subtriangular premolars and
hypocone-bearing quadrate molars. It is a platyrrhine similar in
size to Saimiri, Callicebus, or Leontopithecus based on dental and
cranial dimensions (Tables 1 and 2), with an upper tooth count
of 2.1.3.3. Unlike Cebus and Saimiri, the face is relatively narrow
and the snout tapers anteriorly, making it shorter than Aotus and
Pithecia, for example, but without abbreviated premaxillae as in
Callicebus. The interorbital region is relatively narrow, in con-
trast to callitrichines, pitheciines, atelines, and Chilecebus, but
less so than in existing cebines and Dolichocebus. Orbits are not
enlarged as in Aotus and Tremacebus, and the medial orbital
walls are closely spaced and not fenestrated, in contrast to
Dolichocebus and Saimiri. The orbits are recessed beneath the
arched and uptilted frontal bone, as in modern cebines and
unlike most other platyrrhines, where the frontal trigon is
f lattened in the midline. A relatively large lateral orbital fora-
men is partially preserved, unlike most other platyrrhines.
Postcanine crowns are moderately crested, resembling Saimiri
and unlike the bunodont Cebus. However, in contrast to Saimiri
and Cebus, where P2–3 are transversely wide and lingually
expanded and sometimes have a lingual cingulum, in Killikaike
these teeth are relatively narrower and more triangular, and they
lack lingual cingulum. M1–2 are quadrate with high cusps and well
developed, offset hypocones, strong lingual cingula, and well
developed crests, distinguishing the genus from all pitheciines,
atelines, callitrichines, and Szalatavus. The molars are relatively
narrower than in Branisella and Chilecebus. M1 is considerably
wider than M2, and M3 is reduced but otherwise an unremark-
able two-cusped crown.
Results and Discussion
MPM-PV 5000 is the forehead, face, and palate of a young adult,
probably female. It evidently broke away from the neurocra-
nium, which has not been recovered, behind the craniofacial
junction. The snout and orbits are remarkably well preserved,
bilaterally undamaged except for a slight crack at the left lateral
Fig. 1. Holotype cranium and referred upper molars of K. blakei, a new genus of platyrrhine primate from the Miocene of Argentina. Frontal (A), right lateral
(B), palatal (C), and posterior (D) views of MPM-PV 5000, and an illustration of the cheek teeth (E). (F) MPM-PV 1607 in occlusal view. (Scale bar, 1 cm.)
5438  www.pnas.orgcgidoi10.1073pnas.0506126103 Tejedor et al.