New Early Pliocene Cercopithecidae (Mammalia: Primates) from Aramis, Middle Awash Valley, Ethiopia

36 Pages·2001·1.6 MB·English

by  Stephen R. Frost

PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY
CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024
Number 3350, 36 pp., 12 figures, 2 tables October 31, 2001
New Early Pliocene Cercopithecidae
(Mammalia: Primates) from Aramis,
Middle Awash Valley, Ethiopia
STEPHEN R. FROST1
ABSTRACT
The Middle Awash Research Project has collected a large sample of fossil cercopithecids
from the Aramis, Kuseralee, and Sagantole drainages in the MiddleAwashpaleoanthropolog-
ical study area of Ethiopia. These sites have been securely dated to 4.4 Ma. The craniodental
material from this assemblage supports the diagnoses of two distinct new genera and species,
whicharedescribedhere.Pliopapioalemuiisamid-sizedpapioninrepresentedbyacomplete
cranium, several partial jaw fragments, and many isolated teeth. Kuseracolobus aramisi is a
medium-sized colobine represented by several maxillae, mandibles, and other cranial frag-
ments, as well as by isolated teeth. Stratigraphically associated postcranial remains will be
discussed in a separate report.
Pliopapio alemui is distinctive from other known African papionins in the combination of
its cranial, mandibular, and dental morphology. It lacks the diagnostic facial features of Par-
apapio, as well as the flattened muzzle dorsum, facial fossae, and maxillary ridges of Papio.
Moreover, it does not possess any of the derived dental and cranial specializations of Thero-
pithecus. Kuseracolobus aramisi is larger than all modern African colobines,butsmallerthan
all known Cercopithecoides, Paracolobus, and Rhinocolobus. It is distinctive from Cercopi-
thecoides and the colobine from Leadu in its symphyseal, corporal, and gonial morphology,
and from Libypithecus, Paracolobus, and Rhinocolobus in its facial morphology.
This early Pliocene sample fills a temporal gap between the terminal Miocene and later
Pliocene sites and documents the existence of two new cercopithecid taxa, increasing known
diversity in the family.
1New York Consortium in Evolutionary Primatology, Ph.D. Program in Anthropology, City University of New
York,and DivisionofPaleontology,AmericanMuseumofNaturalHistory.
Copyright(cid:113)AmericanMuseumofNaturalHistory2001 ISSN0003-0082
2 AMERICAN MUSEUM NOVITATES NO. 3350
INTRODUCTION this paper are based on the limited number
of relatively complete specimens. While the
The Cercopithecidae are relatively com-
isolated teeth are only diagnosable to sub-
mon and diverse in most Pliocene and Pleis-
family, they are assigned to the same two
tocene fossil assemblages from sub-Saharan
species as the more complete material based
Africa. During this period, the subfamily
on size and a lack of evidence to the con-
Cercopithecinae is represented by eight gen-
trary.
era or subgenera while the Colobinae is rep-
resented by at least five (Szalay and Delson,
INSTITUTIONAL ABBREVIATIONS
1979; Delson, 1984, 1988, 1994). Few of
these taxa, however, are represented in the KNM National Museums of Kenya, Nairobi,
Early Pliocene. The locality of Aramis inthe Kenya
NME National Museum of Ethiopia, Addis
Awash River valley of Ethiopia has yielded
Ababa, Ethiopia
the hominid Ardipithecus ramidus (White et
NMT National Museum of Tanzania, Dar es
al., 1994, 1995). The large cercopithecid
Salaam, Tanzania
sample from Aramis and sites of similar age
MB Berlin Museum, Berlin, Germany
in the Middle Awash adds considerably to
our knowledge of cercopithecid evolution SYSTEMATIC PALEONTOLOGY
during this period. Thecraniodentalanatomy
CLASSMAMMALIALINNAEUS,1758
and systematics of these cercopithecids are
described here. ORDERPRIMATESLINNAEUS,1758
Between 1992 and 1999, the Middle INFRAORDERCATARRHINIE.GEOFFROY,1812
Awash Research Project collected and cata-
FAMILYCERCOPITHECIDAEGRAY,1821
logued 925 cercopithecidspecimensfromlo-
SUBFAMILYCERCOPITHECINAEGRAY,1821
calities within the Aramis, Kuseralee, and
Sagantole drainages. This sample comes TRIBEPAPIONINIBURNETT,1828
from the Aramis Member of the Sagantole Pliopapio, new genus
Formation between the Ga`ala Tuff Complex TYPE SPECIES: Pliopapio alemui, new spe-
(GATC) and the Daam Aatu Basaltic Tuff cies.
(DABT). These tephra have been radiomet- GENERIC DIAGNOSIS: A genus of African
rically dated to 4.39 (cid:54) 0.03 and 4.39 (cid:54) 0.05 papionin, distinguished from Parapapio, Lo-
Ma respectively (Renne et al., 1999). The phocebus, and Cercocebus by the presence
size, precise stratigraphy, and dating of this of a clear anteorbital drop, although this is
sample make it one of the best documented not as distinct as in most Papio and Man-
in the African Pliocene. drillus. In this aspect, its profile is most sim-
From a limited initial sample, Wolde- ilar to that of Macaca, but Pliopapio has a
Gabriel et al. (1994) listed three cercopithe- relatively longer muzzle. It is different from
cid species at Aramis based on preliminary Papio (Papio), Gorgopithecus, Lophocebus,
identifications by Delson: cf. Paracolobus Cercocebus, and Mandrillus in that the muz-
sp., cf. Colobinae sp. ‘‘A’’ (sensu Eck,1977) zle lacks postcanine and suborbital fossae.
and cf. Parapapio sp. On the basis of the The absence of maxillary ridges distinguish-
current, vastly expanded craniodental sam- es it from Papio, Theropithecus (Omopithe-
ple, two new genera and species are diag- cus) and Mandrillus. The muzzle dorsum is
nosedhere,onecolobineandonecercopithe- saddle-shaped and rounded in paracoronal
cine. In the postcranial sample, two and pos- section. In these aspects it is similartoTher-
siblythreemorphscanbeidentified.Noneof opithecus oswaldi (sensu Leakey, 1993, as is
the postcranial specimens are directly asso- used throughout this paper), but is unlike the
ciated with any of the craniodental material, flattened dorsum and squared paracoronal
and their affinities and functional interpreta- section found in Papio (includingDinopithe-
tions will be presented elsewhere. cus)andMandrillus.Relativetoneurocranial
This is one of the largest Early Pliocene breadth, the rostrum isnarrowincomparison
samples of fossil cercopithecids; however, with those of all known African papionins,
the diagnoses for the two taxa described in although it is in the lowest end of variation
2001 FROST: CERCOPITHECIDAE 3
for Papio, Mandrillus, and Macaca. Crush- with complete but damaged dentition, found
ing in the anterior portion may contribute to by Awoke Amzaye in December 1995.
this impression, but cannot account for it en- HYPODIGM: See appendix 1.
tirely. HORIZON: All specimens are derived from
Unlike those in Parapapio, Cercocebus, the Aramis Member of the Sagantole For-
and Lophocebus, the cranial vault is separat- mation, between the GATC and DABT, and
ed from the brow ridges by a distinct are therefore dated to 4.4 Ma (Renne et al.,
ophryonic groove. The temporal lines in the 1999).
holotype male remain widely separated and DESCRIPTION:Themostcompletespecimen
do not form a sagittal crest, as opposed to is the holotype male skull ARA-VP-6/9332
the situation in Theropithecus, Gorgopithe- (see fig. 1). The mandible is attached to the
cus, Papio (Dinopithecus), and Paradoli- cranium by a thin layer of matrix that pre-
chopithecus. vents the two from being safely separated.
While the mandibular symphysis is shal- Therefore, the palate and muchofthecranial
lower and more sloping in profile than that basearenotavailableforobservation.Ofthe
of most papionins, it is shorter and more main cranial regions, only the left zygomatic
rounded than that of Parapapio ado (from is completely missing. The right orbit is
Laetoli and Kanapoi) or the papionin from damaged and lacks much of the right half,
Lothagam. In these latter taxa the symphysis except for one triangular portion around the
is even longer and more sloping, with the zygoma. The right zygomatic arch is mostly
incisive alveolar process projecting morean- present, but crushed, missing only the region
teriorly, producing a more procumbent inci- around the temporojugal suture. The right
sor row. Corpus fossae are absent, distin- maxilla and mandible are weathered, reveal-
guishing it from most Papio (Papio) (P. h. ing the roots of the teeth. The other cranial
kindae females have very slight fossae, and specimens are all considerably more frag-
some P. izodi lack them), Gorgopithecus, mentary.ARA-VP-6/437(seefig.2)isapar-
Theropithecus (Omopithecus), Mandrillus, tial right male maxillary fragment with the
and Lophocebus. dorsalsurfaceuptothepiriformaperture,the
The molars are higher crowned, more roots of the canine and fourth premolar, and
straight-sided, and less flaring on average complete central incisor and third premolar.
than those of Papio, Macaca, Mandrillus, ARA-VP-1/1723 (fig. 2) is a partial right fe-
and Lophocebus, and far less so than those male maxilla preserving the canine through
ofCercocebus.Asinmostpapionins,butun- third molar. ARA-VP-1/1007 (fig. 2) is a
like Mandrillus and Cercocebus, the premo- slightly crushed left female premaxillomax-
lars are not particularly large relative to the illary fragment with the rostral surface pre-
molars. The mandibular incisors are nearly served nearly to the lateral border of the pir-
vertically implanted, whereas those of Par- iformaperture,adamagedlateralincisor,and
apapio ado from Laetoli and Kanapoi are complete canine through first molar.
more procumbent. Pliopapio alemui is smaller in cranial size
ETYMOLOGY: The name refers to the Plio- than all known Theropithecus and Papio,
cene age of the taxon and itspapioninstatus. other than P. hamadryas kindae, P. angus-
ticeps, and P. izodi, to which it is similar in
Pliopapio alemui, new species size.Itissightlylargerthanallbutthelargest
Macaca, such as M. thibetana and M. ne-
SPECIFIC DIAGNOSIS: As for genus. mestrina. This cranial size estimate is con-
ETYMOLOGY: Named in honor of Alemu firmed by centroid sizes computed from a
Ademassu, Paleoanthropology Laboratory sample of 45 cranial landmarks (see fig. 3).
curator at the National Museum of Ethiopia In dental size, it is marginally smaller than
responsible for assisting with preparation, Parapapio ado from Laetoli and Kanapoi,
molding, and study of all Middle Awash
specimens.
2Sex identifications throughout the text are based
HOLOTYPE:ARA-VP-6/933.Anearlycom- upon the highly dimorphic size and morphology of the
plete male cranium and attached mandible upperand lowercaninesand thelowerthirdpremolar.
4 AMERICAN MUSEUM NOVITATES NO. 3350
Fig.1. HolotypeofPliopapioalemuiARA-VP-6/933.AllviewsareinFrankfurtorientation.Lateral
view of the left side. Opposite page: dorsal view (above); lateral view of the right side (below).
andsimilartospecimensfromEkora,theLo- tinct from Papio and Mandrillus. The max-
mekwi Member of the Nachukui Formation, illary fossae are also extremely shallow.
theTulu BorMemberoftheKoobiForaFor- Once again, this is similar to the above gen-
mation, and Unit 2 of the Chiwondo beds. era and to Papio (Dinopithecus) (see Delson
Dental dimensions for Pl. alemui are listed and Dean, 1993). From what is preserved in
in table 1. ARA-VP-1/1007 and ARA-VP-1/1723 the
Rostrum. The infraorbital foramina are femalesseemtolackthesestructuresaswell.
only preserved on the left side of ARA-VP- The muzzle dorsum of ARA-VP-6/933 is
6/933. The four foramina are arranged in a largely smooth and saddle-shaped, as it is in
superolaterally concave arc, as in Theropi- Theropithecus oswaldi. It is concave in the
thecus(EckandJablonski,1987).Relativeto sagittal plane and forms a convex arc in par-
theorbittheylieroughlyinmid-mediolateral acoronal cross section at the level of thesec-
position and are placed more closely to its ondmolar.Thiscrosssectionissharper,how-
inferior rim than in Theropithecus. ever, with the nasals forming a more acute
In ARA-VP-6/933 and ARA-VP-6/437 anglethantheydoinT.oswaldi.Thisisclos-
there is little to no development of maxillary er to the cross section of Macaca mulatta,
ridges, similar to Parapapio (Freedman, M. nemestrina, or M. thibetana, but with a
1957), Theropithecus (Theropithecus) (sensu relatively longer muzzle. When viewed lat-
Delson, 1993), and most Macaca, but dis- erallythemuzzleprofileisconcavefromgla-
2001 FROST: CERCOPITHECIDAE 5
Fig. 1. Continued.
6 AMERICAN MUSEUM NOVITATES NO. 3350
Fig.2. MaxillaeofPliopapioalemui.Counterclockwisefromtopleft:ARA-VP-1/1007lateralview,
ARA-VP-1/1723(reversed),ARA-VP-6/437lateralview(reversed),ARA-VP-6/437frontalview,ARA-
VP-1/1007 occlusal view, ARA-VP-1/1723 occlusal view.
bella to rhinion, displaying an antorbital sal aperture at a margin of approximately 4
drop, and is also concavefromrhiniontona- mm, as it does in most larger papionins. Un-
sospinale, and finally convex from nasospi- like in T. gelada, it does not enter the piri-
nale to prosthion. While the entire muzzle is form aperture. The nasal process of the pre-
quite long and not unlike that of Papio, the maxilla projects further posteriorly than it
length of the segment from glabella to rhi- does in Papio, approaching to within 1.5 cm
nion comprises less of the total muzzle of the orbits. The premaxillomaxillarysuture
length than it does in Papio (see fig. 4). Rhi- is therefore largely an anterolaterally
nion is also considerably more prominent smoothly curving arc. The premaxillae pro-
than in Papio or Theropithecus. ject relatively far anteriorly beyond the ca-
The sutures of the muzzle are well pre- nine, and there is a modest diastema sepa-
servedontheleftsideofARA-VP-6/933and rating the canine from the incisors (6.5 mm
on ARA-VP-6/437. The premaxillomaxillary on the left side of ARA-VP-6/933).
suture follows the superior portion of thena- When viewed superiorly, the muzzle is
2001 FROST: CERCOPITHECIDAE 7
Fig. 3. The x-axis represents different papionin genera or subgenera as follows: Ccb, Cercocebus;
Din, Papio (Dinopithecus); Lop, Lophocebus; Mac, Macaca; Man, Mandrillus; Omo, Theropithecus
(Omopithecus); Pap, Papio (Papio); Pdo, Paradolichopithecus; Ppa, Parapapio; Pli, Pliopapio; Smo,
Theropithecus oswaldi; The, T. gelada. Sample size for each (sub)genus is given in parentheses below
each label. The y-axis plots values of centroid size computed from45 craniallandmarks.Centroidsizes
werecomputedusingMorpheus(Slice,1998).Thecentralbarrepresentsthemedian,or50thpercentile.
The bottom and top of each box represent the value at the 25th and 75th percentiles, respectively, and
the whiskers extend to the farthest observation that is less than 1.5 times the length of the box. Any
individuals outside of the whisker range are marked separately.
much narrower than the neurocranium (see narrower than that of Papio. The nasals of
fig. 5). In comparison to the length of the ARA-VP-6/933 are distorted, but probably
neurocranium, the muzzle is longer than in would have formed a straight superior mar-
most Macaca or Parapapio and shorter than gin. The premaxillae then bow gently later-
in Papio (Papio) and Mandrillus (see fig. 6). ally to the aperture’s widest point just above
The muzzle of the female ARA-VP-1/1007 therootsof theincisors,thencurveconvexly
is considerably shorter than that of the male to meet at nasospinale in a relatively acute
ARA-VP-6/933. When they are lined up at inferior angle. There is no evidence of ante-
the first molar, the mesial edge of the lateral rior nasal tubercles.
incisor of ARA-VP-1/1007 is even with the The maxillary dental arcade is preserved
middle of the canine of ARA-VP-6/933. in ARA-VP-6/933, and it is preserved from
The piriform aperture is preserved in C to M3 in ARA-VP-1/1723 and from I2 to
ARA-VP-6/933, partially preservedinARA- M1 in ARA-VP-1/1007. Thedentalarcadeis
VP-6/437, and only a small portion is pre- somewhat distorted in ARA-VP-6/933, but
served in the female ARA-VP-1/1007. The appears to have been largely U-shaped, with
outline of the piriform aperture is typically the canines marking the bases of an anterior
papionin, being roughly ovoid but forming a arc composed of the incisors. The alveolar
V at its inferior pole. In breadth it is slightly margins appear to be gently bowed laterally,
8 AMERICAN MUSEUM NOVITATES NO. 3350
TABLE1
Dental Measurements for Pliopapio alemui and Kuseracolobus aramisi
2001 FROST: CERCOPITHECIDAE 9
Fig. 4. Box and whisker plot of the ratio: length nasion–rhinion/length nasion–prosthion. Labeling
is the same as in fig. 3.
with their widest point at the mesial loph of thecus (other than T. gelada and T. oswaldi
M2 and narrowest at P3, bulging laterally leakeyi). ARA-VP-6/933 is the only speci-
again at the canine, although less so in the men to preserve the zygomatic arches. The
females ARA-VP-1/1007 and ARA-VP-1/ anterior surface of its zygoma curves grad-
1723. The molar series forms a short arc, ually and smoothly superoposteriorly, with
with the M2 oriented slightly obliquely. The only a very slight depression in theregionof
premolars are set in a straight line from M1 the infraorbital foramina and maxillozygo-
to C. matic suture. This depression is unrelated to
When viewed laterally, the maxillary den- any maxillary fossae and is the only feature
tition in ARA-VP-6/933 and ARA-VP-1/ to interrupt the otherwise smoothly curving
1723 is basically straight to very slightly surface. The inferior margin of the anterior
concave,asinmostcercopithecines.Thepal- portion of the zygomatic arch is a smooth
ate is preserved in ARA-VP-6/933, but it is semicircular curveinterruptedbyasmallpy-
covered in matrix (which cannot be removed ramidal process where the maxillozygomatic
without causing damage to the specimen). suture intersects. The superiormost point of
ARA-VP-1/1723 preserves a small part of theinferiormarginliesbelowthelateraledge
the palatal process, which is about 0.5 cm in of the orbit, at which point the zygoma
depth anteriorly and deepens slightly poste- curves inferiorly again. The temporalsurfac-
riorly. es do not appear strongly excavated as in
Zygomatic Arch. The maxillaryrootofthe Theropithecus,butthereissomedamageand
zygomatic arch arises from above the distal distortion here.
loph of M2 in the male ARA-VP-6/933 and In superior view, the zygomatic archesare
above the mesial loph of M2 in the female no more laterallyflaredthaninmostMacaca
ARA-VP-1/1723. This is farther anterior or Papio, but are more smoothly curved.
than in Papio, Gorgopithecus, and Theropi- This is particularly notable anteriorly where
10 AMERICAN MUSEUM NOVITATES NO. 3350
Fig. 5. Box and whisker plot of the ratio: width of muzzle at M1/M2 contact/biporionic width.
Labeling is the same as in fig. 3.
they are more posteriorly angled than in Pa- slightly laterally ‘‘drooping’’ appearance.
pio. The zygomata of the latter genus jut out There are no supraorbital notches.
more sharply, perhaps due to greater maxil- Theinterorbitalbreadthisnarrow,andgla-
lary fossa development. The scar for the or- bellaisnotprominent.Thereissomedamage
igin of the masseter muscle is visible in in this area, but nasion was probably the an-
ARA-VP-6/933 and terminates anteriorly teriormost point on the frontal. The orbits
very close to the maxillozygomatic suture. themselves are largely mediolaterally ovalin
The posterior termination is not preserved, outline,being relativelyshortandbroad.The
but must have been anterior to the zygoma- lacrimomaxillary suture seems to lie just at
ticotomporal suture as there is no scar on the the orbital rim, and the lacrimal fossa was
zygomatic process of the temporal. likelycontainedentirelyinthelacrimalbone.
Orbital Region. The orbital region is only Calvaria. The calvaria is only preserved
preserved in ARA-VP-6/933. Internally both in ARA-VP-6/933. It isrelativelyglobularin
orbits are occupied by matrix. The supraor- overall shape, with its greatest width at the
bital torus is relatively prominent, but thin externalauditorymeatus.Itisgenerallylack-
superoinferiorly. It is mildly V-shaped in su- ing in superstructures and is considerably
perior view and separatedfromtheneurocra- broader than the muzzle. When viewed in
nium by a broad ophryonic groove. Unlike Frankfurt horizontal, the frontal bone rises
in Papio, T. oswaldi, and larger Macaca, above the supraorbital torus and achieves its
there are no bulges above the torus at the maximum height about 1 cm anterior to
midpoints of the orbits. In frontal view, the bregma. The cranial vault remains at this
superior orbital rim and torus rise only very heightuntilabout2.5–3cmposteriortobreg-
slightly lateral to the sagittal plane, then ma. The temporal lines are faint and widely
curveinferiorly,givingthetorusamildlysu- separated, curving posteriorly less than 1 cm
periorly bowed surface and the orbits a medial to the lateral orbital margins. Poste-