Nuciruptor rubricae, a new Pitheciin seed predator from the Miocene of Colombia

Nuciruptor rubricae, a New Pitheciin Seed PredatorFrom the Miocene of Colombia

D.J. MELDRUM,1* and R.F. KAY2

1Departments of Biological Sciences and Anthropology, Idaho StateUniversity, Pocatello, Idaho 83209-80072Departments of Biological Anthropology and Anatomy, Duke UniversityMedical Center, Durham, North Carolina 27710

KEY WORDS Nuciruptor rubricae; Cebupithecia sarmientoi; NewWorld monkeys; Pitheciinae; Platyrrhini; Anthropoidea

ABSTRACT A new genus and species of platyrrhine primate, Nuciruptorrubricae, are added to the increasingly diverse primate fauna from the middleMiocene of La Venta, Colombia. This species displays a number of dental andgnathic features indicating that it is related to living and extinct Pitheciinae(extant Callicebus, Pithecia, Chiropotes, Cacajao, and the Colombian middleMiocene Cebupithecia sarmientoi).Nuciruptor is markedly more derived thanCallicebus but possesses a less derived mandibular form and incisor-caninecomplex than extant and extinct pitheciins (Cebupithecia, Pithecia, Chiro-potes, and Cacajao), suggesting that it is a primitive member of the tribePitheciini within the largermonophyletic Pitheciinae.Nuciruptor has procum-bent andmoderately elongate lower incisors and low-crownedmolars, suggest-ing that it was a seed predator, as are living pitheciins. Its estimated body sizeof approximately 2.0 kg places it within the size range of extant pitheciines.The dental and gnathic morphology of Nuciruptor clarifies several aspects ofdental character evolution in Pitheciinae and makes it less likely that theenigmatic Mohanamico hershkovitzi (m. Miocene, Colombia) is a pitheciin.Am. J. Phys.Anthropol. 102:407–427, 1997. r 1997 Wiley-Liss, Inc.

Themonophyly of themodern Pitheciinae,Pithecia (the saki), Chiropotes (the beardedsaki), and Cacajao (the uakari), as proposedby Mivart and many times since, seems wellestablished (reviewed in Kay, 1990). Rosen-berger suggested a special relationship ofCallicebus (the titi) and Aotus (the owl mon-key) to the pitheciines and has advocatedtheir inclusion in the Pitheciinae (Rosen-berger, 1979, 1981). Rosenberger’s alloca-tion of Callicebus to the Pitheciinae isstrongly supported by recent analyses ofDNA nucleotide sequences (Meldrum, 1995;Schneider et al., 1993, 1995), but molecularstudies indicate that Aotus is not related topitheciines, but rather is placed with thecallitrichine clade. The classification ofSchneider et al. (1993) reflects these cladoge-netic events and is followed here. The sub-

family Pitheciinae represents a clade includ-ing the monophyletic tribe Pitheciini withthe extant genera Pithecia, Chiropotes andCacajao and the tribe Callicebini Pocock,1925, Callicebus alone. (Should Homuncu-lus [early Miocene, Argentina] prove to bethe sister taxon to Callicebus, as Rosen-berger et al. [1990] contends, the correct

Abbreviations: IGM, Instituto Nacional de Investigacions Geo-logica Mineras; UCMP, University of California Museum ofPaleontology.Contract grant sponsor: National Science Foundation; Con-

tract grant sponsor: Duke University Research Council; Contractgrant sponsor: Idaho State University Office of Graduate StudiesandResearch; Contract grant sponsor: Faculty ResearchCommit-tee; Contract grant number 00635558.*Correspondence to: D.J. Meldrum, Department of Biological

Sciences, Campus Box 8007, Idaho State University Pocatello, ID83209-8007. e-mail: [email protected] 13 September 1995; revised 14 November 1996;

accepted 30 November 1996.

AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 102:407–427 (1997)

r 1997 WILEY-LISS, INC.

name for the Callicebini would be Homuncu-lini Ameghino, 1894.)To avoid confusion, we call attention here

to the use of formal and informal taxonomicterms in the text. The taxon Pitheciinae aswe use it refers to a ‘‘closed descent commu-nity’’ or stem-based clade (Fig. 1; Ax, 1985;Williams and Kay, 1995). Pitheciinae is theclade of all species, living or extinct, that aremore closely related to living pitheciinesthan to the next most closely related taxon(the clade consisting of Alouatta, Ateles,Lagothrix and Brachyteles; Rosenberger,1979, 1981; Schneider, et al., 1993). Theinformal term ‘‘pitheciine’’ is used for mem-bers of the subfamily Pitheciinae, includingthe extant Callicebus, Pithecia, Cacajao,and Chiropotes. The informal terms ‘‘callice-bin’’ and ‘‘pitheciin’’ are used for the tribes ofthe subfamily Pitheciinae. They should includeCallicebus in the first case, and Pithecia, Caca-jao and Chiropotes (as well as several extincttaxa discussed below) in the second case.In this paper, we describe a new species of

fossil pitheciin from the Miocene of Colom-bia, review its adaptations, and place it intothe context of pitheciine phylogeny and char-acter evolution. Special attention is paid toseveral extinct taxa that are often consid-ered pitheciines. Like the new taxon de-scribed here, Cebupithecia sarmientoi is aspecies that comes from middle Miocenerocks of the Honda Group cropping out inthe Tatacoa Desert north of the village ofVillavieja, in the Magdalena valley of cen-tral Colombia (Kay et al., 1996). This regionis also called La Venta and its mammalianfauna forms the basis for the LaventanStage/Age (Madden et al., 1996). The holo-type (UCMP 38762) was found in the Mon-key Beds at the base of the Villavieja Forma-tion (Guerrero, 1996; Stirton, 1951; Stirtonand Savage, 1951). Other specimens provi-sionally referred to Cebupithecia have beenrecovered from the Monkey Beds nearby inthe El Dinde area (Setoguchi et al., 1987)and elsewhere in the Tatacoa Desert fromolder deposits lying below the ChunchulloSandstone, in the La Victoria Formation ofthe Honda Group (Meldrum et al., 1990;Meldrum and Kay, 1996).Another middle Miocene species possibly

relevant for understanding pitheciine evolu-

tion is Mohanamico hershkovitzi. This spe-cies also comes from the Tatacoa Desert. Thetype mandible (IGM 181500) comes from theMonkey Beds near El Dinde (Luchterhandet al., 1986). A second specimen of a primate(IGM-KU 8601) of similar size and morphol-ogy to Mohanamico and from the samestratigraphic level was allocated to a newspecies ofAotus, A. dindensis (Setoguchi andRosenberger, 1987). Kay argues that IGMKU-8601 should be allocated toMohanamico,whereas Rosenberger and colleagues recog-nize the distinctness of the two specimens asseparate genera and even assign the twospecimens to two different families (Kay,1990; Rosenberger et al., 1990).A third taxon, Soriacebus, with two spe-

cies,S. ameghinorum andS. adrianae, comesfrom a suite of Patagonian localities collec-tively referred to as the Pinturas fauna

Fig. 1. Phylogeny of Pitheciinae. a: Phylogenetictree illustrating the terms crown group, closed descentcommunity (5stem-based clade) and stem lineage (afterWilliams and Kay, 1995). The crown group contains onlyliving taxa and their last common ancestor. A stem-based definition (used here) includes all species, livingor extinct that are more closely related to the livingmembers of that group than to any other living taxon. b:Cladogram of Pitheciinae recognizing two stem-basedtribes Callicebini and Pitheciini. The stem-based tribePitheciini includes Cebupithecia.

408 D.J. MELDRUM AND R.F. KAY

(Fleagle, 1990). The material is of earlyMiocene age, older than the Colombian ma-terial just described, and thought to pertainto the Santacrucian LandMammalAge (Mc-Fadden, 1990). Considerable material of So-riacebus is known includingmandibles, max-illae, and some postcranial bones.We discuss the merits of allocation of

Cebupithecia, Mohamamico and Soriacebusto the Pitheciinae. We demonstrate thatCebupithecia (middle Miocene, Colombia) iscertainly a pitheciin, but that Mohanamico(middle Miocene, Colombia) and Soriacebus(early Miocene, Argentina) are less likelypitheciin candidates.

SYSTEMATICS

Order Primates

Subfamily Pitheciinae Mivart, 1865

Tribe Pitheciini Gray, 1849

Nuciruptor, gen. nov.

Type species. Nuciruptor rubricae, sp. nov.

Included species. The type species only.

Distribution. As for the type and onlyspecies.

Diagnosis. As for the type and only spe-cies.

Etymology. Derived from the Latin nuci-,combining form denoting ‘‘nut’’ and ruptor de-noting ‘‘break,’’suggesting theapparentadapta-tion for seed predation or nut-breaking.

Nuciruptor rubricae, species nov.(Figs. 2–8)

Type specimen. IGM 251074 (Duke Uni-versity field no. 90-23), a mandible, preserv-ing the fused symphysis, right corpus andportions of the ascending ramus, left I1, andright C1–M2. Dental and gnathic dimensionsare provided in Table 1.

Horizon and locality. The type is fromDuke locality 32, in the El Cardon Red Beds,Cerro Colorado Member, Villavieja Forma-tion, Honda Group, Colombia (following geo-logical terms of Guerrero, 1996). The fossilif-erous horizon lies immediately below the

San Francisco Sandstone, dated to 12.8(60.2) Mya by the Argon40/Argon39 method(Flynn et al., 1996; Guerrero, 1996). Thetype specimen of Nuciruptor is thereforeapproximately 0.5 myr younger than theholotype of Cebupithecia, which comes fromthe Monkey Beds of the Villavieja Forma-tion. Locality 32 also has produced a man-dible and associated talus, many dentalspecimens, and an isolated tibia of Neo-saimiri fieldsi (5Laventiana annectens) aswell as an isolated talus referred to Aotusdindensis (Gebo et al., 1990;MeldrumandKay,1996; Rosenberger et al., 1991; Takai, 1994).

Diagnosis. A Pithecia-sized platyrrhinesharing with the living Pitheciini styliform,moderately high-crowned mandibular inci-sors; molars having trigonids and talonids ofsimilar height, shallow hypoflexids and re-duced posterior trigonid walls. Distinct from,and more primitive than, living Pitheciini inlacking an enlarged P2; lacking molarizationof P3–4; in having weak hypoconids on P3–4(versus strong, large hypoconids), and inlacking premolar andmolar enamel crenula-tion. In these features,Nuciruptor comparesfavorably with Callicebus. Distinct from liv-ing pitheciins andCebupithecia in having noincisor-canine diastema, in possessing a ca-nine with a rounded lingual crest and awell-developed heel, and in having molarslacking buccal cingulum, and mandible withamore acute symphyseal angle and rudimen-tary genial fossa. Nuciruptor is also distin-guished fromCebupithecia by having amuchlarger alveolus for M3, implying reduction ofthe third mandibular molar inCebupithecia,but not inNuciruptor.Nuciruptor differs from Callicebus by hav-

ing higher-crowned incisors, a more project-

TABLE 1. Selected dental metrics of the type specimenof Nuciruptor rubricae, gen. et sp. nov. (IGM 251074)

Crown Length (md) Width (bl) Height1

I1 1.85 3.19 5.92C1 3.18 4.60 6.46P2 2.66 3.48 3.82P3 2.93 3.49 3.04P4 3.10 3.43 2.78M1 3.94 3.93 2.60M2 4.09 3.80 2.50

1 Measured from the buccal cervical margin. md 1 mesiodistal;bl, buccolingual. All measurements in mm.

409NEW FOSSIL PITHECIIN PRIMATE

ing canine, and less trenchant premolar andmolar cresting. Nuciruptor differs from Mo-hanamico in having a posteriorly deepeningmandible, more compressed and higher-crowned incisors, and more bunodont molars.Nuciruptor is distinguished fromSoriacebus inhaving a proportionately much smaller I1, ca-nine, and P2, compared with molar size.

Etymology. From the Latin rubrica,mean-ing ‘‘red earth,’’ with reference to the redsediments of the El Cardon Red Beds.

DESCRIPTION

Comparisons and contrasts are empha-sized between Nuciruptor and the roughlycontemporary Cebupithecia, establishing thedistinctness of the two, and are generally re-stricted to the extant pitheciins in this section.Further comparisonswithCallicebus andaddi-tional selected taxa (Soriacebus, Mohanamico)are relegated to subsequent sections.

Mandible

(Figs. 2–4)The specimen preserves the symphysis,

right mandibular corpus and a portion of theascending ramus. The corpus is less robustthan that of Cebupithecia. It is both longer,measuring 23% longer from I1 to M3, andshallower, approximately 13.0 mm at thelevel of P2 compared to 16.6 mm in Cebupi-thecia. The 13.0 mm value for the Nucirup-tor reconstruction should be taken as aminimum. Distally, the corpus deepensmod-erately, and the inferior border has a slightsinusoidal curve. The symphysis is pre-served, as well asmost of the alveolus for theleft central incisor. The external profile ofthe symphysis is more inclined than inCebupithecia, forming an angle with theestimated basal mandibular plane of ap-proximately 35° compared with an esti-mated value of 50° for Cebupithecia. Both ofthese estimated values fall within the ex-treme upper and lower limits for a largesample of Pithecia species (range 30°–57°,n 5 205,Hershkovitz, 1987). The genial fossaand digastric grooves are rudimentary, incontrast toCebupitheciawhere they are welldeveloped. The ascending ramus arises dis-tal to the alveolus for M3 in contrast toCebupitheciawhere theM3 alveolus is nearly

hidden by the ascending ramus. Table 2summarizes the traits discussed above.

Incisors

(Figs. 2, 4, 5)A pattern of derived features of the ante-

rior dentition distinguish the living pitheci-ins from other extant platyrrhines. The lowerincisors are procumbent, styliform and highcrowned (elongate), with indistinct lingualcingula and a reduced or absent lingual heel.The lower incisor roots and crowns are com-pressedmesiodistally. InCacajao andChiro-potes, the central incisors are much smallerthan the lateral incisors, whereas in Pithe-cia, the disparity in the size of the centraland lateral incisors is less. InCallicebus, theincisors are nearly subequal.InNuciruptor, the crown of the left central

incisor is very styliform, and of a heightcomparable to Pithecia, and less elongatedthan those ofChiropotes orCacajao.There isno lingual cingulum and only slight develop-ment of the lingual heel, comparable toCallicebus. The alveoli of the central andlateral incisors are nearly equal in size,another similarity to Pithecia and Callice-bus, as distinct from Chiropotes and Caca-jao. Only the roots of the incisors are pre-served in Cebupithecia: the alveoli of thecentral incisors are considerably smallerthan those of the lateral incisors.

Canine

(Figs. 2–4, 6)In living pitheciins, a diastema separates

the mandibular canine from the procumbentincisor battery. Additionally, in Cacajao andChiropotes, the maxillary and the mandibu-

TABLE 2. Contrasts in mandibularform distinguishing Nuciruptor rubricae

and Cebupithecia sarmientoi

TraitNuciruptorrubricae

Cebupitheciasarmientoi

Corpus robusticity slight moderateDepth at P2 13.0 mm 16.6 mmToothrow length 28.6 mm 26.3 mmSymphyseal angle 35° 50°Genial fossa rudimentary well-developedIncisor row more transverse I2 more set back

from I1Incisor canine dia-stema

none weak

Ascending ramus distal to M3 lateral to M3


lar canines are exceptionally large, splayedand chisel-like in both sexes. Sexual dimor-phism in the linear occlusal dimensions ofthe mandibular canines, however, ranges upto 22% in Cacajao to a low of 5% to 6% inChiropotes. The lingual crest (entocristid) isvery prominent and sharp, producing a trian-gular cross-sectional shape to the caninecrown. Pithecia, and specifically the Pitheciapithecia species group (P. p. pithecia and P.

p. chrysocephala, after Hershkovitz, 1987),presents the most primitive morphology inthat the entocristid tends to be concave inprofile and end at a noticeable distostylid,supported on a small lingual heel of thecanine crown. In the P. monachus speciesgroup (P.monachus, P. irrorata, P. aequatori-alis, andP. albicans, afterHershkovitz, 1987)as also in Chiropotes, and Cacajao, the ento-cristid is sharper, convex in profile and passesmesial to a small distal cusp. There is no crownheel due to expanded convex entocristid.In Nuciruptor, there appears to have been

only a very small (or no) incisor-caninediastema as occurs inCebupithecia andmod-ern pitheciins. The mandibular canine isvertically projecting, not splayed as in Ce-bupithecia and the modern pitheciines. It issmaller and much less chisel-like than Ce-

Fig. 2. Reconstructed mandible and dentition ofNuciruptor rubricae (IGM 251074) as seen in (a) occlu-sal, (b) buccal, (c) lingual, and (d) occlusolingual views.Scale bar equals 5.0 mm.

Fig. 3. Reconstructed mandibular profiles of (a) Nu-ciruptor and (b) Cebupithecia, based on the type speci-mens IGM251074 andUCMP38762, respectively. Recon-structed portions are indicated by stippling. Scale barequals 5.0 mm.


bupithecia, or most living pitheciins, except-ing some Pithecia and Callicebus, having arounded concave entocristid ending in adistostylid on the lingual heel. The lingualcingulum is complete. Awell-marked honingfacet for the upper canine is present. Thistooth most approaches the condition seen insome Pithecia pithecia, as described above,whereas Cebupithecia resembles the conditionseen in P. monachus, Chiropotes, and Cacajao.Given the lack of any apparent sexual

dimorphism in shape (though not in size) inthe highly specialized mandibular caninesof extant pitheciins, the marked distinctionsin canine morphology between Nuciruptorand Cebupithecia, together with the numer-ous distinctions in mandibular morphology,it seems reasonable to rule out the possibil-ity that these represent male and femalespecimens of a single pitheciin taxon.

Premolars

(Figs. 3, 7–9)The combined features of the premolar

row of Nuciruptor is distinct from the living

pitheciin clade. The P2s are massive in bothsexes and project above the level of the otherpremolars. The paracristid is elongated andmay be inflated to form a modified honingplatform for the large splayed triangularupper canine. The P2 has a sharply raisedprotocristid that usually supports a smallbut distinct metaconid. The P3–4 are molari-form in that the talonid is longer than thetrigonid and is bounded bucally by a largehypoconid. The premolar enamel often iscrenulated.Nuciruptor does not conform to this pat-

tern in that the P2 protoconid is not massive,nor does it project appreciably above thelevel of the other premolars. The preproto-cristid is not elongate, nor is that part of thetooth inflated as in living pitheciins. Thereis very little evidence of honing wear by theupper canine, suggesting an only moder-ately projecting, or splayed upper canine. Inthe P2 ofNuciruptor, the protocristid is weakand a metaconid is absent. The trigonid issteep and open lingually as inPitheciamona-chus and Chiropotes satanas; in Cacajao

Fig. 4. Comparison of the occlusal views of the mandibular dentitions of (a) Cebupithecia and (b) Nuciruptor.Scale bar equals 5.0 mm.


there is a strong lingual cingulum on thetrigonid.Adiscrete entoconid is present. TheP2 of Cebupithecia is not preserved andtherefore no direct comparisons can bemadewith Nuciruptor. However, the small alveo-lus for P2 in Cebupithecia resembles that ofNuciruptor, as distinct from the large P2s ofextent pitheciins.The P3 metaconid ofNuciruptor is smaller

and not as widely spaced from the protoco-nid compared with living pitheciins andmore closely resembles the condition in Ce-bupithecia. The trigonid basin is steeplysloped lingually, but enclosed lingually by aslight marginal crest. The talonid is shortmesiodistally, and buccolingually com-pressed. The hypoconid is small. The entoco-nid is present, but does not stand out on thelingual talonid marginal crest. The P3 ofNuciruptor differs markedly from that ofCebupithecia in that the posterior trigonid

wall of the former is deeply notched. Nucir-uptor also displays slightlymore buccal flare.The P4 metaconid of Nuciruptor is larger

and more widely spaced than on the P3, butstill not to the extent seen in living pitheci-ins. In Cebupithecia, the cusps are moreclosely approximated. The trigonid is morehorizontal and enclosed by a more promi-nent marginal crest, as in living pitheciines.The posterior trigonid wall is deeply notched(Figs. 7–9). The talonid is wider mesiodis-tally than the trigonid and bounded by adiscrete entoconid, small hypoconid and aweak hypocristid. This is a resemblance toCebupithecia, but contrasts with the condi-tion in living pitheciins in which the talonidis very expanded, leaving a molarized tooth.While buccal inflation of the crown is evi-dent on all premolars, no cingulum is pre-sent. Although the P4 talonid is slightlyenlarged, the occlusal area of the premolar

Fig. 5. Scanning electron micrographs (SEM) of the left central mandibular incisor of Nuciruptor rubricae (IGM251074) seen in (a) mesiodistal and (b) buccolingual view. Scale bar equals 1.0 mm.


row of Nuciruptor, as also Cebupithecia,remains quite small relative to themolar occlu-sal area, and displays little molarization socharacteristic of the extant pitheciins.

Molars

(Figs. 3, 7–9)The molars of living pitheciins are charac-

terized by virtually no disparity of heightbetween the trigonid and talonid, with theintervening protocristid represented by alow, often indistinct, ridge. The trigonid isvery short mesiodistally, but just as broadbuccolingually as the talonid. The principalmolar cusps (except the paraconid and hypo-conulid, which are absent) are marginalizedand blended with the margins of the crown

leaving the crown generally flat and steepsided. The buccal crests are alignedmesiodis-tally so that the hypoflexid is very shallow.The crown surface of the enamel is oftencrenulated. M3s show little or no reductionin occlusal area relative to M1–2 (Fig. 4 inKay, 1994).In Nuciruptor, only M1–2 are preserved.

The molar crown relief is low, but not as flatas in living pitheciins, while more so than inCallicebus. The enamel lacks any crenula-tion. As in living pitheciines, paraconids arelacking, but the trigonids are very narrowmesiodistally (vs. broad). The metaconidsstand taller than the protoconids and areonly slightly distal to the protoconid. Proto-conids are more bulbous than in living

Fig. 6. SEM of the right mandibular canine of (a, b) Nuciruptor, (c, d) Cebupithecia and (e, f)Mohanamico. Toprow (a, c, e) depict buccal views and bottom row (b, d, f) depict lingual views. Scale equals 1.0 mm.


pitheciin. The posterior trigonid walls andprotocristids are very low, but intermediateto the condition seen in living pitheciins andCallicebus, and are deeply notched by adistinct protoconid/metaconid sulcus. Thetalonids are raised and shallow. The entoco-nids are large and more discrete than inliving pitheciins and Cebupithecia, but less

so than in Callicebus. As in living pitheciins,the cristid obliqua are straight and roundedand reach the trigonid walls distal to theprotoconids, but are more oblique than inliving pitheciins. The hypoflexid is shal-lower than in Callicebus, but not to theextent seen in living pitheciins. No buccalcingulum is present.

Fig. 7. SEM of the postcanine dentition seen in lingual view of (a) Nuciruptor, (b) Cebupithecia, and (c)Mohanamico. Scale equals 1.0 mm.


Compared with Nuciruptor, the M1 of Ce-bupithecia (the only molar preserved in thattaxon) more closely resembles extantpitheciin M1s in that the trigonid is quitebroad, the protocristid is low and the buccalcrests are aligned mesiodistally so that thehypoflexid is extremely shallow. On the other

hand, Cebupithecia resembles Nuciruptor,but not living pitheciins, in having somedisparity in height between the trigonid andtalonid, a mesiodistally slightly longer trigo-nid (compared with the talonid), the principalmolar cusps not so marginalized nor blendedwith the margins of the crown leaving the

Fig. 8. SEM of the postcanine dentition seen in occlusal view, of (a) Nuciruptor, (b) Cebupithecia (reversed), and(c)Mohanamico. Scale equals 1.0 mm.


crownmarginsmoresloping.Further, thecrownsurface of the enamel is not crenulated.The M3 of Nuciruptor is missing, but its

single-rooted alveolus is preserved for com-parison with that of M2. Cebupithecia alsohad a single-rooted M3. Hershkovitz (1987)reports that the third molar of Pithecia canbe either single- or double-rooted, as is alsothe case in Callicebus. In Nuciruptor, theratio of M3 to M2 alveolar area (greatest m-dlength times greatest b-l length) is 0.67,compared with 0.31 for Cebupithecia. TheM3 alveolus in Nuciruptor is approximately95% of the m-d length of the M2 alveolus. Itlies nearly in line with the tooth row, withonly a slight lingual inclination. This con-trasts with the condition in Cebupithecia,where the M3 alveolus has a strong lingualangulation (Fig. 4).

Table 3 summarizes the principal distinc-tions in dental morphology and serves toemphasize the contrasts between Nucirup-tor and Cebupithecia.

Anomalies

(Figs. 1, 8)A localized enamel hypoplasia is seen as a

pitted line, or crease, across the buccal sur-face of the canine and premolars. This prob-ably occurred as the result of a systemicdisturbance during the time of crown forma-tion. The position of the crease on the crownsurfaces indicates the relative state of devel-opment of the crowns when the disturbanceoccurred: P4 was the most developed, fol-lowed by P3, P2 and finally C1. However,without the lateral incisor and third molar

Fig. 9. SEM of the postcanine dentition seen in lingual view, of (a)Nuciruptor and (b)Mohanamico. Scale equals1.0 mm.


little can be deduced about the relativeeruption sequence.

cf. NUCIRUPTORIGM-KU 8602

This is a maxilla with right C1 and P2recovered from the El Dinde area of theMonkey Unit (Setoguchi et al., 1987) andreferred to Cebupithecia sarmientoi on thebasis of similarities in size and morphologybetween its canine and that of the holotypespecimen of Cebupithecia (UCMP 38762,Fig. 10) but the presence of another pitheciinof similar size leaves open the possibilitythat IGM KU-8602 could belong toNucirup-tor. Setoguchi et al. (1987) acknowledgesubtle differences between IGM-KU 8602and UCMP 38762 that leave open the possi-bility that these specimens represent twotaxa. Such a possibility remains conjectural,however, without an associated upper andlower dentition ofNuciruptor.

IGM 184074

This is an isolated left talus recoveredfrom Duke locality 43, El Cardon Red Beds,Cerro Colorado Member, Villavieja Forma-tion (Ford et al., 1991). This locality isimmediately adjacent to, and penecontempo-raneous with, Duke locality 32, where thetype of Nuciruptor was recovered. The talusis well preserved with superficial erosion ofthe head, posterior tubercles and calcaneal

facets. It measures approximately 14.0 mmin length. An analysis of the correlation oftalar length withM1mesiodistal length for alarge sample of platyrrhines (Meldrum,1990) indicates that this talus is of an appro-priate size to belong to Nuciruptor. In gen-eral form, it is very similar to the talus of thetype specimen of Cebupithecia, differing byhaving a slightly narrower head and neckand a slightly more rounded lateral troch-lear crest. These differences could well beaccommodated within intragroup variation.Therefore, on the basis of provenience, appro-priate size, and comparable morphology, it istempting to associate this talus with theclosely related pitheciin, Nuciruptor. How-ever, allocation of this specimen and infer-ences about its functional morphology mustawait complete analysis (Ford et al., inprep.).

IGM 184667

This is a partial pelvis and pelvic limbsrecovered from Duke locality 79, in thePerico Member, below the Chunchullo Sand-stone, La Victoria Formation (Meldrum etal., 1990; Meldrum and Kay, 1996). IGM184667 has been referred to Cebupithecia onthe basis of similarities to the holotypeUCMP 38762. However, owing to the lack ofassociated dental material, and the pres-ence of a second pitheciine in the La Ventan

TABLE 3. Summary of dental contrasts distinguishing Nuciruptor rubricae from Cebupithecia sarmientoi,with comparisons to other selected pitheciines

TraitCallicebustorquatus

Nuciruptorrubricae

Cebupitheciasarmientoi

Pitheciapithecia

Relative size of I1–2 I1 , I2 I1 5 #I2 I1 9 I2 I1 , I2Canine shape gracile; rounded crest;

lingual heelgracile; rounded crest;lingual heel

robust; triangular;chisel-like

robust; triangular;chisel-like

P3 metaconid small small moderate largeP3–4 posterior trigonidwall

notched deeply notched not notched not notched

P3 hypoconid absent absent present/doesn’t standout

large

P4 entoconid small discrete cusp small discrete cusp present/doesn’t standout

large

M1 posterior trigonidwall

notched notched not notched not notched

M1 postentoconidsulcus

absent absent present present

M1 buccal cingulum absent absent present/faint absentRatio M3/2 alveolararea

moderate 0.67 0.31 high

M3 alveolus orienta-tion

in line with toothrow in line with toothrow strong lingual angula-tion

slight angulation


primate fauna, the possibility exists thatthis specimen representsNuciruptor.

CHARACTER EVOLUTIONIN PITHECIINAE

In the following discussion of characterevolution in Pitheciinae, we first describethe dentition in the living taxa. Next wetake up the phyletic position of Nuciruptor,and Cebupithecia. Several nodes and lin-eage segments are numbered in reference tocladogenesis of Pitheciinae (Fig. 11). Clado-genesis and character evolution of livingpitheciines are described elsewhere (Kay,1990).

Node 1

The hypothetical last common ancestor ofPitheciinae and its closest living outgroup(Alouatta, Ateles, Lagothrix, and Brachyte-les) had vertically implanted, low-crowned,and broadly spatulate incisors with promi-nent lingual heels. I1 was smaller than I2.There was no diastema separating the lowerincisors from the moderately large, verti-cally projecting lower canine. The lattertooth had a well-developed paracristid and arounded, indistinct protocristid.The cheek teeth were set in a moderately

deep jaw that did not deepen appreciably

Fig. 10. SEM of the maxillary canine and P2 attributed to Cebupithecia (IGM KU 8602) seen in (a) occlusal and(b) lingual views. Maxillary canine of type of Cebupithecia (UCMP 38762) seen in (c) occlusal and (d) lingual views.


posteriorly. P2 was a simple tooth that lackeda prominent protocristid and had nometaco-nid; it was a nonprojecting tooth that blendedsmoothly in size relative to the other premo-lars. P3 and P4 had metaconids of increasingsize distally. The trigonids dominated theseteeth, whereas the talonids were small. Noneof the premolars bulge bucally towards theircemento-enamel junctions.The molars had low crowns with trigonids

slightly higher than talonids. Molar enamelwas smooth rather than crenulated. Molartrigonids were narrow buccolingually andshort mesiodistally compared with the tal-onids. Trigonids are separated from talonidsby a distinct raised protocristid. Molar cuspswere inset from the buccal and lingual mar-gins of the teeth and shearing features weremoderately developed with moderately deephypoflexids. Molar entoconids were well de-veloped and stood out on the distolingualcrown margin. The posterior marginal crestof the molar crowns was not disrupted by a

postentoconid sulcus. A hypoconulid, if pre-sent, was small.The upper incisors were vertically im-

planted. The first upper incisor was slightlylarger than the second. The second upperincisor flared from cervix to crown apex.Canines were not laterally splayed. Upperincisors, canines, and premolars had moder-ate lingual cingula.Amoderately large hypo-cone was present on the low distolingualcingulum of P4.

Lineage segment 1

This is the lineage segment leading tonode 2, the last common ancestor of livingPitheciinae, i.e., of Callicebus and thepitheciins. In this lineage segment the lowerincisors became more high crowned andmore narrowly spatulate. Jaw depth in-creased markedly posteriorly under the mo-lars. A basal tubercle evolved on the cingu-lum of the upper central incisors. (Thistubercle is also developed in Lagothrix,Brachyteles and Ateles, so it may have char-acterized a more inclusive clade of platyr-rhines.)

Lineage segment 2

This is the stem lineage leading toCallice-bus the posterior marginal crest of the lowermolar crowns was disrupted by a strongpostentoconid sulcus and theM1–2 hypoconu-lids, are expanded in size. I1–2, canine, andpremolar lingual cingulum became muchstronger.

Lineage segment 3

In this lineage segment leading to the lastcommon ancestor of living pitheciins, thelower incisors became very high-crowned,procumbently implanted, and mesiodistallycompressed, and lost their lingual heels. Adiastema separated the lower incisors fromthe larger vertically projecting lower canine.The canine protocristid developed into astrong sharp lingually oriented crest.P2 developed a small metaconid; it became

amassive tooth that projects above the otherpremolars. P3 and P4 talonids became muchlarger, with well-developed hypoconids and en-toconids. The premolar slopes bulge buccallytowards their cemento-enamel junctions.

Fig. 11. Cladogenesis within Pitheciinae in whichNuciruptor figures as the sister taxon to the cladecomprising Cebupithecia and the living pitheciine gen-era. Nodes 1–3 represent branch points on a cladogramfor the last common ancestors of (1) Pitheciidae andAtelidae; (2) Pitheciidae; and (3) Pithecini. Featuresdefining nodes and lineage segments are described inthe text.


Themolar trigonidswere reduced in heightto become the same height as the talonids.Molar enamel developed crenulation. Molartrigonids were broadened. Trigonid-talonidseparation became less distinct and the pro-tocristid was weakened. Molar cusps be-came marginalized and shearing featuresbecame indistinct, with hypoflexids veryshallow. Molar entoconids were reduced insize and blended with the distolingual crownmargin. Hypoconulids were lost.The upper incisors became more procum-

bent. I1 is much larger than I2. The lateralmargins of I2 became straight-sided; that is,the crown was not much wider than the rootat the cervix. The canines developed a lat-eral splaying. P4 hypocones were lost.

Phyletic position of Nuciruptor

The mandibular and lower dental charac-ters of Nuciruptor give a clear indicationthat this taxon fits along lineage segment 3in the above scenario (Fig. 11); that is, that itpossesses a combination of features indicat-ing a closer relationship with living pitheci-ins than to Callicebus. For example, Nucir-uptor resembles living pitheciins in havingelongate, procumbent, and styliform lowerincisors with very weak lingual heels. More-over, as in living pitheciins, the incisors areset in a procumbently oriented mandibularsymphysis, and its mandibular corpus deep-ens appreciably under the molars.At the same time, Nuciruptor does not

possess several of the distinctive synapomor-phies of extant pitheciins. Nuciruptor re-mains more primitive than living pitheciinsin that no diastema separates its lowerincisors from the canine. Its lower caninesretain the primitive structure in not havinga sharply defined protocristid. P2 is not arobust or high-crowned tooth and does nothave a metaconid. Nor are the other premo-lars molarized by the addition of large tal-onids. The molars of Nuciruptor retain thestructures evolved in lineage segment 1 butlack the progressive modifications that musthave evolved along lineage segment 3:Nucir-uptor has smooth rather than crenulateenamel, its trigonids are set off from thetalonids by the protocristids, the trigonidsare relatively narrower and the molar cuspsare situated in from the margins of the

crowns.Nuciruptor does show some progres-sivemolar features resembling living pitheci-ines such as some diminution ofmolar shear-ing (see below) and shallowing of the molarhypoflexids.

Phyletic position of Cebupithecia

As already widely reported in the litera-ture,Cebupithecia sarmientoi displays amo-saic of derived features of extant pitheciinsand derived features of the pitheciines (in-cluding Callicebus), indicating that thistaxon fits along lineage segment 3 in theabove scenario (Fig. 11). The extraordinarilycomplete postcranial remains bear furtherphenetic resemblances to Pithecia, but lackmany of the derived characters of the limbsthat characterize extant pitheciins (Davis,1987, 1988; Fleagle and Meldrum, 1988;Ford, 1986, 1990; Meldrum, 1993; Meldrumand Fleagle, 1988; Meldrum and Kay, 1996;Meldrum and Lemelin, 1991). The pre-served portions of the dentition clearly dis-play pitheciin synapomorphies in the incisor-canine complex, andmandibularmorphology,but to a lesser degree in the postcanine teeth(Kay, 1990; Orlosky, 1973; Rosenberger,1979).In several ways, Cebupithecia is more

derived than Nuciruptor in the direction ofliving pitheciins. The lower canines aremoreenlarged and splay laterally. They possessthe distinctive sharp, raised protocristid ofextant pitheciins, lacking in Nuciruptor,making the tooth chisel-like and triangularin cross-section. The molars are further spe-cialized in the direction of living pitheciinshaving reduced trigonid heights and evenmore shallow hypocristids. Taken together,this dental evidence suggests that Nucirup-tor is the sister taxon to the clade of Cebupi-thecia and the extant pitheciins (Fig. 11).Several instances are noted where some

characters do not agree completely with thisinterpretation. For example, I1 is muchsmaller than I2 in Cebupithecia (as judgedfrom the size of the root cross-section),Caca-jao, and Chiropotes, but not in Pithecia. Thissuggests either that I2 has reenlarged inPithecia or been reduced in size indepen-dently in Cebupithecia and the commonancestor of Cacajao and Chiropotes. Simi-larly, Cebupithecia apparently had more re-


duced M3s than either Nuciruptor or extantpitheciines.We interpret these resemblancesas parallel ‘‘crossing-specializations’’ indicat-ing that Cebupithecia is not a suitable directancestor for the living pitheciins.

Status of Soriacebus and Mohanamico

Two genera of primates, Soriacebus andMohanamico, are considered by some writ-ers to belong in the pitheciin clade. In eachcase, allocation to this clade is far moredoubtful than for either Nuciruptor or Ce-bupithecia. In the case of Soriacebus, whilethe anterior dentition greatly resembles thatof living pitheciins, the cheek teeth show anodd combination of autapomorphies andprimitive platyrrhine or callitrichine traits.The proposed pitheciin resemblences of Mo-hanamico are far less striking, and it alsoshows other apparent primitive platyrrhineand callitrichine traits. While not ruling outthe possibility that either or both taxa ulti-mately may be assignable to Pitheciini, abroader reassessment of fossil recent platyr-rhines will be needed to make such a phylo-genetic allocations more convincing.

Soriacebus ameghinorum. The phyloge-netic position of the Patagonian fossil pri-mate, Soriacebus ameghinorum (earlyMiocene, Pinturas, Santacrucian LandMam-mal Age) is widely debated. Fleagle et al.(1987) draw attention to similarities in themandible and dentition of Soriacebus toseveral platyrrhines and consider severalpossible interpretations of these similari-ties: (1) that Soriacebus is an oddly special-ized callitrichine; (2) that it is a pitheciin; or(3) that it is an early offshoot of all livingplatyrrhines. Fleagle (1990) and Fleagle etal. (1987) withhold an opinion as to therelative merits of these alternatives; Rosen-berger et al. (1990) andTheodor (1995) hold theview that Soriacebus is a pitheciin, whereasKay (1990) has argues that Soriacebus is aprimitive platyrrhine with pitheciine conver-gences. Each of these points of view has meritand each entails substantial homoplasy.In Soriacebus, a suite of mandibular and

dental features bear considerable similarityto callitrichines (Fleagle, 1990; Fleagle etal., 1987). The mandible is V-shaped; thepremolars have reduced metaconids, large

trigonids, and relatively small talonids. Themolars have mesiodistally elongate trigo-nids and very small cingulum-based hypo-cones.Soriacebus resembles pitheciines espe-

cially in the anterior dentition and the lat-eral profile of the mandible (Fleagle, 1990;Fleagle et al., 1987; Kay, 1990; Rosenbergeret al., 1990). Pitheciine resemblances in-clude the possession of a deep mandibularcorpus that deepens posteriorly, having me-siodistally compressed lower incisor roots,and procumbently arranged in a robustman-dibular symphysis. A specimen of Soriace-bus adrianae shows the incisors to havebeen styliform and lacking a heel, as inliving pitheciins (Fleagle, 1990). Also, as inliving pitheciins, P2 is a robust tooth of onlyslightly smaller caliber than the canine,having bulging buccal enamel, and a protoco-nid that projects well above the other cheekteeth. In the molars, the entoconid is re-duced, approaching the condition in pitheci-ins (but also as in callitrichines). Soriacebusis more primitive than living pitheciins (asis Nuciruptor) in lacking a diastema be-tween the lower incisors and canine and inhaving a more vertically implanted, notsplayed, canine root.A third set of structural details of the

premolars and molars of Soriacebus appearsto be primitive for platyrrhines (Fleagle,1990; Kay, 1990), or at least atelids (sensuRosenberger, 1981). In Soriacebus, the P2lacks a metaconid and the P3 metaconid issmall and close to the protoconid; P4 metaco-nid is larger but still compressed against theprotoconid. The M1 metaconid is placed dis-tolingually relative to the protoconid. Also,Soriacebus molars have hypoconulids anddistinct postentoconid sulci running lin-gually to the entoconids. P2–4 have hypo-cones and strong upper premolar lingualcingula.As noted by Fleagle et al. (1987), theupper premolars of Soriacebus are three-rooted.Obviously, Soriacebus cannot at once be a

primitive platyrrhine, a pitheciin, and acallitrichine. With Callicebus securely allo-cated to Pitheciinae (Meldrum, 1995;Schneider et al., 1993, 1995) several appar-ently primitive features of the molars ofSoriacebus might now be regarded as hav-


ing been present in primitive pitheciinesand thus could strengthen the case for itspithecine placement. However, pending abroader phylogenetic analysis including therelevant fossils, it is unclear whether theapparent synapomorphiesSoriacebus shareswith Callicebus actually are synapomor-phies of amore inclusive clade withAlouattaand atelins. Pending such analysis, we willcontinue to interpret Soriacebus as an earlyoffshoot of platyrrhines.

Mohanamico hershkovitzi. Representedby a mandible (Luchterhand et al., 1986),the type specimen (IGM 181500; Figs. 6–9)comes from the Monkey Beds near El Dinde.It was assigned with hesitance to thePitheciinae, while recognizing that it wasnot as specialized as Cebupithecia or theextant pitheciins. In addition, some similari-ties to callitrichines and particularly Cal-limico were noted. A second specimen of aprimate (IGM-KU 8601) of similar size andmorphology to Mohanamico and from thesame stratigraphic level and locality wasdescribed by Setoguchi and Rosenberger(1987) and allocated to a new species ofAotus, A. dindensis.Rosenberger et al. (1990)argue that the phyletic affinities of IGMKU-8601 are (as with other Aotus) withinthe Pitheciinae, whereas IGM186500 shouldbe allied with the callitrichines. Kay (1990)argue that IGMKU-8601shouldbeallocated toMohanamico and emphasized the pitheciin af-finities of both. We still maintain that the twospecimens belong to the same species.Reconsidered in light of the character

evolution described above, a number of fea-tures cited by Kay (1990) to support anaffinity of Mohanamico to the pitheciinsseem less likely. In the referred specimen ofMohanamico (i.e., the type of ‘‘A. dindensis’’)the ventral surface of the orbit closely ap-proximates the maxillary alveolar bone suchthat only a very shallow maxillary sinusextends posterior to the zygomatic arch.Living pitheciins and Callicebus have well-developed maxillary sinuses (Hershkovitz,1977) and personal examination of the typeof Cebupithecia shows it to have had a largemaxillary sinus as well. Both the type andreferred specimen ofMohanamico have jawsthat do not increase in depth posteriorly as

in Callicebus, Nuciruptor, Cebupithecia, andliving pitheciins. While the canine of thetype of Mohanamico is worn in such a wayas to suggest the presence of a sharp trans-verse lower canine crest, as in living pitheci-ins, the less-worn referred specimen has amore rounded crest. While the lower incisorsof the type of Mohanamico are fairly elon-gate, although not as mesiodistally com-pressed as in Callicebus, the referred speci-men has a slightly more low-crownedincisors.WhileMohanamico possesses a pro-jecting P2, this tooth is not massive andmore closely approximates the condition seenin tamarins than in pitheciins.In summary of the above, the addition of

IGM KU-8601 to the hypodigm of Mo-hanamico adds information about the or-bital structure and intraspecific variabilityin the structure of the incisors and canines.Each bit of this new data, considered in lightof what we know about character evolutionin Pitheciinae, especially with the inclusionofCallicebus and the newly describedNucir-uptor, diminishes the likelihood that Mo-hanamico belongs with the Pitheciinae.Other possibilities, including allocation toCallitrichinae, should be reconsidered.

ADAPTATIONS OF NUCIRUPTORBody size

Determination of bodyweight forNucirup-tor is based on its molar occlusal area. Frombody weights of 15 species of female platyr-rhines and molar areas of the same speciesmeasured by Plavcan and Kay (unpublisheddata), the following least-squares regressionwas derived, with an r2 of 0.935:

In female body weight 5

In M1 area (1.565) 1 3.272.

Based on this equation, the estimatedweightof IGM 251074 was 2,044 grams. This issomewhat larger than the estimated weightfor Cebupithecia of 1,792 grams, but bothfall within the reported size ranges of maleand female Pithecia pithecia and female P.monachus (Hershkovitz, 1987).

Dietary patterns

The functional design of the primate den-tition is selectively modified to best deal


with the physical properties of the foods thespecies eats (Anthony andKay, 1993; Fleagleet al., 1996; Kay, 1975; Kay and Anthony,1991; Kay and Covert, 1984; Strait, 1991).One method of quantifying dietary adapta-tion is to measure the relative developmentof the shearing crests on molars, after molarsize has been taken into account. Table 4illustrates the development of molar shear-ing in selected living platyrrhines as a‘‘shearing quotient.’’ (Anthony andKay, 1993;Fleagle et al., 1996). In Figure 12, the shear-ing quotients for living platyrrhine speciesare broken down by dietary preference. Spe-cies that eat considerable amounts of fibrousfoods such as leaves high in cellulose (Al-ouatta) or chitinous insects (Callimico), havewell-developed shearing edges on their mo-lars (large SQs). In contrast, species thatfeed on less fibrous, soft fruits (Ateles) andtree gum (Callithrix) tend to have relativelyflatter teeth, with shorter more rounded

shearing crests. The teeth of species thatspecialize in eating hard seeds or in splittingopen tough, hard fruits (Cebus and thepitheciins Pithecia, Cacajao and Chiropotes)tend to have even less shearing than thesoft-fruit eaters.Nuciruptor and Cebupithecia both have a

suite of dental traits suggesting that theywere specializing in seed predation (Fig. 12).It must be considered, however, that theinterpretation of the dietary adaptations ofthese extinct taxa is each based on singlespecimens and further material is requiredto assess the intragroup variability of thistrait. Both Nuciruptor and Cebupitheciahave very poorly developed shearing on theirmolars, with lower shearing quotients thanany of the living pitheciines. This stronglysuggests that they were masticating hardseeds. However, they lack other of the ex-treme morphological specializations of thepostcanine dentition seen in the living

TABLE 4. The relative development of shearing crests on M1 in platyrrhines1

Taxon NM1

lengthSum,

M1 shearExpectedshear

Shearquotient

Major dietaryfeature

Callimico goeldii 3 2.60 5.48 4.72 16.14 InsectsBrachyteles arachnoides 9 7.22 15.19 3.10 15.93 LeavesAlouatta palliata 10 6.92 13.91 12.56 10.76 LeavesAlouatta caraya 6 6.72 13.09 12.20 7.33 LeavesAlouatta fusca 6 6.70 12.94 12.16 6.42 LeavesAotus trivirgatus 10 3.06 6.16 5.55 10.92 Fruit/LeavesSaimiri sciureus 5 2.87 5.54 5.21 6.36 Insect/FruitLagothrix lagotricha 8 5.47 10.12 9.93 1.94 Fruit/LeavesLeontopithecus rosalia 5 3.09 5.62 5.61 0.22 Fruit/InsectsAteles geoffroyi 10 5.26 9.31 9.55 22.47 FruitCallicebus moloch 10 3.18 5.50 5.77 24.70 FruitSaguinas mystax 5 2.52 4.03 4.57 211.88 Fruit/InsectsCallithrix argentata 4 2.22 4.08 4.03 1.27 Fruit/GumCebuella pygmaea 4 1.78 3.26 3.23 0.92 Gum/FruitPithecia monachus 4 4.00 6.78 7.26 26.60 Fruit/SeedsCebus apella 5 4.79 7.71 8.69 211.31 Fruit/SeedsChiropotes satanas 5 3.64 5.50 6.61 215.53 Seeds/FruitCacajao melanocephalus 2 3.97 5.90 7.20 217.70 Seeds/FruitSoriacebus ameghinorum 1 3.60 5.87 6.53 210.15 Fruit/SeedsSoriacebus adriane 1 3.23 4.67 5.86 220.33 Seeds/Fruit‘‘Aotus dindensis’’ 1 3.23 6.14 5.86 4.74 Insects/FruitMohanamico hershkovitzi 1 3.20 4.96 5.81 214.59 Fruit/SeedsCebupithecia sarmientoi 1 3.52 5.15 6.39 219.38 Seeds/FruitNuciruptor rubricae 1 4.00 5.47 7.26 224.65 Seeds/Fruit1 The estimate of shearing development is based on measurements of six lower molar crests (see Kay, 1975 for further details). A linewas assigned to a bivariate cluster of the natural log of M1 length (lnML) versus the natural log of the sum of the measured shearingcrests (lnSH). The line was assigned a slope of 1.0 (slope of isometry) and passed through the mean lnML and mean lnSH for extanttaxa. The equation expressing this line is:

ln SH 5 1.0(ln ML) 1 0.596

For each taxon, the expected lnSH was calculated from this equation. The observed (measured) lnSH for each species was comparedwith the expected and expressed as a residual (Shear Quotient, or SQ):

SQ 5 100 p (observed-expected)/(expected)

Extant and extinct taxa are listed separately according to dietary categories (Fleagle et al., 1996). Diet is inferred for extinct taxa bycomparison to a modern analog with a similar SQ. All measurements are in millimeters.


pitheciins, e.g., crenulated enamel and mo-larization of the premolar row.The differences in dietary patterns also

are reflected in the structure of the anteriordentition. In the case of living pitheciins,these teeth are highly modified for openingthe hard or tough pericarp preceding masti-cation of the pliable seed (Kay, 1990; Kinzey,

1987; Kinzey and Norconk, 1990). The inci-sors are elongated and mesiodistally com-pressed to form a gouge, while the caninesare enlarged, splayed and chisel-shaped.The extinct pitheciins Cebupithecia andNu-ciruptor show more similarities to the livingpitheciins in these features of the anteriordentition than in the less-specialized mor-phology of their molars. Although the inci-sors of Cebupithecia are not preserved, it isclear from the alveoli that they were com-pressed mesiodistally and the central werenarrower and set slightly forward relative tothe lateral incisors. Furthermore, it can bereasonably deduced from the orientation ofthe preserved portions of the upper centralincisor that the mandibular incisors hadhigh crowns. While the mandibular canineof Cebupithecia closely resembles thestrongly crested chisel-like form of the livingpitheciines, the preserved maxillary caninelacks the distinctive triangular cross-sectionfound in the upper canines of living pitheci-ins.Nuciruptor also shows the pitheciine inci-

sal structure of laterally compressed styli-form incisors, although the crowns are notas elongate and the alveoli of the central andlateral mandibular incisors appear to havebeen approximately subequal. The caninesof Nuciruptor are not as specialized, i.e.,chisel-like, as are those of Cebupithecia orliving pitheciins. Instead the entocristid isweaker and rounded, leaving a well devel-oped lingual heel.From this combination of dental traits a

number of inferences can be made about theevolution of pitheciin dental adaptations.First, dental specializations of extant pitheci-ins may have evolved in a mosaic fashion.Asin Cebupithecia, the anterior dentition ofNuciruptor shows specializations for open-ing tough seed husks but not the characteris-tic pitheciine features of the postcanine den-tition associated with seed crushing. AsKinzey (1992; p. 505) has suggested, ‘‘themore developed shared features in thePitheciinae are found in the anterior denti-tion; it is the anterior dentition that isexpected to evolve sclerocarpic foraging fea-tures first.’’ Second, the dental morphologyof Nuciruptor further supports the scenarioset forth by Kinzey (1992) that the compres-

Fig. 12. Estimated shearing-crest development onthe lower first molars of species of eighteen species ofliving platyrrhines. A shearing quotient is calculatedfrom measurements of six lower molar crests (crests1–6; for anatomical details see Kay, 1975, 1977). A linewas assigned to a bivariate cluster of the natural log ofM1 length (InML) versus the natural log of the sum ofthe measured shearing crests (InSH). The line is as-signed a slope of 1.0 (slope of isometry) and passedthrough themean InML andmean InSH for extant taxa.The equation expressing this line is:

ln SH - 1.0 (ln ML) 1 0.596.

For each taxon, the expected InSH is calculated fromthis equation. The observed (measured) InSH for eachspecies is compared with the expected and expressed asa residual (Shear Quotient, or SQ):

SQ 5 100 p (observed-expected)/(expected).

Extant taxa used are: Callimico goeldii, Brachytelesarachnoides, Alouatta palliata, Alouatta caraya, Al-ouatta fusca, Aotus trivirgatus, Saimiri sciureus, Lago-thrix lagotricha, Leontopithecus rosalia, Ateles geoffroyi,Callicebus moloch, Saguinas mystax, Callithrix argen-tata, Cebuella pygmaea, Pithecia monachus, Cebusapella, Chiropotes satanas, Cacajao melanocephalus.Data are abstracted from Fleagle et al. (1996).


sion and raised crown height of the incisorbattery together with increased canine ro-busticty preceded specialization of the chisel-like canine morphology. Third, the combina-tion of a more blade-like maxillary caninewith a more triangular chisel-like mandibu-lar canine in Cebupithecia, and possibly to alesser extent Nuciruptor, indicates that thehighly derived features of the pitheciin ca-nines first evolved in the mandibular denti-tion.We concur withKinzey (1992) thatCallice-

bus-Pithecia-Chiropotes-Cacajao represent amorphocline of increasingly specialized den-tal features for sclerocarpic foraging. In fact,the mosaic of features displayed byNucirup-tor would seem to bear out Kinzey’s predic-tion that specializations of the anterior den-tition would precede those of the postcaninedentition in the evolution of sclerocarpy.

CONCLUSIONS

The array of taxa comprising the livingPitheciinae, Callicebus-Pithecia-Chiropotes-Cacajao, represents amorphocline of increas-ingly specialized dental adaptations forsclerocarpy.Nuciruptor rubricae represents a new ge-

nus and species of pitheciin, being the sistertaxon to the clade consisting of Cebupitheciaand the extant pitheciin genera, Pithecia,Chiropotes and Cacajao.The unique combinations of dental traits

displayed by Nuciruptor and Cebupitheciaindicate that the dental specializations forseed predation, as seen in the extant pitheci-ins, evolved in a mosaic fashion.The morphology of Nuciruptor and recog-

nition of the pitheciine status of Callicebusdiminishes support to the hypothesis thatMohanamico is a primitive pitheciin. Wewithhold an opinion about the phylogeneticstatus of Soriacebus pending a full analysisof Miocene platyrrhines.

ACKNOWLEDGMENTS

We acknowledge the cooperation and sup-port of the Instituto Nacional de Investiga-ciones Geologica-Mineras (INGEOMINAS).We thank Matt Cartmill, Derek Johnson,the editors and anonymous reviewers forhelpful comments and discussion.

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