AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 56335-257 (1981) Cranial Morphology and Adaptations in Eocene Adapidae. II. The Cambridge Skull of Adapis parisiensis PHILIP n. GINGERICH AND ROBERT n. MARTIN Museum of Paleontology, The University of Michigan, Ann Arbor, Michigan 48109 (P.D.G.),and Department of Anthropology, University College London, Gower Street, W.C. 1, London, U.K. (R.D.M.) KEY WORDS Cranial anatomy, Eocene primates, Adapidae, Adapis, Brain size ABSTRACT One of the most complete skulls of the early primate Adapis parisiensis is in the collection of the Department of Zoology, Cambridge Universi- ty. This exceptionally well-preservedmale skull, from Quercy in southern France, is important in showing relatively small orbits that are highly convergent, a distinct ethmoid component in the medial orbital wall, very small infraorbital foramina, a well-preserved auditory region with the stapedial canal about twice the diameter of the canal for the promontory artery, and a well-preserved braincase 8.8 cm3 in endocranial volume. The frontal lobe of the brain in the Cambridge skull described here is less expanded than that reported previously in a British Museum skull. The average body weight OfAdapisparisiensis is estimated to have been about 2.0 kg, and that of Adapis magnus is estimated to have been about 8.4 to 9.0 kg. The encephalization quotient (EQ) ofAdapisparisiensis is estimated to have been 0.45, which is well below the range found in modern prosimians. There is some indica- tion that the size of the foramen magnum has increased with increasing brain size during primate evo1ution.Adapisparisiensisappears to have been a medium-sized, visually oriented, diurnal, sexually dimorphic arboreal folivore. The first two specimens OfAdapisparisiensis Koenigswald (1979),and others. These new col- to be discovered, a crushed palate and associ- lections have much better stratigraphic docu- ated mandible, were described by Cuvier in mentation than the earlier assemblages from 1812. Some 60 years later, Delfortrie (1873) Quercy, and it is now possible to trace a prob- and Gervais (1873) recognized that Adapis is able evolutionary sequence in Europe from the most similar, among living mammals, to large species Adapis magnus through an in- lemuriform primates. Stehlin’s (1912) exten- termediate species, Adapis stintoni, to Adapis sive monograph on Adapis further substanti- parisiensis (see Table 1 and Gingerich, 1981: ated this resemblance, as did Gregory’s (1920) Fig. 1).Adapis magnus is sometimes placed in monograph on Notharctus. Stehlin illustrated a separate genus or subgenus ‘Zeptadapis,” but several nearly complete skulls of both Adapis that seems unnecessary now that the phyloge- parisiensis and Adapis magnus, derived from netic relationships of the species involved are the Quercy deposits of France, and discussed better documented. the phylogenetic history of European Adapidae Adapis parisiensis is poorly known postcra- in as much detail as was possible at that time. nially, but some 20 or more skulls and partial Since 1912,relatively little has been added to skulls have been found, all collected during the our knowledge of the osteology of Adapis, but nineteenth century from the Phosphorites du much additional dental material ofAdapis and Quercy in France. When collected, these skulls related genera has been collected and described were sold, along with other fossil specimens, to byStehlin(l916),Deperet (1917),Sudre(1969), museums throughout Europe. As a result, some Cray (1973), Schmidt-Kittler (1971), Crusa- font-Pairo and Golpe-Posse (19751, von Received March 11, 1981; accepted June 22, 1981 0002-9483/81/5603-0235$06.500 1981 ALAN R. LISS. INC. 236 P.D. GINGERICH AND R.D. MARTIN TABLE 1. Stratigraphic distribution of the species of Adupis considered in this paper Age Species Characteristics Late Lattorfian Adapis parisiensis Small, with relatively (?Oligocene)' small canines Early Lattorfian Adupis stintoni Intermediate, with (?Oligocene) intermediate canines Late Bartonian Adapis magnus Large, with moderate (Eocene) canines ~ ~ ~~ ~ >TheLattorfian (= Priabonian) is placed In the early Oligocene by Berggren (1972) and others, while some include all pre-"GradeCoupure' mammalian faunas in the Eocene (Berggren et al , 1978) of the best specimens were effectively hidden ble, averaged over eight skulls (four males, from study. In this paper we describe an excep- four females) for each species,while data on tionally complete and well-preserved cranium body and brain size were taken from of Adapis parisiensis now in the Museum of Stephan et al. (1970), with a few modifica- Zoology at Cambridge University. Our purpose tions and additions (Martin, 1980). is not to discuss phylogenetic relationships (3) For analysis of relationships between cra- within Adapidae or between Adapidae and nial dimensions themselves, an enlarged other primates. Rather we shall attempt to sample of 48 extant nonhuman primate characterize the principal morphological fea- species (23 lemurs and lorises, one tarsier, tures of the cranium of Adapis and interpret and 24 monkeys and apes) was measured the adaptive significance of these by compari- (Martin, 1980). son with living primates. As a general rule, it is more appropriate to MATERIALS AND METHODS use the principal or major axis for describing allometric relationships, rather than the com- In order to make effective comparisons be- monly utilized regression, as the former implies tween Adapis species and modern primates, no distinction between dependent and inde- due consideration must be given to nonlinear pendent variables in a bivariate plot. The major scaling of various dimensions with body size, axis is used throughout the following discus- i.e., allometry (cf. Gould, 1966; Martin, 1980). sion, except for the problem of predicting body Reference is therefore made in the following weight from tooth size, where regression analy- discussion to a number of studies conducted to sis is appropriate (Gingerich et al., 1981). Dis- relate different parameters (e.g., length of MP, crepancies between major axes and regressions length multiplied by width of M', orbital di- decrease as the correlation coefficient (r) in- ameter, and cranial dimensions) to body size in creases, so with high r values a regression will samples of living primate species. Apart from yield a result not greatly different from that data specifically mentioned in the text (Table 5; obtained from the major axis. Figs. 4 and 51, the following reference material has been used: CRANIAL DIMENSIONS AND BODY SIZE (1) An analysis of the relationship between The Cambridge skull of Adapis parisiensis, length of Mf and body size in a sample of 38 specimen no. M.538, is illustrated in Figures extant noncercopithecoid species of pri- 1-3. The skull is complete except for the crowns mates, and length x width of M' and body of the anterior teeth, an opening in the right size in males and females of 41 primates, side of the braincase, and the ventral surfaces using average figures for several represen- of the auditory bullae. It is beautifully pre- tatives of each species (Kay, 1975; served, with even the cribriform plate and Gingerich, 1977; Gingerich et al., 1981). ethmoturbinals partially preserved. The skull (2) An analysis of the relationship between appears to represent a relatively young indi- various cranial dimensions and body size or vidual, judging from the clear presence of many brain size in a sample of 36 extant nonhu- cranial sutures, although all teeth have man primate species (18 lemurs and lorises, erupted and the crowns still in place are one tarsier, and 17 monkeys and apes). slightly worn. The dental formula was clearly Cranial dimensions were, whenever possi- 2.1.4.3. SKULL OF ADAPIS PARISIENSIS 237 Fig. 1, Cambridge skull ofAdapis parisiensis (M.538) in dorsal (A) and ventral (B) views. Note damage to right temporal area and preparatory removal of the ventral floor of both bullae. Scale in mm, 1.5 x natural size. 238 P.D. GINGERICH AND R.D. MARTIN Fig. 2. Cambridge skull ofAdapis parisiensis (M.538) in left lateral (A) and right lateral (B) views. Scale in rnm, 1.5 x natural size. Judging from other skulls of this species pre- smaller) median gap. Thus we cannot be sure serving the anterior teeth (represented only by that the nasal structure ofAdapis was anatom- alveoli in the Cambridge skull), the upper cen- ically or functionally like that in modern strep- tral incisors were slightly larger than the lat- sirhine primates. Ceboidea usually have a eral ones and their crowns converged markedly functional Jacobson’s organ (Maier, 1981), al- toward the midline of the skull, as inpropithe- though they do not have a naked rhinarium. In cus among living lemuroids andsaimiri among addition, some ceboids have a median furrow in anthropoids (Fig. 4). Left and right central in- the upper lip possibly representing a vestige of cisors actually contacted each other distally, the schizocheilic labial cleft characteristic of but the roots and proximal parts of the incisor lemuriform primates (Hofer, 1980). crowns were separated, leaving a median gap. The upper canine teeth are also not preserved This median gap may have permitted a naked in the Cambridge skull, but by comparisonwith rhinarium to connect directly to Jacobson’s other specimens of Adapis parisiensis we can organ, as in 1ivingMicrocebu.s (Schilling, 1970; infer that they were probably short-crowned Martin, 1973). On the other hand, some ceboids (see for example Stehlin, 1912: Figs. 244 and (Saimiri) have convergent upper central inci- 254; Gingerich, 1981: Fig. 5). Premolar and sors with a similar (although definitely molar morphology of this speciesis well known; SKULL OF ADAPIS PARISIENSIS 239 Fig. 3. Cambridge skull of Adapis parisiensis (M.538) in anterior (A) and posterior (B) views. Note the median gap (partially broken) between anterior incisor alveoli. Scale in mm, 1.5 x natural size. the last premolars are partly molarized, and are also given for two additional skulls ofAda- the true molars are relatively simple quadrate pis parisiensis preserved in the British Mu- teeth similar to those of Lepilemur or Hapale- seum (Natural History).