American Journal of Primatology 13:271-281(1987) Locomotor Diversity in Prosimian Primates DANIEL L. GEBO Department of Anthropology, Duke University, Durham, North Carolina An understanding of prosimian movement is basic to many anatomical and paleontological studies in that these studies attempt to correlate movement with anatomy and therefore infer movement in fossil primates. Duke University has a large and diverse collection of prosimian primates, which are housed in cages and enclosures large enough for movement studies. Extant prosimians move in many different ways, and none are so specialized that only one mode of travel is used. The most general locomotor patterns are observed for the cheirogaleids, and thus theirs may best resemble the locomotor patterns of the ancestral euprimate. Key words: captive setting, cheirogaleids, lemurids, lorisids INTRODUCTION The movement patterns of prosimian primates are inadequately known at present to provide well established correlations between anatomy and behavior. These correlations are especially important to paleontologists, who must infer movement from anatomy and on this basis try to reconstruct the movement patterns of extinct primates. Thus any information concerning prosimian movement activities is helpful, even data from a captive setting. The Duke Primate Center (DPC) houses 20 species of prosimian primates, of which 17 are housed in cages with a diversity of support types of varying diameters and large enough for movement studies. These caging facilities have largely diminished the problems of space for movement studies. This paper provides quantitative data on prosimian locomotion gathered at the Duke Primate Center. MATERIALS AND METHODS The biggest problem in studying prosimian primates is related to the access and use of these rare materials. The DPC has a large and diverse collection of animals, skeletons, and cadaver specimens, yet, even with the 20 living prosimian species present at the DPC (Table 0, another 15 species exist in the wild and remain largely unstudied. Seventeen of the 20 species at the DPC were observed, and movement was recorded in terms of frequency of locomotor bouts. Caging was judged t o be appropriate for movement studies after consideration of the following variables: 1) the sue of Received July 3,1986; revision accepted April 6, 1987. Address reprint requests to Daniel L. Gebo, Department of Cell Biology and Anatomy, "he Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, MD 21205. 0 1987 Alan R. Liss, Inc. 272 I Gebo TABLE I. Prosimian Primates at the Duke Primate Center Lemuridae 1. Lemur catta 2. Lemur fulvus 3. Lemur macaco 4. Lemur mongoz 5. Lemur rubriventer 6. Lemur coronatus 7. Varecia variegata 8. Hapalemur griseus Indriidae 9. Propithecus verreauxi Cheirogaleidae 10. Cheirogaleus medius 11. Cheirogaleus major 12. Microcebus murinus 13. Mirza coquereli Lorisidae 14. Loris tardigradus 15. Nycticebus coucang 16. Perodicticus potto 17. Galago senegalensis 18. Galago garnettii 19. Galago crassicaudatus 20. Galago demidovii the animal, 2) the number of animals within the cage, 3) the arrangement of supports within the cage, and 4)the amount of space for freedom of movement. The types of caging included two outdoor enclosures; large, silolike cages; large rectangular cages; tall indoor, triangular cages; and indoor rectangular cages. All cages contained from fifteen to hundreds of supports varying in diameter from 2-5 mm to over 50 cm in the outdoor enclosures. Each cage had a variety of horizontal, oblique, or vertical supports arranged for movement diversity. Table I1 lists the cage sizes for the species under observation. Observations were recorded on focal animals when the animals were active and moving, following the technique of Fleagle [1976, 19781, Fleagle and Mittermeier , and Mittermeier . Either early morning or late afternoon observation periods were used for the diurnal prosimians, and nocturnal prosimians were observed during evenings according to their artificial daylnight light schedule. Only adults were observed, and a minimum of 500 locomotor bouts were recorded for all but Cheirogaleus major. A locomotor bout was defined as a movement sequence for one type of movement. For example, if an animal climbed down a pole, leaped to another pole, and then climbed upward, the sequence of movement would be scored as three different locomotor bouts, two for climbing and one for leaping. A switch in the type of movement, eg, changing from a climb to a leap, started a new bout, and each bout continued until the animal stopped moving or changes its type of movement. If an animal stopped moving for 1 min or longer, attention was switched to another animal. Switching was common during any one observation period. Normally, only a few animals inhabited a cage, and all were sampled many times. Prosimian Locomotion I 273 TABLE 11. Cage Sizes for Species That Were Observed for Movement Frequencies Species Cage size (length x width x height) Lemur catta Lemur fulvus Lemur mongoz Lemur coronatus Lemur macaco Varecia variegata rubra Varecia variegata variegata Hapalemur griseus Propithecus verreauxi Cheirogaleus medius Cheirogaleus major Microcebus murinus Mirza coquereli Loris tardigradus Nycticebus coucang Perodicticus potto Galago senegalensis Galago demidovii 0.43 ha enclosure 0.43 ha enclosure 7.6 x 2.4 x 6.6m 3.04 ha enclosure 6.6 x 1.2 x 3.6 m 3.1 x 3.1 x 8.2 m 3.04 ha enclosure 7.6 x 2.4 x 8.7 m 8.7 x 5.5 x 7.6 m 2.4 x 1.5 x 2.1 m 1.8 x 1.8 x 2.1 m 2.4 x 1.5 x 2.1 m 1.8 x 1.2 x 3.6 m 1.8 x 1.2 x 3.6 m 2.4 x 1.8 x 2.1 m 2.4 x 1.8 x 2.1 m 2.1 x 1.8 x 2.1 m 1.8 x 1.2 x 3.6 m Movement frequencies were recorded for 17 species. Definitions for the movements are as follows: Quadrupedalism A movement in which all four limbs move in a regular pattern above a horizontal support or on the ground; walking, running, and galloping were all recorded as a quadrupedalism; leaping: A movement in which the hindlimbs propel an animal across a gap between two supports; dropping down from a branch above was not scored as a leap; climbing: A movement up or down a vertical or steeply inclined support; all four limbs move in an irregular pattern, with variable hand and foot positions; suspensions: A movement or a posture in which the body is held below a support by one, two, three, or four limbs in tension; cantilevering is a special type of suspension in which two feet hold onto a vertical support and the body is unfolded horizontally outward like a flag (Fig. 1);bridging: A movement in which gaps are crossed by body stretching; first, the hands stretch out and grab the distant support and then the body is stretched across; the two feet are then released in succession, and the animal moves across to the new support; bimanual movements: A movement in which only the hands grasp a support and are used to pull the body up to a support from below, to hang below a support, or for arm-swinging; bipedal movements: A movement in which only the hind feet are used to raise an animal up, to hop, or to take a short walk. To check the effect of differences between groups, three different silolike cages of the same size were chosen, each cage containing a different group of Varecia uariegata rubra. Each cage had a different arrangement of supports, but all three cages were similar in the number, the size, and the orientation of the supports. Table 111, which lists the movement frequencies for each cage, shows that the greatest difference occurred in frequency of leaping; this differed by 6% from the lowest to the highest value. Suspensory movements differed by 5% and quadrupedalism by 3%. By averaging the SD values for the four most frequent movements, 274 I Gebo Fig. 1. Mirzu coguereli cantilevering outward from a vertical support. The arrow on the support points upward and thus orients the support relative to the horizontally positioned Mirzu. TABLE 111. Movement Frequencies for Vureicu vuriegutu rubm in Three Separate Silolike Cages (1-111) Quadrupedalism Leaping Climbing Suspension Bridging Bimanual Bipedal Locomotor bouts I (%I I1 (%) III (%) Mean (%) SD (%) 32 27 23 14 1 2 1 612 35 21 24 17 1 2 <1 607 33 27 24 12 2 <1 1 610 33.3 25.0 23.7 14.3 1.3 1.7 1.o 1.53 3.46 0.54 2.32 0.58 0.58 0.00 quadrupedalism,leaping, climbing, and suspension, a value of 1.96 was determined, and, by doubling this value, an approximate error factor of +4% for 95% of the variates was determined. This approximate error factor can be used as a measure of comparison between species for the more frequent movement values listed in Table IV. RESULTS Lemuridae Observations on Lemur cuttu in a 0.43 ha enclosure at the DPC revealed the terrestrial preference of this species (Table v>. Table 4 lists L cuttu’s movement frequencies. L. cuttu moved quadrupedally more than any other lemurid and had a high percentage of bipedalism, consisting of hopping or walking when on the ground. Like all lemurs, they leaped, climbed, and suspended themselves below supports using all possible variations of their four limbs. L cattu climbed large-diameter trees and branches and usually leapt down from branch to branch, as Sussman 119741 has Prosimian Locomotion I 275 TABLE IV. Movement Frequencies for Prosimian Primates at the Duke Primate Center* &(%I L(%) CL(%) S(%) BR(%) BIM(%) BIP(%) Bouts Lemur catta 51 22 10 1 4 <1 7 642 Lemur fulvus 39 34 17 1 9 <1 <I 1,273 Lemur mongoz 29 37 22 2 8 1 1 2,164 Lemur coronatus 33 30 31 2 1 3 <1 842 Lemur macaco 30 31 28 1 6 4 1 525 Varecia variegata 34 25 23 2 14 1 1 1,829 rubra Varecia variegata 35 21 31 11 1 1 1 525 variegata Hapalemur griseus 24 56 15 7 1 1 <1 2,118 Propithecus verreauxi 6 46 30 0 5 10 3 2,149 Cheirogaleus medius 34 21 28 5 11” <1 1 2,131 Cheirogaleus major 41 6 39 4 7a 3 <1 340 Microcebus murinus 29 38 24 3 <1 5a <1 2,149 Mirza coquereli 20 27 24 5 1 1 23a 3,772 Loris tardigradus 15 0 31 1 30a 24 <1 2,496 Nycticebus coucang 0 21 24 23 2ga 2 1 605 Perodicticus p t t o 29 0 31 17 22a 1 <1 645 Galago senegalensis 5 63 26 <1 2 2a <1 2,245 Galago demidovii 25 40 24 6a 4 <1 1 2,163 *Abbreviations: Q, quadrupedalism; L, leaping; CL, climbing; S, suspension;BR, bridging; BIM,bimanual; BE’, bipedal; Bouts, locomotor bouts. ‘Species that perform cantilevering. reported from his observations of L. catta in the wild. L catta also engaged in bridging and bimanual movements at the DPC, although very rarely. Like all other lemurids, they were never observed to perform a cantilever movement. L fulvus leaped, climbed, and engaged in suspensory movements and postures more often than did L catta (Table IV). Although very arboreal, L fulvus often moved on the ground in the outdoor enclosures without apparent difficulty. A comparison of arboreal movements and ground movements between L fulvus and L catta is given in Table V. L filvus used quadrupedalism and suspension in the arboreal setting far more often than did L catta, which tended to leap and climb when in trees. L catta moved using bipedal hops and quadrupedal walking movements when on the ground more often than did L. fulvus. L. mongoz leaped and climbed more than L fulvus (Table IV). Frequency of suspensory movements was about equal for the two. L fulvus was more quadrupedal than L. mongoz. L mongoz climbed downward tail first but would on occasion climb downward head first. L. mongoz would also drop head first to a branch below while hanging by two feet. I, macaco, a generalist among the lemurs, used quadrupedalism, leaping, and climbing in about equal proportions (Table IV). L macaco commonly leaped from vertical support to vertical support with short climbing sequences interposed between leaps. The climbing sequences tended to be over very short distances as compared to those of Varecia. They used their arms significantly more often than did other lemurs. Bimanual “raise-ups” and short arm-swings were fairly common. L coronatus was similar to L. catta in movement frequencies in that it was less suspensory than the other lemurs and used bipedalism more often. L. coronatus was a generalist compared to L. catta in that quadrupedalism, leaping, and climbing 276 I Gebo TABLE V. Arboreal vs Terrestrial Movement Frequencies for Lemur cutta and Lemur fulvus in a 0.43 ha Enclosure* Lemur fuluus (%) Lemur cuttu (%) Arboreal Q L CL S BIP 16 44 26 13 0.1 5 55 38 86 13 0 70 13 0 0 0 18 1 1 Terrestrial Q L CL S BIP BOUTS 1 1,273 68% arboreal 642 22%arboreal *For explanation of the abbreviations,see footnote t o Table 4. were used in about equal amounts (Table IV). Although L. coronatus and L macmo were both generalists in terms of movement frequencies, L. coronatus preferred quadrupedalism to leaping, whereas L. macaco leaped more and made more frequent use of suspension and bimanual movements. Varecia variegata, the largest lemurid, leaped with the same frequency as L. catta but less often than the other lemurs (Table IV). Varecia engaged in suspensory movements more often than the other lemurids. Hanging by two feet was common. Varecia, without hesitation, would let go while hanging by two feet and drop to the branch below. Varecia most frequently engaged in above-branch quadrupedalism (Table IV). Observations on the black-and-white ruffed lemur, Varecia uariegata uariegata, in the 3.04 ha enclosure showed movement frequencies that were similar to those of the red ruffed lemur, Varecia uariegata rubra, which was observed in three separate silolike cages. All movement frequencies for these two subspecies were within 4% of one another, with the exception of climbing. The ruffed lemurs in the outdoor enclosure climbed more frequently than the ones in the silolike cages. The much taller trees in the enclosure are the likely explanation for this difference in climbing frequencies. Hapalemur griseus was far less quadrupedal than the other lemurs and leaped far more frequently (Table IV).Hapalemur climbed and engaged in suspension about as often as L. fulvus. Hapalemur clung vertically; hopped bipedally; dropped downward head first while hanging from two feet; suspended themselves by any combination of four or fewer limbs, including one hand, although rarely; and occasionally bridged across two supports. Hapalemur hopped or made short leaps upward or downward to a branch more often than they climbed to that spot. They climbed downward tail first, as do all lemurids, and would on occasion make bouncy leaps with all four limbs, perform bipedal hops, or rise up on two legs. Indriidae For Propithecus verreauxi, leaping was the most frequent locomotor movement observed at the DPC (Table IV). These indriids never engaged in bridging move- Prosimian Locomotion I 277 ments, nor did they use a hanging rope at the DPC. They were observed to support themselves between two vertical supports with one hand and one foot on different supports. I! verreauxi showed a high frequency of climbing, as do the large-bodied lorisines (Table IV).I! verreauxi climbed downward tail first like lemurids, however, rather than descending head first as has been observed in lorisines. Quadrupedalism and suspension were not common. I! verreauxi did engage in a significant amount of bimanual movements, including brachiation, although for short periods of time. The more frequent use of bimanual movements by I! verreuuxi was very unusual compared to other prosimians in this study. Cheirogalidae Cheirogaleus medius moved in a scurrying quadrupedal manner, with its body held close to the support. Quadrupedalism and climbing were the two most frequent movements (Table IV).C. medius preferred horizontal supports and performed short, cautious leaps. They often leaped up to a support, grabbed on using a four-limb suspensory posture, and pulled themselves up on top of the support. Cheirogaleids were, in general, more suspensory in their movement preferences, climbed more often, and bridged more frequently than lemurids (Table IV). Cheirogaleids climbed downward head first. Suspensory movements included all possible hand and foot combinations. All cheirogaleids at the DPC performed the cantilevering movement (Fig. 1). To perform this suspensory movement, cheirogaleids move their feet to the same side of the vertical support and spread their legs outward for a wider base of support. The body is fully extended horizontally, including the knees. "his leaves only the feet to hold onto the vertical support and leaves the hands free to grab insects. The whole movement of unfolding the body outward is similar to an accordian in the pattern of movement. This insect-catching movement was first noted by Martin  for Microcebus. C. major, which is larger than C. medius, preferred quadrupedalism and climbing over all other movements (Table IV). C. major moved using quadrupedalism more frequently than any other cheirogaleid. C. major was less suspensory and leaped less frequently than C. medius (Table N). Mirza coquereli was the most suspensory of the cheirogaleids, being just below the lorisines in frequency (Table IV). Mirzu was the most generalized, movementwise, of the cheirogaleid species, with quadrupedalism, leaping, climbing, and suspension frequencies being very similar (Table IV).Mirzu preferred short leaps and would size-up large leaps before committing. Bipedal raise-ups were performed with bent knees. Microcebus murinus was the most frequent leaper of the cheirogaleids (Table W. Microcebus made quick, agile movements, and quadrupedalism and climbing were relatively frequent. Suspensory movements and postures were less frequent for Microcebus than for Mirza. Microcebus also contrasted with Mirzu in that quadrupedalism and leaping frequencies were higher (Table IV).On the ground, Micrccebus moved by quadrupedalism or by hopping with all four limbs. Microcebus bridged to other supports, especially to branches above themselves. Microcebus dropped to lower branches if the distance was short. Microcebus, Mirza, and Cheiroguleus all clung vertically and leaped between vertical supports. Lorisinae Lorisines moved with more deliberate movements than did the cheirogaleids. They bridged more often and were the most suspensory of all prosimians (Table IV). Loris turdigradus, a small-bodied lorisine, preferred climbing and suspensory movements over quadrupedalism and bridging. Like the other lorisines, it can cantilever. 278 I Gebo Lorisines, however, do not always place their feet on the same side of the vertical support as do cheirogaleids. Loris was capable of very rapid movements when moving quadrupedally. In this study, Loris was similar to Perodicticus in climbing frequency but was most similar to Nycticebus in suspension and bridging frequencies (Table IV). Loris sometimes climbed vertical supports backward while holding the body vertical and while grasping the support with only two feet. These animals occasionally moved on the ground, but this rarely occurred. Of all lorisines at the DPC, Perodicticus was quadrupedal most frequently (Table IV). Perodicticus moved quadrupedally and climbed more frequently than did the other large-bodied lorisine, Nycticebus. Perodicticus bridged between supports in the small branch periphery. When on the ground, Perodicticus used quadrupedalism that was of a serpentine type and had its feet placed in an everted position. Nycticebus was more suspensory than Perodicticus (Table IV).The most frequent movements for Nycticebus were suspension and quadrupedalism, followed by bridging and climbing, all of which ranked between 20% and 30% (Table IV). Like Perodicticus, Nycticebus moved using a serpentine style of quadrupedalism when on the ground, lifting each foot in a stereotypic sequence that contrasted with the more fluid motion of Perodicticus. First, the foot was lifted off the ground and quickly inverted as it moved forward; it was then everted and abducted just before it was placed on the ground. Nycticebus and Perodicticus moved on the ground rarely but more frequently than did Loris. GaIaginae Table IV shows that Galago demidovii was predominantly a leaping species, with quadrupedalism and climbing being the next two most frequent movements. Quick rather than deliberate quadrupedal movements were made by G. demidovii. G. demidovii was more suspensory than G. senegalensis (Table IV). G. demidovii climbed downward head first, performed the cantilevering suspensory movement, and moved on the ground using quadrupedalism or by bipedal hops. Long, fast leaps from vertical supports were the most common movement for G. senegalensis. Climbing was the only other movement. G. senegalensis performed with any frequency above 5% (Table N). G. senegalensis normally climbed downward head first but would on occasion climb downward tail first. G. senegalensis preferred to hop bipedally on the ground. Suspensory movements were not common, although G. senegalensis did cantilever. DISCUSSION Historically, primate movements have been categorized into locomotor types [Mollison, 1910; Erickson, 1963; Ashton & Oxnard, 1964; Walker, 1967; Napier & Walker, 19671. Stern and Oxnard [19731 reviewed the implications of categorization, suggesting that categories should be an aid to thinking, not a hindrance, and noting that field research has established that greater variation exists for a variety of movements among primates than was previously thought. Stern and Oxnard  concluded that categories no longer serve a useful purpose. General locomotor categories are important to paleontologists, however, who must infer broad movement patterns from anatomy alone. Further field research has suggested that prosimian body postures and movements follow broad phylogenetic patterns but with some interesting exceptions. For example, most lemurs move in ways that distinguish them from cheirogaleids or indriids, yet the frequency of specific movements is related not only to which lemur is being considered but also to forest structure, where plant types and density, support diameters, and support angles may vary. This is especially true for support Prosimian Locomotion I 279 diameters and angles, since foot and body size largely determine the size of arboreal supports a prosimian will use, with some qualifications. In some prosimians, nails have been modified into “c1aws7’[Charles-Dominique, 19771 or the big toe has been shifted into a more abducted position (ie, lorisines); such modifications have allowed prosimians to use larger-diameter supports relative to foot size. The angle of a support on which a prosimian chooses to move is governed by a different set of conditions related to forest structure. These conditions are the type and sizes of trees in a forest, the distribution of food resources in the trees, and the size of the animal relative to the branches. Some species (eg, Lemur catta) have been documented to use forest structure differently in different forests [Jolly, 1966; Sussman, 1972; 1974; Budnitz & Dainis, 1975; Tattersall, 1977; Richard, 19781. The quantitative results of this captive study allow several simple observations to be made concerning prosimian locomotion. First, all prosimians climb. Second, all prosimians move using quadrupedalism, although this movement was rare in G. senegalensis and I? uerreauxi. Third, lorisines never leap. Fourth, only cheirogaleids and lorisids perform cantilevering movements. Last, all prosimians use the posture of vertical clinging, which in reality is nothing more than a stopping position in a vertical climbing sequence. Of course, certain prosimians (eg, G. senegalensis) cling on vertical supports more frequently than others and can maintain this position for long periods of time. Thus the posture vertical clinging differs from the movement vertical climbing only in the amount of time delegated toward maintaining this position. The most important result of this study is that when prosimians are given adequate space and support diversity, data from captive locomotor studies can agree quite well with field observations and thus add to our understanding of locomotor diversity (see, eg, the locomotor descriptions provided by Walker [19741, CharlesDominique , and Tattersall ). When quantitative data are known, for example, in galagines studied by Walker  and Crompton , these data also compare well, although some discrepancies are apparent (Table Vn. CONCLUSIONS 1. Species of extant prosimians move in many different ways, but only a few movements are preferred; these distinctions tend to be highly informative in a comparative approach. Although data from captive locomotor studies are not the final word toward understanding prosimian locomotor adaptations, they agree quite well with results from previous field studies and should be of value to comparative anatomists and paleontologists. 2. Lemurid species move in many different ways, whereas indriid species are less diverse. 3. Cheirogaleids are generalists, but there are interspecific differences in the amount of leaping and suspensory movements. 4.Lorisines are like indriids in that all species move in similar ways, although quadrupedalism, suspension, and bridging frequencies do show species-specific usages. 5. Galagine species differ along two movement gradients, one for leaping and the other for quadrupedalism. 6. The most generalized locomotor patterns are observed for the cheirogaleids, which are active in all four major locomotor categories: quadrupedalism, leaping, climbing, and suspensory movements. Thus the locomotor patterns of cheirogaleids like Mirza coquereli or Cheirogaleus medius, which are the most generalized, movementwise, of all cheirogaleids, might best resemble the locomotor patterns of the ancestral euprimate. 25 40 24 6 4 <1 1 5 63 26 2 <1 <1 2 3.41 - 24.11 45.30 25.86 1.82 Walker (G. demidovii) 21 53 22 4 1 5 40 23 34 2 7 - Crompton G. senegalensis G. crassicaudatus *Walker’sand Crompton’s  data have been modified to be comparablewith my own observations. Quadrupedalism Leaping Climbing Suspension Bridging Bimanual Bipedal This study G. demidovii G. senegalensis TABLE VI. Movement Freauencies (%) for Several Soecies of Guluao* Prosimian Locomotion I 281 ACKNOWLEDGMENTS A special thanks must go to the Director of the Duke Primate Center, Dr. E.L. Simons, and to the staff at the Duke Primate Center for their help throughout this project. I would also like to thank D.T. Rasmussen for his drawing of Mirza coquereli and for his comments on the manuscript. 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