UNIVERSITY OF ILLINOIS 3 MAY THIS IS TO CERTIFY THAT THE THESIS PREPARED UNDER MY SUPERVISION BY Leahanne M, Sarlo Functional Anatomy and Allometry in the Shoulder of ENTITLED........................................................ Suspensory Primates IS APPROVED BY ME AS FULFILLING THIS PART OF THE REQUIREMENTS FOR THE DEGREE OF. BACHELOR OF ARTS LIBERAL ARTS AND SCIENCES 0-1M4 t « w or c o w n w Introduction.....................................................................................................................................1 Dafinibon*..................................................................................................................................... 2 fFunctional m ivw w iiw irwbaola am foriwi irviiiiHbimanual iw 9 jrvafwooaitiona! Vf aai irwbahavlort iiHviw i# in thaahoukter joint complex......................................................................................3 nyvootiua pooioonaiaA^^AlttAAMAl oanainor................................................................................... i4 *4 -TnoOV a awmang.a Ia M AM JI* nwoo—U^AtkA^AA i (snDBDfllluu)/AuMyAlftAlAnAH |At AkJA^AAtlA•wwacwai* |A .............. 4ia i -Tho lar gibbon: KM obate* ]|£.................................................................................15 ANomatry.......................................................................................................................................16 Material* and matooda.....................................................................................................19 Meaeurementa...........................................................................................................................20 RaauN*............................................................................................................................................ 22 Dlacuaalon . .. .28 Conduaion.....................................................................................................................................25 Graph 1 ............................................................................................................................................. 30 Graph 2 ..............................................................................................................................................31 Graph 3............................................................................................................................................. 32 Graph 4 ............................................................................................................................................. 33 Literature cited..........................................................................................................................34 iQtUtUKtiQQ The behavior and anatomy of the leaser ap«t it a topic which h it long interested scientists who study primates. Ths combination of bizarre elongated torsi!mbs (especially tha distal sagmant) with a startling and spectacular form of locomotion is indicativs of a highly apadaiizad adaptive pattsm. Howsvsr, it took an inordinata amount of tima batora scientists bagan to apply tha anatomical studias ol tha gfcbon to thair bahavior; for a long tima, description took tha placa of any typo of functional analysis (Prsuschoft and Croat, 1984). Mora recently, howsvsr, many studias havs boon conductsd which ara aimsd toward finding ths functional morphological basis for ths locomotor and postural behaviors practiced most frequently by hylobatids: bimanual suspensory positions! behaviors. Different approaches havs been taken by different researchers. For example, an approach which utilizes analogies between functionally similar animals to identify anatomical features related to function has bean used by researchers such as Ashton and Oxnard, 1963, 1964b; Ashton, Oxnard and Spence, 1965; Fleagie, 1978b; Oxnard. 1963,1967; Roberts, 1974; and Takahashi, 1990. A more reductionist approach has been used by researchers such as Fleagie at al., 1961; Jenkins et al., 1978; Jungers and Stem, 1980,1981,1984; Larson, 1968; Larson and Stem, 1986; Larson et al., 1991; Stem at al., 19 77,1980a,b; Tuttle and Basmajian, 1977; and Tuttle et al., 1979. These researchers focus their studies on the experimental examination of positional behaviors using analyses of kk«tics, stress patterns, or muscle activity (Fleagie, 1976a). The anthropological community has yet to bring together a compete and agreeable synthesis of the work that has been done. This paper will examine some of the various conclusions which have been reached concerning the shoulder region of suspensory primates, as wen as some of the problems which have arisen, and will look at skeletal data from two closely related suspensory primates which use different amounts of suspensory behaviors in an effort to Identify functional and atometric characteristics of the shoulder girdle in these highly specialized primates. 2 Deflnfflnna First and foremost, a definition of the word locomotion* is essential. A useful definition has been suggested by Prost (1965), who sttlss that "a prfmats performs a set of locomotor actions, or a locomotor pattern, when its body mass (as opposed to limb mass) is grossly displaced rsiatlvs to ns physical surroundings* (pg. 1200). This definition effectively distinguishes locomotion from posture, which Prost describes as a state in which "the positional relations between a primate's body mass and environmental surroundings remain relatively stable* (pg. 1200). It is important to note that posture is by no means neceaaarily a static state of being, for in addition to sitting or standing it includes such activities as hanging beneath a branch or clinging to the trunk of a tree while feeding. It is entirely possible that a given postural activity may require greater energy expenditure than many locomotor activities (Prost, 1965), and the postural repertoire of an animal must not be ignored when studying relationships between behavior and anatomy. Positional behavior can be defined as the totality of the locomotor and postural repertoire. The classification of the different types of positional behaviors is a complicated matter, for there are nearly as many dassificatory schemes as there are reseerchers studying the phenomena being classified. The history of the study of brachiation provides an example of this confusion. The term "brachiation' has long been associated with apes, including the proposed hominkf ancestor (HoHihn, 1984). This was primarily baaed on anatomical studies, which pointed to many similarities between the skeletal and muscular morphology of lesser apes, great apes, and humane (HoHihn. 1964). It was proposed by Avis (1962) that our ancestors brachiated, and that brachiation was preadaptive for bipedalism, due to its requirement of an upright orientation ollhe body (Clark, 1969; Keith, 1899; Gregory, 1928). Although brachiation, or "arm-swinging", has been addressed in the literature for quite some time, a precise definition of the term which can be agreed upon is difficult to come by. it has been described as 'all bimanual suspensory locomotion, with or without the fair (Takahashi, 1990, pg.71 3 ), or a t "bimanual progression along or between overheed suuctures for a distance of antral metres without th« intermittent use of other typw of positional behavior and without support by the hindlimte or tail" (Hollihn, 1964, pg.66). The former definition could include the locomotor activities of both A fla t and Alouitti. while the latter could only truly refer to gibbons and siamangs. For the purpose of this study, brachiation will be defined as bimanual suspensory progression without the support of the hindlimbe or tail. In addition, a locomotor category known u "semibrachiation" was introduced into the literature in the early 1960's. Napier (1963) describee the positional behavior of a semtorachiator as "basically that of an arboreal quadruped, but, in addition, a variable amount of time is spent swinging by the arms and leaping with the forelimbe outstretched to grab a handhold* (pg 166). New World semibrachiators included Atei—. and Old World semtarachiators Included Cotabus and t j m l i (Mittermeier and Fleagte, 1976). Mtttermeier and Fleagle (1976) suggest that this category should probably not be retained, due in part to the great diversity of locomotor patterns which are Included within the group. The shoulder performs different roles in different groups of primates, depending upon the primary positional adaptations present within the group. Primates which move primarily by quadrupedal walking and running, for instance, subject their shoulders to mainly compressive forces, while bimanual suspensory primates subject their shoulder girdle to tensile forces (Oxnard, 1967). In initial studies of functional anatomy, associations between particular skeletal features and positional behavior was often done using analogies. For example, there are certain characteristics of the shoulder which are found In hominoida almost exclusively. These were (and are) often considered to be related to the utilization of overhead suspensory positional behaviors, because this type of behavior is found almost exclusively in hominoids (Larson, 1968). Support for this idea came 4 from the fact that there Is anatomical convergence in this region between hominoids and New World suspensory primates, such as M alta. This convergence is reflected in such anatomical traits as axial elongation of the scapula and the presence of a cranially directed glenoid