Daniel L. Gebo

Estimators of Fruit Abundance of Tropical Trees1

Many types of biological studies require the estimation of food abundance in tropical forests, and a variety of methods have been used to estimate this parameter. Here we compare the accuracy and precision of three methods for estimating the fruit abundance (biomass and number) of tropical tree species: tree diameter, crown volume, and visual estimation. Diameter at breast height (DBH) was the most consistently accurate method and exhibited low levels of interobserver variability. Generally, crown volume was neither precise nor accurate. The visual estimation method was accurate for trees with very large fruit, but exhibited high interobserver variability.

Standardized descriptions of primate locomotor and postural modes

As quantitative studies on primate positional behavior accumulate the lack of a standard positional mode terminology is becoming an increasingly serious deficiency. Inconsistent use of traditional terms and inappropriate conflation of mode categories hamper interspecific and interobserver comparisons. Some workers use common terms without definition, allowing at least the possibility of misunderstanding. Other researchers coin neologisms tailored to their study species and not clearly enough defined to allow application to other species. Such neologisms may overlap, may completely encompass, or may conflate previously defined labels. The result is, at best, the proliferation of synonyms and, at worst, the creation of confusion where clarity had existed. Historical precedents have sometimes resulted in “catch-all” terms that conflate any number of kinematically different behaviors (e.g. “brachiation,” “climbing,” and “quadrumanous climbing”). We recognize three areas where distinction of positional modes has some current importance: (1) Modes that require humeral abduction should be distinguished from adducted behaviors; (2) locomotor modes that involve ascent or descent should be distinguished from horizontal locomotor modes; and (3) suspensory modes should be distinguished from supported modes. We recommend a nomenclature that is not dedicated to or derived from any one taxonomic subset of the primates. Here we define 32 primate positional modes, divided more finely into 52 postural sub-modes and 74 locomotor sub-modes.

Climbing, brachiation, and terrestrial quadrupedalism: Historical precursors of hominid bipedalism

The vertical-climbing account of the evolution of locomotor behavior and morphology in hominid ancestry is reexamined in light of recent behavioral, anatomical, and paleontological findings and a more firmly established phylogeny for the living apes. The behavioral record shows that African apes, when arboreal, are good vertical climbers, and that locomotion during traveling best separates the living apes into brachiators (gibbons), scrambling/ climbing/brachiators (orangutans), and terrestrial quadrupeds (gorillas and chimpanzees). The paleontological record documents frequent climbing as an ancestral catarrhine ability, while a reassessment of the morphology of the torso and forelimb in living apes and Atelini suggests that their shared unique morphological pattern is best explained by brachiation and forelimb suspensory positional behavior. Further, evidence from the hand and foot points to a terrestrial quadrupedal phase in hominoid evolution prior to the adoption of bipedalism. The evolution of positional behavior from early hominoids to hominids appears to have begun with an arboreal quadrupedal-climbing phase and proceeded though an orthograde, brachiating, forelimb-suspensory phase, which was in turn followed by arboreal and terrestrial quadrupedal phases prior to the advent of hominid bipedality. The thesis that protohominids climbed down from the trees to become terrestrial bipeds needs to be reexamined in light of a potentially long history of terrestriality in the ancestral protohominid.

Foot Morphology and Locomotor Adaptation in Eocene Primates

Locomotor diversity of Eocene primates of North America and Europe was well developed, with species of both Adapidae and Omomyidae showing a wide spectrum of movements. Besides documenting the locomotor diversity in the Eocene, this paper shows that adapid foot morphology shares derived features with extant strepsirhines. Thus, the Omomyidae best resemble the ancestral euprimate in terms of foot morphology and locomotion. The generalized locomotor repertoire of the modern cheirogaleids represents the best model for the movement pattern of the ancestral euprimate.

The oldest known primate skeleton and early haplorhine evolution

Reconstructing the earliest phases of primate evolution has been impeded by gaps in the fossil record, so that disagreements persist regarding the palaeobiology and phylogenetic relationships of the earliest primates. Here we report the discovery of a nearly complete and partly articulated skeleton of a primitive haplorhine primate from the early Eocene of China, about 55 million years ago, the oldest fossil primate of this quality ever recovered. Coupled with detailed morphological examination using propagation phase contrast X-ray synchrotron microtomography, our phylogenetic analysis based on total available evidence indicates that this fossil is the most basal known member of the tarsiiform clade. In addition to providing further support for an early dichotomy between the strepsirrhine and haplorhine clades, this new primate further constrains the age of divergence between tarsiiforms and anthropoids. It also strengthens the hypothesis that the earliest primates were probably diurnal, arboreal and primarily insectivorous mammals the size of modern pygmy mouse lemurs.

Anthropoid origins—the foot evidence†

Evolutionary explanations for substrate use and the locomotor origin of Anthropoidea have been presented by Napier & Walker (1967) and Rollinson & Martin (1981) ; however, these explanations present contrasting opinions concerning the use of vertical supports. A comparison of bony foot anatomy in extant and fossil prosimians and anthropoids provides a likely solution concerning support choice and movement preference. Functionally, decreased mobility for abduction in the foot, de-emphasis of the strong grasping hallux, decrease in the length of the fourth digit, and a mid-trochlear position for the flexor hallucis longus groove on the posterior talus all support a more horizontal foot posture for anthropoids than in their “prosimian” ancestors. Thus, the origin of Anthropoidea in part resulted from a shift in movement and support choice, with a decrease in the use of vertical climbing and an increase in the use of above-branch quadrupedalism on horizontal supports. Adapids share derived foot characters with lemuriforms, and thus omomyids are left as the most likely ancestral stock for anthropoids.

The oldest known anthropoid postcranial fossils and the early evolution of higher primates.

The middle Eocene primate family Eosimiidae, which is known from sites in central and eastern China and Myanmar, is central to efforts to reconstruct the origin and early evolution of anthropoid or ‘higher’ primates (monkeys, apes and humans). Previous knowledge of eosimiid anatomy has been restricted to the dentition and an isolated petrosal bone, and this limited anatomical information has led to conflicting interpretations of early anthropoid phylogeny. Here we describe foot bones of Eosimias from the same middle Eocene sites in China that yield abundant dental remains of this primate. Tarsals of Eosimias show derived anatomical traits that are otherwise restricted to living and fossil anthropoids. These new fossils substantiate the anthropoid status of Eosimias and clarify the phylogenetic position of anthropoids with respect to other major primate clades. Early anthropoids possessed a mosaic of primitive and derived traits in their postcranial skeletons, reflecting their derivation from haplorhine ancestors that retained many prosimian-like features.

Foot anatomy, climbing, and the origin of the Indriidae

Abstract Living indriids share a suite of derived osteological and myological features of the foot which are related to three of the most important components of their locomotor repertoire: climbing (primarily on vertical supports), vertical clinging, and leaping. However, the overall structure of the foot bones and musculature reflects the requirements for climbing more than any other behavior. All indriid subfamilies have postcranial morphologies and locomotor behaviors which are derived compared to the probable indriid-lemurid common ancestor. It seems most likely that the ancestral indriid was an “arboreal quadruped” (i.e. lemur-like), not a vertical clinger and leaper.

Locomotor and phylogenetic considerations in anthropoid evolution

Abstract Common locomotor patterns within extant taxonomic groups appear to be evident within Anthropoidea. These common locomotor patterns, as well as the anthropoid fossil record, provide insights into anthropoid locomotor evolution. The locomotor pattern quadrupedalism-leaping (found today among non-ateline ceboids) appears to represent the earliest locomotor adaptation in anthropoid evolution. Atelines and catarrhines increase the frequency of climbing behavior relative to callitrichines, cebines, and pithecines. Here, foot anatomy is analysed to infer locomotor adaptation in extinct anthropoids and to evaluate these common locomotor patterns in terms of anthropoid locomotor evolution. Similarly, primitive versus derived features in catarrhine foot anatomy are analysed. The foot anatomy of Oligocene parapithecids and propliopithecids may not be suitably representative of the ancestral anthropoid or the ancestral catarrhine condition, respectively.

Postcranial adaptation and evolution in lorisidae

With the exception of leaping, lorises and galagos move in many similar ways although frequencies and styles differ. This peculiar locomotor distinction in two closely related subfamilies has profoundly altered their respective postcranial anatomies from their common ancestor. A comparison of postcranial adaptation in extant forms shows that lorises and galagos differ somewhat in forelimb mobility, but are more fundamentally disparate in hindlimb adaptation. Inferences concerning locomotor adaptation in the lorisid fossil record indicate a more generalized locomotor pattern which is more like that of extant cheirogaleids than either living galagos or lorises. Thus, vertical clinging and leaping in galagines and the slow-climbing and suspensory movements of lorisines appear to be evolutionarily recent innovations from a more generalized locomotor past.