[Suprasternal ossicles in primates and the special adaptation of the manubrium sterni in howling monkeys (Alouatta)]

Homology of the reptilian coracoid and a reappraisal of the evolution and development of the amniote pectoral apparatus

As in monotreme mammals, the pectoral apparatus of basal (fossil) amniotes includes two coracoid elements, the procoracoid and metacoracoid. Among extant reptiles the metacoracoid has long been assumed lost; this notion is herein challenged. A comprehensive review of data from numerous sources, including the fossil record, experimental embryology, genetic manipulations and an analysis of morphology at the level cell condensations, supports the conclusion that the metacoracoid gives rise to the majority of the reptilian coracoid. By contrast, the reptilian procoracoid remains as a rudiment that is incorporated as a process of the (meta)coracoid and/or the glenoid region of the scapula early during development, prior to skeletogenesis. Application of this integrated approach corroborates and enhances previous work describing the evolution of the pectoral apparatus in mammals. A revised scenario of amniote coracoid evolution is presented emphasizing the importance of considering cell condensations when evaluating the homology of a skeletal complex.

Locomotion and postures of red howlers in a deciduous forest-savanna interface

Positional (postural and locomotor) patterns and substrates used by the seven adults of a free-ranging troop of red howling monkeys (Alouatta seniculus) were identified and sampled during their feeding and resting. Traveling patterns and substrates were noted but not quantified. Arboreal locomotor behaviors were pronograde quadrupedalism, some leaping, bridging, lowering, and pull up. Sitting and reclining were the most frequent postures. Tail suspension and arboreal bipedal stance were used when feeding. Predominant locomotor behaviors were those in which limbs appeared to be compression stressed. There were no limbs suspensions. The monkeys used the entire tree canopy, that of the low shrubs, and did a good deal of travel on the ground. The lack of forelimb suspension is attributed to the inability of these howlers to hang beneath supports and look forward at the same time; the impediment is created by the size of the vocal organs in the neck. The locomotion of these monkeys is offered to depict that of Aegyptopithecus zeuxis.