Introduction

Members of a species are adequately characterized when all stages of the individual life are understood. All ontogenetic stages have to be investigated as to their canalizing or constraining effects on evolutionary transformations. Comparative life history studies show potential for elucidating microevolutionary processes (Stearns, 1992). Although comparative morphogenetic studies have a long tradition (Garstang, 1922; DeBeer, 1937; Bonner, 1982; Maier, 1993a), they have not yet proven useful for systematics on middle and higher taxonomic levels.

Ontogenetic stages were included by Hennig (1966) as “semaphoronts”. It is sometimes difficult to define stages that are really comparable in more than a few details, because of heterochronic changes in developmental processes. Heterochrony is a descriptive, not causal, concept that needs adaptational explanations for shifts in the developmental program. The shifts themselves might be a valuable source of systematic and adaptational information. Heuristically, ontogenetic studies have proven to be valuable in craniology. Craniogenetic studies have led to a deeper understanding of the morphology of the vertebrate skull (Gaupp, 1906; DeBeer, 1937; Starck, 1967; Novacek, 1993).

The present study applies the comparative morphogenetic approach to the ethmoidal region of anthropoid primates and identifies characteristic features in the ethmoidal and nasal regions of cercopithecoids.

The ethmoidal region is a good example of heterochronic processes. In eutherian mammals, its structural differentiation – as compared to the braincase and some sensory organs – is retarded during intra-uterine development, and it continues to grow and change into postnatal life (Augier, 1931; Starck, 1967).