Timothy G. Bromage

The ontogeny of Pan troglodytes craniofacial architectural relationships and implications for early hominids

Developmental constraints characterize functional growth boundaries of the mammalian face. Enlow and colleagues identified boundary conditions and planes of the midface in humans and other mammal species that are defined on the basis of important growth sites and the developmental disposition of neural and pharyngeal matrices. With few exceptions a conservative mammalian architecture is said to be achieved by the adult stage. Three aspects of this architecture are investigated here for a cross-sectional ontogenetic series of Pan troglodytes crania: (1) a line passing from the maxillary tuberosity through the junction of middle and anterior cranial fossae is perpendicular to the neutral horizontal axis of the orbit (PM-NHA angle), (2) an average 45° angle, whose origin is the external auditory meatus, separates the maxillary tuberosity from the midpoint of the orbital opening (meatus angle) and (3) the base of the brain, maxillary tuberosity and prosthion are on or close to the same plane (anterior maxillary hypoplasia). This investigation considers to what extent samples of chimpanzees and early hominids reflect Enlows characterization of mammalian craniofacial architecture. Evidence derived from the chimpanzee sample bears out the perpendicularity of the PM-HNA angle and a near 45° meatus angle (though slightly higher overall), but does not conform to the absence of marked anterior maxillary hypoplasia seen in other mammals. Pan is instead characterized by considerable ontogenetic variation (noted by Enlow amongst anthropoids) influenced to some extent by sex. Preliminary early hominid data on the meatus angle indicates that Australopithecus specimens are similar to the widespread and probably primitive condition, while Paranthropus and early Homo specimens portray an uncharacteristic mammalian architectural relationship.

Effects of fetal exposure to nicotine on dental development of the laboratory rat.

Nicotine is one of the most widely used toxins in the world today. Most addiction research relating to nicotine in particular, as well as opioids and alcohol, has concentrated on the cellular and molecular biology of the mammalian brain and on features of organ structure and physiology associated with substance abuse. Thus, while numerous studies have been conducted to examine nicotines detrimental physiological effects in a variety of soft tissues, this investigation attempts to examine further the gross morphological consequences of this drug on a hard tissue, the first molar crown of the laboratory rat. It is hypothesised that by providing nicotine to rats during and after the fetal cycle, changes in dental structure will occur, owing to perturbations of development induced by this toxin. The dentitions of Fisher rats exposed to nicotine during and after the fetal cycle, and those of their non‐treated controls, were examined. By carefully measuring the length, width and occlusal (chewing) areas of the first maxillary molars, it was possible to identify any gross morphological effects of nicotine on dental development. It was found that dental asymmetries (calculated as a size difference between a tooth and its antimere) were significantly increased while occlusal areas were significantly decreased in nicotine‐exposed rats compared to control rats. In addition, significant differences were detected within the experimental group, females tending to exhibit the deleterious effects of nicotine more so than males. These results are in accordance with the predicted outcome; in similar studies of physiological systems and soft tissues, dental development is affected by the presence of nicotine. Anat Rec 258:397–405, 2000.