The present research focuses on craniofacial variation in Nubia over approximately 10,000 years. Samples were grouped according to their temporal location and subsistence pattern, and represent a transition from a hunting-gathering adaptation (Mesolithic) to a transitional hunting-gathering-agricultural adaptation (A-C Group) and finally to a fully agricultural adaptation (Meroitic/X-Group/Christian). The purposes were: (1) to compare the Mesolithic sample with the later Nubian populations; and (2) to evaluate further the hypothesis that change in Nubian craniofacial morphology was due to changing functional demands associated with the progressive change in subsistence adaptation and associated behavior. The results tend to support recent views that the Nubian Mesolithic population is probably ancestral to later Nubian groups, and that the masticatory-functional hypothesis can best account for craniofacial change among the Nubians since 12,000 B.P. According to this hypothesis systematic reduction in functional demand placed on the masticatory complex from the Mesolithic led, secondarily, to an alteration of the growth of the maxillomandibular complex such that the face became progressively less robust and more inferoposteriorly located relative to the cranial vault. Both the increase in the height of the vault relative to its length, producing a more "globular" appearance, and the reduction in dental size were tertiary, compensatory responses to altered facial size and position.

The teeth of many fish, amphibia, and reptiles are attached to the alveolar bone via ankylosis. In contrast, mammalian periodontia are characterized by a gomphosis, an attachment of the tooth root in the alveolar bone socket via periodontal ligament fibers. Among the reptiles, the crocodilians are the only group featuring a gomphosis-type connection between tooth root and alveolar bone, while in other reptiles tooth-root and jawbone are connected via ankylosis. The purpose of the present study was to compare several key features of the crocodilian periodontium with those of the mammalian and noncrocodilian reptile periodontium. As experimental models for our study we chose the periodontium of newborn geckos (Hemidacylus turcicus), juvenile caimans (Caiman crocodilus crocodilus), and 10-day-postnatal Swiss-Webster mice (Mus musculus) as representative models for noncrocodilian reptiles, crocodilian reptiles, and mammals. The caiman periodontium emerged as an intermediary between the mineral-free mouse ligament and the mineralized gecko ankylosis-type attachment. Caiman ligament fibers were less organized than mouse ligament fibers but featured distinct fasciae surrounding ligament fiber bundles. Caiman Hertwig's epithelial root sheath (HERS) was similarly perforated as mouse HERS and distinctly different from the continuous gecko HERS. Both caiman and mouse HERS covered the entire tooth root length, while in the gecko HERS was limited to the coronal portion of the root, allowing for cementoid-mediated ankylosis at the apical tip of the root. We interpret our data to indicate distinct differences in mineral distribution, periodontal ligament fiber organization, and HERS distribution between noncrocodilian reptiles, crocodilian reptiles, and mammals. Mineral deposits in the caiman ligament may reflect an evolutionary position of the caiman periodontium between ankylosis and gomphosis.

M uch has been published in the clinical and basic science literature on the growth of the temporomandibular joint. An area of significant controversy is the question of whether the growth of the temporomandibular joint, and of the mandibular condyle in particular, can be influenced to any significant degree through therapeutic or experimental intervention. Despite the number of clinical and experimental studies of this question, no universal agreement has been reached regarding the potential for adaptation in response to an alteration of the structural or functional environment by means of growth and/or remodeling of the temporomandibular joint. Part of the reason for this lack of agreement stems from the fact that competing dogmas exist concerning the growth and adaptability of the temporomandibular joint. A precise definition of the mechanisms by which condylar growth takes place also has been hindered, in many cases, by inadequate clinical and experimental samples and by incomparability of treatment plan or experimental design. Numerous persons have undertaken experimental investigations of temporomandibular joint growth in animal models. An evaluation of the findings from these studies reveals that the age or developmental stage of the animals used in these experiments is a critical factor in determining the potential for temporomandibular joint adaptability. There is little experimental evidence demonstrating that any significant adaptations can occur in the adult temporomandibular joint,13, 16, li, 34 and pathologic changes have been reported to occur in some instances. 6 In contrast, other studies have shown that the temporomandibular joint region, particularly the mandibular condyle of young, growing animals, can be a primary site of craniofacial adaptation to altered occlusal function.', 2. s, *L 28-33, 35 We lhave experimentally studied temporomandibular joint adaptability to alteration of the biomechanical environment, using the rhesus monkey (Macaca mulatta) as our animal From the Departments of Anatomy and Anthropology and the Center for Human Growth and Development, The University of Michigan.

In vivo strain gauge analysis demonstrated that tensile bone strain is transmitted along the cranial vault to the parasagittal region during isotonic temporalis contraction. This strain is sufficient to cause measurable separation of the sagittal suture, and thus could influence growth at the sutural margins.