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G C Conroy

Publications and source records attributed to G C Conroy.

36 records · Page 2Linked to original sources
PubMed1986

The microstructure of dentine in taxonomic and phylogenetic studies.

Traditionally, physical anthropologists have focused their dental studies on features of teeth that can be observed with the unaided eye, measured with calipers, or observed with light microscopes. With the advent of the scanning electron microscope, there has been renewed interest in the use of the microstructure of enamel in phylogenetic reconstruction and taxonomic classification. The microstructure of dentine has received far less research attention than has enamel although several investigators have proposed that dentine has taxon specificity. We report the first results of a study in which we investigated the taxon specificity of dentine. In our study, we exposed the dentinal tubules on the mesial root surfaces of 12 Canis, 11 Papio, and 12 Homo mandibular first molars and compared tubule density and pattern among the three taxa. Based on these parameters, 91.43% of the teeth were correctly identified as being dog, baboon, or human, respectively. We conclude that dentine has taxon-specific structural characteristics, which can be used in anthropological investigations. To our knowledge, this is the first comparative study of the micro-structure of teeth utilizing statistical analysis.

Animals↗
PubMed1986

Advanced computer graphics technology reveals cortical asymmetry in endocasts of rhesus monkeys.

Lengths of cortical sulci were measured on ten endocranial casts (endocasts) from skulls of rhesus monkeys, using advanced computer technology that permits analysis and imaging of surface morphology in three dimensions. Sulcal lengths were compared in left and right hemispheres and, contrary to earlier reports, the length of the left Sylvian fissure was found to be significantly longer than its right counterpart, as is the case for chimpanzees and humans. This asymmetry in humans is thought to be associated with asymmetrical representation of language functions in the left hemisphere and, although this report is the first to demonstrate a significantly longer left Sylvian fissure in rhesus monkeys, our results are in keeping with psychophysical evidence that suggests that Macaca is left hemisphere dominant for perception of meaningful vocalizations. We attribute the difference between our findings and previous reports to the sensitivity of the new computer technology used to collect data from endocasts.

Animals↗
PubMed1985

Three-dimensional cranial surface reconstructions using high-resolution computed tomography.

Until recently, there has been no satisfactory way for anthropologists to visualize intracranial morphology in more than two dimensions without actually "invading" the skull in some manner. Images provided by conventional x-ray and computed tomography (CT) scans are often abstract, flat, two-dimensional representations that fail to reveal three-dimensional relationships. We describe new computer-imaging techniques that reconstruct three-dimensional images from sequential series of narrowly collimated (1-2 mm), high-resolution CT scans of the skull. These computed images represent three-dimensional surface data and can be viewed from any direction. Depth information is encoded in gray scale. In addition, selected portions of the anatomy can be "removed", i.e., made transparent, to allow visualization of previously hidden intracranial morphology. Since the geometric data obtained with the CT scanner are precise, parameters such as linear distances, angles, areas, and volumes can be accurately (and instantaneously) generated. The power and versatility of these computer-imaging techniques are demonstrated by examining living subjects with major craniofacial dysmorphology (Treacher-Collins syndrome and unilateral coronal synostosis); an anthropoid osteological specimen (Gorilla); and a fossil mammal skull.

Cephalometry↗
PubMed1982

Fossil mammals and artefacts from the Middle Awash Valley, Ethiopia.

A review of fossil mammalian faunas from the Middle Awash indicates they span most of the later Neogene and document evolutionary change in several mammalian groups, especially Primates, Proboscidea and Artiodactyla. Oldowan artefacts first appear in the late Pliocene, while Acheulian and later industries and apparent occupation sites occur in Pleistocene beds.

Animals↗
PubMed1981

The anatomy and phylogenetic significance of the carotid arteries and nerves in strepsirhine primates.

The internal carotid artery in lorisiform primates was identified on the basis of its close association with the internal carotid nerve (postsynaptic sympathetic trunk). An atrophic vessel in the lorisine Arctocebus resembles the internal carotid artery of Lemur in that it enters the tympanic bulla and promontory tube closely associated with the internal carotid nerve. According to this criterion of homology, the enigmatic lorisiform extrabullar carotid artery is not homologous with the internal carotid (promontory) artery of lemuriform primates or the medial internal carotid artery of the dog. Hypotheses about strepsirhine evolution must take these morphological facts into account.

Animals↗
PubMed1980

Cerebral venous hemodynamics and the basicranium of Cebus.

The study of basicranial foramina has played an important role in primatological investigations. They are often the only clues for deciphering cerebral vascular evolution in fossil forms. This study illustrates the significance of considering foraminal shape when analyzing or describing basicranial anatomy in living and fossil primates. It is suggested that certain hemodynamic properties of cerebral venous drainage in Cebus represent patterns that were most likely present in ancestral catarrhines.

Animals↗
PubMed1978

Middle ear morphology of Lemur variegatus. Some implications for primate paleontology.

The middle ear morphology of Lemur variegatus, a strepsirhine primate, is described. Although no promontory branch of the internal carotid artery appears, there is a well-developed "promontory canal" containing a nerve trunk. This structure, which is previously undescribed in strepsirhines, is made up of the tympanic nerve and the internal carotid nerve. The implications of this discovery for paleontology, systematics, and future research are discussed.

Animals↗
PubMed1978

Non-metric features in the ulna of Aegyptopithecus, Alouatta, Ateles, and Lagothrix.

A comparison of the non-metric features of the ulnar fragment (YPM 23940) referred to Aegyptopithecus zeuxis with those in the same bone of Alouatta, Ateles, and Lagothrix -- the three living taxa whose ulnae most closely resemble that of the fossil -- reveals that the closest similarities of the fragment are with the ulna of Alouatta.

Alouatta↗
PubMed1975

Ape limb bone from the oligocene of Egypt.

An ulna attributed to Aegyptopithecus zeuxis provides the first evidence for interpreting the locomotor behavior of the earliest apes. The fossil indicates that Aegyptopithecus was an arboreal quadruped and that the primitive hominoid locomotor pattern was most nearly analogous, among living primates, to that of Alouatta, the howler monkey.

Animals↗
PubMed1975

Dental eruption patterns in Parapithecidae (Primates, Anthropoidea).

Radiographic analysis of mandibular fragments of the Oligocene primates Apidium phiomense and Parapithecus grangeri provides sequences of postincisor development and eruption. Although retaining the premolar eruption sequence (P2 leads to P4 leads to P3), the parapithecids possessed the derived feature of delayed canine appearance which, with other characters of cranial and postcranial morphology, aligns them with Anthropoidea and not Prosimii or platyrrhines.

Animals↗
PubMedDate not supplied

Dental development of the Taung skull from computerized tomography.

Just over 60 years ago, Dart's description and analysis of the Taung child's skull triggered an intellectual revolution about human origins. Recently, several authors have suggested that one of the most significant hominid-like traits of australopithecines, delayed maturation, may not after all be valid. This is a radical departure from Mann's classic study of australopithecine maturation and palaeodemography based on dental eruption patterns. The resolution of this debate has important implications for the history of the biological and social evolution of the human species. In view of the controversies generated by recent studies, and particularly because the Taung skull is the type specimen of Australopithecus africanus, we have investigated the relevant anatomy of the Taung 'child' using computerized tomography. We conclude that the Taung 'child' shows some important dental maturational affinities with great apes, although as Dart noted, other hominid-like features are clearly present.

Age Determination by Teeth↗
PubMedDate not supplied

The evolution of the primate foot from the earliest primates to the Miocene hominoids.

The fossil evidence relating to the evolution of the primate foot is reviewed and evaluated. Many of the characteristic features of the primate foot had evolved by the early Tertiary over 40 million years ago. Probably the most significant of these developments was the progressive migration of the talus to a position over the calcaneum. These morphological features are followed through the Miocene hominoid genera from East Africa, Europe, and South Asia. While some features of Miocene hominoids, especially those relating to climbing abilities, are still evident in the predominantly bipedal earliest hominids of the Plio-Pleistocene, there is no evidence yet from the Miocene of the first stages in the evolution of that bipedalism.

Adaptation, Biological↗