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G C Conroy

Publications and source records attributed to G C Conroy.

At least 19 recordsLinked to original sources
PubMed1992

Otavipithecus namibiensis, first Miocene hominoid from southern Africa.

We report here the discovery of a Miocene hominoid from Berg Aukas, Namibia, the first known from the African continent south of equatorial East Africa. This represents a major range extension of Miocene Hominoidea in Africa to latitude 20 degrees S. The holotype, a right mandibular corpus preserving the crowns of the P4-M3, partial crown and root of the P3, partial root of the canine, alveoli for all four incisors, and partial alveolus for the left canine, was found during paleontological explorations of karst-fill breccias in the Otavi region of northern Namibia. The mandible has unique characteristics that differentiate it from other middle Miocene hominoids of Africa and Eurasia and represents the only fossil evidence documenting a pre-australopithecine stage of hominoid evolution in southern Africa. Faunal analyses indicate that the breccia block containing the specimen accumulated during the latter part of the middle Miocene, about 13 +/- 1 Myr. Fauna from other breccia blocks at Berg Aukas are of diverse ages, including the earlier part of the middle Miocene, the upper Miocene, Plio-Pleistocene and Holocene.

Animals↗
PubMed1992

Probit and survival analysis of tooth emergence ages in a mixed-longitudinal sample of chimpanzees (Pan troglodytes).

Tooth emergence data from a mixed-longitudinal sample of 58 chimpanzees of known age were analyzed using probit and survival techniques to produce median emergence ages, ranges of variability, and emergence sequences for primary and permanent teeth. Between-group comparisons were made to test for statistically significant differences in emergence ages. No such differences were found between right and left sides, or between maxilla and mandible, for any primary or permanent teeth. Male-female comparisons did demonstrate significant emergence-age differences for some teeth, although they were not always bilaterally symmetrical. More complete data are required to further clarify the nature of sex differences in tooth emergence in chimpanzees. Regression models for age prediction from the number of emerged teeth were generated and indicate that males achieve a given number of emerged teeth at a significantly later age than females. However, when fewer than five teeth have emerged, males are predicted to be younger than females. The sizable root mean square error values for these models suggest that this method of age prediction has limited usefulness owing to the amount of variability in timing of tooth emergence in chimpanzees. The implications of these data for studies on tooth emergence in early hominids are addressed.

Animals↗
PubMed1990

Endocranial features of Australopithecus africanus revealed by 2- and 3-D computed tomography.

The earliest hominid from South Africa, Australopithecus africanus, is known from only six specimens in which accurate assessment of endocranial capacity and cranial venous outflow pattern can be obtained. This places a severe limit on a number of hypotheses concerning early hominid evolution, particularly those involving brain-body size relationships and adaptations of the circulatory system to evolving upright posture. Advances in high-resolution two- and three-dimensional computed tomography (CT) now allow the inclusion of another important specimen to this list, MLD 37/38 from Makapansgat. A new computer imaging technique is described that "reconstructs" the missing portions of the endocranial cavity in order to determine endocranial capacity. In addition, CT evaluation allows assessment of cranial venous outflow pattern even in cases where the endocranial cavity is completely filled with stone matrix. Results show that endocranial capacity in this specimen is less than originally proposed and also support the view that gracile and robust australopithecines evolved different cranial venous outflow patterns in response to upright postures.

Animals↗
PubMed1989

Imaging workstations for computer-aided primatology: promises and pitfalls.

In this paper, the application of biomedical imaging workstations to primatology will be explained and evaluated. The technological basis, computer hardware and software aspects, and the various uses of several types of workstations will all be discussed. The types of workstations include: (1) Simple - these display-only workstations, which function as electronic light boxes, have applications as terminals to picture archiving and communication (PAC) systems. (2) Diagnostic reporting - image-processing workstations that include the ability to perform straightforward manipulations of gray scale and raw data values will be considered for operations such as histogram equalization (whether adaptive or global), gradient edge finders, contour generation, and region of interest, as well as other related functions. (3) Manipulation systems - three-dimensional modeling and computer graphics with application to radiation therapy treatment planning, and surgical planning and evaluation will be considered. A technology of prime importance in the function of these workstations lies in communications and networking. The hierarchical organization of an electronic computer network and workstation environment with the interrelationship of simple, diagnostic reporting, and manipulation workstations to a coaxial or fiber optic network will be analyzed.

Animals↗
PubMed1989

Three-dimensional surface reconstruction software system for IBM personal computers.

Surface and volumetric three-dimensional imaging methods have found application in fields as diverse as diagnostic medical imaging and paleontological research. The acquisition, modeling, classification, and computer graphics rendering of discrete image volumes will be introduced. Applications in diagnosis (craniofacial, orthopedic, cardiovascular, and others) as well as reconstruction methods for generic serial sections will be described. C language software for three-dimensional reconstruction which operates on an IBM PC/AT clone is described.

Animals↗
PubMed1988

Alleged synapomorphy of the M1/I1 eruption pattern in robust australopithecines and Homo: evidence from high-resolution computed tomography.

Ever since Broom and Robinson (1951) published their claim that the eruption pattern of permanent incisors in robust australopithecines was most similar to that of modern man and different from that of gracile australopithecines and apes, the accuracy of this observation has been the subject of periodic debate (e.g., Wallace: Ph.D. thesis, 1972; Dean: Am. J. Phys. Anthropol. 67:251-257, 1985; Grine: Am. J. Phys. Anthropol. 72:353-359, 1987). Part of the problem is that the developing incisors in one of the specimens most crucial to this argument (SK61) are difficult to visualize clearly by conventional radiographic techniques because of the heavy mineralization in the fossil. This study reanalyzes SK 61 by high-resolution computed tomography in order to contribute to the final resolution of its incisor development. Grine's (op. cit.) assessment of the incisors as the deciduous ones, not the permanent ones, is fully confirmed. This fact, in conjunction with the observation that permanent incisor root formation had only just commenced in this specimen, further weakens the argument of M1/I1 eruption pattern synapomorphy between Homo and robust australopithecines.

Fossils↗
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↗
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↗