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M A McCollum

Publications and source records attributed to M A McCollum.

10 recordsLinked to original sources
PubMed2001

Developmental genetics and early hominid craniodental evolution.

Although features of the dentition figure prominently in discussions of early hominid phylogeny, remarkably little is known of the developmental basis of the variations in occlusal morphology and dental proportions that are observed among taxa. Recent experiments on tooth development in mice have identified some of the genes involved in dental patterning and the control of tooth specification. These findings provide valuable new insight into dental evolution and underscore the strong developmental links that exist among the teeth and the jaws and cranium. The latter has important implications for cladistic studies that traditionally consider features of the skull independently from the dentition.

Animals↗
PubMed2000

Subnasal morphological variation in fossil hominids: a reassessment based on new observations and recent developmental findings.

Quantitative and qualitative assessments of subnasal morphology in fossil hominids yield distinct patterns which have been used both to sort robust from nonrobust australopithecine taxa and to distinguish individual species. Recently, new developmental models have been applied to hominoid subnasal morphological variation. These studies require that certain features of the fossil hominid subnasal region, in particular the topography of the nasal cavity entrance and details of vomeral morphology, be reevaluated. This study does so for the robust and nonrobust australopithecines, early Homo (H. habilis/H. rudolfensis), and African H. erectus. Results reaffirm an overall similarity of the nonrobust Australopithecus subnasal morphological pattern with that of the chimpanzee. They further indicate that a vomeral insertion above the nasal surface of the premaxilla should be added to the list of traits characteristic of the robust australopithecine subnasal morphological pattern. Finally, reassessment of subnasal morphology in the early Homo and H. erectus samples from Africa suggest that these two taxa share a similar subnasal morphological pattern. This pattern consists of a smooth nasal cavity entrance, a horizontal nasal sill whose anterior edge is demarcated by a strong nasal crest, and a well-developed horizontal spine at the posterior edge of the nasal sill. Although none of the African fossil Homo specimens preserve a vomer, indirect evidence suggests that it would have inserted above the nasal sill.

Animals↗
PubMed2000

Adaptationism and the anthropoid postcranium: selection does not govern the length of the radial neck.

The length of the radial neck has been assumed to vary in living and extinct primates in accordance with its role as a moment arm during flexion by the m. biceps brachii. We here use a simple developmental approach to investigate whether or not this trait does, in fact, vary in such a manner. We find, instead, that virtually all variation in radial neck length is explicable as a simple correlate of overall body size, and that there is no evidence to conclude that selection has separately modified radial neck length in response to differing locomotor patterns. Further implications for the interpretation of mammalian skeletal morphology are briefly discussed.

Adaptation, Biological↗
PubMed1999

The robust australopithecine face: a morphogenetic perspective.

The robust australopithecines were a side branch of human evolution. They share a number of unique craniodental features that suggest their monophyletic origin. However, virtually all of these traits appear to reflect a singular pattern of nasomaxillary modeling derived from their unusual dental proportions. Therefore, recent cladistic analyses have not resolved the phylogenetic history of these early hominids. Efforts to increase cladistic resolution by defining traits at greater levels of anatomical detail have instead introduced substantial phyletic error.

Africa↗
PubMed1999

The Depression-Happiness Scale: test-retest data over two weeks.

The present aim was to examine further the psychometric properties of the Depression-Happiness Scale. Test-retest data over 2 wk. are reported for this scale for a sample of 54 female Northern Irish university students. Stability was fairly high as r = .70, and there was no significant change between Time 1 and Time 2 (M = 49.7 and 50.8, respectively). The data suggest that the Depression-Happiness Scale might be considered a trait measure of happiness rather than a state measure.

Adult↗
PubMed1997

Subnasoalveolar anatomy and hominoid phylogeny: evidence from comparative ontogeny.

The present analysis evaluated extant hominoid subnasal morphological variation from an ontogenetic perspective, documenting both qualitative and allometric details of subnasal maturation in Hylobates, great apes and modern humans. With respect to intraspecific variation, results of log-linear modeling procedures indicate that qualitative features of the subnasal region shown previously to discriminate extant taxa (Ward and Kimbel, 1983; McCollum et al., 1993) do not vary appreciably with either age or sex. In terms of quantitative variation, aside from observed changes in the position of the anterior attachment of the nasal septal cartilage relative to the lateral margins of the nasal cavity, the morphology of the subnasal region does not vary appreciably with age. Furthermore, it was found that sexual dimorphism in subnasal form is present only in Pongo and Gorilla and is the result of sexual bimaturism rather than sexual variation in canine size. In considering interspecific variation in subnasal form, there is a propensity among hominoid taxa for the nasal cavity floor to be free of substantial topographic relief. The smoothly continuous nasal floor topography identified in the majority of hominoid taxa appears to be produced by extensive resorption of the anterior nasal cavity floor that accompanies an upward rotation of the anterior maxilla during craniofacial ontogeny. Comparisons of ontogenetic allometric trajectories indicate that relatively little of the variation in hominoid subnasal form can early be attributed to variation in body/cranial size. Instead, variation in craniofacial orientation, vascular anatomy and incisor size and inclination were identified as potential mediators of hominoid subnasoalveolar anatomy. Although results of this analysis confirm that many detail of the orangutan subnasal morphology are derived for this taxon, there is only little conclusive evidence to support recent reports that the morphology displayed by Gorilla is primitive for great apes.

Aging↗
PubMed1997

Palatal thickening and facial form in Paranthropus: examination of alternative developmental models.

Paranthropus is distinctive among hominoids in its possession of a greatly thickened hard palate. Although traditionally considered a structural adaptation to counter high-magnitude masticatory stress, alternative developmental models are equally viable. Three models of palatal thickening were evaluated in this study. A mechanical model interprets palatal thickening as a compensatory response to increased instability of the midpalatal suture effected by an anterior placement of the masseteric muscle mass. This model predicts that palatal thickness is correlated with the length of the palate posterior to the masseteric tubercle. Two non-mechanical models consider the thickness of the hard palate to be structurally related to and therefore correlated with either 1) the degree to which the premaxilla overlaps the hard palate in the subnasal region or 2) the height of the posterior facial skeleton. The correlation of craniofacial variables was assessed intraspecifically in ontogenetic series of great ape and human crania. Tests of correlation were performed for each comparison using both residuals calculated from reduced major axis regression of the variable of interest against a measure of cranial size and shape ratios. A significant correlation of palatal thickness with posterior facial height in Pan suggests that the unusually thick hard palate of Paranthropus is directly related to the increased posterior facial height characteristic of this taxon. Further evaluation suggests that extreme palatal thickening in these specimens occurred by virtue of their possession of a nasal septum morphology in which the vomer extends onto the superior and nasal surface of the premaxilla. Such a morphology would have constrained the palatal nasal lamina to maintain the approximate level of the premaxillary nasal lamina throughout the growth process thereby promoting palatal thickening.

Animals↗
PubMed1994

Mechanical and spatial determinants of Paranthropus facial form.

It is well documented in the anthropological literature that the distinctive morphology of the "robust" hominid facial skeleton reflects its dietary specialization. Rak (1983) has provided the most comprehensive evaluation of Paranthropus facial morphology and this important study concluded that bone strain generated during mastication was responsible for the scaling of measures of facial height and breadth. The present study evaluated Rak's analysis by examining the relationship between bizygomatic breadth and facial height in an ontogenetic series of Pan and Gorilla crania. Results of this analysis indicate that facial height and breadth dimensions were not mechanically scaled in the "robust" australopithecines. Structural analysis of African ape facial maturation was also used to examine alternative spatial methods of malar elongation in Paranthropus. It is concluded that the increased height of the malar region in these specimens is not related to either vertical expansion of the posterior facial skeleton or to expansion of the temporal fossa. Malar elongation is, however, consistent with a derived pattern of facial growth in crania possessing a thickened hard palate.

Analysis of Variance↗