Diversity in the early tertiary anthropoidean radiation in Africa.
(25/163)
Between 1987 and 1991 recent field seasons in the Fayum Depression of Egypt have yielded five species and genera of primates that were earlier unknown. Three of these species and genera are described below. All these genera and species are known only from Fayum site L-41, which has been dated as of late Eocene age. In the Fayum, these 5 species from L-41 are added to 3 kinds of prosimians (1 species formally described) and 11 earlier named species of Anthropoidea. When certain undescribed species are added, the total of known Fayum primate species comes to 21, belonging to at least 10 genera, genera that, in turn, could belong to as many as seven families. This arguably represents more taxonomic diversity of primates, especially higher primates, than has been demonstrated before in one so spatially and temporally limited area. These facts argue that an important, perhaps primary, radiation of anthropoideans took place in the African Eocene. (+info)
An Early Cretaceous tribosphenic mammal and metatherian evolution.
(26/163)
Derived features of a new boreosphenidan mammal from the Lower Cretaceous Yixian Formation of China suggest that it has a closer relationship to metatherians (including extant marsupials) than to eutherians (including extant placentals). This fossil dates to 125 million years ago and extends the record of marsupial relatives with skeletal remains by 50 million years. It also has many foot structures known only from climbing and tree-living extant mammals, suggesting that early crown therians exploited diverse niches. New data from this fossil support the view that Asia was likely the center for the diversification of the earliest metatherians and eutherians during the Early Cretaceous. (+info)
Late Miocene teeth from Middle Awash, Ethiopia, and early hominid dental evolution.
(27/163)
Late Miocene fossil hominid teeth recovered from Ethiopia's Middle Awash are assigned to Ardipithecus kadabba. Their primitive morphology and wear pattern demonstrate that A. kadabba is distinct from Ardipithecus ramidus. These fossils suggest that the last common ancestor of apes and humans had a functionally honing canine-third premolar complex. Comparison with teeth of Sahelanthropus and Orrorin, the two other named late Miocene hominid genera, implies that these putative taxa are very similar to A. kadabba. It is therefore premature to posit extensive late Miocene hominid diversity on the basis of currently available samples. (+info)
Application of dentition and facial morphology integration system for occlusal correction.
(28/163)
A system to provide quantitative information on the angle between dentition and face was developed using a three-dimensional (3D) integrated configuration measured by a non-contact 3D digitizer. The integrated configuration angles between the Camper's plane and occlusal plane on the sagittal and the horizontal projected planes were obtained. Clinical application for a patient to improve the tegmenta of the anterior tooth by setting a temporary bridge on her lower dentition was attempted. Her dentition and face were measured on her first visit and after treatment, and 3D data of them were integrated. The quantitative change of the angle between the Camper's plane and lower occlusal plane were successfully analyzed by the present system, and after treatment, rotation of the lower occlusal plane for 1 degrees in a clockwise direction on the sagittal plane projection, and that for 1 degrees in a counterclockwise direction on the horizontal plane projection relative to the Camper's plane were detected. (+info)
Wild chimpanzee dentition and its implications for assessing life history in immature hominin fossils.
(29/163)
Data from three African field sites on Pan troglodytes demonstrate an unambiguous pattern of a slower growth rate in wild vs. captive chimpanzee populations. A revised dental growth chronology for chimpanzees is similar to estimated timing of Homo erectus and therefore has implications for interpreting life history in hominins. (+info)
Masticatory efficiency before and after surgery in oral cancer patients: comparative study of glossectomy, marginal mandibulectomy and segmental mandibulectomy.
(30/163)
This study evaluated the effect of oral cancer surgery on masticatory efficiency. Masticatory efficiency was measured using the ATP absorption method. Eating ability was measured using a questionnaire. Two groups were employed as controls: The "normal occlusion group" consisted of subjects who had a complete set of natural maxillary teeth opposed to mandibular teeth, and the "unilateral occlusion group" consisted of subjects who had lost their molar and premolar teeth on one side of the mandible as a result of caries or periodontal diseases. Three treatment groups, each of 6 patients, were studied: a glossectomy group, a marginal mandibulectomy group and a segmental mandibulectomy group. There were no differences in masticatory efficiency between two control groups. Masticatory efficiencies of the three oral cancer treatment groups were lower than in the unilateral occlusion group, even 12 months after surgery. Masticatory efficiency of the glossectomy group was significantly higher 12 months after surgery compared with pre-surgery. Masticatory and eating abilities of the marginal mandibulectomy group and the segmental mandibulectomy were reduced at 3 and 6 months after surgery. The masticatory efficiency 12 months after surgery was higher in the marginal mandibulectomy group than the segmental mandibulectomy group, although the difference was not statistically significant. The self assessed eating ability 12 months after surgery was significantly higher in the marginal mandibulectomy group than the segmental mandibulectomy group. These results suggest that discontinuation of the mandible may lead patients to eat only foods that do not require a substantial amount of chewing. Hence, the quality of life of patients in the marginal mandibulectomy group was considered to be better than that in the segmental mandibulectomy group. (+info)
A Late Jurassic digging mammal and early mammalian diversification.
(31/163)
A fossil mammal from the Late Jurassic Morrison Formation, Colorado, has highly specialized teeth similar to those of xenarthran and tubulidentate placental mammals and different from the generalized insectivorous or omnivorous dentitions of other Jurassic mammals. It has many forelimb features specialized for digging, and its lumbar vertebrae show xenarthrous articulations. Parsimony analysis suggests that this fossil represents a separate basal mammalian lineage with some dental and vertebral convergences to those of modern xenarthran placentals, and reveals a previously unknown ecomorph of early mammals. (+info)
An Early Pleistocene hominin mandible from Atapuerca-TD6, Spain.
(32/163)
We present a mandible recovered in 2003 from the Aurora Stratum of the TD6 level of the Gran Dolina site (Sierra de Atapuerca, northern Spain). The specimen, catalogued as ATD6-96, adds to the hominin sample recovered from this site in 1994-1996, and assigned to Homo antecessor. ATD6-96 is the left half of a gracile mandible belonging to a probably female adult individual with premolars and molars in place. This mandible shows a primitive structural pattern shared with all African and Asian Homo species. However, it is small and exhibits a remarkable gracility, a trait shared only with the Early and Middle Pleistocene Chinese hominins. Furthermore, none of the mandibular features considered apomorphic in the European Middle and Early Upper Pleistocene hominin lineage are present in ATD6-96. This evidence reinforces the taxonomic identity of H. antecessor and is consistent with the hypothesis of a close relationship between this species and Homo sapiens. (+info)