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Skull Length (skull + length)
Selected AbstractsSkull shape and feeding strategy in Sphenodon and other Rhynchocephalia (Diapsida: Lepidosauria),JOURNAL OF MORPHOLOGY, Issue 8 2008Marc E.H. Jones Abstract The Rhynchocephalia are a group of small diapsid reptiles that were globally distributed during the early Mesozoic. By contrast, the only extant representatives, Sphenodon punctatus and S. guntheri (Tuatara), are restricted to New Zealand off-shore islands. The Rhynchocephalia are widely considered to be morphologically uniform but research over the past 30 years has revealed unexpected phenotypic and taxonomic diversity. Phylogenetically "basal taxa" generally possess relatively simple conical or columnar teeth whereas more derived taxa possessed stouter flanged teeth and sophisticated shearing mechanisms: orthal in some (e.g., Clevosaurus hudsoni) and propalinal in others (e.g., S. punctatus). This variation in feeding apparatus suggests a wide range of feeding niches were exploited by rhynchocephalians. The relationship of skull shape to skull length, phylogenetic grouping, habit, and characters relating to the feeding apparatus are explored here with geometric morphometric analysis on two-dimensional landmarks. Principle components analysis demonstrates that there are significant differences between phylogenetic groups. In particular, Sphenodon differs significantly from all well known fossil taxa including the most phylogenetically basal forms. Therefore, it is not justifiable to use Sphenodon as a solitary outgroup when studying skull shape and feeding strategy in squamates; rhynchocephalian fossil taxa also need to be considered. There are also significant differences between the skull shapes of aquatic taxa and those of terrestrial taxa. Of the observed variation in skull shape, most variation is subsumed by variation in dentary tooth base shape, the type of jaw movement employed (e.g., orthal vs. propalinal) and the number of palatal tooth rows. By comparison, the presence or absence of flanges, dentary tooth number and palatal tooth row orientation subsume much less. Skull length was also found to be a poor descriptor of overall skull shape. Compared to basal rhynchocephalians members of more derived terrestrial radiations possess an enlarged postorbital area, a high parietal, and a jaw joint positioned ventral to the tooth row. Modification of these features is closely associated with increased biting performance and thus access to novel food items. Some of these same trends are apparent during Sphenodon ontogeny where skull growth is allometric and there is evidence for ontogenetic variation in diet. J. Morphol., 2008. © 2008 Wiley-Liss, Inc. [source] Aspects of achondroplasia in the skulls of dwarf transgenic mice: A cephalometric studyTHE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 3 2006Melissa Wadler Bloom Abstract Achondroplasia, the most common short-limbed dwarfism in humans, results from a single nucleotide substitution in the gene for fibroblast growth factor receptor 3 (FGFR3). FGFR3 regulates bone growth in part via the mitogen-activated protein kinase pathway (MAPK). To examine the role of this pathway in chondrocyte differentiation, a transgenic mouse was generated that expresses a constitutively active mutant of MEK1 in chondrocytes and exhibits dwarfing characteristics typical of human achondroplasia, i.e., shortened axial and appendicular skeletons, mid-facial hypoplasia, and dome-shaped cranium. In this study, cephalometrics of the MEK1 mutant skulls were assessed to determine if the MEK1 mice are a good model of achondroplasia. Skull length, arc of the cranial vault, and area, maximum and minimum diameters of the brain case were measured on digitized radiographs of skulls of MEK1 and control mice. Cranial base and nasal bone length and foramen magnum diameter were measured on midsagittal micro-CT sections. Data were normalized by dividing by the cube root of each animal's weight. Transgenic mice exhibited a domed skull, deficient midface, and (relatively) prognathic mandible and had a shorter cranial base and nasal bone than the wild-type. Skull length was significantly less in transgenic mice, but cranial arc was significantly greater. The brain case was larger and more circular and minimum diameter of the brain case was significantly greater in transgenic mice. The foramen magnum was displaced anteriorly but not narrowed. MEK1 mouse cephalometrics confirm these mice as a model for achondroplasia, demonstrating that the MAP kinase signaling pathway is involved in FGF signaling in skeletal development. © 2006 Wiley-Liss, Inc. [source] The evolution of orbit orientation and encephalization in the Carnivora (Mammalia)JOURNAL OF ANATOMY, Issue 5 2009John A. Finarelli Abstract Evolutionary change in encephalization within and across mammalian clades is well-studied, yet relatively few comparative analyses attempt to quantify the impact of evolutionary change in relative brain size on cranial morphology. Because of the proximity of the braincase to the orbits, and the inter-relationships among ecology, sensory systems and neuroanatomy, a relationship has been hypothesized between orbit orientation and encephalization for mammals. Here, we tested this hypothesis in 68 fossil and living species of the mammalian order Carnivora, comparing orbit orientation angles (convergence and frontation) to skull length and encephalization. No significant correlations were observed between skull length and orbit orientation when all taxa were analysed. Significant correlations were observed between encephalization and orbit orientation; however, these were restricted to the families Felidae and Canidae. Encephalization is positively correlated with frontation in both families and negatively correlated with convergence in canids. These results indicate that no universal relationship exists between encephalization and orbit orientation for Carnivora. Braincase expansion impacts orbit orientation in specific carnivoran clades, the nature of which is idiosyncratic to the clade itself. [source] Skull shape and feeding strategy in Sphenodon and other Rhynchocephalia (Diapsida: Lepidosauria),JOURNAL OF MORPHOLOGY, Issue 8 2008Marc E.H. Jones Abstract The Rhynchocephalia are a group of small diapsid reptiles that were globally distributed during the early Mesozoic. By contrast, the only extant representatives, Sphenodon punctatus and S. guntheri (Tuatara), are restricted to New Zealand off-shore islands. The Rhynchocephalia are widely considered to be morphologically uniform but research over the past 30 years has revealed unexpected phenotypic and taxonomic diversity. Phylogenetically "basal taxa" generally possess relatively simple conical or columnar teeth whereas more derived taxa possessed stouter flanged teeth and sophisticated shearing mechanisms: orthal in some (e.g., Clevosaurus hudsoni) and propalinal in others (e.g., S. punctatus). This variation in feeding apparatus suggests a wide range of feeding niches were exploited by rhynchocephalians. The relationship of skull shape to skull length, phylogenetic grouping, habit, and characters relating to the feeding apparatus are explored here with geometric morphometric analysis on two-dimensional landmarks. Principle components analysis demonstrates that there are significant differences between phylogenetic groups. In particular, Sphenodon differs significantly from all well known fossil taxa including the most phylogenetically basal forms. Therefore, it is not justifiable to use Sphenodon as a solitary outgroup when studying skull shape and feeding strategy in squamates; rhynchocephalian fossil taxa also need to be considered. There are also significant differences between the skull shapes of aquatic taxa and those of terrestrial taxa. Of the observed variation in skull shape, most variation is subsumed by variation in dentary tooth base shape, the type of jaw movement employed (e.g., orthal vs. propalinal) and the number of palatal tooth rows. By comparison, the presence or absence of flanges, dentary tooth number and palatal tooth row orientation subsume much less. Skull length was also found to be a poor descriptor of overall skull shape. Compared to basal rhynchocephalians members of more derived terrestrial radiations possess an enlarged postorbital area, a high parietal, and a jaw joint positioned ventral to the tooth row. Modification of these features is closely associated with increased biting performance and thus access to novel food items. Some of these same trends are apparent during Sphenodon ontogeny where skull growth is allometric and there is evidence for ontogenetic variation in diet. J. Morphol., 2008. © 2008 Wiley-Liss, Inc. [source] Bite forces, canine strength and skull allometry in carnivores (Mammalia, Carnivora)JOURNAL OF ZOOLOGY, Issue 2 2005Per Christiansen Abstract Skull variables were analysed for allometry patterns in 56 species of extant carnivores. As previously reported, many skull variables scale near isometrically with either skull length or lower jaw length. The maximal gape angle scales insignificantly (P<0.05) with skull size, but the clearance between the canines shows a significant relationship with skull size and scales near isometrically. Maximal bite forces were estimated from geometrical cross-sectional areas of dried skulls, and the bending strength of the canines was computed by modelling the canines as a cantilevered beam of solid, homogeneous material with an elliptical cross section. Previous hypotheses of large taxon differences in canine bending strengths, so that felids have stronger canines than canids, are corroborated when actual bite forces at the upper canine are ignored. Incorporation of bite force values, however, nullifies the differences in canine bending strength among felids and canids, and ursids seem to have stronger canines than felids. This is probably because of the significantly longer canines of felids compared to canids and ursids, and the generally high bite forces of felids. [source] A NEW SPECIES OF CLEVOSAURUS (LEPIDOSAURIA: RHYNCHOCEPHALIA) FROM THE UPPER TRIASSIC OF RIO GRANDE DO SUL, BRAZILPALAEONTOLOGY, Issue 4 2006JOSÉ F. BONAPARTE Abstract:, Well-preserved cranial remains of a small sphenodontian lepidosaur from the Upper Triassic Caturrita Formation of Rio Grande do Sul, Brazil, are the first record of the genus Clevosaurus Swinton, 1939 from South America. They represent a new species, Clevosaurus brasiliensis, which is distinguished by a very short antorbital region of the skull (corresponding to about 20 per cent of skull length) and the presence of teeth in addition to two longitudinal rows on the pterygoid. C. brasiliensis most closely resembles C. bairdi from the Lower Jurassic of Nova Scotia (Canada) and C. mcgilli from the Lower Jurassic of Yunnan (China). The discovery of Clevosaurus in the Upper Triassic of southern Brazil provides a significant range extension of this widely distributed sphenodontian genus. Along with other recent finds, it also suggests that there may have been less biotic provincialism among terrestrial vertebrates during the Late Triassic than has previously been assumed. [source] The Relationship Between Cephalic Scales and Bones in Lizards: A Preliminary Microtomographic Survey on Three Lacertid SpeciesTHE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 2 2010David Costantini Abstract In the last two decades, there has been a great deal of interest in the morphology and anatomy of the lizard skull in an ecological and evolutionary perspective. However, the relationship between variations in many key anatomical features remains largely unknown. Using microtomography and geometric morphometrics, we examined the relationship between bones and scales associated with the parietal foramen in the three lizards species most common in the Italian peninsula: Podarcis muralis, P. sicula, and Lacerta bilineata. The imprints of the scales are clearly recognizable on the outer bone surface, and this may suggest a structural interaction between these elements. The temporal osteoderms are visible in the larger males and in the larger females of L. bilineata, but they are absent in the smaller specimens of L. bilineata and in all Podarcis specimens. Two parallel rows of pterygoid teeth are present in all the specimens of L. bilineata and are absent in the smaller male of L. bilineata and in both Podarcis species. Cheek osteoderms occurred only in the largest specimens of our sample (i.e., large L. bilineata), being possibly related to hyperostotic processes and densitometric thresholds more than to phylogeny. Minor differences may be also associated with the form of the parietal foramen. In absolute terms the parietal foramen tends to be largest in L. bilineata but in relation to skull length the foramen tends to be larger in P. muralis. In this latter species the foramen is also more elongated. In all three species the fronto-parietal suture occupies a similar location relatively to the scale spatial organization. A shared allometric pattern shows that the main vault enlargement can be localised at the areas anterior to the fronto-parietal suture, providing further information on the possible morphogenetic dynamics associated with the interaction between scales and bones around this structure. Anat Rec, 2010. © 2009 Wiley-Liss, Inc. [source] Conformation of the Equine Skull: A Morphometric StudyANATOMIA, HISTOLOGIA, EMBRYOLOGIA, Issue 4 2006K. E. Evans Summary There is a lack of an established method for quantifying equine skull morphology. This study proposes a method that is valid for use on both live and deceased horses. A total of nine head measurements (skull length, cranial length, nasal length, ratio of cranial:nasal length, cranial width, zygomatic width, mandibular depth, nasal profile area, cranial profile area) and six indices (skull index, cranial index, nasal index, mandibular index, nasal profile index, cranial profile index) were recorded from 30 horses from a variety of breeds whilst the soft tissues of the head were intact. A line was drawn level with the palpable notches caudal to the caudal lacrimal process of each orbit to estimate the suture line of the nasal and frontal bones and distinguish between the neurocranium and splanchnocranium. There were positive correlations between many of the head measurements. This method also illustrated significant differences in the skull morphology of three breeds (Arabians, thoroughbreds and standardbreds). [source] Osteological Examinations on the Budgerigar (Melopsittacus undulatus Shaw 1805) with Special Reference to Skeletal Alterations Conditioned by BreedingANATOMIA, HISTOLOGIA, EMBRYOLOGIA, Issue 4 2009T. Bartels Summary The aims of this study were to examine the skeleton of domesticated budgerigars of phenotypically different breeding types, to describe the expression of skeletal changes and to discuss the results with special reference to the causes and effects of breed-conditioned alterations. Complete skeletons of 39 adult budgerigars of both sexes were the object of our research. The examinations demonstrated that almost all metrically sized skeleton dimensions of budgerigars of the exhibition type were increased significantly, compared with those of the non-exhibition type. Only for the scapula significant length differences between the budgerigars of both breeding types could not be verified. It can be stated that the measuring parameters ,occipital width', ,maxilla length', ,skull length' and ,prefrontal width' are suitable for the characterization of exhibition budgerigars. However, sexual dimorphisms could be verified in only three parameters (width of the pars symphysialis mandibulae, height of the skull, width of the skull within the range of the occiput). It has to be clarified in future studies to what extent the changes in the skeleton of budgerigars of the exhibition type have already had consequences for their flying ability, metabolism, health and well-being. [source] | ||||||||||