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At least 1,639 records · Page 91Linked to original sources
PubMed1985

Accuracy and direction of error in the sexing of the skeleton: implications for paleodemography.

Determinations of sex by subjective assessment of the skulls from a skeletal series of known sex were compared to fully independent assessments based on pelves of the same specimens. Within-sex correlations of cranial and pelvic morphologies measured on an android-gynecoid scale were smaller than expected. Subjective assessment by means of the skull compared favorably to that of the linear discriminant functions of Giles and Elliot; however, the direction of error was similar for both procedures. Of course, estimations based on the pelves were generally superior to both in terms of frequency and overall bias of error. The bias of sex estimation for paleodemographic purposes is contingent upon completeness of skeletal remains.

Adult↗
PubMed2002

Evolution of median fin modules in the axial skeleton of fishes.

Detailed examples of how hierarchical assemblages of modules change over time are few. We found broadly conserved phylogenetic patterns in the directions of development within the median fins of fishes. From these, we identify four modules involved in their positioning and patterning. The evolutionary sequence of their hierarchical assembly and secondary dissociation is described. The changes in these modules during the evolution of fishes appear to be produced through dissociation, duplication and divergence, and co-option. Although the relationship between identified median fin modules and underlying mechanisms is unclear, Hox addresses may be correlated. Comparing homologous gene expression and function in various fishes may test these predictions.The earliest actinopterygians likely had dorsal and anal fins that were symmetrically positioned via a positioning module. The common patterning (differentiation) of skeletal elements within the dorsal and anal fins may have been set into motion by linkage to this positioning module. Frequent evolutionary changes in dorsal and anal fin position indicate a high level of dissociability of the positioning module from the patterning module. In contrast, the patterning of the dorsal and anal fins remains linked: In nearly all fishes, the endo- and exoskeletal elements of the two fins co-differentiate. In all fishes, the exoskeletal fin rays differentiate in the same directions as the endoskeletal supports, indicating complete developmental integration. In acanthopterygians, a new first dorsal fin module evolved via duplication and divergence. The median fins provide an example of how basic modularity is maintained over 400 million years of evolution.

Animals↗
PubMed2004

Pulmonary pneumaticity in the postcranial skeleton of extant aves: a case study examining Anseriformes.

Anseriform birds were surveyed to examine how the degree of postcranial pneumaticity varies in a behaviorally and size-diverse clade of living birds. This study attempts to extricate the relative effects of phylogeny, body size, and behavioral specializations (e.g., diving, soaring) that have been postulated to influence the extent of postcranial skeletal pneumaticity. One hundred anseriform species were examined as the focal study group. Methods included latex injection of the pulmonary apparatus followed by gross dissection or direct examination of osteological specimens. The Pneumaticity Index (PI) is introduced as a means of quantifying and comparing postcranial pneumaticity in a number of species simultaneously. Phylogenetically independent contrasts (PICs) were used to examine the relationship between body size and the degree of postcranial pneumaticity throughout the clade. There is a high degree of similarity (i.e., clade-specificity) within most anseriform subgroups. As a whole, Anseriformes demonstrate no significant relationship between relative pneumaticity and body size, as indicated by regression analysis of body mass on PI. It is apparent, however, that many clades of diving ducks do exhibit lower PIs than their nondiving relatives. By exclusion of diving taxa from analyses, a significant positive slope is observed and the hypothesis of relatively higher pneumaticity in larger-bodied birds is only weakly supported. However, low correlations indicate that factors other than body size account for much of the variation observed in relative pneumaticity. Pneumaticity profiles were mapped onto existing phylogenetic hypotheses. A reduction in the degree of postcranial pneumaticity occurred independently in at least three anseriform subclades specialized for diving. Finally, enigmatic pneumatic features located in distal forelimb elements of screamers (Anhimidae) result from invasion of bone by a network of subcutaneous air sac diverticula spreading distally along the wings.

Animals↗
PubMed2005

Leis' conundrum: homology of the clavus of the ocean sunfishes. 2. Ontogeny of the median fins and axial skeleton of Ranzania laevis (Teleostei, Tetraodontiformes, Molidae).

One of the most conspicuous characters of the ocean sunfishes, family Molidae, is the punctuation of the body by a deep, abbreviated, caudal fin-like structure extending vertically between the posterior ends of the dorsal and anal fins, termed the clavus by Fraser Brunner. Homology of the clavus has been a matter of debate since the first studies on molid anatomy in the early 1800s. Two hypotheses have been proposed: 1) It is a highly modified caudal fin; 2) It is formed by highly modified elements of the dorsal and anal fins. To resolve this homology issue, we studied the ontogeny of the molid vertebral column and median fins and compared it to that of a less morphologically derived gymnodont (see Part 1 of this study), a member of the family Tetraodontidae. We show that in molids the chorda never flexes during development, that the claval rays form from the posterior ends of the dorsal and anal fins toward the middle, thus closing the gap inward, and that elements of the molid clavus have an identical development and composition as the proximal-middle and distal radials of the regular dorsal and anal fins. We thus conclude that the molid clavus is unequivocally formed by modified elements of the dorsal and anal fin and that the caudal fin is lost in molids.

Animals↗