The skull of Morganucodon

Morganucodon is a triconodont (atherian) mammal from the Lower Jurassic. Two species are described: M. oehleri from China and M. watsoni from Wales. The skull in M. walsoni is 26 mm long; M. oehleri is slightly larger. The dentition is differentiated functionally into incisors, canines, premolars and molars. The pineal foramen is closed. The prefrontals, postfrontals and postorbitals are lost. Septomaxilla, quadratojugal, tabular and pterygoid flanges are retained. The bony external nares are unpaired. The nasal cavity had the mammalian complement of turbinals. The posterior palate has ridges and troughs similar to those in tritylodonts, triconodonts and multituberculates. The alisphenoid ascending process is narrow and is not in contact with the anterior lamina of the petrosal, lying lateral to it. There is a cavum epiptericum, as in late therapsids. The anterior lamina forms the lateral braincase wall, perforated by the foramina pseudovale and pseudorotundum. There is a squamosal-dentary articulation, but the reptilian jaw joint is retained. The ear resembles that in later therapsids, with the tympanum in the lower jaw. The small quadrate was moveable, buttressed medially be a large stapes. Sound conduction from the tympanum was via articular, quadrate and stapes. The systematic position of Morganucodon is discussed.     

The sixth skull cap of Pithecanthropus erectus

The sixth skull cap of Pithecanthropus erectus (or skull V, since the Modjokerto skull has not been given a number) was found in the upper layers of the Trinil beds of Sangiran (Central Java) in 1963, associated with fossils of the Sino-Malayan fauna. No stone tools were discovered in direct association with the find. The specimen consists of the occipital, both parietals, both temporals, sphenoid fragments, the frontal and the left zygomatic bone. We consider the skull to be a male in his early twenties. The occipital, parietal, frontal and temporal bones demonstrate definite pithecanthropine characteristics, and the cranial capacity is estimated to be 975 cm³. Of the superstructures, the supraorbital torus is extraodinarily thick, approaching the condition in Australopithecus boisei and Rhodesian man. And the sagittal torus is certainly higher than in skulls I and II, but lower than in skull IV. In addition, the angle between the occipital and nuchal planes is larger than in the previous finds. As revealed by various features, the gap between the robustness of skull IV on one hand, and skulls I, II and III on the other, is bridged by the present find. There is no reasonable taxonomic need to ascribe this specimen to a new species, because it seems to be merely an intrapopulational variant of the same species. Other skulls of P. erectus suggest that the bregmatic eminence, and hence the vertex, is invariably situated at bregma, but this new skull cap deviates from the pattern. Its pteric regions disclose the anthropoid X and I types. The middle meningeal groove pattern is similar to other Pithecanthropus skulls; however, it betrays a known anomaly in that the main stem is covered for a short distance by a bony plate. The mastoid process is fairly well developed, and is also well pneumatized as in P. pekinensis, with its air cells invading the pronounced supramastoid crest. The zygomatic bone, the first one recovered of P. erectus, does not show characters of particular importance. In fact, its thickness is in the range of modern man. We would like to stress that the absence of the cranial base does not necessarily indicate that the specimen must be a poor victim of cannibalism, since the morphology of the base renders it more susceptible to post-mortem natural traumata.     

The middle ear of the skull of birds The Procellariiformes

Much emphasis has been placed on the middle ear region of reptiles and mammals as a taxonomic character. However, the anatomy of the middle ear region of birds has yet to be described adequately. The literature on the middle ear of birds is reviewed briefly and then the osteology and soft anatomy of the middle ear region of the skull are described for the families of the avian order Procellariiformes. Particular emphasis is paid to the foramina and paths of the nerves and blood vessels. Also discussed is the morphology of the basicranium and the quadrate. Comparative analyses of the characters are used to assess taxonomic conclusions.     

The role of function in the formation of the skull

Partial resection of the mandible, resection of the chewing muscles, amputation of extremities and ligature of the common carotid artery were performed in animals different in chewing type (dogs, sheep, rabbits and rats). These studies revealed a close relation between shape and function. It was shown that changes in function have a decisive effect on the development and shaping of the skull bones and musculature.     

Rigid-body analysis of a lizard skull: modelling the skull of Uromastyx hardwickii

Lizard skulls vary greatly in their detailed morphology. Theoretical models and practical studies have posited a definite relationship between skull morphology and bite performance, but this can be difficult to demonstrate in vivo. Computer modelling provides an alternative approach, as long as hard and soft tissue components can be integrated and the model can be validated. An anatomically accurate three-dimensional computer model of an Uromastyx hardwickii skull was developed for rigid-body dynamic analysis. The Uromastyx jaw was first opened under motion control, and then muscle forces were applied to produce biting simulations where bite forces and joint forces were calculated. Bite forces comparable to those reported in the literature were predicted, and detailed muscular force information was produced along with additional information on the stabilizing role of temporal ligaments in late jaw closing.     

Basicranial axis length v. skull length in analysis of carnivore skull shape

Skull length is the measurement most commonly used as a standard against which other aspects of cranial morphology are compared to derive an index of relative size or proportions. However, skull length is composed of two different functional components, facial skull and cerebral skull, which vary independently and have different scaling relationships with body size. An analysis of carnivore skull shape with measurements standardized against basicranium length produced very different results than an analysis using skull length as the standard. For example, expressions of relative size of cranial measurements were reduced by 13% in mustelids and increased by 20% in canids, reflecting removal of jaw length (short in mustelids and long in canids) from the comparative standard (basicranial axis length). Cranial measurements scale with higher allometric exponents against basicranial axis length than against skull length.