Studies on orthocephalization. 10. Behaviour of the visceral part of the rat head during the first 14 days after gestation

The present paper considers the significance of interosseous flexions of the palatal complex in the process of orthocephalization of the rat skull between birth and 7 d p.n. The study is based on a sample of 90 rats divided into 4 age groups, i.e. 0, 4, 7, and 14 d. These rats have been X-rayed, and their photographs subsequently analysed. During the studied period, the constituents of the bony palate, i.e. the horizontal part of the palatine bone, the palatal process of maxilla and the palatal part of premaxilla, increase markedly in length, but with individual differences in growth rate. There is, in the period, a marked decrease in angulation between the cranial base and the palatal plane. This means that the rat skull becomes more orthocranial. There is also a straightening (orthopalatalization) of the palate, as the angle between maxilla and premaxilla becomes more obtuse, and a marked decrease in angulation between the palatine bone and the cranial base. The patterns of angular changes suggest that the process of orthocephalization in the period between birth and 14 d p.n. primarily is a result of an upwards rotation of the palatine bone relative to the cranial base, while interosseous deflections in the palate only play a minor role.     

Studies on orthocephalization. 2. Flexions of the rat head in the period between 14 and 60 days after gestation

The present paper considers the significance of a variety of cranial flexions in the process of orthocephalization of the rat skull between 14 and 60 days postnatally. The study is based on a sample of 27 male rats, who have been x-rayed at 14, 30 and 60 days with subsequent analyses of the photographs obtained. In this period the angle between the cranial base and the facial part of the skull becomes more obtuse, i.e. the skull becomes more orthocranial. The cranial base becomes at the same time more airobasal (lordotic). Angular changes between the individual bones in the cranial vault straightens the vault markedly. By this it becomes orthodorsal. As the angle between the basisphenoid and the parietal bones stays more or less constant between 14 and 60 days, the impression is created that both the anterior and posterior parts of the neural skull rotate upwards relative to this bone complex. Thus, orthocephalization in the period between 14 and 60 days both consists of flexions between the facial and neural parts of the skull (prebasal flexions), and may be more importantly of interosseous ventral and dorsal flexions.     

Studies on orthocephalization. 8. Behaviour of the visceral part of the rat head in the period between 7 and 60 days after gestation

The present paper considers the significance of interosseous flexions of the palatal complex in the process of orthocephalization of the rat skull between 7 and 60 d after birth. The study is based on a sample of 25 female rats who have been X-rayed at 7, 14, 30, and 60 d with subsequent analysis of the photographs obtained. During this period the constituents of the bony palate, i.e. the palatine bone, the palatal process of maxilla and the palatal part of premaxilla grow steadily but with decreasing rate of increase with age. The premaxilla grows the most, while the palatal bone grows the least. The angle between the cranial base and the palatal plane decreases, i.e. the rat skull becomes more orthocranial with age. At the same time, the palate becomes more orthopalatal, primarily by an increase in the angle between the palatine bone and maxilla. As the angle between the cranial base and the palatine bone after 14 d increases, i.e. rotates in the opposite direction of the palatal plane, it may be concluded that the process of orthocephalization in this period is caused by the deflexion of the angle between the palatine bone and maxilla, while it before 14 d is caused by a combination of an interosseous deflexion in the palate and an upwards rotation of the palatine bone relative to the cranial base.     

The influence of experimental deformation on craniofacial development in rats

Cranial deformation was produced experimentally in rats 8 to 40 days old for the purpose of studying the rotation of the craniofacial bones and the modification of the growth rates of the functional cranial components. One hundred and twenty four skulls (65 males and 59 females) were employed, classified as: deformed , deformed-hydrocephalic, sham-operated and controls. A midsagittal diagram was drawn for each skull and the angle subtended by each bone with respect to the vestibular plane was measured. Growth indices were worked out for both the neural skull and the facial skull. Deformation altered the rotation of the parietal, interparietal and basisphenoidal bones and restricted the rotation of the fronto-ethmo-facial complex. Alteration of the longitudinal growth rates of the dorsal and basilar components of the neurocranium and the splanchnocranium produced the persistence of the klinorynchal state.     

Orthocephalization in the postweaning squirrel monkey

Twenty male squirrel monkeys (Saimiri sciureus boliviensis) raised in captivity were allotted to one of the following groups: weanling control (C6) sampled at 6 months of age; young control (C24) fed ad libitum on a control diet and killed at 24 months of age; and malnourished (M24) fed ad libitum on a low-protein diet and sampled at 24 months of age. Cranial points and the lateral semicircular canals were marked. On each skull, a strict lateral teleradiograph was taken, and the lengths of the midsagittal chords and their angles with respect to the vestibular line were measured. Age changed the lengths in about 70% of the chords and more than 50% of the angles. Malnutrition arrested about 50% of the lengths, but the angles were practically not affected. It is concluded that the postweaning Saimiri sciureus undergoes orthocephalization according to a general pattern already observed in rodents and suggested for pongids. Postweaning malnutrition affected growth in size but not shape changes related to the orthocephalization of the Saimiri skull. © 1996 Wiley-Liss, Inc.     

Influence of food restriction during gestation on craniofacial growth of the weanling rat

Holtzman rats were subjected to food restriction during gestation or lactation, or both periods (overall stress). At weaning, male pup skulls were measured and female brains and cranial masticatory muscles were weighed and a neuromuscular index was calculated. It was found that gestational protein-calorie malnutrition (PCM) without suckling restoration accounted for about 30% of the growth delay observed under overall stress. That effect disappeared after a normal suckling restoration. Under the same conditions of maternal food restriction in both periods, growth delay in the offspring was greater during lactation than gestation. As in lactation, craniofacial changes during gestational restriction were due to an adjustive response of bone growth to PCM. This response seemed to accrue from an altered relationship between the growth of the brain-less sensitive and highly restorable-and the growth of the masticatory muscles-more sensitive and less restorable. Some degree of delay in orthocephalization would be the skeletal outcome of such adjustive neuromuscular response.     

Age factor and the pattern of change in craniofacial structures

Today special emphasis is being placed upon the understanding of human aging and this study is an attempt to shed light on the craniofacial complex during the later years. Postcranial skeletal alteration is clear and it is now evident that cranial and facial structures are no exception to the aging process. The longitudinal information presented here indicates continuing overall growth from early adulthood to later life. The cranium thickens and the skull diameter increases. Endocranial dimensions enlarge as well. This suggests larger overall skull size and expansion of the cranial cavity. The visceral cranial structures also participate in the continuing growth process. Enlargement in all areas seems to be of similar magnitude except for skull thickness, sella turcica, and frontal sinus. The size increase in these three structures is greater than in other segments examined. In essence, the craniofacial complex is in a state of growth throughout life. The entire system is involved in a process of symmetrical enlargement.     

Relative growth of the skull and postcranium in giant transgenic mice

Cross-sectional allometric growth patterns of the cranial and postcranial skeleton were compared between giant transgenic (MT-rGH) mice and their normal littermate controls. Body weights, external body dimensions, and a series of cranial and postcranial linear dimensions of the skeleton were determined for samples of known age. Comparative bivariate and multivariate allometric analyses were completed in order to determine whether (1) the larger transgenic mice differed significantly from the normal controls in aspects of body and skeletal proportions, and (2) any such proportion differences resulted from general allometric effects of overall weight or skeletal size increase. Results demonstrate that the transgenic mice do exhibit significantly different body and skeletal proportions than normal control adults. Allometric comparisons of the skeletal dimensions relative to body weight reveal similar coefficients of growth allometry but several differences in gamma-intercept values in the transgenic vs. control groups. The comparisons among the skeletal dimensions of the skull and postcranium generally reveal the sharing and differential extension of common growth allometries in the two groups. Thus, the elevated levels of growth hormone (GH) and insulin-like growth factor I (IGF-I) in the transgenic mice appear to result in increased overall growth for the various skeletal elements, but in the relative proportions determined by intrinsic growth controls within that system.     

The erectile cheek-spine apparatus in the bristlenose catfish Ancistrus (Loricariidae, Siluriformes), and its relation to the formation of a secondary skull roof

In the South American catfish family Loricariidae, the opercle has been decoupled from the lower jaw, and has also lost its function in expiration. While many loricariid species have a small and slightly mobile opercle with reduced opercular musculature, within the hypostomine subfamily a novel opercular mechanism has developed that erects a tuft of enlarged odontodes anterior to the opercle. This defensive mechanism is examined in Ancistrus cf. triradiatus. The opercle has a prominent anterior process and the orientation of the reinforced articulation hinge to the hyomandibular bone has shifted. The opercular musculature is well developed, with a hypertrophied dilatator operculi that extends deep inside the skull roof bones and toward the midline, over the brain, but below the superficial skull roof. Hence the frontal, sphenotic, parieto-supraoccipital and compound pterotic bones consist of a dorsal, superficial part and a deeper part separating the brain from the muscle: two functional skull roofs are thus formed. The impact on the path of the cranial sensory canals is substantial, moving canals away from the skull surface. Hypertrophy of cranial muscles is known from many teleosts, but the invasion of such large muscles into the skull, which is drastically modified and literally hollowed out, has never been described before. These cranial modifications are greater in males than in females, related to the territorial behavior of the former, in which the erectile spines are usually used.     

A quantitative approach to the cranial ontogeny of <Emphasis Type="Italic">Lycalopex culpaeus</Emphasis> (Carnivora: Canidae)

The study of cranial ontogeny is important for understanding the relationship between form and function in developmental, ecological, and evolutionary contexts. The transition from lactation to the diet of adult carnivores must be accompanied by pronounced modifications in skull morphology and feeding behavior. Our goal was to study relative growth and development in the skull ontogeny of the canid Lycalopex culpaeus, and interpret our findings in a functional context, thereby exploring the relationship between changes in shape and size with dietary habits and age stages. We performed quantitative analyses, including multivariate allometry and geometric morphometrics. Our results indicate that shape changes are related to functional improvements of the jaw mechanics related for food catching/processing. Estimates of full muscle size, mechanical advantage, and adult cranial shape are reached after sexual maturity, while adult mandible and skull size are reached after weaning, which is related to diet change (incorporation of meat and other food items). The ontogenetic pattern observed in L. culpaeus is similar to those observed in Canis familiaris and C. latrans. However, the magnitude of change seen in L. culpaeus is smaller than those seen in the felid Puma concolor and considerably smaller than those seen in the bone cracker hyaenid Crocuta crocuta. These patterns are associated with dietary habits and specializations in skull anatomy, as L. culpaeus, domestic dog and coyote are generalist species compared with hypercarnivores such as C. crocuta and P. concolor.     

Secular changes in craniofacial morphology of the Portuguese using geometric morphometrics

This study examines patterns of secular change in cranial morphology in the New Lisbon collection, a documented skeletal collection from Lisbon, Portugal with birth years from 1806 to 1954. This period represents a time when Lisbon was undergoing increased urbanization and population growth, as well as changes in mortality and fertility patterns. Previous studies from the U.S., Europe, and Japan have reported significant secular changes in cranial morphology over the past 200 years. In the current study, secular changes were analyzed using three-dimensional geometric morphometrics methods. The results from this study demonstrate a significant change in cranial morphology over the roughly 150-year period. Allometry was rejected as a causal factor of this change because there was no association found between temporal change and size. The pattern of temporal change is similar to that observed in other populations in the U.S., Europe, and Japan, including decreased facial breadth and a more inferiorly placed cranial base. This study, along with previous research, suggests a similar pattern of change occurs in genetically and geographically diverse populations experiencing modern environmental conditions. We argue that because the secular changes are focused in the cranial base, a region of the skull that experiences a relatively early growth curve, changes related to declines in childhood morbidity and mortality are likely important factors related to the observed changes.     

Growth of cranial synchondroses and sutures requires polycystin-1

In vertebrates, coordinated embryonic and postnatal growth of the craniofacial bones and the skull base is essential during the expansion of the rostrum and the brain. Identification of molecules that regulate skull growth is important for understanding the nature of craniofacial defects and for development of non-invasive biologically based diagnostics and therapies.Here we report on spatially restricted growth defects at the skull base and in craniofacial sutures of mice deficient for polycystin-1 (Pkd1). Mutant animals reveal a premature closure of both presphenoid and sphenooccipital synchondroses at the cranial base. Furthermore, knockout mice lacking Pkd1 in neural crest cells are characterized by impaired postnatal growth at the osteogenic fronts in craniofacial sutures that are subjected to tensile forces. Our data suggest that polycystin-1 is required for proliferation of subpopulations of cranial osteochondroprogenitor cells of both mesodermal and neural crest origin during skull growth. However, the Erk1/2 signalling pathway is up-regulated in the Pkd1-deficient skeletal tissue, similarly to that previously reported for polycystic kidney.     

Allometry of the postnatal cranial ontogeny and sexual dimorphism in Otaria byronia (Otariidae)

We studied the cranial postnatal ontogeny of Otaria byronia in order to detect sexual dimorphism in allometric terms, analyzing the rate of growth of functional variables linked to specific capacities as bite and head movements. We used 20 linear measurements to estimate allometric growth applying bivariate and multivariate analyses in females and males separately. Males were also analyzed in two partitioned subsets considering non-adult and adult stages, when the dimorphism is accentuated in order to reach optimal performance for intra-sexual competition. In the comparison of the employed techniques, we detected an empirical relationship between our multivariate results and the ordinary least square bivariate analysis. The quantitative analyses revealed different ontogenetic trajectories between non-adult and adult males in most variables, suggesting that the adult skull is not a scaled version of subadult skull. For instance, variables related with longitudinal dimensions decreased their allometric coefficients when the adult stage was reached, whereas those related with breadth or vertical dimensions increased their values. In adult males this could indicate that skull breadth and height are more important than longitudinal growth, relative to overall skull size. Conversely, inter-sexual comparisons showed that females and non-adult males shared similar ontogenetic growth trends, including more allometric trends than did males along their own ontogenetic trajectory. In general, adult males exhibited higher allometric coefficients than non-adult males in variables associated with bite and sexual behavior, whereas in comparison to females the latter showed higher coefficients values in these variables. Such patterns indicate a complex mode of growth in males beyond the growth extension, and are in partial agreement with changes previously reported for this and other species in the family Otariidae.     

A finite element analysis of masticatory stress hypotheses

Understanding how the skull transmits and dissipates forces during feeding provides insights into the selective pressures that may have driven the evolution of primate skull morphology. Traditionally, researchers have interpreted masticatory biomechanics in terms of simple global loading regimes applied to simple shapes (i.e., bending in sagittal and frontal planes, dorsoventral shear, and torsion of beams and cylinders). This study uses finite element analysis to examine the extent to which these geometric models provide accurate strain predictions in the face and evaluate whether simple global loading regimes predict strains that approximate the craniofacial deformation pattern observed during mastication. Loading regimes, including those simulating peak loads during molar chewing and those approximating the global loading regimes, were applied to a previously validated finite element model (FEM) of a macaque (Macaca fascicularis) skull, and the resulting strain patterns were compared. When simple global loading regimes are applied to the FEM, the resulting strains do not match those predicted by simple geometric models, suggesting that these models fail to generate accurate predictions of facial strain. Of the four loading regimes tested, bending in the frontal plane most closely approximates strain patterns in the circumorbital region and lateral face, apparently due to masseter muscle forces acting on the zygomatic arches. However, these results indicate that no single simple global loading regime satisfactorily accounts for the strain pattern found in the validated FEM. Instead, we propose that FE models replace simple cranial models when interpreting bone strain data and formulating hypotheses about craniofacial biomechanics.     

Effects of fronto-occipital artificial cranial vault modification on the cranial base and face.

Artificial reshaping of the cranial vault has been practiced by many human groups and provides a natural experiment in which the relationships of neurocranial, cranial base, and facial growth can be investigated. We test the hypothesis that fronto-occipital artificial reshaping of the neurocranial vault results in specific changes in the cranial base and face. Fronto-occipital reshaping results from the application of pads or a cradle board which constrains cranial vault growth, limiting growth between the frontal and occipital and allowing compensatory growth of the parietals in a mediolateral direction. Two skeletal series including both normal and artificially modified crania are analyzed, a prehistoric Peruvian Ancon sample (47 normal, 64 modified crania) and a Songish Indian sample from British Columbia (6 normal, 4 modified). Three-dimensional coordinates of 53 landmarks were measured with a diagraph and used to form 9 finite elements as a prelude to finite element scaling analysis. Finite element scaling was used to compare average normal and modified crania and the results were evaluated for statistical significance using a bootstrap test. Fronto-occipitally reshaped Ancon crania are significantly different from normal in the vault, cranial base, and face. The vault is compressed along an anterior-superior to posterior-inferior axis and expanded along a mediolateral axis in modified individuals. The cranial base is wider and shallower in the modified crania and the face is foreshortened and wider with the anterior orbital rim moving inferior and posterior towards the cranial base. The Songish crania display a different modification of the vault and face, indicating that important differences may exist in the morphological effects of fronto-occipital reshaping from one group to another.     

The evolution of cranial design and performance in squamates: Consequences of skull-bone reduction on feeding behavior

The evolution of cranial design in lepidosaurians is characterizedby a general trend toward the loss of cranial elements. Theevolution of relatively lighter skulls in squamates appearstightly coupled to a reduction in relative mass of the jaw adductor,implying functional consequences for bite force and feedingbehavior. Interestingly, among squamates the postorbital barwas reduced or lost at least twice independently and taxa characterizedby the loss of these cranial elements (e.g., geckos and varanids)are generally reported as having a mobile skull. In Gekkotans,the loss of the postorbital bar was accompanied by a reductionof the supratemporal bar, resulting in a pronounced cranialkinesis. Our data show that having a kinetic skull has functionalconsequences and results in a reduction in bite force. The lowerbite force may in turn be responsible for the decreased feedingefficiency as reflected in the longer duration of intra-oraltransport cycles. Gekkotans, however, appear to exploit theirintracranial mobility in ways that increases the velocity ofjaw movement during opening and closing, which may allow themto capture more elusive prey. The morphological changes observedin the evolution of the cranial system in squamates appear tightlylinked to functional and constructional demands on the skull,making squamate skull evolution a model system to investigatethe consequences of morphological changes in a complex integratedsystem of performance, behavior, and ecology.     

Effects of developmental and functional interactions on mouse cranial variability through late ontogeny

The mammalian skull performs a variety of functions and its growth and development mirrors this complexity. Cranial growth and development have been actively studied for many years. Despite this interest, the variation in the patterns and processes of skull growth has attracted little attention. An important and unanswered question is the extent to which patterns of cranial covariation and variation are dynamically reworked throughout postnatal growth. To address this question, we examine patterns of variability in random-bred mouse skulls aged 35, 90, and 150 days. Using a battery of both Procrustes coordinate and Euclidean distance-based methods, we measure mean shape, canalization, developmental stability, and morphological integration in these skulls. We predict that the patterns of variability are dynamic, particularly between the youngest and the two oldest age groups due to the influence of functional effects such as postweaning mastication. We also hypothesize that patterns of variability are structured by the same functional and developmental factors that have been shown to influence cranial growth in primates. Our results indicate that contrary to our predictions, patterns of canalization, developmental stability, and morphological integration are stabilized before 35 days. The mean shape, however, changed significantly with growth. We found that only the facial region showed significant integration as predicted by the functional matrix model used in other studies of integration. These results indicate that phenotypic integration in these mice does not closely match those found for primate species, suggesting that comparisons between species should be made with care.