A Phylogenetic Study of Late Growth Events in a Mammalian Evolutionary Radiation—The Cranial Sutures of Terrestrial Artiodactyl Mammals

We recorded the relative timing of fusion of 29 ectocranial sutures in 480 skulls belonging to 35 extant and four fossil species from all major clades of terrestrial artiodactyls. The resulting data were studied in a phylogenetic context, using mapping of event-pairing of suture fusion events and Parsimov. As phylogenetic framework we generated a compound phylogeny from several previously published analyses. Overall suture closure per species ranged from five to all 29 sutures in Hexaprotodon. All living non-ruminants (suids, camelids, and hippopotamids) fuse more than 50% of the studied sutures (most over 75%), whereas in almost all ruminants less than 50% of the sutures fuse completely. Phylogenetic regression found a significant correlation between suture closure and body mass. In all species we observed an early fusion of the sutures surrounding the foramen magnum (Exoccipital-Supraoccipital, Exoccipital-Basioccipital), a consistent scheme also among other mammals. Scaling the number of changes to the number of sutures in each of the usually recognized skull modules reveals relatively equal numbers of changes in the cranial vault, the zygomatic-sphenoid region, the orbit, and the anterior oral-nasal region. Only the basicranium shows a much smaller number in terms of absolute and relative amount of suture fusion change. Some species show a unique pattern of suture fusion, such as the early fusion of many sutures in the palatal region in Pecari or that of premaxillary sutures in †Cainotherium, perhaps related to feeding mode. A strategy to strengthen the skull by obliterating the sutures could explain the pattern of increased sutural fusion in ruminant species with large cranial appendages.     

Population genetic structure and taxonomy of the common dolphin (Delphinus sp.) at its southernmost range limit: New Zealand waters

New Zealand is the southernmost limit of the common dolphin's (genus Delphinus) distribution in the Pacific Ocean. In this area, common dolphins occur in both coastal and oceanic habitats, exhibit seasonal and resident occurrence, and present high morphological variability. Here we investigated the population structure and the taxonomic identity of common dolphins (Delphinus sp.) within New Zealand waters using 14 microsatellite loci, 577 bp of the mtDNA control region, and 1,120 bp of the mtDNA cytochrome b gene across 90 individuals. We found high genetic variability and evidence of population expansion. Phylogenetic analyses conducted to clarify the taxonomic status of New Zealand common dolphins did not show any clustering reflecting geographic origin or morphotypes. The microsatellite analysis showed genetic differentiation between Coastal and Oceanic putative populations, while mtDNA revealed significant genetic differentiation only between the Hauraki Gulf and other putative groups. Our results suggest that differences in habitat choice and possible female site fidelity may play a role in shaping population structure of New Zealand common dolphins.     

BMP9 induces osteogenesis and adipogenesis in the immortalized human cranial suture progenitors from the patent sutures of craniosynostosis patients

The cranial suture complex is a heterogeneous tissue consisting of osteogenic progenitor cells and mesenchymal stem cells (MSCs) from bone marrow and suture mesenchyme. The fusion of cranial sutures is a highly coordinated and tightly regulated process during development. Craniosynostosis is a congenital malformation caused by premature fusion of cranial sutures. While the progenitor cells derived from the cranial suture complex should prove valuable for studying the molecular mechanisms underlying suture development and pathogenic premature suture fusion, primary human cranial suture progenitors (SuPs) have limited life span and gradually lose osteoblastic ability over passages. To overcome technical challenges in maintaining sufficient and long‐term culture of SuPs for suture biology studies, we establish and characterize the reversibly immortalized human cranial suture progenitors (iSuPs). Using a reversible immortalization system expressing SV40 T flanked with FRT sites, we demonstrate that primary human suture progenitor cells derived from the patent sutures of craniosynostosis patients can be efficiently immortalized. The iSuPs maintain long‐term proliferative activity, express most of the consensus MSC markers and can differentiate into osteogenic and adipogenic lineages upon BMP9 stimulation in vitro and in vivo. The removal of SV40 T antigen by FLP recombinase results in a decrease in cell proliferation and an increase in the endogenous osteogenic and adipogenic capability in the iSuPs. Therefore, the iSuPs should be a valuable resource to study suture development, intramembranous ossification and the pathogenesis of craniosynostosis, as well as to explore cranial bone tissue engineering.     

Fusion Patterns in the Skulls of Modern Archosaurs Reveal That Sutures Are Ambiguous Maturity Indicators for the Dinosauria

The sutures of the skulls of vertebrates are generally open early in life and slowly close as maturity is attained. The assumption that all vertebrates follow this pattern of progressive sutural closure has been used to assess maturity in the fossil remains of non-avian dinosaurs. Here, we test this assumption in two members of the Extant Phylogenetic Bracket of the Dinosauria, the emu, Dromaius novaehollandiae and the American alligator, Alligator mississippiensis, by investigating the sequence and timing of sutural fusion in their skulls. As expected, almost all the sutures in the emu skull progressively close (i.e., they get narrower) and then obliterate during ontogeny. However, in the American alligator, only two sutures out of 36 obliterate completely and they do so during embryonic development. Surprisingly, as maturity progresses, many sutures of alligators become wider in large individuals compared to younger, smaller individuals. Histological and histomorphometric analyses on two sutures and one synchondrosis in an ontogenetic series of American alligator confirmed our morphological observations. This pattern of sutural widening might reflect feeding biomechanics and dietary changes through ontogeny. Our findings show that progressive sutural closure is not always observed in extant archosaurs, and therefore suggest that cranial sutural fusion is an ambiguous proxy for assessing maturity in non-avian dinosaurs.     

Evolution of cranial telescoping in echolocating whales (Cetacea: Odontoceti)

Odontocete (echolocating whale) skulls exhibit extreme posterior displacement and overlapping of facial bones, here referred to as retrograde cranial telescoping. To examine retrograde cranial telescoping across 40 million years of whale evolution, we collected 3D scans of whale skulls spanning odontocete evolution. We used a sliding semilandmark morphometric approach with Procrustes superimposition and PCA to capture and describe the morphological variation present in the facial region, followed by Ancestral Character State Reconstruction (ACSR) and evolutionary model fitting on significant components to determine how retrograde cranial telescoping evolved. The first PC score explains the majority of variation associated with telescoping and reflects the posterior migration of the external nares and premaxilla alongside expansion of the maxilla and frontal. The earliest diverging fossil odontocetes were found to exhibit a lesser degree of cranial telescoping than later diverging but contemporary whale taxa. Major shifts in PC scores and centroid size are identified at the base of Odontoceti, and early burst and punctuated equilibrium models best fit the evolution of retrograde telescoping. This indicates that the Oligocene was a period of unusually high diversity and evolution in whale skull morphology, with little subsequent evolution in telescoping.     

Functional implications of dicynodont cranial suture morphology

Cranial suture morphology of Lystrosaurus and the generalized dicynodont Oudenodon was investigated to determine the strain environment during mastication, which in turn may indicate a difference in cranial function between the two taxa. Finite element (FE) analysis indicated that less strain accumulated in the cranium of Lystrosaurus during orthal bite simulations than in Oudenodon. Despite the overall difference in strain magnitude, moderate to high FE‐predicted strain accumulated in similar areas of the cranium of both taxa. The suture morphology in these cranial regions of Lystrosaurus and Oudenodon was investigated further by examination of histological sections and supplemented by observations of serial sections and computed tomography (CT) scans. The predominant type of strain from selected blocks of finite elements that contain sutures was determined, enabling comparison of suture morphology to strain type. Drawing from strain‐suture correlations established in extant taxa, the observed patterns of sutural morphology for both dicynodonts were used to deduce cranial function. The moderate to high compressive and tensile strain experienced by the infraorbital bar, zygomatic arch, and postorbital bar of Oudenodon and Lystrosaurus may have been decreased by small adjustive movements at the scarf sutures in those regions. Disparities in cranial suture morphology between the two taxa may reflect differences in cranial function. For instance, the tongue and groove morphology of the postorbital‐parietal suture in Oudenodon could have withstood the higher FE‐predicted tensile strain in the posterior skull roof. The scarf premaxilla‐nasal suture of Lystrosaurus provided an additional region of sutural mobility in the anterior surface of the snout, suggesting that Lystrosaurus may have employed a different biting regime than Oudenodon. The morphology of several sutures sampled in this study correlated with the FE‐predicted strain, although other cranial functional hypotheses remain to be tested. J. Morphol., 2010. © 2010 Wiley‐Liss, Inc.     

Age estimation of the White rhinoceros (Ceratotherium simum)

Age estimation criteria for the southern White rhinoceros ( Ceratotherium simum simum ) are presented both for free-ranging live animals and for cranial material. These are based on: (i) size appearance and horn development of live animals; (ii) stages of tooth eruption; (iii) tooth wear classes; (iv) attrition in height of the first molar tooth; (v) counts of cementum lines visible in tooth sections. Selected measurements are presented for live animals, skulls and horns.
For live animals, eight size classes are distinguished, seven of these covering immature animals up to ten years of age. Sixteen tooth wear classes are established, based on eruption and surface wear of maxillary dentition. Chronological ages were assigned from individually known animals followed in the field, and from skulls from animals for which exact records of age were available, or which could be assigned to an age category from appearance at death. Cementum line counts corresponded approximately with age in years, despite difficulties in interpreting lines. Some variability was observed, possibly related to nutritional conditions.
The maximum cementum line count obtained indicates a longevity of at least 40 years. Full body weight and socio-sexual maturity are attained by males between 10 and 15 years of age, while females first give birth between six and eight years of age. Sequences and times of tooth eruption are similar to those reported for the Black rhinoceros ( Diceros bicornis ).
Comparative cranial and body measurements are presented for the northern subspecies ( Ceratotherium simum cottoni ).     

A note on the effect of asymmetry in suture closure in mature human skulls

Studies on suture closure in mature European and East African Bantu skulls revealed marked differences in the degree of suture closure on the left and right side. Asymmetrical closure of sutures may lead to erroneous conclusions being made in ageing skulls if only one-half of the skull is available for examination. Asymmetry in suture closure was rather common in recent skulls, being particularly noticeable in the bregmatic and complicate parts of the coronal suture and in intermediate portions of lambdoid sutures.     

Cranial suture complexity in caviomorph rodents (Rodentia; Ctenohystrica)

Due to their flexibility, sutures are regions that experience greater strains than the surrounding rigid cranial bones. Cranial sutures differ in their degree of interdigitation or complexity. There is evidence indicating that a more convoluted suture better enables the absorption of high stresses coming from dynamic masticatory forces, and other functions. The Order Rodentia is an interesting clade to study this because of its taxa with diverse chewing modes. Due to repeated loading resulting from gnawing and grinding, energy absorption by the sutures might be a crucial factor in these mammals. Species within the infraorder Caviomorpha were chosen as a case study because of their ecomorphological and dietary diversity. This study compared five sutures from the rostrum and cranial vault across seven caviomorph families, and assessed their complexity by means of the relative length and fractal dimension. Across these rodents, cranial sutures are morphologically quite diverse. We found that the sutures connecting the rostrum with the vault were relatively more interdigitated than those in the cranial vault itself, especially premaxillofrontal sutures. Suture interdigitation was higher in species that display chisel‐tooth digging and burrowing behaviors, especially in the families Ctenomyidae and Octodontidae, than those in families Dasyproctidae and Cuniculidae, which have more gracile masticatory systems. The reconstruction of the ancestral character state, on family and species phylogeny, points toward low suture interdigitation (i.e., low length ratio) as a likely ancestral state for interfrontal, premaxillofrontal and maxillofrontal sutures. Interspecific differences in suture morphology shown here might represent adaptations to different mechanical demands (i.e., soft vs. tough foods) or behaviors (e.g., chisel‐tooth digging), which evolved in close association with the diverse environments occupied by caviomorph rodents.     

Feeding mechanisms of the sauropod dinosaurs Brachiosaurus,Camarasaurus, Diplodocus and Dicraeosaurus

Skull morphologies and dental wear patterns have been examined in four sauropod genera to evaluate their probable feeding mechanisms. Wear facets on teeth are generally confined to their apices in Brachiosaurus and Dicraeosaurus and they are sometimes also present on the mesial and distal carinae. Skull morphology and dental wear patterns in Diplodocus and Dicraeosaurus are consistent with a raking motion of the jaws during feeding. Diplodocus became mechanically adapted to feed in this way by evolving anteriorly directed teeth in the premaxilla and mesial parts of the maxilla, and by changing the direction of jaw adduction relative to the long axis of the skull. Similar features are present in the few known skulls of Apatosaurus and they may also have been present in Dicraeosaurus. In Brachiosaurus dental wear patterns also imply a raking motion of the jaws, although the more robust skull and teeth and the more vertically directed action of the jaw adductor muscles have led some to suggest the possibility of isognathous occlusion. Camarasaurus employed a powerful bite in its feeding, possibly with slight propaliny of the lower jaw, and its skull was modified to cope with increased stresses arising from mastication. Archaic sauropods appear largely to have employed isognathic occlusion in chopping off vegetation. The raking motion employed by diplodocids and dicraeosaurids was an advanced mode of cropping and stripping, linked evolutionarily to their highly apomorphic cranial morphology.     

Adenovirus-mediated transmission of a dominant negative transforming growth factor-beta receptor inhibits in vitro mouse cranial suture fusion

Recent studies have implicated the transforming growth factor (TGF)-beta family in the regulation of pathological sporadic cranial suture fusion. In addition, these studies have shown that TGF-beta is highly expressed by the dura mater underlying fusing murine cranial sutures. The purpose of the present experiments was to analyze the effects of disrupting TGF-beta signaling during programmed mouse cranial suture fusion. Using recombinant DNA technology, a replication-deficient adenovirus encoding a defective TGF-beta receptor (Ad.DN-TbetaRII) capable of blocking TGF-beta biological activity was constructed. Mouse posterior frontal sutures were harvested before the initiation of suture fusion (postnatal day 25), and the dura mater underlying the suture was infected with vehicle, Ad.DN-TbetaRII, or control virus (Ad.LacZ; n = 10 each). Sutures were cultured for 14 or 30 days in an organ culture system and analyzed macroscopically and histologically.X-gal staining of Ad.LacZ-infected sutures 14 days after culture revealed strong staining of cells localized to the dura mater. Macroscopic analysis revealed complete sutural fusion in vehicle and Ad.LacZ-infected sutures. In contrast, Ad.DN-TBRII-infected sutures demonstrated nearly complete patency. Histological analysis confirmed our macroscopic observations with sutural fusion in 81.3 +/- 10 percent and 74.5 +/- 9 percent of vehicle and Ad.LacZ-infected sutures, respectively, versus 38.1 +/- 12 percent (p < 0.001) in Ad.DN-TbetaRII-infected sutures. In addition, transfection with the Ad.DN-TbetaRII virus resulted in a significant attenuation of anterior-to-posterior suture fusion, with the majority of fused sections localized to anterior sections. These data strongly implicate TGF-beta biological activity in the dura mater underlying the posterior frontal suture in the regulation of programmed sutural fusion. In addition, this study demonstrates the utility of adenovirus-mediated gene transfer in preventing programmed sutural fusion.     

A New Basal Hadrosauroid Dinosaur from the Lower Cretaceous Khok Kruat Formation in Nakhon Ratchasima Province,Northeastern Thailand

A new basal hadrosauroid dinosaur from the Lower Cretaceous Khok Kruat Formation of Thailand, Sirindhorna khoratensis gen. et sp. nov is described. The new taxon is based on composite skull and mandible including premaxilla, maxilla, jugal, quadrate, braincases, predentary, dentaries, surangular, and maxillary and dentary teeth. It is diagnostic by such characters as, sagittal crest extending along entire dorsal surface of the parietal and reaching the frontoparietal suture (autapomorphy), transversely straight frontoparietal suture, caudodorsally faced supraoccipital, no participation of the supraoccipital in the foramen magnum, mesiodistally wide leaf-shaped dentary tooth with primary and secondary ridges on the lingual surface of the crown, perpendicularly-erected and large coronoid process of dentary, and nonvisible antorbital fossa of the maxilla in lateral view. Phylogenetic analysis revealed S. khoratensis as among the most basal hadrosauroids. Sirindhorna khoratensis is the best-preserved iguanodontian ornithopod in Southeast Asia and sheds new light to resolve the evolution of basal hadrosauriforms.     

Assessment of the role of sutures in a lizard skull: a computer modelling study

Sutures form an integral part of the functioning skull, but their role has long been debated among vertebrate morphologists and palaeontologists. Furthermore, the relationship between typical skull sutures, and those involved in cranial kinesis, is poorly understood. In a series of computational modelling studies, complex loading conditions obtained through multibody dynamics analysis were imposed on a finite element model of the skull of Uromastyx hardwickii, an akinetic herbivorous lizard. A finite element analysis (FEA) of a skull with no sutures revealed higher patterns of strain in regions where cranial sutures are located in the skull. From these findings, FEAs were performed on skulls with sutures (individual and groups of sutures) to investigate their role and function more thoroughly. Our results showed that individual sutures relieved strain locally, but only at the expense of elevated strain in other regions of the skull. These findings provide an insight into the behaviour of sutures and show how they are adapted to work together to distribute strain around the skull. Premature fusion of one suture could therefore lead to increased abnormal loading on other regions of the skull causing irregular bone growth and deformities. This detailed investigation also revealed that the frontal-parietal suture of the Uromastyx skull played a substantial role in relieving strain compared with the other sutures. This raises questions about the original role of mesokinesis in squamate evolution.     

Non-metric skeletal age changes in the Darajani baboon

Dental attrition, cranial suture closure, and epiphyseal union are compared as indicators of relative age in baboons, Papio cynocephalus (Linnaeus, 1776). Tooth destruction from wear is extreme. Such destruction is certainly a factor of vital importance to feral baboons and may limit life span. As cusps wear away, they form selenes of dentine and enamel which are effective grinding surfaces. In conditions of extreme wear, functional fourth molars may be quite beneficial. Vault sutures of females remain active longer than those of males. In contrast, most other cranial sutures and sites of epiphyseal activity mature earlier in the female than in males. Attrition scores in this sample are as useful as assessments of closure or epiphyseal union to determine the relative position of an individual in an age sequence. The most reliable estimates rely on all three sources.     

Whistle characteristics of common dolphins (Delphinus sp.) in the Hauraki Gulf,New Zealand

Quantifying the vocal repertoire of a species is critical for subsequent analysis of signal functionality, geographic variation, and social relevance. However, the vocalizations of free‐ranging common dolphins (Delphinus sp.) have not previously been described from New Zealand waters. We present the first quantitative analysis of whistle characteristics to be undertaken on the New Zealand population. Acoustic data were collected in the Hauraki Gulf, North Island from 28 independent dolphin group encounters. A total of 11,715 whistles were collected from 105.1 min of recordings. Seven whistle contours were identified containing 29 subtypes. Vocalizations spanned from 3.2 to 23 kHz, with most whistles occurring between 11 and 13 kHz. Whistle duration ranged from 0.01 to 4.00 s (mean ± SD; 0.27 ± 0.32). Of the 2,663 whistles analyzed, 82% have previously been identified within U.K. populations. An additional six contours, apparently unique to New Zealand Delphinus were also identified. Data presented here offer a first insight into the whistle characteristics of New Zealand Delphinus. Comparisons with previously studied populations reveal marked differences in the whistle frequency and modulation of the New Zealand population. Interpopulation differences suggest behavior and the local environment likely play a role in shaping the vocal repertoire of this species.     

A molecular analysis of the isolated rat posterior frontal and sagittal sutures: differences in gene expression

Although it is one of the most commonly occurring craniofacial congenital disabilities, craniosynostosis (the premature fusion of cranial sutures) is nearly impossible to prevent because the molecular mechanisms that regulate the process of cranial suture fusion remain largely unknown. Recent studies have implicated the dura mater in determining the fate of the overlying cranial suture; however, the molecular biology within the suture itself has not been sufficiently investigated. In the murine model of cranial suture fusion, the posterior frontal suture is programmed to begin fusing by postnatal day 12 in rats (day 25 in mice), reliably completing bony union by postnatal day 22 (day 45 in mice). In contrast, the sagittal suture remains patent throughout the life of the animal. Using this model, this study sought to examine for the first time what differences in gene expression--if any--exist between the two sutures with opposite fates. For each series of experiments, 35 to 40 posterior frontal and sagittal suture complexes were isolated from 6-day-old Sprague-Dawley rat pups. Suture-derived cell cultures were established, and ribonuicleic acid was derived from snap-frozen, isolated suture tissue. Results demonstrated that molecular differences between the posterior frontal and sagittal suture complexes were readily identified in vivo, although these distinctions were lost once the cells comprising the suture complex were cultured in vitro. Hypothetically, this change in gene expression resulted from the loss of the influence of the underlying dura mater. Significant differences in the expression of genes encoding extracellular matrix proteins existed in vivo between the posterior frontal and sagittal sutures. However, the production of the critical, regulatory cytokine transforming growth factor beta-1 was equal between the two suture complexes, lending further support to the hypothesis that dura mater regulates the fate of the overlying cranial suture.