Tooth-root form and function in platyrrhine seed-eaters

Research into the functional and adaptive basis of tooth crown form has provided a useful framework for the inference of diet in extinct primates. However, our understanding of variation in tooth-root form is limited. Studies within the clinical literature emphasize the influence of tooth-root surface area on stress resistance, but it is not known if root form has diversified during primate evolution in relation to dietary specialization. This hypothesis was tested by quantifying maxillary canine and postcanine tooth-root surface areas in four platyrrhine species that differ in the material properties of their diet: Cebus apella, Cebus albifrons, Chiropotes satanas, and Pithecia pithecia. Pairwise comparisons between closely related taxa support predictions based on dietary differences. Taxa that regularly consume resistant seeds (Cebus apella and Chiropotes satanas) exhibit significantly larger relative surface area values for those teeth used in seed processing than closely related taxa that consume resistant foods less often (Cebus albifrons and Pithecia pithecia). Additionally, relative molar-root surface area appears to be greater in Pithecia than in Chiropotes, as predicted from the more folivorous diet of Pithecia. Tooth-root surface area was also found to vary along the tooth row and should therefore have a significant influence on antero-posterior bite-force gradients. The results of this study suggest a close relationship between tooth-root form and patterns of occlusal loading. Further elucidation of this relationship could improve our inferences of diet in extinct taxa, and augment research into the mechanics and evolution of feeding.     

Functional morphology of extreme jaw protrusion in Neotropical cichlids

The New World cichlids Petenia splendida and Caquetaia spp. possess extraordinarily protrusible jaws. We investigated the feeding behavior of extreme (here defined as greater than 30% head length) and modest jaw-protruding Neotropical cichlids by comparing feeding kinematics, cranial morphology, and feeding performance. Digital high-speed video (500 fps) of P. splendida, C. spectabile, and Astronotus ocellatus feeding on live guppy prey was analyzed to generate kinematic and performance variables. All three cichlid taxa utilized cranial elevation, lower jaw depression, and rotation of the suspensorium to protrude the jaws during feeding experiments. Extreme anterior jaw protrusion in P. splendida and C. spectabile resulted from augmented lower jaw depression and anterior rotation of the suspensorium. Morphological comparisons among eight cichlid species revealed novel anterior and posterior points of flexion within the suspensorium of P. splendida and Caquetaia spp. The combination of anterior and posterior loosening within the suspensorium in P. splendida and Caquetaia spp. permitted considerable anterior rotation of the suspensorium and contributed to protrusion of the jaws. Petenia splendida and C. spectabile exhibited greater ram distance and higher ram velocities than did A. ocellatus, resulting primarily from increased jaw protrusion. Petenia splendida and C. spectabile exhibited lower suction feeding performance than A. ocellatus, as indicated by lower suction-induced prey movements and velocities. Thus, extreme jaw protrusion in these cichlids may represent an adaptation for capturing elusive prey by enhancing the ram velocity of the predator but does not enhance suction feeding performance.     

Archosaur adductor chamber evolution: integration of musculoskeletal and topological criteria in jaw muscle homology

The homologies of jaw muscles among archosaurs and other sauropsids have been unclear, confounding interpretation of adductor chamber morphology and evolution. Relevant topological patterns of muscles, nerves, and blood vessels were compared across a large sample of extant archosaurs (birds and crocodylians) and outgroups (e.g., lepidosaurs and turtles) to test the utility of positional criteria, such as the relative position of the trigeminal divisions, as predictors of jaw muscle homology. Anatomical structures were visualized using dissection, sectioning, computed tomography (CT), and vascular injection. Data gathered provide a new and robust view of jaw muscle homology and introduce the first synthesized nomenclature of sauropsid musculature using multiple lines of evidence. Despite the great divergences in cephalic morphology among birds, crocodylians, and outgroups, several key sensory nerves (e.g., n. anguli oris, n. supraorbitalis, n. caudalis) and arteries proved useful for muscle identification, and vice versa. Extant crocodylians exhibit an apomorphic neuromuscular pattern counter to the trigeminal topological paradigm: the maxillary nerve runs medial, rather than lateral to M. pseudotemporalis superficialis. Alternative hypotheses of homology necessitate less parsimonious interpretations of changes in topology. Sensory branches to the rictus, external acoustic meatus, supraorbital region, and other cephalic regions suggest conservative dermatomes among reptiles. Different avian clades exhibit shifts in some muscle positions, but maintain the plesiomorphic, diapsid soft-tissue topological pattern. Positional data suggest M. intramandibularis is merely the distal portion of M. pseudotemporalis separated by an intramuscular fibrocartilaginous sesamoid. These adductor chamber patterns indicate multiple topological criteria are necessary for interpretations of soft-tissue homology and warrant further investigation into character congruence and developmental connectivity.     

Size‐selective feeding on phytoplankton by two morpho‐groups of the small freshwater fish Amblypharyngodon mola

Two morpho‐groups (i.e. small, MGS and big, MGL) of the small freshwater fish Amblypharyngodon mola were studied for their feeding behaviour in the natural environment. Both the morpho‐groups fed on a variety of phytoplankton including Cyanophyceae, Chlorophyceae, Bacillariophyceae and Euglenophyceae. The fish had more Chlorophyceae and Bacillariophyceae in their gut than other phytoplankton. Costello's selectivity plots revealed that the MGS fed on the smaller phytoplankters (2–6 µm in size), whereas the MGL fed on both the small and large (up to 12 µm in size) phytoplankters. The differences in mouth areas between the two morpho‐groups were explained as a possible reason of size‐selective feeding and contribute to overcome gape limitation in A. mola. This is further accompanied by the uniform pore size of the gills (2 µm) in all the morpho‐groups. This study concluded that A. mola exhibits a size‐dependent feeding strategy regulated by gape limitation at the ingestion level. With ontogenetic shifts, flexibility appears to overcome such a limitation in the MGL, having a wider mouth area supported by jaw opening ability.     

Previously undescribed features in the temporalis and masseteric musculature of several large felids raised in captivity

Although the anatomy of the domestic housecat has been examined in meticulous detail, comparative observations on the anatomy of the larger wild cats is scant and information about particularities in their cranial complexes rarer still. In the course of dissecting sets of masticatory muscles in five large felids, all older zoo animals, we had the opportunity to note muscular attachments in the head and jaw apparatus that appeared significantly broader and more distal in their insertion sties than expected. Further investigation may determine whether these masticatory peculiarities are functional adaptations of felids, or instead are associated in some manner with the specialized diets large felids receive in captive environments. Zoo Biol 16:187–191, 1997. © 1997 Wiley-Liss, Inc.     

消息与动态

尼安德特人现今一般被认为是智人种(Homo sapiens)的一个亚种,而最近以色列的拉克(Yoel Rak)教授提出尼人可能是与现代人的祖先平行发展的一个单独的种。 尼人在大约10万至3万年前生活于欧洲和中东,其解剖特征在东欧得到最大的发展。如厚重的骨骼,倾斜的前额,粗壮的眉脊,无颏的颌骨等是其与智人相区别的主要性状。 拉克等近年来在以色列占领区卡梅尔山(Mt.Carmel)的基巴拉(Kebara)洞的发掘中,发现了一具近乎完整的尼人骨架,但头部只保存有下颌骨和一个上第三臼齿,其年代测定为距今6万年。尼人的骨盆过去发现的只有少数破片,而基     

Evolutionary patterns of shape and functional diversification in the skull and jaw musculature of triggerfishes (Teleostei: Balistidae)

The robust skull and highly subdivided adductor mandibulae muscles of triggerfishes provide an excellent system within which to analyze the evolutionary processes underlying phenotypic diversification. We surveyed the anatomical diversity of balistid jaws using Procrustes‐based geometric morphometric analyses and a phylomorphospace approach to quantifying morphological transformation through evolution. We hypothesized that metrics of interspecific cranial shape would reveal patterns of phylogenetic diversification that are congruent with functional and ecological transformation. Morphological landmarks outlining skull and adductor mandibulae muscle shape were collected from 27 triggerfish species. Procrustes‐transformed skull shape configurations revealed significant phylogenetic and size‐influenced structure. Phylomorphospace plots of cranial shape diversity reveal groupings of shape between different species of triggerfish that are mostly consistent with phylogenetic relatedness. Repeated instances of convergence upon similar cranial shape by genetically disparate taxa are likely due to the functional demands of shared specialized dietary habits. This study shows that the diversification of triggerfish skulls occurs via modifications of cranial silhouette and the positioning of subdivided jaw adductor muscles. Using the morphometric data collected here as input to a biomechanical model of triggerfish jaw function, we find that subdivided jaw adductors, in conjunction with a unique cranial skeleton, have direct biomechanical consequences that are not always congruent with phylomorphospace patterns in the triggerfish lineage. The integration of geometric morphometrics with biomechanical modeling in a phylogenetic context provides novel insight into the evolutionary patterns and ecological role of muscle subdivisions in triggerfishes. J. Morphol. 277:737–752, 2016. © 2016 Wiley Periodicals, Inc.