Shin-ichi Fujiwara

Topsy-turvy locomotion: biomechanical specializations of the elbow in suspended quadrupeds reflect inverted gravitational constraints

Some tetrapods hang upside down from tree branches when moving horizontally. The ability to walk in quadrupedal suspension has been acquired independently in at least 14 mammalian lineages. During the stance (supportive) phase of quadrupedal suspension, the elbow joint flexor muscles (not the extensors as in upright vertebrates moving overground) are expected to contract to maintain the flexed limb posture. Therefore muscular control in inverted, suspended quadrupeds may require changes of muscle control, and even morphologies, to conditions opposite to those in upright animals. However, the relationships between musculoskeletal morphologies and elbow joint postures during the stance phase in suspended quadrupeds have not been investigated. Our analysis comparing postures and skeletal morphologies in Choloepus (Pilosa), Pteropus (Chiroptera), Nycticebus (Primates) and Cynocephalus (Dermoptera) revealed that the elbow joints of these animals were kept at flexed angles of 70–100 ° during the stance phase of quadrupedal suspension. At these joint angles the moment arms of the elbow joint flexors were roughly maximized, optimizing that component of antigravity support. Our additional measurements from various mammalian species show that suspended quadrupeds have relatively small extensor/flexor ratios in both muscle masses and maximum moment arms. Thus, in contrast to the pattern in normal terrestrial quadrupeds, suspended quadrupeds emphasize flexor over extensor muscles for body support. This condition has evolved independently multiple times, attendant with a loss or reduction of the ability to move in normal upright postures.

A reevaluation of the manus structure in Triceratops (Ceratopsia: Ceratopsidae)

ABSTRACT A Triceratops, NSM PV 20379, excavated from the Upper Cretaceous Hell Creek Formation, Bowman County, North Dakota, USA, confirms the articulation of the right forearm. Detailed study of the forelimb anatomy presented here indicates the manus is in a semi-supinated orientation. This reconstruction is based upon the following morphology: the row of the metacarpals was arranged in an ‘L’-shape in proximal view, as is the distal articular surface of the forearm is in articulation; the second digit is directed parallel to the rotational plane of the elbow joint, reinforced by neighboring digits I and III, and these three inner digits are articulated with the broad articular surface of the radius. Arrangement and directions of robust inner digits seem to be suitably arranged for a powerful stroke exerted by the elbow joint extension. Cerapods, including ceratopsians and ornithopods, share following morphology of the manus: long and robust metacarpals II and III, ungual phalanges on digits I to III, reduced digits IV and V, and a divergent metacarpal V. A laterally oriented manus with reduced outer digits is present in the basal bipedal group of the Cerapoda. Although reversal to a quadrupedal stance and a evolution to a large, heavy body occurred independently in many lineages of Cerapoda, the basic features of the manus were retained throughout Neoceratopsia.

Elbow joint adductor moment arm as an indicator of forelimb posture in extinct quadrupedal tetrapods

Forelimb posture has been a controversial aspect of reconstructing locomotor behaviour in extinct quadrupedal tetrapods. This is partly owing to the qualitative and subjective nature of typical methods, which focus on bony articulations that are often ambiguous and unvalidated postural indicators. Here we outline a new, quantitatively based forelimb posture index that is applicable to a majority of extant tetrapods. By determining the degree of elbow joint adduction/abduction mobility in several tetrapods, the carpal flexor muscles were determined to also play a role as elbow adductors. Such adduction may play a major role during the stance phase in sprawling postures. This role is different from those of upright/sagittal and sloth-like creeping postures, which, respectively, depend more on elbow extensors and flexors. Our measurements of elbow muscle moment arms in 318 extant tetrapod skeletons (Lissamphibia, Synapsida and Reptilia: 33 major clades and 263 genera) revealed that sprawling, sagittal and creeping tetrapods, respectively, emphasize elbow adductor, extensor and flexor muscles. Furthermore, scansorial and non-scansorial taxa, respectively, emphasize flexors and extensors. Thus, forelimb postures of extinct tetrapods can be qualitatively classified based on our quantitative index. Using this method, we find that Triceratops (Ceratopsidae), Anhanguera (Pterosauria) and desmostylian mammals are categorized as upright/sagittally locomoting taxa.

Shape of articular surface of crocodilian (Archosauria) elbow joints and its relevance to sauropsids

The determination of area and shape of articular surfaces on the limb bones of extinct archosaurs is difficult because of postmortem decomposition of the fibrous tissue and articular cartilages that provide the complex three‐dimensional joint surfaces in vivo. This study aims at describing the shape of the articular cartilages in the elbow joints of six crocodilian specimens; comparing its structure with that of four birds, three testudines, and five squamates; and comparing the shapes of the surfaces of the calcified and the articular cartilages in the elbow joints of an Alligator specimen. The shapes of the articular cartilages of crocodilian elbow joint are shown to resemble those of birds. The humerus possesses an olecranon fossa positioned approximately at the midportion of the distal epiphysis and bordering the margin of the extensor side of the articular surface. The ulna possesses a prominent intercotylar process at approximately the middle of its articular surface, and splits the surface into the radial and ulnar cotylae. This divides the articular cartilage into an articular surface on the flexor portion, and the olecranon on the extensor portion. The intercotylar process fits into the olecranon fossa to restrict elbow joint extension. Dinosaurs and pterosaurs, phylogenetically bracketed by Crocodylia and Aves (birds), may have possessed a similar olecranon fossa and intercotylar process on their articular cartilages. Although these shapes are rarely recognizable on the bones, their impressions on the surfaces of the calcified cartilages provide an important indication of the extensor margin of the articular surfaces. This, in turn, helps to determine the maximum angle of extension of the elbow joint in archosaurs. J. Morphol., 2010.

Olecranon orientation as an indicator of elbow joint angle in the stance phase, and estimation of forelimb posture in extinct quadruped animals

Reconstruction of limb posture is a challenging task in assessing functional morphology and biomechanics of extinct tetrapods, mainly because of the wide range of motions possible at each limb joint and because of our poor knowledge of the relationship between posture and musculoskeletal structure, even in the extant taxa. This is especially true for extinct mammals such as the desmostylian taxa Desmostylus and Paleoparadoxia. This study presents a procedure that how the elbow joint angles of extinct quadruped mammals can be inferred from osteological characteristics. A survey of 67 dried skeletons and 113 step cycles of 32 extant genera, representing 25 families and 13 orders, showed that the olecranon of the ulna and the shaft of the humerus were oriented approximately perpendicular to each other during the stance phase. At this angle, the major extensor muscles maximize their torque at the elbow joint. Based on this survey, I suggest that olecranon orientation can be used for inferring the elbow joint angles of quadruped mammals with prominent olecranons, regardless of taxon, body size, and locomotor guild. By estimating the elbow joint angle, it is inferred that Desmostylus would have had more upright forelimbs than Paleoparadoxia, because their elbow joint angles during the stance phase were approximately 165° and 130°, respectively. Difference in elbow joint angles between these two genera suggests possible differences in stance and gait of these two mammals. J. Morphol. 2009.

Relationship between scapular position and structural strength of rib cage in quadruped animals

Determining scapular position is a major issue in reconstructing the skeletal systems of extinct quadruped archosaurs and mammals, because the proximal portion of the scapulae has no direct skeletal joint with the vertebrae or ribs. When quadrupeds stand or walk, their trunk is suspended between the forelimbs by the serratus muscles, which arises from the lateral sides of the “thoracic” ribs and inserts into the proximal portion of the costal surface of the scapula. Therefore, the “thoracic” ribs are subjected to a static or dynamic vertical compression between the lifting force from the muscle and the gravitational force from the vertebral column. To investigate the body support function of the ribs, we analyzed the mechanical strength of the ribs of extant tetrapods by the two‐dimensional finite element method, and compared the degree of strength through their craniocaudal scapular positions. The result of this simulation showed that the “thoracic” ribs of quadrupeds, to which the serratus muscles attach, have a relatively higher strength against compaction than the other ribs. In bipeds, however, we did not find a similar correlation between the strength of ribs and the serratus muscle. This implies that the location of robust ribs is associated with the arrangement of the serratus muscle, and provides a probable candidate for determination of the scapular position for extinct quadruped archosaurs and mammals. J. Morphol. 2009.

Correlation NMR spectroscopy and its applications

Abstract A correlation NMR system has been described. Several problems which are inherent in implementing the correlation technique on a mini-computer are discussed, and some examples of application are given.

Relay Strategy and Adaptation to a Muddy Environment in Isselicrinus (Isselicrinidae: Crinoidea)

Abstract Abundant columns of Isselicrinus ariakensis occur in a limited interval of the Upper Eocene Sakasegawa Formation in western Japan. Most of these are several centimeters in length, but curiously they usually stand upright, perpendicular to the bedding plane of the mudstone, and occur as bundles of 2 to 10 columns, with their original distal parts oriented downward. Based on detailed observation of the modes of occurrence as well as on CT scanning of the specimens, a reconstruction of the presumed mode of life is presented. The individuals of Isselicrinus adopted a relay strategy in the muddy substrate, using pre-existing upright columns as anchorage. Similar upright columns of Isselicrinus are also found, or have been reported, from other Eocene and Miocene strata in Japan, Argentina, and Denmark, suggesting that these Isselicrinus adopted this specialized mode of life as an adaptation to muddy bottoms.

Crabs grab strongly depending on mechanical advantages of pinching and disarticulation of chela.

A small morphological variation of an organ may cause a major change of its function in animal evolution. The function of decapod chela varies considerably among taxa, between sex, and even within an individual, but also retains a simple mechanism of motion. Therefore, the decapod chela is a suitable structure to study the evolutionary process of functional diversifications, although the relationship of form and function is inadequately understood, yet. We estimated the mechanical advantages of pinching and passive disarticulation resistance, and chela size relative to the carapace in 317 chelae of 168 decapod specimens, and compared these indices with the functions of each chela. Our study revealed that mechanical advantages of pinching efficiency and passive disarticulation resistance were greatest in shell‐crushing chelae, followed by gripping and pinching chelae, whereas the chela size relative to the carapace was not related to differences among these functions. We also found that the chelae are designed to retain the ratio between depth and width of the proximal dactylus. In the evolutionary process of decapods, the diversifications of chela functions were accompanied by the diversifications of the mechanical advantages, and played an essential role in their ecological diversification. J. Morphol. 277:1259–1272, 2016.

Capacitive and conductive dynamic response of ion-selective electrodes

Dynamic response of ion selective electrode, ISE, which is so widely used in analytical chemistry as the monitor or the detector should be studied in detail with respect to the varieties of external triggering to ISE, because the work of ISE actually relies on the response towards the external force which brings ISE into the out—of-equilibrium condition. Investigation has been made with respect to three cases, 1) to see the effect of strong pulse electric field, 2) to see effect of the environmen— tal electromagnetic fields, 3) to see the contact with the aqueous solution of the ISE specific ions. All three cases resulted in a same result showing that the response is formed of a superposition of two relaxation mechanisms, one with a short relaxation time ( ) , and the other with a longer v . It is assumed that the mechanism with a shorter t refers to the relaxation of the electronic energy transfer and that of the longer t to the relaxation due to the ionic energy transfer. The ISEs examined can be classified into two types, one for which the dynamic repsonse is dominantly made by the capacitive, or electronic mechanism and the other by the ionic conductivity. The Ag, Cu2t and Pb2t ISEs belong to the former category and those of F, cr , Br and 1 to the latter. All the ISEs present the dynamic response which is formed of two i s, short and long, regardless of the difference with respect to the classification cited above. This fact may suggest that even the capacity dominant ISE responds to the external perturbation with the conductant relaxation, and vice versa.