SUMMARY Crocodilians, including the alligator (Alligator mississippiensis), perform a spinning maneuver to subdue and dismember prey. The spinning maneuver, which is referred to as the `death roll',involves rapid rotation about the longitudinal axis of the body. High-speed videos were taken of juvenile alligators (mean length=0.29 m) performing death rolls in water after biting onto a pliable target. Spinning was initiated after the fore- and hindlimbs were appressed against the body and the head and tail were canted with respect to the longitudinal body axis. With respect to the body axis, the head and tail bending averaged 49.2° and 103.3°,respectively. The head, body and tail rotated smoothly and freely around their individual axes of symmetry at 1.6 Hz. To understand the dynamics of the death roll, we mathematically modeled the system. The maneuver results purely from conservation of angular momentum and is explained as a zero angular momentum turn. The model permits the calculation of relevant dynamical parameters. From the model, the shear force, which was generated at the snout by the juvenile alligators, was 0.015 N. Shear force was calculated to scale with body length to the 4.24 power and with mass to the 1.31 power. When scaled up to a 3 m alligator, shear force was calculated at 138 N. The death roll appears to help circumvent the feeding morphology of the alligator. Shear forces generated by the spinning maneuver are predicted to increase disproportionately with alligator size, allowing dismemberment of large prey.

No abstract

The flukes of cetaceans function in the hydrodynamic generation of forces for thrust, stability, and maneuverability. The three-dimensional geometry of flukes is associated with production of lift and drag. Data on fluke geometry were collected from 19 cetacean specimens representing eight odontocete genera (Delphinus, Globicephala, Grampus, Kogia, Lagenorhynchus, Phocoena, Stenella, Tursiops). Flukes were imaged as 1 mm thickness cross-sections using X-ray computer-assisted tomography. Fluke shapes were characterized quantitatively by dimensions of the chord, maximum thickness, and position of maximum thickness from the leading edge. Sections were symmetrical about the chordline and had a rounded leading edge and highly tapered trailing edge. The thickness ratio (maximum thickness/chord) among species increased from insertion on the tailstock to a maximum at 20% of span and then decreasing steadily to the tip. Thickness ratio ranged from 0.139 to 0.232. These low values indicate reduced drag while moving at high speed. The position of maximum thickness from the leading edge remained constant over the fluke span at an average for all species of 0.285 chord. The displacement of the maximum thickness reduces the tendency of the flow to separate from the fluke surface, potentially affecting stall patterns. Similarly, the relatively large leading edge radius allows greater lift generation and delays stall. Computational analysis of fluke profiles at 50% of span showed that flukes were generally comparable or better for lift generation than engineered foils. Tursiops had the highest lift coefficients, which were superior to engineered foils by 12-19%. Variation in the structure of cetacean flukes reflects different hydrodynamic characteristics that could influence swimming performance. Anat Rec, 290:614-623, 2007Rec, 290:614-623, . 2007 Wiley-Liss, Inc.

The flukes are the primary locomotor structure in cetaceans, which produce hydrodynamic thrust as the caudal vertebrae are oscillated dorso-ventrally. Effective thrust generation is a function of the kinematics of the flukes, the angle of attack between the flukes and the incident water flow, and the shape of the flukes. We investigated the effect of bending within the caudal region of odontocete cetaceans to determine how changes in angular displacement between caudal vertebrae could effect passive shape change of the flukes. The internal and external changes of bent flukes were examined with computer tomography. Flukes and tailstock were removed from deceased Delphinus delphis, Lagenorhynchus acutus, Peponocephala electra, Phocoena phocoena and Tursiops truncatus, and bent on an adjustable support at 0, 45 and 90 degrees . At 0 degrees , cross-sections of the flukes displayed a symmetrical profile. Cross-sections of bent flukes (45 degrees , 90 degrees ) were asymmetrical and showed a cambered profile. Maximum cambering occurred close to the tailstock and decreased toward the fluke tip. Maximum angular displacement occurred at the 'ball vertebra', which was located posterior of the anterior insertion of the flukes on the tailstock. Bending at the 'ball vertebra' passively cambers the flexible flukes. Cambering could increase hydrodynamic force production during swimming, particularly during direction reversal in the oscillatory cycle.

No abstract

The Hynobiidae is generally regarded as the most phylogenetically basal and least derived extant family of terrestrial salamanders. As in the other families of terrestrial salamanders, prey capture in the Hynobiidae is accomplished by lingual prehension. In Hynobius, the prey capture system appears to be a mosaic of derived and primitive features. This, in conjunction with previous studies, suggests that the hyolingual systems of all families of terrestrial salamanders have evolved various degrees of specialization since the appearance of the common ancestral condition. We propose that the generalized feeding system for the extant terrestrial salamanders includes a hyolingual skeleton comprised of one basibranchial, one pair of radial or radial‐like structures, two pairs of ceratobranchials, two pairs of epibranchials, one pair of ceratohyals, and one urohyal arranged in a configuration similar to that of Hynobius; a simple, sac‐like secondary tongue pad; a lift and thrust system of tongue projection; a four‐part gape cycle; and a forward head and body surge. Modifications to this general plan, previously described for the disparate families, include various changes in the size, shape, and definition of the tongue pad, changes in the specific types of structures and configurations in the anterior hyolingual skeleton, secondary ossification in the posterior hyolingual skeleton, the appearance of various protrusion, projection, and flipping systems for tongue protraction, simplification of the kinematic gape profile, and loss of the forward head and body surge. The evolutionary trends in these modifications have provided a rich data set from which much phylogenetic information has been inferred. © 1996 Wiley‐Liss, Inc.

As revealed by scanning electron microscopy, three basic cusp shapes are found on the premaxillary teeth of mole salamanders: disc, cone, and club. In fully metamorphosed adults, tooth crowns are subdivided into labial and lingual cusps. Except for species of Linguaelapsus, the labial cusps of all adult bifid teeth are disc shaped; lingual cusp shape is more variable, but the taxonomic distribution of the various configurations is generally consistent within the subgroups Rhycosiredon, Ambystoma, and Linguaelapsus. The club shape appears to be a derived character state, but the cone and disc shapes may be either primitive or derived. Prior to the start of metamorphosis, all larvae have conical, monocuspid teeth. During metamorphosis these salamanders develop incipient bifid teeth that have the same basic adult pattern of cusp shapes but in which the cusps are smaller and more generalized. Crown morphology in paedomorphic ambystomatids is similar to that of older larvae; as such, paedomorphosis seems to interrupt and retard the ontogenetic sequence of development rather than to introduce (or reintroduce) novel morphologies into the developmental program. In larvae the crown is firmly attached to the tooth base along the putative zone of weakness, but in transformed adults the crown is separated from a pedicel by a narrow zone of fibrous connective tissue. This latter structural arrangement allows unidirectional lingual flexing of the crowns relative to the pedicel and appears to facilitate the process of tooth replacement.

LARSEN, J. H., JR., and BENESKI, J. T., JR. 1988. Quantitative analysis of feeding kinematics in dusky salamanders (Desnzognathus). Can. J. Zool. 66: 1309 -13 17. Gape formation by the dusky salamander (Desmognathus) involves both upper and lower jaws and occurs in a manner similar to that of other terrestrial salamanders. As Desmognathus opens its mouth, ventral rotation of the mandibles is restricted but not stopped by the atlas-mandibular ligaments; the lower jaw is not propelled anteriorly. Tongue protraction, well beyond the mandibular symphysis, is always a major component of prey capture by this genus. After the sticky tongue pad has made contact with the prey, the salamander's head surges forward and the pad is rapidly retracted with the prey item attached. Aided by a unique suite of characters the mouth then snaps shut with considerable force. Our study supports the premise that Desmognathus is no different from most, if not all, terrestrial salamanders in its employment of tongue projection as a major feature in prey capture. We argue that the primary selective force for the unique configuration of desmognathine cephalic structures was enhancement of the ability of these small salamanders to capture relatively large prey without an increase in the size of the head and body. LARSEN, J. H., JR., et BENESKI, J. T., JR. 1988. Quantitative analysis of feeding kinematics in dusky salamanders (Desmognathus). Can. J. Zool. 66 : 1309-1317. Chez la Salamandre sombre (Desmognathus), l'ouverture de la bouche suppose des mouvements de la mlchoire superieure et de la mlchoire inferieure semblables a ceux d'autres salamandres terrestres. Lorsque la salamandre ouvre la bouche, la rotation ventrale des mandibules est limitee, sans Ctre empCchCe, par le ligament atlas -mandibule; la mlchoire inferieure n'est pas projetee vers l'avant. La protraction de la langue bien au-dela de la symphyse mandibulaire constitue toujours une composante importante de la capture de proies chez ce genre. Dks que le coussinet adhesif de la langue entre en contact avec la proie, la t2te de la salamandre est projetee vers l'avant et la langue est promptement retirCe dans la bouche avec la proie. Grlce a I'intervention d'une sene particulikre de caracteristiques, la bouche est refermee vivement avec une force considerable. Nos resultats confirment I'hypothkse selon laquelle Desmognathus ne differe pas de certaines autres, sinon de toutes les autres, salamandres terrestres, chez lesquelles la projection de la langue constitue une phase primordiale de la capture des proies. Nous croyons que la principale force selective qui a conduit a la configuration unique des structures cephaliques desmognathes a permis a ces petites salamandres de capturer des proies relativement grosses sans que la taille de leur t2te ou de leur corps ait besoin d'stre augmentee.[Traduit par la revue]