84 ANIMAL ABSTRACTS A1 – GENERAL BIOMECHANICS exclusively jaw-powered suction mechanism to capture prey. Analysis of A1.1 the skeletal morphology, high-speed video recordings and computational fluid dynamics simulations show how a fast separation of its large upper Hydrodynamic analysis of suspension feeding and lower jaws creates explosive, high flow velocity suction, while the in extinct and extant crinoids (Echinodermata: viscerocranial elements mainly serve to accommodate the engulfed Crinoidea) water volume. A shift in function of the viscerocranium from its primitive, obligatory active role in powering suction to a more passive, supporting role mgiht have released the biomechanical constraints on the evolution Janina F. Dynowski (State Museum of Natural History and University of the hyobranchial system within the early tetrapod lineage, allowing of Tübingen, Germany), James H. Nebelsick (University of Tübingen, development of a muscular tongue. Germany) and Anita Roth-Nebelsick (State Museum of Natural History, Email address for correspondence: [email protected] Germany) 11:15 Friday 29th June 2012 Crinoids belong to the phylum Echinodermata, which today also includes the echinoids, asteroids, ophiuroids and holothuroids. Based on their long and complete fossil record, their great diversity and their passive A1.3 suspension feeding strategy, crinoids represent ideal objects to study effective biological filter mechanisms. Biting force as a key factor for ecological Fossil representatives can differ strongly in their morphology from diversification in South American caviomorph recent forms and thus alternative feeding positions can be assumed rodents than those effective today. Recent stalked crinoids open their arms in a parabolic filtration fan, creating a three-dimensional filter to capture nutritive particles that are in the water. Some of the fossil representatives Federico Becerra (Universidad Nacional de Mar del Plata, Argentina), were possibly not as flexible, and thus not able to bend their arms to such Aldo I. Vassallo (Universidad Nacional de Mar del Plata, Argentina) and an extent. Furthermore, recent stalked forms are restricted to deeper Adrià Casinos (University of Barcelona, Catalonia, Spain) water settings with relatively constant flow conditions, while fossil crinoids mainly lived in shallow water habitats, where flow velocities and directions Within mammals, the South American caviomorph rodents became one changed more rapidly. of the most diverse clades considering their occupied habitats, diets, The interdisciplinary project presented analyses the filter-feeding locomotor modes and body sizes. This might have been partly achieved mechanisms of recent and fossil crinoids using flume experiments by diversifying their feeding system and its ecological commitment, e.g. (particle image velocimetry) as well as modern computational approaches chisel-tooth digging. Thus, both powerful jaw musculature and biting (computational fluid dynamics). In a first attempt, two crinoids are force, exerted at the tip of the incisors, might have allowed these rodent analysed: Encrinus liliiformis (Middle Triassic, 243–228million years ago) species to differentiate in their environmental use. with 10 simple arms, and recent Hyocrinus sp. with five unbranching The in vivo forces of specimens of three southern South American arms. For Encrinus, analyses reveal that – based on the general crown caviomorph species – the chinchilla (Chinchilla lanigera, which is social shape – a backward current is generated leading food particles back into and ground dwelling), the degu (Octodon degus, which is social and the crown. For the recent crinoid Hyocrinus, further analyses are needed, fossorial) and the sand dune tuco-tuco (Ctenomys australis, which is including more detailed morphological structures that were found to be solitary and subterranean/claw and chisel-tooth digger) – were measured. essential for the circulation pattern around the animal. Estimations of biting forces were also achieved by measuring the Email address for correspondence: [email protected] dissected jaw muscles, and their in- and out-levers, considering biting forces as reaction forces to food particles acting at different angles on the 11:00 Friday 29th June 2012 incisors’ tips (from 30º higher to 30º lower than the maximum out-lever at the incisors’ tips). We found that estimated biting forces were statistically higher than in A1.2 vivo forces. Since the species of tuco-tuco studied displayed the highest in vivo relative values and the chinchilla the lowest ones, we assumed Biomechanics of prey capture in the Chinese that the biting force would mainly be associated to the fossorial status giant salamander and what it might tell us about and aggressive territorial behaviour, which seems common in tuco-tucos. early tetrapod evolution Thus, our functional approach would complement the morphological assessments carried out so far on caviomorph rodents’ skull and jaw structure and muscles. Egon Heiss (University of Antwerp, Belgium and University of Vienna, Email address for correspondence: [email protected] Austria) and Sam Van Wassenbergh (University of Antwerp, Belgium) 11:30 Friday 29th June 2012 An important step in furthering our understanding of tetrapod evolution is to identify how early amphibians managed to capture prey, after substantial changes in the anatomy of their feeding system during the A1.4 fish–tetrapod transition. Similar to their sarcopterygian ancestors, the first amphibians were large aquatic predators that, in many aspects, The muscle, its force, its heat and its structure: resembled today’s basal amphibian species of Asian giant salamanders. Just elasticities in series? Consequently, functional morphological insights into the feeding strategy employed by these ‘living fossil’ amphibians might explain how profound Michael Günther (University of Stuttgart, Germany), Daniel F.B. modifications of the cranial architecture could have occurred without a Haeufle (University of Stuttgart, Germany) and Syn Schmitt (University major loss in prey-capture performance. Here, we show that the broad- of Stuttgart, Germany) skulled Chinese giant salamander, Andrias davidianus, uses a novel, Society for Experimental Biology abstracts.indd 84 08/06/2012 11:38:49 ANIMAL ABSTRACTS 85 Recently, it was demonstrated that the Hill relation can be derived from a The long distal tendons of cursorial animals are thought to have evolved A1 very simple, macroscopic structural arrangement of mechanical elements. to reduce the metabolic cost of running. During level running, force must Compared to the force–velocity relation, the corresponding heat rate be produced to support bodyweight while the cyclical fluctuations of the relation seems to contain even more subtle information about muscle mechanical energy of the body occurring over the course of a step are structure. Based on this, we present a revised muscle model that can fit accommodated. It is assumed that this can be achieved more economically both relations perfectly, using not more than six parameters. For this, a if muscle generates force isometrically and tendon stretches and recoils much lower dissipation coefficient, when compared to that in parallel to the than if muscle produces force while stretching and shortening, as muscle source of active force generation, is predicted in series. The main result is actively shortening and doing work is metabolically expensive. However, that the model explains both relations at once by the interaction of: tendon stretch and recoil also reduces the metabolically-inexpensive • an active force generator (active element); force production during stretch. Thus, to evaluate the metabolic benefits • energy dissipation in parallel to the AE (parallel damping element); of tendon, muscle ergometry and myothermic techniques were used • some partitioning between presumably elastic (serial element) and to determine the cost of producing force in frog iliofibularis muscles dissipative forces (serial damping element) in series to the active element. contracting isometrically and undergoing active stretch–shorten cycles; As a consequence, the assumption that any series elastic element is at conditions that simulated muscle action with and without effective tendon constant length in isotonic contractions should be reconsidered. energy storage and recovery respectively. Email address for correspondence: [email protected] If isometric muscle contraction with tendon stretch and recoil represents the most economical way for muscle to function during 11:45 Friday 29th June 2012 level running, the cost of force production would be lower in isometric than stretch–shorten cycles. However, we found that there was no significant difference (p=0.15) in the cost of force production in isometric A1.5 (20.1 ±3.6 mJ N-1 s-1) and stretch–shorten cycles (15.1 ±3.6 mJ N-1 s-1). This suggests that tendons do not provide some of the energetic benefits Does hibernation affect skeletal muscle previously assumed and that their ability to reduce work done by muscle performance in 13-lined ground squirrels? might not have been the driving force behind their evolution. Email address for correspondence: [email protected] Rob S. James (Coventry University, UK), James F. Staples (University of Western Ontario, Ontario, Canada), Jason C.L. Brown (University 12:15 Friday 29th June 2012 of Western Ontario, Ontario, Canada), Shannon N. Tessier (Carleton University, Ontario, Canada)