Flexibility of Heterocercal Tails: What Can the Functional Morphology of Shark Tails Tell Us about Ichthyosaur Swimming? (original) (raw)
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Heterocercal tail function in leopard sharks: a three-dimensional kinematic analysis of two models
The Journal of experimental biology, 1996
Two different models have been proposed to explain the function of the heterocercal tail in shark locomotion. The classical model proposes that, as a result of lift generated by the tail as it beats, the net force acting on the tail is directed dorsally and anteriorly. In contrast, Thomson's model suggests that the tail generates a net force directed through the shark's center of gravity, i.e. ventrally and anteriorly. In this study, we evaluate these two models by describing the three-dimensional kinematics of the heterocercal tail in the leopard shark Triakis semifasciata during swimming. Lateral and posterior views of the tail were examined from four individuals swimming in a flow tank at 1.2 L s-1 (where L is total length) using two high-speed video cameras filming simultaneously at 250 fields s-1. These two simultaneous views allowed eight landmarks on the tail to be followed in three dimensions through time. These landmarks allowed the tail to be divided into separate ...
Relationships between caudal fin shape and ecomorphotype in extant sharks
2020
Since sharks inhabit this planet for more than 200 million years, they are of big interest for researchers. The interplay between morphological and behavioural adaptations and the constantly changing environment is an important part in scientific shark studies. A perfectly adapted body plan with sophisticated senses is a reason for their long existence. A very prominent characteristic of sharks is the heterocercal caudal fin shape in which the vertebra extends into the elongated dorsal lobe. The caudal fin, as the main locomotory organ in sharks, can be very diverse in shape and therefore, it is of tremendous importance to understand why different caudal fin shapes occur and how strong the influence of factors such as the environment they live in, is on the morphology of the caudal fin. In this thesis, the goal is to quantitatively assess the relationships between the caudal fin shape of various extant shark species and their associated ecomorphotypes. Through geometric morphometric...
Ontogeny of Head and Caudal Fin Shape of an Apex Marine Predator: The Tiger Shark (Galeocerdo Cuvier
How morphology changes with size can have profound effects on the life history and ecology of an animal. For apex predators that can impact higher level ecosystem processes, such changes may have consequences for other species. Tiger sharks (Galeocerdo cuvier) are an apex predator in tropical seas, and, as adults, are highly migratory. However, little is known about ontogenetic changes in their body form, especially in relation to two aspects of shape that influence locomotion (caudal fin) and feeding (head shape). We captured digital images of the heads and caudal fins of live tiger sharks from Southern Florida and the Bahamas ranging in body size (hence age), and quantified shape of each using elliptical Fourier analysis. This revealed changes in the shape of the head and caudal fin of tiger sharks across ontogeny. Smaller juvenile tiger sharks show an asymmetrical tail with the dorsal (upper) lobe being substantially larger than the ventral (lower) lobe, and transition to more symmetrical tail in larger adults, although the upper lobe remains relatively larger in adults. The heads of juvenile tiger sharks are more conical, which transition to relatively broader heads over ontogeny. We interpret these changes as a result of two ecological transitions. First, adult tiger sharks can undertake extensive migrations and a more symmetrical tail could be more efficient for swimming longer distances, although we did not test this possibility. Second, adult tiger sharks expand their diet to consume larger and more diverse prey with age (turtles, mammals, and elasmobranchs), which requires substantially greater bite area and force to process. In contrast, juvenile tiger sharks consume smaller prey, such as fishes, crustaceans, and invertebrates. Our data reveal significant morphological shifts in an apex predator, which could have effects for other species that tiger sharks consume and interact with. J. Morphol. 000:000-000, RMN. 1965. The lift produced by the heterocercal tails of Selachii. J Exp Biol 43:131-138. Alfaro ME, Bolnick DI, Wainwright PC. 2005. Evolutionary consequences of many-to-one mapping of jaw morphology to mechanics in labrid fishes. Am Nat 165:E140-E154. Alfonso SA, Hazin FH. 2015. Vertical movement patterns and ontogenetic niche expansion in tiger shark, Galeocerdo cuvier.
The role of the pectoral fins in body trim of sharks
Journal of Fish Biology, 2000
In a large aquarium the leopard shark Triakis semifasciata, sand tiger shark Odontaspis taurus, sandbar shark Carcharhinus plumbeus, and spiny dogfish Squalus acanthias cruised steadily at 0.1-0.7 body lengths s-'. Relative to the trajectory of the shark, the pectora1 fins were maintained at a positive angle of attack regardless of vertical direction. For level swimming the mean angle of attack for the pectoral fin was 11 k 1.7", 10.1 f 1.3", 9.3 f 1.3", and 1.5-0 f 0.0" for T. semifaciata, C. plumbeus, 0. taurus, and S. acanthias, respectively. The long axis of the body was canted at an angle of attack for T. semlfasciata and S. acanthias, but trim was maintained during level swimming for C. plumbeus and 0. taurus. Hydrodynamic analysis of the body and fin design of I: semifasciata indicated that the pectoral fins could develop sufficient pitching moment to maintain depth and keep the body in trim. Demonstration of positive angles of attack support the hypothesis that lift is generated in the anterior body to counterbalance the lift produced by the heterocercal tail.
A comparative morphological analysis of body and fin shape for eight shark species
Biological Journal of the Linnean Society, 2017
Sharks are diverse and ecologically important predators and are also highly varied in their biology and behaviour. Prior studies have posited basic relationships between body form and lifestyle; previous investigations of body shape in sharks, however, have been restricted to a few species, or measured dead sharks, which may show artefacts of preservation or distortion and/or require lethal sampling. Therefore, using non-lethal field methods, we examined body and fin shape in a group of eight different shark species that co-occur in coastal waters of the Western Atlantic but vary to different degrees in biology and ecology. We measured a series of 12 morphometric variables and body size (pre-caudal length) from wild individuals (N = 90 sharks total) belonging to the families Carcharhinidae [order: Carcharhiniformes (tiger, bull, blacktip, lemon, blacknose, Atlantic sharpnose and sandbar)] and Ginglymostomatidae [order: Orectolobiformes (nurse)]. By taking phylogeny into account using the SLOUCH method, our analysis revealed isometry of all 12 morphological variables measured relative to body length among all species, indicating that despite substantial lifestyle differences, the general body form of these carcharhiniform and orectolobiform species is overall highly conserved. Univariate analyses were consistent with this result in showing no substantial differences among species once the effects of body size were accounted for, although there was a modest difference among the species in leading edge of the caudal fin, which was also revealed by an elliptic Fourier analysis. A multivariate principal component analysis showed some differentiation among species in the height of the dorsal fin, the length of the lower lobe of the caudal fin and in overall body girth, but the lack of significant variation in the univariate analyses suggests that such differences may not be biologically substantial. Our conclusion was that these sharks are similar in gross morphology, which underscores the generality of the shark body form for different niches. Indeed, the most important variable distinguishing the species was variation in body length, which in sharks is generally linked to variation in diet type or breadth.
The Anatomical Record: Advances in …, 2010
The shark heterocercal caudal fin and its contribution to locomotion are of interest to biologists and paleontologists. Current hydrodynamic data show that the stiff dorsal lobe leads the ventral lobe, both lobes of the tail are synchronized during propulsion, and tail shape reflects its overall locomotor function. Given the difficulties surrounding the analysis of shark caudal fins in vivo, little is known about changes in tail shape related to ontogeny and sex in sharks. A quantifiable analysis of caudal fin shape may provide an acceptable proxy for inferring gross functional morphology where direct testing is difficult or impossible. We examined ontogenetic and sex-related shape changes in the caudal fins of 115 Squalus acanthias museum specimens, to test the hypothesis that significant shape changes in the caudal fin shape occur with increasing size and between the sexes. Using linear and geometric morphometrics, we examined caudal shape changes within the context of current hydrodynamic models. We found no statistically significant linear or shape difference between sexes, and near-isometric scaling trends for caudal dimensions. These results suggest that lift and thrust increase linearly with size and caudal span. Thin-plate splines results showed a significant allometric shape change associated with size and caudal span: the dorsal lobe elongates and narrows, whereas the ventral lobe broadens and expands ventrally. Our data suggest a combination of caudal fin morphology with other body morphology aspects, would refine, and better elucidate the hydrodynamic factors (if any) that underlie the significant shape changes we report here for S. acanthias. Anat Rec, 293:1184-1191,
Morphological scaling of body form in four shark species differing in ecology and life history
Biological Journal of the Linnean Society, 2014
Body form can change across ontogeny, and can influence how animals of different sizes move and feed. Scaling data on live apex predatory sharks are rare and, therefore, we examined patterns of scaling in ontogenetic series of four sympatric shark species exhibiting a range of sizes, ecologies and life histories (tiger, bull, blacktip, and nurse shark). We evaluated 13 linear morphological variables and two areas (caudal and dorsal) that could influence both animal condition and locomotor performance. These measurements included dimensions of the dorsal, pectoral, and caudal fins, as well as several dimensions of body circumference, and of the head. For all four species, the body axis (eye-to-eye, lateral span, frontal span, proximal span) scaled close to isometry (expected slope of 1.0). The two largest sharks (tiger and bull sharks) also showed significant negative allometry for elements of the caudal fin. We found significant negative allometry in the lengths of the upper lobe of the caudal fin (caudal fin 1) and the overall height of the caudal fin (caudal fin 2) in tiger and bull sharks, with slopes ranging from about 0.60 to 0.73. Further, tiger sharks showed negative allometry in caudal fin area. These results suggest that in terms of overall body dimensions, small sharks are roughly geometrically similar to large sharks, at least within the species we examined. However, juvenile tiger (and to a lesser extent bull sharks) are notable in having proportionately larger caudal fins compared to adult sharks. As the caudal fin contributes to generating thrust during forward locomotion, this scaling implies differences among adult and juvenile sharks in locomotor ability.