Anatomy and Evolution of Heterocercal Tail in Lamniform Sharks

Abstract

Lamniformes is a small shark group consisting of 15 extant species with remarkably diverse lifestyles and a wide range in heterocercal tail morphology. The caudal fin morphology must be related to their lifestyle because the tail is a main locomotive structure in sharks, but such relationships have remained largely uninvestigated. Here, the morphologylifestyle relationship in lamniforms is examined through phylogenetic mapping. This study suggests that, within Lamniformes, caudal fins with a more horizontally directed curvature of the vertebral column are plesiomorphic, whereas those with a large dorsally directed curvature of the vertebral column are apomorphic. It also shows that caudal fins with posteriorly directed hypochordal rays are plesiomorphic, and that those with ventrally directed hypochordal rays are apomorphic within Lamniformes. Four basic caudal fin types are recognized in lamniforms on the basis of these skeletal variables in which one corollary is that the evolution of external morphology of caudal fin does not necessarily correspond to the evolution of its skeletal anatomy. This study also demonstrates that specific lifestyles seen in different lamniforms are indeed correlative with different caudal fin types in which a less asymmetrical heterocercal tail is a derived feature in lamniforms that evolved for fast swimming to capture fast swimming prey. Anat Rec, 296:433-442, 2013. V C 2013 Wiley Periodicals, Inc.

Negative allometric growth during ontogeny in the large pelagic filter-feeding basking shark

“…The shape of the caudal fin of basking sharks is unique among lamniforms and can be considered "transitional" between the plesiomorphic heterocercal type (e.g., sand tiger shark or megamouth shark) and a nearly homocercal type (e.g., short fin mako or lemon shark) (Kim et al 2013). Considering (1) the rapid ontogenetic change of the caudal fin to a fin type suited for sustained swimming, (2) a caudal fin type unique among lamniform sharks, (3) a very elongated body cavity which contains the huge liver (Compagno 2002), (4) an elongate, "cigar shaped" body (Kunzlik 1988) likely not altered in its hydrodynamic efficiency by the huge liver as it is reported for large, fast swimming lamniform sharks (Gleiss et al 2017), and (5) an obligate ram feeding mode (in contrast, the whale shark and megamouth shark are gulp or suction feeders), the basking shark seemingly occupies a rather unique position within the large pelagic marine vertebrates from an ecomorphological point of view.…”

Spinal deformities in free-ranging bull sharks,Carcharhinus leucas(Müller and Henle, 1839), from the western South Atlantic Ocean

“…Plain radiographs in the left lateral view were taken with Meditronix analogical equipment (55.0 kW, 5.0 mAs, 1.2 m focus‐to‐film distance). To minimize image distortion due to X‐ray dispersion, each caudal fin had two complementary radiographs taken covering contiguous smaller sections of the vertebral spine along the fin, similar to the method used by Kim, Shimada, and Rigsby (). Since radiopacity within each of the image composites is not subject to variation, the contrast interpretation within each composite should be effective in detecting hard‐tissue anomalies, although the two composites may present variation in contrast in relation to each other.…”

Development of the Lunate‐Shaped Caudal Fin in White Shark Embryos

“…). Measurements were based on definitions and methods described by Thomson and Simanek () and Kim et al (). Although the lengths were measured mostly from original specimens using hand calipers, three measurements were taken from Uchida et al () (Table ).…”

“…2b) because this location is a good indicator of the anteriormost caudal vertebra in lamniform sharks ( fig. 2 in Kim et al, 2013).…”

“…The lunate-shaped caudal fin has developed independently in several vertebrate lineages, including lamnid sharks, tunas, extinct ichthyosaurs, and dolphins; this evolutionary convergence has attracted considerable attention (Motani and McGowan 1996;Lingham-Soliar, 2005;Kim et al, 2013). A recent study showed that the lunate-shaped caudal fin of lamnid sharks originated in the heterocercal caudal fin (Kim et al, 2013). In general, the evolution of morphological features is based on modifications in developmental processes (Moczek et al, 2015).…”