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

Abstract

The lunate-shaped caudal fin in lamnid sharks is a morphological specialization for their thunniform mode of locomotion, but its developmental process during gestation has been poorly investigated. Observations of 21 embryonic specimens of the white shark (Carcharodon carcharias) revealed that their caudal fin morphology drastically changes from strongly heterocercal to lunate-shaped through ontogeny. This morphological change involves (1) rapid elongation of the ventral lobe, (2) increased upward curvature of the vertebra within the caudal fin, and (3) formation of keels at both lateral sides of the caudal fin base. These morphological changes are probably shared among the members of the family Lamnidae and are in contrast with the developmental process of the heterocercal tail in the lamniform Carcharias taurus, in which the caudal fin morphology is almost unchanged through the late gestation period. Anat Rec, 301:1068-1073, 2018. © 2018 Wiley Periodicals, Inc.

Insights into ontogenetic scaling and morphological variation in sharks from near-term brown smooth-hound (Mustelus henlei) embryos

“…Moreover, selection relating to locomotion, predation, and nutrient acquisition clearly differs substantially between the prenatal and postnatal environments. In several shark species (including both matrotrophic and oviparous taxa), shifts in embryo morphology have been hypothesised to result from differences between these environments: in white sharks ( Carcharodon carcharias ), embryos undergo a dramatic transition from heterocercal to lunate caudal fins, with the latter is thought to be advantageous to fast-moving active predators such as young white sharks (Tomita et al, 2018). Interestingly, this transition continues well into postnatal ontogeny (Lingham-Soliar, 2005).…”

“…One potential limitation that has not yet been addressed in the literature is that existing ecomorphological studies of scaling in elasmobranchs focus predominantly on postnatal ontogeny, despite the evolutionary and ecological significance of morphological changes occurring during prenatal ontogeny. Those studies that do address embryogenic scaling focus on developing staging tables without much focus on the ecomorphology of scaling itself (Tomita et al, 2018; López-Romero et al, 2020; Byrum et al, 2023). They may, as in other ontogenetic stages (Gayford et al, 2023b) act to maximise fitness in the context of the trophic and spatial ecology of this taxon post-partum.…”

“…Each of these factors is yet to be considered from the perspective of elasmobranch taxa, representing a significant gap in our understanding of morphological evolution within this clade. Studies of scaling in embryos may also provide insight into the selective pressures driving the evolution of allometric and isometric growth, as shark embryos typically exhibit substantial proportional body-size changes (Tomita et al, 2018; López-Romero et al, 2020; Byrum et al, 2023) without undergoing major shifts in the trophic/spatial environment.…”

Exceptionally preserved shark fossils from Mexico elucidate the long-standing enigma of the Cretaceous elasmobranch Ptychodus

“…90°, respectively) and a less vertical ventral lobe (lower hypocercal angle). This ontogenetic difference is known in some modern lamnid and cetorhinid lamniforms [76,77]. The caudal fin of Ptychodus corresponds in its proportions to the type 4 (type 2 in juveniles) defined for lamniform sharks [75].…”

The Analysis of Biomimetic Caudal Fin Propulsion Mechanism with CFD

“…Xin and Wu [15] studied the effect of the shape of caudal fin on swimming speed and efficiency in fish free propulsion and found that the shape of the optimal caudal fin varies with different swimming modes. Tomita et al [16] clarify developmental processes of the white shark caudal fin, based on morphological observations of the caudal fin over several developmental stages.…”