Between shark and ray: The evolutionary advantage of the sea angels

Cortez Deacetis

The common photograph of a shark is that of a rapid and significant ocean predator. Some species, on the other hand, concern this graphic – for instance angel sharks. They have tailored to a life on the base of the oceans, where they lie in hold out for their prey. In get to be ready to hide on or in the sediment, the physique of angel sharks grew to become flattened in the study course of their evolution, generating them extremely comparable to rays, which are closely linked to sharks.

Flattened physique as indicator for a productive way of living

The oldest recognized complete fossils of angel sharks are about 160 million a long time outdated and show that the flattened physique was recognized early in their evolution. This also indicates that these extinct angel sharks presently experienced a comparable way of living as their extant relations – and that this way of living certainly was extremely productive.

Angel sharks are discovered all in excess of the entire world right now, ranging from temperate to tropical seas, but most of these species are threatened. In get to fully grasp the patterns and procedures that led to their current small range and the possible implications of their unique anatomy, the workforce has studied the physique designs of angel sharks given that their origins utilizing modern methods.

Present day species are extremely comparable

For this goal, the skulls of extinct species from the late Jurassic period of time (about 160 million a long time back) and of current-day species were being quantitatively analysed utilizing X-ray and CT photos and ready skulls utilizing geometric-morphometric methods. In carrying out so, the evolution of physique designs could be explained comparatively, impartial of physique dimension.

The effects demonstrate that early angel sharks were being distinct in their exterior form, while modern species demonstrate a comparably reduce variation in form. “Quite a few of the residing species are difficult to detect on the basis of their skeletal anatomy and form, which could be problematic for species recognition,” clarifies Faviel A. López-Romero.

Angel sharks are perfectly tailored, but react slowly and gradually to environmental variations

It has been demonstrated that in residing species the unique parts of the skull skeleton are extra closely built-in than in their extinct relations. This led to a diminished variability in overall look in the course of the evolution of angel sharks. “The outcome of integrating distinct parts of the skull into unique, very interdependent modules can direct to a confined means to evolve in distinct types, but at the same time improves the means to productively adapt to particular environmental disorders,” clarifies Jürgen Kriwet.

In the circumstance of the angel sharks, growing geographical isolation resulted in the development of distinct species with extremely comparable adaptations. “But modular integration also indicates that such animals are no for a longer period ready to react quickly to environmental variations, which improves their risk of extinction,” concludes Jürgen Kriwet.


Publication in Scientific Reports:

Evolutionary tendencies of the conserved neurocranium form in angel sharks (Squatiniformes, Elasmobranchii). López-Romero, F. A., Stumpf, S., Pfaff, C., Marramà, G., Johanson, Z. & Kriwet, J. in: Scientific Reports.

DOI: ten.1038/s41598-020-69525-7

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