Between shark and ray: The evolutionary benefit of the ocean angels

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

Angel sharks are sharks, however with their peculiarly flat physique they relatively resemble rays. A world analysis group led by Faviel A. Lopez-Romero and Jurgen Kriwet of the Institute of Palaeontology has now investigated the origin of this physique form. The outcomes illustrate how these sharks developed into extremely specialised, solely bottom-dwelling ambush predators and thus additionally contribute to a greater understanding of their risk from environmental modifications.

Between shark and ray: The evolutionary advantage of the sea angels
Full skeleton of a sea angel (Pseudorhina acanthoderma; SMNS 86214/41) from the Higher Jurassic interval
(c. 155 Million years) from the Nusplinger Plattenkalke in Baden-Wurttemberg (Germany)
[Credit: J. Kriwet]

The overall image of a shark is that of a quick and huge ocean predator. Some species, nevertheless, query this picture – for instance angel sharks. They’ve tailored to a life on the underside of the oceans, the place they lie in wait for his or her prey. So as to have the ability to cover on or within the sediment, the physique of angel sharks turned flattened in the middle of their evolution, making them similar to rays, that are intently associated to sharks.

Flattened physique as indication for a profitable way of life

The oldest recognized full fossils of angel sharks are about 160 million years previous and exhibit that the flattened physique was established early of their evolution. This additionally signifies that these extinct angel sharks already had an identical way of life as their extant relations – and that this way of life clearly was very profitable.

Angel sharks are discovered everywhere in the world immediately, starting from temperate to tropical seas, however most of those species are threatened. As a way to perceive the patterns and processes that led to their current low variety and the doable penalties of their specific anatomy, the group has studied the physique shapes of angel sharks since their origins utilizing fashionable strategies.

Right this moment’s species are very related

For this function, the skulls of extinct species from the late Jurassic interval (about 160 million years in the past) and of present-day species have been quantitatively analysed utilizing X-ray and CT photographs and ready skulls using geometric-morphometric approaches. In doing so, the evolution of physique shapes might be defined comparatively, impartial of physique measurement.

Between shark and ray: The evolutionary advantage of the sea angels
Cranium of a fossil sea angel (Pseudorhina acanthoderma; GPIT 8214) from the Higher Jurassic interval
(c. 155 Million years) from the Nusplinger Plattenkalke in Baden-Wurttemberg (SW-Germany)
 [Credit: J. Kriwet]

The outcomes present that early angel sharks have been completely different of their exterior form, whereas fashionable species present a comparably decrease variation in form. “Most of the residing species are tough to determine on the premise of their skeletal anatomy and form, which might be problematic for species recognition,” explains Faviel A. Lopez-Romero.

Angel sharks are nicely tailored, however react slowly to environmental modifications

It has been proven that in residing species the person components of the cranium skeleton are extra intently built-in than of their extinct relations. This led to a decreased variability in look in the course of the evolution of angel sharks. “The impact of integrating completely different components of the cranium into particular person, extremely interdependent modules can result in a restricted skill to evolve in several kinds, however on the similar time will increase the power to efficiently adapt to particular environmental circumstances,” explains Jurgen Kriwet.

Within the case of the angel sharks, growing geographical isolation resulted within the growth of various species with very related diversifications. “However modular integration additionally signifies that such animals are now not in a position to react shortly to environmental modifications, which will increase their danger of extinction,” concludes Jurgen Kriwet.

The research is revealed within the journal Scientific Experiences.

Supply: College of Vienna [August 04, 2020]

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