The sharks are very ancient animals, present on the earth already to the times of the dinosaurs, hundreds million of years ago and their evolution was never arrested, arriving thin to today with exemplary practically perfect, among the greatest and improved predatory of the sea (some researchers think that the evolution of the sharks has arrived already at the most level 100 million years ago).
To the genus Cladoselache
belong some of the most ancient sharks of which there is enough precise
information. This genus of sharks (it is not the only one) developed
during the period Devoniano around 400 million years ago and it was
present for 100-150 million years.
The length of the Cladoselache
was of 1,2-1,5 m, its body was tapered, with two dorsal fins. Before to
each of them it was present a thorn made of bony, very porous, light but
strong, important weapon of defense in the oceans of 400 million years
These characteristics make to
think that the shark Cladoselache was a pelagic predator, very fast,
that pursued the preys grabbing them for the tail and also swallowing
The formality of reproduction of the shark Cladoselache is still mysterious, in fact in any rest fossil the claspers are visible, the sexual organs through which these animals reproduce (the terminal part of the ventral fins lengthens and calcifies forming two claspers).
In the fossils of sharks of different genus, always lived in the Devoniano, the claspers have always been individualized and it is sure that this reproduction with internal fertilization was already present 400 million of years ago as today in the modern sharks.
This could mean that, despite the numerous rests fossils, the male of Cladoselache remains not still identified. Some studious, considering statistically difficult to happen, risked the hypothesis that the male shark of Cladoselache had been able to use departs of cloaca and to use her as clasper for the internal fertilization of the female. This method of reproduction is still used by some birds, reptiles and living amphibians.
Marco Angelozzi - www.prionace.it
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