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 name Devoniano derives from that of the county Devon, in England, where the breakthroughs of rocks of the period are abundant) 
The fossil rests of the shark Cladoselache are enough numerous and well preserved: besides the teeth and vertebrae, there are also portions of skin, muscles and inside organs. 
This animal was very particular, he introduced characteristic elements of the ancient sharks of the epoch, but also structures present still in the modern sharks. 
 

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 ago.. 
The pectoral fins were wide and round off, while the anal fin was absent. 
The face of the Cladoselache was typical of that of the ancient sharks: short and rounded and the jaws had terminal position, in front of the head and not ventral, as in the modern sharks. The teeth had the smooth edges, with a greater central point and more side cusps, proper to grab the preys but not to chew her. 
The caudal fin was very strong, with the greater superior lobe slightly. (externally asymmetrical but with symmetrical inside structure) 
 

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 them whole. 
The principal preys were bony fishes, shellfishes and squids. 
Contrarily of the modern sharks the skin of Cladoselache was "naked", not covered by scales, except around the eyes and in the edges of the fins. 
An element that instead make this animal similar to the modern sharks, besides the form and greatness of the caudal fin, are the hulls or keels, prominences along the sides of the shark, before the caudal fin, characteristic of the fast pelagic predator. 

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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