Squaliformes
Dogfish ( Squalus acanthias )
The Dornhaiartigen ( Squaliformes ) form the second largest order of sharks that includes about 120 species in six families. Owes its name to the order of the spines, which are located in most species before the two dorsal fins. At the order includes mainly smaller shark species, including the smallest known species of dwarf lanternshark ( Etmopterus perryi ) and the Cylindrical lanternshark (E. carteri ) with only 16 to 20 centimeters in body length and weighing about 150 grams. Largest Dornhaiartiger is the Greenland shark ( Somniosus microcephalus ), which can be up to seven feet long. Many Dornhaiartige live in the deep sea and have light organs as the Zigarrenhai ( Isistius brasiliensis).
Features
Dornhaiartige have two dorsal fins, each headed by a sting, but they can also be absent. The anal fin is missing. The head is moderately flattened in most species, the rostrum is without barbels. The tail fins stem is sometimes keeled. All species of the order have five gill slits, five functioning gill arches of which four are Holobranchien ( gill arches, which carry both at the front and the rear of respiratory filaments). Behind each eye is a small or large spray hole with or without flap. The lower nictitating membrane is absent, the lateral line is closed.
Families
The order of Dornhaiartigen continues after Compagno et al. 2004 consist of the following families:
- Nail sharks ( Echinorhinidae )
- Roll sharks ( Centrophoridae )
- Dalatiidae
- Lantern sharks ( Etmopteridae )
- Pig sharks ( Oxynotidae )
- Sleeping Sharks ( Somniosidae )
- Dogfish ( Squalidae )
After Nelson 2006 are the two types of nail sharks constitute its own order Echinorhiniformes, which are compared with the Dornhaiartigen.
Systematics and evolution
Together with the orders of the angel sharks ( Squantiniformes ) and the Sägehaie ( Pristiophoriformes ) they belong to the sharks without anal fin, the Squalea. Of the angel sharks, which have a flat and roche -like body, they differ in their rather ' haiartige ' shape of the Sägehaien by the shape of her head.
The origin of the Dornhaiartigen is probably in the Upper Jurassic, when the nail sharks ( Echinorhiniformes ), the Sägehaie ( Pristiophoriformes ), the angel shark ( Squatiniformes ) Protospinax and Dornhaiartigen separated from each other. In the Early Cretaceous, about 130 million years ago, evolved within the Dornhaiartigen two clades, the spiny dogfish ( Squalidae ) and a second unnamed clade, to which all other families and subfamilies belong. Before about 95 to 90 million years, in the Cenomanian and Turonian in, there was a first radiation in the rolling Sharks ( Centrophoridae ) and the sleeping sharks ( Somniosinae ) including the pig sharks ( Oxynotus ) developed. 74 million years ago on the border between Campanian and Maastrichtian two Dornhaigattungen died out, and Cretascymnus Protoxynotus. Three more, Proetmopterus, Microetmopterus and Eoetmopterus not survived the Cretaceous-Tertiary boundary. Immediately thereafter, a second radiation took place and led to the rapid evolution of lantern sharks ( Etmopterinae ) and the Dalatiinae.
The following cladogram shows the probable kinship relationships:
Angel sharks ( Squatiniformes )
Sägehaie ( Pristiophoriformes )
Nail sharks ( Echinorhinidae )
Dogfish ( Squalidae )
Roll sharks ( Centrophoridae )
Sleeping Sharks ( Somniosinae ) incl Oxynotus
Dalatiinae
Lantern sharks ( Etmopterinae )