Dogfish-like
| Dogfish-like | ||||||||||||
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Dogfish ( Squalus acanthias ) |
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| Squaliformes | ||||||||||||
| Goodrich , 1909 |
The dogfish-like (Squaliformes) form the second largest order of the sharks , which includes about 120 species in six families. The order owes its name to the spines that are located in front of the two dorsal fins in most species. The order includes mainly smaller shark species, including the smallest known species, the dwarf lantern shark ( Etmopterus perryi ) and the cylindrical lantern shark ( E. carteri ) with a body length of only 16 to 20 centimeters and a weight of around 150 grams. The largest dogfish-like species is the Greenland Shark ( Somniosus microcephalus ), which can be up to seven meters long. Many dogfish species live in the deep sea and have luminous organs , such as the cigar shark ( Isistius brasiliensis ).
features
Dogfish species have two dorsal fins , each of which has a stinger protruding, which can also be missing. The anal fin is missing. The head is moderately flattened in most species, the rostrum has no barbels . The tail fin stalk is sometimes keeled. All species of the order have five gill slits, five functioning gill arches of which four are holobranchia (gill arches that carry respiratory filaments on both the anterior and posterior sides). Behind each eye there is a small or large spray hole with or without a flap. The lower nictitating membrane is missing, the sideline is closed.
Familys
According to Nelson, Grande & Wilson (2016), the dogfish-like order is composed of the following families:
- Centrophoridae (Centrophoridae) (18 kinds)
- Dalatiidae (10 species)
- Lantern sharks (Etmopteridae) (over 50 species)
- Pig sharks (Oxynotidae) (5 species)
- Sleeping sharks (Somniosidae) (17 species)
- Dogfish (Squalidae) (about 35 species)
Systematics and evolution
Together with the order of the nail sharks (Echinorhiniformes), angel sharks (Squantiniformes) and the saw sharks (Pristiophoriformes) they belong to the sharks without anal fin , the Squalea . They differ from the angel sharks, which have a flat and ray-like body, by their rather 'shark-like' shape, from the saw sharks by the shape of their head.
The origin of the spiny dogfish is probably in the Upper Jurassic , when the nail sharks (Echinorhiniformes), the saw sharks (Pristiophoriformes), the angel sharks (Squatiniformes), Protospinax and the spiny dogfish separated from each other. In the Lower Cretaceous , about 130 million years ago, two clades developed within the dogfish-like species, the dogfish (Squalidae) and a second unnamed clade to which all other families and subfamilies belong. Before about 95 to 90 million years ago, in Cenomanian and Turonian there was a first radiation in the centrophoridae (Centrophoridae) and the somniosidae (Somniosinae) including the oxynotus ( Oxynotus ) developed. 74 million years ago on the border between Campanium and Maastrichtian two spiny species died out, Cretascymnus and Protoxynotus . Three others, Proetmopterus , Microetmopterus and Eoetmopterus did not survive the Cretaceous-Tertiary boundary . Immediately afterwards a second radiation took place and led to the rapid evolution of the lantern sharks (Etmopterinae) and the Dalatiinae .
The following cladogram illustrates the probable family relationships:
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supporting documents
- ^ Alfred Goldschmid: Chondrichthyes , in: W. Westheide and R. Rieger: Special Zoology. Part 2. Vertebrate or skull animals. Spektrum, Munich 2004; P. 199. ISBN 3-8274-0307-3
- ^ Leonard Compagno , Marc Dando, Sarah Fowler: Sharks of the World . Princeton Field Guides, Princeton University Press , Princeton and Oxford 2005, ISBN 978-0-691-12072-0 . Page 103.
- ↑ Adnet, S. & Cappetta, H. 2001 09 14: A palaeontological and phylogenetical analysis of squaliform sharks (Chondrichthyes: Squaliformes) based on dental characters. Lethaia, Vol. 34, pp. 234-248. Oslo. ISSN 0024-1164
- ↑ Gavin JP Naylor, Janine N. Caira, Kirsten Jensen, Kerri AM Rosana, Nicolas Straube & Clemens Lakner: Elasmobranch Phylogeny: A Mitochondrial Estimate Based on 595 Species . in Jeffrey C. Carrier, John A. Musick, Michael R. Heithaus: Biology of Sharks and Their Relatives (Marine Biology). Publisher: Crc Pr Inc, 2012, ISBN 1-43983-924-7
literature
- Kurt Fiedler: Textbook of Special Zoology, Volume II, Part 2: Fish . Gustav Fischer Verlag Jena, 1991, ISBN 3-334-00339-6 .
- Joseph S. Nelson , Terry C. Grande, Mark VH Wilson: Fishes of the World . John Wiley & Sons, 2016, ISBN 978-1-118-34233-6 .
Web links
- Dogfish on Fishbase.org (English)