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Blue shark

Blue shark

Temporal occurrence
Carbon to this day
353.8 to 0 million years


Over trunk : Neumünder (Deuterostomia)
Trunk : Chordates (chordata)
Sub-stem : Vertebrates (vertebrata)
Superclass : Jaw mouths (Gnathostomata)
Class : Cartilaginous fish (Chondrichthyes)
Subclass : Euselachii
Scientific name
Hay , 1902

The Euselachii are a subclass of the cartilaginous fish (Chondrichthyes), in which the sharks (Selachii) and rays (Batoidea) living today are combined as a subclass plate gill (Elasmobranchii), and the extinct Hybodontiformes and other extinct members of the tribe are united.


All primitive Euselachii are of a shark-like shape, had or have an anal fin and two dorsal fins , each supported by a spine. These features have partly disappeared secondarily in more modern groups, the anal fin in all rays and Squalomorphii , except for the Hexanchiformes , the dorsal fin spines in many Squalomorphii and most Galeomorphii , except in the bull-headed sharks ( Heterodontus ).

The South African shark expert Leonard Compagno gives the following characteristics for the Euselachii:

  1. Placoid scales of the synchronomorial type, i.e. the scales do not grow continuously, but only in the initial phase,
  2. shoulder girdle and coracoid that have grown together through a cartilage rod ,
  3. Mixipterygial cartilage consisting of one or two segments between the elongated metapterygium (axis between the shoulder girdle and the pectoral fin) and the base of the clusters ,
  4. three-base pectoral fins with a reduced metapterygial axis ,
  5. aplesodic pectoral fins, d. i.e., the cartilaginous fin carriers do not extend into the outer fin part,
  6. the hearing center in the neurocranium is small,
  7. an incomplete posterior orbital delimitation ,
  8. ossified vertebral centers,
  9. a non-crescent-shaped caudal fin.

Internal system

Fossil of Acronemus tuberculatus , an ancient Euselachian from the Middle Triassic


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