|Carbon to this day|
|353.8 to 0 million years|
|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:
- Placoid scales of the synchronomorial type, i.e. the scales do not grow continuously, but only in the initial phase,
- shoulder girdle and coracoid that have grown together through a cartilage rod ,
- 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 ,
- three-base pectoral fins with a reduced metapterygial axis ,
- aplesodic pectoral fins, d. i.e., the cartilaginous fin carriers do not extend into the outer fin part,
- the hearing center in the neurocranium is small,
- an incomplete posterior orbital delimitation ,
- ossified vertebral centers,
- a non-crescent-shaped caudal fin.
- Joseph S. Nelson , Terry C. Grande, Mark VH Wilson: Fishes of the World. John Wiley & Sons, 2016, ISBN 978-1118342336 .