About This Item
- Full TextFull Text(subscription required)
- Pay-Per-View PurchasePay-Per-View
Purchase Options Explain
Share This Item
Fishes and the Permian-Triassic Boundary
The fishes of the latest Permian are represented by two or three families of sharks, one of ratflshes (holocephalans), one each of coelacanths and lung-fishes and eight families of palaeonisciforms. There is also an occurrence in the Ochoan of one semionotid holostean genus, which is closely related to certain Triassic genera. All of these families continued into the Triassic.
During the Early Triassic (Griesbachian) two new palaeonisciform families appeared, neither of which shows evident relationship to Permian families. In addition, five distinctive families of more advanced actinopterygians, popularly called subholosteans (because they are in various ways intermediate between the palaeonisciforms and holosteans), entered the scene along with one new family of lungflshes (Ceratodontidae). The hybodontid sharks and the coelacanths became more diversified in terms of new genera than they were in the Late Permian.
In assessing the meaning of these data in terms of the Permian-Triassic boundary, it is important to note that the Late Permian fish record is poorer in terms of known localities and assemblages than the Early Triassic one. It is also significant that no satisfactory lineages have been worked out for any of the Permian and Triassic genera. In spite of these limitations, the available facts suggest that the Permian-Triassic boundary has little significance for the fishes in relation to major extinctions or origination bursts. Unless there is an unrecorded time interval related to the boundary (rates of evolution for the pertinent families cannot be realistically estimated), it is reasonable to conclude that all of the families first known in the Early Triassic extended back into the Permian. This is true for the Semionotidae and it is the most reasonable explanation for the Triassic palaeonisciform and subholostean families.
Pay-Per-View Purchase Options
The article is available through a document delivery service. Explain these Purchase Options.
|Protected Document: $10|
|Internal PDF Document: $14|
|Open PDF Document: $24|