Question

Which of the following are extinct classes of fishes?
A) Pterichthys
B) Coccosteus
C) Acanthodii
D) All of the above.

Answer 1

Hint: Fishes are aquatic vertebrates. First of the fishes appeared in the Cambrian period and they continued to evolve and diversify through the Paleozoic period. The primitive fishes were jawless and armored. However, many of the primitive fishes are extinct.

Complete answer:
Option (A) Pterichthys belong to class Placodermi. They were armoured fishes. Bony armors were present on the head and anterior parts of the body but not on the tails. They had wing-like appendages on their bodies which are analogous to pectoral fins of present day fishes. Fossil studies indicate that Pterichthys were bottom dwellers and possibly thrived on decaying detritus.
Option (B) Coccosteus are a class of extinct placoderm fishes. Fossil studies indicate that Coccosteus were present primarily in freshwaters of Europe and North America. The fossil studies have also shown that these fishes had a wide mouth that enabled them to swallow large sized prey. Coccosteus also had bony dental plates in their jaws that formed a beak- like structure.
Option (C) Acanthodii are a class of extinct paraphyletic fishes. They are also known as spiny sharks. Though they resemble the modern day sharks, the Acanthodians had little scales all over their body. Fossil studies have shown that the Acanthodii originated in the Silurian period. The endoskeleton of these fishes was cartilaginous, but they had bony scales covering their gills which are thought to be analogous to the operculum of the present day fishes.

Option (D) is correct. Pterichthys, Coccosteus, Acanthodii are all extinct fishes.

Note: Fishes are aquatic animals. They are limbless and soft-bodies. The fishes may have cartilaginous or bony endoskeleton. They locomote by means of fins. Earliest known fishes lacked jaws and had bony armors covering their body. Some had wing-like appendages and movable heads. The fishes evolved and diversified through millions of years that resulted in the appearance of the modern day fishes. Primitive fishes are extinct.