Question

The term fish is used for any any swimming vertebrate with fins. It includes a diverse group of animals, divided into four taxonomic classes, Agnatha, Chondrichthyes, Osteichthyes, and Placoderma. Taxonomists first divided all "fish" into two classes, Agnatha and Placoderma. The Placoderma are considered ancestors of all other fish. What fossil evidence helped taxonomists separate all "fish" into these two branches for classification? A) jaw or jawless B) ray fins or lobed fins C) skeleton or no skeleton D) cartilage versus bony skeleton

Answer 1

A) jaw or jawless

is your answer :)

Hope this helped!

Answer 2

Answer:

A. Jaw or Jawless

Explanation:

Class Agnatha

Jawless fishes (90 species)

Primitive structures

Oldest known vertebrate fossil (anatolepis)

Upper Cambrian-present

Living forms collectively called cyclostomes

Extinct forms collectively called ostracoderms

Class Placodermi

No extant forms

from here on out (including placodermi) everything is jawed

paired fins present

Most retain bony armor of ostracoderms

Some were quite large (27'), mostly marine types include predaceous forms, bottom dwellers, mollusk crushers, some dorsoventrally flattened

- once considered as ancestral to all higher vertebrates, however exclusion of incorrectly identified forms (bony fishes) indicates that placoderms may have given rise to Class Chondrichthyes