It has long been thought that lizards evolves from a group of amphibians called anthracosaurs, no fossils of which have been found in any rocks older than 300 million years. However, a fossil of a lizard was recently found that is estimated to be 340 million years old. Lizards could not have evolved from creatures that did not exist until after the first lizards. Therefore, lizards did not have evolved from anthracosaurs.
An assumption made in the argument is that there are no
(A) unknown anthracosaur fossils older than 340 million years (The best option)
The premise is Lizards could not have evolved from creatures that did not exist until after the first lizards and the conclusion is lizards did not have evolved from anthracosaurs so the assumption is anthracosaurs did not exist until 340 million years as the lizard was found estimated around 340 million years.
(B) unknown lizard fossils older than 340 million years: ( incorrect)
The option is about only the premise though assumption is a link between premise and conclusion hence it should discuss the relation between anthracosaurs and lizards.
(C) known lizard fossils that predate some anthracosaur fossils (incorrect)
Rejecting the conclusion that says lizards did not have evolved from anthracosaurs.
(D) known anthracosaur fossils that predate some lizard fossils (incorrect)
Out of scope as an argument is about the relation of lizards with anthracosaurs instead of anthracosaurs relation with lizard
(E) known lizard fossils whose age is uncertain (incorrect)
Extra assumption based on no evidence