In paleontology, pertaining to the vanguard of a migrating fossil fauna which gradually invades a new province, but is replaced after its first appearance by the previous tenant.

Having the character of a proem; introductory; prefatory; preliminary.

adjective. Introductory; prefatory; preliminary.

adjective. Of or pertaining to a proem or proemium.

"The epick writers have found the proemial part of the poem such an addition to their undertaking, that they have almost unanimously adopted the first lines of Homer, and the reader needs only be informed of the subject, to know in what manner the poem will begin."

introductory  prefatory  preliminary