The tiktaalik fossil, which dates back 375 million years, is considered a transitional fossil because

- "the civil rights movements"

- "following the american civil war and abolition of slavery, the united states entered a period known as reconstruction, during which black americans continued to suffer from disenfranchisement, racial segregation, and economic oppression. beginning in the early 1950's, black americans launched a series of major campaigns of civil resistance, emphasizing the need for nonviolent protests and civil disobedience."

"such as the montgomery bus boycott of 1955-56, a campaign launched by rosa parks against the policy of racial segregation of the public transit system in alabama. “sit-ins” became popular across the american south, particularly in greensboro, north carolina, increase national sentiment."

- "the counterculture movement"

- "counterculture began to develop in the united states following the rise of conformity in american culture during the 1950s. by 1963, youth, particularly those of the white middle class, began rejecting the cultural standards and normality of their parents, opting for progressive attitudes instead. the movement gained momentum as the civil rights movement became increasingly successful and as the u.s. military intervention of vietnam began to take a negative turn."

"hippie counterculture moved further into popular culture following the summer of love in 1967 when thousands of people came together in the haight-ashbury neighborhood of san francisco. along with greenwich village in new york city, haight-ashbury became a hub for the counterculture movement."

the answer to your question is a. the salt plains

in 1811, he led an expedition, known as the george c. sibley expedition, to improve relations with the pawnee and kansa tribes, and also to locate the rumored jefferson's salt mountain