Crossword puzzle clue "earth bird only"

Earth-bird only?

___ Saknussemm, discoverer of the center of the earth in "Journey to the Center of the Earth"

Only ape to circle the earth

Only place on Earth where crocodiles and alligators co-exist

"Baseball, it is said, is only a game. True. And the Grand Canyon is only a hole in ___." (George Will)

"I can only ___ much!" ("I'm only one person!")

Letter appearing only in down answers; its opposite appears only in across answers

"My only love sprung from my only __!": Juliet