Dodo. It was hunted to extinction for food. I'm not sure if it tasted good, or if it was the only thing available easily. Unfortunately, they were forced into extinction so quickly that none could be protected in the wild, or brought to a farm or zoo.
There are conflicting reports on what Dodo tasted like. StJohn is our resident expert on the topic. If you've not already done so, I recommend reading Dodo a la Orange -great read. b_b
I remember writing this article in February 2012. Two months later a new movie came out called The Pirates! Band of Misfits in which Queen Victoria goes around eating all the rarest animals she can kill (and Charles Darwin has to stop her — great movie!) But to my amazement they cracked the exact same joke about "Dodo à l'orange" that I did. You can imagine me sputtering with delight and indignation in the cinema. But about the elephants, I've read that the number of tusk-less elephants has been steadily climbing over the 20th century. They're apparently evolving quite rapidly to survive the ivory trade. Science is neat.