A man with all his riches does not live forever; he is like a beast that perishes (another translation: that is slaughtered). The same message in other words is that death comes to beasts as well as men. Death is like darkness. In Psalm 73:22 we read: I was brutish and ignorant; I was like a beast toward you.
Here we have a clear difference between man and beast, namely understanding. The theme of our Psalm says that man and beast share the same fate: they both will die. Ecclesiastes 3:19 reads, For what happens to the children of man and what happens to the beasts is the same; as one dies, so dies the other. They all have the same breath, and man has no advantage over the beasts, for all is vanity.
12 Man in his pomp will not remain; he is like the beasts that perish.