Return a List for a Group Code

I am dealing with a report that has several categories. Within each category are varying numbers of members. Each member belongs to only one category. (see example below). I want to be able to link the list of members to the category(either list all values in a cell or as a dropdown menu). So basically like a vlookup that returns all values that correspond to the lookup value. I have explored excel functions and have not found one that will work for this. Is there a way I can use macros to do this? help please!

** note: the letters are the categories, and the animals are the members. I want to be able to create a list of all 'a' animals, 'b' animals etc.
Category Member
a cat
a bird
d dog
d elephant
e giraffe
b croc
b bat
a ant
b otter
c squirrel
c fish
e frog

Use AutoFilter on the category Column