Hi TIm:

We will use a combination of COUNIF() in a helper column and Autofiltering:

Say our data (in Cols A&B) is:

size    type
large    dog
medium    dog
small    dog
large    cat
medium    cat
small    cat
large    bird
medium    bird
small    bird
large    fish
medium    fish
small    fish
tiny           ant

in C2 enter:
=COUNTIF($A$2:A2,A2) and copy down column C, resulting in:

size    type    helper
large    dog    1
medium    dog    1
small    dog    1
large    cat    2
medium    cat    2
small    cat    2
large    bird    3
medium    bird    3
small    bird    3
large    fish    4
medium    fish    4
small    fish    4
tiny    ant    1

Then turn on autofilter and pick 1 for column C