While this won't work for everyone, you can sort your Pokemon by most recently caught in your Pokemon list. As long as you have enough Pokemon to recall who was second or third caught, you can use this filter to see the most recent at top, and the Starter on the bottom.
To access the filter, while looking at your list of Pokemon (Menu/Ball -> Pokemon) there's going to be a button on the bottom right of the screen. This button will have a symbol inside based on the type of filter shown.
Just press it once to get a complete list of filters and click on the "Recent" filter to have your list show them in order caught.