Cretaceous — Robert Appleton

No matter how hard you try, no matter how far you look, you will never find this shop.

It will find you.
 
Dreams, desires, the most outlandish wishes: all are for sale at Esther May Morrow's timeless antiques and sundries store, for the bargain price of...well, that would be telling. You'll have to see for yourself. So come on in. Don't be shy. Make her an offer. She never refuses anyone.

There's just one thing I should mention: each purchase comes with an absolute guarantee--no one who leaves her shop will be ever the same again.

CRETACEOUS (A Short Story):

An old man purchases an elixir to save his dying dog. But their next walk together takes them a little farther than usual ... into the time of the dinosaurs!

5,300 words
 
Other stories from The Little Shop of Wonders* include: Gin Rummy, Lot 62, Spellbound, The Conscripted Man, Miss Olivia, Phenomenal, Happy Meal, and The Temporal Man
 
*Available separately or in The Complete Anthology