Hippo! No, rhino by Jeff Newman.
The inept zookeeper at the zoo accidentally labels the rhinocerous as a hippo.  The rhino is upset by this and tries to get the visitors to the zoo to fix it.  Unfortunately, all of the adults are happy to read the sign and just assume that it is a hippo.  It isn’t fixed until finally a little boy takes care of it.  Then prepare yourself for the twist at the end.
Newman’s almost wordless book is a joy.  His illustrations are hysterically funny, from the rhino using one of the birds on his back as a dart to the dejected rhino at the end who has finally given up.  Read this one aloud with plenty of gusto as the rhino tends to bellow in words that always rhyme-o.  Definitely worthy of the honor of being the final book in a storytime that will keep antsy children glued to their seats.  This will work for preschoolers and kindergarteners as well as older children who enjoy a good laugh.