This is an upcoming movie adaptation of a children's book by Tatsuya Miyanishi about a Tyrannosaurus that adopts a baby Ankylosaurus, who mistakes "Omae Umasou dana" (you look delicious) for its name.
Release Date: October 16
Official website: http://www.umasoudana.com/
Song: "Kimi to Iru Jikan no Naka de" by Ayaka Hirahara
This instantly reminded me of "Land Before Time"