REX 恐竜 物語 (REX Kyōryū Monogatari, REX: A Dinosaur Story) This story seems to be the one never written by CLAMP, since it was written by Ken Hamatsa. It was drawn by CLAMP and serialized in the shojo magazine of the editorial Kadokawa Shoten: Asuka, in 1993, it was compiled into one single volume under Asuka Comics DX.
Plot
This story is the adaptation of a children's movie which appeared the summer of 1993, its script was written by Masanori Hata. This sweet story shows Chie, a girl with wonderful parents: her father is an archaeologist and she lives with her in Hokkaido, her mother is a great scientist who works in the United States. During a local excavation, Chie and her father discover tyrannosaur eggs, and one of them is about to be born! The little girl will do anything to protect Rex (the newborn dinosaur) from those who wish to experiment with him.