What is study of Skulls called as ?

Craniology

The answer is Craniology.

Craniology is the study of the skull, especially its shape and size. It is a branch of physical anthropology that uses the skull to infer information about the individual's or population's biology, behavior, and evolution. Craniologists use a variety of methods to study skulls, including measurements, observations, and comparisons.

Carpology is the study of fruits and seeds. Cryptology is the study of codes and ciphers. Haematology is the study of blood.