Conversation so far:
what is the animal style of migration period art?
He classified animal art of the period roughly from 400 to 900 into three phases: Styles I, II and III.
what animal is mentoned in the articlle?
two bears.
after bear what else?
they tend to be described as serpents, although the heads often have characteristics of other types of animal.
how many style was classsified?
about 700 localised styles develop.

Question: what happened in 1904?
Self-contained rewrite: What happened in 1904 with Migration Period art?