El mamífero marino es muy peludo, lo que es normal.
The marine mammal is very furry, which is normal.
Breakdown of El mamífero marino es muy peludo, lo que es normal.
ser
to be
muy
very
que
that / than
lo
the ... thing (neuter article)
Questions & Answers about El mamífero marino es muy peludo, lo que es normal.
Why can we say muy peludo but we cannot say muy marino?
This highlights the core difference between qualifying and relational adjectives. peludo is a qualifying adjective, meaning it describes a trait that can exist in degrees (very furry, slightly furry). marino is a relational adjective that simply puts the mammal into a strict category (it either belongs to the sea or it does not). You cannot use degree modifiers like muy with relational adjectives.
Could I change the word order to El marino mamífero for a poetic effect?
No. While qualifying adjectives can sometimes be placed before the noun for emphasis, subjective opinion, or poetry, relational adjectives like marino strictly belong after the noun. Their job is to classify the noun objectively, so their syntactic position is fixed.
Why do we need lo que instead of just que for "which"?
Would it be wrong to say lo que está normal since it describes the condition of the animal?