The most common and most likely answer to this crossword clue is the 3 plus 4 plus 7 letter word PIT BULL TERRIER
I've seen this crossword clue in The Guardian
P
I
T
B
U
L
L
T
E
R
R
I
E
R
More clues leading to the result PIT BULL TERRIER
Buddy explains!

The straight part
We know that "Dangerous creature" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dangerous creature = pit bull terrier.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.