Animal in popular end of cattle market bought by writer (4,6)

I believe the answer is:

pine marten

I'm a little stuck... Click here to teach me more about this clue!

'animal' is the definition.
(I've seen this before)

'popular end of cattle market bought by writer' is the wordplay.
I cannot really see how this works, but
'popular' could be 'in' and 'in' is found within the answer.
'market' could be 'mart' (synonyms) and 'mart' is found in the answer.
The remaining letters 'peen' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...

'in' is the link.

Can you help me to learn more?

(Other definitions for pine marten that I've seen before include "Animal" , "furry critter" .)

I've seen this clue in The Guardian.

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