Animals that are one sort sing early (9)

I believe the answer is:

yearlings

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'animals that' is the definition.
'yearlings' can be an answer for 'animals' (yearling is a kind of animal). I'm unsure of the remainder of the definition.

'one sort sing early' is the wordplay.
'one sort' indicates an anagram.
'sing'+'early'='singearly'
'singearly' is an anagram of 'YEARLINGS'.

'are' is the link.

Can you help me to learn more?

(Other definitions for yearlings that I've seen before include "Young horses" , "Racehorses in their second year" , "young runners" .)

I've seen this clue in The Independent.

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