aberrant

adj

1. Differing from the norm.
2. (figuratively, sometimes)Straying from the right way; deviating from morality or truth.
3. Deviating from the ordinary or natural type; exceptional; abnormal.

   “The more aberrant any form is, the greater must have been the number of connecting forms which, on my theory, have been exterminated.”

noun

1. A person or object that deviates from the rest of a group.
2. A group, individual, or structure that deviates from the usual or natural type, especially with an atypical chromosome number.

   “Also I think other birders realise you are struggling a bit when you start talking about aberrants[.]”