In the Proto-Circassian there was a series of aspirated consonants that survived in the Shapsug and Bzhedugh dialect while they became plain consonants in the other dialects.
The Proto-Circassian word кӏэкӏьын "to come out from under" became щӏэкӏьын in Kabardian and ӏекӏьын in Abzakh.
The Proto-Circassian word кӏэгъуэжьын "to regret" became щӏэгъуэжын in Kabardian & ӏегъуэжьын Abzakh.
The Proto-Circassian word пакӏэ "mustache" became пащӏэ in both Kabardian & Abzakh.
The Proto-Circassian word кӏалэ "boy; young man" became щӏалэ in Kabardian and ӏалэ in Abzakh.
The Proto-Circassian word кӏымахуэ "winter" became щӏымахуэ in Kabardian and щӏымафэ in Abzakh.
The Proto-Circassian word кӏэ "new" became щӏэ in both Kabardian & Abzakh.
But words like кӏьапсэ "rope", кӏьакуэ "short" & кӏьэ "tail" were still pronounced with kʲʼ.
Later on, in the majority of Circassian dialects (both Adyghe and Kabardian dialects), the velar consonants гь [ɡʲ], кь [kʲ] and кӏь [kʲʼ] became palato-alveolar consonants дж [d͡ʒ], ч [t͡ʃ] and кӏ [t͡ʃʼ] respectively. Now words like кӏапсэ "rope", кӏакуэ "short" & кӏэ "tail" were pronounced with t͡ʃʼ.
For example, in the following table, you can see how the words "new" & "tail" are distinct in all dialects except Bzhedug & Chemgui.
Word
Proto Circassian
Shapsug
Bzhedug Chemgui
Abzakh
Baslaney
Standard Kabardian
Some Kabardian dialects
tail
kʲʼa ⟨кӏьэ⟩
kʲʼa ⟨кӏьэ⟩
t͡ʃʼa ⟨кӏэ⟩
t͡ʃʼa ⟨кӏэ⟩
kʲʼa ⟨кӏьэ⟩
t͡ʃʼa ⟨кӏэ⟩
kʲʼa ⟨кӏьэ⟩
new
t͡ʃʼa ⟨кӏэ⟩
t͡ʃʼa ⟨кӏэ⟩
t͡ʃʼa ⟨кӏэ⟩
ʃʼa ⟨щӏэ⟩
t͡ʃʼa ⟨кӏьэ⟩
ʃʼa ⟨щӏэ⟩
ʃʼa ⟨щӏэ⟩
winter
t͡ʃʼəmaːxʷa ⟨кӏымахуэ⟩
t͡ʃʼəmaːfa ⟨кӏымафэ⟩
t͡ʃʼəmaːfa ⟨кӏымафэ⟩
ʃʼəmaːfa ⟨щӏымафэ⟩
t͡ʃʼəmaːxʷa ⟨кӏымахуэ⟩
ʃʼəmaːxʷa ⟨щӏымахуэ⟩
ʃʼəmaːxʷa ⟨щӏымахуэ⟩
mustache
paːt͡ʃʼa ⟨пакӏэ⟩
paːt͡ʃʼa ⟨пакӏэ⟩
paːt͡ʃʼa ⟨пакӏэ⟩
paːʃʼa ⟨пащӏэ⟩
paːt͡ʃʼa ⟨пакӏэ⟩
paːʃʼa ⟨пащӏэ⟩
paːʃʼa ⟨пащӏэ⟩
The way the affricate postalveolar consonants became fricative in the Abzakh and the Kabardian dialects:
Proto-Circassian had no labiodental fricatives: voiceless labiodental fricative [f] and voiced labiodental fricative [v]. Western Circassian received the labiodental fricatives from one source while Eastern Circassian received from another.
Proto-Circassian had a series of labialized postalveolar consonants (t͡ɕʷ, ʑʷ, ɕʷ and ɕʷʼ). These consonants survived in the western dialects while they became labiodental consonants in the eastern dialects.
STAROSTIN, Sergei A.; NIKOLAYEV, Sergei L. (1994). A North Caucasian Etymological Dictionary: Preface.
Common West Caucasian: The Reconstruction of its Phonological System and Parts of its Lexicon and Morphology. Leiden, The Netherlands : Research School CNWS, 1996; xxvi, 452 p. : ill. ; 24 cm. ISBN9073782732