Apex domains cannot have CNAME records.
Question and response
Question
dig 128-255.2.163.85.in-addr.arpa. NS
Answer
128-255.2.163.85.in-addr.arpa. 5 NS ns1.128-255.2.163.85.in-addr.arpa.
Authority
The response has no authority records.
Additional
ns1.128-255.2.163.85.in-addr.arpa. 5 A 85.163.8.159
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0