Apex domains cannot have CNAME records.
Question and response
Question
dig 201.188.199.in-addr.arpa. NS
Answer
201.188.199.in-addr.arpa. 5 NS ptrdns4.registrar-servers.com.
201.188.199.in-addr.arpa. 5 NS ptrdns3.registrar-servers.com.
201.188.199.in-addr.arpa. 5 NS ptrdns1.registrar-servers.com.
201.188.199.in-addr.arpa. 5 NS ptrdns2.registrar-servers.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0