Apex domains cannot have CNAME records.
Question and response
Question
dig ptr.terago.net. NS
Answer
ptr.terago.net. 5 NS ns2.terago.ca.
ptr.terago.net. 5 NS ns1.terago.ca.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0