Apex domains cannot have CNAME records.
Question and response
Question
dig fe.pardot.com. NS
Answer
fe.pardot.com. 4 NS ns-993.awsdns-60.net.
fe.pardot.com. 4 NS ns-1825.awsdns-36.co.uk.
fe.pardot.com. 4 NS ns-115.awsdns-14.com.
fe.pardot.com. 4 NS ns-1270.awsdns-30.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0