Apex domains cannot have CNAME records.
Question and response
Question
dig spoerle.com. NS
Answer
spoerle.com. 5 NS pdns77.ultradns.biz.
spoerle.com. 5 NS pdns77.ultradns.org.
spoerle.com. 5 NS pdns77.ultradns.net.
spoerle.com. 5 NS pdns77.ultradns.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0