Apex domains cannot have CNAME records.
Question and response
Question
dig ultradns.COM. NS
Answer
ultradns.com. 4 NS pdns196.ultradns.com.
ultradns.com. 4 NS pdns196.ultradns.co.uk.
ultradns.com. 4 NS ns61.ultradns2.com.
ultradns.com. 4 NS pdns196.ultradns.info.
ultradns.com. 4 NS ns61.ultradns2.org.
ultradns.com. 4 NS pdns196.ultradns.biz.
ultradns.com. 4 NS pdns196.ultradns.org.
ultradns.com. 4 NS pdns196.ultradns.net.
Authority
The response has no authority records.
Additional
ns61.ultradns2.com. 4 A 204.74.104.61
ns61.ultradns2.org. 4 A 204.74.106.61
pdns196.ultradns.co.uk. 4 A 156.154.69.196
pdns196.ultradns.biz. 5 A 156.154.66.196
pdns196.ultradns.com. 4 A 156.154.64.196
ns61.ultradns2.com. 4 AAAA 2610:a1:313d:0:0:0:0:53
ns61.ultradns2.org. 4 AAAA 2610:a1:323d:0:0:0:0:53
pdns196.ultradns.co.uk. 4 AAAA 2610:a1:1017:0:0:0:0:e8
pdns196.ultradns.biz. 5 AAAA 2610:a1:1015:0:0:0:0:e8
pdns196.ultradns.com. 4 AAAA 2001:502:f3ff:0:0:0:0:e8
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0