Mac OS (well, at least older Mac OS) use(s|d) \x0d to represent end of line, so your file probably came from there or hopped through there without proper translation. You could:
- re-fetch the file, this time telling whatever mechanism you're using to treat it as a text file (e.g. FTP in ASCII mode)
- set $/ to \x0D
- use split as you've done
- use the *NIX tr utility to translate the line endings
- use the perl -i -pe equivalent of the above to do the same
Also: see perlport for the section on "Newlines".