Sometimes I think about the occasional stone deer head effigy and the idea that perhaps branches were once added to to these stones to represent the missing horns. Pete's post about the Another Uktena? without the horns made me wonder about branches (actual horns often get chewed up by animals). So I looked back at the links mentioned and found:
"Horned Serpent Petroglyph"
"Tim McSweeney sent me this link, to Kevin Callahan's Minnesota petroglyph web page:
http://www.tcinternet.net/users/cbailey/RA.html." I went to it, found it was working, and with the turtle mention, was surprised to find this further down the page:
"Turtles were both spirit beings and totems and sometimes had horns. The turtle was a symbol of the mother earth seen as a womb and was a symbol of fertility. In mythology the turtle, especially the snapping turtle, was associated with being a great warrior and was a frequent motif on warrior shields and war drums."
There's an interesting article at: http://en.wikipedia.org/wiki/Horned_Serpent, with these other names:
Misi-kinepikw ("great snake") - Cree
Msi-kinepikwa ("great snake") - Shawnee
Misi-ginebig ("great snake") - Oji-Cree
Mishi-ginebig ("great snake") - Ojibwe
Pita-skog ("great snake") - Abenaki
Sinti lapitta - Choctaw
Unktehi or Unktehila - Dakota
And then there's Wiki's link to: http://www.sacred-texts.com/nam/cher/motc/motc050.htm, "The Uktena And The Ulûñsû'tï," the latter "...a bright, blazing crest like a diamond upon its forehead..."
Plus some photos at: Turtle petroforms/petroglyphs over at my blog...