origin of 'Cipactli'

[McDavitt, Matthew T (CAP, CARD)]

I am an anthropological researcher documenting the cultural importance of sharks and rays in world cultures.  I have a question regarding the origin and meaning of the word
'cipactli'.  While this word is often translated as 'caiman', 'alligator', or 'crocodile', to my knowledge, this term never appears as a general word for crocodilians, but appears
exclusively as a proper name for the aquatic earth-monster.  Seler suggested that perhaps the term derives from 'tzihuactli', a spiny wild plant mentioned in several texts, and
thus, the name Cipactli would connote this creature's ubiquitous spines.

However, similar words appear in neighboring languages, some which conceivably predating the appearance of Nahuatl in the Valley of Mexico (e.g. the aquatic monster 'Sipakna' from
the Quiche Popol Vuh).  I have never encountered another Nahuatl term beginning with the morpheme 'sip'; could this indicate that Cipactli is perhaps a loan word from another
language?  Certainly the iconography of Cipactli is found among other societies which predate the Aztecs (such as the Mixtecs).

Another consideration is that 'cipac' appears to function as a root word,  used to name various finned aquatic animals, much as the word 'coyotl' is used to name conceptually
linked animals such as the 'azca-coyotl' ['ant-coyote', = anteater], 'a-coyotl' ['water-coyote'=sea-lion], etc...  Thus we find 'atli-cipactli'  [waterfall?-cipactli] for whale
(Teogonia e historia de los Mexicanos) and 'a-cipaquitli' [water?-cipac-i?] for the sawfish (Sahagun vol. 2 & 11).   This generic finned animal cannot refer to the quadroped
crocodile; could this term designate the shark, the remains of which are found in abundance entombed beneath the Templo Mayor, an animal linked iconographically to the
earth-monster Cipactli?

As I am not an expert in Nahuatl, I would greatly welcome any comments or insights regarding the origin and interpretation of this enigmatic word .  For a cursory account of  the
iconography and significance of Cipactli, please see:

McDavitt, M.T.  2002.  "Cipactli's sword, Tlaltecuhtli's teeth:  deciphering the sawfish & shark remains in the Aztec Great Temple".  SHARK NEWS 14 (March):  6-7.

Kind regards,

Matthew McDavitt
email:  nokogiri at aol.com