... the pair of fish fins ... is a rebus sign: the fish is a shark, xoc in Maya (Tom Jones has recently proved that xoc is the origin of the English word "shark"). And xoc also means "to count" in Maya. (p. 141)The idea that the word shark was as recent as post-Columbus was a bit shocking to me, and it was irksome that Coe didn't footnote the source for Jones's proof.
I checked the American Heritage, 3rd Edition, which lists the etymology as "origin unknown," and the Shorter OED, which is equally unsure of the origin. The Shorter OED does suggest, however, that it may come from the German word Schurke (worthless person). While that would fit the shark in loan shark, that sort of usage postdates the first for the fish shark by a few decades.
Take Our Word for It takes on the shark/xoc connection in this entry, saying that "shark's etymology simply is not known with certainty." That said, however, the word does seem to have come into English following Sir John Hawkins's expedition to the Caribbean in 1586, putting Hawkins (whose ships were attacked by the Spanish off the coast of Veracruz) in the right place and time to have picked up the word xoc/shark from some Mayan language or dialect.
So assuming xoc is the source word for shark, what were cartilaginous fish (with lots of sharp, pointy teeth) called?
From what I can gather online, there may have been specific names for specific sharks but no generic name, or maybe they were called sea dogs or sea wolves or something similar. (At least one term for shark in both Croatian and Serbian, morski pas, literally means "sea dog," as does the Maltese kelb il-baħar; the Corsican pesciucane is similar, meaning "fish dog.")
Casting about into other languages doesn't help much either. I can't find any definitive etymologies for any of these, but there do seem to be some connections within various languages.
In northern and central Europe, some descendant of the Old Norse hār seems to dominate: haai (Afrikaans), haj (Danish), haai (Dutch), hai (Estonia), háv (Faroese), hai (Finnish), hai (Frissian), Hai or Haifisch (German), hákarl (Icelandic), haizivs (Latvian), hai (Norwegian), haj (Swedish), and הײַפֿיש (Yiddish). [I probably have the Hebrew characters wrong for the Yiddish heifish.]
Romance tongues are more all over the place, but with some spread into other languages: tiburoi (Basque†), tauró (Catalan), tiburón (Galician), tubarão (Portuguese), tiburón (Spanish), and tubaraun (Tetum†); requin (French), rèkin (Haitian Creole), rekin (Polish), and rechin (Romanian); cagnaccia (Corsican); quenlla (Galician); squalo (Italian); squalus (Latin) and canísca (Sardinian).
A few languages, however, seem to base their word on "shark" (or maybe xoc): shark (English), ŝarkó (Esperanto), shaa'k (Gullah), siorc (Irish), sherk (Scots), sak (Tok Pisin), jak (Volapük), and siarc (Welsh).
And just to round out the list of other words and languages (with the caveat that some of these may refer to specific species/types of sharks): peshkaqën (Albanian), القرش (Arabic), marraxo (Basque), 鲨鱼 (Chinese), žralok (Czech), qiō (Fijian), ზვიგენი (Georgian), καρχαρίας (Greek), manō (Hawaiian), כדיש (Hebrew), cápa (Hungarian), ikan hiu or cucu (Bahasa Indonesian), 鮫 (Japanese), NORG (Klingon), 샤크 (Korean), ikan yu (Bahasa Melayu), mango (Māori), əwḫáym (Mehri), ᐃᖃᓗᔾᔪᐊᖅ (North Baffin Inuktitut), акула (Russian), sutsxlá (Sahaptin), k'wet'thenéchte (Salish), hacat (Seri), žralok (Slovak), léḥem (Soqotri), papa (Swahili), ma'o (Tahitian), köpek baliği (Turkish), oboodede (Twi), cá mập (Vietnamese), ekurá (Yoruba), and imfingo (Zulu).
UPDATE: Digging around, I recently found reconstructions for the word shark in a handful of proto languages: *(s)kʷálos (Proto-Indo-European); *cot-ac- (Proto-Dravidian), *maŋo (Proto-Polynesian), and *laḫm- (Proto-Semetic).
* Since the baby seems to like to stop kicking as soon as I get anywhere near, one of Evelin's friends suggested I read a story aloud each night to get the baby used to my voice or something. Instead of picking a kid's book, I decided to go with what I was already reading. Evelin said the baby stayed pretty still for most of the time I was reading; I don't know if there was listening going on, or if the baby was just embarrassed by my bad pronunciation of the Russian, French, Spanish, and Mayan names/words.
†Yes, Basque is not a Romance language, but tiburoi looks to a loan from the Spanish tiburón or similar. The same for Tetum tubaraun.