Ragged-Tooth Sharks — 2 species
- gill slits fairly large (not extending onto the dorsal surface of the head), all 5 pairs in front of the pectoral fin origin
- eyes relatively small
- tail stalk thick, without lateral keels
- upper precaudal pit present, but no corresponding lower pit
- anal fin broad-based, non-pivoting
- caudal fin asymmetrical, with a relatively short lower lobe
- snout conical, relatively long (length greater than mouth width)
- 2 rows of large anterior teeth
- second dorsal fin noticeably smaller than the first, originating closer to the pelvic fin bases than to the pectoral fin bases
- spottily distributed in the eastern and western Atlantic (northern Gulf of Mexico and southern Brazil), central and western Pacific, and Indian (off Madagascar and eastern South Africa) oceans
The ragged-tooth shark genus Odontaspis was, until recently, a hopelessly confused slush-pile of similar-looking sharks. From disparate corners of the globe — including Argentina, Australia, China, India, Japan, Madeira, South Africa, New Zealand, and both coasts of the United States — came descriptions of unsettlingly similar snaggle-toothed sharks that differed only in minor details. In each of these locations, the shark was assumed to be a different species and given its own scientific name. Yet for a researcher attempting to identify a specimen of one of these look-alike sharks, the most reliable way to affix a species name to it was not to examine the specimen itself, but to look at the museum tag indicating where it was caught. The situation was, as artist-author Richard Ellis once put it, "enough to make the most intrepid researcher throw up his hands."
Chaos reigned until Leonard Compagno examined museum specimens from all over the world, corrected misidentifications and sorted out synonyms. When the taxonomic dust settled, only two species of Odontaspis were left standing: the Bumpytail Ragged-Tooth Shark (O. ferox) and the Bigeye Ragged-Tooth Shark (O. noronhai). Thanks to Compagno's efforts, the Odontaspis slush-pile was at long last reduced and organized, simplifying matters enormously.
The odontaspidid lineage extends back at least 83 to 74 million years, represented in the fossil record by mineralized teeth of a species known as Odontaspis aculeata. Naylor et al.'s (1997) comparative study of mtDNA sequences of lamnoids suggests that the odontaspidids share a closer common ancestor with the distinctively small-toothed, whip-tailed thresher sharks (family Alopiidae) than they do with the more similar-appearing Sandtiger Shark (Carchariidae). This suggests that the Sandtiger-like form has evolved more than once in lamniform sharks, adding credence to the heretical notion that the extinct giant-toothed shark, Carcharocles megalodon — long presumed to be very similar in form to the modern White Shark (Carcharodon carcharias) — may have resembled a stout-toothed Sandtiger.