Mako

Isurus hastalis
("Big-Tooth Mako")

This extinct shark is likely the ancestor of the Great White. It's teeth are very similar, but without serrations. Teeth have been found with very fine serrations, which may represent a "transitional" species. The shark grew somewhat larger than the modern Great White, perhaps up to 30 feet. Fossil teeth are found in many places on both the east and west coasts of the Western Hemisphere (eg. Carolinas, Florida, California, Peru, Chile).

Isurus sp.
("Narrow-Form Mako")

Is it OK for me to say,
"I don't know"?
(info below)

Isurus planus
("Hook-Tooth Mako")

This extinct shark is likely related to the Isurus hastalis (far left). It seems to be a "dead-end" species though, with no living (extant) relatives. It probably grew to around 20 feet. The teeth are commonly found in only one place, the Temblor Formation, near Bakersfield, California. In the past, they were also found in Japan, but real estate development has covered previously accessible sites.

NARROW-FORM Species - Some believe that these teeth are from certain jaw positions in the Isurus hastalis (could be, but they seem different to me). Some believe they are a transitional species between Isurus hastalis and the modern Makos. That "in-between" species could be Isurus retroflexus, Isurus precursor, Isurus desori or something else. Some think they could actually be from the modern Mako species like Isurus oxyrinchus (Short-Fin Mako) or Isurus paucus (Long-Fin Mako). My personal belief is that there is a wide spectrum of variations, from the wide-tooth Isurus hastalis and the narrow-tooth modern Makos. Which ones inter-breeded - who knows? That's the accepted way to differentiate species (not how their teeth look). One thing that can be said for sure is that the narrower-toothed sharks did not grow as large. In places where both types are found, the anterior teeth around 1 to 1 1/2 inches will mostly be the narrower teeth. Teeth around 2 to 2 1/2 inches will mostly be the wider teeth. P.S. - There is also an extra wide tooth that some believe is from another separate species, that is generally called Isurus (Cosmopolitis) xiphodon. For now, we will try to stay above the fray and just call all wide mako teeth Isurus hastalis, though I'm sure that'll be like fingernails on a blackboard for you purists.

GREAT WHITE ANCESTRY - It has long been assumed that the "Big-Tooth Mako" (Isurus hastalis) is the ancestor of the modern Mako. For that reason, it was placed in the genus Isurus, the same as modern Mako species. It is now becoming more accepted that the I. hastalis is also the ancestor of the modern Great White (Carcharodon carcharias). So should it's genus be Isurus or Carcharodon? Eventually, it's genus will change, probably to something unique, such as Cosmopolitodus (used now by some). The informal process in which such things happen can take a long time. The primary reason for the belief that I. hastalis is the Great White ancestor, is that there are "transitional" teeth in the fossil record (found in the same fossil layer as both Big-Tooth Mako and Great White teeth). It currently has no name, other than "transitional" Great White. The teeth have "developing" serrations. Near the root, the serrations look much like the Great White. As you proceed toward the tip though, the serrations become smaller, disappearing completely at the tip. To see examples of this rare type of tooth, go to the Great White section and click "transitionals."