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Imagine a shark. If you are normal, you most likely thought about a lamniform (mackerel shark) or carcharhiniform (grey) shark (unless you just watched "Finding Nemo 2" I suppose, which has a whale shark).
While it is not essential to identify the differences between these two groups to help fend off a hungry shark or even enjoy their fossils, I find phylogeny/ classifying sharks interesting so I've included it here on this site.
Sharks in these two orders appear extremely similar (and are in many aspects; Individuals in both are streamlined, perfectly adapted relatively intelligent predators with a variety of similar adaptations) but they are separate shark groups that diverged hundreds of millions of years ago (Early or Mid Jurassic). These top of the food chain predators evolved independently from modest sharks and this is apparent through several key differences.
*Specialized predators are more specifically adapted for hunting a specific type of prey (such as adult great white sharks being specialized for hunting seals via broad serrated teeth and being built for speed) and generalist predators are more adapted for hunting a wider range of prey (such as bull sharks having clutching and slicing teeth; and having an unusually wide salinity tolerance. More specialized predators are more prone to extinction).
**Although the Largest Carcharhiniform teeth of all time, those from very large Giant Extinct Snaggletooth Sharks (Hemipristis serra) exceed 2 inches (5 cm).
Additonal Facts:
-About 60 to 80 percent of shark teeth found in most Neogene (Miocene- Pleistocene) deposits belong to Carcharhiniforms (Hulbert 2001), (but I sense among larger (1 inch+) shark teeth the ratio must be more even).
Lamniform vs Carcharhiniform bite wounds: Coming soon!
(see notes in pg. 97 HOL notebook + add fossil forum pic of fossil bite wounds from fossil forum?)
Caudal fins of several shark species. Notice for great whites & porbeagles the upper & lower sections are roughly the same size, to reduce drag in extended high speed pursuits (or likely just moving faster in general? Better migration?). Other species with the much larger upper section are more adapted for speed in short bursts (or mostly "cruising" although tiger sharks do make long migrations)
Interpretting Phylogenetic Trees
Extant Lamniform diversity/ phylogeny
Extant Carcharhiniform Phylogeny
Extant Weasel Shark (Family Hemigaleidae) Phylogeny
Extant Carcharhiniform Phylogeny (Family Carcharhinus expanded)
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