Ask a Shark Expert
Read shark researcher Mark Marks' responses on the following shark topics:
Disappearing sharks
Shark evolution
Shark deterrent?
Nonstop swimmers?
Shark posturing
Swimming with the sharks?
Shark diving
Shark education
Shark enemies
Shark reproduction
Great white disposition
Favorite shark
Shark eyes
Shark companions
Bite pressure
Bladderless sharks
Warmblooded killers
Hammerheads
Thresher sharks
Great whites in captivity
Shark protection
Q: On Shark Evolution
Dear Mark,
A few years back, I wrote a college report on the evolution of elasmobranchs. The shark hasn't really changed in millions of years. What would you say is the biggest evolutionary change in sharks? Just curious about what you have to say.
Suzette
Good question. I had to think about this a bit. Keep in mind that when someone says the word shark, they are referring to the generalized shark body plan we all instantly recognize, the large fusiform (bullet-shaped) predator. In fact, elasmobranch fishes (sharks, skates and rays) are one of the most successful and taxonomically adaptive groups of animals ever to inhabit the hydrosphere, evolving successfully for over 400 million years of changing evolutionary pressures. OK, so the Readers' Digest answer to your question (bear with me...) is that the greatest change in elasmobranch evolution is their extraordinary diversity and species radiation over time. At present there are nearly 600 species of shark. The modern cartilaginous fishes may comprise between 900 and 1,100 known species, which include approximately 170 genera and over 50 families. As impressive as these numbers are, stop and remember that the living elasmobranchs swimming around today represent only a small fraction of nature's extensive experimentation in shark body plans, which includes those creatures that once inhabited our primordial seas. For example, take the lineage of the white shark, Carcharodon carcharias. It belongs to the order Lamniformes and the Lamnidae family. There are 7 distinct families within the order Lamniformes, including Lamnidae, of which there are 15 living species. Compare this with the fossil record for the same lamnoid lineage (most are dead!): families = extinct (23 percent), living (77 percent); genera = living (21 percent), extinct (79 percent); and finally, as for species only 4 percent are living, meaning...96 percent of white shark-like species didn't make it! So the evolutionary change is still taking place, provided that we Homo saps don't cause what the great sociobiologist E.O. Wilson calls the third great extinction.
