This article is based on one written by Steven A. Alter for use on his website. It is copyright and may not be used without his permission. See the "Cool Links" page to contact him
The Great White (GW) Shark, Carcharodon carcharias, which is the most feared and most well known shark alive today can reach more than 20 feet long and weigh up to 2.5 tons. The origin of it however has been argued by many and still hasn't shown any signs of agreement from both camps. The enormous Carcharocles Megalodon (Meg), which you will find out about in other chapters, was not a relative of the GW Shark. The Meg died out somewhere between 2-3 million years ago and didn't produce any descendents. Other than the fact that the Meg and GW Shark both had large serrated teeth they have little else in common and there are no "transitional" features in their evolution, i.e. there are not GW or Meg teeth showing characteristics of both in some of the teeth. GW teeth are much thinner than Meg teeth even when they are the same size, GW don't have the enamel band or "bourlette" characteristic of Meg teeth and the serrations of GW teeth are more coarse than those of the Meg. Simply put, these are two distinctly different animals.
So where did the GW evolve ? To find the answer you need to go back around 50-55 million years ago (MYA) when the first of the extinct Mako Sharks came into being. This was a species known as Isurus praecursor which lived during the Eocene and probably early Oligocene epochs. See my Contents page to show a chart with Geological Time Periods. This is the "grandfather" of all the Mako species, both living (extant) and extinct. During the Oligocene epoch, a couple of separate forms of Mako began to take shape. One was Isurus desori which would prove to be a very wide-reaching species and the next step towards the Great White. The Great White lineage got a huge kick in the early Miocene when Isurus hastalis was born out of I. desori. Back then the teeth from this species were not really large and seldom exceeded 2 inches. This species is referred to as the "narrow form" because the teeth are not as wide for their length as later versions of this shark. Throughout the Miocene this species evolved slightly larger sizes.
By the middle Miocene (very roughly about 10-12 MYA), a very strange thing happened with the "narrow form" I. hastalis. In the Atlantic Ocean, (and from the fossil record ONLY the Atlantic Ocean), one group of the narrow form extinct Makos began to evolve very fine serrations along its edge. The name Isurus escheri was coined to name this odd species of finely serrated Makos. Fossil teeth from this species have only been found in Middle Miocene deposits in Europe, and in a couple of extremely rare instances in South Carolina, USA. The rarity along the Atlantic coast of the USA is probably because of a general lack of fossil deposits of this age, most are older or younger. At roughly the same time in the Pacific Ocean another species of extinct Mako was evolving. This species was called Isurus planus and is restricted to the Late Middle Miocene (around 7-10 MYA) fossil deposits from the Pacific Ocean. This species did not survive past the Late Miocene at latest.
Unfortunately natures first experiment with the serrated GW failed and I. escheri died out shortly after it evolved. One of the reasons for the failure of this species may have been the weak serrations weren't efficient enough. Perhaps the main reason was the further evolution of the main branch of "narrow-form" Makos. About the same time as this the narrow-form Makos began to evolve much larger tooth sizes and a much different tooth shape. This is where we get the "broad-form" I.hastalis. During the Late Miocene, the broad-form extinct Mako had teeth which reached a huge 3 1/2 inches in length (25 feet + in length) and were much wider than the previous form. This form appears in fossil deposits almost worldwide, showing how successful the species was. During the Early Pliocene (roughly 4-4.5 MYA), one isolated population of I.hastalis began to evolve weak serrations. This change took place off of the west coast of the Americas and is seen in the fossil record in S. California, Mexico, Peru and Chile. Nowhere else has this evolution been noted despite countless fossil deposits of the same age. Not enough fossil material has been studied to know whether this evolution was occuring throughout the Pacific Ocean.
Nature managed the evolution of serrations a bit differently this time. The smooth edged broad-form extinct Makos slowly began evolving large serrations instead of the extremely fine serrations of I.escheri. Typically these "transitional" teeth, which will be named Carcharodon sp. as there is no scientific name for them, show serrated cutting edges near the root. The serrations would have allowed the GW to go after different fatty prey such as seals and whales (which continue to be the main prey today).This area where the GW evolved was an area extremely rich in seals and whales, previously prey hunted almost exclusively by the larger Megs. The serrations would have allowed the GW to use less energy during feeding. It's much easier to cut meat with a steak knife than a table knife !!
THIS ARTICLE IS CONTINUED IN PART 2. .