Few predators terrorize our imaginations as fiercely as the great white shark. The immense fish is sublimely attuned to an environment that is alien to us, and, despite the rarity of accidents, the nightmare of slipping down the shark’s throat has obscured the fact that we have done far worse things to these apex predators. And, in a culture where bigger is frequently confused with better, the great white’s prehistoric cousin Carcharocles megalodon has gained almost as much fame. A 15-foot-long white shark is imposing enough, but the 50-foot-long version has inspired even more awful novels and blood-soaked b-movies than its living relative.
Today’s Carcharodon carcharias and the extinct Carcharocles megalodon have often been linked together on account of their teeth. With the exception of rare vertebrae, that’s really all we know of the “megashark.” The rest of the shark’s cartilaginous frame has never been found, and may forever remain that way. Still, since the triangular, finely serrated teeth of Carcharocles megalodon roughly resembled the more coarsely serrated teeth of today’s great white sharks, some ichthyologists and paleontologists connected the two together as close relatives – if not actually ancestor and descendant. The great white shark could be a dwarfed version of its massive, whale-crunching forerunner, or a very close cousin.
Not everyone has agreed that the two sharks were close kin, though. In fact, recent analyses have underscored a different scenario that drives a wider gap between the two sharks.
The teeth of modern great white sharks are broadly similar to those of Carcharocles megalodon, but they differ in the specifics. In detail, great white teeth more closely resemble those of broad-toothed mako sharks, of the sort seen in the fossil species Carcharodon (formerly “Cosmopolitodus“) hastalis. Today’s great white sharks are more likely modified broad-tooth makos, with Carcharocles megalodon falling within a separate subgroup in the same shark family (called Lamniformes) that branched from the great white lineage sometime during the Cretaceous.
A paper just published by Monmouth University paleontologist Dana Ehret and colleagues in Palaeontology supports the growing consensus behind the broad-tooth mako link, and does so through the description of a new shark species. Discovered in 1988 within southwestern Peru’s Pisco Formation, the previously unrecognized shark species is represented by an absolutely gorgeous specimen – a beautifully preserved set of fossilized jaws, with teeth still in their original positions, and a short string of articulated vertebrae. Following a previous 2009 study of the fossil, Ehret and colleagues have now named the shark Carcharodon hubbelli in honor of fossil shark expert Gordon Hubbell. The species appears to be an intermediate form between today’s great white sharks and their broad-tooth mako ancestors.
Teeth are the key to the connection. The triangular teeth in Carcharodon hubbelli are not quite as serrated as those of the great white shark, for example, but more so than Carcharodon hastalis. The newly-named species may have also been intermediate between the two in its natural history. Based on aspects of the shark’s teeth and vertebrae, Ehret and coauthors estimate that the shark was about 16 feet long, and annual growth rings on the vertebrae indicate that the animal was about 20 years old when it perished. In comparison with details of modern white sharks, these details indicate that Carcharodon hubbelli grew at a relatively slower pace than its living relative.
While identifying direct ancestors and descendants is extremely difficult, and often impossible, in paleontology, Ehret and collaborators make the case that the three sharks represent a chronospecies – or a single lineage – evolving over time. In this scenario, the smooth-toothed Carcharodon hastalis was the ancestor of Carcharodon hubbelli, which was the progenitor of the great white shark.
The age of Carcharodon hubbelli plays a critical role in this hypothesis. In addition to a detailed review of fossil Carcharodon identifications and relationships, the researchers behind the new study also reexamined the geological age of the marine sediments the newly-named species was found in. Previous studies hypothesized that the jaws were those of a modern great white shark that swam Peru’s prehistoric coast around four million years ago, but the new analysis suggests an older age – about six to eight million years old.
Based on the age and relationships of Carcharodon hubbelli, Ehret and collaborators propose that modern great white sharks evolved in the Pacific Basin. Exactly where the sharks first originated, however, is unclear. The researchers point out that teeth similar to those of Carcharodon hubbelli – and, in fact, now assigned to that species by the authors of the new study – have been found in Asia, Australia, and North and South America in deposits of similar age. Now that the species has a name, paleontologists can examine these fossil clues for greater resolution on great white origins. The study is absolutely clear about one thing, though. The great white shark is not simply a pygmy megatooth, and this makes the appearance and biology of our favorite prehistoric leviathan more enigmatic than ever.
Ehret, D., Hubbell, G., Macfadden, B. 2009. Exceptional preservation of the white shakr Carcharodon (Lamniformes, Lamnidae) from the early Pliocene of Peru. Journal of Vertebrate Paleontology. 29, 1: 1-13
Ehret, D., Macfadden, B., Jones, D., Devries, T., Foster, D., Salas-Gismondi, R. 2012. Origin of the white shark Carcharodon (Lamniformes: Lamnidae) based on recalibration of the Upper Neogene Pisco Formation of PeruOrigin of the white shark Carcharodon (Lamniformes: Lamnidae) based on recalibration of the Upper Neogene Pisco Formation of PeruOrigin of the white shark Carcharodon (Lamniformes: Lamnidae) based on recalibration of the Upper Neogene Pisco Formation of Peru. Palaeontology 55, 6: 1139-1153