Reconstructing Megalodon

Large fossilized Megalodon teeth are among the most startling of natural objects. They are huge blackish triangles that appear 'puffed up', resembling fresh-baked (fresh-burned?) cookies. The root is bilobed and rough, in stark contrast to the smooth, enamel-like polish of the blade. The blade itself is often cracked longitudinally and the edge has about 50 serrations per inch (20 per centimetre). The heft of a good-sized specimen is remarkable - about three-quarters of a pound (0.4 kilograms). It is hard to think of these massive stones as ever having been teeth. But that's exactly what they were. This undeniable fact has generated much awestruck speculation about what the entire shark must have looked like.

Fossilized teeth are almost all that remains of Megalodon. Therefore, placing some of these teeth in a model of the long-gone cartilaginous jaws is an expedient way to start reconstructing this creature. But how many teeth and how big to make the jaws? Since Megalodon teeth so closely resemble those of the modern white shark in form but are about three times as large, it seemed to early museum curators that a scaled-up model of White Shark jaws would be a reasonable approximation. Despite their huge size, these early reconstructions were not as scary-looking as one might imagine: resembling gigantic, white lips filled with hundreds of blackish fossil teeth. (Fossil shark teeth can be almost any color - black, purple, blue, green, brown, red, pink, orange, yellow, beige, or almost white - depending upon the precise chemistry of the sediment in which they were deposited. Because most commercially-sold megalodon teeth come from Cooper River and other South Carolina deposits rich in dark phosphates, these fossils are almost always dark grey, brown, or black.) But the stand-in jaws did give an impression of the sheer enormity of megalodon. Measuring eleven feet (3.4 metres) tall and nine feet (2.75 metres) across, the reconstructed megalodon jaws suggested a monster shark more than 80 feet (25 metres) in length. Small wonder that, even today, plaster reconstructions of Megalodon jaws are among the most popular paleontological exhibits in museums.

Reconstruction of the jaws and skull of Megalodon, left
based on an extrapolation from the White Shark, right.  
Re-drawn from Gottfried, Compagno, and Bowman 1996
(pp 55-66 In Klimley and Ainley [eds.] Great White Sharks: 
the Biology of
Carcharodon carcharias [Academic Press, San Diego])

How Big was Megalodon?

Comparing the largest known White Shark teeth with those of Megalodon seems a natural way to figure out how large the fossil species was. Ichthyologist John E. Randall was the first to point out that in the White Shark, the largest upper teeth (second anteriors) are about as tall as the jaw that contains them is high. The early Megalodon reconstructions, however, featured jaws about three times too high in proportion to the teeth. Randall also suggested that there is a more-or-less direct linear correlation between a White Shark's tooth enamel height and its total length. When Randall plotted a graph of tooth enamel height for white sharks of known length and the enamel height for the largest-known megalodon teeth, the position of the latter correlated to a total length of about 43 feet (13 metres). How could the museum curators have been so far off in their estimated size of Megalodon? Apparently, the original reconstructions relied on fossil teeth collected from several sites (thus representing several individuals), but they were all about the same size. However, in all extant lamnoids - including the White Shark - posterior teeth (those toward the corners of the jaws) are much smaller than anterior teeth (near the symphysis, or center, of the jaws). As a result of Randall's work, early reconstructions of Megalodon are now known to be at least a third too large.

In 1992, paleontologist John Maisey oversaw the construction of a model set of Megalodon jaws for the Smithsonian Institution. The reconstruction was inspired by the fortuitous discovery of a relatively complete set of fossil Megalodon teeth found in a North Carolina quarry by amateur fossil collector Peter Harmatuk. Starting with these fossilized teeth, Maisey based his interpretation of the jaws that had once contained them on both Randall's estimate of Megalodon's size and his own extensive studies of shark teeth and jaw suspension. Maisey's model Megalodon jaws are about six feet (1.8 metres) across - corresponding to a 40-foot (12-metre) shark - and include more accurate muscle attachment sites, making them look decidedly less lip-like than earlier reconstructions. Maisey's version thus provides us with a smaller (though still awesome) - but more accurate - impression of the Incredible Shrinking Megalodon.

But few things die more reluctantly than a Really Big Fish story. A 1996 paper by paleontologist Michael Gottfried, shark systematist Leonard Compagno, and S. Curtis Bowman of the Hughes-Bowman Design Group casts some doubt on Randall's method for estimating the size of Megalodon. According to Gottfried and his co-workers, White Shark tooth enamel height does not necessarily increase in proportion with the animal's total length. In white sharks longer than about 16 feet (5 metres), tooth size seems to level off at a maximum size independent of further increase in body length. To remedy these shortcomings, Gottfried et al. used new data and several techniques to better estimate the size and weight of megalodon. They came up with a maximum total length of about 52 feet (15.9 metres) and an approximate mass of 48 tons (tonnes). By comparison, the largest known White Shark was about 23.5 feet (7.1 metres) long and had a mass of roughly 2.3 tons (tonnes).

Reconstruction of the skeleton of Megalodon,
based on an extrapolation from the White Shark.
Re-drawn from Gottfried, Compagno, and Bowman 1996
(pp 55-66 In Klimley and Ainley [eds.] Great White Sharks: 
the Biology of
Carcharodon carcharias (Academic Press, San Diego)

In the Flesh

A creature over twice the length of the largest known Great White with teeth more than three times as large suggests a 'monster' shark with disproportionately huge jaws and a stout, over-sized head. Gottfried, Compagno, and Bowman also attempted to reconstruct what Megalodon might have looked like in life. Since the only fossil material definitely assignable to megalodon is a few dozen vertebral centra and several hundred teeth, the authors had to rely heavily on extrapolations from the modern White Shark, which they believe to be its closest living relative. Leonard Compagno has made extensive studies of the jaws, teeth, gill arches, crania, muscles, et cetera, of most species of extant shark, including recent work on the skeletal anatomy of the white shark. Guided by Compagno's formidable expertise, Gottfried and his co-workers reconstructed Megalodon as having a broader and more domed cranium than the White Shark, with a shorter snout, less elevated eye sockets, and with its very robust teeth set in more massive jaws. They also suggested that Megalodon had a greater number of vertebrae and proportionately larger pectoral fins than the White Shark.  If this latest reconstruction is accurate, Megalodon was probably stouter than a scaled-up White Shark would be, with a blunter and wider head and bigger pectoral fins to support all that extra mass up front - sort of a great white on steroids.





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Tiburones,monstruos de tiempos remotos

Desde siempre al tiburon,aparte de calificarsele de insaciable maquina de matar,se ha dicho que es un ser muy primitivo¿Por que?Tal vez por su aspecto ya que todos los tiburones tienen la misma forma corporal(aunque algunos como el tiburon-sierra o los angeles son mas bien planos) y en tiburones fosiles se ha descubierto que tenian esa misma forma.Pero es un claro error llamar a los tiburones actuales seres primitivos o poco evoluciuonados,ya que de hecho,la mayoria evoluciono hace tan solo 20 millones de años.En verdad,la evolucion de los tiburones es una historia muy antigua y fascinante,que nos muestra a autenticos monstruos que no creeriamos que fueran escualos.Asi que voy a contarla.

Los primeros tiburones aparecieron hace 370 millones de años en el periodo conocido como Devonico.De estos,el mas conocido es el cladoselache perteneciente al genero de los cladolontos,media 2 metros de largo y seguramente se alimentaria de peces y cefalopodos.Se han hallado buenos esqueletos de este animal de la zona de los Grandes Lagos de Norteameruica.No parece ser el ancestro de todos los tiburones ya que no presenta todas las caracteristicas presentes en otras familias de tiburones.

A finales del Devonico comenzo la diversificacion de los tiburones y para el Carbonifero habia una gran cantidad de especies.Muchas de ellas resultaban realmente extrañas y raras,y mas de uno pensaria que ni siquiera eran tiburones.Entre ellos destacan criaturas como el Inyopteragyans ,un tiburon con aletas que como los peces voladores podia planear!!!!Tambien estaba el Helicoprion con su extraña mandibula  circular Edestus y sus  mandibulas como tijeras o el Stetacanthus y su horrenda  aleta en forma de yunque.Todas estas formas tuvieron un cruento final en la gran extincion del Permico.

Debido a esa gran extincion muchas especies tuvieron que evolucionar,algunos se aplanaron y evolucionaron hasta convertirse en las celebres rayas.Otros decidieron adentrarse en los rios,como el Orthacunthus,  y otros prefirieronseguir siendo lo que fueron,antiguos depredadores,como el Hybodus.Pero la irrupcion de los reptiles marinos desplazo a los tiburones a un segundo plano.Tras la extincion de estos en la extincion K-T,los tiburones volvieron a ser los grandes depredadores que antaño fueron y evolucionaron hasta dar lugar a las especies actuales.Pese a todo aun quedabangrandes monstruos rondando en los mares.

En el Plioceno,al mismo tiempo que nuestros ancestros comenzaron a andar erguidos,un gigantesco y mosntruoso tiburon acechaba bajo aquellas aguas.Si el tiburon de Jaws os aterrorizo,con este morireis de miedo,se trata de Carcharodon Megalodon,posiblemente una de las bestias mas aterradoras que la evolucion haya dado.Lo unico que queda de el son sus gigantescos  dientes del que se ha tratado de averiguar su longitud.Al principio se penso en una medida de 18-20 m,pero actualmente se habla de un animal de unos 13-14 m.¿Esta criatura como vivia?Comparandolo con el tiburon blanco,los cientificos creen que seria un cazador que acecharia en el fondo a sus presas a las cuales propinaria una terrible mordedura ya las que dejaria desangrarse.Sus presas predilectas serian las ballenas,de hecho,se han hallado fosiles de ballenas con dientes de Megalodon incrustados.Sea como sea,desaparecio a comienzos de la Era Glacial.
Hoy en dia,el tiburon sigue siendo un gran depredador de los mares,pese a la irrrupcion de los mamiferos,aunque se encuentra en peligro por nuestra culpa,que como siempre metemos las narices en todo.Creo que esta magnifica criatura,una de las obras culmen de la evolucion,no merece desaparecer por nuestra avaricia,ya que si han sobrevivido a tantas extinciones,no vale la pena que desaparezcan ahora,por lo menos,de la mano de una especie como la nuestra.