So, Just How Big Was Megalodon?

A reconstruction of Megalodon at the Smithsonian

Pretty darn big. A new paper on how to estimate the size of fossil sharks from their teeth:  Body length estimation of Neogene macrophagous lamniform sharks (Carcharodon and Otodus) derived from associated fossil dentitions Victor J. Perez, Ronny M. Leder, and Teddy Badaut

ABSTRACT

The megatooth shark, Otodus megalodon, is widely accepted as the largest macrophagous shark that ever lived; and yet, despite over a century of research, its size is still debated. The great white shark, Carcharodon carcharias, is regarded as the best living ecological analog to the extinct megatooth shark and has been the basis for all body length estimates to date. The most widely accepted and applied method for estimating body size of O. megalodon was based upon a linear relationship between tooth crown height and total body length in C. carcharias. However, when applying this method to an associated dentition of O. megalodon (UF-VP-311000), the estimates for this single individual ranged from 11.4 to 41.1 m. These widely variable estimates showed a distinct pattern, in which anterior teeth resulted in lower estimates than posterior teeth. Consequently, previous paleoecological analyses based on body size estimates of O. megalodon may be subject to misinterpretation. Herein, we describe a novel method based on the summed crown width of associated fossil dentitions, which mitigates the variability associated with different tooth positions. The method assumes direct proportionality between the ratio of summed crown width to body length in ecologically and taxonomically related fossil and modern species. Total body lengths were estimated from 11 individuals, representing five lamniform species: Otodus megalodon, Otodus chubutensis, Carcharodon carcharias, Carcharodon hubbelli, and Carcharodon hastalis. The method was extrapolated for the largest known isolated upper tooth of O. megalodon, resulting in a maximum body length estimate of 20 m.

My Meg from a week ago

Doing the math sloppily (which is about all it's worth) that's a 66 foot meat eating machine. By macrophagous, they mean sharks that eat big things, to exclude filter feeders like Whale and Basking Sharks. By associated, they mean fossils (in this case teeth) found together, and reasonably thought to be from a single individual shark (it may or may not have a skeleton; shark skeletons are cartilaginous and fossilize poorly, although in large sharks, there is calcium in the vertebrae that leave decent fossils.

The largest Meg teeth found are close to (I don't know if any exceed) 7 inches. This means the Meg I found the other day, a lower tooth (and hence smaller than the upper teeth) and 3.5 inches long, probably came from a shark a mere 35  or so feet long.

Dang!

And just for fun. South Carolina fossil hunter's dreams come true with huge megalodon tooth

A dream came true for a South Carolina fossil hunter this week, when he found an enormous megalodon tooth in the Lowcountry.

Matthew Basak was doing some fossil hunting at a construction site in Summerville when he says he found this fossil shark tooth of a lifetime.

Basak, who guides fossil hunts professionally with the team at Palmetto Fossil Excursions, said he noticed what looked like a promising soil layer exposed in a drainage ditch at the construction site.

When he hopped down to take a closer look, Basak says he began probing and found one nice sized tooth before something else caught his eye in the muddy ditch bank.

A few inches below the first tooth was a truly massive megalodon. With 5 inches of tooth showing before he'd even excavated it, Basak knew he'd found something special.

Basak says the monstrous tooth ultimately measured an astounding 6.45 inches, and initially tipped the scales at 3 pounds. Basak was in disbelief. His friends, also experienced fossil hunters, were almost speechless.