CBC Radio’s Quirks & Quarks has a segment about megalodon.  A new paper in the journal Palaeontologia Electronica reveals that may not have been as robust as previously thought.

The extinct shark megalodon was likely the largest predatory shark to ever swim the oceans, but a new reconstruction suggests it was not quite the behemoth we thought it was. Scientists had assumed it was beefy and thick like a modern great white shark, but a new study says the evidence suggests it was a slim, sleek killer. Philip Sternes, a PhD candidate at the University of California, Riverside in the department of evolution, ecology and organismal biology, worked with a team of 26 international scientists on the study featured in Palaeontologia Electronica.

Abstract

The megatooth shark, Otodus megalodon, which likely reached at least 15 m in total length, is an iconic extinct shark represented primarily by its gigantic teeth in the Neogene fossil record. As one of the largest marine carnivores to ever exist, understanding the biology, evolution, and extinction of O. megalodon is important because it had a significant impact on the ecology and evolution of marine ecosystems that shaped the present-day oceans. Some attempts inferring the body form of O. megalodon have been carried out, but they are all speculative due to the lack of any complete skeleton. Here we highlight the fact that the previous total body length estimated from vertebral diameters of the extant white shark (Carcharodon carcharias) for an O. megalodon individual represented by an incomplete vertebral column is much shorter than the sum of anteroposterior lengths of those fossil vertebrae. This factual evidence indicates that O. megalodon had an elongated body relative to the body of the modern white shark. Although its exact body form remains unknown, this proposition represents the most parsimonious empirical evidence, which is a significant step towards deciphering the body form of O. megalodon.