Otodus megalodon, which lived nearly worldwide roughly 15-3.6 million years ago and reached at least 50 feet (15 meters) in length, has a rich fossil record. Its biology remains poorly understood like most other extinct sharks because the cartilaginous fish is primarily known only from its teeth.
A new study sheds light on the reproductive biology, growth, and life expectancy of Megalodon or megatooth sharks. The study has shown that the megatooth shark gave birth to babies larger than most adult humans.
Kenshu Shimada, a paleobiologist at DePaul University in Chicago and lead author of the study, said, “The study indicates that, from the moment of birth, Megalodon was already a big fish.”
“As one of the largest carnivores that ever existed on Earth, deciphering such growth parameters of O. megalodon is critical to understand the role large carnivores play in the context of the evolution of marine ecosystems.”
Using the CR scanning method, scientists examined incremental ‘growth bands’ putatively recorded annually (analogous to tree rings) in Megalodon vertebral specimen housed in the Royal Belgian Institute of Natural Sciences Brussels.
Measuring around 6 inches (15 centimeters) in diameter, the vertebrae were recently assessed to have come from a person around 30 feet (9 meters) long, dependent on comparisons with vertebrae of modern great white sharks.
CT images reveal the vertebrae to have 46 growth bands, meaning that the 9-meter Megalodon fossil died 46. By back-calculating its body length when each band formed, the research suggests that the shark’s size at birth was about 6.6 feet (2 meters) in length, a result that suggests Megalodon gave live birth to possibly the largest babies in the shark world. These data also indicate that, like all present-day lamniform sharks, embryonic Megalodon grew inside its mother by feeding on unhatched eggs in the womb—a practice known as oophagy, a form of intrauterine cannibalism.
According to the data, the study also shows that the shark grew without significant ‘growth spurts’ at an average rate of about 6.3 inches (16 centimeters) per year, at least during the first 46 years of its life.
Becker said, “Results from this work shed new light on the life history of Megalodon, not only how Megalodon grew, but also how its embryos developed, how it gave birth and how long it could have lived.”
Scientists noted, “Interestingly, ‘early-hatched embryos’ in the shark group called Lamniformes will begin to eat surrounding unhatched eggs, and at least in the present-day sandtiger shark, occasionally even feed on other hatched siblings for nourishment. The outcome is that only a few embryos will survive and develop, but each of them can become considerably large at birth.”
Shimada said, “Although likely energetically costly for the mother to raise such large embryos, newborns have an advantage because their large size reduces chances of being eaten by other predators.”
Michael Griffiths, William Paterson University, New Jersey, said, “The information presented in this new paper and our other recent work demonstrating just how large Megalodon was relative to other sharks have greatly increased the understanding of the Megalodon biology.”
Matthew Bonnan, Stockton University, New Jersey, said, “My students and I examine spiny dogfish shark anatomy in class and to think that a baby Megalodon was nearly twice as long as the largest adult sharks we examine is mind-boggling.”
This finding indicates that Megalodon was sufficiently large (6.6 feet) at birth to compete with other predators and avoid being eaten.
- “Ontogenetic growth pattern of the extinct megatooth shark Otodus megalodon—implications for its reproductive biology, development, and life expectancy,” DOI: 10.1080/08912963.2020.1861608