Megalodon Likely Gave Birth To Live Young That Were Already Almost 4 Meters Long

Megalodon pose a curious challenge to scientists because despite being one of the largest animals ever to grace the oceans, we don’t often find much beyond their teeth in the fossil record. We have, however, found vertebrae and scales, and can use sharks that are alive today to answer questions about long-extinct species.

Megalodon size and body shape

A team of 29 shark, fossil, and vertebrate experts led by Kenshu Shimada, a paleobiology professor at DePaul University in Chicago, set out to do just that for the warm-blooded “megatooth shark” Otodus megalodon. Armed with a near-complete Megalodon vertebral column from Belgium, they filled in the missing pieces by looking at the proportions of 145 modern and 20 extinct sharks.

If Megalodon followed the trends of the vast majority of sharks, then when this vertebral column still had a head and tail, the animal would’ve been 16.4 meters (54 feet) long. This shark likely wasn’t done growing just yet, however, and if we scale up that size to the largest Megalodon vertebrae found in Denmark, we get a shark that’s a whopping 24.3 meters (80 feet) long.

Their analysis also supports an idea that’s been emerging over the years that Megalodon didn’t have a chunky body like that of a great white, instead having a longer and more slender body shape, like a lemon shark. This may have actually been crucial to their gigantism as when we look at other ocean giants like the whale shark and basking shark, they also have longer, more slender bodies.

Don’t be fooled, however – a slender body type doesn’t take away from Megalodon’s predatory prowess.

“There are multiple examples of marine mammal bones with putative Megalodon bite marks in the fossil record,” Shimada told IFLScience. “So, we know that Megalodon at least fed on animals such as whales and pinnipeds, and that fact does not change.”

It’s probably no coincidence that this body type is more hydrodynamically efficient than the stocky bodies of great whites, who can’t achieve gigantism with a maximum length of 7 meters (23 feet). In discovering this, the team thinks they may have unexpectedly unlocked the mystery as to why some aquatic vertebrates can grow to enormous sizes while others don’t.

Our new study suggests that Megalodon newborns were possibly already 3.6–3.9 meters in length.

Prof Kenshu Shimada

Megalodon gave birth to live young

Another key takeaway from the study – and one that this writer found the most mind-bending – is that it suggests that Megalodon were probably already reaching lengths of 3.6–3.9 meters (12–13 feet) in length when they were born. Megalodon likely birthed live young that grew so big through oophagy, which is a kind of intrauterine cannibalism where developing young effectively snack on their siblings.

“Building on one of my previous analyses, our new study suggests that Megalodon newborns were possibly already 3.6–3.9 meters (12–13 feet) in length,” said Shimada to IFLScience. “The large neonatal size suggests that Megalodon gave live birth, and like all present-day lamniform sharks (a shark group Megalodon belongs), embryonic Megalodon likely grew inside its mother by feeding on unhatched eggs in the womb. Furthermore, the neonates were large enough likely to be able to already feed on marine mammals and to avoid being eaten by other predators.”

Their babies might have been big, but they weren’t out of danger, and Shimada’s team recognized a curious similarity between the size at which Megalodon’s growth spurt petered out and the maximum size of great whites.

Why did Megalodon go extinct?

We don’t yet know for certain why Megalodon went extinct, and while it was likely a combination of factors rather than one defining moment, it’s possible that the emergence of great whites may have played a pivotal part.

The great white shark could have at least in part contributed to the demise of the much larger, less maneuverable Megalodon through competitive exclusion.

Prof Kenshu Shimada

“In our new growth pattern analysis based on a vertebral specimen of Megalodon, we took notice of the slight reduction in the growth rate when the shark was about 7 or 8 years old and approximately 6.5 meters (21 feet) in length,” explained Shimada. “The length of 6.5 meters is intriguing because it corresponds well with the maximum possible size of the great white shark.”

“So, our team postulated that Megalodon grew faster when young in order to possibly ‘outgrow’ the largest great white shark quickly to be able to complete better.  The likely competition between the great white shark lineage and Megalodon has been previously noted and our data nicely fit to the inferred competition scenario.”

“The great white shark lineage eventually evolved serrated teeth as we see in the modern-day, suggesting that it became even more efficient in consuming marine mammals, where we suspect the smaller, hence likely more agile, great white shark could have at least in part contributed to the demise of the much larger, less maneuverable Megalodon through competitive exclusion.”

Great whites may seem a little scary, but perhaps we should be thanking them now that we don’t have to contend with something three times bigger.

The study is published in the journal Palaeontologia Electronica.