As per a new study investigating the fossilised megalodon teeth, ancient giant predatory sharks used to rear their young ones in nurseries millions of years ago.
Five potential nurseries, dating from 3.6 to 16 million years ago, have been identified by University of Bristol researchers using fossilised teeth of different lengths.
Slow to reproduce, megalodon nurseries likely contributed to the success – and later demise – of this iconic top predator, the authors discovered.
They examined nine areas where megalodon remains have been found, and say five may have been nurseries, because most of the remains found there were from newborn or young juvenile animals.
Raising these ancient baby sharks in this way may have improved survival, but it may also have contributed to the demise of the monster sharks, they say, as a lack of suitable nursery sites could have contributed to their extinction.
Nursery areas are fundamental for the success of many marine species and play a key role in maintaining viable adult populations, the researchers explained.
As part of the study, the international team – from the US and UK – examined the size-class structure of the extinct gigantic shark through these potential nursery sites.
Otodus megalodon is the largest shark to have ever lived, with body length estimates of up to 50–60 feet for the largest adult individuals.
This species inhabited the warm and temperate waters of all major ocean basins, spanning a range of almost 20 million years, from the early Miocene to the Pliocene.
Most of the studies assessing the causes of the global distribution, the evolution of gigantism, and the extinction of these massive sharks, have focused on the impact of climatic factors and or the abundance and migration patterns of potential prey.
They also looked at competition with other large predatory species, the availability of suitable habitats, and the presence of regional body temperature.
However, much less attention has been paid to important aspects of their reproductive biology – including how they raise their young.
Shark nurseries are often located in geographically discrete regions with high productivity – defined by the high abundance of infants.
These nursery areas have been identified in a number of living shark species and it was assumed by scientists that megalodon used them – but no evidence existed.
As part of this new study the team examined nine sites around the world and found megalodon teeth representing sharks of different sizes – including juveniles.
They found this distribution of sizes was similar to those seen from modern sharks.
‘The use of nursery areas is likely to play a key role in the evolutionary history of some shark species,’ explained the researchers.
This is particularly the case when it comes to megalodon, which is thought to have been a slow-growing species with a high age of maturity.
They benefited from a strategy of maximising survival of their young through nurseries is evidence in the growth rings found in fossils.
‘It, therefore, seems plausible that the use of nursery areas could have been essential for O. megalodon, in order to reduce neonate and juvenile mortality,’ the team said.
This would have allowed them to ‘provide maximum recruitment, thus maintaining viable populations on a long-term temporal scale.’
The findings have been published in the journal Biology Letters.