The more than 15-meter-long monster sharks that once roamed the world’s oceans were apparently already born as large fish, according to a study: Megalodons gave birth to young animals about two meters tall, according to analysis results of the growth lines of a fossil vortex . The features also suggest that the sea predators could possibly reach an age of up to 100 years. As the researchers explain, the considerable size at birth was probably made possible by the cannibalistic diet of the young in the womb, which is also found in some of today’s viviparous shark species.
Finds of hand-sized teeth and a few vertebrae bear witness to a gigantic shark that swam through the seas of the earth until about three million years ago. The size of the sharp walkers suggest that Megalodon (Otodus megalodon) was more than twice the size of the up to seven meters long great white shark (Carcharodon carcharias). Who the monster shark once chased is clear from bite marks on fossil whale bones: Large marine mammals were apparently on its menu.
Why the probably largest shark of all time died out remains largely unclear. The smaller but more adaptable great white shark may have ousted him. Based on comparisons of the tooth structures, it is assumed that megalodons were probably not a direct ancestor of the great white shark. Like him, however, he also belonged to the family of jack sharks (Lamnidae). A characteristic of this shark family is that none of today’s representatives lay eggs, but rather give birth to comparatively well-developed young animals.
Megalodon vortices with growth lines
Although its existence is well documented by the numerous dental finds, megalodon remains a mysterious predator of the past. Because hardly any other fossil body parts of these cartilaginous fish have been preserved that give more precise information about their anatomy and biology. There is only one exception: A few fossil eddies were found that are attributed to the mega-shark. The researchers led by Kenshu Shimada from DePaul University in Chicago have now devoted an investigation to three megalodon vortices from the collection of the Royal Belgian Institute for Natural Sciences in Brussels. Using CT scan technology, the researchers were able to reveal the lines in the vertebrae, which, similar to tree rings, have formed annually in the animal as it grew.
The vertebrae were found to have 46 growth lines. That means: The animal died at the age of 46. From the diameter of the vertebrae of up to 15 centimeters, comparisons with counterparts of great white sharks show that this megalodon was about nine meters long. The features of the growth lines suggest that the animal had reached this length at an average rate of about 16 centimeters per year. As part of their study, the researchers also developed a growth curve model that allows an assessment of the life expectancy of megalodons. With reference to the maximum size of around 15 meters, the animals reached an age of 88 to 100 years, according to the researchers’ calculations.
Cannibalism in the womb
As they further report, their analysis results also allowed conclusions to be drawn about how big the shark was when it was born: They came to a length of about two meters. The record giants apparently gave birth to the largest shark babies of all time, say the scientists. “It is noteworthy that megalodon babies were already larger than adults of many of today’s shark species,” says co-author Matthew Bonnan Stockton University in Galloway.
It can be assumed that the offspring evidently developed similarly to today’s representatives of the mackerel sharks in the womb: They were fed by a cannibalistic diet called oophagia or intrauterine cannibalism. Embryos that hatch early begin to eat neighboring eggs. At least in today’s sand tiger shark, they even eat other hatched siblings. The result of this strategy is that few embryos survive and develop, but they grow to be significant in size at birth.
Obviously, when the megalodon was reproduced, class was more important than mass: “With this strategy, the bottom line is that more young animals survive if they are already born as highly developed fish, as they are less likely to be eaten by other predators and are more competitive”, explains Shimada. Co-author Michael Griffiths from William Paterson University of New Jersey in Wayne concludes with the study results: “Overall, the information presented in this work has now greatly expanded our understanding of the biology of the megalodon,” emphasizes the scientist.
Source: Taylor & Francis, Articles: Historical Biology, doi: 10.1080 / 08912963.2020.1861608