“Baby Shark” has taken on a whole new meaning. A new study suggests that newborn megalodon sharks were larger in size than most adult humans.
An analysis of the growth rates of ancient oceanic predators, which lived between 23 million and 2.5 million years ago, estimates that sharks began life about 2 meters long, according to researchers on Jan. 11 in Historical Biology.
Otodus megalodon is right up there with Tyrannosaurus rex in the pantheon of fearless extinct predators, but little is actually known about shark biology (SN: 8/10/18). Its skeleton was made of hard-to-fossilize cartilage, so what scientists know comes mostly from fossilized teeth. For example, paleobiologist Kenshu Shimada of DePaul University in Chicago and colleagues previously used megalodon teeth, as well as those of other ancient and modern sharks, to estimate a total adult body length of fish of at least 14 meters (SN: 10/5 / 20).
In the new study, Shimada and colleagues had extra, rare evidence: megalodonic vertebrae. Although shark skeletons are made of cartilage, the spines of animals can be hardened and strengthened by deposits of calcium salts, which can then be fossilized. These vertebrae also preserve the annual growth bands, such as the rings of a tree, which show how the fish grew.
The researchers used an imaging technique called microcomputed tomography to study three well-preserved vertebrae of a shark. Those images revealed 46 growth bands, suggesting that this shark lived to the maturity of 46 years. It is estimated that the creature was about 9 meters long at the time of its death, and the size of the bands suggests that the animal grew at a rate of about 16 centimeters each year. This means that the shark would be about 2 meters long at birth, large enough for a newborn to be a fearsome enemy at sea, scientists conclude.
Shimada’s team has already suggested that while in the womb, megalodon sharks, like some of their modern cousins, were able to feed on eggs without incubating in the womb. That practice can help giant fish gain such a large size even before they enter the world.