Baby shark! Newborn megalodons larger than humans, scientists say
Enormous megatooth sharks, or megalodons, which patrolled the world’s oceans more than three million years ago, gave birth to babies larger than most adult humans, scientists say.
Researchers made the unsettling discovery when they X-rayed the vertebra of a fossilised megalodon and found that it must have been about two metres (6.5 ft) long when it was born.
Remnants of megalodons, which lived in most of the world’s oceans from 15m to 3.6m years ago, have revealed that adults grew to more than 15 metres in length, but until now their size at birth was unclear.
“The new study is really the first of its kind for megalodon that has given us good insight into its size at birth, reproductive mode and growth pattern,” said Kenshu Shimada, a professor of palaeobiology who led the research at DePaul University in Chicago.
Formally known as Otodus megalodon, the gigantic fish rank among the largest carnivores in the history of life on Earth. Scientists have uncovered plenty of fossils, but megalodon biology is poorly understood because the teeth are often all that remains of the cartilaginous creatures.
Working with colleagues at Stockton and William Paterson universities in New Jersey, Shimada took CT scans of a rare megalodon vertebra kept in a collection at the Royal Belgian Institute of Natural Sciences in Brussels.
The 15cm (6in) wide fossil was estimated to come from a megalodon nine metres long, based on comparisons with similar vertebrae seen in great white sharks, a distant descendant.
The scans revealed 46 growth bands in the fossil which scientists believe indicate the animal’s age in years, much as tree rings reveal annual growth in trees. Working backwards, the researchers estimate that the newborn
megalodon reached two metres from nose to tail.
“Based on the sizes of the smallest known megalodon teeth, I had a hunch that the size at birth may be around two to 2.5 metres,” Shimada said.
With the scans in hand, the researchers plotted a probable growth curve for the animal. The X-rays found no evidence of growth spurts during the fish’s younger years, but point instead to a steady growth rate of more than 16cm a year at least until the age of 46. The typical lifespan of the species was at least 88 years, they conclude. Details of the work are published in Historical Biology.
The enormous size of the newborn suggests that, in line with some other shark species such as great whites, threshers and makos, baby megalodons fed on the unhatched eggs of their siblings in the womb. The practice, known as oophagy, means few offspring survive, but those that do are large and well-nourished, and stand a better chance against predators. Mature megalodons fed on marine mammals such as sea lions, dolphins and whales.
Matthew Bonnan, a professor of biology on the team at Stockton University, said he and his students studied spiny dogfish shark anatomy in class. “To think that a baby megalodon was nearly twice as long as the largest adult sharks we examine is mind-boggling.”
The work follows research by scientists at Bristol and Swansea universities in September, who sought to reconstruct the dimensions of megalodons in greater detail. Led by Michael Benton, a palaeontologist at Bristol, the team used mathematical models and comparisons with living relatives to paint a picture of the prehistoric beasts. They found that a 16-metre megalodon was likely to have a head about 4.6 metres long and a dorsal fin 1.6 metres tall.