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.
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.
The new study is really the first of its kind for megalodon that has given good insight into its size at birth, reproductive mode and growth pattern. 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.
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.
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.
Seed-sized chameleon is the world’s tiniest reptile
Two of the miniature lizards, one male and one female, were discovered by a German-Madagascan expedition team in northern Madagascar.
The male Brookesia nana, or nano-chameleon, has a body that is only 13.5mm (0.53 inches) long, making it the smallest of all the roughly 11,500 known species of reptiles. Its total length from nose to tail is just under 22mm (0.87 inch). The female nano-chameleon is significantly larger, with an overall length of 29mm.
The species’ closest relative is the slightly larger Brookesia micra, whose discovery was announced in 2012.