Chinese fossil ‘rewrites history of reproduction’
First evidence found that group of animals that includes dinosaurs and birds also gave live birth to babies rather than only laying eggs
A fossil found in China has provided the first evidence that a group of animals that includes dinosaurs, birds and crocodiles also gave live birth to babies rather than only laying eggs to produce offspring.
The remains of a baby were found inside the fossil of a marine reptile called a Dinocephalosaurus discovered about 100km from Kunming in Yunnan province in southwest China.
The 245-million-year-old fossil belongs to a class of animals called Archosauromorpha, which include birds and some reptiles.
It was previously thought the group only laid eggs to produce offspring, but the find questions this assumption.
“Our discovery calls for a rethink of the evolutionary history of reproduction,” said Dr Liu Jun, a palaeontologist at the Hefei University of Technology in Anhui province and the lead scientist on the multinational research.
“Further evolutionary analysis reveals the first case of live birth in such a wide group containing birds, crocodilians, dinosaurs and pterosaurs among others, and pushes back evidence of reproductive biology in the group by 50 million years.”
The fossilised remains of the baby with an extremely long neck were found inside the belly of the animal.
The marine reptile may have eaten the baby, but scientists have ruled this out as the foetus is facing towards the front half of its mother and animals usually swallow prey head first to aid digestion.
“The neck of the embryo slightly curves towards its forelimbs and ribs,” the researchers wrote in their paper published in the journal Nature Communications. Such a curled posture was typical of vertebrate embryos, they said.
The study, also co-authored by researchers from the United States, Britain and Australia, was published on Wednesday.
With an extremely elongated neck and large paddle-like limbs, the mother Dinocephalosaurus would not have been able to leave the water to lay eggs on a beach like turtles or crocodiles.
Live birth, or viviparity, was previously regarded a late event in evolutionary history.
Although a few reptiles, such as some snake and lizard species, can give live birth to young, the feature was mainly developed in mammals.
Dinocephalosaurus may have been an exception with most Archosauromorpha still laying eggs, the researchers said, but other animal within the group may also have given live birth
“Ancestrally there was no genetic or developmental impediment to evolve live birth in this diverse group,” the researchers wrote.
