Paleontologists have found an extraordinary fossil of a pregnant Dinocephalosaurus, a member of a now-extinct reptilian group of animals that include birds, crocodiles and dinosaurs.
Evidence That Archosaurs Gave Birth To Live Babies
The fossil of the pregnant long-necked marine archosauromorph was found in southwestern China. The preserved remains of the fetus inside its belly indicate that the creature gave birth to live youngs and did not lay eggs as scientists previously believed.
Possibly The Creature's Last Meal
Scientists who discovered the 245-million-year-old creature with its young curled inside its belly initially did not want to jump into conclusion since the smaller animal inside the ribcage could have been the larger creature's last meal.
A closer examination, however, revealed that the two animals belong to the same species. Just like its mother, the fetus has the long neck joint of Dinocephalosaurus.
Not A Case Of Cannibalism
Researchers also considered the possibility of cannibalism but it apparently is not the case here. Researchers are sure that the Dinocephalosaurus ate fish given its small mouth and long thin neck which are perfect for gulping down the slippery bodies of fish. Swallowing a chunky baby belonging to its own species would have been a feat for the prehistoric creature.
The little bones of the smaller creature did not also show evidence of acid digestion, which would be expected if it went to the bigger animal's belly as a meal.
The position of the fetus likewise indicates that it was no food. The fetus was facing forward. The preys of Dinocephalosaurus tend to be swallowed head first and this position is often preserved during digestion. The embryo was also curled. Researchers said that if the animal was ingested, there is no way to preserve this shape.
Giving Birth To Live Young As An Adaptation To Aquatic Life
The pregnant Dinocephalosaurus backs up a dominant idea about what makes reptiles stop laying eggs and start giving birth to live young. It also showed that the creature was fully marine. It did not have to leave the ocean to lay eggs on land just like turtles do.
"Reptilian eggs cannot be incubated underwater; amniote embryos in shelled eggs must exchange respiratory gases with the environment across the eggshell, and this exchange is much slower in water than in air," researchers wrote in their study, which was published in Nature Communications on Feb. 14.
"Therefore, viviparity would have been highly adaptive for Dinocephalosaurus to reproduce in the sea."
Viviparity or giving birth to live young is believed to be an adaptation needed for reptiles to move to a fully aquatic lifestyle. The transition from land to sea has happened multiple times in history particularly during periods of mass extinction.
"This combination of live birth and genotypic sex determination seems to have been necessary for animals such as Dinocephalosaurus to become aquatic," said study researcher Mike Benton, from the University of Bristol. "It's great to see such an important step forward in our understanding of the evolution of a major group coming from a chance fossil find in a Chinese field."
