Researchers have found a well-preserved fossil of an aquatic reptile from several millions of years ago that provides further evidence that prehistoric reptiles were caring parents.
Discovered by a farmer in the Yixian Formation of western Liaoning Province in China, the fossil shows a family group of Philydrosaurus, where six juveniles surround an adult of unknown sex all by just a tail's length. Phylidrosaurus is a type of choristodere, which is a group of small, aquatic and semi-aquatic diapsid reptiles that existed more than 160 million years ago during the Middle Jurassic Period.
Diapsids, which are amniotes that have developed holes on the sides of their skulls 300 million years ago and from which all existing birds, snakes, and lizards have evolved, have always been believed to provide post-natal care. This type of behavior is evidently seen in modern birds and crocodilians, which fiercely care for and protect their young, providing food for their offspring and protecting them from predators.
However, fossil evidence of this behavior has always been scarce, with only two types of dinosaurs and monitor lizard-like pelycosaurs exhibiting this behavior in the fossil record.
Upon closer look by a team of paleontologists at the Institute of Geology at the Chinese Academy of Geological Sciences in Beijing, University of Lincoln in the United Kingdom, and Hokkaido University in Japan, researchers have come to the interpretation that the well-preserved fossil is one of an adult surrounded by its offspring, all apparently from the same clutch.
However, they could not determine the sex of the adult. In some modern bird species, such as emus, penguins, and sandpipers, the male parent is the primary caregiver while the female parent goes off to search for food or find another mate.
Dr. Charles Deeming of the School of Life Sciences of the University of Lincoln says the fossil is currently the oldest record of post-natal care in diapsids and also the latest addition to a growing choristoderes collection in varying stages of parental care and reproduction.
"That Philydrosaurus shows parental care of the young after hatching suggests protection by the adult, presumably against predators," Dr. Deeming says. "Their relatively small size would have meant that choristoderes were probably exposed to high predation pressure and strategies such as live birth and post-natal parental care may have improved survival of the offspring."
Although it is possible that the animals were all swept together during or after the event that killed them, the researchers are more inclined to believe that the fossil is evidence of post-natal care.
The specimen was discovered four years ago and was donated by its discoverer to the Jinzhou Paleontological Museum in Jinzhou City.
A report of the discovery is published with more details in Geosciences Journal.
