Canadian researchers have discovered the earliest evidence of parental care in a fossil. The partial skeletons of an adult and juvenile from around 309 million years ago were found within a fossilized tree stump.

The discovery of the creature, called Dendromaia unamakiensis, pushes back the date when extended parental care first developed by about 40 million years. The lizard-looking animal is a varanopid synapsid, the ancestor of what will eventually become mammals.

“This is the earliest evidence of prolonged postnatal care in a vertebrate,” lead author Professor Hillary Maddin, from Carleton University, said in a statement. “The adult animal appears to be concealing and protecting a juvenile in a den. This behavior is very common in mammals today. It is interesting to see this animal, which is on the evolutionary line leading to mammals, exhibiting this behaviour so early.”

Parental care is one of the behaviors animals exhibit to increase offspring survival, but it is not a cheap and easy approach. Parental care – and especially extended postnatal care – is costly, with the parents having to sacrifice energy and resources for their babies.

In the case of this finding, researchers report the adult was discovered covering its young with a hindlimb and encircled tail. This position is common in denning animals. For this reason, the team suspects the adult and young took refuge in the tree stump before their untimely death.

Fossilized evidence of extended parental care is rare to come by as environmental conditions need to be just right for the fossilization of parent and offspring to happen.

“Attempts to address questions about the origin of parental care have been made through study of the fossil record. Evidence of parental care in the fossil record is generally limited to the preservation of articulated assemblages of individuals pertaining to different age classes of the same species,” wrote the researchers in their paper published in Nature Ecology & Evolution.

This specimen was discovered on Cape Breton Island, Nova Scotia.

“This discovery shows that Nova Scotia still has plenty of amazing secrets to be discovered in its fossil record,” co-author Brian Hebert added.