A partnership between a Nova Scotia fossil hunter and Carleton University researchers has yielded the earliest fossil evidence of a parent caring for its offspring — a skeleton of a 300-million-year-old animal that appeared to be concealing and protecting a juvenile in a den.
The two creature were “synapsids” — commonly known as mammal-like reptiles. While prehistoric synapsids were lizard-like in appearance, they belong to the evolutionary line that eventually led to mammals. The larger of the pair — the parent — was about 30 centimetres long from the tip of the nose to the end of its tail. The juvenile was about a third of that size.
These particular synapsids were likely hiding inside the trunk of tree when they were apparently trapped by a sudden flood. The two skeletons were discovered in 2017 by Brian Hebert, who has been searching for fossils in Nova Scotia for 30 years.
Hebert was combing a section of the east coast of Cape Breton Island near Sydney when he found the fossils in a lithified tree stump from the Carboniferous Period, a time in which the area was covered by a swampy forest, millions of years before the rise of dinosaurs.
Hebert has often found such tree stumps in his searches, but many are empty. Even those with skeletons inside had only one skeleton.
“The tree was not a well-preserved tree, but everything inside was amazingly well-preserved,” he said of the find he made in 2017. “I knew it was something special as soon as I opened it.”
Paleontologist Hillary Maddin, who analyzed the finding with the Carleton University team, said Hebert’s finding predates the previous oldest record of this behaviour by 40 million years. The adult’s tail is wrapped around the juvenile’s hind limbs in a manner common among denning animals.
It is likely the parent was carnivorous, while the juvenile ate insects. “The bugs were quite big back then,” said Maddin.
It is not common to see fossils this well-preserved, she said. “This fossil is just so beautifully articulated,” she said.
Parental care is common in mammals — all mammal offspring require nourishment from their mothers. Some other animals, including birds, some amphibians, reptiles and even fish also care for their young.
Parental care requires animal parents to make an investment, or divert resources away from themselves, to give their young a better chance of survival, said Maddin. Prolonged care of offspring after birth can have the highest cost to parents.
How parental care has evolved as a behavioural strategy is a question not yet answered. Understanding of how parental care evolved can only be done by studying fossils. So far, most evidence of prehistoric parenting has been limited to finding groups of individuals of different ages of the same species.
There are evolutionary advantages and disadvantages to parental care, said Maddin. Some animals demonstrate extended care for their young and some don’t. Some just ditch their offspring, while others protect them until they are better able to care for themselves.
“This confers some sort of advantage to this animal,” said Maddin.
The findings of the Carleton team have been published in the journal Nature Ecology & Evolution. It has created a stir worldwide.
Reaction to the published article has bad been “pretty crazy,” said Maddin. The story has appeared in more than 70 general interest publications and on more than 50 national news broadcasts. “It really kind of exploded.”
Are these two lizard-like animals apparently cuddling together the first example of mother love? Not in the way that humans think of it, said Maddin. Some modern animals not considered intelligent, such as some shrimp and crabs, also demonstrate parental care, she said.
“It’s quite a common strategy. This is just the first example we have seen of it.”
Hebert said fossil hunters have been searching Nova Scotia for almost 200 years. Storm surges can erode cliffs, exposing more finds.
“There’s an untapped resource of amazing fossils to be found,” he said.
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