[Radio Audio / News] Cape Breton fossils are the oldest evidence of parental behaviour

from Quirks & Quarks with Bob McDonald (CBC)

A 300 million year old animal was preserved huddled around a juvenile in a den in a hollow tree.

Maddin’s team recently discovered an adult and juvenile fossils of a varanopid synapsid — one of the earliest animals on the mammalian evolutionary lineage — inside a lithified tree stump on Cape Breton Island, Nova Scotia. (Henry Sharpe)

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More than 300 million years ago, a lizard-like creature more closely related to mammals than reptiles died in what is now Cape Breton, N.S. with its tail curled around what was likely its offspring. The team of Canadian researchers who found and analyzed the fossil think this is the earliest evidence of parenting behaviour yet identified in the fossil record.

Their study was published in the journal Nature Ecology & Evolution.

Hillary Maddin, a paleontologist from Carleton University, and her colleagues discovered the fossils which they identified as a species called Dendromaia unamakiensis. The adult animal would have been perhaps 30 centimetres long, and would have looked somewhat like a modern lizard, though in fact they were on the evolutionary lineage that would eventually lead to mammals.

The remains were found in a tree-like stump the creatures were likely using as a den. The fossils were dated as about 309 million years old, pushing back the earliest known evidence of extended parental care by 40 million years.

A unique find likely capturing their final moment

"They're preserved in very close articulation in a tight relationship together in very pristine preservation, which suggests we captured them at a very lifelike moment," said Maddin.

Maddin said the fact they found some of the fossils' more delicate bones intact suggests these animals died in the tree-like stump where they were discovered because otherwise those bones would have been washed away and destroyed.

"The delicate skull of the baby, which had it been transported very far it would have almost certainly been blown to bits," she said, "so we think they didn't move very far from where they originally died."

Photographs of the skull from the small individual of D. unamakiensis (Hillary Maddin / Nature Ecology & Evolution)

Tree-like tombs encasing precious fossils

The land that eventually became this part of Nova Scotia looked quite different 300 million years ago. It would have been a subtropical swampy delta, covered with tree-like structures more closely related to today's moss than modern day trees.

These plants would have had strong outer shells, but their soft interior would have been easily hollowed out for habitation by animals. When the animals died, "they kind of would have acted as tombs," said Maddin.

"We see them still standing erect in the cliff faces where piles of sediment have built up around them and still inside the contents are absolutely pristine," she added.

The adult and juvenile fossils from Cape Breton were discovered in a tree-like structure like this one, which is located in Joggins, N.S. (Alex Prieditis )