A dinosaur nesting site older than any discovered before suggests the creatures were caring mothers early in their evolution.
Scientists uncovered multiple clutches of fossilised eggs at the site in South Africa, many containing embryos.
They also found tiny footprints of hatchlings showing that young dinosaurs stayed in the nest long enough to at least double in size.
The nests belonged to Massospondylus, a six-metre (20ft) ancestor of long-necked "sauropod" dinosaurs that lived 190m years ago.
The newly discovered nesting ground, in Golden Gate Highlands national park, is 100m years older than any found before.
At least 10 nests were uncovered at several different rock levels. Each contained up to 34 round eggs in tightly clustered clutches.
The distribution of the nests indicated that dinosaurs returned repeatedly to the same spot to lay their eggs.
Their highly organised nature suggests the mothers may have arranged their eggs carefully after laying them, according to the research published in the journal Proceedings of the National Academy of Sciences.
"Even though the fossil record of dinosaurs is extensive, we actually have very little fossil information about their reproductive biology, particularly for early dinosaurs," said Dr David Evans, curator of vertebrate palaeontology at the Royal Ontario Museum in Canada.
"This amazing series of 190m-year-old nests gives us the first detailed look at dinosaur reproduction early in their evolutionary history, and documents the antiquity of nesting strategies that are only known much later in the dinosaur record."
The scientists believe many more nests at the site, now buried in rock, remain to be discovered.