<mediar rid='m1'/>Fossil hunters in China have unearthed what looks like the final resting place of an adult dinosaur with 34 offspring. The unique discovery shows that at least some dinosaurs cared for their young after they hatched out, and suggests that the parental instincts of present-day birds and reptiles such as crocodiles may have a common evolutionary precursor.
In the fossilized group of horned dinosaurs called Psittacosaurus, a fully grown individual is surrounded by 34 youngsters, all huddled within an area of 0.5 square metres. It is almost certainly a family group rather than a happenstance collection of dead dinosaurs, says David Varricchio of Montana State University in Bozeman, part of the team who unearthed the bones in Liaoning, China.
"It does have that 'wow' aspect to it," he told news@nature.com. "It's more likely than not a family. It's hard to imagine [unrelated] whole skeletons being transported to the same place all together."
Simply the nest?
Although some groups of dinosaurs, such as theropods and hadrosaurs, are thought to have made nests, the find seems to be the first clear example of dinosaur parenting. It is not clear whether the 75-centimetre-long adult is a male or a female, Varricchio says. But the doting parent's sex was not necessarily of any consequence when it came to looking after the kids. Varricchio points out that in many living bird species, both parents help out in the nest.
It is also uncertain what parental care might have involved for these dinosaurs. Perhaps the parent simply kept the young close to keep an eye on them, Varricchio suggests, as chickens do today. "In many birds, the young stay with the parent; the adult leads them to food and the young generally mill about behind them," he says.
"It is an amazing snapshot, a really nice, serendipitous finding," says Paul Barrett, a dinosaur expert at the Natural History Museum in London. But he cautions that the evidence for family life remains circumstantial at this stage.
Nevertheless, the arrangement is "very suggestive of post-hatching parental care", Barrett admits. The youngsters are all around 20-centimetres long, suggesting that they represent a single brood.
Cause of death
The fossils' lifelike crouching poses also raise the question of what killed and preserved them. Although a volcanic eruption might seem the obvious culprit, Varricchio says that it is hard to imagine volcanic ash burying the dinosaurs quickly enough to preserve them like this.
It is more probable, he suggests, that they were entombed when an underground burrow collapsed, or drowned by rising flood waters. Many of the dinosaurs have their heads raised, which might indicate such an event. Barrett adds that the bowl-like depression in which the fossils were found is reminiscent of a nest, although he adds that this is very speculative.
The question of whether the dinosaurs lived (and perished) in burrows is one that Varricchio hopes to answer soon, ideally with the aid of further fossil finds. Such discoveries could give further insight into prehistoric family life, he adds. Earlier findings have hinted at the possibility that psittacosaurs might have lived in groups containing three or four adults, meaning the single-parent family may not have been the norm.
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