It Takes A Village

 

The fossil. Image by https://observationdeck.kinja.com/this-dinosaur-babysitting-session-didnt-end-well-1630006866

Dinosaurs are often depicted as giant, frightening beasts. But every creature is a baby once; and dinosaurs were no exception. And a 120-million year old fossil found from China has given us a revolutionary insight into Cretaceous Family Values.

The fossil in question was found in 2004, but, for 10 years, it was never been studied in detail. It features 25 animals in total; 24 hatchlings of the species Psittacosaurus lujiatunensis and a larger individual. The 24 juveniles were all the same size; ergo, they were all likely the same age, possibly even from the same clutch.

For almost a decade after it was discovered, it was thought the adult was a parent with its offspring and the find was left as a footnote. However, an in-depth study of the fossil in 2014 found that the larger individual was about five years old; Psittacosaurus reached sexual maturity at the age of 10. Whilst it was clearly older than the hatchlings, the larger individual was not old enough to reproduce; basically, it couldn't have been the parent of the hatchlings.

What was the solution to this problem? The scientists answered this by looking to today's species; in particular, the dinosaurs' living descendants, the birds. From the evidence, they surmised that the association was not coincidental, but, rather, an exemplar of co-operative breeding.

You see, humans aren't the only species where friends and relatives pitch in to help look after babies - 9% of birds and 3% of mammals carry out some kind of co-operative breeding where other family members help look after the babies. According to this theory, the older juvenile was not a parent, but a subadult helping look after its younger relatives. Basically, a dinosaur babysitter.

They would have needed the help. Psittacosaurus was on the low end of the food chain in Cretaceous China. Predators such as Dilong, a smaller precursor to the mighty Tyrannosaurus rex and just as rapacious a carnivore, and Repenomamus, a Staffie-sized predatory mammal, would all have had baby psittacosaurs on the menu. Faced with these marauders, a few extra hands (or, in this case, beaks) around the nest would have probably been very much appreciated. Sadly, what worked for theropods, did not work for fast-moving volcanic mudslides; however, the system clearly worked to some degree.

Other fossils indicate that Psittacosaurus was, indeed, a social animal; several other mixed-age associations are known and the relatively large size of Psittacosaurus' brain suggests a degree of intelligence that would be in line with an animal that lived a complex social life.

The Psittacosaurus remains also give us a potential insight into the social organisation of Psittacosaurus' bigger and more famous descendants, the horned dinosaurs (Triceratops and its relatives); from quite a few marvellously preserved bonebeds, we know that these, too, were herd animals.

What do you think about this new insight into dinosaur family values? Let me know in the comments below! And don't forget to share and subscribe!