The discovery of a tiny, toothy-beaked skull of a creature that lived about 99 million years ago has given scientists a rare glimpse into life in the Cretaceous.
The diminutive specimen, encased in a honey-coloured medallion of amber, is described in the journal Nature.
Amber is a precious commodity in the world of palaeontology. Ancient conifer forests exuded the sticky resin aeons ago, trapping everything from wasps and scorpions to salamanders and snakes.
Small animals are usually crushed or flattened beyond recognition when trapped and fossilised in mud or sand. But amber preserves soft tissues such as skin and feathers. Sometimes features right down to the subcellular level can be preserved.
Burmese amber is especially prized. Its age – 99 million years – puts it smack bang in the middle of the Cretaceous. The shear diversity of creatures found in it is also unmatched.
One palaeontologist has described the flood of Burmese amber – often spirited out of conflict zones in northern Myanmar to bustling markets across the border in China – as an “orgy” of discovery.
The new species, named Oculudentavis khaungraae, is the smallest bird-like dinosaur to be discovered to date.
At a hair over seven millimetres from beak tip to back of head, the skull’s owner would have been roughly the size of the bee hummingbird (Mellisuga helenae), which, weighing in at just 2 grams, is the smallest living bird.
Its oversized eye socket with a narrow opening for light suggests that Oculudentavis (meaning “eye tooth bird”) was active during the day. Numerous tiny teeth suggest that it was probably a predator, eating insects and other small prey rather than sipping nectar.
But its unique combination of features – a lizard-like eye socket, toothed beak, and fused skull bones – made pinning it to the evolutionary tree of life a challenge.
One possibility is that Oculudentavis is a member of the most common group of birds from the Cretacesous – the enantiornithines.
It could also be more closely related to dinosaurs, on an evolutionary branch midway between birds and Archaeopteryx, the famous winged dinosaur that lived during the earlier Jurassic period.
Either way, the discovery of Oculudentavis suggests that miniaturisation in birds occurred earlier than previously thought. The smallest fossil bird to be found before now weighed approximately 12 grams, and the smallest dinosaurs would have weighed hundreds of grams.
“Its unique anatomical features point to one of the smallest and most ancient birds ever found,” says palaeontologist Lars Schmitz from the W.M. Keck Science Department in Claremont, California.
“No other group of living birds features species with similarly small crania in adults,” he adds.
More remains would help, according to palaeontologist Roger Benson from the University of Oxford.
“The challenge of determining how Oculudentavis is related to other early birds and bird-like dinosaurs would be greatly assisted by knowing more about its skeleton,” he writes in an accompanying commentary on the discovery.
Whether another specimen of Oculudentavis turns up in the globs of Burmese amber remains to be seen. But it’s just as likely that another equally illuminating relative has been frozen in time.
“This discovery shows us that we have only a small glimpse of what tiny vertebrates looked like in the age of the dinosaur,” says Schmitz.
The Royal Institution of Australia has an education resource based on this article. You can access it here.