Researchers from China, Canada, and the University of Bristol reported the most amazing fossil ever in 2016 (Xing et al. 2016): a dinosaur tail complete with its feathers trapped in a piece of amber! While the feathers were not the first examples to be found in amber, earlier specimens were difficult to link to their source animal.
The specimen is a piece of amber that would sit in the palm of your hand, and it contains ants and twigs, as might be expected for a substance that solidifies from tree resin. But, most unexpectedly, there is a tiny tail, some 3 cm long, consisting of eight vertebrae from a juvenile dinosaur; these are surrounded by feathers and skin that are preserved in 3D and with microscopic detail.
Could the tail come from a bird? Probably not, because the vertebrae are not fused into a rod or pygostyle as in modern birds and their closest relatives. Instead, the tail is long and flexible, with keels of feathers running down each side.
The study’s first author Lida Xing from the China University of Geosciences in Beijing discovered the remarkable specimen at an amber market in Myitkyina, Myanmar (Burma) in 2015.
The amber piece was originally seen as some kind of plant inclusion and destined to become a curiosity or piece of jewellery, but Xing recognized its potential scientific importance and suggested the Dexu Institute of Palaeontology buy the specimen.
The specimen is the feathered tail of a theropod preserved in mid-Cretaceous amber about 99 million years old. The feathers suggest the tail had a chestnut-brown upper surface and a pale or white underside. The specimen also offers insight into feather evolution. The feathers lack a well-developed central shaft or rachis. Their structure suggests that the two finest tiers of branching in modern feathers, known as barbs and barbules, arose before a rachis formed.
How could a dinosaur be caught in amber?
This is clearly a small dinosaur, which may have lived in the trees as many lizards do today, perhaps crawling around seeking bugs. One day, he must have got his tail caught in the resin, and then presumably died because he could not wrestle free. But there is no suggestion that dinosaurs could shed their tails, as some lizards do today.
It was possible also to examine the chemistry of the tail where it was exposed at the surface of the amber. The analysis shows that the soft tissue layer around the bones retained traces of ferrous iron, a relic left over from haemoglobin that was also trapped in the sample.
Bird specimens in amber
Several tiny portions of birds have also been reported from the Burmese amber. For example, Xing et al. (2016) described two tiny wings from fledgling birds, in which it seems the birds might have become stuck in the resin, and then died. As the resin hardened around the wing, the rest of the body presumably rotted away.
In each case, the wings are about the size and shape of your thumb nail, and the short shape shows it was from a fledgling that could not yet fly. The fossil wings are only two or three centimetres long, and they contain the bones of the wing, including three long fingers armed with sharp claws, for clambering about in trees, as well as the feathers, all preserved in exquisite detail. The anatomy of the hand shows these come from enantiornithine birds, a major group in the Cretaceous, but which died out at the same time as the dinosaurs, 66 million years ago.
These fossil wings show amazing detail. The individual feathers show every filament and whisker, whether they are flight feathers or down feathers, and there are even traces of colour – spots and stripes.
These birds did not hang about in the nest waiting to be fed, but set off looking for food, and sadly died perhaps because of their small size and lack of experience. Isolated feathers in other amber samples show that adult birds might have avoided the sticky sap, or pulled themselves free.
The specimens come from a famous amber deposit in northeastern Myanmar, which has produced thousands of exquisite specimens of insects of all shapes and sizes, as well as spiders, scorpions, lizards, and isolated feathers. This is the first time that whole portions of birds have been noted. The Burmese amber deposits are producing a treasure trove of remarkable early fossils, and they document a particularly active time in the evolution of life on land, the Cretaceous terrestrial revolution. Flowering plants were flourishing and diversifying, and insects that fed on the leaves and nectar of the flowers were also diversifying fasts, as too were their predators, such as spiders, lizards, mammals, and birds.
- Mummified precocial bird wings in mid-Cretaceous Burmese amber. Nature Communications 7, 12089 (doi: 10.1038/ncomms12089) (Xing, L., McKellar, R.C., Wang, M., Bai, M., O’Connor, J.K., Benton, M.J., Zhang, J.P., Wang, Y., Tseng, K.W., Lockley, M.G., Li, G., Zhang, W.W., and Xu, X.). pdf. Supplementary data.
- Xing, L., McKellar, R.C., Xu, X., Li, G., Bai, M., Persons, W.S., IV, Miyashita, T., Benton, M.J., Zhang, J.P., Wolfe, A.P., Yi, Q.R., Tseng, K.W., Ran, H., and Currie, P.J. 2016. A feathered dinosaur tail with primitive plumage trapped in mid-Cretaceous amber. Current Biology 26, 3352-3360. pdf. Supplementary file.