Transitional Bird Wings In Cretaceous Amber!

For description see original paper

Mummified precocial bird wings in mid-Cretaceous Burmese amber : Nature Communications : Nature Publishing Group

More bad news for creationists to find coping strategies for. An interesting find in amber deposits from Myanmar has revealed a little more about the evolution of birds, or more precisely feathers, during the Cretaceous. It shows a bird wing with a transitional skeleton!

The details were published in an open access paper in Nature Communications a few days ago by an international research team was led by Dr Xing Lida from the China University of Geosciences, and colleagues from Canada, United States and Professor Mike Benton from the University of Bristol, UK. It shows tiny wings in astonishing detail, including bones, skin, muscles and feathers. The fine structure of the feathers even shows what is probably evidence of colour.

The significance of this find, apart from the fact that the wings were tiny - only two to three centimeters long - is that they are from hatchling enantiornithine birds which still had fingers with well-developed claws. This group of early birds became extinct along with dinosaurs at the end of the Cretaceous.

For description see original paper

Our knowledge of Cretaceous plumage is limited by the fossil record itself: compression fossils surrounding skeletons lack the finest morphological details and seldom preserve visible traces of colour, while discoveries in amber have been disassociated from their source animals. Here we report the osteology, plumage and pterylosis of two exceptionally preserved theropod wings from Burmese amber, with vestiges of soft tissues. The extremely small size and osteological development of the wings, combined with their digit proportions, strongly suggests that the remains represent precocial hatchlings of enantiornithine birds. These specimens demonstrate that the plumage types associated with modern birds were present within single individuals of Enantiornithes by the Cenomanian (99 million years ago), providing insights into plumage arrangement and microstructure alongside immature skeletal remains. This finding brings new detail to our understanding of infrequently preserved juveniles, including the first concrete examples of follicles, feather tracts and apteria in Cretaceous avialans.

Lida Xing, Ryan C. McKellar, Min Wang, Ming Bai, Jingmai K. O’Connor, Michael J. Benton, Jianping Zhang, Yan Wang, Kuowei Tseng, Martin G. Lockley, Gang Li, Weiwei Zhang, Xing Xu.
Mummified precocial bird wings in mid-Cretaceous Burmese amber.
Nature Communications, 2016; 7: 12089 DOI: 10.1038/ncomms12089

© 2016 Macmillan Publishers Limited. Reprinted under a Creative Commons Attribution 4.0 International License. (CC BY 4.0).

The fact that the tiny birds were clambering about in the trees suggests that they had advanced development, meaning they were ready for action as soon as they hatched. 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.

Dr Xing Lida, lead author, quoted in ScienceDaily.

It is possible that these birds never actually flew in the sense that modern birds fly, but clambered about in trees hunting insects. The fact that these hatchlings became entrapped in the pine resin which was destined to become amber in the first place suggests they were well-developed from an early age and probably left the nest early to become at least partially self-reliant. Evidence from feathers in other samples of amber suggests that the adults could probably free themselves from the resin. Inexperienced and small chicks would not have been able to.

Such well-developed, even advanced, feathers on such a 'primitive' skeleton suggests feathers had been evolving for a long time and probably served a purpose other than flight. In fact even in modern birds, only the specialised wing and tail feathers play a significant role in flight; other feathers perform other functions such as controlling heat loss and maintaining body temperature; brooding eggs and young and colour displays/camouflage. Flight may well have been a much later development as an example of evolution finding a new function by adaptation of existing structures.

The period when these birds were active was a time of rapid biological diversification as new ecological niches were opening up. Flowering plants were beginning to appear and diversify as were pollinating and leaf-eating insects in their turn, creating opportunities for small lizards, birds, spiders and even early mammals to find ways of catching them. At least this one group of small, feathered dinosaurs was clearly evolving to occupy this niche by climbing about in trees and bushes.

This find is of course, entirely consistent with the prevailing view of bird evolution from bipedal dinosaurs, so it will be interesting to see how the creation industry handles it. No doubt the usual tactics of denial will be employed including deliberate confusion with the usual process of fossilisation where the preservation of this degree of detail would be highly unusual.

Preservation in amber is of course an entirely different process involving little or no replacement of original structures by minerals and loss through leaching, etc. Amber preservation is similar to embedding an object in modern resins or plastics, isolating it from the atmosphere and from any putrefying or degrading microorganisms. No doubt we will see the usual attempt to mislead people by pretending this high degree of preservation 'proves' these early birds lived just a few thousand years ago and the fact that they lived contemporaneously with other dinosaurs 'proves' dinosaurs also lived just a few thousand years ago.

This isn't J.B.S. Haldane's proverbial 'Cretaceous rabbit'. It is an exquisite confirmation of something we have known about for a very long time now - birds evolved out of feathered, flightless dinosaurs and so were contemporaneous with many of them. The skeletal structure of the wing very clearly corresponds exactly to what we would expect a species close to the ancestral group to look like. In other words, this is an exquisite example of a 'transitional' form.

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