Dec 13 2016

Feathered Dino Tail Trapped in Amber

amber-feathered-tail2Lida Xing from the China University of Geosciences in Beijing was walking through an amber market in Myitkina, Myanmar when he discovered a rather interesting specimen. The seller believed that the large chunk of fossilized tree sap they were selling contained plant material. Xing recognized that it contained primitive feathers. Even more exciting, those feathers were not connected to a bird ancestor, but to the tail of a dinosaur.

A scientific analysis of that specimen has now been published in Current Biology.

This is a tremendous specimen for a number of reasons. Scientists interested in the evolution of feathers have been trying to piece together the developmental steps that occurred and in what order in order to transform scales into feathers. Developmental biology itself provides some clues – the path that feathers take when they develop in the embryo likely reflect their evolutionary history. It would be nice, however, to confirm this hypothesis with actual specimens.

Up until now paleontologists have had two kinds of fossil feathers. The first is feather impressions associated with fossil specimens. The advantage of this kind of evidence is that we know exactly what species the feathers belong to and so they can be placed in a phylogenetic tree of feathered dinosaurs, both avian and non-avian. The disadvantage is that the feather impression are compressed, so the three-dimensional information may be lost, and they often lack fine detail.

The other source of fossil evidence is from feathers trapped in amber. These specimens, however, usually contain feathers in isolation, without and piece of the creature to which they belong. So while we can see fine details of ancient feathers, we don’t know where to place them on the tree.

This new specimen is the best of both worlds – it contains fine details of wonderfully preserved feathers attached to the tail of a dinosaur that can be identified (a juvenile coelurosaur). Jackpot.

The authors write:

Many feathers exhibit a short, slender rachis with alternating barbs and a uniform series of contiguous barbules, supporting the developmental hypothesis that barbs already possessed barbules when they fused to form the rachis.

The rachis is the central shaft of feathers, while the barbs are the side branches coming off the shaft, and barbules are side branches coming off the barbs. As feathers evolved they started as just hair-like structures which then formed side branches to become downy and fluffy. Eventually some of these barbs fused down the middle to form the rachis. This sequence was hypothesized from studying how feathers develop, and that sequence has been partially confirmed by this new specimen.

It is completely clear that this specimen is not a bird or bird ancestor. This was a long bony tail belonging to a non-avian feathered dinosaur.

This history of our advancing knowledge of bird evolution is a great example of the ridiculous denialist strategy of some creationists. It is a wonderful demonstration of their shifting “god of the gaps” strategy.

At first they claimed that birds represent a distinct group without any connection to another group. They offered this as evidence for creation and against evolution. Evolutionary theory predicted that we would find specimens that fill in the morphological and phylogenetic space between birds and whatever group they evolved from.

The Berlin Specimen (an archaeopteryx) was the first specimen to fill in this space, and to connect birds to dinosaurs. Archaeopteryx, while not on the direct line to birds, is a close cousin, and is a great transitional specimen. It is a clear mix of theropod dinosaur and avian features. Creationists, like Duane Gish, simply denied its transitional status. He seriously argued that it is either a dinosaur or a bird, and therefore was not transitional. So, it’s either a dinosaur with feathers who could fly or a bird with teeth, claws, and a long bony tail. Got it.

Then different feathered dinosaur specimens started to come out of China. It became clear that the entire theropod clade had feathers, many different kinds of feathers. One branch of these feathered dinosaurs led to birds. Creationists then said – Aha, you only have fully formed feathers. You don’t have any transitional feathers. Then we found transitional feathers. They then denied that they were feathers at all, just decomposing collagen. This was already an absurd claim, but the amber evidence blows it out of the water.

Over the last two decades scientists have found and described more and more feathered dinosaurs and bird ancestors, dramatically filling in the morphological space between theropods and birds, showing feather evolution, and a nice pattern of adaptive radiation. This is all happening in a temporal sequence that is compatible with an evolutionary origin. This is a stunning confirmation of predictions made by evolutionary theory. The evidence establishes that birds are dinosaurs, it establishes common descent in this clade, and evolutionary change over time.

Creationists, however, are always about what the evidence does not show, as if each piece of evidence must, by itself, establish every single aspect of evolution, or evolution is called into question. They also keep looking for gaps to point out, or missing pieces to the fossil puzzle. They are playing a losing game, but they count on their audience wearing historical blinders.

The gaps keep shrinking. Creationist naysaying gets more and more desperate. Meanwhile, the evidence keeps piling on.

I do wonder how many creationists experience even a little cognitive dissonance when they see scientific reports of specimens like this (if they encounter it). Down deep does some part of them feel queasy that we keep finding more and better fossil evidence of evolution? Think about it – we had nothing, and now we have feathered dinosaurs evolving all over the place, with one line clearly leading to modern birds. It has to give them at least a moment of pause.

But then I remember the power of motivated reasoning. Facts just don’t matter. Humans are not built that way. We need to consciously dedicate ourselves to evidence and logic, or else we will be slaves to our own motivated reasoning.

Even a feathered dinosaur tail in amber will not be enough.

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