|Evolution in the News - August 2011|
|by Do-While Jones|
Scientists now admit that Archaeopteryx was not a missing link between dinosaurs and birds.
A DEITY couldn't have planned it better. Just two years after On The Origin of Species was published, a fossil found in Germany gave Charles Darwin's controversial ideas an almighty boost. Archaeopteryx sported a mouthful of teeth and armfuls of feathers - facts that Darwin's supporters immediately leapt on as evidence that birds descended from dinosaurs.
This week, Darwin's "strange bird" has finally lost its perch on the lowermost branch of the bird evolutionary tree (see "Archaeopteryx knocked off its perch as first bird"). 1
New Scientist seems to be admitting that scientists were biased by evolutionary prejudice and rashly jumped to the conclusion that Archaeopteryx was a missing link. It has taken evolutionists a mere 150 years to admit their mistake. Better late than never.
When reading the technical literature (as we hope you will), you will run into some confusing terms. Scientists try to make a distinction between bird-like dinosaurs and dinosaur-like birds, and aren’t always certain about it. Both groups are called Paraves (which means, “like birds”).
The main players here are an assemblage of bird-like dinosaurs — oviraptorosaurs and deinonychosaurs (including troodontids and dromaeosaurids) — and dinosaur-like birds that belong to the avialans. Deinonychosaurs and avialans together comprise a group known as Paraves, with oviraptorosaurs being a bit more distantly related. As more fossils of basal members of each of these groups have been collected, distinctions between the groups have predictably blurred, and some species have bounced around from group to group. For example, Anchiornis, which recently made headlines for its colourful plumage, was originally regarded as a basal avialan, then a basal troodontid, and is now considered an archaeopterygid. 2
But why is this such a big deal? Archaeopteryx has always been something of a celebrity and has monumental historical, sociological and even political importance. It was discovered, with perfect timing, in mid-1861, less than two years after Darwin's Origin of Species hit the bookstalls. With its blend of avian and reptilian characteristics (not to mention the charismatic beauty of the fossils themselves), Archaeopteryx was seemingly the ideal evolutionary intermediate, instantly entering the debates over evolution in Victorian England and elsewhere, and gaining prominence in textbooks.
Given this iconic role, Archaeopteryx has also been in the cross-hairs of creationists, and remains a lightning rod for political debates and legal proceedings about teaching evolution in schools. Of course, Xu and co-workers' finding only deepens the impact of Archaeopteryx by highlighting the rich evolutionary nexus of which it is a part, but how the ever-clever creationist community will 'spin' it remains to be seen.
Politics aside, the historical importance of Archaeopteryx stands, even if we need to add the footnote that current evidence no longer regards it as the oldest bird. The impact of losing Archaeopteryx from the avian clan is, nevertheless, likely to rock the palaeontological community for years to come simply because, for the past century and a half, these familiar fossils have guided almost all scientific thought about the beginnings of birds. The late John Ostrom, the most influential modern worker on avian origins, began his seminal 1976 article, itself entitled 'Archaeopteryx and the origin of birds', with the statement, “The question of the origin of birds can be equated with the origin of Archaeopteryx, the oldest known bird.” Indeed, virtually all our notions about early avian evolution have been viewed through the lens of Archaeopteryx. Hundreds of publications (including several of my own) draw on the structure of Archaeopteryx to formulate and evaluate hypotheses about birds. Some published phylogenetic analyses have even used Archaeopteryx as the sole representative of birds. To what species do we now turn to ground our understanding of early birds? 3
These observations necessitate a re-evaluation of widely accepted hypotheses of paravian phylogeny; such an exercise will have significant implications for our understanding of avialan origins and related issues such as the origin of flight. 4
The primary source is an article about the discovery of a fossil called Xiaotingia. Most of the article deals with a description of the fossil, including the number of teeth, the size and shape of its forelimbs, and various other skeletal elements. Based on all these measurements of Xiaotingia, they conclude that Archaeopteryx wasn’t a bird at all. Here is perhaps the most important paragraph summarizing the analysis.
When Xu et al. ran a phylogenetic analysis combining the attributes of Xiaotingia with those of Archaeopteryx, other basal avialans, deinonychosaurs, and oviraptorosaurs, not only did Xiaotingia and Anchiornis cluster with Archaeopteryx, but these archaeopterygids now were yanked out of Avialae and placed in Deinonychosauria. In other words, Archaeopteryx was no longer a bird. Surprised by this outcome, the authors re-ran the analysis with identical parameters, but this time omitting Xiaotingia. The result was that Archaeopteryx was restored to Avialae as the most basal bird. This experiment affirmed how crucial Xiaotingia is to understanding the evolution of advanced theropods. 5
Here’s what that means. They wrote a computer program that compares selected physical characteristics to decide how closely related various species are and assigns them to various groups. The comparisons that the computer makes are all based on what the programmer tells it to compare, and how heavily to weight each feature. The validity of the conclusion depends entirely upon the subjective decisions made by the programmer.
When they ran the program without including data about Xiaotingia, the computer program said that Archaeopteryx was a bird. When they added Xiaotingia, the computer changed its mind and said that Archaeopteryx wasn’t a bird.
Suppose someone wrote a program to determine how beautiful a woman is based on physical features of many women. The program tells you that a Julia Roberts is a pretty woman. But then, you add data about Marilyn Monroe, and it says that Julia Roberts is no longer pretty.
It isn’t the computer that decides if the woman is pretty or not—it’s the algorithm chosen by the programmer that determines the outcome. The fact that adding data about one individual changes the classification of another individual makes the algorithm questionable. Julia Roberts may not be as pretty (in someone’s opinion) as Marilyn Monroe was; but that does not make Julia Roberts ugly.
Witmer said, “This experiment affirmed how crucial Xiaotingia is to understanding the evolution of advanced theropods.” We would say, “This experiment affirmed how subjective the thinking about evolution is.”
Regardless of how similar Xiaotingia and Archaeopteryx are to modern birds or extinct dinosaurs, it doesn’t prove anything evolved from anything else. They could just as easily been created with similar characteristics.
Evolution isn’t science. It’s opinion. It’s speculation. It’s prejudice. This is evident from Witmer’s conclusion:
In truth, this chapter of the scientific story is just beginning. Just as Xiaotingia moved Archaeopteryx out of the birds, the next find could move it back in — or to somewhere else within this fuzzy tangled knot that makes up the origins of birds and bird-like dinosaurs. That said, during this sesquicentennial anniversary of Archaeopteryx, which is being honoured with exhibits and commemorative coins, the bitter irony may be that it may not have been the bird we've always thought it was. But Archaeopteryx will remain an icon of evolution, perhaps even more so now, providing compelling evidence that, as we should expect, evolutionary origins are rather messy affairs. 6
They are messy because they are wrong!
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New Scientist, 30 July 2011, “It’s been fun, feathered friend”, page 3, http://www.newscientist.com/article/mg21128233.000-we-shouldnt-mourn-the-demotion-of-archaeopteryx.html
2 Witmer, Nature, 28 July 2011, “An icon knocked off its perch”, pages 458-9, http://www.nature.com/nature/journal/v475/n7357/full/475458a.html
4 Xu et al., Nature, 28 July 2011, “An Archaeopteryx-like theropod from China and the origin of Avialae”, pages 465-470, http://www.nature.com/nature/journal/v475/n7357/full/nature10288.html
5 Witmer, Nature, 28 July 2011, “An icon knocked off its perch”, pages 458-9, http://www.nature.com/nature/journal/v475/n7357/full/475458a.html