A proposal has been made to remove beloved Archaeopteryx from the bird family tree and push it over to some non-avian dinosaur subtree. This is not the first time that the ancient species has had its position on the tree of bird life threatened, but this time it may be for real. The proposal is reasonable.
I've talked about this issue before, but I'm bringing it up now because there is a new paper, just out. Lets get right down to business and start with the abstract:
Archaeopteryx is widely accepted as being the most basal bird, and accordingly it is regarded as central to understanding avialan origins; however, recent discoveries of derived maniraptorans have weakened the avialan status of Archaeopteryx. Here we report a new Archaeopteryx-like theropod from China. This find further demonstrates that many features formerly regarded as being diagnostic of Avialae, including long and robust forelimbs, actually characterize the more inclusive group Paraves (composed of the avialans and the deinonychosaurs). Notably, adding the new taxon into a comprehensive phylogenetic analysis shifts Archaeopteryx to the Deinonychosauria. Despite only tentative statistical support, this result challenges the centrality of Archaeopteryx in the transition to birds. If this new phylogenetic hypothesis can be confirmed by further investigation, current assumptions regarding the avialan ancestral condition will need to be re-evaluated.
Glossary:
maniraptorans is a group of dinosaurs that includes birds. It consists of Avialae (which includes birds) and Deinonychosauria (which does not include birds).
Here's what happened. They found new fossils in China. When they looked at these fossils they realized that some of the traits thought to be unique to the Avialae group of maniraptorans are actually not, but rather, are found in a larger group that includes both the bird-inclusive Avialae and non-birds. (This larger group is the Paraves).
"Archaeopteryx was [thought to be] a bird because it had feathers and nothing else had them. But then other animals started being found that had wishbones, three-fingered hands and feathers. Heck, even T. rex had a wishbone. So one by one we've learned Archaeopteryx 's uniquely avian traits weren't so unique. The writing was really on the wall," says Lawrence Witmer, a palaeontologist at Ohio University in Athens.
Here's the thing. A valid phylogeny (tree of relatedness) requires a perfect understanding of both the timing (in relation to speciation, not chronology) and polarity of traits. You need to know which trait gave rise to which trait; The direction of the change has to be unambiguous. This means you also have to know which species did not have the trait. If you see a trait in what you think is a new species but not in its ancestors, you may have a case for a particular evolutionary tree. But if it turns out that the trait in question is also found in the ancestor, your tree is invalid.
If in fact Archaeopteryx was misplaced before, it was because a trait thought to be derived in that group was actually primitive to it and found in a larger group, and is thus disqualified as a distinguishing character. After this, other traits became more important in positioning Archaeopteryx, and thus the shift.
Among the key traits responsible for this shift are features of the head of the animals studied. Archaeopteryx has the head of a Deinonychosauran, not an Avialan.
Huxley is very happy to see this new development.
Xu, X., You, H., Du, K., & Han, F. (2011). An Archaeopteryx-like theropod from China and the origin of Avialae Nature, 475 (7357), 465-470 DOI: 10.1038/nature10288
- Log in to post comments
More like this
But...it built a nest in that family tree and everything!
Worse than that Raging Bee. There are all these hippy looking and pointy-headed academic folks who have chained themselves to that tree and/or taken up housekeeping in it. And every time anyone comes close they start singing "We Shall Overcome" and throwing themselves in front of the heavy equipment.
First Pluto and now Archaeopteryx! Science is ruining my childhood!
this is not correct!This information is correct not yours!Archaeopteryx (meaning "ancient wing") is a very early prehistoric bird, dating from about 150 million years ago during the Jurassic period, when many dinosaurs lived. It is one of the oldest-known birds.
Archaeopteryx seemed to be part bird and part dinosaur. Unlike modern-day birds, it had teeth, three claws on each wing, a flat sternum (breastbone), belly ribs (gastralia), and a long, bony tail. Like modern-day birds, it had feathers, a lightly-built body with hollow bones, a wishbone (furcula) and reduced fingers. This crow-sized animal may have been able to fly, but not very far and not very well. Although it had feathers and could fly, it had similarities to dinosaurs, including its teeth, skull, lack of a horny bill, and certain bone structures. Archaeopteryx had a wingspan of about 1.5 feet (0.5 m) and was about 1 foot (30 cm) long from beak to tail. It probably weighed from 11 to 18 ounces (300 to 500 grams). Paleontologists think that Archaeopteryx was a dead-end in evolution and that coelurosaurian theropods (a group of dinosaurs that included the Dromaeosaurs Deinonychus, Utahraptor, and Velociraptor) led to the birds.
Fossils: Amazingly detailed Archaeopteryx fossils have been found in fine-grained Jurassic limestone in southern Germany. This fine-grained limestone is used in the lithographic process, hence the species name "lithographica" given to the early Archaeopteryx specimen. The first Archaeopteryx fossil (a feather) was found in 1860 near Solnhofen, Germany, and was named by the German paleontologist Hermann von Meyer in 1861. That year he also discovered the first specimen of Archaeopteryx. A total of eight Archaeopteryx specimens have been found, plus the feather.
The Solnhofen area was a stagnant lagoon during the Jurassic period (Europe was a series of islands at this time). The lagoon's waters had little or no oxygen (anoxic) near the bottom, a situation that helped preserve many dead organisms, and boost the chances of fossil formation, since decay after death is very slow in anoxic waters.
Bird fossils are rare because bird bones are hollow and fragile, and usually deteriorate instead of fossilizing. However, a few Jurassic, mid-Cretaceous, Eocene and Miocene-Pliocene bird fossils have been found.
The Origin of Birds: In 1868, Thomas Henry Huxley interpreted the Archaeopteryx fossil to be a transitional bird having many reptilian features. Using the fossils of Archaeopteryx and Compsognathus, a bird-sized and bird-like dinosaur, Huxley argued that birds and reptiles were descended from common ancestors. Decades later, Huxley's ideas fell out of favor, only to be reconsidered over a century later (after much research and ado) in the 1970's.
In 1986, J. A. Gauthier looked at over 100 characteristics of birds and dinosaurs and showed that birds belonged to the clade of coelurosaurian dinosaurs. [Gauthier, J.A., 1986. Saurischian monophyly and the origin of birds, in: The Origin of Birds and the Evolution of Flight, California Academy of Sciences Memoir No. 8
that was all from my memory so you can put this on from my information
But...it built a nest in that family tree and everything!