Not just for the birds- Archaeopteryx

May 01, 2013  •  Leave a Comment
One of the most profound insights Darwin made with his research on evolution, was the notion of common descent. Common descent meant that every species today, descended from different species in the past. Many of the species today would also share the same common ancestor.

Darwin did not have much in the way of evidence to support this. The Origin of The Species did not employ fossil evidence to demonstrate evolution because in 1859, there wasn't a lot of fossil evidence of any kind. Likewise, Darwin did not have the molecular evidence we have today.

This made the discovery of Archeopteryx in Germany, in Late Jurassic rocks, suddenly important. This 1861 discovery, soon after the publication of the Origin, provided fossil vindication of what Darwin had deduced. Here was a species that was a genuine mosaic of avian and non-avian (theropod) traits. Birds aren't found throughout the geological column- there are none in the Permian or the Triassic. They don't appear until the Jurassic. Their ancestor had to be non-avian. This fossil confirmed that.



What set Archeopteryx apart from many earlier transitional fossils (Caudipteryx, Anchiornis) was that it was capable of basic flight. With its laterally facing shoulder joint and split propulsion lift wing, with asymmetric feathers, basic flight was now possible. The hallux (the 4th digit) also appears reversed which would give a basic perching function [1].



Nonetheless, the long bony tail of Archeopteryx, the simple shape of its sternum, the fact it still had bony jaws with teeth, all showed its transitional status [1]. Without a keel on the sternum, the flight muscles would be limited in size. Likewise, the long bony tail (the species lacked the pygostyle of modern birds) would also have compromised flying ability.

References

[1] Sereno, P.C. (1999) The Evolution of Dinosaurs, Science 284:5423, pp2137-2147

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