In 1861 an intriguing fossil was found in the Jurassic Solnhofen Limestone of southern Germany, a source of rare but exceptionally well-preserved fossils. Given the name Archeopteryx lithographica the fossil appeared to combine features of both birds and reptiles: a reptilian skeleton, accompanied by the clear impression of feathers. This made the find highly significant as it had the potential to support the Darwinians in the debate that was raging following the 1859 publication of "On the origin of species".
While it was originally described as simply a feathered reptile, Archaeopteryx has long been regarded as a transitional form between birds and reptiles, making it one of the most important fossils ever discovered. Until relatively recently it was also the earliest known bird. Lately, scientists have realised that Archaeopteryx bears even more resemblance to the Maniraptora, a group of dinosaurs that includes the infamous velociraptors of "Jurassic Park", than to modern birds. Thus the Archaeopteryx provides a strong phylogenetic link between the two groups. Fossil birds have been discovered in China that are even older than Archaeopteryx, and other discoveries of feathered dinosaurs support the theory that theropods evolved feathers for insulation and thermo-regulation before birds used them for flight. This is an example of an exaptation.
Closer examination of the early history of birds provides a good example of the concept that evolution is neither linear nor progressive. The bird lineage is messy, with a variety of “experimental” forms appearing. Not all achieved powered flight, and some looked quite unlike modern birds e.g. Microraptor gui, which appears to have been a gliding animal and had asymmetric flight feathers on all four limbs, while its skeleton is essentially that of a small dromaeosaur. Archaeopteryx itself did not belong to the lineage from which modern birds (Neornithes) have evolved, but was a member of the now-extinct Enantiornithes. A reconstruction of the avian family tree would show a many-branched bush, not a single straight trunk.
While it was originally described as simply a feathered reptile, Archaeopteryx has long been regarded as a transitional form between birds and reptiles, making it one of the most important fossils ever discovered. Until relatively recently it was also the earliest known bird. Lately, scientists have realised that Archaeopteryx bears even more resemblance to the Maniraptora, a group of dinosaurs that includes the infamous velociraptors of "Jurassic Park", than to modern birds. Thus the Archaeopteryx provides a strong phylogenetic link between the two groups. Fossil birds have been discovered in China that are even older than Archaeopteryx, and other discoveries of feathered dinosaurs support the theory that theropods evolved feathers for insulation and thermo-regulation before birds used them for flight. This is an example of an exaptation.
Closer examination of the early history of birds provides a good example of the concept that evolution is neither linear nor progressive. The bird lineage is messy, with a variety of “experimental” forms appearing. Not all achieved powered flight, and some looked quite unlike modern birds e.g. Microraptor gui, which appears to have been a gliding animal and had asymmetric flight feathers on all four limbs, while its skeleton is essentially that of a small dromaeosaur. Archaeopteryx itself did not belong to the lineage from which modern birds (Neornithes) have evolved, but was a member of the now-extinct Enantiornithes. A reconstruction of the avian family tree would show a many-branched bush, not a single straight trunk.
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