Abstract from Dominguez Alonso et al. (2004):

Archaeopteryx, the earliest known flying bird (avialan) from the Late Jurassic period, exhibits many shared primitive characters with more basal coelurosaurian dinosaurs (the clade including all theropods more bird-like than Allosaurus), such as teeth, a long bony tail and pinnate feathers. However, Archaeopteryx possessed asymmetrical flight feathers on its wings and tail, together with a wing feather arrangement shared with modern birds. This suggests some degree of powered flight capability but, until now, little was understood about the extent to which its brain and special senses were adapted for flight. We investigated this problem by computed tomography scanning and three-dimensional reconstruction of the braincase of the London specimen of Archaeopteryx. Here we show the reconstruction of the braincase from which we derived endocasts of the brain and inner ear. These suggest that Archaeopteryx closely resembled modern birds in the dominance of the sense of vision and in the possession of expanded auditory and spatial sensory perception in the ear. We conclude that Archaeopteryx had acquired the derived neurological and structural adaptations necessary for flight. An enlarged forebrain suggests that it had also developed enhanced somatosensory integration with these special senses demanded by a lifestyle involving flying ability.

Excerpted by permission from Chapter 10 of The Mistaken Extinction, by Lowell Dingus and Timothy Rowe, New York, W. H. Freeman and Co., 1998, 332pp. (full text of Ch. 10 available as pdf)

When The Origin of Species hit the news stands, one of the most glaring gaps in the fossil record was the early history of birds. Birds are highly distinctive. Nobody would mistake a bird for any other animal. But in the mid-19th century their fossil record appeared to begin abruptly during the Tertiary. Some naturalists argued that some three-toed Mesozoic trackways were made by more ancient birds. But some of these were much too large for known birds to make, so most naturalists agreed with Richard Owen that these "Foot-prints alone....are insufficient to support the inference of the possession of the highly developed organization of a bird of flight by the creatures which have left them."

Two years after publishing On The Origin of Species, Darwin was under attack in both the scientific and popular press. And then, Archaeopteryx was discovered. It was an instant scientific sensation as both evolutionists and anti-evolutionists claimed it as their prize, and used it to open a new battlefront in the escalating war over evolution.

Was Archaeopteryx a feathered pterosaur or some other kind of feathered reptile? Was it really a reptile-like bird--a transitional fossil like Darwin's theory predicted? Grasping instantly its pivotal importance to the debate over evolution, Owen snatched up the specimen for the British Museum. It arrived in London in 1862.

Now, with both the specimen and one of the world's premiere skeleton collections to compare it with, Owen wasted little time in responding to the speculations of evolutionists, who had never even seen it. In 1863 he published a thorough description, masterfully crafted to rebut the publicity Archaeopteryx had already received as a potential link between birds and reptiles.

Along with its size, proportions, and feathers, the skeleton showed many other resemblances to modern birds, including a wishbone or furcula. Among living species, the furcula is known only in birds and had never before been discovered in a fossil reptile. It represents a fusion of the right and left collar bones or clavicles. As a young bird embryo develops, the collar bones form separately, reflecting the condition found in most adult tetrapods. But by hatching time, the avian clavicles fuse to form the highly characteristic U-shaped furcula. Once fused, the wishbone acts as a spring to help power the flight stroke and may also facilitate breathing during flight. Because the furcula is absent in flightless birds like ostriches, some naturalists have argued that it must be an essential component of flight. Who else but a fully volant bird would have a furcula?

Also bird-like are the shoulder and arm of Archaeopteryx. The wrist has the half-moon-shaped semilunate carpal, just like Deinonychus. The hand proportions, the three fingers, and the relationships of the wing feathers to the fingers are also bird-like. Owen went to great length to show that pterosaur wings found around Solnhofen are different from Archaeopteryx. The pterosaur wing's membrane of skin often forms an impression on the lithographic stone. The membrane supported by the fourth finger, a digit that is entirely absent in Archaeopteryx and adult living birds. In Owen's view, Archaeopteryx fell squarely in the Class Aves; it was not transitional between birds and reptiles.

But to an equally famous evolutionist like Thomas Huxley, Archaeopteryx looked like a perfect transition between birds and reptiles, suggesting that one Class could "transmute" into another. Unlike Owen, Huxley compared Archaeopteryx to fossil reptiles as well as to living birds, noting that today "no two groups of beings can appear to be more entirely dissimilar than reptiles and birds. Placed side by side, a Humming-bird and a Tortoise, an Ostrich and a Crocodile offer the strongest contrast, and a Stork seems to have little but animality in common with the Snake it swallows.” He then asked, “How far can this gap be filled up by the fossil records of the life of past ages? This question resolves itself into two: - 1. Are any fossil birds more reptilian than any of those now living? 2. Are any fossil reptiles more bird-like than living reptiles?”

Huxley answered both in the affirmative. For a fossil bird more reptilian than any modern bird, Huxley of course pointed to Archaeopteryx. Like reptiles, the digits of the hand are unfused, and two of them have claws, whereas in living birds there is never more than one claw. The long tail made up of separate vertebrae is also reptilian. Owen's objection that these were merely embryonic and transitory structures notwithstanding, Huxley concluded “it is a matter of fact that, in certain particulars, the oldest known bird does exhibit a closer approximation to reptilian structure than any modern bird.”

Huxley even inferred that the physiology of dinosaurs might have achieved a level found in modern birds. "Birds have hot blood, a muscular valve in the right ventricle, a single aortic arch, and remarkably modified respiratory organs; but it is, to say the least, highly probable that the Pterosauria, if not the Dinosauria, shared some of these characters with them." Huxley and Owen had both seen bird-like features in extinct dinosaurs.

Photographs of BMNH 37001:

This braincase is taken from the London specimen of Archaeopteryx (BMNH 37001). It was collected from the Solnhofen limeston (Tithonian - late Jurassic in age) in Bavaria, Germany in 1861. This specimen was scanned for Dr. Angela Milner of the Department of Palaeontology, The Natural History Museum (London), John Cookson of the University of Hertfordshire at Hatfield, and Dr. Timothy Rowe of The University of Texas at Austin.

Additional information on the history of Archaeopteryx:
Excerpted by permission from Chapter 9 of The Mistaken Extinction, by Lowell Dingus and Timothy Rowe, New York, W. H. Freeman and Co., 1998, 332pp. (full text of Ch. 9 available as pdf)

Archaeopteryx: the oldest known bird
To museum curators the name Archaeopteryx rings like that of Rembrandt, Stradivarius, or Michelangelo. Archaeopteryx is known from the world's most celebrated, controversial, valuable, and rare fossils. The importance of Archaeopteryx rests upon its antiquity of 150 million years, the transitional nature of its skeleton, and the timing of its discovery, which occurred only two years after Darwin's On the Origin of Species was published. The peerless preservation of the specimens, one a single, perfect feather, has further enhanced their importance and mystique.

In addition to the exquisite but uninformative feather, only seven specimens of Archaeopteryx are known. Each preserves some or all of the skeleton, along with feather impressions that are more or less obvious. Each is named according to its proprietor or place of discovery. The first skeleton to be discovered is now in England, the London Archaeopteryx, arriving in 1862 to become the center of historic debates about evolution that erupted into scientific and public forums with publication of On the Origin of Species. Consequently, it is considered a "Crown Jewel." Four specimens are in Germany and one is in the Netherlands, where they are similarly acclaimed. The seventh specimen has vanished.

The London Specimen
The first Archaeopteryx specimen recognized to be a bird was the perfectly preserved impression of a single feather found in 1860. Early the next year, Dr. Hermann von Meyer, a preeminent paleontologist from the Senckenberg Natural History Museum, published a short report, announcing the unprecedented discovery of a Mesozoic bird. He quickly followed with another publication that included an illustration--a lithograph--showing the unmistakable resemblance of this ancient fossil to the flight feathers of modern birds. His announcements raised a rumble of controversy. The authenticity and age of the fossil were immediately questioned. But a few months later the discovery of the first skeleton temporarily put to rest the question of authenticity. Most of the skeleton was preserved, along with impressions of the feathers radiating fanwise from each of the forelimbs and along each side of the long bony tail. In that same year in which he had announced the feather, von Meyer published a two-page announcement of the first skeleton of a Mesozoic bird. For this specimen, he coined the name Archaeopteryx lithographica, the root "archaios" meaning ancient and "pteryx" meaning wing. The species name, lithographica, refers to the lithographic limestone in which it was buried and the state of its preservation. By the end of the year, von Meyer's short announcements had grabbed the attention of the scientific community.

The hype surrounding this skeleton was promoted by its first owner, Dr. Karl Häberlein, a medical officer for the district of Pappenheim. Häberlein was a collector who accepted the fossil in payment for his medical services. He appreciated the potential value of such an ancient and well preserved bird. He let several people inspect it, but no one could make drawings or take photographs. One visitor did make a drawing from memory shortly after viewing the specimen, fueling speculation about the specimen's importance and raising its value. Häberlein offered the specimen for sale at, probably, the highest price yet asked for a fossil, some £750. A scramble for the fossil bird ensued. The German court tried to secure it for the State Collection in Munich, but the British Museum succeeded in negotiating Häberlein's unprecedented final price of £700. The Museum's payment for this and other fossils in Häberlein's collection had to be spread across two fiscal years. The slab and counter slab became known as the London Archaeopteryx.

A century later, Dr. Alan Charig was the Curator at the British Museum in charge of the London Archaeopteryx. Charig regarded it as the most valuable fossil in both the museum and the world. Although the museum usually displays real specimens, only a cast of Archaeopteryx is exhibited for safety, and the museum avoids publicly divulging exactly where the original is stored in the museum.

The braincase of BMNH 37001 was scanned at the University of Texas at Austin’s High-Resolution X-ray CT Facility on 24-25 June 2002 by Matthew Colbert and Richard Ketcham. The specimen was scanned twice, at low and high X-ray energies (120 kV and 180 kV, respectively); the former accentuates compositional differences, whereas the latter is more noise-free and less prone to beam-hardening artefacts and interference from high-attenuation phases. The resulting serial sections were saved as two independent series of 1313 16-bit TIFF files. The specimen was scanned along the coronal axis with a slice thickness and inter-slice spacing 0.0230 mm; field of reconstruction 21.0 mm.

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Animations of three-dimensional reconstructions of the braincase of Archaeopteryx:

Yaw Spin (2mb)	Roll Spin (3.7mb)	Pitch Spin (3.5mb)

Animations of endocasts of the cranial cavity and inner ear of Archaeopteryx:

Cranial Cavity (2.5mb)	Inner Ear (3.7mb)

Images of the reconstructed braincase and endocasts of Archaeopteryx.
Taken from Dominguez Alonso et al. (2004):

Braincase of the holotype of Archaeopteryx lithographica (BMNH 37001).

Right quadrate of BMNH 37001 in medial view.

Restored endocast of the brain of BMNH 37001 rendered as a shell. Elements from the left side are reversed.

Right inner ear of BMNH 37001. 3D model based on X-ray CT.

Animation (6.4mb) with before (left) and after (right) images showing ring correction algorithm developed for this dataset by Richard Ketcham.

The first specimen of Archaeopteryx found in Solnhofen, Germany in 1861.