(Ancient wing). Archaeopteryx is sometimes
called Urvogel which is German for ‘first bird’, but this is not an
alternate binomial name.
Named By: Christian Erich Hermann von Meyer - 1861.
Synonyms: Archaeornis, Griphosaurus, Griphornis, Jurapteryx, Pterodactylus crassipes, Rhamphorhynchus crassipes, Scaphognathus crassipes. Possibly also Wellnhoferia.
Classification: Chordata, Aves, Archaeopterygidae.
Species: A. lithographica (type). A. albersdoerferi. Additional species previously established include Archaeopteryx bavarica, Archaeopteryx owenii, Archaeopteryx macrura, Archaeopteryx recurva and Archaeopteryx siemensii, but there validity is not in agreement by all. See main text for details.
Size: Up to about 50 centimetres long.
Known locations: Various locations in Germany.
Time period: Tithonian of the Jurassic.
Fossil representation: Many specimens, some almost complete and preserved flat on a slab, some just of feathers.
controversy and the facts
Very few genera have shaken both the worlds of palaeontology and evolutionary theory as much as Archaeopteryx. The story begins in the limestone quarries near Solnhofen, Germany. The limestone here is the result of geologic processes changing deposits of aquatic sediment all the way back to the late Jurassic. Here the fossils of all kinds of creatures from ammonites to fish to even pterosaurs have been found, but it was one fossil in particular that caught the eye of Christian von Meyer; the fossil of a feather.
The fossil of a feather by itself might not sound interesting, but you need to realise that this discovery took place in 1861 when the scientific field of palaeontology was still in its infancy. The idea of extinct animals that roamed the land before man had only been properly realised in the early nineteenth century. The first pterosaur Pterodactylus had been named in 1809, the first dinosaur Megalosaurus in 1824 and Charles Darwin’s On the Origin of Species had only been published a couple of years earlier in 1859. The truly radical thing about the discovery of this single feather impression was that it came from a Jurassic aged deposit, a fact that shook the then and relatively new theory that birds did not appear until the Eocene after the dinosaurs had disappeared.
Christian von Meyer named a new genus in 1861, Archaeopteryx lithographica, with the feather as holotype, but as you might expect naming a new genus of bird by only a feather means that it is hard to accurately reconstruct the animal. But in the same year a new fossil was found at Solnhofen, and this time it was a partial skeleton. Now known as the London Specimen (or BMNH 37001 for its catalogue number), this fossil was first given to a physician named Karl Häberlein who went on to sell it to the National History Museum of London for £700, a sum of money that back then was worth far more than it is today. The London Specimen was described 1863 by Richard Owen, who was one of the chief naturalists in Britain at the time. Owen recognised that the skeleton probably belonged to the same kind of creature as the feather, but also recognised the difficulty in assigning skeletal remains to only a feather. So with this in mind Owen created a second species, A. macrura, though this would be the start of further controversy discussed more fully in the next section.
Missing only the head and neck, the London Specimen gave the first true glimpse at what Archaeopteryx looked like. However, the skeletal remains were not those of a bird that we would recognise today. The most obvious difference was the tail, long and lizard-like, but there were also two free claws on each wing. This came as a bit of a shock to those who were expecting Archaeopteryx to actually look more like a bird, but for evolutionists the find was a dream come true. Evolutionary theory back in the nineteenth century was still a very new idea, one that many naturalists considered to be complete nonsense. To the evolutionists however, the London Specimen was proof that the birds did not just magically appear and that their origins could be found within the reptiles.
Around 1874/1875 a new specimen of Archaeopteryx was found by a farmer name Jakob Niemeyer. Niemeyer sold this to an inn keeper named Johann Dörr in 1876 before it was later sold to Ernst Otto Häberlein. The specimen was then later sold at auction to Ernst Werner von Siemens and donated to the Humboldt Museum für Naturkunde. Today known as the Berlin Specimen (HMN 1880), this was the first specimen to include the head, and again things were not as expected. The skull seen here was also more reptile-like and the jaws still had conical teeth within them.
After this time many other specimens began to be discovered, and these discoveries have continued into the twenty-first century. The Maxberg Specimen (S5), an almost complete skeleton lacking only the head and tail was discovered in 1956 and described in 1959. In 1970 it was discovered the Christian von Meyer, the man who named the first feather in 1861, had actually handled and named the first known specimen of Archaeopteryx in 1857, but had mistakenly named it as the pterosaurs Rhamphorhynchus crassipes and Pterodactylus crassipes Described from partial post cranial bones, this individual is now known as both the Haarlem Specimen and the Teyler Specimen (TM 6428).
The smallest individual was found in 1951 and named in 1974 is the Eichstätt Specimen (JM 2257). Originally thought to be a specimen of the dinosaur Compsognathus, the Solnhofen Specimen (BSP 1999) was named in 1988. The Munich Specimen (S6) was described in 1993 and represents an almost complete specimen missing only the anterior (front) portion of its face. The Daiting Specimen was discovered in 1990 and although fragmentary, is known from slightly younger deposits than the Solnhofen specimens. The Bürgermeister-Müller Specimen is of a single wing and was discovered in 2000 and described in 2004. After this the Thermopolis Specimen was described in 2005, and is known by an almost complete skeleton that more clearly displays theropod dinosaurian features. An additional specimen of what is thought to be Archaeopteryx was discovered in 2011, but at the time of writing this has not been made available for scientific description.
While all of these new specimens were being found, some palaeontologists were working upon piecing together the wider evolutionary link between birds and reptiles, although during this time the link was narrowed down to the maniraptorian theropod dinosaurs. Other primitive birds were being found but to further confuse things, the existence of some dinosaurs that had feathers covering their bodies became established fact. The exact line between bird-like dinosaurs and dinosaur-like birds is blurry to say the least, and opinions on where to draw it can vary greatly amongst different palaeontologists. In the past, Archaeopteryx has been considered to be both a dinosaur and a bird, but most thinking by the early twenty-first century places it as a bird. In a wider sense Archaeopteryx is more universally treated as a transitional form that shows a stage in the evolutionary change between dinosaurs and birds.
Archaeopteryx has been accused of not being a transitional form and even not being real upon numerous occasions. These accusations however have always come from people who do not know what they are talking about with very little to no understanding of fossilisation processes as well as wider discoveries in other areas. A lot of people who have accused Archaeopteryx of being fake are also not even aware that the genus is known by more than one specimen, or at least choose not to tell people that they are trying to convince. Most of these claims go back into the nineteenth and twentieth centuries, but the rise of personal blogging during the early twenty-first century has meant that many of these old and since long discredited theories are now being put forward as ‘fact’ again.
Great care should be taken not to confuse Archaeopteryx with ‘Archaeoraptor’, the name of an actual fake composite fossil that came to light in 1999.
Which species of Archaeopteryx
This is a good question but one that has no universally accepted answer at this time. There have been many names and species put forward to represent specimens of Archaeopteryx, but many of these to begin with were either unnecessary or contained spelling/grammatical errors that had to be later altered.
The first complication comes from a spat between Christian von Meyer and another German palaeontologist named Johann Andreas Wagner who proposed the alternative Griphosaurus in 1862. Another 1862 alternative put forward by Woodward was Griphornis, so now there were three names for one animal. The Pterodactylus crassipes confusion was still not known at the time, but if it were it would have had no more bearing than the type species being changed to A. crassipes because Archaeopteryx obviously was not a pterosaur.
Things began to be cleared up a little in 1951 when Gavin de Beer treated the London Specimen, previously named A. macrura, as the holotype of the genus because this was at least a partial skeleton rather than just a feather. The type species of A. lithographica had already been established for the original feather description, so A. macrura became a synonym to A. lithographica. This was backed up in 1960 by another named Swinton. The ICZN, the international scientific body that governs the naming of animals not only agreed with de Beer, they also suppressed the earlier alternative names for Archaeopteryx so that they were then known as synonyms for the clarity of later generations, listed but no longer used.
This meant that the type species of Archaeopteryx was now represented by the original feather of 1861 and the first known skeletal remains of 1863, but another problem was about to raise its head. Closer study of the feather with the later referred remains resulted in the observation that the original feather was not a perfect match, and may have actually come from a different bird, or perhaps even a feathered theropod dinosaur. Apart from possibly being different, in modern palaeontology a single feather would be considered to be too indeterminate to describe a new genus, and beginning in 2007 this was pointed out by two groups of scientists that petitioned the ICZN to recognise the London Specimen remains instead of the feather. Although the London Specimen remains had been proposed in 1951 by de Beer, and added to the type species, they could never become the holotype because the feather was already listed. Instead in 2011 the London Specimen became the neotype, the term for a fossil specimen that is added to a genus after the holotype, but becomes the set of remains that future discoveries are referred to instead of the holotype. Today the original feather is considered just that, a feather of indeterminate origin, probably not Archaeopteryx.
The type species of Archaeopteryx with the London Specimen designated as neotype is the only species that has been universally accepted as valid. The other specimens of Archaeopteryx have all been credited as different species due to differences in things such as form and size, but a few of these species have been questioned. Some of the specimens of Archaeopteryx can form to create small groups. The London (A. lithographica), Berlin (A. siemensii) and Haarlem specimens are fairly similar to one another. But the Munich (A. bavarica), Eichstätt (A. recurva), Thermopolis (A. siemensii) and Solnhofen specimens are noted as having more slender snouts, forward pointing teeth, possible presence of sternums and being either smaller of larger than the London, Berlin and Haarlem specimens. A. recurva was also originally described as a different genus, Jurapteryx, while the Solhofen specimen is particularly large and was renamed as a new genus, Wellnhoferia, by Andrzej Elzanowski in 2001, though this has had a mixed reception with a 2003 study by Senter and Robins supporting this, but a 2007 study by Mayr et al. finding Wellnhoferia to still be specimen of Archaeopteryx lithographica.
One argument that may one day unify all of the specimens under Archaeopteryx is that they simply represent different growth stages throughout the lifespan of Archaeopteryx. The precedent for this has actually already been set in other genera’s of prehistoric creatures, the pterosaur genera Pterodactylus and Rhamphorhynchus being two good examples. Both of these genera were once each known by multiple species, and while some of these species were later named as new genera, many of them were realised to be just juveniles and subadults that had differing physical proportions to adults. In time, more specimens of Archaeopteryx will likely be discovered given that so many are already known, and these together may conclusively prove one way or another which theory or indeed a measure of both is more correct.
By the early twenty-first century Archaeopteryx is most widely considered to be a bird, but one with many dinosaur-like characteristics. Quite surprisingly, Archaeopteryx has been considered to have been similar to a modern bird called the Hoatzin (Opisthocomus hoazin) which is native to upper South America. Although not a perfect match, juvenile Hoatzin possess claws that enable them to climb branches until their wings are strong and developed enough to enable flight.
Being popularly defined as a bird. the obvious question would be could Archaeopteryx fly? It would seem that the answer depends on whether you mean powered flight or just gliding, but first we need to consider what is necessary to enable flight in the first place. First and foremost would be the feathers since birds don’t rely upon extended flaps of skin or membranes like other flying/gliding vertebrates. Birds require special kinds of feathers which as you might guess are called ‘flight feathers’, and these are found on the rear edges of the wings for primary lift, and the tail for steering. Aside from lift these feathers can also be angled by wing and tail movements to alter things like drag to control flying speed in a similar fashion to the flaps on the wing of an aeroplane (in fact engineers copied this from watching birds).
A flight feather is generally much longer than it is wide and is reinforced by a rigid spine that runs down the length of the feather so that it keeps straight and does not bend with the up and down movements of the wing. These kinds of feathers are like those on the wings of Archaeopteryx, which means that the genus has at least one of the things necessary for flight. The flight feathers on Archaeopteryx though are not exactly like the feathers of modern birds because they lack things called barbicles. Barbicles are like tiny hooks on the fronds of the feather that hook around the fronds of the feather they are next to, the barbicles of that feather then hook onto the next and so on. Barbicles are simple features but they allow all of the feathers on the wing to act as one large complete unit rather than lots of smaller individual ones. This reinforces the wing, making the feathers not only stronger but capable of providing more lift. The fact that Archaeopteryx lacked these barbicles does not mean that they could not fly, just that Archaeopteryx were not yet evolved into modern forms, something we already knew. As time went on and barbicles began to appear, they became more standardised, but the principal here is that they had to evolve somewhere, and it seems that it was not with Archaeopteryx, but possibly a later and more advanced form.
The next thing to consider is was Archaeopteryx capable of producing a ‘flight stroke’? A flight stroke is a movement of the wings that allows for the production of lift to get the body into the air, and then repeating that stroke or a variation of to stay in the air. The key to producing a flight stroke is to have flexibility, ideally to be able to move the wings (which remember are really just modified arms) above the back for an extended down stroke which can produce a greater amount of lift. The analysis of Archaeopteryx skeletons however is not promising. In modern birds the shoulder is aligned dorsally (to the spine) whereas in Archaeopteryx the shoulder has a sideways alignment. This is a throwback to more dinosaurian ancestors, but it terms of flight it means that the wings of Archaeopteryx did not have the same range of motion as modern birds. This means that at best if Archaeopteryx could fly, it could not fly as well as modern birds.
A reduced range of motion does not mean that Archaeopteryx could not take to the air. By holding the arms out to the sides it is conceivable that Archaeopteryx could be gliders since the developed flight feathers of the wings would have still acted to reduce the rate of descent. The wings of Archaeopteryx were fairly short and rounded on the ends, similar to birds that live in woodland environments today. Assuming Archaeopteryx lived in these environments, and it seems quite possible, then they may have climbed trees with the claws on their wings for either food or shelter, and then jumped and glided to the next tree along. But so far we have only looked at two areas that are necessary for flight, and from here we need to go from beyond just wings and feathers.
Powered flight by flapping wings requires the development of muscles capable of maintaining the same repetitive movement for a long time, and these muscles in turn require skeletal attachments to secure them in place. The muscles for flight in modern birds are concentrated on the breast (analogous to your pectoral muscles) which is why birds tend to have really deep and round chests. These large muscles require an equally large attachment, and in this case it’s the sternum, the solid bone that connects the ribs together. If you have ever carved a chicken or a turkey, then you will know that as you cut into the breast you have to cut around a large flat bone that rises up from the ribs; this is the sternum.
Evidence for strongly developed flight muscles is mixed between specimens of Archaeopteryx, but one thing for certain is that there is no enlarged bony sternum like that seen in modern birds. Some specimens currently assigned to Archaeopteryx though show the possible presence of a cartilaginous sternum which would have functioned in the same way as a bony one. Cartilage is a tissue that can be rigid in life, but rarely survives long enough to fossilise except in cases where the cartilage has become ossified (turned to bone) before death. Also going back to carving chickens, while the main sternum is bone, there is always a cartilaginous extension to this bone. If Archaeopteryx possessed and enlarged cartilaginous sternum, then they may have been able to maintain a modified flight stroke that although not as efficient as a modern bird, may have been able to allow for sustained powered flapping flight. Otherwise all Archaeopteryx would be able to do was manage a few flaps of the wings before becoming tied and having to stop, though this in itself might have been enough to allow an individual to get airborne so that it could then glide the rest of the way. It is also conceivable that from such a point as this, later decedents that modified skeletons and musculatures could eventually extend the length of time that they could keep flapping until they evolved into birds more similar in form to what we know today.
An additional bit of support for flight in Archaeopteryx actually comes from analysis of the brain, specifically its size. Two studies by Witmer and Alonso et al., and both in 2004 showed that relative to the size of the body, the brain of Archaeopteryx was actually quite large. Reconstructions of the brain also indicated that the area dedicated to vision accounted for one third of the total brain size, while the areas of muscle co-ordination and hearing are also well developed. The inner ear of Archaeopteryx is also more like that of modern birds that non-avian dinosaurs. What this all means is that the brain of Archaeopteryx was already hardwired with all of the necessary features for controlling wings and moving in a three dimensional environment like you would if you were flying.
When you piece together the brain, the skeletal structure, the musculature and feathers of Archaeopteryx, you are left with a creature that could definitely glide, and was perhaps capable of limited powered flapping flight. In this respect Archaeopteryx might not have been a graceful flyer, but it possessed everything necessary for further developments that appeared in later descendants. It should always be remembered though that Archaeopteryx is a transitional form, if it were better developed for flight it probably would not be so valuable for our understanding in bird evolution.
What did Archaeopteryx
like, and where did it live?
As already mentioned, Archaeopteryx had a number of dinosaur-like features such as the arrangement of the shoulders, and the long tail. The tail in modern birds is used to help with steering and slowing down when descending, but the tail of Archaeopteryx might not have been that useful. The tail could have feasibly been used to steer with minute adjustments, though its primary function may have been that of a counterbalance while an Archaeopteryx was on the ground, just like with the theropod dinosaur ancestors.
The flight feathers of the wings have already been mentioned, but smaller downy feathers also covered the main body. So far no specimen has shown the presence of feathers on either the head or the neck, but there is actually uncertainty as to whether this was actually the case in life. Up to 2013 all known specimens of Archaeopteryx were found in marine sediments, which means that they were exposed to water before being buried in sediment. Outlined in a 2012 study by Reisdorf and Wuttke, many dinosaurs are preserved in a characteristic ‘death pose’ where the muscles and tendons of the neck stiffen after death causing the head and neck to arc back, and Archaeopteryx would have still been dinosaur-like enough for this to happen. This meant that as a body floated on the surface, the neck and head would be the most underwater, causing the skin to soften and the feathers to come loose giving the appearance of being bald. Another study in 2002 by Elzanowski also suggested that the feathers of the head and neck may have been worked loose as the body rubbed against the sea bed before being buried.
The colour of Archaeopteryx is not known for certain, but a 2011 study by Carney et al. has given us a glimpse at what Archaeopteryx might have been like. In this study a covert feather (a feather that covers and protects others) from the wing was placed under an electron microscope where melanosomes were discovered. A melanosome is basically a pigment, and when the melanosomes in the specimen were compared next to those of 87 known bird species, the highest likelihood was that in life the feather would have been black. This means that the covert feathers on the wings of Archaeopteryx were possibly all black, but it is still unknown what colour the other feathers were. They may of course have been black as well, but we still do not know for certain.
Some feathered dinosaurs and potential bird ancestors are better understood. In the genus Anchiornis, most of the feathers were black, but white stripes ran down the wings, while red speckling was on the face and an orange Mohawk style crown of feathers was on top of the head. The dinosaur genus Sinosauropteryx is known to have had bands of deep brown and white running all the way down its tail. We still do not know what the remainder of Archaeopteryx looked like, but looking at other genera tells us that we should expect anything.
Archaeopteryx is now known to have had three clawed fingers on each wing, and as mentioned above, these may have been used to climb trees in a similar way to juvenile Hoatzin. In Archaeopteryx though there is no indication that they were lost in adulthood, and were instead an indication of dinosaurian heritage. The study of the Thermopolis specimen (WDC CSG 100) in 2005 also revealed that Archaeopteryx lacked a reversed toe, which means that Archaeopteryx could not grip hold of perches like modern birds. A hyperextensible second toe was also found to be present, though this feature was actually first conceived by Gregory S. Paul in 1988. The hyperextensible second toe with claw and the three claws of the wings may indicate that Archaeopteryx were ‘trunk-climbers’, climbing to the trees instead of flying to them, but possibly jumping off and gliding from tree to tree. Again this hints at the evolution in flight for birds in that adaptations for gliding from tree to tree leads to further adaptations for extended gliding ranges until full powered flapping flight developed.
This leads us to the ecosystems that Archaeopteryx lived in. By 2013 all known specimens of Archaeopteryx are from various locations in Germany with the specimens from the Solnhofen limestone deposits being the most famous. Central Europe during the Jurassic was actually a series of islands surrounded by shallow seas and lagoons. Rhamphorhyncoid pterosaurs were very common, but more advanced pterodactyloid pterosaurs were also present. Many of the islands seemed to have been quite arid, with some growths of cycads and conifers. There were not a lot of opportunities for Archaeopteryx to climb up high, but then they might not have had to, the island plants might have been large enough to provide cover and possibly be used as gliding platforms. We still have much to learn about these ancient island ecosystems, and the picture of their reconstructions might change dramatically with future discoveries.
The structure of the foot being more suited to ground locomotion than grasping coupled with the still relatively long legs have been taken by some as signs that Archaeopteryx may have been cursorial, which means that they spent their time on the ground instead of in the air. It may be that Archaeopteryx climbed up into shrubs and small trees for night time protection from potential predators. Analysis of the scleral rings of Archaeopteryx shows that they match diurnal birds, which means that Archaeopteryx would have only been active during the day time only.
Archaeopteryx seems to have been fairly slow growing creatures that took two years and eight months to grow to adult size. This is based upon a 2009 study by Erickson et al. which studied the growth stages of the bones which also found that other primitive birds such as Jeholornis and Sapeornis also grew slowly, though others such as Confuciusornis grew comparatively quickly. It may be that the slow growth of Archaeopteryx may be a primitive trait that was sped up in later bird forms as their metabolisms altered.
So was Archaeopteryx
and ancestor of birds?
Short answer; probably not. The fossil record is always only ever going to be a portion of what once lived, and will in that respect always be incomplete. There are already other genera’s of animals similar to Archaeopteryx that fall on either side of the dinosaur/bird definition line that may be older than Archaeopteryx. As always in palaeontology, it only takes one new fossil discovery to trigger a change in an accepted theory, and with fossil genera being discovered and named at a faster rate from so many more locations around the world than ever before, this is more and more likely to happen.
We also cannot prove that Archaeopteryx was ‘the’ definitive ancestor of modern birds, it is more likely just one of many forms that existed during the late Jurassic, and if the development of birds can be narrowed down to just one genus, then any one of those, including Archaeopteryx could be the origin of the genetic line to modern birds. But you also need to be certain about how you define ancestor. Do you use the first bird, the first theropod dinosaur, reptile, amphibian, vertebrate fish or single celled organism? Any one of them and an almost uncountable number more could be defined as the ancestors of birds, it’s just down to where you choose to begin.
This is why palaeontologists tend to prefer to take the safer option of regarding Archaeopteryx as a representative of the form of an ancestral candidate, rather than the actual ancestor, it allows for the genus to be studied as it should, without requiring too much of a re-write for later when new discoveries are made.
- On the Archaeopteryx of Von Meyer, with a description of the fossil remains of a long-tailed species from the lithographic stone of Solnhofen - Richard Owen - 1863.
- On the animals which are most nearly intermediate between birds and reptiles - Thomas Henry Huxley - 1868.
- Remarks upon Archaeopteryx lithographica - Thomas Henry Huxley - 1868.
- Further evidence of the affinity between the dinosaurian reptiles and birds - Thomas Henry Huxley - 1870.
- Archaeopteryx and the origin of birds - J. H. Ostrom - 1976.
- Feathers of Archaeopteryx: Asymmetric vanes indicate aerodynamic function - A. Feduccia & H. B. Tordoff - 1979.
- Flight capability and the pectoral girdle of Archaeopteryx - S. L. Olson & A. Feduccia - 1979.
- What size was Archaeopteryx? - D. W. Yalden - 1984.
- Archaeopteryx Relationship With Modern Birds - Thomas Holtz Jr - 1995.
- A new genus and species for the largest specimen of Archaeopteryx - Andrzej Elzanowski - 2001.
- Body plumage in Archaeopteryx: a review, and new evidence from the Berlin specimen - P. Christensen & N. Bonde - 2004.
- Structure and function of hindlimb feathers in Archaeopteryx lithographica - N. Longrich - 2006.
- Was Dinosaurian Physiology Inherited by Birds? Reconciling Slow Growth in Archaeopteryx - Gregory M. Erickson, Oliver W. M. Rauhut, Zhonge Zhou, Alan H. Turner, Brian D. Inouye, Dongyu Hu, Mark A. Norell - 2009.
- Narrow Primary Feather Rachises in Confuciusornis and Archaeopteryx Suggest Poor Flight Ability. - Science. 328 (5980): 887–889. - Robert L. Nudds & Gareth J. Dyke - 2010.
- Archaeopteryx was robed in black - Brian Switek - 2011.
- New evidence on the colour and nature of the isolated Archaeopteryx feather - R. Carney, Jakob Vinther, Matthew D. Shawkey, Liliana d'Alba & Jörg Ackermann - 2012.
- Re-evaluating Moodie's Opisthotonic-Posture Hypothesis in fossil vertebrates. Part I: Reptiles - The taphonomy of the bipedal dinosaurs Compsognathus longipes and Juravenator starki from the Solnhofen Archipelago (Jurassic, Germany) - A. G. Reisdorf & M. Wuttke - 2012.
- Synchrotron-based chemical imaging reveals plumage patterns in a 150 million year old early bird - Phillip L. Manning, Nicholas P. Edwards, Roy A. Wogelius, Uwe Bergmann, Holly E. Barden, Peter L. Larson, Daniela Schwarz-Wings, Victoria M. Egerton et al. - 2013.
- Archaeopteryx in 4D. - Journal of Vertebrate Paleontology. 103. - Ryan Carney, Julia Molnar, Earl Updike, William Brown, Jessie Jackson, Matthew Shawkey, Johan Lindgren, Peter Sjövall, Peter Falkingham & Jacques Gauthier - 2014.
- Wing bone geometry reveals active flight in Archaeopteryx. - Nature Communications. 9 (1): 923. - Dennis F. A. E. Voeten, Jorge Cubo, Emmanuel de Margerie, Martin Röper, Vincent Beyrand, Stanislav Bureš, Paul Tafforeau & Sophie Sanchez - 2018.