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The Mona Lisa of Ornithology
The Mona Lisa of Ornithology:
a short history of Archaeopteryx lithographica
Click here for an easy-to-read PDF file
Article by Erwin D. Riedner
Original Art by Julie Zickefoose
I. The Death of a Bird
A very, very long time ago, during an age so remotely gone from us as to be counted in millions of years past, the period
classified as the Jurassic, a fascinating and beautiful bird died. Although the cause or causes of the feathered creature’s
death are unknown and doubtless will ever be, its final resting place has been uncovered. Such a find is not ordinarily the
case with light-boned and fragile beings such as birds. Birds perish in enormous numbers from starvation, cold, exhaustion,
accident or disease, and often become meals for stalking or soaring predators. To know the location of any among their last
stops is considered most fortuitous.
In addition to the location of bird’s burial, we possess a few other facts about the little vertebrate’s demise. At its end it was
not dismembered or eaten by another animal. Rather, it died whole after having somehow flapped, run, or perhaps even
having been blown by storms into the waters of an ancient and hyper-saline tropical lagoon. As it succumbed, its intact body
rapidly sank, bones and feathers neither disintegrating nor scattering during the descent to the lagoon’s anoxic bottom.
There the corpse came to rest in an accumulating, calcareous muck slowly filling the briny depths, to be interred within a
viscous, ever-deepening tomb.
In the larger scheme of things the passing of one primitive bird would hardly seem a major historical event considering the
vast time scale we’re dealing with. Others of its kith and kin soon occupied its place in the species’ preferred niches. Life
continued and expanded. New days dawned. Time moved on. Deep time. Monumental time. Time of such an extent that the
course of its inexorable flow saw whole mountain ranges grow and weather away, saw floating continents reorient the
world, and panoplies of new life forms arise and flourish while others faded into extinction.
As the ages came and went, as millennia adding to millennia ticked away, astounding forces acted upon the buried ooze
and silts containing the body of the long-deceased Jurassic bird. The now-dried salty lagoon, the bird’s cemetery, was
compressed, hardened and layered until, in the amazing fashion by which geologic powers combine and prevail, there were
created expanses of limestone within which was fixed the stony accounting of a seemingly insignificant early flying being.
More than the fossilized remains of a departed feathered species was conserved within the densely hardened sediments.
Cast within those vast limestone sheets was a record of inestimable value to biology and to all of science, a Darwinian
bridge marking the adapting transformation of one group of animals into another. The encased vertebrate would one day be
named Archaeopteryx lithographica. Its feather impressions, the detailed remnants of its bones, its graceful structures, to our
good fortune, have glided down through the eons to furnish a truly magnificent page in the great illuminated manuscripts
recounting the history of life on our planet.
The strata holding the mineralized bones and feathers are fine-grained, Middle Jurassic deposits named the Solnhofen
formation, accessible today in a region of Western Europe called German Bavaria. The Solnhofen are massive plattenkalk
sheets, measuring fifty miles long by nineteen miles wide. In many places the sheets are nearly three hundred feet thick,
and underpinning a land presently experiencing a continental climate of moderate precipitation, warm summers and cold
winters.
The Bavaria of the Jurassic was far different in its meteorological makeup than today’s Bavaria. In those ancient times it was
a monsoon place, with drier periods alternating with lengthy rainy seasons, where plants and animals thrived in great and
varied profusion. The conditions of temperature, sunshine and rainfall may be compared, according to those who study
paleoclimates, to the environs of the Gulf of Cariaco along today’s northern coast of modern Venezuela.
The Solnhofen region of the Jurassic was probably not a bad place in which to make a living for the expanding diversity of
crawling, creeping, burrowing, running, jumping, swimming, slithering, pouncing, dashing, leaping or flying creatures of the
time. Paleologic evidence clearly reveals a vibrant and busy scene. Besides a multitude of different plants to dine upon, there
were vertebrate and invertebrate organisms of unimaginable shapes and sizes to capture and swallow, whether these latter
were sedentary, or moving by any means of locomotion imaginable. Denizens had water to drink, bushes and trees to hide
or nest in, and good air to breathe. These plants, animal or otherwise organisms formed a web of being that fed on the soils,
the minerals, plants and each other. There were new and developing habitats to explore and exploit, and of course there
were the more skilled hunters to avoid while in quest of one’s own sustenance.
Not just the lands and waters teemed with life – could we have been there to look into the sky we would have seen, flying
above the fray or gliding down to join in as the need occurred, a varied and complex volant fauna – plethoras of mayflies,
dragonflies, wasps, crickets, beetles, cicadas, or flying cockroaches to list just a few. And because the Jurassic marks the
great age of dinosaurs, there were the airborne of that heterogeneous tribe, skin-winged and long-jawed terrors called
pterosaurs, ranging from the sparrow-sized to far beyond the proportions of even today’s Andean Condors (one species of
pterosaur, Pteranodon, had a twenty-three foot wingspan). These extraordinary flyers spent their days patrolling from and
through the air, in search of each other for mating or a good meal, or for the two combined.
Living alongside and among that ancient flying menagerie was another host of animals neither insect nor pterosaur, an
elegant family that fluttered and sailed on feathered wings, that journeyed from bush to bush or from tree to tree using
extended forelimbs turned to wings. We would have wanted to call them birds. The little feathered animal engulfed into the
muck of that old Bavarian lagoon that eventually turned to limestone was one among them. While it and its fellow avian
wonders were more than somewhat reptilian, leather-winged pterosaurs or gossamer invertebrates they were not. Beside
body and wing feathers, they sported tails with rectrices, tail feathers, for steering, braking, and balancing; and well-
developed beaks. They had hollow-boned skeletons evolved for lightness, wishbone arrangements to anchor flight muscles
and although it has not yet been proven, almost certainly warm-blooded circulatory systems to fuel the rigors of taking and
keeping to the air. Much, much later in the span of their record, as they became known to science, our German colleagues
would designate these first as-much-birds-as-reptiles “Urvogels.” The word Urvogel translates as “ultimate” or “original bird.”
The title of ultimate or original bird, Urvogel, might seem to fall somewhat on the windy side of hyperbole, but the tribute has
long been accepted in the scientific community. The rich and varied trove of evidence we possess today does permit the
creatures to be called the first birds. In their assemblage they form an elaborate divergence in the complex transition from
reptiles through to the class Aves.
Were there a goodly number of these Urvogels, moving from one place to another, spreading over the world, searching for
food, building nests, mating, laying eggs, teaching young to fly or run like the wind, taking dinner from among the myriad
organisms with which they lived, or on occasion serving as snack or dinner for others of their neighbors? Because
Archaeopteryx fossils are relatively rare, we cannot be sure. The dense rocks of Solnhofen and vicinity have yielded only a
few specimens.
II. Urvogels
It was not long ago, not until the mid-nineteenth century, that unequivocal evidence of
of Urvogels came to light. The first startling hint came in 1860; a fossilized feather showing
asymmetrical vanes and a clearly defined rachis (a feather shaft) was discovered in a quarry
near the town of Solnhofen, after which the great limestone deposits had been named. The
feather was a bird’s flight feather, unquestionably dating from the Jurassic. News of a
paleofeather older than anyone had believed possible (and by extension the bird that had
worn it) set the world of natural science a-buzz. Many who saw the fossil or studied its
drawings and descriptions realized it was a harbinger, a long awaited herald bringing tidings
announcing that somewhere within those great Solnhofen archives lay evidence of an ancient
bird species.
Only a year later, in 1861, the gem that had been anticipated, the fossilized skeleton of a
Archaeopteryx lithographica: potential bird, was reported. Although the fossil was nearly headless, it showed distinct feather
the Berlin specimen impressions emanating from its limbs and body. The quarryman who made the find took his prize
to a local physician and well-known specimen-accumulator named Karl Häberlein, who had purchased
the feather uncovered the year before. When Dr. Häberlein examined the new relic, when he saw the feather impressions
with clear evidence of a bird’s wishbone, he did not hesitate. He happily accepted it in exchange for a medical debt the
stoneworker had earlier incurred.
To ascertain the fossil’s authenticity and value, Dr. Häberlein brought his treasure to Germany’s preeminent paleontologist
of the day, Herr Doctor Professor Hermann von Meyer. After studying the specimen, after assuring himself the animal had
feathers and could doubtless fly, von Meyer declared it to be the long-hoped-for Urvogel. He assigned to both the fossil and
the earlier 1860 feather a genus and a species name: Archaeopteryx lithographica; ‘Archaeo-’ meaning of ancient age, ‘-pteryx’
meaning winged; and ‘lithographica’ meaning from lithographic stone.
Physician Häberlein was not a paleontologist. Neither was he a sentimental collector. He immediately put the fossil feather
and skeleton on the market. Offers to buy poured in. But to the dismay of many among his compatriots, powerful anti-
evolutionists of the day fought tooth and claw to keep the Archaeopteryx specimens out of Germany’s museums. And they
were able to. No institution in the country could touch either piece. Dr. Häberlein was left little choice but to sell to the
highest foreign bidder, which turned out to be the British Museum of London, which handed over 700 pounds for the feather
and the skeleton. No trivial sum – seven hundred pounds represented two entire years’ budget for museum acquisitions, so
much as to require payment to be made in two installments.
A few years passed without a new quarry find. In the meanwhile heated and acrimonious debates raged between those
who subscribed to Charles Darwin’s new and exciting theory of evolution (On the Origin of Species by Means of Natural
Selection had been published in 1859) and those who rejected the work as anathema. Along with Darwin’s theories, the
importance and meaning of Archaeopteryx lithographica was the subject of bitter controversy. Scientists such as the brilliant
British naturalist T.H. Huxley saw Archaeopteryx as proof positive of Darwin’s breathtaking proposals. In the opposing camp,
one German scientist, in his hands-down rejection of the entire Darwinian ethos, went so far as to craftily disparage
Archaeopteryx with a different name entirely – the reptilian title of Griphosauros (gryps, mythical beast; sauros, lizard).
In the spring of 1877 another worker in another quarry not far from the town of Solnhofen cleaved free a lithographic slab
containing a complete crow-sized bird fossil, showing a head, legs, clear outlines of feathered wings, clawed feet and an
easily-seen wishbone. The workman informed quarry owner who, on the spot, generously rewarded his employee for his
good work, and gave him the rest of the day off. The owner then communicated with one Ernst Häberlein, son of the
physician-collector who, fifteen years earlier, had acquired by barter the first complete Archaeopteryx specimens. This next-
generation Häberlein also knew his stuff when it came to trading in paleontology. Upon seeing the stunning new fossil, he
bought it from the quarryman for 140 deutsche marks.
Like his father, Häberlein the younger was a good businessman. He put out word that he had a most amazing bird fossil in
his possession, and that it was for sale. As the news and description of this second Archaeopteryx spread, a frenzy of bidding
began. Learned professors, collectors, and museum curators from several countries went after it. The Dutch wanted the
fossil. The English wanted the fossil. The French wanted it. So did the Danes, the Swedes and the Italians. Even the
Americans, in the person of Professor Othniel Charles Marsh of Yale University, were parties to the escalating rounds of bids
and counter-offers. But this time the Germans were not going to let their bird in hand escape to the bush as they had done
earlier. After months upon months of haggling, price increases and endless negotiating, the wealthy industrialist, Werner von
Siemens, founder of the Siemens Corporation that thrives to this day, paid the junior Häberlein the princely sum of 20,000
marks for his Archaeopteryx slab and its counterslab.
But Baron von Siemens was not in the game for profit. In 1881 he resold the Archaeopteryx to the Prussian ministry for the
same amount he paid for it, 20,000 marks, thus permitting its two imprints, the slab and counterslab, to go to Berlin’s
Humboldt Museum für Naturkunde. The 1877 Archaeopteryx has been housed there ever since. It has come to be referred to
as the “Berlin specimen.” The earlier but less complete Archaeopteryx in the British museum is known as the “London
specimen.”
The London and the Berlin specimens were the only ones publicly and academically known for nearly a century to follow.
Then, in 1959, a third example of an Archaeopteryx was reported from the same quarry that produced the London specimen.
The fossil was apparently found in 1955 and sold to a man named Eduard Opitsch, who allowed it to be displayed for a time
in the local museum, then removed it to keep in his home to which he refused public access. When Opitsch’s estate was
being settled after his death, the fossil could not be located. To this day it is missing.
A fourth specimen was identified in 1970 when Professor John Ostrum of Yale University realized a fragmented Solnhofen
fossil in a Dutch museum, earlier classified as a pterosaur, was in fact a poorly preserved Archaeopteryx. The fossilized
remains Ostrum recognized as Urvogel are referred to as the Teylers specimen, after the Haarlem Museum in which it was
and still is displayed. A fifth Urvogel came to light in 1973 when a fossil in the Eichstätt City Museum in Bavaria thought to be
a diminutive dinosaur was reclassified as an Archaeopteryx. It was again the alert Professor Ostrum who pointed out its
barely faintly feather impressions.
Archaeopteryx fossil number six appeared in 1987, located among the holdings in a private collection of a former mayor of
Solnhofen. That fossil resides to this day in Solnhofen’s Bürgermeister-Müller Museum. In 1992, a very much smaller
Archaeopteryx, in good condition but which the German paleontologist Peter Wellnhofer considers a different species, was
found in the same quarry that had furnished the London specimen over 130 years earlier. Wellnhofer named this seventh
fossil Archaeopteryx bavarica, although it may well be a juvenile Archaeopteryx lithographica. It is owned by the Bavarian State
Collection of Paleontology and Historical Geology in Munich, and called the Munich specimen.
In 1997 an eighth Archaeopteryx was reported, the specimen consisting of a damaged skull and portions of forelimbs. The
exciting aspect of this fossil is that it dates from rocks laid down in the late Jurassic called the Mörnsheim Formation, meaning
the Archaeopterygidae spanned many hundreds of thousands of years more than originally thought. Unfortunately, as the
fossil remains in private hands, it has not enjoyed direct and exacting scientific scrutiny. Only a cast has been released by its
owner.
A ninth specimen, the right wing of an Archaeopteryx, was discovered in 2004. It too is privately owned but is currently on
loan to Solnhofen’s Bürgermeister-Müller Museum. Chiappe (2006) describes the wing as three-dimensionally preserved, with
feathers still attached.
Finally, a tenth Solnhofen Archaeopteryx of unknown provenance was reported in 2005 (Mayr et al., 2005). It was purchased
by and is now displayed at the Wyoming Dinosaur Center in Thermopolis, Wyoming. It is referred to as the Thermopolis
specimen. The skull and feet are in particularly good condition. The toe structure shows evidence of a running animal, as
were the theropod dinosaurs, the ancestors of birds (Mayr et al., 2007). Those who have studied the fossil prefer it be
named Archaeopteryx siemensii, in other words a distinct species from Archaeopteryx lithographica (Hartman, 2008).
The Urvogel Archaeopteryx, the first bird, is thus represented, in addition to the feather found in 1860, by only ten skeletons
or partial skeletons of which one has gone missing (number three), by another yet to be studied (number eight), and by
another that is a wing only (the ninth). Among that small number the Berlin Archaeopteryx is considered the typal because of
its superb state of preservation and clarity of features. One of America’s premier paleornithologists, Alan Feduccia, has
written that the Berlin Archaeopteryx “may well be the most important natural history specimen in existence, comparable
perhaps in scientific and even monetary value to the Rosetta stone….”
III. Art and Science, Science and Art
Likening Archaeopteryx lithographica to the Rosetta stone emphasizes its scientific importance, and that is good. The fossil is
truly a keystone in the bridge toward understanding the complexities of natural selection and avian evolution. On the other
hand, comparing the delicate Archaeopteryx to cold, carved rock is somewhat dissatisfying because we cannot forget that
Archaeopteryx was once a living, moving and agile form of life able to make itself lighter than air. While the species no longer
inhabits this earth, we nevertheless owe this marvelous antecedent its due as our earliest representative among the
several forerunners to today’s multitudes of birds.
Happily, another of our great avian paleontologists, Dr. Luis Chiappe, adeptly softens the stone analogy by referring to
Archaeopteryx as a kind of “Mona Lisa, a comparison that nicely stresses the scientific importance of Archaeopteryx as well as
conveys the iconic value of this ephemeral creature from a long-past and mysteriously fascinating time. Still, while
characterizing Archaeopteryx lithographica as a Mona Lisa might be both efficient and emotionally appealing, it could also be
seen as frankly anthropomorphic if not downright precious. If we really want to get down to brass tacks, how does all of this
paleontology and grandiose reference to one of the Western world’s greatest paintings meaningfully relate to the
occupation and pleasures of birding?
After all, we can list none of the Archaeopteryx’s field marks – the color of its feathers, its posture, its flight style or how it
folded its wings. Nor do we know if the bird sang, called, squawked or croaked. What was its preferred habitat or niche? Did
it soar or glide? Did its feathered legs function as lift-generating secondary wings as has been postulated by Canadian
paleontologist Nick Longrich? Did it confine itself to the trees, either perching on branches and limbs or clinging to trunks, or
did it hop or scamper along the ground? Was it shy or curiously aggressive? Were there ritualized social behaviors? Were
there well-fashioned nests? Did it live in flocks or was it inclined to the solitary? We don’t know what it ate, if it migrated or
not, if it was monogamous or polygynous, if it molted, if the female of the species or her mate, or both, incubated their
clutches, if the hatchlings were precocial or altricial. Since we know so little about its appearance, habits and it cohorts, why
not just say, “How interesting,” and return to our living birds, an occupation which keep us busy enough? Why not leave a
dead bird lie? In fact, there are good reasons to look and consider more deeply.
All species that exist or existed have, or had, immediate and more distant precursors. The immediate precursors were of
course parents, which in turn have had parents, which themselves had parents, and so on back farther and father in time
such that we speak of the preceding forms that lived as ancestors. Ancestors and decedents, particularly when separated by
large expanses of time, are not the same. If we examine the status of a species at various points along an historical line, if
we look at a species separated by many dozens of generations let us say, we will find the conspecifics living or having lived
at a later period to be different, sometimes very different, from the earlier assemblages of interbreeding individuals.
The changes that occurred between the two distant points can be quantified, and those changes, when compared, whether
the changes be large, small or incredibly complicated, are a measure of evolution. The younger generations may be bigger,
more streamlined, have developed new physical features or behavioral capacities, have gained or lost attributes and skills,
or even have gone through an entire change of appearance. Whales are such an example.
Evolution occurs because some among the diverse genetic mutations that alter characteristics, behaviors and features are
those advantageous enough to carry forward, while those mutations providing for reduced survival and reproductive
advantages are left by the wayside as innovations that didn’t pay off. This is the process underlying evolution. It is called
natural selection. Natural selection is the interacting dynamic that amplifies advantageous traits and culls out
disadvantageous traits, both of which occur sporadically in the genetic machinery of a group capable of interbreeding. What
is called evolution is the sum total of descent by modification through natural selection.
As already pointed out, Archaeopteryx lithographica represents a transitional species. The creature was not a reptile. It was a
good part bird. While it had upper and lower bills containing pointed teeth, those bills were formed into a beak. It had feet
with the curved toes resembling the gripping claws of a passerine. Admittedly there was a jointed boney tail consistent with
reptiles as well as with a group of contemporaneous, cursorial dinosaurs called theropods. But the tail had well-developed
feathers, organized biserially and symmetrically along the horizontal plane, an airfoil arrangement predicting the rectrices of
modern birds. On Archaeopteryx lithographica’s body were overlapping contour feathers. Its wings had interlocking
aerodynamic flight feathers, remiges, and the wings could be widely extended to reach for air. The skeleton had evolved
weight-reducing hollow bones that included a wishbone, the fundamental anchor for flight muscles that flap the wings that
render a bird airborne.
Here was structure become more avian than anything earlier in the record, a product of the selective pressures moving
precursors along their paths into and through the Jurassic, precursors whose offspring evolved into a unique species
showing the earliest integrated complex of avian traits. Archaeopteryx lithographica represents an astounding biological
synthesis, a coming together of adaptations assembled up until that distant moment.
When we find ourselves fascinated and moved before Leonardo da Vinci’s graceful Mona Lisa, we soon realize we are not
merely experiencing an astounding work of art. The portrait is a powerful cultural synthesis of the highest forms of beauty,
nobility and humility of the Renaissance. The painting is a great work of human achievement due not to its technical power
alone but because it is a perfected example of a moment in time. Gazing at it permits us to look back to what was a
momentous portion in human history. In the Mona Lisa we recognize a cultural precursor to our own value systems and
concepts of the beautiful. Leonardo’s Mona Lisa helps us to locate the signposts along path along by which we came.
Precursors such as she tell us much about what we once were in our intellectual and social development. Yet her emblematic
and enigmatic smile only hints at, but does not easily reveal, the countless complexities of the past that were selected,
recombined, carried forward or discarded as time when on. She engages our search for those ever-changing aggregations of
preferences, mores and clusters of ideas that eventually brought us to our own so very fleeting moments on this earth.
In this respect, human cultural selection and biologic or natural selection have similarities. Both lead on to something else.
But the works and workings of selection, cultural or biologic, can only be recognized after the fact, when we examine their
respective artifacts. In the case of art and culture those artifacts are the paintings, the sculptures, the books and the myriad
other products of creative minds coupled to skill. In biology, the artifacts are fossils. Biology, like art, leaves us to consider
remains.
If human cultural selection and biologic selection share commonalities as they go about generating outcomes, their
respective selective mechanisms do not function at the same levels. Human achievements are the product of a creators, or
groups of creators, with ability. Those creators consciously interpret and manipulate materials available to them according to
their ideas and the surrounding ideas that are in play. They have a goal in mind. By contrast natural selection is devoid of a
purposeful creator. Within the natural sciences, a family, a genus, a species and the individuals comprising that hierarchy are
the result of processes absent a centralizing, overarching agent. Natural selection has no
foresight.
This distinction between cultural and biologic selection suggests that we use a modicum of
caution when applying the Mona Lisa mantel to one of our most important fossils, lest we un-
consciously, or perhaps even consciously, assume the bird to have been the work of an omni-
potent, talented creator, thereby facilitating our anthropometric biases and further tricking us
into designating that creator as either evolution with a purpose, or a chosen deity. There is no
reason, of course, if we keep this caveat in mind, that we cannot honor Archaeopteryx as the
Mona Lisa of ornithology, a title that justifiably elevates the bird to a deserved high status.
We just need to keep our self-aggrandizing, romantic inclinations in check, because it is peren-
nially tempting to consider ourselves and our present century as the apogee of perfection and
progress. But neither the ancestral bird forms on which we focus our microscopes nor the
contemporary birds toward which we aim our binoculars, spotting scopes or cameras were the
product of a creative genius having the present avian glory in mind, and most surely not our
personal satisfactions. Natural selection is just that – natural. It has no favorite species. It is
not divine. It does not plan for an ultimate future nor compose for a grand finale. I just keeps
churning haphazardly along.
When the earliest humans of Africa began their world-wide expansion out from their changing savannah homelands, it is
difficult to imagine they had our twenty-first century in mind as they trekked along meeting new environments, then either
adapting or perishing. So let us admire Archaeopteryx for what the species represents: a momentous interlude within the
history of avian life. In the great pantheon of biology Archaeopteryx was a creature that fortuitously, fortunately, and to our
unintended delight, traveled part way along the broad flyways leading to the airborne creatures we admire each day as we
take to the field. It is for this reason, because Archaeopteryx reveals this wonderfully expansive historical perspective onto
our natural world, that we can fittingly honor the fossil, a once-living living bird, as the Mona Lisa of ornithology, whether our
avocations flow to birding or to the others of those diverse and noble pursuits which search to understand the intricate
pageant of life.
References and Works Consulted:
Bakker, Robert T. ((1986). The Dinosaur Heresies. Kensington Publishing Corporation, New York.
Chiappe, Luis M. (2006). Glorified Dinosaurs: The Origin and Early Evolution of Birds. John Wiley and Sons, Hoboken, N.J.
Darwin, Charles (1859). The Origin of Species by Means of Natural Selection. Barnes and Noble Classics Edition, 2004.
Introduction and notes by George Levine. Barnes and Noble, New York.
Feduccia, Alan (1999). The Origin and Evolution of Birds. Yale University Press, New Haven. Second Edition.
Gill, Frank B. (2007). Ornithology. Third Edition. W.H. Freeman and Co., New York.
Hartman, Scott (2008). Personal Communication.
Longrich, Nick (2006). “Structure and function of hindlimb feathers in Archaeopteryx lithographica,” Paleobiology 32 (3): 417-
431.
Mayr, Gerald, Pohl, Burkhard and D Stefan Peters (2005). “A Well-Preserved Archaeopteryx Specimen with Theropod
Features,” Science 310: 1483-1486.
Mayr, Gerald., Pohl, Burkhard., Hartman, Scott and D. Stefan Peters (2007). “The tenth skeletal specimen of Archaeopteryx,”
Zoological Journal of the Linnean Society 149: 97-116.
Podulka, S., Rohrbaught, R.W., Jr. and Bonney, R. (2004). Handbook of Bird Biology. Cornell Laboratory of Ornithology, Ithaca,
N.Y.
Shipman, Pat (1998). Taking Wing: Archaeopteryx and the Evolution of Bird Flight. Simon and Schuster, New York.
Archaeopteryx lithographica Click on photo to enlarge
Artist's rendering by Julie Zickefoose
Artist's rendering by Julie Zickefoose
Click on photo to enlarge
Click on photo to enlarge