Author: Chris Nedin (cnedin@geology.adelaide.edu.au) Title: All About _Archaeopteryx_ Upda
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Author: Chris Nedin (cnedin@geology.adelaide.edu.au)
Title: All About _Archaeopteryx_
Update: 6/28/94
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Contents
Introduction
Archaeopteryx specimens
Archaeopteryx features
Archaeopteryx's avian features
Archaeopteryx's reptile features
Cranial features of Archaeopteryx
Protoavis
Conclusions
References
Introduction
_Archaeopteryx lithographica_ ("ancient wing from the printing stone")
Named after the limestone in which it was discovered. The stone is a
smooth, fine grained limestone which was used in printing. Quarried from in
and around the Solnhofen area of Germany. Formed on the bottom of a
hypersaline lagoon in the Cretaceous.
There have been 7 specimens of _Archaeopteryx_ found (6 actual specimens
and one feather). These finds are documented chronologically (by
description) below.
1) The Feather
Found in 1860 near Solnhofen and a revelation when it was described by H. v
Meyer in 1861. The surprise was not the age of the fossil, since several
ornithopod dinosaur footprints erroneously ascribed to birds were known
from the Triassic, but the detail that was preserved.
2) The London Specimen
Found in 1861, near Langenaltheim. Probably the best known (together with
the Berlin specimen). Its discovery was announced by H. v Mayer in 1861 and
the specimen was subsequently bought by the Richard Owen for the British
Museum of Natural History in London. It cost 700 UK Pounds - a small
fortune in those times, but for that price Owen also received a number of
other fossils from Solnhofen. The specimen was sold by amateur collector
and local doctor Carl Haberlein. Owen described the specimen in 1863. He
saw at once that it was an important find and recognised that it
represented a transitionary form - but not in the 'Darwin' sense. Owen was
a staunch 'evolutionist', however he did not believe in Darwins model of
evolution. Interestingly Huxley, who *was* a staunch 'Darwinist' failed to
recognise the true import of the fossil and mearly remarked on it as a
"reptile-like bird". It wasn't until close comparisons were made with the
dinosaur _Compsognathus_ that Archae's true worth was realised.
3) The Berlin Specimen
Found in 1877 near Blumenberg. This was a better specimen that the London
specimen, principally because it had a complete head, albeit badly crushed,
and was snapped up by the Berlin museum. It was sold to them by Carl
Haberlein's son (talk about keeping it in the family!). It was described by
W. Dames in 1884.
4) The Maxburg Specimen
Found in 1958 near Langenaltheim (same as London Specimen). This specimen
is of the torso only and as of 1990 was the only specimen to still be in
private hands [note: I recall a specimen going on sale a year or two ago,
it may well have been this specimen - cn]. The specimen was described by P.
Wellnhofer in 1959.
5) The Haarlem or Teyler Specimen
This specimen was actually found near Reidenburg in 1855, 5 years *before*
the feather! It lay in a museum after being classified as _Pterodactylus
crassipes_ by H. v Meyer in 1875. A re-examination of the fossil in 1970 by
Ostrom revealed feathers and its true identity.
6) The Eichstatt Specimen
Found near Workerszell in 1951, it was described by P. Wellnhofer in 1974.
This is the smallest of all the specimens, being some 2/3 the size of the
others. It also differs in other aspects such as the tooth structure and
the poorly ossified sholder bones. It has been suggested that this is a
separate genus, however the differences can also be ascribed to the
possible juvenile stage of the animal and/or a different feeding niche.
However, this specimen has the best preserved head and from which the
litany of Archae's reptilian cranial features were described. At the moment
it still resides within _A. lithographica_.
7) The Solnhofen Specimen
Found in the 1960's near Eichstatt by a Turkish worker. First identified as
_Compsognathus_, but further examination showed that the arms were too long
for the body size and preparation revealed feather traces. Described by P.
Wellnhofer in 1988
_Archaeopteryx_ features
Much has been made in pseudoscientific circles about the position of Archae
with the evolutionary scheme of things. The usual 'arguement' (and here I
use the term in it's loosest possible sense) put forward is that Archae
cannot be a transitionary fossil between birds and dinosaurs because it is
a bird. This simplistic line belies the fact that, whilst Archae is indeed
classified as a bird, it has been done so on the strength of 4 characters -
2 of which are not unique to birds. This classification ignores the fact
that Archae has some15 characters which *are* unique, unique in that they
are *not* possessed by birds. Archae's avian affinities are allowable on
the strength of the following 4 characters:
Archae's avian features:
1) Feathers
Feathers are *the* diagnostic feature of birds. This is the main criterion
for classifying Archae as a bird, as no other animal has feathers. The
possession of feathers is a characteristic of birds, so strike one up for
the birds.
2) Opposable hallux (big toe)
This also is a character of birds and not dinosaurs. Although opposable big
toes are found in other groups, they are not, as far as I am aware, found
in dinosaurs. So strike another for the birds
3) Furcula (wishbone) formed of two clavicals fused together in the midline.
Now we start getting on shaky ground. It used to be though that the
possession of a furcula distinguished birds from dinosaurs. Indeed, up
until recently even clavicles were few and far between in even non-avian
theropod dinosaurs (the suggested closest group to the birds and from which
the birds evolved - see Ostrom 1976). However, it has been found that
theropod dinosaurs did indeed have clavicles (e.g. Bryant & Russell 1993)
and they have been found in several species, e.g.:
_Segisaurus_
_Velociraptor_
_Euparkeria_
_Ornithosuchus_
_Saltoposuchus_
_Ticinosuchus_
etc.
It has been found that the clavicles are often small and poorly ossified.
This is no surprise, since they are of little evolutionary advantage to
your average theropod dinosaur. However, birds too show this variation in
ossification, especially amongst the carniates and so the apparent absence
of clavicles in some theropod dinosaurs may well be due to poor
ossification rather than true absence.
However, furculas *have* been found in some non-avian theropod dinosaurs,
namely the Oviraptorosauria (Barsbold et al 1990, Bryant & Russell 1993).
these include _Oviraptor_ and _Ingenia_.
Thus furculas do *not* appear to be diagnostic to birds and certain members
of the suggested closest group to the birds now appear to possess furculas
so it is a neutral character
A commonly cited critisism of this is that most of the non-avian theropod
dinosaurs listed here post-date Archae. However, none of these is claimed
as the ancester anyway. The presence of clavicles shows that this
character is a feature of theropod dinosaurs and thus was probably present
in early theropods (indeed _Euparkeria_ is a Triassic form).
4) Pubis elongate and directed backward
This is a feature of birds, but it is also a feature of some theropod
dinosaurs so is not diagnostic of birds - another neutral character
Archae reptile features:
5) Premaxilla and maxilla are not horncovered
This is posh talk for 'does not have a bill'
6) Premaxilla and maxilla bear teeth
Birds do not possess teeth. Teeth are expressed in the embryo, but are lost
before the chick is hatched
7) Nasal opening far forward, seperated from the eye by a large preorbital
fenestra
This is typical of reptiles, but not of birds
8) Cerebral hemispheres elongate, slender and cerabellum is situated
behind the midbrain and does not overlap it from behind or press down on
it.
This again is a reptilian feature. In birds the cerebral hemispheres are
stout, cerabellum is so much enlarged that it spreads forwards over the
midbrain and compresses it downwards
Skull and brain of Archae is basically reptilian and has *NO* unambiguous
avian features and is not "totally birdlike" (contrary to a certain
creationists claims)
9) Center of cervical vertebrae have simple concave articular facets.
This is the same as the archosaur pattern. In birds the vertebrae are
different, they have a saddle-shaped surface.
10) Long bony tail with many free vertebrae up to tip (no pygostyle).
Birds have a short tail and the caudal vertebrae are fused to give the
pygostyle.
11) Trunk region vertebra are free.
In birds the trunk vertebrae are always fused.
12) Ribs slender, without joints or uncinate processes and do not
articulate with the sternum.
Birds have stout ribs with uncinate processes (braces between them) and
articulate with the sternum
13) Pelvic girdle and femur joint is archosaurian rather than avian.
With the exception of the backward pointing pubis as mentioned above. Here
Archae really shows its transitionary nature. Whilst the pelvic girdle as a
whole is basically free and similar to archosaur girdles, the pubis points
backward - a character shared with birds and some other bird-like theropod
dinosaurs.
14) Sacrum occupies 6 vertebra.
This is the same as in reptiles and especially ornithipod dinosaurs. The
bird sacrum (the vertebrae developed for the attachment of pelvic girdle)
covers between 11-23 vertebrae!
15) Metacarpals (hand) free (except 3rd metacarpal) , wrist hand joint
flexable.
This is as in reptiles. In birds the metacarpals are fused together and
with the distal carpals in the carpo-metacarpus, wrist /hand fused. All
modern birds have a carpo-metacarpus, all fossil birds have a
carpo-metacarpus - except one (guess! clue: the answer contains the letters
a.r.c.h.a.e.o.p.t.r.y.x. in that order) :-)
16) Bones not pneumatic.
I.e. they do not have air-sacs. They do in birds.
17) Claws on 3 digits,
No modern bird has claws. The juvenile Hoatzin and ostrich do have 2 claws
but loose them as they grow. In the case of the Hoatzin it is thought that
these claws alow the juvenile to climb.
18) The fibula is equal in length to the tibia in the leg
This again is a typical character of reptiles. In birds the fibula is
shortened and reduced.
19) Metatarsals ( foot bones) free.
In birds these are fused to form the tars-metatarsus
20) Gastralia present.
Gastralia are "ventral ribs", elements of dermal bone in the ventral wall
of the abdomen. Typical of reptiles, they are absent in birds.
1 = present; * = present in some; x = absent
Dinosaurs Archae Birds
1 x 1 1
2 x 1 1
3 * 1 1
4 * 1 1
5 x x 1
6 1 1 x
7 1 1 x
8 1 1 x
9 1 1 x
10 1 1 x
11 x x 1
12 1 1 x
13 1 1 x
14 6 6 11-23
15 1 1 x
16 x x 1
17 1 1 *
18 1 1 x
19 1 1 x
20 1 1 x
It can be seen that Archae possesses many more characters which are present
in dinosaurs and *not* in birds, than it does characters which are present
in birds but not in dinosaurs.
This is why Archae is a true transitionary species, because it shares some
characters which are diagnostic of one group whilst still retaining
characters diagnostic of its ancestral group.
Anyone who claims that Archae is 100% bird is wrong.
Anyone who claims that Archae's skeleton is even predominantly bird-like is
wrong.
Anyone who claims Archae has a "totally birdlike" skull is wrong.
This latter point is made in reference to the claim by Duane Gish that the
skull of Archae is "totally birdlike. This is false. To show this we need
to consider the skull of Archae further.
Cranial features of Archae
As stated above, Duane Gish claims that the skull of Archae is "totally
birdlike". This is false. Romer (1950 p. 261) describes Archae thus: "The
skull, as far as can be seen, was rather birdlike. . . ". However, not only
is this a far cry from "totally birdlike", but Romer was using the detailed
reconstruction of the Berlin Specimen, by Heilmann (1926). Ostrom (1976 p.
131) has this to say on the Heilmann reconstruction:
"Despite the details shown there [Heilmann's reconstruction of the skull -
cn], the actual specimen does not permit such detailed and precise
conclusions. It [the Berlin specimen's skull - cn] is badly crushed and the
bones are extensively fracture, chipped and distorted - to the extent that
very few cranial or mandibular sutures unmistakably indentifiable.
Heilmann's reconstructions have been republished by many authors and
subsequent interpretations and hypotheses based on it. Quite probably, some
authors have been unaware of the inadequate basis of Heilmann's
reconstruction, and understandably so unless they have had the opportunity
to examine the specimen itself."
And again on the same page:
"Fortunately, the Eichstatt speciman now provides a comparative basis for
evaluating and correcting past reconstructions of the Berlin skull."
As mentioned above, the Eichstatt speciman was not described until 1974,
therefore Romer's description was based on the Heilmann reconstruction.
Using both specimens, Ostrom (1976 p. 132) delineated 9 characters on the
skull of Archae which it shares with other theropod dinosaurs such as
_Ornitholestes_, _Compsognathus_, _Velociraptor_ and perhaps
_Saurornithoides_. These are:
1) A sharply tapered snout.
2) long elliptical external nares bounded almost exclusively above and
below by the premaxilla (a bone at the front of the upper jaw).
3) A large triangular antorbital fossa which contains two small anterior
openings and a large triangular posterior fossa.(these are holes in the
skull, one in front of the eye -with two openings - the other behind the
eye)
4 A slender, nearly vertical preobrital bar separating the antorbital fossa
and the orbit. (there's that hole again! This means that there is a
vertical bar of bone separating the hole in front of the eye with the eye
itself)
5) A large circular orbit which contains a large scleotic ring.(the
sclerotic ring is common to reptiles, birds and actinoptygian fish, but
most fossil reptiles and all fossil birds have them. They are a series of
ossified plates which circle the eye)
6) A thin, straight jugal bone. (this is the bone that runs under the eye -
the cheek-bone, as it extends back towards your ear, to you)
7) A stout quadrate of maderate length which is inclined forward. (this is
the bone in the upper jaw which forms part of the jaw articulation - with
the articular - in reptiles, and Archae has a big one, um if you see what I
mean! Incidentally - for those of you who are still with us, the quadrate
is attached to the stapes in the upper jaw, and as we all know, the stapes
is the bone which vibrate in the ear so that we can all hear. Thus the
stapes and quadrate were attached in reptiles and it is not a great leap
forward to have both the stapes and the quadrate in the ear as it is in
mammals. This also shows that Gish's claim that in order for the bones to
enter the ear in the transition from reptiles to mammals they would have
had to gone through a stage whereby the 'mammal' would have deafened itself
every time it opened its mouth is bullshit since the condition of
stapes+quadrate articulating in the jaw joint *is found in fossil and
extant reptiles*, but I digress.
8) A lower jaw which is unusually shallow and has a conspicuous bend behind
the tooth row.
9) A long retroarticular process. (again a classic reptile jaw-joint feature)
Heilmann described an external mandibular fenestra (a hole in the lower
jaw) bordered below by the dentary bone - which is the condition in birds -
rather than by the angular bone - as it is in reptiles. This would
indicate that Archae has a lower jaw which contained both avian (said
mandibular fenestra) and reptilian features (toothed lower jaw). This is
all very well and dandy and is a feature which one would like to see in
Archae. However, as Ostrom (1976 p. 132) point out:
"Much as I would like to accept this interpretation, the highly fractured
condition of the lower jaw bone (or bones) that border the supposed
mandibular fenestra, either below or above, make it impossible to certify
their identifications. in fact, the fractured upper margins of the supposed
fenestra leave considerable doubtas to the very existance of a 'fenestra' -
a doubt which has not been removed by the Eichstatt specimen."
Thus, far from conspiring to present Archae in the best possible light, a
very useful feature which would have aided in the description of Archae as
a true transitionary fossil has in fact been show to be, in all
probability, not true. So much for the evilutionist conspiracy!
Another important feature of the skull of Archae is the occipital condyle
and the foramen magnum. In Archae these are well above the dorsal end of
the quadrate. As Ostrom (1976 p. 136) says:
"This primative condition is characteristic of both pseudosuchians and
theropods, in contrast to all later birds where the occipital condyle and
foramen magnum are at the base of the skull, well below the level of the
upper extremity of the quadrate. In this feature, _Archaeopteryx_ was far
from avian."
As can be seen, Archae's skull possesses no diagnostically avian features,
let alone is "totally birdlike". The "totally birdlike" claim is without
foundation.
_Protoavis_
Some people like to claim that the finding of a fossil bird from the
Triassic of Texas (_Protavis_), proves that Archae cannot be transitionary
between dinosaurs and birds because _Protoavis_ predates Archae by 75
million years.
This is, of course, errant nonsense, mainly because no-one is claiming that
Archae is *the* transitionary species between dinosaurs and birds, mearly
that Archae represents a grade of organisation which the proposed lineage
went through to get from dinosaurs to birds. Archae is, I'm sorry to say,
out on a limb, evolutionarily speaking. It represents a side branch, useful
for comparative purposes, but not in the thick of things. So even if there
were birds in the Triassic, that fact would not diminish Archae's
importance as an indicator that 'yes, birds could have evolved from
dinosaurs".
However, notice the "if" in the previous sentence. There are major problems
with _Protoavis_. On the Chatterjee (1991) interpretation, Ostrom (1991)
has this to say: [abridged] The only published material from the fossil is
a monograph in the Philosophical Transactions of the Royal Society of
London. However, this only describes the head. This is badly crushed and
all the pieces have been extracted from the matrix, rendering precise
placement of the pieces open to question. The description is done from an
avian viewpoint, with no counterview (ie is this a dinosaur?) used. The
skull is so badly crushed that diagnostic features are not preserved.
Therefore the published material does not support the view that this is a
bird. Indeed a viewing of the fossil by Ostrom (in admittedly less than
ideal surroundings) showed that the diagnostic features which could
identify the fossil either way are badly crushed and it is doubtful wether
any definative statement could be supported by the fossil.
It may be a bird, it may not.
Please note that this questioning of _Protoavis_ as a bird is no "it
can't be a bird because it predates Archae" evilutionist backlash. As has
been pointed out, even if it is a bird, it does not detract from the
evolutionary importance of Archae.
Conclusions
_Archaeopteryx_ is a bird because it had feathers.
However, it retaines many dinosaurian characters which are not found in
birds, whilst having certain characters found in birds but not in
dinosaurs.
By virtue of this fact _Archaeopteryx_ represents a example of a group in
transition. A representative which, although on the sidelines in the
dinosaur to bird transition, an echo of the actual event, still allows a
brief glimpse into the possible mechanism which brought about the evolution
of the birds and by its very existance shows that such a transition is
possible.
Referencess
Barsbold, R. et al 1990. Oviraptorosauria. In The Dinosauria, Weishampel,
Dodson & Osmolska (eds) pp 249-258.
Bryant, H.N. & Russell, A.P. (1993) The occurrence of clavicles within
dinosauria: implications for the homology of the avian furcula and the
utility of negative evidence. Journal of Vertebrate Paleontology, 13(2):
171-184.
Chatterjee, S. (1991) Cranial anatony and relationships of a new Triassic
bird from Texas. Phil. Trans. R. Soc. Lond. B. 332: 277-342
Heilmann, G. (1926) The Origin of Birds. 208pp. Witherby, London
Ostrom, J. H. (1976) Archaeopteryx and the origin of birds. Biological
Journal of the Linnean society, 8(2): 91-182.
Ostrom, J.H. (1991) Bird in the Bush. Nature, 353: 212
Romer. A.S. (1950) Vertebrate Paleontology. p 261. University of Chicago
Press, Chicago.
Acknowledements
This came about as the result of a series of discussions with Rich Trott,
who was fighting the systematic misuse of Archae by His Gishness and
others, and still managed to find the time to suggest improvements to this
post
E-Mail Fredric L. Rice / The Skeptic Tank