[quote]T-Doff wrote:
beaudry wrote:
I found this site.
Seems to show evidence of an interspecies transition.
“Archaeopteryx is a bird because it had feathers. However, it retained many dinosaurian characters which are not found in modern birds, whilst having certain characters found in birds but not in dinosaurs. By virtue of this fact Archaeopteryx represents an 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 existence shows that such a transition is possible.”
Archaeopteryx may look like an example of a transitional intermediate in the fossil record; however, it is classified as a bird from a biological standpoint. Certainly evolutionists jumped on the idea that it was part bird, part reptile. A recent study in “Nature” indicates that it is fully bird not a transitional form. Also, Archaeopteryx appears suddenly in the fossil record and transitional forms the precede it are still absent.
Nature vol.430 (2004): 666-69. “The Avian Nature of the Brain and inner Ear of Archaeopteryx”[/quote]
It is classified as a bird, but it contains both reptile and avian characteristics.
Archaeopteryx’s reptile features
5) Premaxilla and maxilla are not horn-covered.
This is posh talk for “does not have a bill.” The premaxilla does not have a keratinized covering, so Archaeopteryx has no bill. The bill is produced via the process of ‘cornification’ which involves the mucus layer of the epidermis (Romanoff 1960) and thus its formation is independant of jaw bone formation.
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Trunk region vertebra are free.
In birds the trunk vertebrae are always fused.
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Bones are pneumatic.
I.e. they appear to have air-sacs, as they do in birds and in some dinosaurs (e.g. Witmer 1990, Brooks 1993). It should be pointed out that previous claims suggesting the bones of Archae were not pneumatic (Lambrecht 1933; de Beer 1954), was based on negative evidence, i.e. that the bones do not exhibit pneumatic pores (through which the air sacs enter the bones) and the bones show none of the plumpness and bulges which characterise the pneumatic bones of modern birds. Britt et al. (1998) found evidence for the presence of pnematic bones in Archaeopteryx:
“Here we re-examine two specimens of Archaeopteryx. These specimens show evidence of vertebral pneumaticity in the cervical and anterior thorasic vertebrae, thus confirming the phylogenetic continuity between the pneumatic systems of non-avialan theropods and living birds” (Britt et al. 1998, p. 374)
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Pubic shafts with a plate-like, and slightly angled transverse cross-section
A Character shared with dromaeosaurs but not with other dinosaurs or birds
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Cerebral hemispheres elongate, slender and cerebellum is situated behind the mid-brain and doesn’t overlap it from behind or press down on it.
This again is a reptilian feature. In birds the cerebral hemispheres are stout, cerebellum is so much enlarged that it spreads forwards over the mid-brain and compresses it downwards. Thus the shape of the brain is not like that of modern birds, but rather an intermediate stage between dinosaurs and birds (e.g. Alexander 1990).
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Neck attaches to skull from the rear as in dinosaurs not from below as in modern birds.
The site of neck attachement (from below) is characteristic in birds, Archaeopteryx does not have this character, but is the same as theropod dinosaurs:
“Notice that this coelurosaurian-like neck extended back from the rear of the skull in Archaeopteryx - as it does in coelurosaurs [theropod dinosaurs], rather than from beneath as in later birds.” (Ostrom 1976, p. 137).
Skull and brain of Archae is basically reptilian and is not “totally birdlike” (contrary to a certain creationist’s claim).
- 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:
“The most striking feature of the vertebrae is the simple disk-like facets of their centra, without any sign of the saddle-shaped articulations found in other birds” (de Beer 1954, p. 17).
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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.
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Premaxilla and maxilla bones bear teeth.
No modern bird possess teeth (e.g. Romanoff 1960; Orr 1966, p. 113). Bird embryos form tooth buds, but do not actually produce teeth. Some birds subsequently produce ridges in the bill, but there is no connection between them and the embryonic tooth buds, since the ridges also form in other areas of the bill where no tooth buds have previouslu formed. Some birds produce hook-like structures which are papillae, and appear to be related to the process of keratinization of the beak (Romanoff 1960), and have nothing to do with teeth. They do not possess blood vessel or nerve connections, nor do they produce dentine.
The expression of tooth buds in the bird embryo has a simple evolutionary explanation, since it suggests that the ancestors of modern birds possessed teeth and that this character has been supressed in modern birds. The presence of tooth buds in the embryos of organisms which do not possess teeth in the adult is a difficulty for anti-evolutionists, since why should a character be expressed that is never used in the organism? Some fossil birds exhibit a reduction in the number of bones which have teeth. Both Hesperornis and Baptornis lack teeth on the premaxilla (Archaeopteryx and theropod dinosaurs have teeth on both the maxilla and premaxilla). Not only that, Hesperornis has a beak, but on the upper jaw only (Gingerich 1975). It therefore has half a beak and teeth. A good example of a morphologicaly intermediate structure between toothed birds which lack a beak, and beaked, toothless birds.
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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.
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Pelvic girdle and femur joint is archosaurian rather than avian (except for the backward pointing pubis as mentioned above).
Here Archae really shows its transitional 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.
What is interesting is that with the bird pelvis:
“The ischium lies beneath the posterior part of the ilium and beneath this again is the pubis, which is directed backwards (i.e. like this: =). Embryological studies show that the peculiar position of these bones is the result of secondary rotation and that the pectineal process, in front of the ascetabulum, is not the true pubis as some workers have maintained.” (Bellairs & Jenkin 1960, p. 258).
In other words, the embyonic pelvis of the bird, when first formed, looks, in shape and angle between the ilium and the pubis (45 degrees), very similar to the “A”-frame pelvis of Archaeopteryx (i.e. like this: <) (e.g. Romanoff 1960). The fully formed pelvis with all bones lying parallel is the result of secondary rotation of the pubis from “<” to “=”. This supports the view that birds had an ancester with a saurischian pelvis such as the type possessed by Archaeopteryx and other theropod dinosaurs. (see also A tale of two pelvises below)
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The Sacrum (the vertebrae developed for the attachment of pelvic girdle) occupies 6 vertebra.
This is the same as in reptiles and especially ornithipod dinosaurs. The bird sacrum covers between 11-23 vertebrae! So, while the variation seen in modern birds is large, it is nowhere near the number found in Archaeopteryx
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Metacarpals (hand) free (except 3rd metacarpal), wrist hand joint flexible.
This is as in reptiles. In birds the metacarpals are fused together 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!) :-). However, the carpals of several coelurosaur dinosaur groups show a trend towards fusion, and in the Late Cretaceous form Avimimus, a true carpo- metacarpus is formed.
It has been suggested that the ostrich and/or other Ratites also possess unfused wrist/hand bones. This is not correct:
“The ostrich, emus, rheas, cassowaries and kiwis are often referred to together as the Ratites, though they may not be closely related to each other. They have tiny wings and cannot fly, but the bones of their hands are fused together in the same peculiar way as in flying birds, which suggest that they evolved from flying birds.” (Alexander 1990, p. 435).
Some similarity between the hand of the ostrich and some of the more derived theropod dinosaurs was once used to suggest that the Ratites were ‘primitive’ and evolved before the advent of flight in birds. However Tucker (1938b) showed that such similarities are entirely superficial.
“He has directed attention to the bird-like characters of the hand of the dinosaur Ornitholestes as evidence that a bird-like hand can be developed independantly of flight, but the writer has pointed out in the communication mentioned above [Tucker 1938b] that the resemblance is utterly superficial and that the peculiar bowing and terminal fusion of metacarpals 2 and 3 which charcaterise both the Carnate and the Ratite hand are in no wise [sic?] reproduced in the dinosaur.” (Tucker 1938a, p. 334).
“Reverting now to the reasons on which have sought to base the view that the Ratites were primitive birds whose ancesters had never flown, one: the similarity between the hand of the ostrich and that of the dinosaur, has been dismissed as invalid. Tucker (1938b) has shown that such resemblances as there are between them are only superficial and without significance.” (de Beer 1956, p. 65).
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Nasal opening far forward, separated from the eye by a large preorbital fenestra (hole).
This is typical of reptiles, but not of birds. Where a fenestra is present in birds, it is always greatly reduced, and is involved in prokinesis (movement of the beak)
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Deltoid ridge of the humerus faces anteriorly as do the radial and ulnar condyles.
Typical of reptiles but not found in birds
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Claws on 3 unfused digits.
No modern adult bird has 3 claws, nor do they have unfused digits. The juvenile hoatzin and Touracos do have 2 claws but loose them as they grow, the ostrich appears to retain its 2 claws into adulthood, due to the early termination of development (see section on Ratites). In the case of the hoatzin it is thought that these claws allow the juvenile to climb. It had been claimed that since these birds do have claws, even in the juvenile stage, then the presence of claws cannot be used as a reptilian character. This is not so, however. In fact almost all birds exhibit claws, but in the embryonic stage and they are lost by the time the bird leaves the egg. In the case of the few which do retain claws into the juvenile stage, this is merely the extension of the condition into the post-embryonic stage. As McGowan (1984, p 123) says:
“In retaining a primitive reptilian feature which other birds lose just before leaving the egg [the hoatzin] is showing us its reptilian pedigree. Far from being evidence to the contrary, the hoatzin is additional evidence for the reptilian ancestry of birds.”
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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.
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Metatarsals (foot bones) free.
In birds these are fused to form the tarsometatarsus. However, in modern bird embryos, the foot bones are initially separate as in the adult Archaeopteryx and is another character supporting a reptilian ancestry for birds. After all, why bother producing separate bones in the embryo and then fuse them? Why not produce a fused mass to start with? No adult modern bird has separate metatarsals, but they are separated, initially, in the embryo. This can be explained in terms of evolution - birds evolved from a group which had unfused metatarsals.
Ceratosaurians, Avimimus, and Elmisauridae all show true tarso-metatarsi. Archae itself only shows the beginning of this structure.
- 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, e.g.:
“In addition to the true ribs the British Museum specimen shows a large number of so-called ventral ribs or gastralia, elements of dermal bone lying in the ventral wall of the abdomen.” (de Beer 1954, p. 18)
“The gastralia of the Berlin specimen are identical with those of the British Museum specimen, but more have been preserved.” (de Beer 1954, p. 19)
“The “new” specimen was found 8 September 1970 on display in the Teyler Museum, Haarlem, Netherlands. It consists of two small slabs (specimens 6928 & 6929), part and counterpart which contain impressions or parts of the left manus and forearm, pelvis, both legs and feet, and some gastralia.” (Ostrom 1970, p. 538)
"Also present are numerous fragments of gastralia, faint impressions of three or four dorsal vertebrae, . . " (Ostrom 1972, p. 291).
“The counterpart slab (No. 6929) contains additional gastralia, phalanges, …” (Ostrom 1972, p. 291)
“Gastralia, or dermal abdominal ribs are present in all five skeletal specimens of Archaeopteryx” (Ostrom 1976, p. 139-140).
Gastralia are present on the Eichstatt specimen (See Wellnhofer 1974, fig. 7C)
Here is a webpage that lists other transitional vertebrate fossils.