Bretski wrote:What exactly are creationists looking for in the way of "half this kind half that kind" which would be convincing?

Bretski wrote:What exactly are creationists looking for in the way of "half this kind half that kind" which would be convincing?

Bretski wrote:What exactly are creationists looking for in the way of "half this kind half that kind" which would be convincing?

laklak wrote:

Bretski wrote:What exactly are creationists looking for in the way of "half this kind half that kind" which would be convincing?

Rachel Bronwyn wrote:

Evolution.

But we all know, even if creationists admitted it's part shark, part bear, part octopus, they'd say god just made it that way.

Rachel Bronwyn wrote:

Evolution.

But we all know, even if creationists admitted it's part shark, part bear, part octopus, they'd say god just made it that way.

Rumraket wrote:Hm... so he hasn't bothered returning to this thread since his first 3 posts?

Polanyi wrote:Archaeopteryx:

Polanyi wrote:why evolutionists

Polanyi wrote:have to let go

Polanyi wrote:Most evolutionists

Polanyi wrote:still cling to the idea that the Archaeopteryx is the perfect example of a transitional fossil

Polanyi wrote:that proves reptiles evolved into birds.

Polanyi wrote:I will ignore the fact

Polanyi wrote:for now that even if this was true, this would still have nothing to do with proving

Polanyi wrote:that birds evolved via Darwinian mechanisms

Polanyi wrote:and focus just on the problem for common ancestry here

Polanyi wrote:Evolutionists

Polanyi wrote:claim the fact that Archaeopteryx had claws on its wings, teeth in its beak, and a long bony tail is enough to show that this was a transitional creature or at least to show that this was a feathered dinosaur.

Erickson et al, 2009 wrote:Abstract

Background

Archaeopteryx is the oldest and most primitive known bird (Avialae). It is believed that the growth and energetic physiology of basalmost birds such as Archaeopteryx were inherited in their entirety from non-avialan dinosaurs. This hypothesis predicts that the long bones in these birds formed using rapidly growing, well-vascularized woven tissue typical of non-avialan dinosaurs.

Methodology/Principal Findings

We report that Archaeopteryx long bones are composed of nearly avascular parallel-fibered bone. This is among the slowest growing osseous tissues and is common in ectothermic reptiles. These findings dispute the hypothesis that non-avialan dinosaur growth and physiology were inherited in totality by the first birds. Examining these findings in a phylogenetic context required intensive sampling of outgroup dinosaurs and basalmost birds. Our results demonstrate the presence of a scale-dependent maniraptoran histological continuum that Archaeopteryx and other basalmost birds follow. Growth analysis for Archaeopteryx suggests that these animals showed exponential growth rates like non-avialan dinosaurs, three times slower than living precocial birds, but still within the lowermost range for all endothermic vertebrates.

Conclusions/Significance

The unexpected histology of Archaeopteryx and other basalmost birds is actually consistent with retention of the phylogenetically earlier paravian dinosaur condition when size is considered. The first birds were simply feathered dinosaurs with respect to growth and energetic physiology. The evolution of the novel pattern in modern forms occurred later in the group's history.

Polanyi wrote:What is the problem?

Polanyi wrote:It is true that Archaeopteryx had claws on its wings and teeth in its beak, the problem is that the teeth was not the same as the teeth found on theropod dinosaurs

Polanyi wrote:Archaeopteryx had unserrated teeth which are vastly different from the serrated teeth of theropod dinosaurs

Xu et al, 2000 wrote:Abstract

Non-avian dinosaurs are mostly medium to large-sized animals, and to date all known mature specimens are larger than the most primitive bird, Archaeopteryx. Here we report on a new dromaeosaurid dinosaur, Microraptor zhaoianus gen. et sp. nov., from the Early Cretaceous Jiufotang Formation of Liaoning, China. This is the first mature non-avian dinosaur to be found that is smaller than Archaeopteryx, and it eliminates the size disparity between the earliest birds and their closest non-avian theropod relatives. The more bird-like teeth, the Rahonavis-like ischium and the small number of caudal vertebrae of Microraptor are unique among dromaeosaurids and improve our understanding of the morphological transition to birds. The nearly completely articulated foot shows features, such as distally positioned digit I, slender and recurved pedal claws, and elongated penultimate phalanges, that are comparable to those of arboreal birds. The discovery of these in non-avian theropods provides new insights for studying the palaeoecology of some bird-like theropod dinosaurs.

Polanyi wrote:and besides Ichthyornis dispar is also another extinct bird which had teeth and yet was 100 percent bird.

Polanyi wrote:These traits do not imply that the creature bore any kind of relationship to reptiles.

Polanyi wrote:With regards to the claws on its wings, two bird species living today, the touraco and the hoatzin, have claws which allow them to hold onto branches, yet these creatures are fully birds, with no reptilian characteristics.

Harris [i]et al[/i], 2006 wrote:Summary

Modern birds do not have teeth. Rather, they develop a specialized keratinized structure, called the rhamphotheca, that covers the mandible, maxillae, and premaxillae. Although recombination studies have shown that the avian epidermis can respond to tooth-inductive cues from mouse or lizard oral mesenchyme and participate in tooth formation [1, 2], attempts to initiate tooth development de novo in birds have failed. Here, we describe the formation of teeth in the talpid 2 chicken mutant, including the developmental processes and early molecular changes associated with the formation of teeth. Additionally, we show recapitulation of the early events seen in talpid 2 after in vivo activation of β-catenin in wild-type embryos. We compare the formation of teeth in the talpid 2 mutant with that in the alligator and show the formation of decidedly archosaurian (crocodilian) first-generation teeth in an avian embryo. The formation of teeth in the mutant is coupled with alterations in the specification of the oral/aboral boundary of the jaw. We propose an epigenetic model of the developmental modification of dentition in avian evolution; in this model, changes in the relative position of a lateral signaling center over competent odontogenic mesenchyme led to loss of teeth in avians while maintaining tooth developmental potential.

Results and Discussion

Early dinosaurian ancestors of birds (avialan and nonavialan theropods [3]) possessed conical teeth homologous to those of their reptilian ancestors; however, avian teeth were lost at least 70–80 million years ago. In addition, teeth have been independently lost several times within nonavialan theropods, avialans, and chelonians; this loss is correlated with the formation of the horny, keratinized epithelium and the beak [4–6]. In the epidermis of embryonic birds, there remains a transient thickening that is comparable to the early formation of the dental lamina in the mouse [7, 8]; this structure regresses, and invaginations associated with tooth formation do not form. However, the avian oral epithelium has the developmental capacity to initiate tooth developmental programs with underlying grafts of non-avian oral ectomesenchyme [1, 2] as well as avian mesenchyme competent to form integumentary appendages [8]. Additionally, the avian mandibular mesenchyme can respond to inductive signals from mouse mandibular epithelium and form tooth-like structures with differentiation of pre-dentine [9]. This demonstration of dormant developmental programs revealed in recombination experiments emphasized the study of experimental atavisms, such as ‘‘Hen’s Teeth,’’ in understanding the role of development in evolutionary change [1, 10–12]. Given the latent capacity of the chicken mandibular epidermis to participate in tooth morphogenesis, the problem remains as to what extent tooth programs are maintained in birds in an in vivo context of the developing jaw andhow this relates to the loss of avian teeth in evolution.

Here, we describe the first evidence of tooth developmental programs and morphology initiated in an extant bird as a result of either mutation or experimentation and, importantly, without xenoplastic tissue grafts or tissue manipulation. Because birds and mammals evolved in parallel (avian and mammalian lineages shared a common ancestor in the early amniotes at least 300 million years ago), the relevant comparison for avian tooth developmental programs is within the archosaurs, with crocodilians, the closest living relative of birds. Among other things, crocodilian tooth development, e.g., in alligators, differs from that of mammals in that the formation of first-generation teeth is initiated as an evagination of the integument rather than an invagination of the epithelium [13]. The subsequent generations of tooth formation in the alligator form epithelial invaginations as in mammals. This pattern of tooth formation is thought to be similar for other reptiles [13]. Our analysis of the developmental programs of tooth formation of the talpid2 (ta2) chicken shows similarity with the formation of first-generation crocodilian teeth. In addition, we propose that the oral/aboral boundary establishes a signaling center that, depending on its apposition to underlying competent mesenchyme, controls the initiation and suppression of teeth.

Harris [i]et al[/i], 2006 wrote:Developmental Specification of Teeth in ta2

ta2 is an autosomal recessive mutation that affects the development of several organ systems in the chick [14]. We observed the formation of integumentary outgrowths on the developing jaw of 14- to 16-day-old ta2 embryos (E14–E16). These structures were only formed in close association with the lateral boundary of the oral cavity and were found at the distal boundary of the jaw (Figures 1B and 1D). On the mandible, these structures were equally spaced in a line positioned more centrally in the oral cavity than the formation of the distal lamellae of the wild-type chick jaw (compare Figures 1A and 1B). The maxilla, deformed in the mutant, showed similar outgrowths clumped at the altered distal margin of the jaw (Figure 1D).

ta2 embryos rarely survive past E12. However, we were able to isolate several near-hatching stages (n = 5). The loss of the rhamphotheca during preparation for skeletal analysis in several of these specimens uncovered the formation of a set of conical, saber-shaped outgrowths from the distal mandible; these outgrowths had previously been hidden by the horny epidermis of the beak (Figures 1E and 1F; 100%, n = 3). Underlying these outgrowths, remodelling of the mandible can be seen (Figures 1E and 1F). Furthermore, sectioning of near-hatching-staged ta2 jaws with an intact rhamphotheca revealed the formation of a lamina at the lateral oral/aboral boundary (Figures 1G and 1H). At the base of the lamina, there was evidence of differentiation of the surface epithelial cells away from the normal keratinized squamous morphology (Figure 1H).

Histological analysis of the outgrowths of E14 ta2 embryos indicated a shift of the oral/aboral boundary when compared to wild-type siblings, as marked by specific epithelial histology of the horny stratified squamous epithelium of the aboral epithelium compared to the stratified squamous, nonkeratinizing, epithelium of the oral cavity (dotted line, Figures 1I–1N). The formation of paired outgrowths occurred at this new boundary. The morphology and histology of these outgrowths, including the organization of the dental mesenchyme and vascularization, are identical to those of the early evaginations seen in the development of first-generation teeth of the alligator (Figures 1K–1P, and see [13]). Neither the chick nor alligator dental structures make enamel, and there was no evidence of dentine in either [13]. However, the outgrowths in ta2 show a circumferential layer of cells that resemble early odontoblasts and show evidence of matrix deposition (Figures 1K–1N; see also [15]). These data suggest that the ta2 chick is capable of forming early dental structures anatomically similar to the first-generation teeth of the alligator.

Initiation of Latent Tooth Developmental Programs in ta2

To compare the initial developmental programs of tooth formation in the alligator and chick, we looked at the expression of sonic hedgehog (shh) in comparably staged embryos of the two species. Shh is expressed in the early odontogenic epithelium of vertebrate teeth [16, 17] and is necessary for tooth formation in the mouse [18, 19]. Alligators show distinct round foci of shh expression in forming tooth anlagen connected together by expression that may mark the forming lamina (Figures 2A and 2D). In ta2, similar expression of shh is seen in the oral appendages of E10-staged embryos (Figures 2B and 2E). The expression of shh along the oral/aboral junction and teeth primordia is analogous in both alligators and ta2 embryos (arrows; Figures 2A, 2D, 2B, and 2E). ta2 wild-type siblings showed only diffuse shh expression in the lateral, aboral epidermis (Figures 2C and 2F).

In addition to shh expression, we analyzed the expression of other tooth developmental genes, necessary for tooth formation in the mouse, that are conserved in vertebrate tooth development [16]. patched (ptc) expression is a sensitive marker for shh signalling. Analysis of ptc expression demonstrated the activation of shh signaling in the lateral oral/aboral boundary and punctate foci at the distal margins of the jaw (Figures 2G and 2J). We also analyzed the expression of pitx2, a marker of odontogenic epithelium [20, 21], as well as that of bone morphogenetic protein 4 (bmp4), which is expressed in early odontogenic epithelium but is expressed later and primarily in the mesenchyme [22]. In ta2, pitx2 is expressed in punctate foci on the oral epithelium concomitantly with shh and ptc (Figures 2H and 2K); this expression is in stark contrast with that in the wild-type sibling (Figures 2H and 2K, inset). It is noteworthy that pitx2 is not known to be expressed during the formation of other integumentary appendages and thus is a putative specific marker for tooth formation (see below). Chen et al. [8] noted the absence of bmp4 expression laterally in the chick when compared to the mouse and postulated that this may be a limiting factor in the ability to make teeth in the bird. Consistent with this view, we show that bmp4 is regionally expressed in the mutant around presumptive tooth placodes in the maxilla (Figure 2I) and is upregulated in the distal mandible and lateral aspects of the lower jaw, where tooth formation is seen in older embryos (arrows, Figure 2L). These data indicate that tooth-specific developmental programs are being activated in the ta2 chicken.

Early Disruption of Lateral-Boundary Formation in the Developing Oral Integument in ta2

The affected gene in ta2 is unknown. However, the effect of the ta2 gene on limb development has been shown to be due to an activation of the shh signaling pathway, resulting in an inappropriate activation of shh downstream genes in the absence of increased shh expression [23]. Gene expression analysis in ta2 facial primordia indicates that similar misregulation of shh signaling is occurring there as well [24]. Current work in mouse suggests that early shh signaling in the epidermis may play a role in positioning the sites of tooth formation on the oral epidermis [25, 26]. In addition, the antagonistic signaling function between fibroblast growth factor 8 (fgf8) and bmp4 in the early frontonasal and branchial arch ectoderm is thought to function in a similar manner [27]; how these signaling pathways are integrated remains to be determined.

Given the observed change in the lateral boundary of the jaw seen in histological sections of ta2, we investigated the regulation of early oral/aboral markers in developing facial prominences to see whether early developmental specification of tooth development may be altered in the mutant. Expression of fgf8 in Hamburger and Hamilton stage 21 (s21, [28]) ta2 embryos showed ectopic expression in the presumptive oral cavity and forming maxillary and mandibular processes (Figures 3A–3D). Similarly, the expression of bmp4 outlines a smaller region of the frontonasal ectoderm and coincides with changes in the fgf8 expression domain in the mutant (Figures 3E and 3F). As noted above, in the mouse, pitx2 is an early marker for odontogenic epithelium, in which pitx2 expression straddles the forming oral/aboral boundary as a result of antagonistic interactions between fgf8 and bmp4 [20]. Analysis of pitx2 expression in s22 ta2 embryos shows expression in the frontonasal epidermis that correlates with the altered medial expression domains of fgf8 and bmp4 (Figures 3G and 3H). Importantly, pitx2 shows ectopic expression along the lateral aspect of the forming maxillary process and punctate foci of expression on the lateral maxillary process marking sites of tooth formation (arrows and arrowheads respectively, Figure 3H). Analysis of shh expression shows expression in the presumptive oral cavity (Figure 3I). In ta2, shh expression mirrors the changes seen in fgf8 and bmp4 expression boundaries, and it marks a reduced region of oral epidermis (Figure 3J). The coordinated change in expression of these genes at this early stage correlates with the formation of a novel oral/aboral boundary formed in the mutant as shown in anatomical and histological analyses (Figure 1). This is accompanied by early initiation of gene expression, consistent with the specification of toothforming regions in the mutant.

Developmental Potential of the Oral/Aboral Epidermis

As shown in recombination studies, the avian ectoderm and mesenchyme both have potential to participate in tooth development. Given the association of the observed outgrowths and the novel position of the oral/aboral boundary in the mutant, we postulated that initiation of tooth programs in the ta2 chick was due to the developmental repositioning of an epithelium with signaling potential to overlie mesenchyme competent to form teeth.

Constitutive activation of β-catenin in the epidermis has been shown to be sufficient to induce ectopic integumentary appendages during hair development in mice and feather formation in birds [29–31]. We used forced expression of an activated β-catenin [29] in the forming jaw as an epithelial signal to test the hypothesis that there is differential potential to form appendages in the oral versus aboral epidermis. Ectodermal expression of activated β-catenin (RCAS-β-catenin) resulted in the formation of tooth-like appendages in wild-type chickens (100%, n = 3; control, 0%, n = 3; Figures 4A–4J). The epidermal structures formed evaginated outgrowths that were histologically similar to those found in ta2 (Figures 4B–4D). These ectopic structures expressed shh in a punctate pattern, indicating that appendage developmental programs were initiated (Figures 4E–4J). We found that the majority of forced expression of activated β-catenin in the aboral epidermis, as measured by expression of the viral glycoprotein 3c2, was not sufficient to elicit shh expression or appendage growth (compare Figures 4E–4H with Figures 4K–4N). Thus, there is an intrinsic difference in developmental potential between the chick oral and aboral epidermis: Given expression of activated β-catenin, the chick oral epidermis is capable of making integumentary outgrowths whereas the aboral epidermis is not. Interestingly, when epithelium from the developing chick mandible is grafted to competent mesenchyme of feather-forming regions, new appendages are made only on the oral side of the graft (see Figure 4 of reference [8]); these outgrowths resemble the formations seen in the ta2 mutant.

Development and Evolution of Avian Teeth

Reports in the 19th century byG. St. Hillaire [32], followed by Blanchard [33] andGardiner [34], described the formation of transient papillae, initially argued as homologous to reptilian teeth, on the jaw of embryonic birds. These, however, were later discounted as similar to the dermal papillae seen in other integumentary structures, and the proposal was abandoned ([35], discussed in [34]). We show the initiation of tooth developmental programs as well as the formation of conical, saber-like structures on the lower jaw of the ta2 chicken. The structures formed are similar to those seen in the first-generation teeth of the alligator in position, histological differentiation, and morphogenesis. This finding is consistent with the idea that developmental programs are hierarchical and that atavisms will reinitiate early steps before later processes of more complex teeth. Previous reports interpreted tooth formation in light of knowledge of mammalian tooth development and thus searched for the elusive chick molar. Our work demonstrates a phylogenetic framework in which to interpret the latent ability of avian embryos to form teeth apart from mammalian tooth development.

We show that in ta2, the initiation of tooth developmental programs at a novel boundary formed as a result of altered specification of the oral/aboral junction early in development. We propose that this altered positioning of the oral/aboral boundary in the mutant leads to a juxtaposition of a presumptive boundary signaling center with underlying oral mesenchyme competent to form teeth (Figure 4O). The outgrowths in the mutant are patterned and show regional regulation of gene expression as well as specific differentiation, consistent with tooth formation in other vertebrates. Whether the matrix seen in both ta2 and alligator outgrowths is dentine awaits further biochemical and molecular analysis. Because grafting of the putative epithelial boundary region over competent mesenchyme leads to ta2-like tooth outgrowths in the oral region [8], we believe that the effect of the ta2 gene on tooth developmental programs
is secondary, resulting from changes in the regional specification of a lateral tooth-inductive signaling center rather than specifically altering a molecular modifier of ontogenetic pathways.

We hypothesize that the loss of teeth in birds was due to the loss of direct apposition between an epithelial signaling center at the oral/aboral boundary and the underlying mesenchyme of the oral cavity competent to form integumentary appendages. Our model provides a unique developmental mechanism for understanding how specific structures are lost and reinitiated and goes beyond contemporary models of selective gene loss or loss of signaling capability during tooth ontogeny in evolution [2, 8]. Importantly, the control of this inductive event in different facial prominences during development would permit the regional, or modular, loss of teeth as seen in many nonavialan dinosaurs and avialans [4–6] while allowing them to retain the ability to form teeth on separate regions of the jaw derived from different facial prominences.

Our data support and revitalize the controversial anatomical findings of G. St. Hilaire [32], Blanchard [33], and Gardnier [34] by demonstrating the initiation of tooth developmental programs in embryonic birds, and we propose that the structures formed, and the early developmental processes involved, are homologous with the formation of the first rudimentary teeth in the alligators.

Polanyi wrote:Ichthyornis dispar: A toothed, flying bird from the Late Cretaceous of Kansas
http://www.oceansofkansas.com/Ichthyornis.html

"In the lower teeth of Ichthyornis, the pulp-cavity passes well up into the base of the crown. The fang is compressed, and directed downward and forward. It is firmly set in a deep socket, which it nearly or quite fills. The dental succession took place vertically, as in Crocodiles and Dinosaurs; not laterally as in Hesperornis and the Mosasaurs, a fact of no little significance. The young teeth are much inclined when they first appear above the jaw, after the old teeth have been expelled." Marsh, 1883.

Polanyi wrote:What about the long bony tail?

Polanyi wrote:Birds with long bony tails are rare, but ancient birds have been discovered which also possessed long bony tails, one such bird is Longicrusavis.

This is from an article appeared in the March (2010) issue of the Journal of Vertebrate Paleontology:

"Longicrusavis adds to the magnificent diversity of ancient birds, many of them sporting teeth, wing claws, and long bony tails, that recently have been unearthed from northeastern China," said Luis Chiappe, a co-author of the study.

http://www.sciencedaily.com/releases/20 ... 233003.htm

Polanyi wrote:Other things to consider, Archaeopteryx had fully formed flying feathers (including asymmetric vanes and ventral, reinforcing furrows as in modern flying birds)

Polanyi wrote:the classical elliptical wings of modern woodland birds, and a large wishbone for attachment of muscles responsible for the downstroke of the wings.

Polanyi wrote:Its brain was essentially that of a flying bird, with a large cerebellum and visual cortex.

Polanyi wrote:Furthermore, like other birds, both its maxilla (upper jaw) and mandible (lower jaw) moved.

Polanyi wrote:In most vertebrates, including reptiles, only the mandible moves.

Polanyi wrote:

ALL fucking fossils are exactly as transitional as all others (with the exception of those for which the fossils represent a dead end).

And evolutionists go into denial, I've heard this a thousand times already, Archaeopteryx supposedly was more dinosaur than bird because it had a long bony tail, teeth in it's beak, and claws on its wings, this was suppose to imply one thing: birds evolved from dinosaurs.

My purpose of this thread was merely to show why this assertion is problematic.

Rumraket wrote:Fucking hell Cali, I think that post comes in at a good 3rd place in disintegrating creotard canards, behind the ones on Radiometric dating and Thermodynamics.

Calilasseia wrote:Plus, if you're about to erect the fatuous "no transitional fossils exist" creationist canard, then you really do need to go back to school and re-learn science from the ground up. Not least because, in case you hadn't worked this out, every living organism is a transitional form between its parents and its offspring.

Calilasseia wrote:Even if we make the massively conservative assumption that all the genes in an organism's genome obey simple Mendelian laws (which underestimates the number of possible genomic combinations by a large factor, given the data that exists with respect to genes such as the Rhesus D factor gene in humans), such an assumption leads to the conclusion that, for an organism with 25,000 such genes, the number of possible combinations is 225,000, a gigantic number of possible variations that can exist even in the absence of mutations. Consequently, the scope for variation to be disseminated to future generations is enormous, and with each new generation, the population will change.

Calilasseia wrote:Actually, Ichthyornis is regarded as being a member of a sister clade to modern birds, the Subclass Ichthyornithes, which is taxonomically distinct from the Neoaves to which modern birds belong, but sharing a common ancestor therewith via the Carinatae. Therefore your above assertion that this was "100% bird" is not supported by the taxonomic evidence. It's part of a lineage with no modern descendants. Tell me, did you ever bother to learn anything about basic cladistics?

Calilasseia wrote:Indeed, modern scientists do not consider reptiles to be a monophyletic clade if the birds are omitted.