may have considered the problem of numbering the fingers of birds to overcome? The truth is that embryologists have probably not find stronger evidence the fact that the fingers of adult birds grow from mesenchymal condensation (Anlagen), II, III and IV than the repeated observations of the originally five-finger hand, which disappears during the development of fingers I and V (Larsson & Wagner, 2002; Galis et al. 2003) . Paleontologists have similarly strong evidence for the reduction of the number of fingers - but this time on I, II and III - there even longer. Homeotického shift hypothesis, which was designed to unify the two types of evidence, furthermore, it was tested (Vargas et al. 2008; Tamura et al. 2011). Therefore the question answered?
Two new articles from evo-devo logs indicate it is not. Neither side of the problem is not completely closed: embryologists we still have an interesting question of what mechanisms are involved in homeotické transformation (in this issue made strides made strides Tamura et al. 2011), paleontologists can again be addressed by the in theropod evolution of the shift occurred. Xu et al. (2009) as a wave of indignation when he suggested that this could become really early - even before the emergence tetanur, so I lay, which in addition includes a number of bird-like dinosaurs to birds (who are grouped with birds Maniraptoriformes ) tyrannosauroidy, including the popular allosauroidy karcharodontosaurů and megalosauroidy spinosaura type.
New studies are devoted to both these parties. Among the names of their authors find some intersections, especially the name of Günter P. Wagner, who along with paleontologist JA Gauthier homeotického shift hypothesis for late 90 years proposed (Wagner & Gauthier 1999). The first of these studies (Bever et al. 2011) Palaeontological and it is only logical that they participate in it as Gauthier himself. Abstract The authors note that the paleontological support for the hypothesis has been challenged by the shift. It may sound odd, but the authors have in mind its "description limusaura. What this study we tried to say I have a blog zreprodukoval times, not once, but I'm not completely satisfied with the outcome. So I'll try it again: the authors point of Wagner Gauthier and the idea that condensation on the first finger (C1) at the same time evolution ceased and the first finger (D1) instead of the condensation started to develop a second (C2), came up with was that while metakarpály tříprstých tetanur resemble metakarpálům II, III, IV older theropods, fingers at them drinks for a change reminiscent of fingers I, II, III. Xu et al. (2009) therefore suggested that the morphological features ("identity") of fingers I, II, III disappeared, so that the re-modeled tetanur fingers II, III, IV. The Wagner et al. perceived as a legitimate attack on his hypothesis, because it really means something else entirely - as and when the authors stated in their first response to the problem (Vargas et al. 2009; see here), it is not too sure if something like that we could even say homeotický shift.
Bever et al. (2011) agrees with the authors describe limusaurova that the shift occurred earlier than suggested by Wagner & Gauthier (1999), their idea of \u200b\u200bthe whole event, but still not shared. Such a conclusion is led reflection questions about a) how progress can be seen from the shift homeotického bone, b) whether now known fossil data support the hypothesis of a shift and c) at what point teropodního development tree to the transformation I, II, III → II, III, IV occurred. Recall that Wagner & Gauthier (1999) planted between this event and the rest megalosauroidy tetanur ( Neotetanurae , equivalent vided Allosaurus + sparrow). The new model, Bever et al. present, allows for a relatively large area "developmentálního polymorphism. About him more in the next section, which concerns the second study (in which the composition is partly the same authors):
Two new articles from evo-devo logs indicate it is not. Neither side of the problem is not completely closed: embryologists we still have an interesting question of what mechanisms are involved in homeotické transformation (in this issue made strides made strides Tamura et al. 2011), paleontologists can again be addressed by the in theropod evolution of the shift occurred. Xu et al. (2009) as a wave of indignation when he suggested that this could become really early - even before the emergence tetanur, so I lay, which in addition includes a number of bird-like dinosaurs to birds (who are grouped with birds Maniraptoriformes ) tyrannosauroidy, including the popular allosauroidy karcharodontosaurů and megalosauroidy spinosaura type.
New studies are devoted to both these parties. Among the names of their authors find some intersections, especially the name of Günter P. Wagner, who along with paleontologist JA Gauthier homeotického shift hypothesis for late 90 years proposed (Wagner & Gauthier 1999). The first of these studies (Bever et al. 2011) Palaeontological and it is only logical that they participate in it as Gauthier himself. Abstract The authors note that the paleontological support for the hypothesis has been challenged by the shift. It may sound odd, but the authors have in mind its "description limusaura. What this study we tried to say I have a blog zreprodukoval times, not once, but I'm not completely satisfied with the outcome. So I'll try it again: the authors point of Wagner Gauthier and the idea that condensation on the first finger (C1) at the same time evolution ceased and the first finger (D1) instead of the condensation started to develop a second (C2), came up with was that while metakarpály tříprstých tetanur resemble metakarpálům II, III, IV older theropods, fingers at them drinks for a change reminiscent of fingers I, II, III. Xu et al. (2009) therefore suggested that the morphological features ("identity") of fingers I, II, III disappeared, so that the re-modeled tetanur fingers II, III, IV. The Wagner et al. perceived as a legitimate attack on his hypothesis, because it really means something else entirely - as and when the authors stated in their first response to the problem (Vargas et al. 2009; see here), it is not too sure if something like that we could even say homeotický shift.
Bever et al. (2011) agrees with the authors describe limusaurova that the shift occurred earlier than suggested by Wagner & Gauthier (1999), their idea of \u200b\u200bthe whole event, but still not shared. Such a conclusion is led reflection questions about a) how progress can be seen from the shift homeotického bone, b) whether now known fossil data support the hypothesis of a shift and c) at what point teropodního development tree to the transformation I, II, III → II, III, IV occurred. Recall that Wagner & Gauthier (1999) planted between this event and the rest megalosauroidy tetanur ( Neotetanurae , equivalent vided Allosaurus + sparrow). The new model, Bever et al. present, allows for a relatively large area "developmentálního polymorphism. About him more in the next section, which concerns the second study (in which the composition is partly the same authors):
Figure 1 (top left) presents three hypotheses that seek to reconcile conflicting paleontological and embryological data - pyramid reduction hypothesis (A), the hypothesis of the primary axis of movement (B) and homeotického shift hypothesis (C). The left column lists the position of condensation, which will grow your fingers, in the true identity of each final finger. Colors are chosen according to the identity (orange - fingers, yellow - Finger II Blue - Finger III, green - fingers, in black - a finger missing). "X" indicates that the position of a finger missing. Black box shows the position of the primary axis of the hypothesis. The hypothesis presented in the description limusaura (Xu et al. 2009) is considered a variation on the pyramid reduction hypothesis.
Figure 2 (top right): phylogenetic occurrence homeotického shift in the theropods. (A) Model of lateral loss of toes - toes are losing the one (outer side) hand. (B) bilateral model, assuming the conservation of Morse's rule, that they are preferentially lost ontogenetic latest toes 1 and 5 Bilateral model requires that the shift occurred before the loss of finger IV. (C) Model developmentální variability; bilateral variant of the model, which puts homeotický shift just before the emergence vided Averostra (in the authors' conception of the exclusionary dilofosauridy). Cladogram is adapted from Xu et al. (2009). Illustrations are scaled to the hand to maintain the same length proximodistální. For sources of illustrations, see the original publication. Colors represent the same finger as in Figure 1, except that the missing fingers (bare = metakarpály) are now captured in white.
Figure 3 (bottom) position, identity and expression of HoxD genes in the fingers of the original (A) and transformed homeoticky (B) of the hand. Ancestral state, as represented by mice, characterized by the identity of fingers coupled with their position (D1 arises from C1, etc.). HoxD-13 is expressed in all five fingers, HoxD-8 - 12 all outside the top condensation (C1). The transformed positions 2-4 hands to develop the identity of I-III, which corresponds to a shift in gene expression. HoxD-13 is again expressed in all developing fingers, but the expression of HoxD-8 - 12 condensation is limited to 3 and 4, respectively. Identity II and III. The gray area shows the area of \u200b\u200bexpression of HoxD-8 - 12th
second of these studies presented by Young et al. (2011). This again comes with the homeotického hypothesis that the shift (Frame shift hypothesis) is a good explanation for the observed data. Also note that the fact that bird fingers grow from condensation, which are homologous with fingers 2, 3, 4 other quadrupeds, nothing. This is quite an important message for some paleontologists - I do not want any of his knowledge of the issue to question Darren Naish repeatedly identified as embryological evidence as " misinterpreted" and believes that the bird actually grows an inch from the first position. Nice, but because the entire line of embryologists would be (and was ) prepared to mark the misinterpreted paleontological evidence, much to the approach we type it wrong you're doing! " received. But back to Young et al. They argue that similarly growing evidence to suggest that "programs developmentální" bird's toes are inherited from the finger, the archaic theropods found in positions 1, 2, 3 Here it is important to note that, contrary to intuition, the identity of the fingers (ie, shape, number of finger cells or "falangeální formula" and morphological features) are totally independent of the position of the finger increases. Experiments in chickens have demonstrated that appropriate interventions in ontogeny can leave any finger grow virtually anywhere .* What determines the identity finger, the expression of specific genes, called HoxD (eg, the identity of an inch frames that genes HoxD-10, HoxD-11 and HoxD-12 here do not express). Young et al. (2011) presented new questions that future research will need to answer - to deal with, however, by whether homeotickému shift did take place, it is unnecessary. Here the debate is over.
authors show again, what is the main difference (and the original Wagner-Gauthier) hypotheses than the one presented by Xu et al. (2009): they assume the identity of the fingers (D1) was preserved theropod evolution and during the shift only "přepla" condensation of C2, while "limusaurův model" assumes that the identity and disappear with time, little by little , reappeared on the finger D2. It is homeotický shift but homely convergence, where the morphology of the fingers II, III, IV, converge with the morphology ("identity") of fingers I, II, III, former theropods. Xu et al. (2009) are the first who suggested that the loss of fingers in theropods took place in the normal way, ie from both sides ("pyramid reduction hypothesis"), and that the morphology of the remaining positions to adapt to the way they looked before your fingers in different positions because it be beneficial - as interpreted this event Kundrat (2009, Kundrat et al. 2002) and Galis et al. (2003). This hypothesis requires that each of the original condensation disappeared completely independently of each feature, which together comprise the identity of fingers I-III (and possibly IV, considering tetanury The four basal), and that these features were independently re-acquired by the convergent positions 2 to 4 (or 5). Xu et al. (2009), this did not take into account when their hypothesis described as efficient. Young et al. (2011) also cite Bever et al. that the concept of team and Xu homeotickém shift - namely that it may be long and gradually - they are wrong. Loss of identity and fingers, to which the proved limusaura occurred (as indicated by its plain metakarpál finger without cells), then Young et al. (2011) interpret as apomorfii ceratosaurů, which has no relevance to the discussion of bird evolution. In this statement are cited work Vargas et al. (2009) and Bever et al. (2011).
Young et al. comes with a new model reduction and loss of fingers in theropod evolution, which corrects an earlier draft of Wagner and Gauthier. With the penetration teams of authors, we can be sure that it is the same model, by Bever et al. (2011). As the authors note, all agree that the first finger, which lost pleziomorficky pětiprstá hand, was the fifth. So far everything is clear. Previous Model homeotického shift then assumed that the next in line is the fourth finger, and only then what was lost and he was followed by the transformation. This event can therefore be dated to a later time than when they disappeared in the latest Jurassic marks the fourth finger, but before than in the Cretaceous bird was Crown asset. Because we know that the dinosaur is a general tendency to reduce the outer fingers of the hand, such a scenario makes sense. The authors point out, however, that the order in which the fingers are reduced may not correspond to the order in which they lost . Fingers 1 and 5 during ontogeny developed last, and therefore are the first lost during phylogeny. It would be highly unusual if the loss of fingers advanced theropods from the outside by (in order of 5, 4 ,...) - authors tend rather to the general developmental pattern called Morse Code (which assumes that the later developing distant fingers disappear sooner than the middle finger earlier) and paid for them. Then it would be necessary to shift homeotickou transformation into the fourth period, the loss and 5 finger, which of course is the development tree need to look deeper - at the birth vided Averostra (which the authors interpret as Ceratosauria + Tetanurae , although in the tree, according to the original definition apomorphy-based Paul [2002] still include dilofosaura **). This means that the move was not just fingers I, II and III, as well as finger IV. Hand-toed modern birds arose when condensation from the fifth (C5) disappeared identity toe IV (D4). Developmentální variability model (DVM), which introduced Bever et al. (2011), then says that there was a time (a specific place on the cladograms), which was relatively high probability that the identities of fingers I-IV to grow as a condensation of 1-4, and 2 to 5 When they reduce the ability to develop functional C1 condensation finger, there were two parallel phenomena. Already "displaced" individuals whose offspring are all living birds, it did not trespass, because their fingers have grown up in positions 2 to 5 "Neposunutí" specimens completely lost their identity and fingers, but they still left fingers II-IV on the initial positions 2 to 4 That seems to demonstrate Limusaurus which, according to Young et al. not moved from the area developmentálně variable. It is thus quite possible then that dichotomy "displacement / neposunutí" exactly fits the specific cleavage of cladograms, and Tetanurae / Ceratosauria .
authors wonder whether it is possible that the variability developmentální left an impression even in the ontogenesis of birds today, and whether or not an extreme reduction in forepaw ceratosaurů (along with the reduced selection pressure, which on influence them) to explain why the modification of their hands so radically different from other tetrapods.
The study is a valuable one practical suggestion. So when we know that conflicting numbering used embryology and paleontology, in either case is true, what to do in order to avoid confusion? It really keeps your thumb as an inch, when the growing space for a finger? There is reason to impose one group numbering in the second, as proposed by Tamura et al.? Apparently not - we just sometimes more depending on the position of the fingers, sometimes to their identity. Young et al. (2011) therefore propose the following: if it places us on the homology of condensation regardless of what they at a later stage of development HoxD genes is entrusted by the identity, use Arabic numbers, ie 1 to 5 From this perspective, bird's toes 2, 3, 4, which when compared with the primitive pětiprstou hand (which should be conserved by humans), grow from a position in which it develops 2, 3 and 4 finger. If you are interested in us but the identity of the fingers, as the number of finger cells and their morphological features - features that They later imprint HoxD genes - use Roman numbers I-V. Both views are equally authentic, but only in the context of different developmental stages. soul of this scheme is to Blog .
* To avoid confusion, but the only known cases of "frame shift" (shift = homeotického) artificially create ourselves: Young et al. (2011) cite the case as scinka serpentine, Chalcides Chalcides , where the position of the primary growth axis during embryonic development suggests numbering fingers as 2, 3, 4, while the morphological features, such as adhesion and foremost distal karpálu metakarpálu - militate in favor of Model I, II, III. Likewise falangeální formula suggests that the identities of the fingers are, in fact I, II and III. Italian scink is equivalent to a perfect bird.
** Averostra sense Paul's name vided based on the presence of so-called window promaxillárního to tetanury, ceratosauři, Dilophosaurus and several of his relatives. Although the third group is usually considered vided as part Coelophysoidea whose basal representatives of this feature is missing. In some phylogenetic hypotheses but dilofosauridi stands at between cladograms and celofyzoidy ceratosaury (Smith et al. 2007), and then the part Averostra should go. For it was not so easy to override this name as a reference to the node Ceratosauria + Tetanurae who suffer from such instability (CUNY & Ezcurra 2007). In this sense, it also used by Xu et al. (2009) and Young et al. (2011).
Note: It's a bit sad, but to after two years and a well-written study, I understand, what is the difference between Wagner-Gauthierovým model "frame shift" proposal and Xu et al. This in the Articles section Errata classified with reference to this article.
authors show again, what is the main difference (and the original Wagner-Gauthier) hypotheses than the one presented by Xu et al. (2009): they assume the identity of the fingers (D1) was preserved theropod evolution and during the shift only "přepla" condensation of C2, while "limusaurův model" assumes that the identity and disappear with time, little by little , reappeared on the finger D2. It is homeotický shift but homely convergence, where the morphology of the fingers II, III, IV, converge with the morphology ("identity") of fingers I, II, III, former theropods. Xu et al. (2009) are the first who suggested that the loss of fingers in theropods took place in the normal way, ie from both sides ("pyramid reduction hypothesis"), and that the morphology of the remaining positions to adapt to the way they looked before your fingers in different positions because it be beneficial - as interpreted this event Kundrat (2009, Kundrat et al. 2002) and Galis et al. (2003). This hypothesis requires that each of the original condensation disappeared completely independently of each feature, which together comprise the identity of fingers I-III (and possibly IV, considering tetanury The four basal), and that these features were independently re-acquired by the convergent positions 2 to 4 (or 5). Xu et al. (2009), this did not take into account when their hypothesis described as efficient. Young et al. (2011) also cite Bever et al. that the concept of team and Xu homeotickém shift - namely that it may be long and gradually - they are wrong. Loss of identity and fingers, to which the proved limusaura occurred (as indicated by its plain metakarpál finger without cells), then Young et al. (2011) interpret as apomorfii ceratosaurů, which has no relevance to the discussion of bird evolution. In this statement are cited work Vargas et al. (2009) and Bever et al. (2011).
Young et al. comes with a new model reduction and loss of fingers in theropod evolution, which corrects an earlier draft of Wagner and Gauthier. With the penetration teams of authors, we can be sure that it is the same model, by Bever et al. (2011). As the authors note, all agree that the first finger, which lost pleziomorficky pětiprstá hand, was the fifth. So far everything is clear. Previous Model homeotického shift then assumed that the next in line is the fourth finger, and only then what was lost and he was followed by the transformation. This event can therefore be dated to a later time than when they disappeared in the latest Jurassic marks the fourth finger, but before than in the Cretaceous bird was Crown asset. Because we know that the dinosaur is a general tendency to reduce the outer fingers of the hand, such a scenario makes sense. The authors point out, however, that the order in which the fingers are reduced may not correspond to the order in which they lost . Fingers 1 and 5 during ontogeny developed last, and therefore are the first lost during phylogeny. It would be highly unusual if the loss of fingers advanced theropods from the outside by (in order of 5, 4 ,...) - authors tend rather to the general developmental pattern called Morse Code (which assumes that the later developing distant fingers disappear sooner than the middle finger earlier) and paid for them. Then it would be necessary to shift homeotickou transformation into the fourth period, the loss and 5 finger, which of course is the development tree need to look deeper - at the birth vided Averostra (which the authors interpret as Ceratosauria + Tetanurae , although in the tree, according to the original definition apomorphy-based Paul [2002] still include dilofosaura **). This means that the move was not just fingers I, II and III, as well as finger IV. Hand-toed modern birds arose when condensation from the fifth (C5) disappeared identity toe IV (D4). Developmentální variability model (DVM), which introduced Bever et al. (2011), then says that there was a time (a specific place on the cladograms), which was relatively high probability that the identities of fingers I-IV to grow as a condensation of 1-4, and 2 to 5 When they reduce the ability to develop functional C1 condensation finger, there were two parallel phenomena. Already "displaced" individuals whose offspring are all living birds, it did not trespass, because their fingers have grown up in positions 2 to 5 "Neposunutí" specimens completely lost their identity and fingers, but they still left fingers II-IV on the initial positions 2 to 4 That seems to demonstrate Limusaurus which, according to Young et al. not moved from the area developmentálně variable. It is thus quite possible then that dichotomy "displacement / neposunutí" exactly fits the specific cleavage of cladograms, and Tetanurae / Ceratosauria .
authors wonder whether it is possible that the variability developmentální left an impression even in the ontogenesis of birds today, and whether or not an extreme reduction in forepaw ceratosaurů (along with the reduced selection pressure, which on influence them) to explain why the modification of their hands so radically different from other tetrapods.
The study is a valuable one practical suggestion. So when we know that conflicting numbering used embryology and paleontology, in either case is true, what to do in order to avoid confusion? It really keeps your thumb as an inch, when the growing space for a finger? There is reason to impose one group numbering in the second, as proposed by Tamura et al.? Apparently not - we just sometimes more depending on the position of the fingers, sometimes to their identity. Young et al. (2011) therefore propose the following: if it places us on the homology of condensation regardless of what they at a later stage of development HoxD genes is entrusted by the identity, use Arabic numbers, ie 1 to 5 From this perspective, bird's toes 2, 3, 4, which when compared with the primitive pětiprstou hand (which should be conserved by humans), grow from a position in which it develops 2, 3 and 4 finger. If you are interested in us but the identity of the fingers, as the number of finger cells and their morphological features - features that They later imprint HoxD genes - use Roman numbers I-V. Both views are equally authentic, but only in the context of different developmental stages. soul of this scheme is to Blog .
* To avoid confusion, but the only known cases of "frame shift" (shift = homeotického) artificially create ourselves: Young et al. (2011) cite the case as scinka serpentine, Chalcides Chalcides , where the position of the primary growth axis during embryonic development suggests numbering fingers as 2, 3, 4, while the morphological features, such as adhesion and foremost distal karpálu metakarpálu - militate in favor of Model I, II, III. Likewise falangeální formula suggests that the identities of the fingers are, in fact I, II and III. Italian scink is equivalent to a perfect bird.
** Averostra sense Paul's name vided based on the presence of so-called window promaxillárního to tetanury, ceratosauři, Dilophosaurus and several of his relatives. Although the third group is usually considered vided as part Coelophysoidea whose basal representatives of this feature is missing. In some phylogenetic hypotheses but dilofosauridi stands at between cladograms and celofyzoidy ceratosaury (Smith et al. 2007), and then the part Averostra should go. For it was not so easy to override this name as a reference to the node Ceratosauria + Tetanurae who suffer from such instability (CUNY & Ezcurra 2007). In this sense, it also used by Xu et al. (2009) and Young et al. (2011).
Note: It's a bit sad, but to after two years and a well-written study, I understand, what is the difference between Wagner-Gauthierovým model "frame shift" proposal and Xu et al. This in the Articles section Errata classified with reference to this article.
Sources:
- http://scienceblogs.com/tetrapodzoology/2009/06/limusaurus_is_awesome.php
- http://scienceblogs.com/tetrapodzoology/2010/06/clubs_spurs_spikes_and_claws.php
- http://scienceblogs.com/pharyngula/2009/06/digit_numbering_and_limb ... # c1716886
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