Dinosaur to bird proponents take a characteristic and try to make a case that the characteristic evolved from coelurosaur dinosaur to bird. But each time we look in detail at the actual evidence for that characteristic, we see that the avian-like characteristics appear at Oviraptors/Paraves and are not found in coelurosaur dinosaurs.
1. Semilunate carpal
http://pterosaurnet.blogspot.ca/2016/04/semilunate-carpal.html
2. Feathers
See
http://pterosaurnet.blogspot.ca/2016/10/feathers.html
Pterosaurs
https://en.wikipedia.org/wiki/Pterosaur#Pycnofibers
Some (Czerkas and Ji, 2002) have speculated that pycnofibers were an antecedent of proto-feathers, but the available impressions of pterosaur integuments are not like the "quills" found on many of the bird-like maniraptoran specimens in the fossil record.[33] Pterosaur pycnofibers were structured similarly to theropod proto-feathers.[16]
Research into the genetic code of American alligator embryos could suggest that pycnofibres, crocodile scutes and avian feathers are developmentally homologous, based on the construction of their beta-keratin.[34]
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2842671/
There are also questions about the presence and nature of some filamentous structures covering the epidermis, the so-called ‘hair-like’ fibres or ‘fur’ (Goldfuss 1831; Sharov 1971; Unwin & Bakhurina 1994), which were also found in specimens from the Jehol Group and regarded as potential protofeathers (Czerkas & Ji 2002; Ji & Yuan 2002).
3. Breathing sacs and uni-directional lungs
http://pterosaurnet.blogspot.ca/2010/05/another-thing-to-watch-for.html
http://pterosaurnet.blogspot.ca/2013/12/respiratory-cycle-of-bird_16.html
http://pterosaurnet.blogspot.ca/2011/11/breathing-pterosaurs-are-like-birds.html
http://pterosaurnet.blogspot.ca/2010/05/uncinate-processes.html
http://pterosaurnet.blogspot.ca/2013/12/respiratory-cycle-of-bird_16.html
https://www.academia.edu/1578001/Basic_avian_pulmonary_design_and_flow-through_ventilation_in_non-avian_theropod_dinosaurs
Sacral pneumaticity in theropoddinosaurs, the basis for inferring caudally positioned air sacs, is consistent with a ‘caudal origin model’ and establishes the potential for flow-through ventilation in the dinosaurian ancestors of living birds.
Although our model does not predict the specific type of intrapulmonary airflow in non-avian theropods (unidirectional versus bidirectional), it does establish both pulmonary and skeletal prerequisites required for flow-through ventilation, a plausible early stage in the evolution of the highly derived avian pulmonary apparatus.
4. Postcranial pneumatization
http://www.ivpp.ac.cn/qt/papers/201403/P020140314368593911410.pdf
In comparison with the gigantic, derived Late Cretaceous tyrannosauroids, Liaoning tyrannosauroids have a less pneumatic skeleton. Postcranial pneumatization is, as in tyrannosauroids, also less developed in small, basal members of many non-avian coelurosaurian groups15,24 and more developed in large, derived members of these groups. The distribution of postcranial pneumatization is thus very complex among coelurosaurians15,24, rather than displaying a continuous evolutionary trend along the line to birds.
5. Miniaturization
https://www.sciencedaily.com/releases/2014/02/140223215134.htm
Puttick et al were really surprised to discover that the key size shifts happened at the same time, at the origin of Paraves," (Puttick et al 2014). Before the origin of Aves, on the branch leading to Paraves, high rates of evolution led to a smaller body size and a relatively larger forelimb in Paraves. These changes are on a single branch leading to Paraves, representing a shift to a new smaller size and larger forelimb at this point.Paraves, rather than Aves alone, shifted to a different evolutionary model relative to other coelurosaurian theropods (Table 2). On all trees and for both femur and forelimb size, the model with a regime shift at Paraves, rather than Aves, is favored (Table S10). (Puttick et al 2014)
Michael J. Benton (2015)
These studies of bird origins [56–59] used different datasets, different phylogenies, and different analytical techniques, and yet they converged on the same result. As an example, Puttick et al. [56] showed that miniaturization and wing expansion, critical anatomical requirements to be a bird, arose some 10 Myr before Archaeopteryx among the wider clade Paraves (figure 4), and that the rate of change was 160 times the normal evolutionary rate, suggesting a rapid, adaptive switch that enabled the diversification and success of this clade of tiny, possibly tree-climbing and gliding dinosaurs.http://onlinelibrary.wiley.com/doi/10.1111/evo.12363/full
Using recently developed phylogenetic comparative methods, we find an increase in rates of body size and body size dependent forelimb evolution leading to small body size relative to forelimb length in Paraves
Paraves, rather than Aves alone, shifted to a different evolutionary model relative to other coelurosaurian theropods (Table 2). On all trees and for both femur and forelimb size, the model with a regime shift at Paraves , rather than Aves, is favored.
As noted above, the trait MEDUSA algorithm cannot distinguish between rapid periods of evolution at the origin of a focal clade, and sustained periods of directional evolution among constituent lineages of the focal clade (Thomas and Freckleton 2012). Our results suggest that the detected rapid branch-based increases probably arise from rapid branch-specific evolution at the clade origin, as we find no evolution for directional trends in Paraves.http://science.sciencemag.org/content/345/6196/562
These approaches identify two drivers underlying the dinosaur-bird transition. The theropod lineage directly ancestral to birds undergoes sustained miniaturization across 50 million years and at least 12 consecutive branches (internodes) and evolves skeletal adaptations four times faster than other dinosaurs.
Rates of Dinosaur Body Mass Evolution Indicate 170 Million Years of Sustained Ecological Innovation on the Avian Stem Lineage
Roger B. J. Benson,1,* Nicolás E. Campione,2,3 Matthew T. Carrano,4 Philip D. Mannion,5 Corwin Sullivan,6 Paul Upchurch,7 and David C. Evans3,8
Table 36 Origin of small body size in Paraves, which has very small primitive body mass— around 1 kg (Anchiornis, 0.68 kg; Microraptor, 1.5 kg; Archaeopteryx, 0.97 kg (subadult)) 7 Origin of small body size in Coelurosauria (e.g., Ornitholestes, 14 kg ; Zuolong, 88 kg)
6. Sternum
http://pterosaurnet.blogspot.ca/2010/05/keeled-breastbone.html
Basal Paraves used the same flight stroke and muscles as Pterosaurs which is sufficient for flapping flight. It does not require a deeply keeled sternum.
7. Enlarged brain
Notably, major bird characteristics often exhibit a complex, mosaic evolutionary distribution throughout the theropod tree, and several evolutionary stages are characterized by accelerated changes (70). For example, the early evolution of paravian theropods features cerebral expansion and elaboration of visually associated brain regions (71)
8. Ankle
More remarkably, however, this finding reveals an unexpected evolutionary transformation in birds. In embryos of the land egg-laying animals, the amniotes (which include crocodilians, lizards, turtles, and mammals, who secondarily evolved live birth) the intermedium fuses to the anklebone shortly after it forms, disappearing as a separate element. This does not occur in the bird ankle, which develops more like their very distant relatives that still lay their eggs in water, the amphibians. Since birds clearly belong within land egg-laying animals, their ankles have somehow resurrected a long-lost developmental pathway, still retained in the amphibians of today -- a surprising case of evolutionary reversal .
This work has revealed that the ascending process does not develop from either the heel bone or the ankle bone, but from a third element, the intermedium. In the ancient lineage of paleognath birds (such as tinamous, ostriches and kiwis) the intermedium comes closer to the anklebone, producing a dinosaur-like pattern. However, in the other major avian branch (neognaths), which includes most species of living birds, it comes closer to the heel bone; that creates the impression it is a different structure, when it is actually the same.
The ASC [ascending process of the astragalus] originated in early dinosaurs along changes to upright posture and locomotion, revealing an intriguing combination of functional innovation and reversion in its evolution.
http://www.jstor.org/pss/4085810
"The structure of the avian tarsus has recently been cited as evidence for the derivation of birds from theropod dinosaurs. Although birds and theropods have a long triangular ossification in front of the tibia and attached to the proximal tarsals, the morphological relationships of this bone are fundamentally different in the two groups. In modern birds and in all Mesozoic birds, this "pretibial" bone is a high, narrow structure associated primarily with the calcaneum, but independently ossified. The corresponding structure in dinosaurs is a broad extension [ascending process] of theastragalus" [The astragalus is also called the talus bone].
(L.D. Martin et al)
In birds and theropods, a sheet of bone that braces the anterior face of the tibia is usually called the “ascending process of the astragalus” or simply the “ascending process.” It is less evident in adult neornithines than in juvenile (or embryonic) neornithines and Mesozoic birds. This sheet of bone is particularly conspicuous in basal birds, including Archaeopteryx. This common feature has consistently been regarded as one of the most striking homologies shared by birds and theropods (e.g., Paul 2002), but comparative anatomical research reveals that establishing the homologies of the ascending processes of theropods and birds is difficult.
In neornithines a triangular, late-developing cartilage appears, after fusion of the proximal tarsals, on the lateral face of the tibia, dorsal to the calcaneum (Martin et al. 1980, and references therein). Subsequently, this cartilage fuses with the calcaneum, with which it is primarily associated in both Mesozoic and modern birds (Martin et al. 1980; Fig. 6). Morse (1872) called this structure the “pretibial.” Ostrom (e.g., 1976a,1985) argued that this structure is homologous with a similar structure in the tarsus of theropods (see also Paul 2002), but according to Martin et al. (1980:88) “differences in placement and (the pretibial's) late appearance during development suggest that it is a uniquely derived character for birds and is properly termed a pretibial bone, rather than an astragalar process.”
In contrast to the situation in neornithine and Mesozoic birds, the ascending process of theropods is usually a broad sheet of bone, continuous and exclusively associated with the astragalus (compare Fig. 6A and B).
10. Lengthening and thickening of the forelimbs
An Archaeopteryx-like theropod from
China and the origin of Avialae
Xing Xu1,2, Hailu You3
, Kai Du4 & Fenglu Han2 (2011)
The discovery of Xiaotingia further demonstrates that many features previously regarded as distinctively avialan actually characterize the more inclusive Paraves. For example, proportionally long and robust forelimbs are optimized in our analysis as a primitive character state for the Paraves (see Supplementary Information). The significant lengthening and thickening of the forelimbs indicates a dramatic shift in forelimb function at the base of the Paraves, which might be related to the appearance of a degree of aerodynamic capability (Xu et al 2011)
Archaeopteryx is widely accepted as being the most basal bird, and accordingly it is regarded as central to understanding avialan origins; however, recent discoveries of derived maniraptorans have weakened the avialan status of Archaeopteryx. Here we report a new Archaeopteryx-like theropod from China. This find further demonstrates that many features formerly regarded as being diagnostic of Avialae, including long and robust forelimbs, actually characterize the more inclusive group Paraves (composed of the avialans and the deinonychosaurs).
A REVIEW OF DROMAEOSAURID SYSTEMATICS
AND PARAVIAN PHYLOGENY
Turner et al (2012)
Turner et al (2012)
Paraves, exclusive of Epidexipteryx hui, is marked by a suite of modifications to the shoulder girdle typically associated with the origin of the ‘‘avian’’ flight stroke (Ostrom, 1976b; Jenkins, 1993). The acromion margin of the scapula has a laterally everted anterior edge (char. 133.1) (fig. 55), the coracoid is inflected medially from the scapula forming an L-shaped scapulocoracoid in lateral view (char. 137.1) and the glenoid fossa faces laterally (char. 138.1) as opposed to the plesiomorphic posterior orientation (fig. 50). Additionally, the furcula is nearly symmetrical in shape as opposed to the asymmetry present in the furcula of more basal taxa (char. 474.1).
Along with this modification, the laterally oriented glenoid allows the humerus to be abducted to a greater degree than in more basal coelurosaurs, although still probably not greatly above horizontal. Early analyses of these morphological modifications and/or coelurosaur phylogeny placed these changes at the avialan node (Sereno, 1997, 1999; Jenkins, 1993), but it is now clear that they are paravian synapomorphies.
Glenoid fossa:
A critical ligamentous mechanism in the evolution of avian flight (2007)
David B. Baier1, Stephen M. Gatesy1 & Farish A. Jenkins2
David B. Baier1, Stephen M. Gatesy1 & Farish A. Jenkins2
Despite recent advances in aerodynamic1, 2, neuromuscular3,4, 5 and kinematic6, 7 aspects of avian flight and dozens of relevant fossil discoveries8, the origin of aerial locomotion and the transition from limbs to wings continue to be debated9, 10. Interpreting this transition depends on understanding the mechanical interplay of forces in living birds, particularly at the shoulder where most wing motion takes place. Shoulder function depends on a balance of forces from muscles, ligaments and articular cartilages, as well as inertial, gravitational and aerodynamic loads on the wing11. Here we show that the force balance system of the shoulder evolved from a primarily muscular mechanism to one in which the acrocoracohumeral ligament has a critical role. Features of the shoulder of Mesozoic birds and closely related theropod dinosaurs indicate that the evolution of flight preceded the acquisition of the ligament-based force balance system and that some basal birds are intermediate in shoulder morphology.
Lateral view of right scapulocoracoids of Alligator mississippiensis (a), Sinornithoides youngi (b), Sinornithosaurus millenii (c), Archaeopteryx lithographica (d), Confuciusornis sanctus (e) and Columba livia (f) on a simplified phylogeny23. The changing orientation of the CHL/AHL (dashed lines) and the reduction of the scapulocoracoid plate anterior to the glenoid for muscle attachment (orange surfaces) record the transition to a novel, ligament-based force balance mechanism in modern birds. The dashed lines do not represent ligament length.
Note that all but (a) are paravians. This chart tells us nothing about any supposed connection between coelurosaur dinosaurs and basal paraves.
Glenoid fossa - PTEROSAURS
https://www.researchgate.net/publication/249551431_Middle-_and_bottom-decker_Cretaceous_pterosaur_Unique_designs_in_active_flying_vertebrates
"As in birds, the glenoid fossa in most pterosaurs is elevated by a dorsolaterally directed elongation of the coracoid and lies almost level with the vertebral column"
Scapula orientation in theropod dinosaurs is quite interesting and it is worth looking, to begin with, at what orientation is displayed in primitive reptiles. The scapula is generally held at an angle of 90 degrees to the horizontal line held by the backbone – in other words it was held in a perpendicular fashion. At the other extreme, extant birds rotated the scapula so that it lies parallel to backbone – a position also evolved by the pterosaurs.
Also see:
http://pterosaurnet.blogspot.ca/2014/11/shoulder-pectoral-girdle.html12. Furcula
https://en.wikipedia.org/wiki/Interclavicle
An interclavicle is a bone which, in most tetrapods, is located between the clavicles. In birds, the interclavicle is fused with the clavicles to form the furcula (wishbone). In chickens the furcula forms a "Y" shape and the interclavicle is the stem of the "Y".
http://onlinelibrary.wiley.com/doi/10.1002/jmor.10724/epdf
The interclavicle is lost at the dinosaur node or at an unknown node among early dinosauromorphs.
An interclavicle is a bone which, in most tetrapods, is located between the clavicles. In birds, the interclavicle is fused with the clavicles to form the furcula (wishbone). In chickens the furcula forms a "Y" shape and the interclavicle is the stem of the "Y".
http://onlinelibrary.wiley.com/doi/10.1002/jmor.10724/epdf
The interclavicle is lost at the dinosaur node or at an unknown node among early dinosauromorphs.
(Xu et al 2014)
The iconic features of extant birds, for the most part, evolved in a gradual and stepwise fashion throughout theropod evolution. However, new data highlight occasional bursts of morphological novelty at certain stages close to the origin of birds and an unavoidable complex, mosaic evolutionary distribution of major bird characteristics on the theropod tree. ........ Newly discovered fossils and relevant analyses demonstrate that salient bird characteristics have a sequential and stepwise transformational pattern, with many arising early in dinosaur evolution, undergoing modifications through theropods, and finally approaching the modern condition close to the origin of the crown group birds (Fig. 2). For example, the unusually crouched hindlimb for bipedal locomotion that characterizes modern birds was acquired in stepwise fashion through much of theropod evolution (67), and both the furcula (68) and the “semilunate” carpal (69) appeared early in theropod evolution. Notably, major bird characteristics often exhibit a complex, mosaic evolutionary distribution throughout the theropod tree, and several evolutionary stages are characterized by accelerated changes (70). For example, the early evolution of paravian theropods features cerebral expansion and elaboration of visually associated brain regions (71), forelimb enlargement (22, 67), acquisition of a crouched, knee-based hindlimb locomotor system (67), and complex pinnate feathers associated with increased melanosome diversity, which implies a key physiological shift (72). Together these features may suggest the appearance of flight capability at the base of the Paraves (22, 67). (Xu et al 2014)
Several flight-related anatomical features, such as hollow bones and the furcula, originated in early theropods; basal paravians had many hallmark features necessary for flight, including extremely small body size (50, 70); a laterally oriented, long, and robust forelimb (22, 67); an enlarged forebrain and other derived neurological adaptations (71); and large flight feathers (Figs. 1 and 2). Particularly surprising are the recent discoveries of large flight feathers forming a planar surface on the legs of some basal paravians—for example, those with asymmetrical vanes on both the tibia and metatarsus of some basal dromaeosaurs, such as Microraptor (59); large feathers with symmetrical vanes on both the tibia and metatarsus of the troodontid Anchiornis (45), the basal bird Sapeornis, and several other basal paravians (135); and large vaned feathers on tibiae of several basal birds including Archaeopteryx, confuciusornithids, and enantiornithines (135). These structures clearly would have been relevant to flight origins.
The wings before the bird: an evaluation of flapping-based locomotory hypotheses in bird antecedents
T. Alexander Dececchi,
1 Hans C.E. Larsson,2 and Michael B. Habib3,4
14. Ulna
https://matthewbonnan.wordpress.com/2012/06/03/lets-face-it-birds-are-dinosaurs-part-2/
http://www.nature.com/articles/ncomms2389
https://en.wikipedia.org/wiki/Guanlong
http://www.ivpp.ac.cn/qt/papers/201403/P020140314389417822583.pdf
T. Alexander Dececchi,
1 Hans C.E. Larsson,2 and Michael B. Habib3,4For all behaviours tested here [flap running and leaping] there is a sharp contrast in performance levels between a small number of paravian taxa (Microraptor, Anchiornis, Changyuraptor, Aurornis and Eosinopteryx) and all other non-avian taxa. This discrepancy is marked not only because it does not correlate to the origin of pennaceous feathers at pennaraptora but it also does not include all members of Paraves within the high performing category. Multiple small bodied and basal members of both deinonychosaurian subgroups, such as Mahakala, Xiaotingia, Jinfengopteryx, Mei, Sinovenator and Sinornithosaurus, show little evidence of benefit from flapping assisted locomotion. As these taxa are similar in size to the paravians that do show potential benefits, the argument that this loss is a byproduct of allometry is not possible. Allometric loss of performance is possible though in the larger, feathered dromaeosaurs like Velociraptor (∼15 kg, Turner et al., 2007) or Dakotaraptor(∼350 kg, Depalma et al., 2015), but our data from embryonic maniraptorans does not support this postulate. As our measurements for the small paravian wing areas are based either on preserved feather length (Sinornithosaurus) or on long feathered close relatives (Anchiornis for Xiaotingia, Jinfengopteryx, Mei, Sinovenator and Microraptor for Mahakala) our values for them are likely overestimates and suggests that locomotion was not a major driver for forelimb evolution, even among small sized paravians.
This shows that performance in flap running and leaping are irrelevant. Neither flap running nor leaping can explain the appearance of avian flight characteristics in oviraptors/paraves.
14. Ulna
https://matthewbonnan.wordpress.com/2012/06/03/lets-face-it-birds-are-dinosaurs-part-2/
Within coelurosaurs are the maniraptorans, the predatory dinosaurs that include Deinonychus and the now universally-known Velociraptor. These dinosaurs have highly flexible necks, elongate forelimbs, and the ulna is bowed outwards — the only other vertebrates with these features? Birds.https://en.wikipedia.org/wiki/Coelurosauria
Characteristics that distinguish coelurosaurs include:a sacrum (series of vertebrae that attach to the hips) longer than in other dinosaurs, a tail stiffened towards the tip, a bowed ulna (lower arm bone), a tibia (lower leg bone) that is longer than the femur (upper leg bone)https://en.wikipedia.org/wiki/Maniraptora
In 1994, Thomas R. Holtz attempted to define the group [maniraptora] based on the characteristics of the hand and wrist alone (an apomorphy-based definition), and included the long, thin fingers, bowed, wing-like forearm bones, and half-moon shaped wrist bone as key characters.https://pterosaurheresies.wordpress.com/2013/01/31/eosinopteryx-part-3-to-scale/
The ulna is not bowed in Aurornis or Eosinopteryx. It is bowed in Xiaotinigia and Archaeopteryx and more greatly bowed in subsequent flapping taxa, including oviraptorids by convergence
http://www.nature.com/articles/ncomms2389
As in Anchiornis, the radius and ulna of Eosinopteryx are straight with only a narrow gap between them.
Preliminary phylogenetic analysis places E. brevipenna sister to Anchiornis huxleyi at the base of Troodontidae (Fig. 3) (subject to change in subsequent analyses; see Supplementary Methods for details). Both taxa share a dorsally curved ilium shaft, a pubis moderately oriented posteriorly and a straight ulna that is not bowed away from the humerus.
The straight and closely aligned ulna-radius of Eosinopteryx also means that pronation/supination of the manus with respect to the upper arm would have been limited; combined with the absence of a bony sternum and weakly developed proximal humerus, these attributes suggest that Eosinopteryx had little or no ability to oscillate the arms to produce a wing beat.http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.661.634&rep=rep1&type=pdf
Also similar to some derived coelurosaurs is the posteriorly bowed ulna
A few other features, however, are closer to the conditions present in more derived tyrannosauroids than are those of IVPP V14531, such as a shorter humerus relative to the femur, a less bowed ulna
https://en.wikipedia.org/wiki/Guanlong
About 3 m (9.8 ft),[1][2] its fossils were found in the Shishugou Formation dating to about 160 million years ago, in the Oxfordian stage of the Late Jurassic period,[1] 92 million years before its well-known relative Tyrannosaurus. This bipedal saurischian theropod shared many traits with its descendants, and also had some unusual ones, like a large crest on its head. Unlike later tyrannosaurs, Guanlong had three long fingers on its hands. Aside from its distinctive crest, it would have resembled its close relative Dilong, and like Dilong may have had a coat of primitive feathers.[3]
http://www.ivpp.ac.cn/qt/papers/201403/P020140314389417822583.pdf
An Archaeopteryx-like theropod from China and the origin of Avialae Xing Xu1,2, Hailu You3 , Kai Du4 & Fenglu Han2276.
Ulna not bowed away from humerus (0), or bowed away from humerus (1).
APPENDICES
Appendix A:
Reversals Required by dino to bird theory
Reversals Required by dino to bird theory
For wrist reversal see
http://pterosaurnet.blogspot.ca/2016/04/semilunate-carpal.html
Ankle reversal
More remarkably, however, this finding reveals an unexpected evolutionary transformation in birds. In embryos of the land egg-laying animals, the amniotes (which include crocodilians, lizards, turtles, and mammals, who secondarily evolved live birth) the intermedium fuses to the anklebone shortly after it forms, disappearing as a separate element. This does not occur in the bird ankle, which develops more like their very distant relatives that still lay their eggs in water, the amphibians. Since birds clearly belong within land egg-laying animals, their ankles have somehow resurrected a long-lost developmental pathway, still retained in the amphibians of today -- a surprising case of evolutionary reversal .
The anklebone (astragalus) of dinosaurs presents a characteristic upward projection, the ‘ascending process’ (ASC). The ASC is present in modern birds, but develops a separate ossification centre, and projects from the calcaneum in most species. These differences have been argued to make it non-comparable to dinosaurs. We studied ASC development in six different orders of birds using traditional techniques and spin–disc microscopy for whole-mount immunofluorescence. Unexpectedly, we found the ASC derives from the embryonic intermedium, an ancient element of the tetrapod ankle. In some birds it comes in contact with the astragalus, and, in others, with the calcaneum. The fact that the intermedium fails to fuse early with the tibiale and develops an ossification centre is unlike any other amniotes, yet resembles basal, amphibian-grade tetrapods. The ASC originated in early dinosaurs along changes to upright posture and locomotion, revealing an intriguing combination of functional innovation and reversion in its evolution.
Finger reversal
(Xu et al 2009)
Based on this study, the most parsimonious alignment is for the four digits of ceratosaurs to be I-II-III-IV and the three (and sometimes four) digits of all Tetanurae to be II-III-IV(V). Accepting such a topological shift at the base of Tetanura requires that the positional homology of the three digits of tetanurans is II-III-IV(-V), as suggested by Wagner and Gauthier34. Because the four digits of ceratosaurs are therefore most parsimoniously interpreted as I-II-III-IV, the small lateral metacarpal ossification of Guanlong35, Sinraptor36, and Coelurus represents the re-ossification of metacarpal V after it is lost at the base of Ceratosauria. The poor phylogenetic resolution for basal tetanurans in our study precludes us from hypothesizing whether this re-ossification event occurred once or more than once in the evolution of Theropoda. Likewise, the fourth metacarpal, which is reduced in primitive theropods and bears an unknown number of phalanges in Ceratosauria, re-acquires at least three phalanges in Tetanurans.
This implies the reduction of digit I before the divergence of the Ceratosauria and the
Tetanurae, the appearance of some polleciform features in digit II and the acquisition of a novel phalangeal formula (X-2-3-4-X) early in tetanuran evolution. Both modifications are partially indicated by the manual morphologies of ceratosaurs and more basal theropods. Also, they are indirectly supported by observations in living animals that a digit will display features normally associated with the neighbouring medial digit if the latter fails to chondrify in early development21, that phalangeal counts can vary even within species29, 42 and that secondarily cartilaginous elements can regain their ability to ossify43.
If BDR [Bilateral Digit Reduction] applies to the more inclusive Averostra, as the II-III-IV hypothesis suggests, early stages of tetanuran evolution must have involved loss of the already highly reduced metacarpal I, reduction in the length of metacarpal II, and the reappearance of additional phalanges on metacarpal IV. Both the I-II-III and II-III-IV hypotheses can claim a degree of support from morphological data, but the II-III-IV hypothesis is more parsimonious when developmental data from extant birds are considered.
For reference:
1. Homoplasies (convergence, polyphyletic)
2. Ghost lineages
3. Reversals (reappearance) characters disappear and reappear (eg. SLC reappearance of distal carpal 4)
4. Homeotic transformations (eg hand and carpals) SLC "shift in position and composition"
5. Exaptations
6. Big morphological gap and sudden appearance of bird characteristics at oviraptor/paraves
http://pterosaurnet.blogspot.ca/2016/01/summary.html (See Appendix 7)
7. Implausible rates of evolution
7. Implausible rates of evolution
http://www.cell.com/current-biology/fulltext/S0960-9822(14)01047-1
There is growing evidence that changes in discrete character evolution, body size, and limb anatomy occurred quickly in the vicinity of the origin of birds, either at the node Avialae, in close avialan outgroups, or beginning with slightly more derived birds [3, 4, 5, 6, 19, 20, 21, 22]. It is likely that different types of data will pinpoint changes at slightly different positions on phylogeny, but in general, recent studies converge in identifying the dinosaur-bird transition as an abnormally rapid period of morphological evolution.
8. Evolvability
The recovered pattern of sustained evolutionary rates, and the repeated generation of novel ecotypes, suggests a key role for the maintenance of evolvability, the capacity for organisms to evolve, in the evolutionary success of this lineage. Evolvability might have also played a central role in the evolution of other major groups such as crustaceans [78] and actinopterygians [15], supporting its hypothesised importance in organismal evolution [79].
Rates of evolution declined through time in most dinosaurs. However, this early burst pattern, which characterises the niche-filling model of adaptive radiation [6],[7], does not adequately describe evolution on the avian stem lineage . The recovered pattern of sustained evolutionary rates, and the repeated generation of novel ecotypes, suggests a key role for the maintenance of evolvability, the capacity for organisms to evolve, in the evolutionary success of this lineage.
References:
Makovicky, P. J., and L. E. Zanno. 2011.
Theropod diversity and the refinement of avian characteristics.
Living dinosaurs: the evolutionary history of modern birds 9–29.
Living dinosaurs: the evolutionary history of modern birds 9–29.
HIGH RATES OF EVOLUTION PRECEDED THE ORIGIN OF BIRDS. Evolution, 2014;
A REVIEW OF DROMAEOSAURID SYSTEMATICS AND PARAVIAN PHYLOGENY
Turner et al (2012)
Turner et al (2012)
Xing Xu1,2, Hailu You3 , Kai Du4 & Fenglu Han2 (2011)
An Archaeopteryx-like theropod from China and the origin of Avialae
Xu et al 2014
