Dino to bird claims

What we see again and again is that there is no actual link between ground-based coelurosaur dinosaurs and arboreal paravians. They inhabit different niches (obviously) with no link between them. And even more importantly, they do not share characteristics. Almost all (if not all) the bird-like characteristics that are found in the paravians are not found in the ground-based coelurosaur dinosaurs. That is because they are not related.

So the question arises:
How in the world could there be so many claims for years and years that birds evolved from dinosaurs? 

In addition to the points noted above:

First, is the misleading convention of calling paraves "dinosaurs". So any bird-like character found in paraves is said to confirm the dino to bird theory. But paraves are not dinosaurs, they did not evolve from dinosaurs. People focus on the wrong place. The Achilles Heel of the dino to bird theory is that there is no connection between actual dinosaurs and paraves.

Next is to misinterpret the characters of actual dinosaurs as if they were bird-like or "proto" bird-like characters. Thus for example, we get the claim of "protofeathers" on ground-based coelurosaur dinosaurs, which does not stand up. 

Also we get secondarily flightless paravians being called "non-paraves maniraptors" (eg. oviraptors). As if they were transitional between actual dinosaurs and arboreal paravians. That does not stand up. They are secondarily flightless members of paraves.

And also the cladistic analyses that have been done, generally include only dinosaurs and use an inappropriate outgroup. The very significant exception to this is the James and Pourtless study, which not co-incidentally found other explanations as credible as the dino to bird theory. 

Exaptation

In the dino to bird theory, there is a good deal of claimed exaptation.
Abducted wrists, feathers and enlarged brains are claimed to have evolved before they were used for flight. These are simply stories. These stories are made up in response to evidence that contradicts the dino to bird theory.

http://en.wikipedia.org/wiki/Exaptation

Exaptation and the related term co-option describe a shift in the function of a trait during evolution. For example, a trait can evolve because it served one particular function, but subsequently it may come to serve another.

ABDUCTED WRISTS

http://rspb.royalsocietypublishing.org/content/early/2010/02/24/rspb.2009.2281.full.ht

Carpal asymmetry [abducted wrists] would have permitted avian-like folding of the forelimb in order to protect the plumage, an early advantage of the flexible, asymmetric wrist inherited by birds.

However, it is likely that mobility of the wrist was initially associated with other functions, such as predation (Padian 2001).

http://www.smithsonianmag.com/science-nature/bird-wrists-evolved-among-dinosaurs-65035237/?no-ist

It had originally been proposed that this flexibility could be attributed to hunting, but the same changes are seen in maniraptorans that were herbivores and omnivores so it is unlikely that hunting provides the answer. Instead, the authors of the new study propose, the ability to fold the hands backwards would have protected the feathers of the arms. This would have prevented the feathers from getting damaged or from being in the way as the dinosaurs moved about, although the authors recognize that this hypothesis requires further evidence.

Perhaps more significant, however, is how this wing-folding mechanism may have allowed birds to take to the air. Birds do flex their wrists while flapping their wings to fly, and so it appears that the wrist flexibility that first evolved in dinosaurs was later co-opted for flight in birds. This is what is known as "exaptation," or when a previous adaptation takes on a new function. Indeed, as more is discovered about the evolution of birds, the more traits paleontologists find that evolved for one function but have been co-opted for another at a later point (feathers themselves being the most prominent
example). There is relatively little separating birds from their feathered dinosaur ancestors.

FEATHERS

http://en.wikipedia.org/wiki/Exaptation

As Darwin elaborated in the last edition of The Origin of Species,[14] many complex traits evolved from earlier traits that had served different functions. By trapping air, primitive wings would have enabled birds to efficiently regulate their temperature, in part, by lifting up their feathers when too warm. Individual animals with more of this functionality would more successfully survive and reproduce, resulting in the proliferation and intensification of the trait.
Eventually, feathers became sufficiently large to enable some individuals to glide. These individuals would in turn more successfully survive and reproduce, resulting in the spread of this trait because it served a second and still more beneficial function: that of locomotion. Hence, the evolution of bird wings can be explained by a shifting in function from the regulation of temperature to flight.

http://www.livescience.com/39688-exaptation.html

Exaptation is a term used in evolutionary biology to describe a trait that has been co-opted for a use other than the one for which natural selection has built it.
It is a relatively new term, proposed by Stephen Jay Gould and Elisabeth Vrba in 1982 to make the point that a trait’s current use does not necessarily explain its historical origin. They proposed exaptation as a counterpart to the concept of adaptation.
For example, the earliest feathers belonged to dinosaurs not capable of flight. So, they must have first evolved for something else. Researchers have speculated early feathers may have been used for attracting mates or keeping warm. But later on, feathers became essential for modern birds’ flight.

http://en.wikipedia.org/wiki/Microraptor#Wings_and_flight

This further supports the hypothesis that "flight feathers" that first evolved in dinosaurs for non-aerodynamic functions were later adapted to form lifting surfaces.^[15]

ENLARGED BRAINS

http://www.bbc.com/news/science-environment-23514985

Several ancient dinosaurs evolved the brainpower needed for flight long before they could take to the skies, scientists say.
Bird brains tend to be more enlarged compared to their body size than reptiles, vital for providing the vision and coordination needed for flight.
Scientists using high-resolution CT scans have now found that these "hyper-inflated" brains were present in many ancient dinosaurs, and had the neurological hardwiring needed to take to the skies. This included several bird-like oviraptorosaurs and the troodontids Zanabazar junior, which had larger brains relative to body size than that of Archaeopteryx.

OTHER
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0028964

Placed in context of avian evolution, the grasping foot of Deinonychus and other terrestrial predatory paravians is hypothesized to have been an exaptation for the grasping foot of arboreal perching birds. Here we also describe “stability flapping”, a novel behaviour executed for positioning and stability during the initial stages of prey immobilisation, which may have been pivotal to the evolution of the flapping stroke. These findings overhaul our perception of predatory dinosaurs and highlight the role of exaptation in the evolution of novel structures and behaviours.

GENERAL
See page 261 of "Riddle of the Feathered Dragons"
http://books.google.ca/books?id=SihlpQTlVdAC&pg=PA154&lpg=PA154&dq=parasagittal+stance+for+Archaeopteryx.&source=bl&ots=jTl0YCn6be&sig=B9WKpEcJJ8Xr3U4_haeHeZFUToE&hl=en&sa=X&ei=xHMYVMWbAsGOyAT3loGQDg&ved=0CDwQ6AEwAw#v=snippet&q=exaptations&f=false

Also:
http://onlinelibrary.wiley.com/doi/10.1111/evo.12363/full

Did preadaptations for flight precede the origin of birds (Aves)? The origin of flight in birds is one of the great evolutionary transitions and has received considerable attention in recent years (Padian and Chiappe 1998; Clarke and Middleton 2008; Dececchi and Larrson 2009; Benson and Choiniere 2013; Dececchi and Larrson 2013). The evolution of birds is often considered coincident with the origins of flight, but many traits associated with flight evolved before the origin of Aves (Padian and Chiappe 1998).

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2756958/

This suggests that the initial conquest of the air was achieved using lower metabolic rates than are characteristic of today's avian flyers. It appears that the closest non-avialan relatives of birds were physiologically preadapted for powered flight and only anatomical adaptations were involved when birds first ventured into the air. 

Not required to become terrestrial

Here is an objection to the pterosaur to bird theory:

To derive birds from pterosaurs would require some pterosaur to give rise to terrestrial maniraptors, because non-paraves maniraptorans are terrestrial, and the bird lineage evolved within the maniraptorans

Response:

It must first be recognized that the so-called "non-paraves maniraptorans" are secondarily flightless and come after the most basal paraves*.
In the dinosaur to bird theory, the so-called "non-paraves maniraptors"  are incorrectly considered to come before (ancestral to) basal paraves.
However when we work with the idea that they are secondarily flightless (descended from basal paraves) then the objection above would not be relevant.
Pterosaurs did not give rise to terrestrial maniraptors. 

The pterosaur to bird theory proposes that flying pterosaurs gave rise to flying basal paraves.


* they are actually members of paraves

Artist's Renderings

Here are artist's renderings of the taxa we are interested in. They show that the pterosaur is much closer to basal paraves than the dinosaur is.

BASAL PARAVES
http://en.wikipedia.org/wiki/Scansoriopterygidae

DINOSAUR

http://en.wikipedia.org/wiki/Compsognathus

PTEROSAUR

http://en.wikipedia.org/wiki/Rhamphorhynchus

Aerodynamics

Notice that the charts for basal Paraves and Rhamphorhynchus are very similar.
This is what you would expect if basal Paraves descended from Rhamphorhynchidae. 

https://peerj.com/articles/632/

Figure 3. Representative aerodynamic measurements for pitching stability and control effectiveness. Long-tailed taxa (a) have a stable equilibrium point at 10-25 (yellow line) and the tail is effective in generating pitching moments at low angles of attack (pale yellow box indicates measurable moments for given tail deflections). In short-tailed taxa (b), including extant Larus, the equilibrium point at 0-5 is unstable (red line) and the tail control effectiveness is reduced (no measurable moments for the given tail deflections). One example (Rhamphorhynchus) drawn from pterosaurs illustrates similar possibilities in a phylogenetically distant [actually quite close] taxon.

NOT CONVERGENCE
This is not convergence because ground-based dinosaurs and pterosaurs did not live in similar ways and/or similar environment, and so did not face the same environmental factors. 

http://en.wikipedia.org/wiki/Convergent_evolution

In morphology, analogous traits will often arise where different species live in similar ways and/or similar environment, and so face the same environmental factors. When occupying similar ecological niches (that is, a distinctive way of life) similar problems lead to similar solutions.[4]

Wrists

Pterosaur and basal paraves wrists are very similar,

PTEROSAUR

http://en.wikipedia.org/wiki/Pterosaur

The pterosaur wrist consists of two inner (proximal) and four outer (distal) carpals (wrist bones), excluding the pteroid bone, which may itself be a modified distal carpal. The proximal carpals are fused together into a "syncarpal" in mature specimens, while three of the distal carpals fuse to form a distal syncarpal.

Notice figure (b) in the chart below:
https://blogger.googleusercontent.com/img/proxy/AVvXsEgpB6L-30fKY90YAUw3Wr1b64R357Lzy9T6q8590CbHywRS5I-13PIEcLHStJv0oBofMY1dJyLZh7IKjTZ2C-Sw6HkKWCUhNEj2A_PaLatjV7iJHUzmQZeHCvpKR35JERnz_nSnTuBWnMkqr6DXjS0=

BASAL PARAVES

Now let's compare to Yixianosaurus (Pennaraptora):
http://en.wikipedia.org/wiki/Yixianosaurus

The describers considered the exact placement of Yixianosaurus within Maniraptora to be uncertain, but because the hand length resembled that of another feathered dinosaur, Epidendrosaurus (now Scansoriopteryx), they suggested it was a close relative of the Scansoriopterygidae.

Comparing the Yixianosaurus wrist to the pterosaur wrist is a very good comparison because I have been proposing that Rhamphorhynchidae developed into a taxon like Scansoriopterygidae.

http://www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.1001957#close

Pterosaur:

In the transition from pterosaur to basal paraves, the two proximal carpals continued to be fused. One distal carpal was lost. The other two distal carpals continued to be fused. 


Sullivan et al
http://rspb.royalsocietypublishing.org/content/early/2010/02/24/rspb.2009.2281.full

Extant volant birds possess a highly specialized wrist joint, in which two proximal carpals articulate with a fused carpometacarpus. The proximal part of the carpometacarpus forms an articular trochlea, comprising two convex ridges separated by a transverse groove

http://en.wikipedia.org/wiki/Scansoriopterygidae

Like other maniraptorans, scansoriopterygids had a semilunate carpal (half-moon shaped wrist bone) that allowed for bird-like folding motion in the hand.

The pterosaur proximal carpal articulated in a groove in the distal carpal and that is how it worked in basal paraves as well.

http://www.nature.com/srep/2014/140813/srep06042/full/srep06042.html

Figure 1: Diagram showing the position and general morphology of the transversely trochlear proximal articular facet of the carpometacarpus in selected theropod hands with the phalanges omitted (upper: proximal view; lower: dorsal view; medial side of hand to left).

(a) The basal coelurosaurian condition (based on Guanlong). (b) The basal paravian condition (based on Sinovenator). (c) The neornithine condition (based on Crossoptilon). Yellow indicates the ‘semilunate’ carpal; grey-yellow indicates the transverse groove; green indicates the metacarpals.

http://en.wikipedia.org/wiki/Trochlea

Trochlea (Latin for pulley) is a term in anatomy. It refers to a grooved structure reminiscent of a pulley's wheel.

This is also a very helpful link:
http://www.pterosaur.org.uk/PDB2012/I/wings/carpal.htm

The proximal carpal is seen articulating with the Ulna and Radius.  This carpal in turn articulates with the Distal Carpal in a saddle like gliding joint.

A story to rationalize a purported dino to bird transition:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4131224/

The homology of the ‘semilunate’ carpal, an important structure linking non-avian and avian dinosaurs, has been controversial. Here we describe the morphology of some theropod wrists, demonstrating that the ‘semilunate’ carpal is not formed by the same carpal elements in all theropods possessing this feature and that the involvement of the lateralmost distal carpal in forming the ‘semilunate’ carpal of birds is an inheritance from their non-avian theropod ancestors. Optimization of relevant morphological features indicates that these features evolved in an incremental way and the ‘semilunate’ structure underwent a lateral shift in position during theropod evolution, possibly as a result of selection for foldable wings in birds and their close theropod relatives. We propose that homeotic transformation was involved in the evolution of the ‘semilunate’ carpal. In combination with developmental data on avian wing digits, this suggests that homeosis played a significant role in theropod hand evolution in general.

FOR REFERENCE (MODERN BIRDS)

http://en.wikipedia.org/wiki/Carpus

The following seems to be inconsistent with the other references:

The wing of a modern bird, for example, has only two remaining carpals; the radiale (the scaphoid of mammals) and a bone formed from the fusion of four of the distal carpals.^[14]

http://etc.usf.edu/clipart/48100/48103/48103_bird_limbs_lg.gif
Bird limbs

Description
"Fore-limb and hind-limb compared. H., Humerus; R., radius; U., ulna; r., radiale; u., ulnare; C., distal carpals united to carpo-metacarpus; CC., the whole carpal region; MC.I., metacarpal of the thumb; I., phalanx of the thumb; MC.II., second metacarpus; II., second digit; MC.III., third metacarpus; III., third digit. F., femur; T.T., tibio-tarsus; Fi., fibula; Pt., proximal tarsals united to lower end of tibia; dt., distal tarsals nited to upper end of tarso-metatarsus (T.MT.); T., entire tarsal region; MT.I., first metatarsal, free; I.-IV., toes." -Thomson, 1916

http://squidlifecrisis.deviantart.com/art/Orientation-of-the-Folded-Wing-472267115

METACARPALS


Metacarpal to humerus ratio:

https://www.academia.edu/11078228/A_new_rhamphorhynchid_pterosaur_Pterosauria_from_Jurassic_deposits_of_Liaoning_Province_China

Table 2 shows that Rhamphorhynchinae varies between 0.39 to 0.68. 

https://www.researchgate.net/publication/249551426_Pterosaur_phylogeny_and_comments_on_the_evolutionary_history_of_the_group

Primitively, pterosaurs have comparatively small metacarpals, with the humerus at least 2.5 times longer. 

https://en.wikipedia.org/wiki/Dorygnathus

Dorygnathus in general has the build of a basal, i.e. non-pterodactyloid pterosaur: a short neck, a long tail and short metacarpals — although for a basal pterosaur the neck and metacarpals of Dorygnathus are again relatively long.

Arboreal theory and the pterosaur to bird theory

The arboreal theory of bird evolution ("trees down") is held by a number of researchers and academics. The core of the theory is that the lineage leading to birds began in the trees (not on the ground).
The pterosaur to bird theory is a different idea. Pterosaurs were already flying in the trees, by flapping their skin membrane, and they later developed feathers.
The ancestor of birds was not a dinosaur, nor was it a thecodont. It was a pterosaur.

The trees down theory begins with a gliding arboreal creature. This is closer to being correct except that the gliding phase took place earlier, in the evolution of the pterosaur. This is a key point.

Why did they change?

I have been asked this question a few times:
“why would a pterosaur give up a functional skin-and-bones wing structure to evolve a different, feather-based structure with the same function”?
Here are some things to consider:
In the dinosaur to bird theory, it is said that the first feathers were for display and for insulation. If those answers make sense in the dino to bird theory, then they could be equally applied to the pterosaur situation.
Another answer is that the pterosaur’s long wing finger makes it difficult/dangerous for a pterosaur to fly in the trees. It would damage the bone and tear the membrane. Feathers on shorter wings made it possible to inhabit the forests.
Another answer is that the ability of the feathers to open up when elevating the wing, reducing drag, is an advantage over the skin membrane.
And additionally, even though we may wonder what value the pterosaur got from feathers, the fact is that the birds were successful and the pterosaurs went extinct. The feathered version must have had additional value.

The question about WHY pterosaurs would develop feathers is often teamed up with the point that pterosaurs were doing exceptionally well for millions of years. Why change?
But exactly the same argument can be made about dinosaurs who were doing exceptionally well for millions of years. Why would they change? Same question.

Pelvic Girdle

ACETABULUM

Basal paraves had a partially closed (cup-like) acetabulum that allowed them to abduct (splay, sprawl) their legs.
Pterosaurs had a completely closed (cup-like) acetabulum that allowed them to abduct (splay, sprawl) their legs.
Dinosaurs had a completely open acetabulum that did not allow them to abduct (splay, sprawl) their legs.

DINOSAURS 

http://books.google.ca/books?id=idta...lum%2C&f=false

Quote:

In theropods, the femoral component is cylindrical without any distinctive head and neck. It projects medially at a right angle from the shaft and fits into a perforated [completely open] acetabulum of up to 1.5 times its diameter. As a result, the hip joint is stable and fully congruent during parasagittal motion, permitting a wide range of flexion and extension but very little abduction and adduction

http://www.ucmp.berkeley.edu/diapsids/dinomm.html

Quote:

One important dinosaurian synapomorphy is the perforate [completely open] acetabulum, simply a "hip bone" (actually three connected bones, together called the pelvis) with a hole in the center where the head of the femur ("thigh bone") sits. This construction of the hip joint makes an erect stance (hindlimbs located directly beneath the body) necessary — like most mammals, but unlike other reptiles which have a less erect and more sprawling posture. Dinosaurs are unique among all tetrapods in having this perforate [completely open] acetabulum.

BASAL PARAVES

http://ncsce.org/pdfs/home/aukfeduc2013.pdf

Quote:

A number of intriguing four-winged feathered Jurassic forms—such as the tiny scansoriopterids Epidendrosaurus (= Scansoriopteryx) and Epidexipteryx, the latter without preserved wing remiges, and anchiornithids (Anchiornis and Xiaotingia)—exhibit numerous non-theropod skeletal features. ) They are provisionally best interpreted as early birds at a pre-theropod stage, with partially closed hip joint or acetabulum, and without a dinosaurian supra-acetabular shelf, characters associated with a fully theropodan parasagittal gait, which diagnose the clade. Although there is no reasonable morphological definition of “theropod,” one sine qua non for dinosaur status in general is the presence of a completely open acetabulum, associated with the suite of changes seen in posture and gait, by which a more upright posture is attained, with a parasagittal hindlimb positioning (front to back axis). A partially closed acetabulum is seen in basal archosaurs and is characteristic of the scansoriopterids and Jurassic feathered forms such as Anchiornis initially described as near Aves by Xu et al (2009)

http://www.pnas.org/content/106/13/5002.full

Quote:

The [Hesperonychus] acetabulum is similar to those of other dromaeosaurids in that it lacks a prominent supracetabular crest (30, 36). However, anteriorly, the contribution of the ilium to the acetabulum is broad, and the anterior rim projects strongly laterally, as it does in Unenlagia(36). The medial opening of the acetabulum is partially closed, as it is in other Dromaeosauridae (36). The [Hesperonychus] acetabulum opens dorsolaterally rather than laterally, as is the case in Velociraptor (38), suggesting the ability to partially abduct the hindlimbs. This morphology is of interest in light of proposals that Microraptor gui abducted its feathered hindlimbs to function as airfoils (24).

http://bioweb.uwlax.edu/bio203/s2014...adaptation.htm

Quote:

Velociraptor mongoliensis had a pelvis with a characteristic pubis that pointed downward and forward at an angle toward the ischium. The acetabulum of V. mongoliensis opened dorsolaterally, indicating that it could abduct and adduct its hind limbs. This morphological characteristic demonstrates that the ancestors of V. mongoliensis were probably capable of flight and therefore the flightlessness of Velociraptor was secondarily lost (Longrich and Currie. 2009).

http://www.aou.org/auk/content/130/1/0001-0013.pdf

Quote:

Microraptors have been reconstructed in two distinctive models, the four-winged gliding model with sprawled hindlimb wings, by which it was originally described in Nature (Xu et al. 2003), and a dinosaurian bipedal model, or biplane model, by which it is reconstructed with the hindlimbs held beneath the body, incapable of sprawling, in other words, like a tiny T. rex. The problem,of course, is that there is absolutely no reason the hindlimbs could not have been sprawled, as is the case in flying squirrels (Glaucomys spp.), flying lemurs (Dermoptera), etc., and even falling cats. Too, the sprawled model performs superiorly inwind-tunnel experiments (Alexander et al. 2010), most specimensare preserved with a sprawled posture, and the wingclaws are adapted for trunk climbing (Burnham et al. 2011). In addition, it would be difficult to imagine how selection could produce elongate, asymmetric hindlimb flight remiges by the most current paleontological reconstructions, in which the hindlimbs are held in flight beneath the body in obligate bipedal fashion, with elongate hindlimb wing feathers trailing behind, simply slicing through the air (Balter 2012)

http://www.pnas.org/content/107/7/2972.full.pdf+html

Quote:

Fossils of the remarkable dromaeosaurid Microraptor gui and relatives clearly show well-developed flight feathers on the hind limbs as well as the front limbs. No modern vertebrate has hind limbs functioning as independent, fully developed wings; so, lacking a living example, little agreement exists on the functional morphology or likely flight configuration of the hindwing. Using a detailed reconstruction based on the actual skeleton of one individual, cast in the round, we developed light-weight, three-dimensional physical models and performed glide tests with anatomically reasonable hindwing configurations. Models were tested with hindwings abducted and extended laterally, as well as with a previously described biplane configuration. Although the hip joint requiresthe hindwing to have at least 20° of negative dihedral (anhedral),all configurations were quite stable gliders. Glide angles rangedfrom 3° to 21° with a mean estimated equilibrium angle of 13.7°,giving a lift to drag ratio of 4.1:1 and a lift coefficient of 0.64. The abducted hindwing model’s equilibrium glide speed corresponds to a glide speed in the living animal of 10.6m·s−1. Although the biplane model glided almost as well as the other models, it was structurally deficient and required an unlikely weight distribution (very heavy head) for stable gliding. Our model with laterally abducted hindwings represents a biologically and aerodynamically reasonable configuration for this four-winged gliding animal. M. gui’s feathered hindwings, although effective for gliding, would have seriously hampered terrestrial locomotion.

http://en.wikipedia.org/wiki/Scansoriopteryx

Quote:

Scansoriopteryx also lacks a fully perforated acetabulum, the hole in the hip socket which is a key characteristic of Dinosauria and has traditionally been used to define the group.

http://dinosaur-museum.org/feathered...niraptoran.pdf

Quote:

Scansoriopteryx is clearly more primitive than Archaeopteryx in many respects such as its saurischian-style pelvis which has remarkably short pubes; elongate and robust ischia; and comparatively small pubic peduncles. These primitive features further suggest that the nearly closed acetabulum is not a reversal, but a true plesiomorphic condition.

http://www.actazool.org/temp/%7B296C...66A60B2%7D.pdf

Quote:

This results in a somewhat sprawling position for the [Archaeopteryx] femur that is corrected at the knee joint, resulting in a functionally vertical leg. The pelvis has an incompletely open acetabulum, and there is no characteristic dinosaurian supra-acetabular shelf. The femoral head turns forwards rather than extending perpendicular to the shaft.

There is a reference to the splayed posture of Scansoriopterids here (page 154):
http://books.google.ca/books?id=Sihl...osture&f=false

There is a reference to the splayed posture of Archaeopteryx here (page 399):
http://books.google.ca/books?id=8QRK...0angle&f=false


http://link.springer.com/article/10.1007%2Fs10336-014-1098-9#page-1

head of [Scansoriopteryx] femur lacks a distinctive neck and is instead more proximally oriented as in reptiles with sprawling limbs

http://books.google.ca/books?id=SihlpQTlVdAC&pg=PA154&lpg=PA154&dq=Certainly+the+fact+that+scansoriopterids&source=bl&ots=jTl6Uvn68h&sig=WRNGO1pzEQdzfw0F8HUmvrTHaVE&hl=en&sa=X&ei=ONVsVJ-GMI-nyASPzYCAAQ&ved=0CCEQ6AEwAA#v=onepage&q=Certainly%20the%20fact%20that%20scansoriopterids&f=false

Certainly the fact that scansoriopterids could spread the hind limbs outward in a splayed posture, more than in typical birds, indicates that a true upright stance was achieved only later and independently from true dinosaurs.

Also see the info about splayed hindlimbs here and here.

http://dinosaur-museum.org/featheredinosaurs/arboreal_maniraptoran.pdf

the [Scansoriopteryx] acetabulum is not as fully perforated as in any known theropod

http://link.springer.com/article/10.1007%2Fs10336-014-1098-9

Jurassic archosaur is a non-dinosaurian bird
Stephen A. Czerkas, Alan Feduccia

Unlike theropod dinosaurs, invariably exhibiting a
completely perforated and open acetabulum, Scansoriopteryx
has a partially closed acetabulum, and no sign of a
supra-acetabular shelf or an antitrochanter. Along with the
mostly enclosed acetabulum indicated by the surface texture
of the bone within the hip socket, the proximally
oriented head of the femur is functionally concordant with
a closed or partially closed acetabulum and with sprawling
hindlimbs. There is additional phylogenetic evidence that
the largely closed acetabulum was not directly inherited
from dinosaurian ancestors with fully open acetabulae and
subsequentially modified as a secondary reversal. The
similar condition seen in Anchiornis (Hu et al. 2009) and
Microraptor (personsal observations; Xu et al. 2000; Gong
et al. 2012) with the partially open acetabulum in
Scansoriopteryx creates a sequential phylogenetic pattern
consistent with being inherited from non-dinosaurian
archosaurs which had not yet achieved a fully upright
stance as in dinosaurs (Fig. 2).
A fully perforated acetabulum is a sine qua non for
dinosaurian status associated with major changes in posture
and gait, by which a more upright posture and parasagittal
stance is attained.

PTEROSAUR
The pterosaur acetabulum was completely closed because during development the ilium, ischium and pubis extended to come completely together at the bottom of the cup-shaped acetabulum.
In the transition to basal paraves, the ilium, ischium and pubis no longer came completely together. (ie. it was partially open). This may well be an example of neoteny.

http://pterosaur.net/terrestrial_locomotion.php

Now, this is not to say that basal pterosaurs were locomotory inept from the moment they landed. They may, however, have spent more time running around trees and cliffs than over floodplains and tidal flats. Basal pterosaurs typically have deepened, highly recurved manual and pedal claws with comparatively large flexor tubercles compared to the relatively slender claws of pterodactyloids. These claws are extremely thin despite their depth and would make excellent crampons to provide purchase when climbing, especially when combined with the antungual sesamoids and elongate penultimate phalanges that characterise the hands and feet of many basal forms. Furthermore, the orientation of the femoral head in basal pterosaurs means that the femur is projected forward, upward and laterally from the acetabulum, thereby causing the sprawling gait for the hindlimbs that acted in concert with the relatively short metacarpals to bring the bodies of these pterosaurs close to any surface they happened to be climbing over. These are all excellent adaptations to climbing (Fig. 5), and we should expect early Mesozoic environments to be covered with pterosaurs hanging from cliff faces, tree trunks and branches.

Lunate Surface
https://en.wikipedia.org/wiki/Acetabulum

The rest of the acetabulum is formed by a curved, crescent-moon shaped surface, the lunate surface, where the joint is made with the head of the femur.
Its counterpart in the pectoral girdle is the glenoid fossa.^[3]

Related links:
http://pterosaurnet.blogspot.ca/2010/05/acetabulum.html
http://pterosaurnet.blogspot.ca/2013/01/pelvic-bones-summary.html

https://finstofeet.com/2010/07/14/the-pelvis

What is the function of the pelvis? – The pelvis connects the hind limbs to the trunk of the body (through the acetabulum). In Dinosaurs, a robust ridge [supra-acetabular shelf, crest, ridge] present above the acetabulum on the ilium helps transmit the weight of the animal to the hind limb.

https://sites.google.com/site/dinolore/learn/dinosaur-groups/dinosauria

The [dinosaur] parasagittal limb posture was achieved by making the process (bump) on the head of the femur (thigh bone) that articulates with the hip socket (or acetabulum) protrude at a right angle from the rest of the femur, which as a result will point directly downward.However, this process is cylindrical, not ball-like as for most vertebrates. This means that the femur cannot roll around along the joint, but is restricted to rotating only. As a result, the leg can only be swung forward and backward, and not to the sides as, for example, we humans can. In addition, the ankle joint of the dinosaurs was relatively simple: in humans, there are seven ankle bones (or tarsals), and they form a synovial joint, a highly flexible joint that allows movement in several planes; dinosaurs, however, only have two ankle bones, and the joint (referred to as the mesotarsal joint) forms a linear hinge joint, which only enables movement in a single plane only, in this case back and forward. Consequently, the dinosaur hindlimb had a highly restricted range of movement: it could only move along the sagittal plane – the line parallel to the body. Thus, dinosaurs would not have been very agile regarding sidewise movement; they were specialised for running forward. 

https://sites.google.com/site/dinolore/_/rsrc/1318797976741/learn/dinosaur-groups/dinosauria/Sprawling_and_erect_hip_joints_-_horiz.png



https://en.wikipedia.org/wiki/Acetabulum

The well-fitting surfaces of the femoral head and acetabulum, which face each other, are lined with a layer of slippery tissue called articular cartilage, which is lubricated by a thin film of synovial fluid. Friction inside a normal hip is less than one-tenth that of ice gliding on ice.^[4][5] 

Changes

Here is a first draft list of changes that would have taken place from
Rhamphorhynchidae (pterosaur) to Scansoriopterygidae (basal paraves):

Large 4th finger reduced
Patagium greatly reduced
Pycnofibres developed into wing flight feathers
Uropatagium replaced with flight feathers
Distal syncarpal becomes semilunate carpal and fuses to metacarpals
The pteroid bone and lateral carpal are lost
Acetabulum is not completely closed
Second toe becomes hyper-extended
5th toe is lost?
Clavicles no longer incorporated into the sternum
Humerus saddle-shaped head becomes bulbous
External mandibular fenestra appeared
Posterior teeth reduced
First toe is turned backwards?

If anyone would care to suggest a change or addition, please do. Just provide reference link(s) and copy and paste the material that you think supports your suggestion.

NEW
The discovery of Yi qi would change the transition steps*.
The major changes would be:
The large 4th finger is first reduced to just the metacarpal (in Yi) [or last phalange] and then that is also lost (in other scansoriopteryids).
The remaining digits would be digits 1, 2 and 3. (The first digit would not be lost, the 4th digit would be lost).

*  if the interpretation of the Yi characteristics by Xu et al is correct.

Rhamphorhynchidae to Scansoriopterygidae

I suggest that Rhamphorhynchidae (basal pterosaur group) is the ancestor of Scansoriopterygidae (basal paraves group).

Scansoriopterygidae are basal paraves with flight feathers on the arms and legs.
Scansoriopterygidae (or a group very much like it) is the ancestor of the later Paraves such as Microraptor, Archaeopteryx etc.
Rhamphorhynchidae pycnofibres are homologous (ancestral) to Scansoriopterygidae feathers.
The Rhamphorhynchidae long bony tail is homologous to the Scansoriopterygidae long bony tail.
The Rhamphorhynchidae caudal rods are homologous to the Scansoriopterygidae caudal rods.

The Scansoriopterygidae elongate outermost digit is transitional between Rhamphorhynchidae and later Paraves.
The Scansoriopterygidae wing feathers replaced the function of the wing membrane of their pterosaur ancestor. The membrane close to the arm (patagium) remained.
The Scansoriopterygidae hindwing feathers replaced the function of the uropatagium of their pterosaur ancestor.
The Scansoriopterygidae propatagium IS the propatagium from their pterosaur ancestor.

Scansoriopterygidae is one of the most basal (primitive) members of paraves.
It used the same muscles as pterosaurs for flying. It could splay its hind limbs like pterosaurs for flying.
The evidence strongly supports the transition from pterosaur to basal paraves, with Scansoriopterygidae being transitional.


http://en.wikipedia.org/wiki/Scansoriopterygidae

Flight Strokes Compared

Basal Paraves used the same flight stroke as Pterosaurs and both had splayed hindlimbs for flying.

FLIGHT STROKE

PTEROSAURS

http://press.princeton.edu/witton/sampler-pterosaurs.pdf

Detailed reconstruction of the proximal arm
musculature of pterosaurs shows that ... the arm was more likely
lifted by large muscles anchored on the scapula and
back, and lowered by those attached to the sternum
and coracoid (fig. 5.8; Bennett 2003a). Unlike [modern] birds,
where two vastly expanded muscles are mainly used
to power flight, it appears that pterosaurs used several
muscle groups to form their flapping strokes.

http://eurekamag.com/research/019/478/morphological-evolution-pectoral-girdle-pterosaurs-myology-role.php (2003)

The musculature of the pectoral region of representative rhamphorhynchoid (Campylognathoides) and large pterodactyloid (Anhanguera) pterosaurs was reconstructed in order to examine the function of various muscles and the functional consequences of the evolution of the advanced pectoral girdle of large pterodactyloids. The reconstructions suggest that m. supracoracoideus was not an elevator of the wing, but instead depressed and flexed the humerus. m. latissimus dorsi, m, teres major, m. deltoides scapularis, and m. scapulohumeralis anterior were wing elevators. 

BASAL PARAVES

http://biology.kenyon.edu/courses/biol241/bird%20flight%202003%20Chatterjee_Sankar.pdf

Its lack of a supracoracoideus (SC)
pulley, the primary elevator of the wing, would prevent
Archaeopteryx from executing humeral rotation on the
glenoid during the upstroke,

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1780066/

Anatomical evidence indicates that Microraptor was not capable of ground or running takeoff, because it lacked the supracoracoideus pulley to elevate the wings.

http://jeb.biologists.org/content/200/23/2987.full.pdf

The lack of a morphologically derived SC in Late
Jurassic and Early Cretaceous birds precluded a high velocity
recovery stroke which undoubtedly limited
powered flight in these forms. Subsequent evolution of the
derived SC capable of imparting a large rotational force to
the humerus about its longitudinal axis was an important
step in the evolution of the wing upstroke and in the ability
to supinate (circumflex) the manus in early upstroke, a
movement fundamental to reducing air resistance during
the recovery stroke.

The highly derived morphology of the SC,
a characteristic of modern birds capable of powered flight, was
not present in Archaeopteryx (Ostrom, 1976a,b; Wellnhofer,
1988, 1993), nor is there firm evidence for its presence in
recently described Mesozoic species (Chiappe, 1995; Sanz et
al. 1996).

https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CB4QFjAA&url=https%3A%2F%2Frepository.si.edu%2Fbitstream%2Fhandle%2F10088%2F6524%2FVZ_93_Archaeopteryx.pdf%3Fsequence%3D1&ei=uUF2VZyMFcqlyASSo4LYCQ&usg=AFQjCNFW5HcrkvSBGaZvOkczCMZAErCEow&sig2=0o1CnMU3Vz-DQ8_S-sw-Bw&bvm=bv.95039771,d.aWw

Pterosaurs and basal paraves flapped their wings in the same way. 

___________________________________________________________


SPLAYED HINDLIMBS

Basal paraves had a femur/acetabulum articulation that was different than dinosaurs and that allowed them to abduct (splay) their legs.

See also these links
http://pterosaurnet.blogspot.ca/2010/05/acetabulum.html
http://pterosaurnet.blogspot.ca/2013/01/pelvic-bones-summary.html

PTEROSAUR

http://en.wikipedia.org/wiki/Pterosaur

"Pterosaur's hip sockets are oriented facing slightly upwards, and the head of the femur (thigh bone) is only moderately inward facing, suggesting that pterosaurs had a semi-erect stance. It would have been possible to lift the thigh into a horizontal position during flight as gliding lizards do."

BASAL PARAVES

http://en.wikipedia.org/wiki/Microraptor

Some paleontologists have doubted the biplane hypothesis, and have proposed other configurations. A 2010 study by Alexander et al. described the construction of a lightweight three-dimensional physical model used to perform glide tests. Using several hind leg configurations for the model, they found that the biplane model, while not unreasonable, was structurally deficient and needed a heavy-headed weight distribution for stable gliding, which they deemed unlikely. The study indicated that a laterally abducted hindwing structure represented the most biologically and aerodynamically consistent configuration for Microraptor.[3] A further analysis by Brougham and Brusatte, however, concluded that Alexander's model reconstruction was not consistent with all of the available data on Microraptor and argued that the study was insufficient for determining a likely flight pattern for Microraptor. Brougham and Brusatte criticized the anatomy of the model used by Alexander and his team, noting that the hip anatomy was not consistent with other dromaeosaurs. In most dromaeosaurids, features of the hip bone prevent the legs from splaying horizontally; instead, they are locked in a vertical position below the body. Alexander's team used a specimen of Microraptor which was crushed flat to make their model, which Brougham and Brusatte argued did not reflect its actual anatomy.[15] Later in 2010, Alexander's team responded to these criticisms, noting that the related dromaeosaur Hesperonychus, which is known from complete hip bones preserved in three dimensions, also shows hip sockets directed partially upward, possibly allowing the legs to splay more than in other dromaeosaurs.[16]

There is a reference to the splayed posture of Scansoriopterids here (page 154):
Riddle of the Feathered Dragons

http://books.google.ca/books?id=SihlpQTlVdAC&pg=PA154&lpg=PA154&dq=Certainly+the+fact+that+scansoriopterids&source=bl&ots=jTl6Uvn68h&sig=WRNGO1pzEQdzfw0F8HUmvrTHaVE&hl=en&sa=X&ei=ONVsVJ-GMI-nyASPzYCAAQ&ved=0CCEQ6AEwAA#v=onepage&q=Certainly%20the%20fact%20that%20scansoriopterids&f=false

Certainly the fact that scansoriopterids could spread the hind limbs outward in a splayed posture, more than in typical birds, indicates that a true upright stance was achieved only later and independently from true dinosaurs.

There is a reference to the splayed posture of Archaeopteryx here (page 399):
The Origin and Evolution of Birds
http://books.google.ca/books?id=8QRKV7eSqmIC&pg=PA399&lpg=PA399&dq=archaeopteryx+femur+angle&source=bl&ots=fqR1hR9GAi&sig=7grokjyLDiND0WyvJNaAJC8e0Ko&hl=en&sa=X&ei=p1UYVJW0H5OtyATf5YCYCA&ved=0CB0Q6AEwAA#v=onepage&q=archaeopteryx%20femur%20angle&f=false


http://www.bioone.org/doi/pdf/10.1525/auk.2013.130.1.1

Microraptors have been reconstructed in two distinctive models, the four-winged gliding model with sprawled hindlimb wings, by which it was originally described in Nature (Xu et al. 2003), and a dinosaurian bipedal model, or biplane model, by which it is reconstructed with the hindlimbs held beneath the body, incapable of sprawling, in other words, like a tiny T. rex. The problem,of course, is that there is absolutely no reason the hindlimbs could not have been sprawled, as is the case in flying squirrels (Glaucomys spp.), flying lemurs (Dermoptera), etc., and even falling cats. Too, the sprawled model performs superiorly inwind-tunnel experiments (Alexander et al. 2010), most specimensare preserved with a sprawled posture, and the wingclaws are adapted for trunk climbing (Burnham et al. 2011). In addition, it would be difficult to imagine how selection could produce elongate, asymmetric hindlimb flight remiges by the most current paleontological reconstructions, in which the hindlimbs are held in flight beneath the body in obligate bipedal fashion, with elongate hindlimb wing feathers trailing behind, simply slicing through the air (Balter 2012)

http://www.pnas.org/content/107/7/2972.full.pdf+html
Alexander et al

Fossils of the remarkable dromaeosaurid Microraptor gui and relatives clearly show well-developed flight feathers on the hind limbs as well as the front limbs. No modern vertebrate has hind limbs functioning as independent, fully developed wings; so, lacking a living example, little agreement exists on the functional morphology or likely flight configuration of the hindwing. Using a detailed reconstruction based on the actual skeleton of one individual, cast in the round, we developed light-weight, three-dimensional physical models and performed glide tests with anatomically reasonable hindwing configurations. Models were tested with hindwings abducted and extended laterally, as well as with a previously described biplane configuration. Although the hip joint requires the hindwing to have at least 20° of negative dihedral (anhedral),all configurations were quite stable gliders. Glide angles ranged from 3° to 21° with a mean estimated equilibrium angle of 13.7°,giving a lift to drag ratio of 4.1:1 and a lift coefficient of 0.64. The abducted hindwing model’s equilibrium glide speed corresponds to a glide speed in the living animal of 10.6m·s−1. Although the biplane model glided almost as well as the other models, it was structurally deficient and required an unlikely weight distribution (very heavy head) for stable gliding. Our model with laterally abducted hindwings represents a biologically and aerodynamically reasonable configuration for this four-winged gliding animal. M. gui’s feathered hindwings, although effective for gliding, would have seriously hampered terrestrial locomotion.

Primitively, early archosaurs are sprawling, with the legs set
laterally and elevated at around 75° (6), a preadapted posture for
gliding.
Modern birds normally have the thigh elevated and sprawled to the side in different degrees; for example, it is nearly perpendicular to the midline in loons and grebes (7).

This variation shows that the degree of splaying needed to use the
hindlegs in gliding is not unusual when compared with that in
modern birds. The absence of an antitrochanter and a supraacetabular
acetabular shelf (SAC) in the eumaniraptorans, including dromaeosaurids,
would make elevation and splaying of the legs even
easier (8). Air pressure could have provided most of the force
needed to elevate the leg into a gliding position similar to that in
gliding mammals. This simple positioning was originally assumed
for the four-winged Microraptor gui (5); but later, workers hoping
to recover an upright posture proposed arrangements of the
hindlimbs that would have required complicated systems of locks
and muscles to hold the leg in an only partially elevated position,
e.g., the “biplane” model (9). New anatomical information based
on the discovery of several hundred specimens similar to the
four-winged glider M. gui (and related taxa) has produced converging
lines of evidence demonstrating that the original
describers of M. gui (5) were correct in their interpretation of the
flight posture. We postulate, based on examination of this new
material, that M. gui was capable of abducting the hind limbs at
least 65–70° to achieve a gliding posture.

 http://bioweb.uwlax.edu/bio203/s2014/gibbs_eliz/adaptation.htm

Velociraptor mongoliensis had a pelvis with a characteristic pubis that pointed downward and forward at an angle toward the ischium. The acetabulum of V. mongoliensis opened dorsolaterally, indicating that it could abduct and adduct its hind limbs. This morphological characteristic demonstrates that the ancestors of V. mongoliensis were probably capable of flight and therefore the flightlessness of Velociraptor was secondarily lost (Longrich and Currie. 2009).

http://www.pnas.org/content/106/13/5002.full
(Longrich and Currie. 2009)

The acetabulum is similar to those of other dromaeosaurids in that it lacks a prominent supracetabular crest (30, 36). However, anteriorly, the contribution of the ilium to the acetabulum is broad, and the anterior rim projects strongly laterally, as it does in Unenlagia(36).

The medial opening of the acetabulum is partially closed, as it is in other Dromaeosauridae (36). The [Hesperonychus] acetabulum opens dorsolaterally rather than laterally, as is the case in Velociraptor (38), suggesting the ability to partially abduct the hindlimbs. This morphology is of interest in light of proposals that Microraptor gui abducted its feathered hindlimbs to function as airfoils (24).

GENERAL

Possible shape:

http://pterosaurheresies.wordpress.com/2012/11/01/microraptor-leg-feathers-and-the-evolution-of-bird-flight/

Also interesting:
http://dml.cmnh.org/2005Dec/msg00079.html
That the leg winged dromaeosaurs have modified femoral heads that in some ways resemble those of some pterosaurs suggests they had evolved a different function, later lost in most secondarily flightless examples. Which is why so many specimens are splayed out spread eagle style. The hip sockets and leg musculature would not have to be fully functional when splayed out in flying dromaeosaurs because they were not using them for walking or running (many joints are not in full articulation in animals when they are not bearing full loads). (G. Paul)


Consider the following. We can see that they are assuming a dino to bird theory when concluding it could not splay its legs. 

http://blogs.scientificamerican.com/tetrapod-zoology/2013/11/18/flight-of-the-microraptor/

One debate that surrounds the aerodynamic performance of Microraptor concerns hindlimb posture. In the very first study to discuss Microraptor’s possible flight abilities, it was depicted as being capable of a full-on sprawl, its hindlimbs projecting laterally in parallel with its arms (Xu et al. 2003). This sprawling pose was also promoted in another study (Alexander et al. 2010).
Given that the form of the theropod femur and hip socket generally prevents the hindlimb from being abducted this far from the sagittal plane (there are proximally placed trochanters on the femur, and supra-acetabular shelves and antritrochanters on the ilium that prevent this sort of posture), this is surely incorrect (Brougham & Brusatte 2010). http://www.nature.com/ncomms/2013/130918/ncomms3489/full/ncomms3489.html

Very good reference on pterosaur hip structure.
http://books.google.ca/books?id=idta6AVV-tIC&pg=PA10&lpg=PA10&dq=pterosaur+acetabulum+hip+socket&source=bl&ots=2GUU4Y1aSx&sig=f5JZsHtyLQHlEb3P4A9BIshxIkE&hl=en&sa=X&ei=DiMeVPrNCZG2yATXwICQCQ&ved=0CDcQ6AEwAw#v=onepage&q=pterosaur%20acetabulum%20hip%20socket&f=false

Related references:

http://www.sciencedaily.com/releases/2010/01/100125173238.htm

A joint team from the University of Kansas and Northeastern University in China says that it has settled the long-standing question of how bird flight began.

http://www.app.pan.pl/archive/published/app59/app20111109.pdf
Pterosaur pelvis

http://icb.oxfordjournals.org/content/early/2011/09/21/icb.icr112.full
"Tent" model:

http://www.pnas.org/content/107/7/2733.full.pdf+html
John Ruben

http://www.pnas.org/content/106/13/5002.abstract?ijkey=b80c6cec04b5f05bcbf67870ea44df19a403ed62&keytype2=tf_ipsecsha
Hesperonychus

http://www.pnas.org/content/107/40/E155.full
Argument (Brougham and Brusatte)

The hypothesis that birds are theropod dinosaurs is supported by anatomical and molecular similarities, shared growth dynamics and physiology, and fossil theropods covered in feathers. A recent paper by Alexander et al. (1) and an associated commentary by Ruben (2) attempted to understand one of the greatest remaining riddles of avian evolution: the origin of flight itself.
Alexander et al. (1) examined the aerodynamic capabilities of Microraptor, a Cretaceous dromaeosaurid (avian sister taxon), by subjecting a reconstructed model to glide tests (1). They concluded that Microraptor was an arboreal glider that used all limbs as a single airfoil. We applaud the empirical approach of the study by Alexander et al.(1) and agree that Microraptor was capable of gliding. We disagree, however, with their anatomical reconstruction of Microraptor and, most importantly, with the assumption that any discovery about the habits of a single dromaeosaurid may solve the riddle of the origin of avian flight.
Alexander et al. (1) reconstructed Microraptor as a sprawling animal, with femora oriented at 140° to one another, a pelvic anatomy unlike that of other dromaeosaurids. The authors claimed that “new anatomical information,” gleaned from “examination of new material,” supported their reconstruction (1). However, this is simply asserted, with no description or illustration of this new material. Similarly, the authors argued that the lack of a supracetabular crest and an antitrochanter in Microraptor and other dromaeosaurids allows for a greater range of motion in the hind limb (1). This is incorrect: dromaeosaurids actually have enlarged antitrochanters, which limit femoral abduction (3), and although the supracetabular crest is reduced, it is still present (3). Finally, one author (J.B.) examined the cast pelvis used by Alexander et al. (1) and found that it, like all known Microraptor specimens, was crushed flat. With this in mind, it is important that the recent discovery of a 3D pelvis of a close relative, Hesperonychus (4), seems to allow only minor lateral splaying of the hind limbs.
We disagree with Ruben (2) on his presumption that different postural reconstructions of Microraptor “imply profoundly different scenarios for the origin of flight” (2). The implicit assumption is that this single species can be analyzed biomechanically, and whatever configuration glides best when launched from a catapult is the probable anatomy of the ancestor of birds. There is a clear fallacy in this reasoning: Microraptor itself cannot be an ancestor of birds, because it lived after birds had originated. It could only help understand avian flight if it retained the gliding abilities of that ancestor, which is not at all certain (5). There are nearly 40 known dromaeosaurid and troodontid dinosaurs—the closest relatives to birds. These animals exhibit a wide range in morphology, body size, integumentary covering, limb proportions, and inferred habitat. Fixation on a single derived dromaeosaurid species is not the path to understanding the origins of avian flight. We do commend Ruben (2), however, on acknowledging that an arboreal theropod dinosaur may have given rise to birds, which departs from his previous criticism of the dinosaur–bird hypothesis and is in line with the robustly supported theory that birds are living theropods.

http://www.pnas.org/content/107/40/E156.full
Reply to Brougham and Brusatte

Brougham and Brusatte (1) agree with us that Microraptor was an arboreal glider but disagree with the posture of our model's hind limbs (1). They offer no suggestion for an alternative, other than the implied parasagittal posture of a typical dromaeosaur, which we showed was aerodynamically and mechanically unlikely (2). They cast doubt on the sprawled (abducted) hind-limb posture of our reconstruction—a key feature—by claiming that dromaeosaurid hips have structures (antitrochanters and supracetabular crests) that prevent abduction and that our specimen was too flattened to see such features. Whereas large dromaeosaurids may possess such structures, apparently, in small ones such as Microraptor, these structures are greatly reduced (3). The authors (1) misrepresent the small dromaeosaurid Hesperonychus as providing evidence against a sprawling posture, when the original description of Hesperonychus specifically mentions the lack of processes on the acetabulum preventing abduction and states that the “acetabulum opens dorsolaterally rather than laterally… suggesting the ability to partially abduct the hind limbs. This morphology is of interest in light of proposals that Microraptor gui abducted its feathered hind limbs to act as airfoils” (reference 4 in ref. 1). Their crushed flat claim is based on examining an incomplete cast (1). They did not examine the original fossil or its X-rays and X-ray computed tomography scans, and thus made a judgment using incomplete information. This Microraptor pelvis has been figured and described (4), and a complete 3D cast of the specimen is also available in our collections for examination. Furthermore, our pelvic morphology was checked against dozens of other specimens (as stated in ref. 2). We stand by our anatomical observations and are currently describing this specimen, along with other material, which will support the accuracy of our interpretation.

Brougham and Brusatte (1) devote a large portion of their letter to defending the dinosaurian origin of birds. We find this somewhat puzzling, because we did not address that issue in our paper. They choose to regard this feathered dromaeosaur as a derived member of the group, although most cladistic analyses show it as basal (5) or even as the primitive sister group of that clade (3). Moreover, much older taxa with large, pennaceous feathers on the lower hind limb (Pedopenna, Anchiornis) have been discovered from radiometrically dated Jurassic rocks in China (5). Anchiornis is cladistically a troodontid, suggesting that four-winged gliding is also primitive for deinonychosaurs. Brougham and Brusatte (1) suggest that Microraptor is of no relevance to understanding bird flight, because they doubt that it inherited its mode of gliding from an ancestor that it shared with birds. We think that such a shared ancestry is actually reasonable given the feathered hind limbs of Anchiornis, to which other authors have attributed an aerodynamic function (5). We never argued that Microraptor must be a direct ancestor of birds to be informative about the origin of avian flight, any more than Archaeopteryx must be ancestral to modern birds to be informative about avian origins. We think Microraptor displays a four-winged mode of gliding that it inherited from more primitive, arboreal ancestors, and we are confident that our model is anatomically reasonable.

___________________________________________________________

The idea that flapping must have been first 

The trees down theory begins with a gliding arboreal creature. This is closer to being correct except that the gliding phase took place much earlier in the evolution of the pterosaur. This is a key point.

http://blogs.scientificamerican.com/WSS/post.php?blog=43&post=9336

Kevin Padian of the University of California at Berkeley, an expert on bird evolution, observed that the presentations focused on the effect of the hindlimb on a gliding animal instead of one that flapped its wings. Last year at the SVP meeting he presented evidence that gliders and flyers are completely unrelated to each other. He says that “there is not a shred of evidence that says gliding is involved in the evolution of flapping flight.” He questioned why the team's model would focus on gliding parameters when the forelimb shape was consistent with flapping, not gliding, and the hindlimb would have generated so much drag.  

http://www.economist.com/blogs/babbage/2011/11/evolution-flight

Rather, it was a challenge to the discipline's long-held belief that flapping wings, with their complicated nerve, muscle and bone structure, must, surely, have evolved from a simpler variety that allowed its owners to glide.

At first, Dr Padian and Dr Dial were expecting to find fossilised bats that were gliders, not flappers. To their surprise, they discovered nothing of the sort. They then expanded their search to all flying and gliding animals. What they found was, if anything, even more shocking: gliding and flapping fauna appear to have no direct common ancestor. This suggests that the prevailing [trees down] theory is wrong. It also, however, leaves open the question of where powered flight comes from.

 http://gwawinapterus.wordpress.com/2014/02/21/on-the-origins-of-flight-no-gliders/

An alternative option is what is reflected by an examination of gliding animal groups: gliding simply does not translate into flight, simply never leads to powered volancy, and that the flying vertebrates we know and love, as well as insects, have simply evolved under extremely anomalous sets of behaviour completly unrelated to gliding.

Based on birds and bats, as well as modern gliders, gliding appears to be effectively independent from flight, gliding animals seemingly unable to produce powered flight and animals that have evolved powered flight having developed it in unusual circumstances. Exceptions might exist, including possibly pterosaurs, but as it stands vertebrate flight has only been able to evolve from behaviours that promote forelimb movement, with aerodynamic speciation not leading at all to volancy.

http://www.nature.com/news/ancient-bats-got-in-a-flap-over-food-1.9304

“It is a simple but amazing observation that there are no flying lineages of vertebrates with gliders as a sister group,” says evolutionary biologist Nancy Simmons at the American Museum of Natural History in New York.

More:
https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CB0QFjAA&url=http%3A%2F%2Fwww.springer.com%2Fcda%2Fcontent%2Fdocument%2Fcda_downloaddocument%2F9781461473961-c1.pdf%3FSGWID%3D0-0-45-1409215-p175092519&ei=6FMvVMmLGeKbjALf04CQDg&usg=AFQjCNHWM-i3q0hYliEZtZSLr-UJWlm40w&sig2=7sv3satbA1kcbbROg0H6dw&bvm=bv.76802529,d.cGE



A FANCIFUL RATIONALIZATION:

The passage below offers up a very weak rationalization for thinking that even if the trees down theory is correct the arboreal creatures could still be dinosaurs. As the writers admit, "It would require stages in the origin of flight not preserved in our current sample of extinct nonavian dinosaurs."


http://az.oxfordjournals.org/content/amzoo/40/4/486.full.pdf

AMER. ZOOL., 40:486–503 (2000)
Phylogenetic Context for the Origin of Feathers1
STUART S. SUMIDA2,* AND CHRISTOPHER A. BROCHU†

The cursorial hypothesis, in its modern incarnation, is the simplest model for the origin of flight in the context of the preferred phylogenetic hypothesis. But is it a necessary corollary, as implied by some authors? We can infer the mechanism for the origin of flight from a phylogenetic tree, but this will always be a secondary inference. A strict reading of current cladograms does not necessarily reject a trees-down model of flight origins—the fossil record is incomplete, and one can always posit an unpreserved arboreal dinosaurian relative of birds. Additionally, rejection of a ground-up model for flight origins need not imply rejection of the dinosaurian hypothesis (Gauthier and Padian, 1985; Padian and Chiappe, 1998a), and some authors who derive birds from theropods explicitly prefer a trees-down model for flight origins (e.g., Chatterjee, 1999). The origin of a group, the origin of a structure, and the origin of a behavior or function are fundamentally different questions, and a cladogram primarily addresses the first. Some authors find legitimate reason to prefer a less-parsimonious scenario for a give cladogram on the basis of some sort of external evidence (e.g., Zaher and Rieppel, 1999).
One could argue that nonavian maniraptorans could climb, or that small arboreal theropods are yet to be discovered. Such a model would be much less parsimonious than the cursorial model, at least from the perspective of present phylogenetic understanding. It would require stages in the origin of flight not preserved in our current sample of extinct nonavian dinosaurs. The arboreal model is thus less parsimonious, but is not strictly falsified by the cladogram in Figure 1; an arboreal nonavian theropod may await discovery somewhere. The statement by Geist and Feduccia (2000) that cladistic analyses posit that “avian flight necessarily developed within a terrestrial context” (our emphasis) reflects a misunderstanding of how cladograms are constructed and what they can actually falsify.