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]