* Dinosaurs did not have feathers

http://news.nationalgeographic.com/news/2006/03/0315_060315_dinosaur.html

The fossil of a small, predatory dinosaur discovered in Germany has experts rethinking how feathers developed among the dinosaurs that likely gave rise to birds.

The authors say the new species undermines the notion that a covering of simple, hairlike feathers was characteristic of such early theropods as was previously believed.

Given its position in the dinosaur family tree, Juravenator "should bear filamentous feathers," Xing Xu said in an interview. But Chiappe says the new fossil didn't seem to bear any physical evidence of feathers, missing or not. "You could expect to see follicle [in the skin], small pits that contain feather buds. We don't see them in Juravenator," Chiappe said.

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

Juravenator is a genus of small (70 cm long) coelurosaurian [Compsognathidae] dinosaur, which lived in the area which would someday become the Jura mountains of Germany, about 151 or 152 million years ago.

Taking a break from pterosaurs

Here is a study:
http://www.sciencedaily.com/releases/2011/07/110718111421.htm

The face of a frog: Time-lapse video reveals never-before-seen bioelectric pattern

For the first time, Tufts University biologists have reported that bioelectrical signals are necessary for normal head and facial formation in an organism and have captured that process in a time-lapse video that reveals never-before-seen patterns of visible bioelectrical signals outlining where eyes, nose, mouth, and other features will appear in an embryonic tadpole.

https://www.youtube.com/watch?v=ndFe5CaDTlI


http://onlinelibrary.wiley.com/doi/10.1002/dvdy.22685/full

Using voltage and pH reporter dyes, we have discovered a never-before-seen regionalization of the Xenopus ectoderm, with cell subpopulations delimited by different membrane voltage and pH. We distinguished three courses of bioelectrical activity. Course I is a wave of hyperpolarization that travels across the gastrula. Course II comprises the appearance of patterns that match shape changes and gene expression domains of the developing face; hyperpolarization marks folding epithelium and both hyperpolarized and depolarized regions overlap domains of head patterning genes. In Course III, localized regions of hyperpolarization form at various positions, expand, and disappear. Inhibiting H⁺-transport by the H⁺-V-ATPase causes abnormalities in: (1) the morphology of craniofacial structures; (2) Course II voltage patterns; and (3) patterns of sox9, pax8, slug, mitf, xfz3, otx2, and pax6. We conclude that this bioelectric signal has a role in development of the face. Thus, it exemplifies an important, under-studied mechanism of developmental regulation. Developmental Dynamics 240:1889–1904, 2011. © 2011 Wiley-Liss, Inc.

ALSO:

http://link.springer.com/article/10.1007%2Fs12064-014-0200-4

In developmental and evolutionary biology, particular emphasis has been given to the relationship between transcription factors and the cognate cis-regulatory elements of their target genes. These constitute the gene regulatory networks that control expression and are assumed to causally determine the formation of structures and body plans. Comparative analysis has, however, established a broad sequence homology among species that nonetheless display quite different anatomies. Transgenic experiments have also confirmed that many developmentally important elements are, in fact, functionally interchangeable. Although dependent upon the appropriate degree of gene expression, the actual construction of specific structures appears not directly linked to the functions of gene products alone. Instead, the self-formation of complex patterns, due in large part to epigenetic and non-genetic determinants, remains a persisting theme in the study of ontogeny and regenerative medicine. Recent evidence indeed points to the existence of a self-organizing process, operating through a set of intrinsic rules and forces, which imposes coordination and a holistic order upon cells and tissue. This has been repeatedly demonstrated in experiments on regeneration as well as in the autonomous formation of structures in vitro. The process cannot be wholly attributed to the functional outcome of protein–protein interactions or to concentration gradients of diffusible chemicals. This phenomenon is examined here along with some of the methodological and theoretical approaches that are now used in understanding the causal basis for self-organization in development and its evolution.

http://www.scientificamerican.com/article/bioelectrical-signals-can-stunt-or-grow-brain-tissue/

Bioelectrical Signals Can Stunt or Grow Brain Tissue

http://www.nature.com/news/bioelectric-signals-spark-brain-growth-1.17087

Bioelectric signals spark brain growth

http://www.jneurosci.org/content/35/10/4366

http://www.sciencedaily.com/releases/2015/04/150427082851.htm

Flamingo Lineage (2)

Here is an enhancement to the possible flamingo lineage:

• Pterosaur (Ctenochasmatidae )   Pterodaustro  --->
• Presbyornithid subgroup--> 
• Primitive bird, Palaelodidae (Phoenicopteriformes)  --> 
• Flamingo (Phoenicopteriformes)

Pterosaurs lasted till late Cretaceous

Presbyornithids spanned from late Cretaceous? to Early Oligocene

Palaelodidae spanned from early Oligocene to Middle Pleistocene

Modern flamingos span from 30 mya to the present day


http://www.flamingos-world.com/flamingo-evolution.html
* There is evidence to indicate the Flamingo evolved at least 30 million years ago, perhaps longer. 

Note: I have added in the flamingos here:
http://pterosaurnet.blogspot.com/2011/10/waterfowl_07.html



http://onlinelibrary.wiley.com/doi/10.1002/ar.20990/pdf
"Our investigation of skeletal and ontogenetic variation in Pterodaustro  gives insights into  the
developmental  growth  dynamics of this  unusual  ctenochasmatid pterodactyloid   from  early
ontogeny  through  to  adulthood  and  also pro vides   information  pertaining  to  histological   variability   within   and between bones of individuals. This  study  also documents the presence of what  appears to be medullary bone tissue within the medullary cavity  of a large femur  of Pterodaustro.  This  suggests that,  like  birds,  reproductively  active female  pterosaurs  may have deposited a special bone tissue (medullary bone) to cope with  the demand of  calcium  during  eggshelling."

Summary

Here is a summary of the basic ideas of this site. This is a work in progress.:

Birds developed in a lineage from proto-pterosaurs (eg. cosesaurus)

to pterosaurs (eg. pterodactyls)

to primitive pygostylia birds (eg. enantiornithes)

to modern flying birds (neognathae) and modern flightless birds (palaeognathae).

AND

Primitive pterosaurs (rhamphorhynchids) developed into long-bony-tailed feathered creatures (eg. dromaeosaurs) which went extinct. Advanced pterosaurs (pterodactyls) developed into short-tailed feathered birds (Pygostylia).

AND

The category called "coelurosaur dinosaurs" includes only actual dinosaurs (eg. tyrannosaurs). It does not include birds.

AND

The fossil record does not support the dinosaur-to-bird idea. The fossil record does support the pterosaur-to-bird idea.

pycnofibres to feathers

breathing

warm blooded

propatagium

particular pterosaurs to particular birds

ghost lineages

finger phalanges

The Flamingo Lineage

Here is an introduction to the flamingo lineage:

A preliminary, possible lineage:

Pterosaur (Ctenochasmatidae) Pterodaustro --> Primitive bird, Palaelodidae (Phoenicopteriformes)
--> Flamingo (Phoenicopteriformes)

See this earlier post on the flamingo pterosaur:
http://pterosaurnet.blogspot.com/2010/05/flamingo.html

http://en.wikipedia.org/wiki/Pterodaustro
Pterodaustro is a genus of Cretaceous pterodactyloid pterosaur [Ctenochasmatidae] from South America, which lived 105 million years ago.

http://dinosaurs.about.com/od/aviandinosaurs3/p/pterodaustro.htm
The modern bird that's most often compared to the South American Pterodaustro is the flamingo, which this pterosaur closely resembled in appearance, if not in every aspect of its anatomy. Based on its thousand or so distinctive, bristlelike teeth, paleontologists believe that the early Cretaceous Pterodaustro dipped its curved beak into the water to filter out plankton, small crustaceans, and other tiny aquatic creatures. Since shrimp and plankton are predominantly pink, some of these scientists also speculate that Pterodaustro may have had a distinctly pinkish hue, another trait it would have shared with modern flamingos.

http://en.wikipedia.org/wiki/Pterodaustro
Pterodaustro probably waded in shallow water like flamingos, straining food with its tooth comb, a method called "filter feeding".[4] Once it caught its food, Pterodaustro probably mashed it with the small, globular teeth present in its upper jaw.
According to Robert Bakker, like with flamingos, this pterosaur's diet may have resulted in a pink hue. Thus, it is often dubbed the "flamingo pterosaur".[5]

http://pterodata.blogspot.com/2009/06/very-peculiar-pterosaur.html
"Pterodaustro is represented by a number of specimens from Argentina. There is a complete skeleton, a partial juvenile and an egg, just to mention a few. This unusual pterosaur is quite well represented in the fossil record, certainly enough is known to make a convincing reconstruction.
Most unusually, this was a filter feeder with a fine sieve of unusually adapted teeth that would have been ideal for filter feeding on small aquatic living organisms. This was the Flamingo of the ancient world!
It is also the first pterosaur where gizzard stones have been observed to be present."

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

An extinct family of peculiar "swimming flamingos", the Palaelodidae, are believed to be related to, or to be THE ANCESTORS OF, the modern flamingos. This is sometimes rejected, since the fossil Elornis is known to be from some time before any palaelodid flamingos have been recorded.

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

"The Palaelodidae are a family of extinct birds in the order Phoenicopteriformes, which today is represented only by the flamingos.[1] They have been described as "swimming flamingos."

Three genera are recognised:

Adelalopus, called the "stout-legged flamingos" (Borgloon Early Oligocene of Hoogbutsel, Belgium)[2]

Palaelodus (Middle Oligocene -? Middle Pleistocene)

Megapaloelodus (Late Oligocene - Early Pliocene)"

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

"A wide variety of birds have been proposed as their closest relatives, on a wide variety of evidence. To reflect the uncertainty about this matter, flamingos are generally placed in their own order. [Phoenicopteriformes]"

http://en.wikipedia.org/wiki/Palaelodus
"Palaelodus is an extinct genus of birds distantly related to flamingos. They were slender birds with long, thin legs and a long neck. Little is known about the shape of their skull or beak. Some paleontologists think Palaelodus was able to swim under water, chasing prey, but the morphology of their feet seems not very well adapted for diving. Rather, it is more likely that they were adapted to browsing for food while swimming or standing in shallow water.
The family, Palaelodidae, is the sister taxon of modern flamingos, and the order Phoenicopteriformes, to which both belong, probably evolved from a grebe-like ancestor. It is easy to see how a bird like Palaelodus represents an intermediate form between a diving, fish-eating grebe and a wading, invertebrate-filtering flamingo. This does not mean that the palaelodids are the ancestors of the flamingos. Rather, they were a sister group that remained in the ecological niche of their common ancestor."

Since cladistics does not recognize ANCESTORS, it really means nothing to say that they "probably evolved from a grebe-like ancestor" or that  "they were a sister group". Cladistics always says something like that. That tells us nothing.
Palaelodids may well have been the ancestors of the flamingos. Anything cladistics says on that question is irrelevant.

BUT EVEN Without regard to the question of whether Palaelodus was an ancestor or a "sister taxon", we have confirmation of the idea that a separate line led to Phoenicopteriformes. 

It is one of the parallel lines I talk about.

Categories

For ease of reference, here is the list of links to the categories I have analyzed to this point. This is a work in progress.
SEE UPDATED CATEGORY LIST HERE:

http://pterosaurnet.blogspot.com/2012/02/categories-updated.html

Cladistics - Sleight of Hand

http://archosaurmusings.wordpress.com/2008/12/19/monophyletic-paraphyletic-and-polyphyletic/
"Birds are dinosaurs, that is, they are the direct descendents of an ancestor that spawned the dinosaurs, yet palaeontologists typically refer to dinosaurs while explicitly not referring to birds. Thus one should formally call them non-avian dinosaurs (basically all dinosaurs except birds)."
and
"First off the rhamphorhynchoid pterosaurs (or more properly ‘rhamphorhynchoids’ as the quotes denote it as paraphyletic) which often come up here in my frequent posts on pterosaurs. As with non-avian dinosaurs, the term persists as one of convenience as basically it’s easier to write than “non-pterodactyloid pterosaurs”."


Note the sleight of hand. 
The author says:
"Birds are dinosaurs, that is, they are the direct descendents of an ancestor that spawned the dinosaurs". 

In other words, birds did NOT evolve from dinosaurs but rather (according to the author) birds and dinosaurs evolved from some OTHER unnamed "common ancestor". 
But the author does not make this point clear at all. In fact, he misleadingly compares it to the paraphyletic (ANCESTRAL) rhamphorhynchus relationship which is a true ANCESTOR relationship - an ancestor of pterodactyls.
He talks as if they were the same type of relationship. 
Of course it is not the same relationship at all - they are opposites.

NOTE:  Birds are not even related to dinosaurs. Cladistics makes it even more difficult to establish correct ancestry. In this post I am just showing the absurdity of cladistics. If we just kept to ancestor/descendant relationships we would not have these cladistic obfuscations.

An excellent analysis of issue with cladistics:
http://joelvelasco.net/teaching/systematics/laporte%2005%20-%20single%20tree%20of%20life.pdf.

The absurdity of cladistics

http://en.wikipedia.org/wiki/Evolutionary_grade
"An evolutionary grade is a group of species united by morphological or physiological traits, that has given rise to another group that differs markedly from the ancestral condition, and is thus not considered part of the ancestral group. The ancestral group will not be phylogenetically complete (i.e. will not form a clade), so will represent a paraphyletic [ancestral] taxon".

This is the absurdity of cladistics. 
When "a group of species has given rise to another group that differs markedly from the ancestral condition, it  is not considered part of the ancestral group."

So an ANCESTOR is not an ANCESTOR!!!

I expect that not many cladists even know about the absurdity buried within cladistics.

Ancestral relationships

Here is another example of cladists struggling with an ancestral relationship. Keep in mind that cladistics does not recognize ancestral relationships.

http://en.wikipedia.org/wiki/Neoazhdarchia
"There are currently two primary but competing views of azhdarchoid relationships. The first, presented by Felipe Pinheiro and colleagues in 2011, considers the tapejarids to be a monophyletic clade including the thalassodromines and chaoyangopterines.[4] The second, found by Lu et al. 2008 as well as Naish & Martill 2006, considers the tapejarids to be a paraphyletic [ANCESTRAL] grade of primitive azhdarchoids. All azhdarchoids closer toAzhdarcho than to Tapejara are included in the clade Neoazhdarchia("new azhdarchids").[2]"

Azhdarchoidea	Azhdarchidae Tapejaridae Thalassodrominae Chaoyangopterinae Tapejarinae

Azhdarchoidea	Tapejaridae Neoazhdarchia Thalassodromidae Chaoyangopteridae Azhdarchidae

If we analyze these two competing views they actually come down to two different conclusions about the ANCESTRAL relationships.
In the first view, Azhdarchidae is the ancestor (which is not acknowledged). In the second view, Tapejaridae is the ancestor (and is acknowledged).
Since cladistics does not even recognize ancestral relationships, the cladists are stymied about how to even think about these ancestral relationships.

* "An important unanswered question"

More from this 2011 study:
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0028672
"The timing and sequence of events that led to the origin and subsequent evolution of flapping flight in birds remains an important unanswered question in vertebrate evolutionary biology." 


The question is "unanswered". That is quite an admission. 
The dino to bird enthusiasts themselves acknowledge that on the most important question they have no idea. 
They cannot even figure out a story to explain how a purported unknown, unfound dinosaur lineage somehow developed wings and feathers and became birds. 
It is an absurd idea. And for most of history it has been recognized as absurd. 

Enantiornithes - versatile fliers

Here is a new study that contains some very interesting material.
Here is one small part concerning Enantiornithes:
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0028672

Four flight styles for living birds were used:‘continuous flapping’ (CF) (e.g. grebes, ducks and auks); ‘flapping and soaring’ (FS) (e.g. storks, pelicans and large raptors); ‘flapping and gliding’ (FG) (e.g. swifts, falcons and gulls); ‘passerine-type flight’ (PT). 
AND
sampled enantiornithines fall across the range of all defined flight styles


I have proposed that enantiornithines are the ancestors of many modern bird taxa. When it comes to flight style we see the versatility within enantiornithes. 
And we already saw that they inhabited all the different niches. 

* No dino to bird lineage

It may be surprising for some people to learn that the dino to bird theory is not supported by any fossils. Those who propose the dino to bird theory acknowledge the fact that they have never found one fossil that is on the purported line from dino to bird.
There are a number of dinosaur taxa  that have been found, but it has been determined that none of them are ancestors to birds.
Even so, the dino to bird enthusiasts still imagine that birds evolved from dinosaurs.

This lack of fossils is well known but never mentioned.
All that has ever been found are dinosaur taxa that are NOT ancestors. The dino to bird theorists claim they are "sister taxa". But of course that makes no sense because there is no evidence of any actual dino to bird lineage for those sister taxa to be related to. None.
It is all imagination.

New opinions ...

“New opinions are always suspected, and usually opposed, without any other reason but because they are not already common."
~John Locke

"In the choice between changing one's mind and proving there's no need to do so, most people get busy on the proof."
~John Kenneth Galbraith

"Our wretched species is so made that those who walk on the well-trodden path always throw stones at those who are showing a new road."
~Voltaire

"You have enemies?  Good.  That means you've stood up for something, sometime in your life."
~Winston Churchill

What is the alternative?

http://www.jstor.org/pss/4085810
According to this reference, for a long time, folks thought that birds evolved from "pseudosuchian archosaurs". Then that fell from favour and was replaced by a purported "direct derivation of birds from theropod dinosaurs". 


When that was shown to be untenable, some folks moved to the idea that birds evolved from crocodile type ancestors. (Yes, crocodiles). 
But then that idea fell from favour and the folks moved to some purported vague dinosaur ancestry. But they do not give any specifics so that it can never be evaluated. 
Perhaps someone could do us all a favour and tell us what the current thinking is about the purported dino to bird lineage.

I have proposed a lineage. What is the alternative? 

Pterosaur teeth are like bird teeth

Pterosaur teeth:

https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhAHLEntit9Gt4iqsjZqcfoT5IHjB8ISKCbqCaIAJ2dy7x8YMypjw1ZzUHBCmP2o4M5N2l2mz0yfn18o2UPg9LWsksWrSycP0h2bXKDVyQXDteu9VeotuTJYb6M-xLtPjYQxPgZrAD3pld9/s400/PterosaurTeeth.jpg

Here is a theropod dinosaur tooth:

http://australianmuseum.net.au/image/Theropod-dinosaur-tooth/
"SEM of theropod dinosaur tooth, showing serrated edge."

http://www.palaeodiversity.org/pdf/03/Palaeodiversity_Bd3_Nesbitt.pdf

The presence of an external mandibular fenestra, along with morphological evidence elsewhere in the body of pterosaurs (serrated teeth, antorbital fossa present, fourth trochanter on the femur present), supports a placement of Pterosauria within Archosauriformes and is consistent with a position within Archosauria.

https://pterosaurheresies.wordpress.com/2011/08/30/the-truth-about-toothless-pterosaurs/

In several pterosaurs the medial or first premaxillary tooth was procumbent
[excessive inclination of the incisor teeth toward the lips]. It angled forward as well as downward. In B St 1967 I 276 (No. 6 of Wellnhofer 1970), the tiniest pterosaur, the anterior premaxillary tooth was procumbent. 

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

The teeth of deinonychosaurs were curved and serrated, but not blade-like except in some advanced species such as Dromaeosaurus albertensis. The serrations on the front edge of deinonychosaur teeth were very small and fine, while the back edge had serrations which were very large and hooked.^[3] 

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

The most primitive members have four pairs of teeth in the premaxillae, such as in Caudipteryx[9] and in Incisivosaurus they are enlarged and form bizarrely prominent bucktoothed [procumbent] incisors.

http://blogs.scientificamerican.com/tetrapod-zoology/yi-qi-is-neat-but-might-not-have-been-the-black-screaming-dino-dragon-of-death/

The scansoriopterygid skull is short-faced and robust, the anterior end of the lower jaw is slightly downturned, and the teeth are procumbent.

http://en.wikipedia.org/wiki/Yi_(dinosaur)

[Yi qi] Like other scansoriopterygids, the head was short and blunt-snouted, with a downturned lower jaw. Its few teeth were present only in the tips of the jaws, with the four upper front teeth per side being the largest and slightly forward-pointing, and the front lower teeth being angled even more strongly forward.^[1] 

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

The most primitive members have four pairs of teeth in the premaxillae, such as in Caudipteryx^[9] and in Incisivosaurus they are enlarged and form bizarrely prominent bucktoothed incisors

Uniqueness

http://bigcat.fhsu.edu/biology/cbennett/flotsam/Bennett-2008-forelimb-myology.pdf
"...the large size, great length, and unconventional arrangement such that it swung backward in flight position enabled digit IV to spread and support the wing yet fold it out of the way when the animal was not flying.
Such an arrangement of fingers with one swinging away from the others is unique among vertebrates."
Let's consider this "uniqueness".
Whenever an explanation requires a characteristic that is "unique among vertebrates" we have to question whether this explanation is correct. 
After all, if someone says to you - okay here is how it worked. It worked in a way that is found NOWHERE ELSE IN THE VERTEBRATE WORLD. Then you have to think that perhaps that explanation is not correct. 
So I think we can put such an explanation to the side. 

In case people are having trouble visualizing what I am proposing, work with your own hand. 
Hold your hand out, palm down. Your index finger is the wing finger so it is very long. Bend your index finger toward your palm. Now imagine that you could continue bending it in that direction so that the index finger would point back toward the elbow. 
That is what I am suggesting. 
Now the question arises as to how that could be accomplished, given the length of the index finger.
I can see how that could be accomplished but if anyone would like to offer up a suggestion please do.

Here is how it could work:
Begin with the pterosaur on all fours (or standing) with the index finger bent (toward the palm and then toward  the elbow). 
The unfolding of the index finger is a combined motion of lifting the arm, rotating the arm slightly backward (palm back) and unfolding the finger. Then at the top of the arm extension, rotating the arm back again.

What I am saying does not require a vault launch method but it would work with that method as well. 
See video:
http://www.newscientist.com/article/dn19724-did-giant-pterosaurs-vault-aloft-like-vampire-bats.html

A question about the pterosaur wing finger folding

Does this drawing represent the current thinking about how the pterosaur folded its wing finger?

http://pterosaurheresies.files.wordpress.com/2011/10/standing-pteranodon-72.jpg?w=584&h=793

AND

Here is a basic question about the current thinking - that the 4th finger is the wing finger and that it is turned 90 degrees. Is it turned 90 degrees TOWARD the THUMB or 90 degrees AWAY from the THUMB? I have not seen any reference that explicitly answers that question.
Can anyone provide a reference that gives the answer to that question? 

Propatagium

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

"The pterosaur wing membrane is divided into three basic units. The first, called the propatagium ("first membrane"), was the forward-most part of the wing and attached between the wrist and shoulder, creating the "leading edge" during flight."


Bird:

http://www.brendanbody.co.uk/flight_tutorial/index.html

"Here is an image of a White Ibis in flight showing full breeding plumage, in this instance the bird is pushing it's wings down and the arm is stretched out. As you can see, we get a good view of where the bones are positioned in the wing, notice that they don't run along the front of the wing. The elbow is set back from the leading edge and the bend in the arm is hidden by the Propatagium, a fold of skin inside the front part of the wing which connects to the shoulder and the wrist."


http://onlinelibrary.wiley.com/doi/10.1002/jmor.1052190209/abstract
"The [bird] propatagium is variably deployed, relative to elbow extension, in flight; support for its cambered shape is maintained by multilayered collagenous and elastic tissue networks suspended between leading edge and dorsal antebrachium." 

Birdman

For fun:
http://www.youtube.com/watch?v=5N9t5qOSzCU&feature=related

Ventilation - pterosaurs are like birds

http://news.sciencemag.org/sciencenow/2009/02/19-02.html

"Modern birds sustain their flight with an efficient ventilation system that keeps air flowing to their muscles. But no one knew how pterosaurs, the first flying vertebrates, powered their wings. A new study in PLoS One concludes that ancient pterosaurs, flying reptiles that lived 220 million to 65 million years ago, did much the same, with a mobile rib cage and a system of air sacs distributed throughout the bones to help move air around."
"The researchers also studied the air spaces in pterosaur bones and concluded that they were associated with air sacs, arranged in patterns similar to those seen in modern birds. The bigger the pterosaur, the more air sacs, just like in modern birds. The air spaces help oxygen circulate and probably also made bones light enough for flight."

Note as always there are dissenting opinions:

"But matching anatomy in pterosaurs to modern animals may be misleading, says Jaap Hillenius, a functional morphologist at the College of Charleston in South Carolina. Pterosaurs left no descendants and are only distantly related to birds. It's possible that the new study is correct, Hillenius says, but he's skeptical. For example, he thinks the model of rib-cage movement doesn't allow enough air for active flight, and that the sternum was not strong enough to support such movement. "Until we find a living pterosaur," there's no way to know for sure—"and that's not going to happen."".

The study itself:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2637988/



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

John Ruben et al. (1997, 1999, 2003, 2004) disputed this and suggested that dinosaurs had a "tidal" respiratory system (in and out) powered by a crocodile-like hepatic piston mechanism – muscles attached mainly to the pubis pull the liver backwards, which makes the lungs expand to inhale; when these muscles relax, the lungs return to their previous size and shape, and the animal exhales. They also presented this as a reason for doubting that birds descended from dinosaurs.[5][6][7][8][9]
Critics have claimed that, without avian air sacs, modest improvements in a few aspects of a modern reptile's circulatory and respiratory systems would enable the reptile to achieve 50% to 70% of the oxygen flow of a mammal of similar size,[10] and that lack of avian air sacs would not prevent the development of endothermy.[11] Very few formal rebuttals have been published in scientific journals of Ruben et al.’s claim that dinosaurs could not have had avian-style air sacs; but one points out that the Sinosauropteryx fossil on which they based much of their argument was severely flattened and therefore it was impossible to tell whether the liver was the right shape to act as part of a hepatic piston mechanism.[12] Some recent papers simply note without further comment that Ruben et al. argued against the presence of air sacs in dinosaurs.[13]

Also see these links:
http://pterosaurnet.blogspot.ca/2010/05/another-thing-to-watch-for.html

http://pterosaurnet.blogspot.ca/2014/04/pneumaticity.html

http://pterosaurnet.blogspot.ca/2013/12/respiratory-cycle-of-bird_16.html

https://en.wikipedia.org/wiki/Pterosaur#Air_sacs_and_respiration

A 2009 study showed that pterosaurs had a lung-air sac system and a precisely controlled skeletal breathing pump, which supports a flow-through pulmonary ventilation model in pterosaurs, analogous to that of birds. The presence of a subcutaneous air sac system in at least some pterodactyloids would have further reduced the density of the living animal.^[18]Like modern crocodilians, pterosaurs appeared to have had a hepatic piston, seeing as their shoulder-pectoral girdles were too inflexible to move the sternum as in birds, and they possessed strong gastralia.^[45] Thus, their respiratory system had characteristics comparable to both modern archosaur clades.