Alvarezsauridae (2)

Let's analyze this a bit more:

http://www.pnas.org/content/108/6/2338.full

"Alvarezsauroids were originally considered to be a group of flightless birds, but it is now widely accepted that they are not nested within Aves (1–3) and instead represent a basal maniraptoran lineage."

This quote does not make the necessary distinction that I have been emphasizing. Namely that the word "maniraptoran" is not precise enough.
We need to distinguish between Aviremigia on the one side and dinosaurs on the other.
Alvarezsaurids are members of Aviremigia. They are primitive birds.

Alvarezsauridae (1)

The dino to bird folks incorrectly consider creatures like Alvarezsaurids to be dinosaurs. However, Alvarezsaurids were secondarily flightless primitive birds.
The dino to bird folk make that mistake because the Alvarezsaurids were land-based.


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

"Alvarezsauridae is an enigmatic family of small, long-legged running dinosaurs. Although originally thought to represent the earliest known flightless birds, a consensus of recent work suggests that they are primitive members of the Maniraptora."

http://www.pnas.org/content/108/6/2338.full

"Alvarezsauroids were originally considered to be a group of flightless birds, but it is now widely accepted that they are not nested within Aves (1–3) and instead represent a basal maniraptoran lineage."

As part of this, it would follow that alvaresaurids had backward pointing pubic bones. There does not seem to be much material on this, but see the following:

http://www.thescelosaurus.com/alvarezsauridae.htm

"Patagonykus puertai Novas, 1997 Coniacian (LK) of Argentina. This animal is apparently transitional between Alvarezsaurus and the rest of Parvicursorinae. It is known from vertebrae, coracoids, a forelimb, partial hips (weakly opisthopubic [pointing backwards, like in dromaeosaurids and birds]), and hindlimbs."

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

"Mononykus [Alvarezsauridae] is currently represented by a single holotype specimen, catalog number IGM N107/6. This specimen consists of a partial skeleton lacking a tail, and only small fragments of skull bones, including a complete braincase."

http://www.geol.umd.edu/~tholtz/G104/lectures/104coelur.html

In the Cretaceous Alvarezsauridae, the forelimbs are further transformed into bizarrely poweful arms with a huge thumb claw and exceedingly small digits II and III. The alvarezsaurids have a backwards pointing pubis. 

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

Perle et al. (1993) described the next alvarezsaur to be discovered, naming it Mononychus olecranus (meaning "one claw"). A month later they changed the genus name to Mononykus, because the earlier spelling was already the genus name of an extant butterfly.[4] Perle et al. (1993) mistakenly described Mononykus as a member of Avialae, and one more advanced than Archaeopteryx. They argued that the family Alvarezsauridae was actually a group of Mesozoic flightless birds on the basis of derived features that were unique to birds.[5] Novas (1996) described another member of the class called Patagonykus puertai.[6] Karhu and Rautian (1996) described a Mongolian member of the family;Parvicursor remotus.[7] Chiappe et al.(1998) described another Mongolian member, Shuvuuia mongoliensis and mistakenly found it to be even more derived, concluding that the alvarezsaurs were actually crown-group (that is, modern) birds.[8]
These mistaken assignments of alvarezsaurs to birds were caused primarily by features that are strikingly, or even uniquely, avian. The sternum, for example, is elongated and deeply keeled for an enlarged pectoralis muscle, as it is in neognathous birds and volant ratites. One bone in the skull of Shuvuuia appeared to be an ectethmoid fused to a prefrontal. The ectethmoid is an ossification known only in Neornithes. Other birdlike characters included the palatine, foramen magnum, cervical and caudal vertebrae, and many others.[9]

http://www.dinosaur-world.com/feathered_dinosaurs/alvarezsauridae.htm

Although these animals are extremely bird-like, no fossilized feathers have been found. If it had feathers, then they were not preserved. Mary Schweitzer has made an important study of the "dino fuzz" fossilized integument found with Shuvuuia desertit [Alvarezsauridae] and arrived to the conclusion that the main chemical component is Beta-Keratin: Important demonstration that "dino fuzz" is in reality feathers.

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

AlvarezsaursTemporal range: Late Jurassic-Late Cretaceous,160–65.5 Ma

http://archosaurmusings.wordpress.com/2010/01/27/guest-post-a-brief-history-of-alvarezsaur-research/
Although very little fossil material was known from the head of Mononykus (and little is still known about its cranium), the postcranial anatomy of this new species strongly hinted that it belonged somewhere within birds. Like birds, Mononykus has a wrist that is fused to the metacarpals, a keeled sternum, a thin, posteriorly-projecting pubis, an extra ridge medial to the cnemial crest, and unserrated teeth with constricted roots. However, the very short, powerful arm of Mononykus could not have been used in flight. Scientists at the time hypothesized that Mononykus was a member of a flightless lineage of early birds, and that it might have used the robust forelimb to dig out insects.

==========================================================


Possibly relevant:

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

Phorusrhacids, colloquially known as "terror birds", were a clade of large carnivorous flightless birds that were the largest species of apex predators in South America during the Cenozoic, 62–2 million years (Ma) ago.^[3]They were roughly 1–3 metres (3.3–9.8 ft) tall. Their closest modern-day relatives are believed to be the 80 cm-tall seriemas. Titanis walleri, one of the larger species, is known from Texas and Florida in North America. 

and

http://www.newanimal.org/moas.htm

South America had birds of this type, but they are thought to have become extinct when the land bridge formed to North America and predators such as the cougar and coyote gradually replaced them. However, this assumption was recently overturned. Fossils from Texas and Florida show that at least one species of South American terror bird managed to establish itself in North America, and was still alive two million years ago. This species had wings that had evolved back into arms, with clawed "hands" on them. It may have looked remarkably like a small, predatory dinosaur [Alvarezsauridae?]. Estimates of its height range from a modest six feet to possibly as big as twelve feet for adult birds. The two-million-year-old fossils have been dated accurately without a doubt. Other North American terror bird fossils might date to as recently as 15,000 years ago, a time when people could have seen them. In fact, there is North American Indian folklore that is rather suggestive of the terror bird, even getting the details right, such as clawed arms instead of wings.

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

The seriemas are the sole extant members of the small and ancient clade Cariamidae, which is also the sole surviving lineage of the Cariamae group. Once believed to be related to cranes, they have been placed by one recent study near the falcons, parrots and passerines, as well as the extinct terror birds.[1] The seriemas are large, long-legged terrestrial birds that range from 70 to 90 cm. They live in grasslands, savanna, dry woodland and open forests of  Brazil, Bolivia, Argentina, Paraguay and Uruguay.

Ghost lineages problem

The mainstream opinion is that birds developed from dinosaurs. But in the cladogram of that, all the sister taxa require ghost lineages. This does not seem to bother dino to bird people, but here is a problem. 

The "sister taxa" fossils appear after (closer to today than) the first birds, but folks think that the fossils that would fill the ghost lineage simply have not yet been found. 
However if the found taxa that are considered "sister taxa" are actually secondarily flightless birds, then that would explain them. And their timing would be consistent. The lineage would be quite different (than the current mainstream thinking) and there would be no need for assumed ghost lineages.

It shows that we need to be cautious about a purported lineage that requires ghost lineages, because the real explanation may be quite different.

No connection between dinosaurs and birds

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

Unlike most other saurischian dinosaurs, which have pubic bones that point forward, several groups of maniraptorans have an ornithischian-like backwards-pointing hip bone. A backward-pointing hip characterizes the therizinosaurs, dromaeosaurids, avialans, and some primitive troodontids. The fact that the backward-pointing hip is present in so many diverse maniraptoran groups has led most scientists to conclude that the "primitive" forward-pointing hip seen in advanced troodontids and oviraptorosaurs is an evolutionary reversal, and that these groups evolved from ancestors with backward-pointing hips.[1]
Holtz and Osmólska (2004) diagnosed the clade Maniraptora based on the following characters: reduced or absent olecranon process of the ulna, greater trochanter and cranial trochanter of the femur fused into a trochanteric crest. An elongated, backwards-pointing pubic bone is present in therizinosauroids, dromaeosaurids, avialans, and the basal troodontid Sinovenator, which suggests that the propubic condition in advanced troodontids and oviraptorosaurs is a reversal.[1] Turner et al. (2007) named seven synapomorphies that diagnose Maniraptora.[4]

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

It [Scansoriopteryx] also had a pubis (hip bone) which pointed forward, a primitive trait among theropods, and unlike some maniraptorans more closely related to birds, where the pubis points downward or backward.^[6]

http://www.psjournals.org/doi/abs/10...-8373-24.4.450

"This information can be used to interpret patterns of locomotor evolution within Dinosauria. The evolution of quadrupedalism with large body size and the acquisition of cursorial or graviportal limb morphologies occurred repeatedly but did not affect the underlying uniformity of dinosaur locomotor morphology. Only derived coelurosaurian theropods (paravians) developed significant modifications of the basic dinosaurian patterns of limb use. Changes in theropod hindlimb kinematics and posture apparently began shortly prior to the origin of flight, but did not acquire a characteristically modern avian aspect until after the later acquisition of derived flight characteristics."

Again no connection between dinosaurs and birds.
But notice how it is worded, to not highlight that fact.

Another example of no connection between dinosaurs and birds:
http://connection.ebscohost.com/c/ar...nction-balance

"The antitrochanter serves as a brace to prevent abduction of the hindlimb and to absorb stresses that would otherwise be placed on the head of the femur during bipedal locomotion. The drum-in-trough-like form of the antitrochanter-femur articulation tends to assist in the transfer of long-axis rotational movements of the femur to the pelvis. The avian antitrochanter is a derived feature of birds that evolved as an aid in maintaining balance during bipedal terrestrial locomotion."

http://intl-icb.oxfordjournals.org/content/40/4/640.full

Theropod hips and hindlimbs show marked morphological changes (Fig. 3) that are consilient with functional changes during their evolution: (1) The antitrochanter repositioned from its primitive archosaurian location on the ischium, facing craniodorsally, to a more craniolateral orientation on the ischium and ilium in dinosaurs and their closest relatives. The antitrochanter then enlarged and re-oriented to face cranioventrally in birds. (2) The femoral head shifted from a craniomedial orientation in basal theropods to a more offset medial orientation in avetheropods, especially birds. (3) The ectocondylar tuber of the distal femur enlarged in “theropods” and moved distally from the proximal popliteal region onto the distal lateral condyle in birds. (4) The main weight-bearing axis of the crus shifted medially in theropods onto the tibia as the fibula and calcaneum were reduced, and elements of the knee and ankle joint became more rigidly appressed. (5) The fibular tubercle, the insertion of the knee flexor M. ilio-fibularis (Müller and Streicher, 1989), moved from a plesiomorphic craniolateral position on the proximal fibula in “theropods” to a caudolateral position in birds, consistent with a change in the action of this muscle related to increased knee flexion.


Notice the general pattern. Researchers see that characteristics appear for the first time in the primitive birds. Characteristics that are not found in dinos. But they just blandly acknowledge this and go on.
They never challenge their preconception that birds developed from dinos.
No matter how much contrary evidence accumulates.

It is not just feathers. Feathers is just the most dramatic example.



http://www.plosone.org/article/info:doi/10.1371/journal.pone.0002271

The azhdarchid mandibular joint is typical of pterosaurs in being a simple hinge permitting slight lateral movement of the mandible during jaw extension.

http://www.nbcnews.com/id/3077253/ns/technology_and_science-science/t/birds-dinosaurs-new-flap/#.URQYIaWMCvt

There are some marked differences in the bones of dinosaurs and birds: Dinosaurs had serrated teeth, while birds have peg-like teeth. Bird feet have reversed toes used for perching in branches - something dinosaurs never developed. Dinosaurs had a characteristic joint in their lower jaws for grasping prey - something never found in birds.

Multiple filaments arising from the edge of a membranous structure

I noticed something interesting in the list (see earlier post):

Quote:

Stage 5. Multiple filaments arising from the edge of a membranous structure

So I went to the article itself:
http://www.ivpp.cas.cn/cbw/gjzdwxb/x...2654347399.pdf

And did a search on "membrane" in the article. It came up in a reference to another study entitled:

"A nearly completely articulated rhamphorhynchoid pterosaur with exceptionally well-preserved wing membranes and “hairs” from Inner Mongolia, northeast China" http://www.ivpp.cas.cn/qt/papers/201...6827022386.pdf

Feathers - no connection between the dinosaurs and the birds.

Consider this chart and the text that accompanies it from here:
http://en.wikipedia.org/wiki/Feather#Evolutionary_stages
Click to enlarge:

"Feather evolution was broken down into the following stages by Xu and Guo in 2009:^[65]

1. Single filament
2. Multiple filaments joined at their base
3. Multiple filaments joined at their base to a central filament
4. Multiple filaments along the length of a central filament
5. Multiple filaments arising from the edge of a membranous structure
6. Pennaceous feather with vane of barbs and barbules and central rachis
7. Pennaceous feather with an asymmetrical rachis
8. Undifferentiated vane with central rachis

However, Foth (2011) showed that some of these purported stages (stages 2 and 5 in particular) are likely simply artifacts of preservation caused by the way fossil feathers are crushed and the feather remains or imprints are preserved. Foth re-interpreted stage 2 feathers as crushed or misidentified feathers of at least stage 3, and stage 5 feathers as crushed stage 6 feathers.^[72]The following simplified diagram of dinosaur relationships follows these results, and shows the likely distribution of plumaceous (downy) and pennaceous (vaned) feathers among dinosaurs and prehistoric birds. The diagram follows one presented by Xu and Guo (2009)^[65] modified with the findings of Foth (2011).^[72] The numbers accompanying each name refer to the presence of specific feather stages. Note that 's' indicates the known presence of scales on the body."

There is much to be said about this chart.
The major thing is that pennaceous feathers appear only in the paraves and oviraptors (oviraptors are secondarily flightless birds). Pennaceous feathers do not appear in the dinosaurs. The jump is from purported earlier stage "feathers" in the dinosaurs* to pennaceous feathers in the primitive birds.
This is noted by Prum and Brush:

http://prumlab.yale.edu/sites/default/files/prum_n_brush_2002.pdf

"Feathers, however, are hierarchically
complex assemblages of numerous
evolutionary novelties—the feather follicle,
tubular feather germ, feather branched structure,
interacting differentiated barbules—that
have no homolog in any antecedent structures"

This is the Achilles Heel of the dino to bird theory:
There is no connection between the dinosaurs and the birds.


* purported to be early stage "feathers" but even that is a dino to bird biased interpretation 

Feathers extend where the finger used to extend

Confuciusornis:

When looking at this type of picture notice that the feathers in the wing's leading edge exhibit the exact same form as the pterosaur long finger.
The feathers extend where the pterosaur finger used to extend.

This would be the exact result when the finger was shortened.
The change is not that great, facilitated by "facilitated variation". 

Sternum

Here is some material on the sternum:

DINOSAURS
Tyrannosaurs - sternum not suitable for flight
Compsognathus -sternum not suitable for flight?
Ornitholestes - sternum not suitable for flight
Therizinosaur - sternum not suitable for flight?

Deinonychus - sternum not suitable for flight
Dromaeosaurus - sternum not suitable for flight
Utahraptor - sternum not suitable for flight

BIRDS
Bambiraptor* - sternum suitable for flight
Alvarezsaurs** - sternum suitable for flight
Microraptor - sternum suitable for flight
Velociraptor - sternum suitable for flight?
Ornithothoraces (Hesperornithes, Presbyornithids, Confuciusornithids, Ichthyornithes) - sternum suitable for flight

Pterosaur - sternum suitable for flight


*  http://en.wikipedia.org/wiki/Bambiraptor

Bambiraptor had quite a few features in common with modern birds. It had a wishbone, something all modern birds have that allow them to flap their wings, and its arms and hands were very long for its body size. In fact, the length of its arms and hands approached the lengths needed for flight. It also had an ossified sternum, a bone that is essential for birds to be able to move their wings for flying. Even with these similarities, however, there is no doubt that Bambiraptor was still a dinosaur from the raptor family. It had the killer claw on its foot like Velociraptor, and it had a mouth full of sharp teeth. It is considered by many to be the North American version of Archaeopteryx. Clearly a short step away from its European relative, this specimen is an exceptionally important piece of the bird/dinosaur puzzle. With more than 90 percent of the animal discovered, along with the remains of what may be a second individual, this specimen will continue to provide insight into the evolution of birds.

**  http://en.wikipedia.org/wiki/Alvarezsauridae

These mistaken [actually correct] assignments of alvarezsaurs to birds were caused primarily by features that are strikingly, or even uniquely, avian. The sternum, for example, is elongated and deeply keeled for an enlarged pectoralis muscle, as it is in neognathous birds and volant ratites. One bone in the skull of Shuvuuia appeared to be an ectethmoid fused to a prefrontal. The ectethmoid is an ossification known only in Neornithes. Other birdlike characters included the palatine, foramen magnum, cervical and caudal vertebrae, and many others.[9]

Metornithes

• Alvarezsauria
• Aviremigia

http://www.ucmp.berkeley.edu/museum/profiles/padian/padianresearch2.html

A comparison of bird, pterosaur and
bat skeletal structure, focusing on the sternum.

Dinosaurs do not have a sternum suitable for flying.
Metornithes (Alvarezsauria + Aviremigia) have a sternum suitable for flying.
Pterosaurs have a sternum suitable for flying.

We can see there is no relationship of dinosaurs to primitive birds. 
There is a relationship with pterosaurs.

Diving Pterosaurs?

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

"Traditionally, most researchers have suggested that Pteranodon would have taken fish by dipping their beaks into the water while in low, soaring flight. However, this was probably based on the assumption that the animals could not take off from the water surface.[2] It is more likely that Pteranodon could take off from the water, and would have dipped for fish while swimming rather than while flying. Even a small, female Pteranodon could have reached a depth of at least 80 centimetres (31 in) with its long bill and neck while floating on the surface, and they may have reached even greater depths by plunge-diving into the water from the air like some modern long-winged seabirds.[2] In 1994, Bennett noted that the head, neck, and shoulders of Pteranodon were as heavily built as diving birds, and suggested that they could dive by folding back their wings like the modern Gannet.[2]"

What can't these amazing pterosaurs do?

In the same place

What would we expect if pterosaurs developed from birds? Well one thing is that we would find pterosaurs in the same place as birds.
If we never found them in close proximity, we would rather doubt that they were related On the other hand, if we were to find them living in the same place that would support the pterosaur to bird theory.
Well they have been found living in the same place:

http://news.discovery.com/animals/pterosaur-tracks-japan-birds.html

"The world's first pterosaur tracks from Japan, documented in a new study, suggest these Dinosaur-Age flying reptiles not only coexisted with birds, but that the two groups also hung out together when they weren't soaring the Cretaceous skies.

A lone siltstone slab contains the fossilized footprints, made by pterosaurs, birds and amphibians. It provides a literal slice of what prehistoric life was like in Japan around 127 million years ago.

"I think that a group of small pterosaurs was feeding together near a pond or near a lake," lead author Yuong-Nam Lee told Discovery News, adding "there are lots of feeding beak marks."

For the latest study, accepted for publication in the journal Cretaceous Research, Lee and his colleagues focused on the pterosaur tracks. The scientists identified a total of 64 imprints made by five to six individuals that "show a clear quadrupedal gait pattern" with feet bearing curved "hook-like sharp" claws.

"The high density of the tracks suggest gregarious behavior, but the random orientation of the trackways does not show that they were moving in the same direction as a herd," Lee said.
He and his team instead think the pterosaurs and birds randomly gathered to feed. The eating marks consist of "small round depressions on the slab," possibly where the animals repeatedly pecked away for food."

Another pterosaur to bird theorist

Here is a summary of the pterosaur to bird ideas of Larry Febo.
They are startlingly similar to what I have been proposing.


"NAME OF THEORY: Larry Febo`s , Birds are Pterosaur Offshoots

ORIGINATORS: May have been briefly considered by Seeley in the 1800`s. "Seeley (1881) and Weidershiem (1883, 1886) proposed a pterosaur-like ancestor for Archaeopteryx." (The Beginnings of Birds (1985) pg 16.) Otherwise, Larry believes he's the only one proposing this at the moment.

TIME OF ORIGIN OF BIRDS: Mid-Triassic (c 230mya).

IMMEDIATE ANCESTOR OF BIRDS: A hypothetical Pterosaur-bird with small cranium, and relatively small wings, itself descended from the Prolacertiform group (with Cosesaurus as an appropriate example).

TIME OF FIRST FEATHER: Mid-Triassic

EXTINCT FEATHERED GROUPS: Protoavis (of the Triassic),...and of course the late Jurassic and early Cretaceous finds.

WEAKNESSES: Dependant on a hypothetical "missing link".

STRENGTHS: Resolves the "Digit Homology" controversy between the ornithologists and the paleontologists. The missing anterior digit is accounted for as being the pteroid bone, yeilding the homologous digit count 1,2,3 as preferred by paleontologists. Uses minimal dependence on the concept of Convergence.

PREDICTIONS: More pre-Archaeopteryx feathered birds will be found, eventually closing the gap back to the Mid-Triassic.

CHANGES NEEDED FOR CONVERSION TO 2F: Nothing simple would do it.

EVIDENCE REQUIRED FOR SUCH CHANGES:

GENERAL COMMENTS:"



OTHER RELATED MATERIAL:

http://dml.cmnh.org/1999Jan/msg00453.html

Hi folks, I just got around to reading "The Beginnings of Birds" (Hect et. al.). (Hey!...I told you I was playing "catchup" with my old paleontological interests!).Anyways, ...got to the article by Hinchliffe 'One, Two, Three' or 'Two,Three,Four', and it struck me immediately that my theory on "Birds as Pterosaur Descendants" seemed to fit in...(like that annoying missing piece of a large jigsaw puzzle that was never considered because of it`s "unlikely" color). The article describes how Holmgren (1955) and Montagna (1945) (quite a while back)..."claimed to find either a transient digit or its associated distal carpal preaxial to that developing digit which eventually forms the anterior digit of the adult wing". This transient element, I call "X", because I agree with the paleontological view that it cannot be called digit 1, as digits 1,2 and 3 are already identified (via phalangeal count), in both Theropod manus and Avian wing. Yet, it has to be something, as embryologists have determined its presence. ...There`s only one creature, (that I`m aware of), that fits the bill as having and "extra" preaxial "digit", and that would be the Pterosaur, with its "pteroid bone".

http://dml.cmnh.org/2001Jan/msg00135.html
From Larry Febo:

I`m not sure exactly how feathers developed,but actinofibrils arranged in a
pattern similar to flight feather rachis is very suggestive. Whatever the
path, a changeover from a fully functional membrane to feathers would have
to be gradual, and would require a "reason" for it to happen. I believe the
reason might have been the invasion of a new, and colder enviornment.
Perhaps a more upland enviornment, and natural selection acting on this
primitive wing to cut down on exposed area in a colder enviornment. Contour
feathers, once developed, could have extended to long flight feathers as the
membrane, and wing finger gradually (over generations) shrunk, until this
wing finger was itself no longer necessary.

"Suggestive"

The ideas I am presenting differ from the current mainstream theory that birds developed from dinosaurs. That is why I was intrigued by the following passage from a discussion group from years ago:

http://dml.cmnh.org/2001Jan/msg00135.html
From Larry Febo:

I`m not sure exactly how feathers developed,but actinofibrils arranged in a
pattern similar to flight feather rachis is very suggestive. Whatever the
path, a changeover from a fully functional membrane to feathers would have
to be gradual, and would require a "reason" for it to happen. I believe the
reason might have been the invasion of a new, and colder enviornment.
Perhaps a more upland enviornment, and natural selection acting on this
primitive wing to cut down on exposed area in a colder enviornment. Contour
feathers, once developed, could have extended to long flight feathers as the
membrane, and wing finger gradually (over generations) shrunk, until this
wing finger was itself no longer necessary.

The passage includes the idea that this transition must have been "gradual". I do not think that is necessarily so. A saltation is also a possibility.

Making the Connection

James and Pourtless' analysis links Longisquama with birds.
And Peters' work links Longisquama (and other protopterosaurs) to pterosaurs.
I propose that protopterosaurs (eg. Longisquama, cosesaurus) developed into pterosaurs which in turn developed into birds.

James and Pourtless list Longisquama as a possibilty as follows:

 "These results nevertheless support the possibility of a
sister-group relationship between Longisquama
and Aves (inclusive of some maniraptorans)."

In fact, Longisquama is a good candidate along with the other protopterosaurs such as Sharovipteryx and Cosesaurus.

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

If Sharovipteryx was a relative of pterosaurs, then its membrane may have stretched to its front legs, or it may have had a separate membrane joined to its front limbs alone. A secondary membrane is visible between the thighs and the trunk. Front wing membranes have not been seen; Peters (2006) has claimed to have traced the fingers[2] and that they show similarities to Cosesaurus and Longisquama and to a lesser extent, pterosaurs.

This is an important connection to the idea of protopterosaurs (David Peters' work). This is consilience.

Early archosaur hypothesis

Here is some background on the idea that an early archosaur (eg. Longisquama,) could be the ancestor of birds. The pterosaur to bird theory is much more credible.

James and Pourtless:
http://www.bio.fsu.edu/James/Ornithological%20Monographs%202009.pdf

"The   “early ­archosaur  hypothesis”
states that the origin of birds is more likely to be
among early archosaurs than among the theropod
dinosaurs (e.g., Tarsitano and hecht 1980; feduccia
and wild 1993; welman 1995; feduccia 1999, 2002;
Czerkas and yuan 2002; Czerkas et al. 2002; Martin
2004; feduccia et al. 2005, 2007). As presently un­
derstood, this hypothesis includes the propositions
that most maniraptorans are flying and flightless
lineages within Aves (as in figs.  1B and 3f)  and
that they are, in fact, not theropod dinosaurs (Czer­
kas et al. 2002; feduccia 2002; Martin 2004; feduc­
cia et al. 2005, 2007). According to this alternative,
the  Theropoda  as  presently  constituted  are  not
monophyletic. Aves, including various manirap­
torans, is not nested inside Theropoda. Similarities
between nonmaniraptoran theropods and birds are
accounted for by homoplasy."

I would suggest they are also accounted for by symplesiomorphy .

"The best ­studied current candidate for a potential archosaurian ancestor or sister taxon is
Longisquama. Sharov (1970) noted similarities to birds in the skeleton and integument of
Longisquama and sug­ gested that it may be close to avian ancestry. Jones et al. (2000, 2001)
described the birdlike osteologi­ cal characters and the featherlike morphology of the
integumentary appendages of Longisquama, but the latter was disputed by Prum et al. (2001) and
Unwin and Benton (2001). Unwin and Ben­ ton (2001) and Senter (2004) questioned the status of
Longisquama as an archosaur, but its antorbital fenestra (Jones et al. 2000, 2001; Martin 2004; f.
James and J. Pourtless pers. obs.; see Table 1) sup­ports the classification of Sharov (1970) and Jones
et al. (2000, 2001). Martin (2004) elaborated on the osteological similarities between Longisquama and
birds in dentition, characters of the skull, and the presence of a boomerang­shaped furcula similar
to that of basal birds. Unfortunately, the pelvic girdle and hind limb are not known. Longisquama
is best considered a basal archosaur of uncertain affinity (see fig. 2)".

In addition to the results obtained through use
of Kishino-Hasegawa tests, we also recovered a
clade of maniraptorans, birds, and the basal archosaur Longisquama, though we note that it was only weakly supported (Figs. 9 and 12). These
results nevertheless support the possibility of a
sister-group [ancestral] relationship between Longisquama
and Aves (inclusive of some maniraptorans). In
addition, birds and maniraptorans were never
unambiguously associated with nonmaniraptoran theropods in any of our trees (Figs. 9–13)." 

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

Temporal range: Middle or Late Triassic

Longisquama means "long scales"; the specific name insignis refers to its small size. The Longisquama holotype is notable for a number of long structures that appear to grow from its skin. These structures have been interpreted as either primitive feathers suggesting Longisquama is a close relative of birds, or as feather-like structures that have evolved independently and do not indicate a close relationship with birds. Longisquama has been used in a heavily publicized debate on of the origin of birds. To some, Longisquama is the gliding, cold-blooded, protobird predicted by Gerhard Heilmann's hypothetical "Proavis" in 1927, and it proves that birds are not dinosaurs. The current opinion is that Longisquama is an ambiguous diapsid and has no bearing on the origin of birds.

http://www.reptileevolution.com/cosesaurus.htm

Ellenberger and DeVillalta (1974) and Ellenberger (1978, 1993) considered Cosesaurus a bird ancestor, and as such Ellenberger interpreted many aspects of Cosesaurus as proto-avian.

Here is an analysis by Peters of cosesaurus:
http://pterosaurheresies.wordpress.com/2012/03/27/dr-ellenberger-and-his-petite-cosesaurus-part-1-cranial-traits-2/

The origin of pterosaurs (2)

From David Peters:
http://www.reptileevolution.com/cosesaurus.htm
Click to enlarge:

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

Cosesaurus is a genus of  prolacertiform archosauromorph reptile. It is known from a single, hand-sized fossil from the middle Triassic period of Spain. The fossil is a perfect impression of a largely articulated and complete specimen preserving soft parts, including an adhering jellyfish, but no bones remain in these impressions.
In 1977, Ellenberger proposed that Cosesaurus was an ancestor of modern birds.^[1] That publication followed the description of the bird-like theropod,Deinonychus, but it appeared long before the theropod ancestry of birds had been widely accepted. In his large and highly detailed treatise, Ellenberger interpreted the following traits in the fossil: a strap-like scapula, a furcula(wishbone), a keeled sternum, beak-like jaws, a retroverted pubis and tailfeathers. Some of these interpretations have not been supported by subsequent research. Padian and Chiappe (1998) regarded Cosesaurus as a member of the archosauromorph clade Prolacertiformes.^[2]

http://www.reptileevolution.com/cosesaurus.htm

Ellenberger and DeVillalta (1974) and Ellenberger (1978, 1993) considered Cosesaurus a bird ancestor, and as such Ellenberger interpreted many aspects of Cosesaurus as proto-avian.

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

Sharovipteryx ("Sharov's wing", known until 1981 as Podopteryx, "foot wing"), was an early gliding reptile, from the middle-late Triassic period (230-225 million years ago). Fossils have been found from the Madygen Formation ofKyrgyzstan along with the unusual reptile Longisquama. It was approximately eight inches (20 cm) long, with an extremely long tail, and weighed about 7.5 grams. It may have been closely related — or perhaps even ancestral — to pterosaurs,^[1] although this remains controversial. Unlike pterosaurs, its main flight membrane was stretched between long back legs rather than its very short front limbs.If Sharovipteryx was a relative of pterosaurs, then its membrane may have stretched to its front legs, or it may have had a separate membrane joined to its front limbs alone. A secondary membrane is visible between the thighs and the trunk. Front wing membranes have not been seen; Peters (2006) has claimed to have traced the fingers^[2] and that they show similarities to Cosesaurusand Longisquama and to a lesser extent, pterosaurs.

Note that David Peters no longer considers Cosesaurus to be a member of Archosauromorpha.

The origin of pterosaurs (1)

To this point I have not posted about the origin of pterosaurs. I will do that now in a series of posts.
I will work on the basic idea that pterosaurs stem from the archosauromorpha.
And I will build upon the work of David Peters who has developed (in amazing detail) the case that pterosaurs developed from gliding creatures like Sharovipteryx and Longisquama..

Here are some helpful references:

http://pterosaurheresies.wordpress.com/2011/09/07/sharovipteryx-and-the-origin-of-pterosaurs/

http://pterosaurheresies.wordpress.com/2012/05/26/protopterosaurus-still-the-official-poster-child-for-pterosaur-ancestry/

More on Feathers

Here is a bit more about feathers:

See these earlier posts for more details about feathers:

http://pterosaurnet.blogspot.ca/2011/10/bird-feathers-are-analogous-to-wing.html

http://pterosaurnet.blogspot.ca/2012/02/pterosaur-brachiopatagium-to-bird.html

http://pterosaurnet.blogspot.ca/2010/05/pterosaur-wing-covering-1.html

Pterosaur Launch

http://www.livescience.com/24636-giant-pterosaurs-in-flight.html

CHARLOTTE, N.C. — It's a bird … It's a plane … It's a plane-size bird! If humans had lived 67 million years ago in what is now Texas, they would've had a hard time missing the giant flying pterosaur calledQuetzalcoatlus, which was the size of an F-16 fighter jet.  The biggest animal ever to fly in the history of the world, this pterosaur dominated the sky with its 34-foot (10 meters) wingspan.

Fossils of the creature have been found in Big Bend National Park, in an area that was heavily forested in the late Cretaceous.   But this presents a puzzle: How did it fly? The region lacked the cliffs that make flight for such large birds easy to conceive.  

A new computer simulation has the answer: These beasts used downward-sloping areas, at the edges of lakes and river valleys, as prehistoric runways to gather enough speed and power to take off, according to a study presented Wednesday (Nov. 7) here at the annual meeting of the Geological Society of America.

First the animal would start running on all fours, Texas Tech University scientist Sankar Chatterjee, a co-author of the study, told LiveScience. Then it would shift to its back legs, unfurl its wings and begin flapping. Once it generated enough power and speed, it finally would hop and take to the air, said Chatterjee, who along with his colleagues created avideo simulation of this pterosaur taking flight.

Chatterjee said the flight and landing of Quetzalcoatlus probably looked like that of an albatross or the Kori bustard, the heaviest modern-day bird capable of flight.[Avian Ancestors: Dinosaurs That Learned to Fly]

https://gsa.confex.com/gsa/2012AM/finalprogram/abstract_205827.htm

Kori bustard in flight:

https://www.youtube.com/watch?v=qBkmFYuDKUc&feature=related

Albatross takeoff:
https://www.youtube.com/watch?v=gKTfcs6LL6A

Walking Pterosaurs

A question occurred to me concerning pterosaurs walking.
They could be walking either with their arms held off the ground or with their hands being placed on the ground (walking on all fours).
Would the footprint of the feet be the same in both cases?

Let's look at this diagram:

http://www.nature.com/nature/journal/v391/n6670/images/391886aa.tif.2.gif
http://www.nature.com/nature/journal/v391/n6670/full/391886a0.html


It would seem possible that the plantigrade footprint is an artifact of all-fours walking.
It could well have been digitigrade when the arms were held off the ground.
This would explain the plantigrade footprints of a pterosaur found (based on an instance of all-fours walking). And explain the digitigrade footprints of birds which never walk on all fours.

* Foot posture in a primitive pterosaurJ. M. Clark¹, J. A. Hopson², R. Hernández R.³, D. E. Fastovsky⁴ & M. Montellano³

Ornithomimosaurs

http://www.sciencemag.org/content/338/6106/510.full

"FEATHERED NON-AVIAN DINOSAURS FROM NORTH AMERICA PROVIDE INSIGHT INTO WING ORIGINS
Previously described feathered dinosaurs reveal a fascinating record of feather evolution, although substantial phylogenetic gaps remain. Here we report the occurrence of feathers in ornithomimosaurs, a clade of non-maniraptoran theropods for which fossilized feathers were previously unknown. The Ornithomimus specimens, recovered from Upper Cretaceous deposits of Alberta, Canada, provide new insights into dinosaur plumage and the origin of the avian wing. Individuals from different growth stages reveal the presence of a filamentous feather covering throughout life and winglike structures on the forelimbs of adults. The appearance of winglike structures in older animals indicates that they may have evolved in association with reproductive behaviors. These specimens show that primordial wings originated earlier than previously thought, among non-maniraptoran theropods."

Ornithomimosaurs have been considered as secondarily flightless birds.  

For pictures:
http://www.sciencemag.org/content/338/6106/510.figures-only

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

"Gregory S. Paul has proposed that Ornithomimosauria might be a group of primitive, flightless birds, more advanced than Deinonychosauria and Oviraptorosauria.^[9]"

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

"Flightless birds are birds which lack the ability to fly, relying instead on their ability to run or swim. They evolved from flying ancestors.^[1] There are about forty species in existence today,^[2] the best known being the ostrich, emu,cassowary, rhea, kiwi, and penguin." 

http://www.prehistoric-wildlife.com/articles/ornithomimids-ornithomimosaurs.html

Because ornithomimosaurs are treated as being members of the Maniraptoriformes they are expected by many to have had feathers like many other dinosaurs that belong to this group have been confirmed to have had.‭ ‬Unfortunately there is currently no firm evidence to confirm this for ornithomimosaurs,‭ ‬and the impression that confirms a gular‭ (‬throat‭) ‬pouch in Pelecanimimus does not show the presence of feathers.‭

Page 145
"pubis is long and rostroventrally directed"
http://books.google.ca/books?id=h4WRTHfTzXsC&pg=PA144&lpg=PA144&dq=ornithomimus++pubis&source=bl&ots=j84USGCsKi&sig=uRem95Ncjo23LlGOSKN4HjEAAFQ&hl=en&sa=X&ei=1ATjUOPZC-ne0gGAx4CQCA&sqi=2&redir_esc=y#v=onepage&q=ornithomimus%20%20pubis&f=false