Hesperornithiformes

http://en.wikipedia.org/wiki/Hesperornis
"Hesperornis is an extinct genus of flightless aquatic birds that lived during the Santonian to Campanian sub-epochs of the Late Cretaceous (89–65 mya).
Although some of the smaller species might have been able to fly, Hesperornis and Baptornis had only vestigial wings. Like living foot-propelled diving birds, the femur and metatarsus were short, whereas the tibia was long. The legs were also set far back on the body, as in loons, grebes or penguins."

http://en.wikipedia.org/wiki/Grebe
"The cladistics vs. phenetics debate of the mid-20th century revived scientific interest in generalizing comparisons. As a consequence, the discredited grebe-loon link was discussed again. This even went as far as proposing monophyly for grebes, loons, and the toothed Hesperornithiformes "

http://www.jstor.org/pss/2413412
"A cladistic analysis of the skeletons of loons (Gaviidae), grebes (Podicipedidae), and the Cretaceous diving birds, Hesperornis and Baptornis, supports the hypothesis that they form a monophyletic group (here called the Gaviomorphae) within the class Aves. Two lineages within the gaviomorphs can be delineated: (1) loons + grebes, and (2) Hesperornis + Baptornis. The Early Cretaceous Enaliornis and the Late Cretaceous Neogaeornis are related to the second lineage; the Late Cretaceous Lonchodytes, often placed near loons, is apparently not a gaviomorph but perhaps a charadriiform. Skeletal evidence also suggests that penguins (Spheniscidae) are the sister-group of the Gaviomorphae. Arguments that similarities of gaviomorph taxa represent convergence are not well founded. First, morphological differences among taxa do not constitute valid evidence against their monophyly, as many previous workers have argued. Second, in no case has anyone supporting convergence presented a corroborated alternative phylogenetic hypothesis. A close relationship among gaviomorphs, penguins, and apparently also the Procellariiformes and Pelecaniformes implies that a lineage of aquatic birds was established very early in avian history, presumably in the Early Cretaceous or Late Jurassic." (Joel Cracraft 1982)

Looks like Joel Cracraft was on the right track!
(Note the issue here is not whether grebes and loons go together but that hesperornithiformes is linked to modern birds such as grebes and/or loons.)

More on Timing

Note the timing of the various creatures in the bird line.
Most pterosaurs are replaced by (develop into) enantiornithes etc. well before the end of the Cretaceous. Then most of the enantiornithes are replaced by (develop into) modern birds in the Late Cretaceous.

http://mbe.oxfordjournals.org/cgi/content/abstract/23/6/1144
"...and describe the gradual decline of pterosaurs at the same time modern birds radiate."
"It is clear that modern birds from at least the latest Cretaceous lived at the same time as archaic birds including Hesperornis, Ichthyornis, and the diverse Enantiornithiformes. Pterosaurs, which also coexisted with early crown [modern] birds, show notable changes through the Late Cretaceous. There was a decrease in taxonomic diversity, and small- to medium-sized species disappeared well before the end of the Cretaceous. A simple reading of the fossil record might suggest competitive interactions with birds, but much more needs to be understood about pterosaur life histories."

Who actually had feathers?

We saw earlier the definition of "non-avian dinosaur": "Dinosauria minus Aves".
Now let's look at which of these so-called "non-avian dinosaurs" had feathers. We see that only maniraptora had feathers! The others had "decomposed collagenous fibers" - which are so-called "protofeathers" by the dino-to bird enthusiasts but which are just decomposed skin.

http://en.wikipedia.org/wiki/Dinosaur
"[so-called] protofeathers (thin, filament-like structures) are known from dinosaurs at the base of Coelurosauria, such as compsognathids like Sinosauropteryx and tyrannosauroids (Dilong),^[104] but barbed feathers [ie. actual feathers] are known only among the coelurosaur subgroup Maniraptora, which includes oviraptorosaurs, troodontids, dromaeosaurids, and birds.^[13][105] The description of feathered dinosaurs has not been without controversy; perhaps the most vocal critics have been Alan Feduccia and Theagarten Lingham-Soliar, who have proposed that protofeathers are the result of the decomposition of collagenous fiber that underlaid the dinosaurs' integument,^{[106][107][108]} and that maniraptoran dinosaurs with barbed feathers were not actually dinosaurs, but convergent with dinosaurs.^[102][107] However, their views have for the most part not been accepted by other researchers, to the point that the question of the scientific nature of Feduccia's proposals has been raised.^[109]"

What does "non-avian dinosaur" mean?

The phrase "non-avian dinosaurs" crops up in many articles. What does it mean? As we see below it means Dinosauria minus Aves. It lumps in the primitive flying and secondarily flightless birds with the real dinosaurs such as Tyrannosaurus - all of them under the same label - "non-avian dinosaur". In other words, it lumps in Paraves with actual dinosaurs. 

http://www.miketaylor.org.uk/dino/faq/s-class/phyletic/
"Now consider the group consisting of the non-avian dinosaurs (which is what people usually mean by the informal term ``dinosaurs''). This is a paraphyletic group, because it can't be defined simply as ``this animal plus all its descendants'', but must be described as one clade minus another: in this case, Dinosauria minus Aves. The ``non-avian dinosaurs'' make up a singly paraphyletic group because only one clade need be omitted from its base definition."

http://en.wikipedia.org/wiki/Feathered_dinosaurs
"it was not until the early 1990s that clearly nonavian dinosaur fossils were discovered with preserved feathers. Today there are more than twenty genera of dinosaurs with fossil feathers, nearly all of which are theropods. "
"By the 1990s, most paleontologists considered birds to be surviving dinosaurs and referred to 'non-avian dinosaurs' (all extinct), to distinguish them from birds (aves)."

AND notice these variations:

http://www.ncbi.nlm.nih.gov/pubmed/19800747
"Recent studies by Varricchio et al. reveal that males cared for the eggs of troodontids and oviraptorids, so-called "non-avian theropods" of the Cretaceous".

http://en.wikipedia.org/wiki/Theropoda
"The smallest non-avialan theropod known from adult specimens is the troodontid Anchiornis huxleyi, at 110 grams in weight and 34 centimeters (1 ft) in length.^[3] "

"Essentially Modern Waterfowl" in the Cretaceous

http://en.wikipedia.org/wiki/Galloanserae
"Fowl were the first neognath lineages to evolve. From the limited fossils that have to date been recovered, the conclusion that they were already widespread - the predominant group of modern birds - by end of the Cretaceous is generally accepted nowadays. Fossils such as Vegavis indicate that essentially modern waterfowl - albeit belonging to a nowadays extinct lineage - were contemporaries of the (non-avian) dinosaurs."

http://en.wikipedia.org/wiki/Vegavis
"Vegavis is a genus of extinct bird that lived during the Late Cretaceous (Maastrichtian stage) of Antarctica, some 65 mya. It belonged to the clade Anseriformes. Among modern birds, Vegavis is most closely related to ducks and geese (Anatidae), but it is not considered to be a direct ancestor of them.^[1]
The discovery of the type species, Vegavis iaai, demonstrates that the major groups of bird alive today had already diversified in the Cretaceous. This supports the longstanding phylogenetic inferences of paleornithologists.^{[citation needed]} It has been hailed as the first definitive physical proof that representatives of some of the groups of modern birds lived in the Mesozoic.^[1]"

http://www.digimorph.org/specimens/Vegavis_iaai/nature03150.pdf
and
http://www.livescience.com/animals/050125_dino_chickens.html
"We have more data than ever to propose at least the beginnings of the radiation of all living birds in the Cretaceous," Clarke says. "We now know that duck and chicken relatives coexisted with non-avian dinosaurs. This does not mean that today's chicken and duck species lived with non-avian dinosaurs, but that the evolutionary lineages leading to today's chicken and duck species did." (Julia A. Clarke1,2, Claudia P. Tambussi3, Jorge I. Noriega4,
Gregory M. Erickson5,6,7 & Richard A. Ketcham8)

Scapula structure

Scapulocoracoid

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

The Scapulocoracoid is the unit of the pectoral girdle that contains the coracoid and scapula. The coracoid itself is a beak-shaped bone that is commonly found in most vertebrates with a few exceptions. The scapula is commonly known as the shoulder blade. The humerus is linked to the body via the scapula, the clavicle is connected to the sternum via the scapula as well.

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

In birds (and generally theropods and related animals), the entire unit is rigid and called scapulocoracoid. This plays a major role in bird flight. In dinosaurs the main bones of the pectoral girdle were the scapula (shoulder blade) and the coracoid, both of which directly articulated with the clavicle.^[2]

http://pterosaur.net/anatomy.php

There were two major bones in the [pterosaur] chest that anchored most of the flight muscles. The first was the sternum, which is the breastbone in birds and the front plate of our chest. The second was the pair of scapulocoracoids, which were single bones made from the fusion of the shoulder blade (scapula) and coracoid on each side (we do not have a coracoid bone, but it was a broad plate that formed part of the shoulder in pterosaurs).

http://fossiladay.wordpress.com/page/28/

Some pterosaur bones are quite unusual. This scapulo-coracoid is photographed from both sides. The glenoid cavity of the shoulder joint can be seen, where the humerus articulates the wing to the body.

Strap-like scapula

http://books.google.ca/books?id=8CKYxcylOycC&pg=PA191&lpg=PA191&dq=strap+like+scapula&source=bl&ots=SprXeCwFa6&sig=JjdgGySd1yPPHLN0eyNigzrUPj0&hl=en&sa=X&ei=LEgwU_yuK4er2gXWxoCIDg&ved=0CEkQ6AEwBw#v=onepage&q=strap%20like%20scapula&f=false

The pectoral girdle of basal pterosaurs consisted of a long strap-like scapula.

http://pterosaurheresies.wordpress.com/2012/03/01/the-locked-down-coracoid-and-the-origin-of-flapping/

Bats, birds and pterosaurs are united by the convergent ability to flap their forelimbs/wings. In this way they generate thrust for true flying. Gliders don’t flap and they don’t have elongated scapula anchors.

http://www.ucmp.berkeley.edu/vertebrates/flight/pter.html

Scapula Orientation

http://saurian.blogspot.ca/2012/04/weird-world-of-theropod-scapulae.html

Scapula orientation in theropod dinosaurs is quite interesting and it is worth looking, to begin with, at what orientation is displayed in primitive reptiles. The scapula is generally held at an angle of 90 degrees to the horizontal line held by the backbone – in other words it was held in a perpendicular fashion. At the other extreme, extant birds rotated the scapula so that it lies parallel to backbone – a position also evolved by the pterosaurs.

Theropods, and non-avian dinosaurs in general (but not bird-like theropods), evolved a condition that can be described as something in between – an intermediate position if you will. The scapula is held in an oblique position laterally to the ribcage but actually determining the exact position is somewhat problematic. There are not that many fully articulated specimens that can be referred to and there is always the spectre of both taxanomic and taphonomic variation to throw yet another spanner into the works.

http://www.researchgate.net/publication/259438884_Agnoln_and_Novas._2013._Avian_ancestors 

In this way, the scapulae of unenlagiids lie close to the vertebral column, dorsal to the ribcage, with the flat costal surface of the scapular blade facing ventrally, a condition seen in microraptorans (i.e. Microraptor), basal avialans (e.g. Archaeopteryx, Rahonavis), and ornithothoracine birds (Senter 2006), in which the shoulder socket sits high on the back, and the margins of the glenoid are smooth, thus this surface becomes shalower and consequently more continuous with the rest of the lateral surface of scapula

(Burnham 2008). In sum, the lateral orientation of the scapular glenoid in unenlagiids
(and probably also in other basal averaptorans), together with the absence
of acute ridges delimitating the glenoid cavity, suggest that the humerus in these
taxa was able to be elevated close to the vertical plane, as proposed by Novas and Puerta (1997) (Figs. 5.1, 5.2).

It is important to mention that scansoriopterygids retained a caudoventrally oriented glenoid, a subrectangular coracoid with reduced biceps tubercle, and a distally fan-shaped scapular blade, all representing plesiomorphic character states in respect to paravians.

Dinosaur:
https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg8Pv7jaAzYwroXKKX3jU0AJ5aoxbFUFhcOIht6IdtYGyWIRQDQ7729gqhgHcBgwLwvRYnqvGnMYKWw6QV6_UlJNNQS5u-79WUdIgO1Ttqj6hqhgHfzz0t5e4wIiFsYyjEFaVK6XHMuGI0C/s400/rex_pex.jpg

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

MODERN BIRD 

http://courses.washington.edu/chordate/453photos/skeleton_photos/bird-scapula-coracoid.jpg

More about the secondarily flightless birds (3)

Hesperornithes are Cretaceous Ornithurae. They are an excellent candidate as the ancestor of modern "foot-propelled diving birds".

http://en.wikipedia.org/wiki/Hesperornithes
"Hesperornithes is an extinct and highly specialized clade of Cretaceous toothed birds. Hesperornithine birds, apparently limited to former aquatic habitats in the Northern Hemisphere, include genera such as Hesperornis, Parahesperornis, Baptornis, Enaliornis, and probably Potamornis, all strong-swimming predatory waterbirds. Many, if not all species were completely flightless.
Although some of the smaller species might have been able to fly, Hesperornis and Baptornis had only vestigial wings. Like living foot-propelled diving birds, the femur and metatarsus were short, whereas the tibia was long. The legs were also set far back on the body, as in loons, grebes or penguins. "

http://en.wikipedia.org/wiki/Aves
One order of Mesozoic seabirds, the Hesperornithiformes, became so well adapted to hunting fish in marine environments that they lost the ability to fly and became primarily aquatic. Despite their extreme specialisations, the Hesperornithiformes represent some of the closest relatives of modern birds.^[20]

Note that "some of the smaller species might have been able to fly". 

More about the secondarily flightless birds (2)

Caudipteryx is an oviraptor - a primitive secondarily-flightless bird.

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

"Caudipteryx (which means "tail feather") is a genus of peacock-sized theropod dinosaurs [flightless birds] that lived in the Aptian age of the early Cretaceous Period (about 124.6 million years ago). They were feathered and remarkably birdlike in their overall appearance.Caudipteryx has a short tail stiffened toward the tip, with few vertebrae, like in birds and other oviraptorosaurs.Caudipteryx had uncinate processes on the ribs, birdlike teeth, a first toe which may or may not be partially reversed and overall body proportions that are comparable to those of modern flightless birds.^{[1][2][5][6][3]}The hands of Caudipteryx supported symmetrical, pennaceous feathers that had vanes and barbs, and that measured between 15–20 centimeters long (6–8 inches). These primary feathers were arranged in a wing-like fan along the second finger, just like primary feathers of birds and other [flightless bird] maniraptorans. No fossil of Caudipteryx preserves any secondary feathers attached to the forearms, as found in dromaeosaurids, Archaeopteryx and modern birds.^[3] Either these arm feathers are not preserved, or they were not present on Caudipteryx in life. An additional fan of feathers existed on its short tail. The shortness and symmetry of the feathers, and the shortness of the arms relative to the body size, indicate that Caudipteryx could not fly."

http://www.nature.com/nature/journal/v406/n6797/full/406716a0.html

Modern birds have markedly foreshortened tails and their body mass is centred anteriorly, near the wings^{1, 2, 3, 4, 5}. To provide stability during powered flight, the avian centre of mass is far from the pelvis, which poses potential balance problems for cursorial birds. To compensate, avians adapted to running maintain the femur subhorizontally, with its distal end situated anteriorly, close to the animal's centre of mass; stride generation stems largely from parasagittal rotation of the lower leg about the knee joint^{6, 7, 8, 9, 10, 11, 12}. In contrast, bipedal dinosaurs had a centre of mass near the hip joint and rotated the entire hindlimb during stride generation^{4, 5, 6, 7, 8, 11, 12, 13}. Here we show that these contrasting styles of cursoriality are tightly linked to longer relative total hindlimb length in cursorial birds than in bipedal dinosaurs. Surprisingly, Caudipteryx , described as a theropod dinosaur^14, 15, possessed an anterior centre of mass and hindlimb proportions resembling those of cursorial birds. Accordingly,Caudipteryx probably used a running mechanism more similar to that of modern cursorial birds than to that of all other bipedal dinosaurs. These observations provide valuable clues about cursoriality in Caudipteryx , but may also have implications for interpreting the locomotory status of its ancestors.

More about the secondarily flightless birds (1)

Support for the idea  that troodontids and oviraptorids were secondarily flightless

http://www.ncbi.nlm.nih.gov/pubmed/19800747
"Recent studies by Varricchio et al. reveal that males cared for the eggs of troodontids and oviraptorids, so-called "non-avian theropods" of the Cretaceous, just as do those of most Paleognathic birds (ratites and tinamous) today. Further, the clutches of both groups have large relative volumes, and consist of many eggs of relatively large size. By comparison, clutch care by most extant birds is biparental and the clutches are of small relative volume, and consist of but few small eggs. Varricchio et al. propose that troodontids and oviraptorids were pre-avian and that paternal egg care preceded the origin of birds. On the contrary, unmentioned by them is that abundant paleontological evidence has led several workers to conclude that troodontids and oviraptorids were secondary flightless birds. This evidence ranges from bird-like bodies and bone designs, adapted for climbing, perching, gliding, and ultimately flight, to relatively large, highly developed brains, poor sense of smell, and their feeding habits. Because ratites also are secondarily flightless and tinamous are reluctant, clumsy fliers, the new evidence strengthens the view that troodontids and oviraptorids were secondarily flightless. Although secondary flightlessness apparently favors paternal care of clutches of large, abundant eggs, such care is not likely to have been primitive. There are a suite of previously unknown independent findings that point to the evolution of, first, maternal, followed by biparental egg care in earliest ancestors of birds. This follows from the discovery of remarkable relict avian reproductive behaviors preserved by virtue of the highly conservative nature of vertebrate brain evolution. These behaviors can be elicited readily by exposing breeding birds to appropriate conditions, both environmental and with respect to their eggs and chicks. They give significant new clues for a coherent theory of avian origin and early evolution." (Kavanau JL.)

Maniraptors (3)

http://en.wikipedia.org/wiki/Microraptorinae#Relationship_with_birds
"Martin believes that maniraptorans are secondarily flightless birds, and that birds evolved from non–dinosaurian archosaurs [pterosaurs according to my thesis], so that most of the species formerly called theropods [ie. the maniraptors] would now not even be classified as dinosaurs.^[43]"
(Martin, L.S. (2004). "A basal archosaurian origin for birds." Acta Geologica Sinica, 50(6): 978–990.)

Maniraptors (2)

The creatures labeled "Maniraptors" are birds (not dinosaurs). They developed in a line separate from the dinosaurs.
Since the category names such as Maniraptors (Maniraptora, Eumaniraptora etc.) are now so entrenched as being dinosaur-related names it would be helpful to stop using that name entirely.
Here is what we would have:
"Theropod" dinosaurs would still be a valid group but would include only the actual dinosaurs and not the creatures presently labeled "Maniraptors".
A completely separate, bird-related line extends from the Pterosauria through to modern flying birds (Neognathae) and modern flightless birds (Palaeognathae).

Maniraptors (1)

When you look at the diagrams (cladograms) put forward for theropods you see a branch called "maniraptors" which has been tacked onto the theropod line, where it does not belong at all.
See here for an example of a typical diagram:
http://en.wikipedia.org/wiki/Theropoda

The creatures labeled "maniraptors" are actually birds (not dinosaurs). They do not belong in the theropod line at all.

Here is a reference to that idea:
http://www3.interscience.wiley.com/journal/112101271/abstract?CRETRY=1&SRETRY=0
"We suggest that a possible solution to the disparate data is that Aves plus bird-like [flightless] maniraptoran theropods (e.g., microraptors and others) may be a separate clade [separate line], distinctive from the main lineage of Theropoda, a remnant of the early avian radiation, exhibiting all stages of flight and flightlessness". (Alan Feduccia ^{1 *}, Theagarten Lingham-Soliar ², J. Richard Hinchliffe ³⁾

The early bird catches the worm

How early did primitive birds appear? By "primitive bird" I mean feathered and flying, but not yet modern. For example the Enantiornithes were "primitive birds".

http://en.wikipedia.org/wiki/Enantiornithes
"One biogeographic study in the 1990s suggested that the distribution of enantiornithines implies a Middle Jurassic origin for the clade, but this theory has not been widely accepted by paleoornithologists; a Late Jurassic/Early Cretaceous origin is more in line with the fossil record".

Let's look at some particular finds:

http://en.wikipedia.org/wiki/Liaoningornithiformes
"Liaoningornis is a surprisingly advanced bird for the Early Cretaceous. Zhou and Hou in 2002 considered it the oldest known member of the Ornithurae. It has advanced flight, perching, and respiratory adaptations like a long, deeply keeled sternum, a pair of anterolateral processes on the sternum near the articulations with the coracoids, fused, short, metatarsals, and highly curved pedal claws indicating good perching ability. "

http://sciencemag.org/cgi/content/abstract/274/5290/1164
"Late Jurassic and Early Cretaceous birds from northeastern China, including many complete skeletons of Confuciusornis, provide evidence for a fundamental dichotomy in the class Aves that may antedate the temporal occurrence of the Late Jurassic Archaeopteryx. The abundance of Confuciusornis may provide evidence of avian social behavior. Jurassic skeletal remains of an ornithurine bird lend further support to the idea of an early separation of the line that gave rise to modern birds. Chaoyangia, an ornithurine bird from the Early Cretaceous of China, has premaxillary teeth."
(Lianhai Hou, Larry D. Martin, Zhonghe Zhou, Alan Feduccia)

So we can see that there were primitive (feathered, flying) birds in the Late Jurassic/Early Cretaceous!
Modern birds developed from those primitive birds. Modern birds did not develop from dinosaurs.

Putting the Picture Together

From Top to Bottom:

Rhamphorhynchus

!
!

Pterodactyl

!
!

Primitive Birds (eg. Enantiornithes)

!
!
<------------------->

Cretaceous Flightless Birds

Modern Flying Birds

!
!

Modern Flightless Birds

Enantiornithes

Here is an introduction to the Enantiornithes.


http://en.wikipedia.org/wiki/Enantiornithes
"Enantiornithes is an extinct group of primitive birds. They were the most abundant and diverse avialans of the Mesozoic [251 - 65.5 million years ago]. Almost all retained teeth and clawed hands, like other primitive birds. Enantiornithines are thought to have left no living descendants. See protobirds.
A consensus of scientific analyses indicates that Enantiornithes is one of two major sister groups of derived birds. The other group is the Ornithurae, which includes all living birds as a subset. This means that Enantiornithines are a successful branch of bird evolution, but one that diversified entirely separately from the lineage leading to modern birds.^[1] This consensus has never been universally accepted and is being challenged by new studies, so that it is possible that enantiornithines may actually represent successive outgroups on the lineage leading to modern birds.^[2] See Apsaravis."

Note that there is a growing awareness that the Enantiornithes may actually be on the direct line to modern birds. Here is additional info on that question:

http://en.wikipedia.org/wiki/Enantiornithes#Phylogeny
"The 2002 phylogenetic analysis by Clarke and Norell, though, reduced the number of enantiornithine autapomorphies to just four.^[2] This raises the possibility that the discovery of new fossils could unite Enantiornithes and the birds closer to living species into one clade. If this proves to be true, then Enantiornithes is a paraphyletic taxon and thus phylogenetically invalid. All enantiornithines would then be united in the next larger clade Ornithothoraces instead, and called "ornithothoracines". (see Apsaravis for more on the possible invalidation of Enantiornithes)".

http://en.wikipedia.org/wiki/Apsaravis
"In their cladistic analyses, Clarke and Norell (2002) found that Apsaravis had a mixture of primitive and advanced characters (described above in "Sauriurae") that removed most of the supporting characters for the clade Enantiornithes. Twenty-seven characters have been used to support enantiornithine monophyly, but Apsaravis brings the number down to only four. The discovery of further basal ornithurine fossils like Apsaravis could render the Enantiornithes paraphyletic. This would mean that, rather than a radiation of primitive birds separate from the radiation that led to modern birds, "enantiornithines" would actually be steps along the way to becoming modern birds.<sup>[3]"

THIS IS EXACTLY THE POINT THAT I AM MAKING.</sup>

From Pterosaur to Modern Bird

Here is what I said in the earlier post:
In the idea that I am presenting, the advanced pterosaurs (pterodactyls) developed into primitive flying birds (with feathers and all) during the Cretaceous. A branch of those primitive flying birds settled on the land and developed into the primitive flightless birds of the Cretaceous, such as the Ornithomimosauria and the Oviraptorosauria.
Those primitive flightless birds then developed into the modern flightless birds such as the ostrich etc.
For example, Struthiomimus is a genus within the family of Ornithomimosauria. It was long-legged and ostrich-like. It developed into the modern ostrich. So that is the pattern of the development of flightless birds.
Pterodactyls developed into primitive flying birds (with feathers and all). Those flying primitive birds then split into those that continued flying and those that settled on the land and gave up flying (like the ostrich).

Flightless Birds (5)

There is very strong support for the idea that the Cretaceous flightless creatures such as the Ornithomimosauria and the Oviraptorosauria were secondarily flightless (and not dinosaurs at all):

http://www.dinosaur-museum.org/featheredinosaurs/exhibit.pdf
"Dromaeosaurs have been thought to be ground-dwelling
dinosaurs that represented ancestral stages of how birds
evolved. Fossils in this exhibit show that they have been
misinterpreted as dinosaurs when they are actually birds.
Feather impressions reveal that they had flight feathers on the
wings and a second set on the hind legs. Even without the
feathers preserved, the avian characteristics of the skeleton
demonstrate that these dromaeosaurs are birds. This discovery
means that the larger dromaeosaurs, like Deinonychus and
Velociraptor of “Jurassic Park” fame, were really feathered and are secondarily flightless birds."

http://en.wikipedia.org/wiki/Dromaeosauridae
"Martin believes that maniraptorans are secondarily flightless birds, and that birds evolved from non–dinosaurian archosaurs [pterosaurs, according to what I am saying], so that most of the species formerly called theropods would now not even be classified as dinosaurs.^[43]"

http://www.ncbi.nlm.nih.gov/pubmed/19800747
"On the contrary, unmentioned by them is that abundant paleontological evidence has led several workers to conclude that troodontids and oviraptorids were secondary flightless birds. This evidence ranges from bird-like bodies and bone designs, adapted for climbing, perching, gliding, and ultimately flight, to relatively large, highly developed brains, poor sense of smell, and their feeding habits. Because ratites also are secondarily flightless and tinamous are reluctant, clumsy fliers, the new evidence strengthens the view that troodontids and oviraptorids were secondarily flightless." (Kavanau JL.)

http://en.wikipedia.org/wiki/Origin_of_birds#Secondary_flightlessness_in_dinosaurs
"A hypothesis, credited to Gregory Paul and propounded in his books Predatory Dinosaurs of the World (1988) and Dinosaurs of the Air (2002), suggests that some groups of non-flying carnivorous dinosaurs, especially deinonychosaurs but perhaps others such as oviraptorosaurs, therizinosaurs, alvarezsaurids and ornithomimosaurs, are actually descended from birds. Paul also proposed that the bird ancestor of these groups was more advanced in its flight adaptations than Archaeopteryx. This would mean that Archaeopteryx is thus less closely related to extant birds than these dinosaurs are.[110]
Paul's hypothesis received additional support when Mayr et al. (2005) analyzed a new, tenth specimen of Archaeopteryx, and concluded that Archaeopteryx was the sister clade to the Deinonychosauria, but that the more advanced bird Confuciusornis was within the Dromaeosauridae. This result supports Paul's hypothesis, suggesting that the Deinonychosauria and the Troodontidae are part of Aves, the bird lineage proper, and secondarily flightless.^[111] This paper, however, excluded all other birds and thus did not sample their character distributions. The paper was criticized by Corfe and Butler (2006) who found the authors could not support their conclusions statistically. Mayr et al. agreed that the statistical support was weak, but added that it is also weak for the alternative scenarios.<sup>[112]"

http://en.wikipedia.org/wiki/Oviraptorosauria
"</sup>Oviraptorosaurs ("egg thief lizards") are a group of feathered maniraptoran dinosaurs from the Cretaceous Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot - like skulls, with or without bony crests atop the head.
Analyses like those of Osmolska et al. (2004) suggest that they may in fact represent primitive flightless birds.^[2]"

Flightless Birds (4)

In the idea that I am presenting, the basal pterosaurs developed into primitive flying birds (with  feathers and long bony tails) during the Cretaceous. A branch of those flying birds developed into the primitive flightless creatures of the Cretaceous such as the Ornithomimosauria .
For example, Struthiomimus is a genus within the family of Ornithomimosauria.
http://en.wikipedia.org/wiki/Struthiomimus
"Struthiomimus (meaning "ostrich mimic", from the Greek στρουθιον/strouthion meaning "ostrich" and μιμος/mimos meaning "mimic" or "imitator") is a genus of ornithomimid dinosaur from the late Cretaceous of Alberta, Canada. It was a long-legged, ostrich-like dinosaur  [primitive bird]."

In fact, it was not a dinosaur, but was a flightless bird that had developed from the basal pterosaur line. Such a bird is called a "secondarily flightless bird". (It is called "secondarily flightless" because they developed from creatures that were able to fly).
More to come.

Flightless Birds (3)

As I said, there is an interesting wrinkle to the subject of flightless birds.

There are recognized categories of Cretaceous creatures (145.5 to 65.5 million years ago) that were very much like modern flightless birds including Ornithomimosauria and Oviraptorosauria.
http://en.wikipedia.org/wiki/Ornithomimosauria
"The Ornithomimosauria, ornithomimosaurs ("bird-mimic lizards") or ostrich dinosaurs^[1] were theropod dinosaurs which bore a [more than] superficial resemblance to modern ostriches. They were fast, omnivorous or herbivorous dinosaurs from the Cretaceous Period of Laurasia (now Asia, Europe and North America). The group first appeared in the Early Cretaceous and persisted until the Late Cretaceous."

http://en.wikipedia.org/wiki/Oviraptorosauria
"Oviraptorosaurs ("egg thief lizards") are a group of feathered maniraptoran dinosaurs from the Cretaceous Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot - like skulls, with or without bony crests atop the head."

Flightless Birds (2)

Note this sentence from the wikipedia entry:
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, and are thought to have evolved from their flying ancestors.[1"

In the current dino-to-bird thinking, the modern flightless birds are thought to have evolved "from their flying ancestors."
The idea is that dinosaurs evolved into flying birds and then some of those flying birds became land dwellers and lost the ability to fly. There is an element of correctness in this. Current flightless birds did develop from flying ancestors but those flying ancestors did not develop from dinosaurs - they developed from pterosaurs.

There is a additional interesting wrinkle to this, which I will cover in the next post.