Monday, January 28, 2013

Pelvic Bones Summary

Here is a summary of the material about pterosaur, dinosaur and basal paraves pelvic bones.
See also this link

"Several aspects of the pelvic girdle suggest that pterosaurs were specialized for pelvic aspiration during flight. As in birds, the three pelvic bones of pterosaurs were solidly fused into a single unit (Fig. 9), and an increased number of dorsal vertebrae were incorporated into the sacrum (3 to 5 in Rhamphorhynchusand as many as 10 in Pteranodon) (Wellnhofer, 1978Go, 1987Go)"
"The claws were thought to come from juveniles — they were just so small. But when we studied the pelvis, we found the hip bones were fused, which would only have happened once the animal was fully grown," Longrich said. "Until now, the smallest carnivorous dinosaurs we have seen in North America have been about the size of a wolf. Judging by the amount of material that was collected, we believe animals the size of Hesperonychus [a dromaeosauridmust have been quite common on the landscape."

The pelvis of the orinithocheiroid Coloborhynchus


partially closed acetabulum is seen in basal archosaurs and is characteristic of the scansoriopterids and Jurassic feathered forms such as Anchiornis initially described as near Aves by Xu et al (2009)
The transition to partially open acetabulum (from fully closed) would have taken place in the transition from pterosaur to basal paraves.

See page 10
The hip joint of pterosaurs is more mobile and profoundly different from that of theropods but is reminiscent of that of mammals, especially of humans, allowing a wide range of adduction and abduction in the vertical plane.
The femoral component [of the Anhanguera pterosaur femur]  is a well defined spherical head which is distinctly separated from the shaft by a narrow non-articular neck at an obtuse angle of 160 degreesThe head forms a ball and socket joint with the close-fitting, shallow and imperforate acetabulum. 
In theropods [dinosaurs], the femoral component is cylindrical without any distinctive head and neck. It projects medially at a right angle [90 degrees] from the shaft and fits into a perforated acetabulum of up to 1.5 times its diameter. As a result, the hip joint is stable and fully congruent during parasagittal motion, permitting a wide range of flexion and extension but very little abduction and adduction.
Two pterodactylid pterosaurs:

But notice the Anchiornis femur (d):
Figure 4 IVPP V 14378 selected elements. (a) Anteriormost caudal vertebrae in ventral view; (b) left carpal region; (c) right ilium in lateral view; (d) left femur in posteromedial view; (e) left pes in dorsolateral view. Abbreviations: bs, brevis fossa; ?dc3, ?distal carpal 3; fh, femoral head; MTII-IV, metatarsals II-IV; mw, medial wall; pst, supra-trochanteric process; ra, radius; rle, radiale; sac, superacetabular crest; ?‘se’, ?‘semilunate carpal; ul, ulna; ?ule, ?ulnare. Scale bar = 3 mm for (a)―(d) and 1 mm for (e).



Birds are the only living vertebrate whose hind limb includes three long bones in sequence. The innermost of the two long bones are similar to those found in most vertebrates. At the hip, the femur, is held more or less parallel to the ground and is bound to the hipbones by the massive thigh muscles. In effect, the femur is an addition to the hipbones and its rotation contributes little to the length of the bird’s stride. 

During walking and running in birds, hindlimb movement is generated primarily at the knee and ankle joints; in humans, movement occurs at the knee, ankle and hip joints. The bird's thigh does not move substantially from its nearly horizontal position where it provides rigid lateral support to the thin walled air-sacs of the respiratory system. (Credit: Image courtesy of Oregon State University).

Note the pterosaur prepubis:
The “dark wing” specimen of Rhamphorhynchus muensteri JME SOS 4785 (Tischlinger and Frey 2002) has one overlooked oddity worth mentioning. It had an incredibly deep prepubis (Figure 1.)
So much so normal, but pterosaurs also have a fourth pelvic bone in the form of the pre-pubis.
The Auk 124(3):789–805, 2007
Fritz Hertel1,3 and Kenneth E. Campbell, Jr.2
Abstract.—The antitrochanter is a uniquely avian osteological feature of the
pelvis that is located lateral to the postero-dorsal rim of the acetabulum. This feature
makes the avian hip joint unique among all vertebrates, living and fossil, in
that a significant portion of the femoral–pelvic articulation is located outside of the
acetabulum. This additional acetabular articulation occurs between the neck of the
femur and the antitrochanter, and operates as a hinge joint or ginglymus. It is complementary
to the articulation of the head of the femur with the acetabulum, which
is a pivot joint or trochoides. The size, location, and spatial orientation of the antitrochanter
were determined for 77 species of birds representing a variety of hindlimb
functions (e.g., highly cursorial, vertical clinging, foot-propelled diving) and spanning
a wide range of body sizes (swifts to rheas). The area of the antitrochanter is
a good predictor of body mass in birds; its position and orientation are reasonably
consistent within hindlimb morphofunctional groups, but not among all birds. 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.
Pterosaurs' hip sockets are oriented facing slightly upwards, and the head of the femur (thigh bone) is only moderately inward facing, suggesting that pterosaurs had a semi-erect stance. It would have been possible to lift the thigh into a horizontal position during flight as gliding lizards do.
Evolution of the pterosaur pelvis
The sacrum (/ˈsækrəm/ or /ˈskrəm/; plural: sacra or sacrums;[1] Latin os sacrum[2]) in human anatomy is a large, triangular boneat the base of the spine, that forms by the fusing of sacral vertebrae S1S5, between 18 and 30 years of age.[3]
In birds the sacral vertebrae are fused with the lumbar and some caudal and thoracic vertebrae to form a single structure called the synsacrum
The synsacrum is a skeletal structure of birds and dinosaurs, in which the sacrum is extended by incorporation of additional fused or partially fused caudal or lumbar vertebrae.
Archaeopteryx, as we have seen, had many features that are far from the condition found in living birds, including teeth, an unfused hand, a bony tail, no synsacrum, and gastralia.Subsequent events included the formation of a pygostyle as well as the development of the synsacrum and other features for a rigid trunk, all of which contribute to the efficient flight that characterizes modern birds.
Closer related yet to Aves were the toothed Ichthyornithiformes (see Figure 11.2). Unlike hesperornithiforms, ichthyornithiforms were excellent flyers (Figure 11.7). Ichthyornis, from the Late Cretaceous of North America, had a massive keeled sternum and an extremely large deltoid crest that was probably an adaptation for powerful flight musculature. In other respects, it shared many of the adaptations of modern birds including a shortened, fused trunk, a carpometacarpus, a pygostyle, a completely fused tarsometatarsus, and a synsacrum formed of 10 or more fused vertebrae. Found exclusively in marine deposits, ichthyornithiforms must have been rather like Mesozoic sea gulls - but with teeth.
The sacral enlargements of non-avian dinosaurs do not share much structural similarities with the lumbosacral specializations of modern birds. Furthermore these species were quadrupedal and had a long tail, i.e. there was no need for a sense organ of equilibrium. It seems that early birds with a pygostyle and a well-developped synsacrum show structural specializations which resemble that of modern birds. However, there is a need for more details and more examples of well-preserved fossils.
During evolution the reduction of the tail is accompanied by a melting of lumbosacral vertebrae named „synsacrum“.
Rahona ostromi lived in the late Cretaceous but its pelvic bones resemble those of the first birds. (Rahona means “menacing cloud.) It possessed a number of theropod characteristics (such as a pubic boot and the articulations between its vertebrae) but had the distinctive sickle claw and hyperextensible 2nd toe found in dinosaurs such as Velociraptor. It had primitive theropod characteristics such as a long tail, a saurischian vertebral articulation (also seen in Patagonykus), a pubic boot (as in Archaeopteryx and the enantiornithine birds) and some pelvic features (similar to Archaeopteryx and Unenlagia). It possessed a synsacrum which is an advanced feature (Forster, 1998; Gibbons, 1998).
The oldest known bird, Archaeopteryx, dated to 150 million years ago, defines the clade Aves [5, 6, 7] or Avialae [8]. Its fully formed flight feathers, elongated wings, and evidence of capable powered flight, all ally Archaeopteryx with birds [9, 10]. Yet, the presence of teeth, clawed and unfused fingers, and an elongated, bony tail are characteristics shared with non-avian theropod dinosaurs. Paravians, including Archaeopteryx, are characterized by long tails [11, 12], some fusion of synsacral vertebrae, and varying flight capability (Figure 1). Most deinonychosaurians had between 20 and 30 caudal vertebrae. Oviraptorosaurs, probably the immediate outgroup to Paraves, had relatively shorter tails. These shorter tails were due not just to a modest decrease in the number of caudal vertebrae relative to other non-avian theropods, but more generally to a reduction in individual lengths of the more distal caudals [13]. Interestingly, several oviraptorosaurs have been documented to have the distal caudal vertebrae co-ossified into a pygostyle-like structure that braced a fan-like arrangement of retrices [13, 14, 15, 16]. Another more prominent independent reduction of tail length occurred in Epidexipteryx, a Mid- or Late-Jurassic maniraptoran dinosaur [17]. Its tail had only 16 caudal vertebrae with the distal ten tightly articulated to form a stiffened rod supporting four unique, ribbon-like, tail feathers.
The holotype specimen of Xiaotingia zhengi has completely closed neurocentral sutures on all exposed vertebrae and has a completely fused synsacrum, indicative of a late ontogenetic stage (probably adult).
Five sacral vertebrae form a short synsacrum (less than 60% as long as the ilium), as in other archaeopterygids and basal deinonychosaurs.
W. Scott Persons, IV, Philip J. Currie, and Mark A. Norell
Oviraptorosaur caudal osteology is unique among theropods and is characterized by posteriorly persistent and exceptionally wide transverse processes, anteroposteriorly short centra, and a high degree of flexibility across the pre-pygostyle vertebral series. Three-dimensional digital muscle reconstructions reveal that, while oviraptorosaur tails were reduced in length relative to the tails of other theropods, they were muscularly robust. Despite overall caudal length reduction, the relative size of the M. caudofemoralis in most oviraptorosaurs was comparable with those of other non-avian theropods. The discovery of a second Nomingia specimen with a pygostyle confirms that the fused terminal vertebrae of the type specimen were not an abnormality. New evidence shows that pygostyles were also present in the oviraptorosaurs Citipati and Conchoraptor. Based on the observed osteological morphology and inferred muscle morphology, along with the recognition that many members of the group probably sported broad tail-feather fans, it is postulated that oviraptorosaur tails were uniquely adapted to serve as dynamic intraspecific display structures. Similarities, including a reduced vertebral series and a terminal pygostyle, between the tails of oviraptorosaurs and the tails of theropods widely accepted as basal members of the Avialae, appear to be convergences.

The (Archaeopteryx) synsacrum is also smaller and less fused, and the pubis is not fully reversed.
Pterosaurs all have a diapsid skull showing two openings behind the orbit. They have air sacs and pneumatic bones, a sclerotic ring around the eye and a distinctly fused synsacrum and pelvis.

The (Archaeopteryx) synsacrum consists of 5 fused vertebrae.

Friday, January 25, 2013

Alula Summary

Here is a summary of material about the bird alula.


The alula, or bastard wing, is a small projection on the anterior edge of the wing of modern (and some ancient) birds. The word is Latin and means "winglet"; it is the diminutive of ala, meaning "wing". The alula is the freely moving first digit, a bird's "thumb," and is typically covered with three to five small feathers, with the exact number depending on thespecies. Like the larger flight feathers found on the wing's trailing edge, these alula feathers are asymmetrical, with the shaft running closer to anterior edge.
What is the origin of digits in birds? The question has long puzzled evolutionary biologists. Using genomic analysis, researchers have now solved a key part of this mystery.

Evolution adds and subtracts, and nowhere is this math more evident than in vertebrates, which are programmed to have five digits on each limb. But many species do not. Snakes, of course, have no digits, and birds have three.

Yale scientists now have a good handle on how these developmental changes are orchestrated in the embryo. But there is still one outstanding debate on birds: Which digits are they? A thumb with index and middle fingers, or the index, middle and ring fingers?
In five-digit vertebrates, the thumb comes from the precursor stem cells labeled pa. While birds have a digit that looks like a thumb, pa precursor cells die off during development and never produce a digit in adults. As a result, scientists have wondered whether precursor cells in pb can make a thumb.
Yale scientists have completed a genomic analysis of birds that reveals the answer. It is a hands-down "yes" -- even though the first bird digit develops where the index finger on a five-finger vertebrae should be.

Also interesting info here:

Thursday, January 24, 2013

Feather tracts

Here is some general info on bird feather tracts:
Feather Tracts:
Feathers are not attached to birds in a random manner over the entire body of the bird. Instead they are usually found in often linear tracts celled pterylae. The spaces on the bird's body without feather tracts are referred to as apteria. The densest area for feathers is often on the bird's head and neck.

Propatagium and Patagium Summary


Here is a summary of material about the connection between the pterosaur propatagium and the bird propatagium. The pterosaur propatagium developed into the bird propatagium.

"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."
"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."
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."

Through flight experiments with live birds and computer modeling we define the aerodynamic contributions of the propatagium in avian flight.  
We conclude that the cambered propatagium is the major lift generating component of the wing proximal to the wrist.
This possibly advanced shoulder anatomy, combined with the presence of a propatagium linking the wrist to the shoulder (which fills the space in front of the flexed wing and may support the wing against drag in modern birds) and an alula or "bastard wing" may indicate that Microraptor was capable of true, powered flight.[13]
a. A slightly arched surface, as of a road, a ship's deck, an airfoil, or a snow ski.b. The condition of having an arched surface. 



Note that the word "patagium is used in two different ways.
In the flying pterosaurs, the patagium is also composed of the skin forming the surface of the wing. In these ornithodirans, the skin was extended to the tip of the elongated fourth finger of each hand.
The patagium of a pterosaur had three distinct parts:
Propatagium: the patagium present from the shoulder to the wrist
Brachiopatagium: the portion stretching from the fourth finger to the hindlimbs.
Uropatagium or cruropatagium: the anterior portion between the two hindlimbs, depending on whether it did or did not include the tail
In birds, the propatagium is the elastic fold of skin extending from the shoulder] to the carpal joint, making up the leading edge of the inner wing. Many authors use the term to describe the fold of skin between the body (behind the shoulder) and the elbow that houses the outer segments of the latissimus dorsi caudalis and triceps scapularis muscles.[1] Similarly the fleshy pad that houses the follicles of the remiges (primary and secondary feathers) caudal to the hand and the ulna is also often referred to as a patagium.[2] The interremigial ligament that connects the bases all the primary and secondary feathers as it passes from the tip of the hand to the elbow is thought to represent the caudal edge of the ancestral form of this patagium.
The importance of a propatagium to the evolution of the avian wing is significant, as it has no apparent function other than contributing to the aerodynamics of the animal. Therefore, its presence in flightless forms lends support to the neoflightless hypothesis (Olshevsky 1992; Paul 2002; Feduccia 2012). The discovery of a propatagium in members of all clades of core maniraptorans, including Caudipteryx (oviraptorosaurs), Microraptor (dromaeosaurs), Anchiornis (a putative troodontid; Chatterjee and Templin 2012), Archaeopteryx (a basal urvogel; Martin and Lim 2005), and the basal avian Scansoriopteryx (Czerkas and Feduccia 2014), is additional evidence that flight was basal in Aves. Similarly, four-winged tetrapteryx wings can best be interpreted in a flight context.

Patagium and Bird Feather Summary

Here is a summary of material about actinofibrils.

"Wellnhofer [4, 5] and Padian [6, 7], following von Zittel [8],described a system of fine structural fibers investing the [pterosaur] wing membrane, in a pattern similar to the orientation of the feather shafts of birds and the wing fingers of bats, both principal structural elements supporting the patagium and responsible for the transmission of aerodynamic force."
The wing membrane was supported and controlled through a system of stiffened, intercalated fibers, which were oriented like the main structural elements in the wings of birds and bats.

"There are presently four competing models for the internal structure of the pterosaur wing membrane.Wellnhofer (1987) suggested that the actinofibrils were structural fibres embedded in the wing membrane.Pennycuick (1988) disagreed with this interpretation and regarded the ‘fibres’ as wrinkles caused by the inner elastic fibres contracting after the animal's death. In a review of pterosaur wing membrane, Padian & Rayner (1993) argued for the presence of structural fibres on the surface of the ventral part of the wing membrane, closely associated with the epidermis. Lastly, Tischlinger & Frey (2002) and Frey et al. (2003), based on a Rhamphorhynchus specimen from Solnhofen and an exceptionally well-preserved material from the Romualdo Formation (DGM 1475-R) of Brazil (Martill & Unwin 1989Kellner 1996), interpreted the pterosaur plagiopatagium as consisting of five layers from dorsal to ventral: a thin and ‘hairless’ epidermis, a spongy subdermis, a layer of actinofibrils, a layer of dermal muscles and a vascular layer. Regarding the last model, it should be noted that Kellner (1996) regarded the soft tissue present in the specimen of the Romualdo Formation as closely associated with the body."

"The actual function of the actinofibrils is unknown, as is the exact material from which they were made. Depending on their exact composition (keratin, muscle, elastic structures, etc.), they may have been stiffening or strengthening agents in the outer part of the wing.[6] The wing membranes also contained a thin layer of muscle, fibrous tissue, and a unique, complex circulatory system of looping blood vessels.[7]"
"Since they [actinofibrils] were external, they were probably epidermal structures composed of keratin as in scales and feathers."

"research has since shown that the wing membranes of pterosaurs were actually highly complex and dynamic structures suited to an active style of flight. First, the outer wings (from the wing to the elbow) were strengthened by closely spaced fibers called actinofibrils.[5] The actinofibrils themselves consisted of three distinct layers in the wing, forming a crisscross pattern when superimposed on one another."
"The plagiopatagium can be divided into the distal, comparatively more rigid actinopagatium and a proximal, more tensile tenopatagium. The actinopatagium extends from the wing finger to the articulation between the humerus and the forearm, and shows the presence of at least three layers containing actinofibrils. In each layer, the actinofibrils are parallel to subparallel, but this direction diverges from layer to layer.

Modern bird:

The uropatagium is not well preserved. Most of this membrane is encased in the bottom slab (plate I, fig. 2 in Wang et al. 2002), but traces can also be found in the top slab (figures 1 and 2). The shape of the uropatagium cannot be determined owing to the lack of a distinct posterior edge and the medially displaced feet. Two sets of fibres are observed: one running parallel to the longitudinal axis of the body and the second running perpendicular to the tibiae. This pattern is not as well developed as in the actinopatagium but, based on the thickness of the fibres, they are of the same nature as the actinofibrils. Integumental covering is also found.

Monday, January 21, 2013

Primitive bird:
In modern birds (Neornithes), the wing is composed of a layer of long, asymmetrical flight feathers overlain by short covert feathers [1-3]. It has generally been assumed that wing feathers in the Jurassic bird Archaeopteryx [4-9] and Cretaceous feathered dinosaurs [10, 11] had the same arrangement. Here, we redescribe the wings of the archaic bird Archaeopteryx lithographica [3-5] and the dinosaur Anchiornis huxleyi [12, 13] and show that their wings differ from those of Neornithes in being composed of multiple layers of feathers. In Archaeopteryx, primaries are overlapped by long dorsal and ventral coverts. Anchiornis has a similar configuration but is more primitive in having short, slender, symmetrical remiges. Archaeopteryx and Anchiornis therefore appear to represent early experiments in the evolution of the wing. This primitive configuration has important functional implications: although the slender feather shafts of Archaeopteryx [14] and Anchiornis [12] make individual feathers weak, layering of the wing feathers may have produced a strong airfoil. Furthermore, the layered arrangement may have prevented the feathers from forming a slotted tip or separating to reduce drag on the upstroke. The wings of early birds therefore may have lacked the range of functions seen in Neornithes, limiting their flight ability.
Longrich NR, Vinther J, Meng Q, Li Q, Russell AP.

Modern bird feather layers:

Saturday, January 19, 2013

The significant propatagium;2-R/abstract
Through flight experiments with live birds and computer modeling we define the aerodynamic contributions of the propatagium in avian flight. From flight trials we found that in House Sparrows, with all flight feathers removed except for the distal six primaries, the loss of approximately 50% of the propatagium's projected area and its cambered profile produced a significant reduction in the distance a bird was able to cover in flight. Removal of the secondary feathers, leaving six distal primaries and an intact propatagium, did not have a noticeable affect upon flight. From the computer model which is representative of the bird wing's mid-antebrachial chord (cambered propatagium, symmetrical musculoskeletal elements, and flat secondary flight feathers), we found that the propatagium: (1) produced the majority of the lift; (2) had a higher (relative to secondary feathers) production of lift in relation to its angle of attack, i.e., steeper lift-curve slope; and (3) produced more lift with a chord only 1/5 that of the feather subsection. We conclude that the cambered propatagium is the major lift generating component of the wing proximal to the wrist.

a. A slightly arched surface, as of a road, a ship's deck, an airfoil, or a snow ski.b. The condition of having an arched surface. 

Chicken Police

For fun - the chicken police!

Tuesday, January 15, 2013

Categories Updated

NOTE that I am now working with a simplified version of all this. This is for documentation of a more complicated hypothesis:
Here is the list of updated categories (proposed lineages). This is a work in progress.
(Click the links to view details).



  • Landbirds (General)
    • Pterosaur (eg. Dsungaripteroidea)  eg. Nemicolopterus -->
    • Enantiornithes/Confuciusornithids landbird subgroups -->
    • Modern landbird groups  (eg. Passerines, Falconiformes etc)
  • Landbirds (Owl)
    • Pterosaur (eg. Dsungaripteroidea)  eg. Nemicolopterus -->
    • Enantiornithes/Confuciusornithids landbird subgroup -->
    • Primitive owls, (eg. Sophiornithidae?--> 
    • Strigiformes (eg. owls), Caprimulgiformes (eg. nighthawks)
  • Landfowl
    • Pterosaur (eg.  Dsungaripteroidea)  eg. Nemicolopterus -->
    • Enantiornithes/Confuciusornithids landbird subgroup -->
    • Modern "Galliformes"(eg. Chicken, Turkey, Pheasant, Quail) and Tinamiformes (Tinamou)

  • Waterfowl (Presbyornithid line)
    • Pterosaur (eg. Ctenochasmatidae ) --->
    • Presbyornithid subgroup--> 
    • Modern Anseriformes (eg. Duck, Geese , Swan)
    • Pterosaur (eg.  Ctenochasmatidae) eg. Pterodaustro   -->
    • Presbyornithid subgroup--> 
    • Primitive bird, Palaelodidae (Phoenicopteriformes)  --> 
    • Flamingo (Phoenicopteriformes)
  • Aquatic birds (Hesperornithes line)
    • Pterosaur (eg.  Ctenochasmatidae)    eg. Pterodactylus --> 
    • Baptornithidae  (Hesperornithes) --> 
    • (primarily foot-propelled) WEB FOOT diving bird orders, eg. Cormorants (Phalacrocoracidae), Loons (Gaviidae),  Penguins  (Sphenisciformes)
    • Pterosaur (eg.  Ctenochasmatidae)    eg. Pterodactylus -->
    • Hesperornithidae (Hesperornithes) --> 
    • (primarily foot-propelled) LOBE FOOT diving bird orders eg. Grebes (Podicipedidae).
  • Seabirds (Ichthyornithes line)
    • Pterosaur (eg. Ornithocheiroideaeg. PteranodonAnhanguera -> 
    • An Ichthyornithes subgroup --> 
    • Gulls, Skimmers (Charadriiformes/Lari)
    • Pterosaur (eg. Ornithocheiroidea ) eg. Pteranodon Anhanguera -> 
    • An Ichthyornithes subgroup --> 
    • Petrels, Albatross (Procellariiformes)

  • Waders/shorebirds
    • Pterosaur (eg. Azhdarchoidea) --->
    • Primitive shorebird (eg. Graculavus) --> 
    • Modern shorebirds - eg. plovers, oystercatchers, sandpipers (Charadriiformes/Charadrii) and storks (Ciconiidae)

  • Flightless birds
    • Pterosaur -->
    • Primitive flying birds? -->
    • Modern (flightless) ratites - Ostrich (Struthio), Rhea (Rheidae), Cassowary, Emu (Casuariidae), Kiwi (Apteryx) 

For reference:

Cladogram showing the most recent classification of Neoaves, based on several phylogenetic studies.
The Cretaceous saw the rise of more modern birds with a more rigid ribcage with a carina and shoulders able to allow for a powerful upstroke, essential to sustained powered flight. They also had a more derived pygostyle, with a ploughshare-shaped end. An early example is Yanornis. Many were coastal birds, strikingly resembling modern shorebirds, like Ichthyornis, or ducks, like Gansus. Some evolved as swimming hunters, like the Hesperornithiformes – a group of flightless divers resembling grebes and loons. While modern in most respects, most of these birds retained typical reptilian-like teeth and sharp claws on the manus.
Gansus was described as the oldest known ornithuran. The Ornithurae, however, has been given several very different definitions. In the definition used by You and colleagues (that is, the clade containing all living birds plus Hesperornis and Ichthyornis), Gansus is indeed the oldest known member. However, several birds from the older Yixian Formation and contemporary Jiufotang Formation are considered ornithurans under other definitions. Under any definition, all living birds, including taxa as diverse as ostriches, hummingbirdsand eagles, are descended from basal ornithurans, many of which were semi-aquatic. It is now thought possible that all modern birds descended specifically from a semi-aquatic bird similar to Gansus. Thus, while Gansus is not necessarily a direct ancestor of today's birds, it is closely related to such an ancestral species.[5] This hypothesis was corroborated by later phylogenetic studies that included this taxon.[3][8]

Not yet categorized:
  • Pelican
  • Vulture
  • Condor