The two most significant separations between subgroups are those between the Paraves andThe reason that there is a "significant separation" between Paraves and coelurosaur dinosaurs is because they are not related.othercoelurosaurs and between the paravian clades Avialae and Deinonychosauria.
Palaeocursornis is a monotypic genus of pterosaurs. The only known species, P. corneti, was described in 1984 based on a single bone (MTCO-P 1637) interpreted as the distal part of a left femur, found in Early Cretaceous (Berriasian rocks (dating to around 143 mya) from a mine at Cornet near Oradea in northwestern Romania. It was initially assumed to be a flightless paleognathe bird, possibly a ratite, and later as a more primitive ornithuromorph or non-avialan theropod (Benton et al., 1997). However, re-evaluation of the specimen suggested that it was not a femur at all, but the upper arm bone (humerus) of a pterodactyloid pterosaur similar to Azhdarcho.[1]
Piksi is a genus of pterosaurs containing the single species Piksi barbarulna (meaning "strange elbowed big bird ", from Blackfoot piksi, "big bird" or, specifically, "chicken" and Latin barbarus "strange, outlandish" + ulna, elbow[1]). It lived roughly 75 million years ago in what is now Montana, USA. Known from parts of a right wing – the humerus, ulna and radius bones – the only specimens found so far are housed in the Museum of the Rockies(collection number MOR 1113). The genus Piksi is monotypic at present.
The bones are fragmentary and represent roughly the elbow area. Comparing the fossils' size to the wing bones of other ground birds, P. barbarulna seems to have been about as large as a Common Pheasant, i.e. some 15 in (35–40 cm) long excluding tail, and with a wingspan of perhaps 30 in (80 cm) or somewhat less. It would thus have weighed maybe 1 – 2 pounds (some 500 g – 1 kg).[2]The original description of the fossils found its affinities unresolvable except that it was probably an ornithothoracine bird. Agnolin and Varricchio (2012) reinterpreted Piksi barbarulna as a pterosaur rather than a bird, most likely a member of Ornithocheiroidea.[3]Original article::
Varricchio (2002 ) described some forelimb bones from the Late Cretaceous (Campanian) Two Medicine Formation, Glacier County, Montana (USA), as the holotype of Piksi barbarulna, a supposed ornithothoracine bird. However reevaluation of Piksi Varricchio, 2002 instead recognizes this genus as belonging to Pterosauria Kaup, 1834 and not Aves Linnaeus, 1758. Piksi exhibits the following derived humeral traits of pterosaurs: 1) very large ectepicondyle; 2) large trochlea; 3) with a deep, wide and poorly deliminated brachial depression that is proximodistally extended; 4) a wide and deep olecranal fossa not marked dorsally by a ridge; and 5) lacking a distal depression of the groove for the m. humerotricipitalis. Moreover, the putative Early Cretaceous birds Eurolimnornis Jurcsák & Kessler, 1986 and Palaeocursornis Jurcsák & Kessler, 1986 , based on distal humeri, are also regarded as pterosaurs. The record of Piksi constitutes an important addition to the Latest Cretaceous pterosaurian record.
At one stage, it was thought that the flight muscles ofhttp://eurekamag.com/research/019/478/morphological-evolution-pectoral-girdle-pterosaurs-myology-role.php (2003)
pterosaurs were very birdlike, with the arm lifted by
a muscle, m. supracoracoideus, anchoring on the sternum
rather than the shoulders. In birds, this muscle
arcs over the glenoid to attach on the dorsal surface
of the humerus, elevating the wing with a pulley-like
system (e.g., Kripp 1943; Padian 1983a; Wellnhofer
1991a). Detailed reconstruction of the proximal arm
musculature of pterosaurs shows that this is not
the case, however, and that the [pterosaur] arm was more likely
lifted by large muscles anchored on the scapula and
back, and lowered by those attached to the sternum
and coracoid (fig. 5.8; Bennett 2003a). Unlike [modern] birds,
where two vastly expanded muscles are mainly used
to power flight, it appears that pterosaurs used several
muscle groups to form their flapping strokes.
The musculature of the pectoral region of representative rhamphorhynchoid (Campylognathoides) and large pterodactyloid (Anhanguera) pterosaurs was reconstructed in order to examine the function of various muscles and the functional consequences of the evolution of the advanced pectoral girdle of large pterodactyloids. The reconstructions suggest that m. supracoracoideus was not an elevator of the wing, but instead depressed and flexed the humerus. m. latissimus dorsi, m, teres major, m. deltoides scapularis, and m. scapulohumeralis anterior were wing elevators.BASAL PARAVES
Its lack of a supracoracoideus (SC)
pulley, the primary elevator of the wing, would prevent
Archaeopteryx from executing humeral rotation on the
glenoid during the upstroke,
For example, Archaeopteryx could nothttp://www.ncbi.nlm.nih.gov/pmc/articles/PMC1780066/
position its wing high in an upstroke position, since it
lacked a modern avian supracoracoideus (SC) pulley, the
primary elevator of the wing (Poore et al. 1997).
Anatomical evidence indicates that Microraptor was not capable of ground or running takeoff, because it lacked the supracoracoideus pulley to elevate the wings.http://en.wikipedia.org/wiki/Confuciusornis
The first of these regarded problems to attain a steep flight path due to a limited wing amplitude. In the interpretation of Senter (2006) of the position of the shoulder joint, a normal upstroke would be impossible precluding flapping flight entirely. Less radical is the assessment that due to the lack of a keeled sternum and a high acrocoracoid, the [Confuciusornis] Musculus pectoralis minor could not serve as a M. supracoracoideus lifting the humerus via a tendon running through a foramen triosseum. This, coupled with a limited upstroke caused by a lateral position of the shoulder joint, would have made it difficult to gain altitude.http://jeb.biologists.org/content/200/23/2987.full.pdf
The lack of a morphologically derived SC in Late
Jurassic and Early Cretaceous birds precluded a high velocity
recovery stroke which undoubtedly limited
powered flight in these forms. Subsequent evolution of the
derived SC capable of imparting a large rotational force to
the humerus about its longitudinal axis was an important
step in the evolution of the wing upstroke and in the ability
to supinate (circumflex) the manus in early upstroke, a
movement fundamental to reducing air resistance during
the recovery stroke.
The highly derived morphology of the SC,Pterosaurs and basal paraves flapped their wings in the same way.
a characteristic of modern birds capable of powered flight, was
not present in Archaeopteryx (Ostrom, 1976a,b; Wellnhofer,
1988, 1993), nor is there firm evidence for its presence in
recently described Mesozoic species (Chiappe, 1995; Sanz et
al. 1996).
| Scansoriopterygidae are basal paraves with flight feathers on the arms and legs. Scansoriopterygidae (or a group very much like it) is the ancestor of the later Paraves such as Microraptor, Archaeopteryx etc. Rhamphorhynchidae (or a group very much like it) is the ancestor of Scansoriopterygidae. Rhamphorhynchidae pycnofibres are homologous to Scansoriopterygidae feathers. The Rhamphorhynchidae acetabulum is homologous to the Scansoriopterygidae acetabulum. The Rhamphorhynchidae caudal rods are homologous to the Scansoriopterygidae caudal rods. The Rhamphorhynchidae long bony tail is homologous to the Scansoriopterygidae long bony tail. The Scansoriopterygidae outermost digit is transitional between Rhamphorhynchidae and later Paraves. |
A dynamic, modular flight system (as in birds) required a chaotic, unstable system to operate in, and modulating the body to compensate. Nonexistent or gently controlled air flow is not a good way to determine performance of a glide path, especially since NO living glider today maintains an absolutely fixed physical posture during its trajectory, and this goes triple for parachuting animals.
In their conclusion, Alexander et al. state: "Obviously, the living animalIn fact flying pterosaurs did precede them.
was capable of active control, but we suggest that the tandem wing
configuration may have been advantageous because it requires less active
stabilizing ability."
I am not quite sure how one can develop a system of
unstable flight control from a passively stable system. Abilities to develop
control over the wing and perform a dynamic powered operation seem to require a
powered operation to precede it
Microraptors have been reconstructed in two distinctive models, the four-winged gliding model with sprawled hindlimb wings, by which it was originally described in Nature (Xu et al. 2003), and a dinosaurian bipedal model, or biplane model, by which it is reconstructed with the hindlimbs held beneath the body, incapable of sprawling, in other words, like a tiny T. rex. The problem,of course, is that there is absolutely no reason the hindlimbs could not have been sprawled, as is the case in flying squirrels (Glaucomys spp.), flying lemurs (Dermoptera), etc., and even falling cats. Too, the sprawled model performs superiorly inwind-tunnel experiments (Alexander et al. 2010), most specimensare preserved with a sprawled posture, and the wingclaws are adapted for trunk climbing (Burnham et al. 2011). In addition, it would be difficult to imagine how selection could produce elongate, asymmetric hindlimb flight remiges by the most current paleontological reconstructions, in which the hindlimbs are held in flight beneath the body in obligate bipedal fashion, with elongate hindlimb wing feathers trailing behind, simply slicing through the air (Balter 2012)http://www.pnas.org/content/107/7/2972.full.pdf+html
Fossils of the remarkable dromaeosaurid Microraptor gui and relatives clearly show well-developed flight feathers on the hind limbs as well as the front limbs. No modern vertebrate has hind limbsfunctioning as independent, fully developed wings; so, lacking a living example, little agreement exists on the functional morphologyor likely flight configuration of the hindwing. Using a detailed reconstruction based on the actual skeleton of one individual, cast in the round, we developed light-weight, three-dimensional physical models and performed glide tests with anatomically reasonable hindwing configurations. Models were tested with hindwings abducted and extended laterally, as well as with a previously described biplane configuration. Although the hip joint requiresthe hindwing to have at least 20° of negative dihedral (anhedral),all configurations were quite stable gliders. Glide angles rangedfrom 3° to 21° with a mean estimated equilibrium angle of 13.7°,giving a lift to drag ratio of 4.1:1 and a lift coefficient of 0.64. The abducted hindwing model’s equilibrium glide speed corresponds to a glide speed in the living animal of 10.6m·s−1. Although the biplane model glided almost as well as the other models, it was structurally deficient and required an unlikely weight distribution (very heavy head) for stable gliding. Our model with laterally abducted hindwings represents a biologically and aerodynamically reasonable configuration for this four-winged gliding animal. M. gui’s feathered hindwings, although effective for gliding, would have seriously hampered terrestrial locomotion.
Primitively, early archosaurs are sprawling, with the legs set
laterally and elevated at around 75° (6), a preadapted posture for
gliding. Modern birds normally have the thigh elevated and
sprawled to the side in different degrees; for example, it is nearly
perpendicular to the midline in loons and grebes (7). This variation
shows that the degree of splaying needed to use the
hindlegs in gliding is not unusual when compared with that in
modern birds. The absence of an antitrochanter and a supraacetabular
acetabular shelf (SAC) in the eumaniraptorans, including dromaeosaurids,
would make elevation and splaying of the legs even
easier (8). Air pressure could have provided most of the force
needed to elevate the leg into a gliding position similar to that in
gliding mammals. This simple positioning was originally assumed
for the four-winged Microraptor gui (5); but later, workers hoping
to recover an upright posture proposed arrangements of the
hindlimbs that would have required complicated systems of locks
and muscles to hold the leg in an only partially elevated position,
e.g., the “biplane” model (9). New anatomical information based
on the discovery of several hundred specimens similar to the
four-winged glider M. gui (and related taxa) has produced converging
lines of evidence demonstrating that the original
describers of M. gui (5) were correct in their interpretation of the
flight posture. We postulate, based on examination of this new
material, that M. gui was capable of abducting the hind limbs at
least 65–70° to achieve a gliding posture.
Some paleontologists have doubted the biplane hypothesis, and have proposed other configurations. A 2010 study by Alexander et al. described the construction of a lightweight three-dimensional physical model used to perform glide tests. Using several hind leg configurations for the model, they found that the biplane model, while not unreasonable, was structurally deficient and needed a heavy-headed weight distribution for stable gliding, which they deemed unlikely. The study indicated that a laterally abducted hindwing structure represented the most biologically and aerodynamically consistent configuration for Microraptor.[3] A further analysis by Brougham and Brusatte, however, concluded that Alexander's model reconstruction was not consistent with all of the available data on Microraptor and argued that the study was insufficient for determining a likely flight pattern for Microraptor. Brougham and Brusatte criticized the anatomy of the model used by Alexander and his team, noting that the hip anatomy was not consistent with other dromaeosaurs. In most dromaeosaurids, features of the hip bone prevent the legs from splaying horizontally; instead, they are locked in a vertical position below the body. Alexander's team used a specimen of Microraptor which was crushed flat to make their model, which Brougham and Brusatte argued did not reflect its actual anatomy.[15] Later in 2010, Alexander's team responded to these criticisms, noting that the related dromaeosaur Hesperonychus, which is known from complete hip bones preserved in three dimensions, also shows hip sockets directed partially upward, possibly allowing the legs to splay more than in other dromaeosaurs.[16]Related references:
