Wednesday, December 17, 2014

Pubis evolution

The pterosaur pubis is homologous with the basal paraves superior pubic ramus and pubic body.
The pterosaur prepubis is homologous with the basal paraves inferior pubic ramus.
pterosaurs also have a fourth pelvic bone in the form of the pre-pubis. This pair of bones (one for each side) lie, and no points for guessing this, in front of, and articulate with, the pubes.
The prepubis of pterosaurs is a pelvic bone not found in the vast majority of tetrapods. It is not homologous with the prepubis of monotremes and marsupials. Nor is it homologous with the so-called “prepubic” bones of crocodilians, which are homologous with the pubic bones of other amniotes (Seeley 1901). The prepubis of ornithischian dinosaurs is a process of the pubis and not a separate ossification.
Pterosaur pubis (in green) and prepubis (in yellow). The drawing of MPUM 6009 is the most relevant.

The pterosaur pubis is homologous with the basal paraves superior pubic ramus and pubic body.
The pterosaur prepubis is homologous with the basal paraves inferior pubic ramus.

For example:
The pubis/prepubis parts of MPUM 6009 above, correspond to the 3 parts of the pubis in the oviraptor pubis in "C" below.

Working hypothesis:
Pterosaurs could not walk upright because the acetabulum was complete, but they could splay their legs. In the transition to basal paraves the acetabulum no longer closed completely. Thus a hole in the bottom of the acetabulum appeared. This allowed an upright stance as well as continuing the ability to splay the legs. This made flying with hindlimb feathers possible using splayed legs, while also gaining the ability to walk upright.

Sunday, December 14, 2014


Pterosaur feet are like basal paraves feet. Dinosaur feet are not like basal paraves feet.
The foot of Epidendrosaurus [a Scansoriopterygidae] is unique among nonavian
theropods. Although it does not preserve a reversed
hallux, metatarsal I is articulated with metatarsal II at
such a low position that the trochleae of metatarsals I–IV
are almost on the same level (see Figs. 1, 2d), which
is similar to
those of perching birds including the Early
Cretaceous flying birds Sinornis (Sereno 1992) and
Longipteryx (Zhang and Zhou 2001), as well as many arboreal
It [Scansoriopteryx] also had an unusually large first toe, or hallux, which was low on the foot and may have been reversed, allowing some grasping ability.[1]
The Scansoriopterygidae are among the most basal members of Paraves.
Other features of digits I-IV of the D. weintraubi foot indicate a capacity for grasping that is consistent with an ability to climb but is unexpected in an obligate cursor. The claws are moderately curved (nearly as strongly as the claws of the manus); all phalanges except the most proximal have well developed flexor tubercles for the insertion of digital flexors (Fig. 2); and all of the IP joints allow for extensive flexion of the digits (as exhibited by digit IV; Fig. 2). Furthermore, the phalangeal proportions of the digits of Dimorphodon and other basal pterosaurs are similar to those of birds with grasping feet (that is, perching, climbing, and raptorial species) and unlike those of primarily ground-living birds, bipedal dinosaurs and the primitive dinosauromorphs Lagerpeton and Marasuchus.

Friday, December 12, 2014

The [Epidendrosaurus] material described in this paper was collected from a new locality, Daohugou, in east Nei Mongol, northeast China, which is west of Liaoning Province. Many salamanders(Wang 2000), plants and insects (Zhang 2002)have recently been discovered from this new locality. It is notable that an anurognathid rhamphorhynchoid pterosaur with beautiful hair [pycnofibers] covering the whole body has also been reported from this locality (Wang et al. 2002). The estimated age of the deposit at this locality is very controversial and ranges from the Middle Jurassic or the Early Cretaceous according to various authors (Wang etal. 2000; Zhang 2002); however, most workers currently regard it as being Late Jurassic.
Epidendrosaurus is a Scansoriopterygidae and one of the most basal members of Paraves.

Monday, December 8, 2014


It needs to be kept in mind that the vocabulary that is routinely used in discussing the origin of birds is based on the dino to bird theory. The vocabulary is not neutral. It assumes the dino to bird theory*.
This makes it tricky to even describe the pterosaur to bird theory. You have to use very qualified expressions, which even so, imply a dino to bird theory.
For example, I often use the phrase "basal paraves". This is intended to mean the long-bony-tailed feathered flying and secondarily flightless creatures. For example, Scansoriopterygidae.
But the category "paraves" is defined WITHIN the dino to bird theory. It assumes the dino to bird theory. So I obviously do not mean to include the baggage that the term "paraves" carries within the dino to bird theory.
For example, I do not mean that basal paraves evolved from dinosaurs and I do not mean to exclude oviraptors from the group.

* for example consider this:
Paraves is a branch-based clade defined to include all dinosaurs which are more closely related to birds than to oviraptorosaurs.

Sunday, November 30, 2014

Intramandibular joint

Basal paraves and pterosaurs do not have an intramandibular joint. Dinosaurs do have an intramandibular joint.

The unusual intra-mandibular joint described above is found only in herrerasaurids and theropods among dinosaurs. Dinosaurian outgroups (pterosaurs, crurotarsal archosaurs) also lack an intra-mandibular joint.


Page 21:
[Archaeopteryx] does not appear to have had an intramandibular joint
.....intramandibular articulation something that is actually absent in Archaeopteryx, but found in many of its theropod relatives.[2]


It would not tax the imagination to engender a long list of obstacles for the now dominant model of a theropod origin of birds, including....the sliding lower jaw joint [intramandibular joint] of theropods (absent in birds)
The traits uniting Theropoda seem to include:
An intramandibular joint between the dentary and post-dentary bones: this may have served as a shock absorber will feeding on live prey. (Herrerasaurs have a slightly different configuration of the intramandibular joint, and thus may be convergent.)
the analysis of Benton (2004) demonstrated that the only unequivocal synapomorphy diagnosing Theropoda is the presence of an intramandibular joint.


Friday, November 21, 2014


Here is a comparison of basal pterosaur, basal paraves and coelurosaur dinosaur. This is a work in progress.
As we can see, basal paraves are like pterosaurs. Basal paraves are not like dinosaurs
(If anyone would like to contribute to this analysis, please feel free).

Basal Pterosaur: Rhamphorhynchidae
Basal Paraves: Scansoriopterygidae
Coelurosaur Dinosaur: Proceratosauridae
(or Compsognathoidea)

Basal Basal
Pterosaur Paraves Dinosaur
Back 1 Notarium: absent (0) present (1) ? ? 0
2  Hyposphene-hypantrum: absent (0) present (1) ? 0 1
Breathing 1 Respiratory air sacs: absent (0) present (1) 1 1 x 0
2 Aspiration pump: absent (0) present (1) 1 1 x 0
3 Rib lever processes: absent (0) present (1) 1 1 x 0
Chest 1 Keeled breastbone: absent (0) present (1)  1 1 x 0
2 Furcula (wishbone): absent (0) present (1) 0 0 ?
Leg 1 Thigh bone: horizontal (0) not horizontal (1) 1 1 1
Foot 1 Hyperextended second toe: absent (0) present (1) 0 x 1 x 0
2 Hinge-like ankle joint: absent (0) present (1) 1 1 1
Pelvis 1 Pubic bone: pointing to back (0) to front (1) downward (2) 1 1 1
2 Pubic bones: not fused (0) fused (1) 0 ? ?
3 Acetabulum: not perforated (0) partial (1) full (2) 0 x 1 x 2
4 Pelvic bones: not fused (0) fused (1) * * ?
5 Pre-pubic bone: absent (0) present (1) 1 ** **
Tail 1 Caudal vertebrae: less than 15 (0) greater than 15 (1) 1 1 1
2 Caudal rods: absent (0) present (1) 1 1 x 0
3 Muscle mass of M. caudofemoralis longus: small (0) large (1) 0 0 x 1
Skull 1 Beak like jaw: absent (0) present (1) 1 1 x 0
2 Teeth: absent (0) present (1) 1 1 1
3 Crest: absent (0) present (1)  1 1 1
4 Neck attaches to skull; from rear (0) from below (1) 0 0 0
5 Serrated teeth: absent (0) present (1) 0 0 x 1
6 Semicircular canals:  expanded (0) not expanded (1) 0 ? ?
7 Intramandibular joint: absent (0) present (1) 0 0 x 1
8 Mandibular fenestra: absent (0) present (1) * * *
Shoulder 1 Strap-like scapula: absent (0) present (1) 1 1 x 0
2 Scapula orientation to backbone: subparallel  (0) parallel (1) 1 1 x 0
3 Glenoid fossa: elevated (0) not elevated (1) 0 0 x 1
Feather 1 Stage 2 feathers: absent (0) present (1) 1 1 x 0
2 Pennaceous feathers: absent (0) present (1) 0 x 1 x 0
Wing 1 Propatagium: absent (0) present (1) 1 1 x 0
2 Patagium: absent (0) present (1)  1 1 x 0
3 Wing membrane: absent (0) present (1) 1 x 0 0
4 Elongated 4th finger: absent (0) present (1) 1 1 x 0
5 Number of fingers: 2 fingers (2) 3 fingers (3) 4  fingers (4) 4 x 3 2/3
6 Pteroid bone: absent (0) present (1) 1 x 0 0
7 Capable of flapping flight: absent (0) present (1) 1 1 x 0
Wrist 1 Semilunate carpal: absent (0) present (1) 0 x 1 x 0
2 Proximal carpals: not fused (0) fused (1) 1 ? ?
3 Distal carpals: not fused (0) fused (1) 1 ? ?
4 Carpometacarpus: absent (0) present(1) 0 x 1 x 0
5 Angle of abduction:  less than 25% (0) greater than 25% (1) ? ? 0
General 1 Warm blooded: absent (0) present (1) 1 1 ?
2 Neural flight control system: absent (0) present (1) 1 ? 0
3 Pneumatic bones: absent (0) present (1) 1 1 x 0

                 * = varies within group
                 ** = see link
                 x = Difference

Sunday, November 9, 2014

Shoulder Joint


From the article on page 267 (by Frey et al.):
As in birds, the glenoid fossa in most pterosaurs is elevated by a dorsolaterally directed elongation of the coracoid and lies almost level with the vertebral column
Among living tetrapods, birds are unique in having completely separated the locomotor functions of fore and hindlimbs. The propulsive excursions of the forelimbs, which primarily involve elevation and depression in a transverse plane, differ fundamentally from those of most other tetrapods (pterosaurs and bats excepted) in which the forelimbs protract and retract in anteroposterior planes.
Pterosaurs and birds present a number of striking parallelisms in the structure of their flight apparatus and the glenoid is yet another example of their independent derivation of similar features.
In both rhamphorhynchoid and pterodactyloid pterosaurs the glenoid is distinctly saddle shaped with laterally as well as dorsally facing regions of the articular surface.
The origin of the pterosaurian glenoid must have involved the same evolutionary migration of position and orientation that has been outlined here for the avian lineage.
In contrast to the bulbous humeral head of birds, however, the humerus of pterosaurs bears a saddle-shaped facet, thus constraining the wingbeat excursion. This difference is likely a reflection of the relative structural versatility of the two wing types: an outstretched, sail-like membrane supported principally by a single digit versus a flexible airfoil composed of individual feathers, each with its own structural and functional integrity.
The [pterodactyl pterosaur] coracoid is about 75 per cent of the length of the scapula. It is expanded at its contact with the scapula, but has a more gentle decrease in width over its length. A small, blunt coracoid process is present, but it is not possible to tell if a groove separates it from the glenoid fossa. The sternal articulation is concave, faces posteroventrally, and lacks a posterior expansion. A large glenoid fossa faces anterodorsally with a dorsoventrally concave and anteroposteriorly convex saddle shape.
Wing skeleton. Both [pterodactyl pterosaur] wings are present in NGMC 99-07-1 (Text-figs 2, 4; Table 2). The humeri are complete though the right deltopectoral crest has become detached and rotated from its anatomical position (Text-fig. 2). The humeral head has an anteroposteriorly concave and dorsoventrally convex, saddle-shaped articulation so that it mirrors the shape of the glenoid.
Whether or not Microraptor could achieve powered flight or only passive gliding has been controversial. While most researchers have agreed that Microraptor had most of the anatomical characteristics expected in a flying animal, some studies have suggested that the shoulder joint was too primitive to have allowed flapping. The ancestral anatomy of theropod dinosaurs has the shoulder socket facing downward and slightly backward, making it impossible for the animals to raise their arms vertically, a prerequisite for the flapping flight stroke in birds. Some studies of maniraptoran anatomy have suggested that the shoulder socket did not shift into the bird-like position of a high, upward orientation close to the vertebral column until relatively advanced avialans like the enantiornithes appeared.[12] However, other scientists have argued that the shoulder girdle in some paravian theropods, including Microraptor, is curved in such a way that the shoulder joint could only have been positioned high on the back, allowing for a nearly vertical upstroke of the wing. 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] 

It is not an easy task to get all the needed information about the shoulder joint but this is how it appears:
Rhamphoryncidae had a saddle joint. Both the glenoid fossa and the humerus head were saddle-shaped.
Basal paraves had a half-saddle joint. The glenoid fossa was still saddle shaped but the humerus head was bulbous.

PTEROSAUR scapula, coracoid and glenoid
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.
 A large [pterodactyl] glenoid fossa faces anterodorsally with a dorsoventrally concave and anteroposteriorly convex saddle shape.
The lower (right?) coracoid doesn't seem to be articulated with the scapula either, with its narrow proximal neck lower than and partially overlapping the base of the scapula. I would argue the coracoid would be bent so that the neck is in a different plane from the oval distal end, and this makes the C-shape we see in the Epidendrosaurus and Scansoriopteryx holotypes. The glenoid may be oriented ventrally or laterally- I cannot discern it.
On the other hand:
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 scapula, coracoid, glenoid and tiny arm.
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.

Here is a very interesting video:
Agnolín 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, 
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.

Here is a good overview of the shoulder girdle of modern birds:

Friday, October 31, 2014

Dino to bird claims

What we see again and again is that there is no actual link between ground-based coelurosaur dinosaurs and arboreal paravians. They inhabit different niches (obviously) with no link between them. And even more importantly, they do not share characteristics. Almost all (if not all) the bird-like characteristics that are found in the paravians are not found in the ground-based coelurosaur dinosaurs. That is because they are not related.

So the question arises:
How in the world could there be so many claims for years and years that birds evolved from dinosaurs? 
In addition to the points noted above:

First, is the misleading convention of calling paraves "dinosaurs". So any bird-like character found in paraves is said to confirm the dino to bird theory. But paraves are not dinosaurs, they did not evolve from dinosaurs. People focus on the wrong place. The Achilles Heel of the dino to bird theory is that there is no connection between actual dinosaurs and paraves.

Next is to misinterpret the characters of actual dinosaurs as if they were bird-like or "proto" bird-like characters. Thus for example, we get the claim of "protofeathers" on ground-based coelurosaur dinosaurs, which does not stand up. 

And also we get secondarily flightless paravians being called "non-paraves maniraptors". As if they were transitional between actual dinosaurs and arboreal paravians. That does not stand up. They are secondarily flightless members of paraves.

Also the cladistic analyses that have been done, generally include only dinosaurs and use an inappropriate outgroup. The very significant exception to this is the James and Pourtless study, which not co-incidentally found other explanations as credible as the dino to bird theory. 

Thursday, October 30, 2014


In the dino to bird theory, there is a good deal of claimed exaptation.
Feathers, enlarged brain and abducted wrists are claimed to have evolved before they were used for flight. These are simply stories. These stories are made up in response to evidence that contradicts the dino to bird theory.
Exaptation and the related term co-option describe a shift in the function of a trait during evolution. For example, a trait can evolve because it served one particular function, but subsequently it may come to serve another.

Carpal asymmetry [abducted wrists] would have permitted avian-like folding of the forelimb in order to protect the plumage, an early advantage of the flexible, asymmetric wrist inherited by birds.
However, it is likely that mobility of the wrist was initially associated with other functions, such as predation (Padian 2001).
It had originally been proposed that this flexibility could be attributed to hunting, but the same changes are seen in maniraptorans that were herbivores and omnivores so it is unlikely that hunting provides the answer. Instead, the authors of the new study propose, the ability to fold the hands backwards would have protected the feathers of the arms. This would have prevented the feathers from getting damaged or from being in the way as the dinosaurs moved about, although the authors recognize that this hypothesis requires further evidence.
Perhaps more significant, however, is how this wing-folding mechanism may have allowed birds to take to the air. Birds do flex their wrists while flapping their wings to fly, and so it appears that the wrist flexibility that first evolved in dinosaurs was later co-opted for flight in birds. This is what is known as "exaptation," or when a previous adaptation takes on a new function. Indeed, as more is discovered about the evolution of birds, the more traits paleontologists find that evolved for one function but have been co-opted for another at a later point (feathers themselves being the most prominent
example). There is relatively little separating birds from their feathered dinosaur ancestors.

As Darwin elaborated in the last edition of The Origin of Species,[14] many complex traits evolved from earlier traits that had served different functions. By trapping air, primitive wings would have enabled birds to efficiently regulate their temperature, in part, by lifting up their feathers when too warm. Individual animals with more of this functionality would more successfully survive and reproduce, resulting in the proliferation and intensification of the trait.
Eventually, feathers became sufficiently large to enable some individuals to glide. These individuals would in turn more successfully survive and reproduce, resulting in the spread of this trait because it served a second and still more beneficial function: that of locomotion. Hence, the evolution of bird wings can be explained by a shifting in function from the regulation of temperature to flight.
Exaptation is a term used in evolutionary biology to describe a trait that has been co-opted for a use other than the one for which natural selection has built it.
It is a relatively new term,proposed by Stephen Jay Gould and Elisabeth Vrba in 1982 to make the point that a trait’s current use does not necessarily explain its historical origin. They proposed exaptation as a counterpart to the concept of adaptation.
For example, the earliest feathers belonged to dinosaurs not capable of flight. So, they must have first evolved for something else. Researchers have speculated early feathers may have been used for attracting mates or keeping warm. But later on, feathers became essential for modern birds’ flight.

Several ancient dinosaurs evolved the brainpower needed for flight long before they could take to the skies, scientists say.
Bird brains tend to be more enlarged compared to their body size than reptiles, vital for providing the vision and coordination needed for flight.
Scientists using high-resolution CT scans have now found that these "hyper-inflated" brains were present in many ancient dinosaurs, and had the neurological hardwiring needed to take to the skies. This included several bird-like oviraptorosaurs and the troodontids Zanabazar junior, which had larger brains relative to body size than that of Archaeopteryx.

See page 261 of "Riddle of the Feathered Dragons"

Did preadaptations for flight precede the origin of birds (Aves)? The origin of flight in birds is one of the great evolutionary transitions and has received considerable attention in recent years (Padian and Chiappe 1998; Clarke and Middleton 2008; Dececchi and Larrson 2009; Benson and Choiniere 2013; Dececchi and Larrson 2013). The evolution of birds is often considered coincident with the origins of flight, but many traits associated with flight evolved before the origin of Aves (Padian and Chiappe 1998).

Wednesday, October 29, 2014

Not required to become terrestrial

Here is an objection to the pterosaur to bird theory:
To derive birds from pterosaurs would require some pterosaur to give rise to terrestrial maniraptors, because non-paraves maniraptorans are terrestrial, and the bird lineage evolved within the maniraptorans
It must first be recognized that the so-called "non-paraves maniraptorans" are secondarily flightless and come after basal paraves*.
In the dinosaur to bird theory, "non-paraves maniraptors"  are incorrectly considered to come before (ancestral to) basal paraves.
However when we work with the idea that they are secondarily flightless (descended from basal paraves) then the objection above would not be relevant.
Pterosaurs did not give rise to terrestrial maniraptors. 
The pterosaur to bird theory proposes that flying pterosaurs gave rise to flying basal paraves.

* they are actually members of paraves

Tuesday, October 28, 2014

Artist's Renderings

Here are artist's renderings of the taxa we are interested in. They show that the pterosaur is much closer to basal paraves than the dinosaur is.




Saturday, October 25, 2014


Notice that the charts for basal Paraves and Rhamphorhynchus are very similar.
This is what you would expect if basal Paraves descended from Rhamphorhynchidae. 

Figure 3. Representative aerodynamic measurements for pitching stability and control effectiveness. Long-tailed taxa (a) have a stable equilibrium point at 10-25 (yellow line) and the tail is effective in generating pitching moments at low angles of attack (pale yellow box indicates measurable moments for given tail deflections). In short-tailed taxa (b), including extant Larus, the equilibrium point at 0-5 is unstable (red line) and the tail control effectiveness is reduced (no measurable moments for the given tail deflections). One example (Rhamphorhynchus) drawn from pterosaurs illustrates similar possibilities in a phylogenetically distant [actually quite close] taxon.

This is not convergence because ground-based dinosaurs and pterosaurs did not live in similar ways and/or similar environment, and so did not face the same environmental factors.
In morphology, analogous traits will often arise where different species live in similar ways and/or similar environment, and so face the same environmental factors. When occupying similar ecological niches (that is, a distinctive way of life) similar problems lead to similar solutions.[4]

Friday, October 24, 2014


Pterosaur and basal paraves wrists are very similar,

The pterosaur wrist consists of two inner (proximal) and four outer (distal) carpals (wrist bones), excluding the pteroid bone, which may itself be a modified distal carpal. The proximal carpals are fused together into a "syncarpal" in mature specimens, while three of the distal carpals fuse to form a distal syncarpal.

Now let's compare to Yixianosaurus.
The describers considered the exact placement of Yixianosaurus within Maniraptora to be uncertain, but because the hand length resembled that of another feathered dinosaurEpidendrosaurus (now Scansoriopteryx), they suggested it was a close relative of the Scansoriopterygidae.
Comparing the Yixianosaurus wrist to the pterosaur wrist is a very good comparison because I have been proposing that Rhamphorhynchidae developed into a taxon like Scansoriopterygidae.

In the transition from pterosaur to basal paraves, the two proximal carpals were not fused. Two of the distal carpals continued to be fused. The outermost distal carpal was not fused.
This allowed the wrist to bend a great deal.
Extant volant birds possess a highly specialized wrist joint, in which two proximal carpals articulate with a fused carpometacarpus. The proximal part of the carpometacarpus forms an articular trochlea, comprising two convex ridges separated by a transverse groove, and is largely homologous to the structurally similar semilunate carpal (SLC) of derived non-avian theropods (Ostrom 1976).
Like other maniraptorans, scansoriopterygids had a semilunate carpal (half-moon shaped wrist bone) that allowed for bird-like folding motion in the hand.
The pterosaur proximal carpal articulated in a groove in the distal carpal and that is how it worked in basal paraves as well.
Figure 1: Diagram showing the position and general morphology of the transversely trochlear proximal articular facet of the carpometacarpus in selected theropod hands with the phalanges omitted (upper: proximal view; lower: dorsal view; medial side of hand to left).

(a) The basal coelurosaurian condition (based on Guanlong). (b) The basal paravian condition (based on Sinovenator). (c) The neornithine condition (based on Crossoptilon). Yellow indicates the ‘semilunate’ carpal; grey-yellow indicates the transverse groove; green indicates the metacarpals.
Trochlea (Latin for pulley) is a term in anatomy. It refers to a grooved structure reminiscent of a pulley's wheel.

This is also a very helpful link:
The homology of the ‘semilunate’ carpal, an important structure linking non-avian and avian dinosaurs, has been controversial. Here we describe the morphology of some theropod wrists, demonstrating that the ‘semilunate’ carpal is not formed by the same carpal elements in all theropods possessing this feature and that the involvement of the lateralmost distal carpal in forming the ‘semilunate’ carpal of birds is an inheritance from their non-avian theropod ancestors. Optimization of relevant morphological features indicates that these features evolved in an incremental way and the ‘semilunate’ structure underwent a lateral shift in position during theropod evolution, possibly as a result of selection for foldable wings in birds and their close theropod relatives. We propose that homeotic transformation was involved in the evolution of the ‘semilunate’ carpal. In combination with developmental data on avian wing digits, this suggests that homeosis played a significant role in theropod hand evolution in general.


The following seems to be inconsistent with the other references:
The wing of a modern bird, for example, has only two remaining carpals; the radiale (the scaphoid of mammals) and a bone formed from the fusion of four of the distal carpals.[14]
Bird limbs
"Fore-limb and hind-limb compared. H., Humerus; R., radius; U., ulna; r., radiale; u., ulnare; C., distal carpals united to carpo-metacarpus; CC., the whole carpal region; MC.I., metacarpal of the thumb; I., phalanx of the thumb; MC.II., second metacarpus; II., second digit; MC.III., third metacarpus; III., third digit. F., femur; T.T., tibio-tarsus; Fi., fibula; Pt., proximal tarsals united to lower end of tibia; dt., distal tarsals nited to upper end of tarso-metatarsus (T.MT.); T., entire tarsal region; MT.I., first metatarsal, free; I.-IV., toes." -Thomson, 1916