Tuesday, March 25, 2014

Body size and forelimb length

Mark Puttick and colleagues investigated the rates of evolution of the two key characteristics that preceded flight: body size and forelimb length.  In order to fly, hulking meat-eating dinosaurs had to shrink in size and grow much longer arms to support their feathered wings. 
"We were really surprised to discover that the key size shifts happened at the same time, at the origin of Paraves," said Mr Puttick of Bristol's School of Earth Sciences.  "This was at least 20 million years before the first bird, the famous Archaeopteryx, and it shows that flight in birds arose through several evolutionary steps." 
Being small and light is important for a flyer, and it now seems a whole group of dozens of little dinosaurs were lightweight and had wings of one sort or another. Most were gliders or parachutists, spreading their feathered wings, but not flapping them.                                               
'High rates of evolution preceded the origin of birds' by Puttick, M.N., Thomas, G.H., and Benton, M.J. in Evolution: DOI: 10.1111/evo.12363 

Notice that the changes appear for the first time at the origin of Paraves (not earlier).

There are basal coelurosaur dinosaur fossils and there are basal feathered flying Paraves fossils.
The basal coelurosaur fossils show all the characteristics of basal coelurosaur dinosaurs.
The basal Paraves fossils show all the characteristics of basal feathered flying Paraves.
And nothing in between.


Monday, March 17, 2014

Harry Govier Seeley - Pterosaurs to Birds

The idea that birds are descended from pterosaurs has an interesting history. The idea was proposed by Harry Govier Seeley. But note the negative reaction he received. Not much has changed in that respect.

Seeley was also an authority of pterosaurs, and in 1901 published a popular book on the subject, Dragons of the Air. In it, he gave an overview of animal flight, reptiles, the discovery of pterosaurs and pterosaur skeletal structure. He initially believed that birds descended from pterosaurs, but under intense criticism from his peers, backed off this assertion and argued that they shared common ancestry. "It would therefore appear from the vital community of structures with Birds, that Pterodactyles and Birds are two parallel groups, which may be regarded as ancient divergent forks of the same branch of animal life," he wrote. 

His popular book on Pterosaurs, Dragons of the Air (1901) found that birds and pterosaurs are closely parallel. His belief that they had a common origin has been proved, for both are archosaurs, just not as close as he thought.
I suggest that pterosaurs and birds are as close as Seeley thought. 

Ornithodesmus (meaning "bird link") is a genus of small, deinonychosaurian dinosaur from the Isle of Wight in England, dating to about 125 million years ago. The name was originally assigned [by Harry Govier Seeley] to a bird-like sacrum (a series of vertebrae fused to the hip bones), initially believed to come from a pterosaur. More complete pterosaur remains were later assigned to Ornithodesmus, until recently a detailed analysis determined that the original specimen in fact came from a small theropod, specifically a dromaeosaur. All pterosaurian material previously assigned to this genus has been renamed Istiodactylus.

Saturday, March 15, 2014

Comparison of characters

(Click on the links for more detail).

Basal Pterosaur: Rhamphorhynchidae
Basal Paraves: Dromaeosauridae
Basal Coelurosaur: Proceratosauridae

Basal Basal Basal
Pterosaur  Paraves  Coelurosaur
Diff Diff
Back 1 Notarium: absent (0) present (1) 0 0 0
Breathing 2 Respiratory air sacs: absent (0) present (1) 1 1 x 0
3 Breathing pump: absent (0) present (1) 1 1 x 0
4 Uncinate processes: absent (0) present (1) 1 1 x 0
Chest 5 Keeled breastbone: absent (0) present (1)  1 1 x 0
6 Furcula (wishbone): absent (0) present (1) 1 ? ?
Feather 7 Stage 2 feathers: absent (0) present (1) 1 1 x 0
8 Pennaceous feather: absent (0) present (1) 0 x 1 x 0
Foot 9 Hyperextended second toe: absent (0) present (1) 0 x 1 x 0
10 Hinge-like ankle joint: absent (0) present (1) 1 1 1
Leg 11 Thigh bone: horizontal (0) not horizontal (1) ? ? 1
Pelvis 12 Pubic bone: pointing to back (0) to front (1) downward (2) ? ? ?
13 Pubic bones: not fused (0) fused (1) 0 0 x 1
14 Acetabulum: not perforated (0)  perforated (1) ? ? 1
15 Pelvic bones: not fused (0) fused (1) 1 1 x 0
Skull 16 Beak like jaw: absent (0) present (1) 1 ? 0
17 Teeth: absent (0) present (1) 1 1 1
18 Crest: absent (0) present (1)  1 1 1
19 Neck attaches to skull; from rear (0) from below (1) 0 0 0
20 Serrated teeth: absent (0) present (1) 1 1 1
21 Semicircular canals:  expanded (0) not expanded (1) ? ? ?
Tail 22 Caudal vertebrae: less than 15 (0) greater than 15 (1) 1 1 1
23 Caudal rods: absent (0) present (1) 1 1 x 0
24 Muscle mass of M. caudofemoralis longus: small (0) large (1) 0 0 x 1
Wing 25 Strap-like scapula: absent (0) present (1) 1 1 x 0
26 Scapula orientation to backbone: subparallel  (0) parallel (1) 1 1 x 0
27 Glenoid fossa: elevated (0) not elevated (1) 0 0 x 1
28 Propatagium: absent (0) present (1) 1 1 x 0
29 Patagium: absent (0) present (1)  1 1 x 0
30 Wing membrane: absent (0) present (1) 1 x 0 0
31 Elongated 4th finger: absent (0) present (1) 1 x 0 0
32 Number of fingers: 2 fingers (2) 3 fingers (3) 4  fingers (4) 4 x 3 2/3
33 Pteroid bone/thumb: absent (0) present (1) 1 x 0 0
34 Capable of flapping flight: absent (0) present (1) 1 1 x 0
Wrist 35 Semilunate carpal: absent (0) present (1) 0 x 1 x 0
36 Proximal carpals: not fused (0) fused (1) 1 ? ?
37 Distal carpals: not fused (0) fused (1) 1 ? ?
38 Carpometacarpus: absent (0) present(1) 0 x 1 x 0
39 Angle of abduction:  less than 25% (0) greater than 25% (1) ? ? 0
General 40 Warm blooded: absent (0) present (1) 1 1 ?
41 Neural flight control system: absent (0) present (1) 1 ? 0
42 Pneumatic bones: absent (0) present (1) 1 1 x 0

Sunday, March 9, 2014

Caudal Rods (2)

In the tails of dromaeosaurids dinosaurs and rhamphorhynchid pterosaurs, elongate osteological rods extend anteriorly from the chevrons and the prezygapophyses. These caudal rods are positioned in parallel and are stacked dorsoventrally.

Remember the quickly reduced neural spines, caudal ribs, and chevrons? Those all indicate that the caudal muscles of both dromaeosaurids and pterosaurs were substantially reduced.

This is very strong evidence for the pterosaur to bird theory. 



The tails of pterosaurs and dromaeosaurids are so similar that, in the fossil-forging black-markets of China, the tail of one is often used to “complete” a partial skeleton of the other. Skeletal image of Rhamphorhynchus courtesy of Scott Hartman (www.skeletaldrawing.com).

For comparison:



Friday, February 7, 2014

Caudal Rods (1)

Let's turn to the topic of "caudal rods" in the long-tailed pterosaurs and the dromaeosaurs:

In the tails of dromaeosaurid dinosaurs and rhamphorhynchid pterosaurs, elongate osteological rods extend anteriorly from the chevrons and the prezygapophyses. These caudal rods are positioned in parallel and are stacked dorsoventrally. The fully articulated and three-dimensionally preserved caudal series of some dromaeosaurid specimens show that individually these caudal rods were flexible, not rigid as previously thought. However, examination of the arrangement of the caudal rods in cross-section indicates that the combined effect of multiple caudal rods did provide substantial rigidity in the dorsoventral, but not in the lateral, plane. The results of digital muscle reconstructions confirm that dromaeosaurids and rhamphorhynchids also shared greatly reduced caudofemoral muscles in the anterior tail region. The striking similarities between the tails of dromaeosaurids and rhamphorhynchids suggest that both evolved under similar behavioral and biomechanical pressures. Combined with recent discoveries of primitive deinonychosaurs that phylogenetically bracket the evolution of dromaeosaurid caudal rods between two arboreal gliding/flying forms, these results are evidence that the unique caudal morphologies of dromaeosaurids and rhamphorhynchids were both adaptations for an aerial lifestyle.
Here is a link to the full pdf.


At the start, the tail skeleton of Deinonychus appears normal. Just past the hips, the neural spines, caudal ribs, and chevrons all have a typical shape and they all project to a respectable extent. But, as the tail progresses towards the tip (and it doesn’t take long) things start to get weird. The neural spines, caudal ribs, and chevrons all shrink in, with the former two disappearing entirely . . . and then come the caudal rods. Both the vertebrae and chevrons abruptly develop pairs of elongated rods of bone that project towards the hips. These rods are slender, but very long (the longest easily overlap seven other sequential vertebrae), and they split, each becoming two still thinner rods. Together, rods of the vertebrae form a quiver that virtually encapsulates the dorsal (upper) portion of the tail, and together the rods of the chevrons do the same to the ventral (lower) portion.
The tail of Deinonychus and its raptor relatives is bizarre, but it is not (as Professor Ostrom himself realized) unique. Among all known vertebrates, a similar tail anatomy has evolved in one other group. . . and now we come to why I have been allowed to spend so much time discussing dinosaurs on what is supposed to be a blog about pterosaurs.
While later and more advanced pterosaurs (like Pterodactylus) only had short, stubby tails, early pterosaurs had long ones. The caudal skeletons of these long-tailed pterosaurs (with the exceptions of the dimorphodontids and very primitive forms) are strikingly similar to that of Deinonychus. In the case of long-tailed pterosaurs, the function of the caudal rods has always seemed obvious. As flying animals, increased rigidity would have helped a tail to serve as a stabilizer or as a rudder.
It is now also possible to think a step further and consider the muscles of the tail. Let’s first try to do that in very general qualitative terms. Remember the quickly reduced neural spines, caudal ribs, and chevrons? Those all indicate that the caudal muscles of both dromaeosaurids and pterosaurs were substantially reduced.
To help consider the problem quantitatively, a technique I used was to create digital models of the tail skeleton of aVelociraptor and a Rhamphorhynchus (a pterosaur) and to sculpt the corresponding muscles over the skeletal models. The results of this modeling concur with the qualitative inference. In particular, raptors and pterosaurs were found to have very weak caudofemoral muscles (indeed, some pterosaurs may not have had caudofemoral muscles at all).

However in 2010, Scott Persons, a graduate student from the University of Alberta proposed that Tyrannosaurus's speed may have been enhanced by strong tail muscles.[108] He found that theropods such as T rex had certain muscle arrangements that are different from modern day birds and mammals but with some similarities to modern reptiles.[109]

I will post more material on this topic in the next post.

Thursday, February 6, 2014

An Elaboration

Here is an elaboration of the basic ideas listed in the right sidebar:

The current mainstream thinking is that birds developed from coelurosaur dinosaurs. I propose that birds did not develop from any kind of dinosaur, but rather that birds developed from pterosaurs.

I propose that long-bony-tailed basal pterosaurs (eg. Rhamphorhynchidae) developed into long-bony-tailed feathered flying basal Paraves (eg. dromaeosaurs, basal avialans). Which then developed into short-tailed feathered birds (Pygostylia). Which then developed into modern birds (Neornithes).

Let's look at what would be involved in a transition from basal pterosaur wing to basal paraves wing. The analysis shows the following:

1. The wing membrane would need to retract toward the wing bones.
2. The pterosaur long wing finger would need to shorten and be lost.
3. The pterosaur protofeathers would need to develop into pennaceous feathers.
4. The pteroid bone would be lost.

Altogether not a great amount of change.

Also see here:

Tuesday, February 4, 2014

Introduction to Pterosaurs

Here is a good introduction to the basics of pterosaurs. Note the similarities to birds.

It mentions many interesting aspects, including the sternum, the pneumatic bones, the pteroid bone, the semi-circular canals, the flocculus etc. Also it includes the distinction between the primitive Rhamphorhynchoids and the advanced Pterodactyloids.

Monday, January 27, 2014

Pycnofibres to Feathers

The evidence indicates that pterosaur pycnofibres were Stage 1 and Stage 2 feathers.


Early stages in the development of a feather:

"The first feathers were likely hollow cylinders (Stage I) with undifferentiated collars that developed from an evolutionary novel follicle collar (From: Prum and Brush 2003)."

"The next step in feather evolution (Stage II) involved the differentiation of the follicle collar into barb ridges to generated unbranched barbs (From: Prum and Brush 2003)."

The long, hollow filaments on theropods posed a puzzle. If they were early feathers, how had they evolved from flat scales? Fortunately, there are theropods with threadlike feathers alive today: baby birds. All the feathers on a developing chick begin as bristles rising up from its skin; only later do they split open into more complex shapes. In the bird embryo these bristles erupt from tiny patches of skin cells called placodes. A ring of fast-growing cells on the top of the placode builds a cylindrical wall that becomes a bristle.
Reptiles have placodes too. But in a reptile embryo each placode switches on genes that cause only the skin cells on the back edge of the placode to grow, eventually forming scales. In the late 1990s Richard Prum of Yale University and Alan Brush of the University of Connecticut developed the idea that the transition from scales to feathers might have depended on a simple switch in the wiring of the genetic commands inside placodes, causing their cells to grow vertically through the skin rather than horizontally. In other words, feathers were not merely a variation on a theme: They were using the same genetic instruments to play a whole new kind of music. Once the first filaments had evolved, only minor modifications would have been required to produce increasingly elaborate feathers.





The “hair-like” structures [pycnofibres]
are also unique in being preserved in fully three
dimensionally forms as compared to two
dimensional staining or impressions. The hairs 
[pycnofibres] are shown to be complex multi-strand structures instead of single strands or actual hairs. The complex nature
of these filaments most closely resembles natal
down feathers, but apparently without having
 As such, they may represent the earliest
known form of feathers. This implies that such
integumentary structures may have originated
independently among pterosaurs from that of birds,
or that birds and pterosaurs may share a common
ancestor which had evolved this kind of insulation
before fight had been achieved in either group.
Feathers differ significantly from hair in that their multiple strands, the barbs,emanate from a single hollow structure, called the calamus. The integumentary structures seen in Pterorhynchus bear a striking similarity to that of a natal down feather with only the notable absence of having the additional barbules branching from the barbs. This absence is significant all the more because without the barbules, the barbs emanating from a calamus represents the hypothetical “Stage II” structure speculated as being an incipient step in the evolution of feathers (Prum, 1999).
Proto-feathers have been attributed to two pterosaurs which are of similar animals (Ji and Yuan, 2002; Wang, et al., 2002). Even more so, the morphology details seen in Pterorhynchus demonstrate that the integumentary structures of pterosaurs are not like hair, but are analogous to being proto-feathers. Specifically, they resemble natal down feathers where individual filaments are seen to spread from a single follicle.
Therefore, the
individual filaments are not representative of hair,
but are analogous to being the barbs of a feather.
Barbules, if present, cannot be discerned which
suggests that they either did not exist, or that the
limits of preservation have obscured them.
Nonetheless, the morphology of having several
barbs stemming from a short calamus indicates that
the body covering of Pterorhynchus are feather
Without barbules, these structures
would represent the second stage of feather
development as speculated by Prum (1999). The
feather homologues of Pterorhynchus also
demonstrate that a primary function achieved by
these plumulaceous feathers was that of thermal
insulation, and that feathers with a true rachis and
barbs aligned into well developed vanes represent
a derived condition.

Reptiles have placodes too. But in a reptile embryo each placode switches on genes that cause only the skin cells on the back edge of the placode to grow, eventually forming scales. In the late 1990s Richard Prum of Yale University and Alan Brush of the University of Connecticut developed the idea that the transition from scales to feathers might have depended on a simple switch in the wiring of the genetic commands inside placodes, causing their cells to grow vertically through the skin rather than horizontally. In other words, feathers were not merely a variation on a theme: They were using the same genetic instruments to play a whole new kind of music. Once the first filaments had evolved, only minor modifications would have been required to produce increasingly elaborate feathers.

Kellner et al
On the tenopatagium close to the body and on the tail, a third type of fibre with somewhat diffuse edges is observed (figures 3a and ​and44a). Type C fibres can be easily separated from other fibres by their dark-brown colour and their general lack of organization. They are distributed along the body, the tail and the tip of the actinopatagium close to the fourth wing finger phalanx (figures 1​,22 and ​and44c). Sometimes clustering together, they are not found covering the external portion of the plagiopatagium and are apparently rare on the actinopatagium.

As Wang et al. (2002) pointed out, these fibres are best interpreted as structures covering the body, commonly referred to as ‘hair’ or hair-like structures (e.g. Sharov 1971Bakhurina & Unwin 1995). This pterosaur hair, which is not homologous to the mammalian hair (a protein filament that originates deep in the dermis and grows through the epidermis), is here called pycnofibre (from the Greek word pyknos, meaning dense, bushy). The pycnofibres are further formed by smaller fibrils of unknown nature. They were possibly mostly composed of keratin-like scales, feathers and mammalian hair.

Two other Chinese specimens were reported with integumental covering, coming from the same stratum (the Daohugou Bed) as Jeholopterus. So far we have not had the opportunity to examine this material. The first one is a small unnamed anurognathid with extensive preservation of soft tissue, including fibres that have been interpreted as protofeathers (Ji & Yuan 2002). The published pictures show that the soft tissue interpreted as protofeathers is of the same nature as the pycnofibres of Jeholopterus. There is no indication of branching structures that are expected for feather precursors. Although from the phylogenetic position most authors tend to agree that pterosaurs are closely related to dinosaurs (e.g.Sereno 1991Padian & Rayner 1993Kellner 2004a), regarding those structures as protofeathers implies that dinosaurs and closely related taxa must originally have had similar integument covering that in more derived theropod taxa (including birds) eventually developed into feathers. There is presently no such evidence, despite much well-preserved dinosaur material (e.g. Zheng et al. 2009). If other phylogenetic positions regarding pterosaurs as more primitive within archosaurormorphs (e.g. Bennett 1996) or even closely related to protorosaurs (Peters 2000; but see Hone & Benton 2007) are accepted, the case regarding pycnofibres as protofeathers is even less appealing.

For comparison to a dromaeosaur:
Here we describe our observations of the filamentous integumental appendages of the basal dromaeosaurid dinosaur Sinornithosaurus millenii, which indicate that they are compound structures composed of multiple filaments.


On the other hand, dinosaurs only had bristles:

A specimen of the horned dinosaur Psittacosaurus from the early Cretaceous of China is described in which the integument is extraordinarily well-preserved. Most unusual is the presence of long bristle-like structures on the proximal part of tail. We interpret these structures as cylindrical and possibly tubular epidermal structures that were anchored deeply in the skin. They might have been used in display behavior and especially if one assumes that they were colored, they may have had a signal function. At present, there is no convincing evidence which shows these structures to be homologous to the structurally different integumentary filaments of theropod dinosaurs. Independent of their homology, however, the discovery of bristle-like structures in Psittacosaurus is of great evolutionary significance since it shows that the integumentary covering of at least some dinosaurs was much more complex than has ever been previously imagined.

Coelurosaurs were not the only dinosaurs to sport unique body coverings, though. In 2002, palaeontologist Gerald Mayr and colleagues reported on long, bristle-like structures growing out of the tail of Psittacosaurus. This dinosaur was not a theropod, but instead was one of the early ceratopsians ("horned dinosaurs") which were part of a separate radiation of dinosaurs known as ornithischians. Psittacosaurus was about as distantly related to feathered theropods as it was possible to be while still remaining a dinosaur, yet it had tail bristles which were similar in structure to the wispy fuzz of coelurosaurs such as Sinosauropteryx.
It was complemented last year by the announcement of Tianyulong, a different sort of ornithischian that also had a row of bristles going down its back. Since these dinosaurs had bristles structurally similar to the protofeathers of some theropods, it either indicates that such body coverings evolved at least twice within each part of the dinosaurian split, or, as strange as it might seem, such body coverings were a common trait among dinosaurs that was lost in some lineages and modified in others.
The discovery that structurally unique "filamentous integumentary appendages" are associated with several different non-avian dinosaurs continues to stimulate the development of models to explain the evolutionary origin of feathers. Taking the phylogenetic relationships of the non-avian dinosaurs into consideration, some models propose that the "filamentous integumentary appendages" represent intermediate stages in the sequential evolution of feathers. Here we present observations on a unique integumentary structure, the bristle of the wild turkey beard, and suggest that this non-feather appendage provides another explanation for some of the "filamentous integumentary appendages." Unlike feathers, beard bristles grow continuously from finger-like outgrows of the integument lacking follicles. We find that these beard bristles, which show simple branching, are hollow, distally, and express the feather-type beta keratins. The significance of these observations to explanations for the evolution of archosaurian integumentary appendages is discussed.

  • A male turkey grows a cluster of long, hairlike feathers from the center of its chest. This cluster is known as the turkey's beard.
  • On adult males, these beards average about 9 inches long.
  • 10 to 20 percent of hens also grow beards.
  • The longest beard on record is more than 18 inches long.
Concavenator had structures resembling quill knobs on its forearm, a feature known only in birds and other feathered theropods, such as Velociraptor. Quill knobs are created by ligaments which attach to the feather follicle, and since scales do not form from follicles, the authors ruled out the possibility that they could indicate the presence of long display scales on the arm. Instead, the knobs probably anchored simple, hollow, quill-like structures. Such structures are known both in coelurosaurs such as Dilong and in some ornithischians like Tianyulong and Psittacosaurus. If the ornithischian quills are homologous with bird feathers, their presence in an allosauroid like Concavenator would be expected.[3] However, if ornithischian quills are not related to feathers, the presence of these structures in Concavenator would show that feathers had begun to appear in earlier, more primitive forms than coelurosaurs.

Pegomastax africanus
A bizarre dinosaur had vampire-like fangs, a parrot beak and porcupine bristles, researchers say.

More links:

It was complemented last year by the announcement of Tianyulong, a different sort of ornithischian that also had a row of bristles going down its back. Since these dinosaurs had bristles structurally similar to the protofeathers of some theropods



The beard of the wild turkey




There is no evidence that the true dinosaur (eg. tyrannosaurs, compsognathus) bristles, were anything other than simply bristles. There is no evidence that those bristles have any relationship to feathers in the long-bony-tailed feathered creatures such as the dromaeosaurs. 

Monday, January 20, 2014

The development of wing feathers

I had earlier been working with the idea that bird wing feathers developed from actinofibrils in the pterosaur wing membrane.
However, there are other fibres on the pterosaur wing membrane that are close (proximal) to the arm called pycnofibres. (These pycnofibres also cover the body of the pterosaur).
I am now leaning to a refinement, that wing feathers developed from these pycnofibres on the wing membrane.
This is a more straightforward development path for wing feathers and also applies to the development of feathers on the body as well.


Czerkas, S.A., and Ji, Q. (2002). A new rhamphorhynchoid with a headcrest and complex integumentary structures.
"A new rhamphorhynchoid is described with a headcrest that is unprecedented among the long-tailed pterosaurs. The preservation of the headcrest presents significant implications regarding the physical appearance and aerodynamics of all pterosaurs. Also, "hair-like" [pycnofibre] integumentary structures of this pterosaur are shown to be complex multi-strand structures which presents evidence on the origin of feathers and the possibility of a remarkably early ancestral relationship between pterosaurs and birds."

The soft tissue preserved in the holotype of J. ningchengensis indicates that the wing membrane is attached to the body until reaching the ankle. It also concurs with the general notion that the plagiopatagium can be divided into two distinct functional parts: the more distal actinopatagium that contains extensive actinofibrils and a softer, perhaps more flexible, proximal tenopatagium. The Chinese specimen further shows that the plagiopatagium of this pterosaur is formed by an external epidermis, followed by several layers (at least three) with closely packed actinofibrils. Part of the plagiopatagium, particularly the region closer to the body (the tenopatagium), was extensively covered by elongated and thick fibres here called pycnofibres. Individual pycnofibres are formed by fibrils of a different diameter, the nature of which is unknown. Regarding other pterosaur specimens, at least S. pilosus has a similar extensive integumental covering as noted in the original description.

At least some pterosaurs had hair-like filaments known as pycnofibres on the head and body, similar to, but not homologous (sharing a common structure) with, mammalian hair. Though a fuzzy "integument" (natural covering/outer coat) "was first reported in 1831" by Goldfuss,[29] recent pterosaur finds and the technology for histological and ultraviolet examination of pterosaur specimens have provided incontrovertible proof: pterosaurs had pycnofibre coats. Pycnofibres were not true hair as seen in mammals, but a unique structure that developed a similar appearance. Although, in some cases, actinofibrils (internal structural fibres) in the wing membrane have been mistaken for pycnofibres or true hair, some fossils such as those of Sordes pilosus (which translates as "hairy demon") and Jeholopterus ninchengensis do show the unmistakable imprints of pycnofibres on the head and body, not unlike modern-day bats, another example of convergent evolution.[21] The head-coats do not cover the pterosaur's large jaws in many of the specimens found so far.[29]
Some (Czerkas and Ji, 2002) have speculated that pycnofibres were an antecedent of proto-feathers, but the available impressions of pterosaur integuments are not like the "quills" found on many of the bird-like maniraptoran specimens in the fossil record.[29] Pterosaur pycnofibres were structured differently from proto-feathers [quills].[30][14] Pycnofibres were flexible, short filaments, "only 5-7mm in some specimens," and rather simple, "apparently lacking any internal detail aside from a central canal."[29] Pterosaur "pelts" found "preserved in concentrated, dense mats of fibers, similar to those found surrounding fossilized mammals" suggest coats with a thickness comparable to many Mesozoic mammals,[29] at least on the parts of the pterosaur covered in pycnofibres. Coat thickness, and surface area covered, definitely varied by pterosaur species, aside from pycnofibres on the wings, which have never been found.
The presence of pycnofibres (and the demands of flight) imply that pterosaurs were endothermic (warm-blooded). The absence of pycnofibres on pterosaur wings suggests that the coat didn't have an aerodynamic function, lending support to the idea that pycnofibres evolved to aid pterosaur thermoregulation, as is common in warm-blooded animals, insulation being necessary to conserve the heat created by an endothemic metabolism.[29]Pterosaur "hair" was so unique, so obviously distinct from mammalian fur and other animal integuments, it required a new, separate name. The term "pycnofibre", meaning "dense filament", was first coined in a paper on the soft tissue impressions of Jeholopterus by palaeontologist Alexander W.A. Kellner and colleagues in 2009.[14]

Two other Chinese specimens were reported with integumental covering, coming from the same stratum (the Daohugou Bed) as Jeholopterus. So far we have not had the opportunity to examine this material. The first one is a small unnamed anurognathid with extensive preservation of soft tissue, including fibres that have been interpreted as protofeathers (Ji & Yuan 2002). The published pictures show that the soft tissue interpreted as protofeathers is of the same nature as the pycnofibres of Jeholopterus. 

Sordes was a small basal pterosaur from the Late Jurassic (Oxfordian - Kimmeridgian) Karabastau Svita of Kazakhstan.The genus is based on holotype PIN 2585/3, a crushed relatively complete skeleton on a slab. It was found in the sixties at the foothills of the Karatau in Kazakhstan. The fossil shows remains of the soft parts, such as membranes and hair. This was the first unequivocal proof that pterosaurs had a layer of fur [pycnofibres]. The integument served as insulation, an indication the group was warm-blooded, and provided a streamlined flight profile. The hairlike structures (pycnofibres) are present in two main types: longer at the extreme part of the wing membrane and shorter near the body. In the 1990s, David Unwin argued that both types were essentially not hairs but reinforcing fibres of the flight membranes. Later he emphasized that "hair" in the form of fur was indeed present on the body, after the find of new specimens clearly showing this.

In 1998, the discovery of one specimen assigned to P. kochi shed light on the life appearance of Pterodactylus, as it preserved unique soft-tissue traits not present in previous fossil skeletons, including long, bristly pycnofibres (a fur-like body covering known only in pterosaurs) on the neck, details of an urpatagium (hind wing membrane between the legs and tail) that also stretched between the toes as webbing, and a pelican-like throat pouch.[6] An additional specimen, studied using ultra-violet light, revealed even more information on the soft anatomy of Pterodactylus. This specimen (catalog number JME SOS 4784) showed that like many other pterosaurs, Pterodactylus had a striated soft-tissue crest on the skull. Soft tissue impressions also showed unusually long, sharp, and recurved keratin sheaths on its claws. This specimen was also covered in hair-like pycnofibres, with unusually long pycnofibres covering the back of its neck. The remains of a small, hooked beak were preserved at the tips of the jaws between its upper and lower front teeth.[5]


It is likely that feathers evolved from a conical shaped tubercle rather than a plate-like structure. Although the morphology of the presumably most primitive feather is unknown, minimal conditions for its production include the cellular capacity to synthesize feather proteins (=ϕ-keratin) which provides the molecular phenotype, and a follicular mechanism for production and assembly of molecular and gross structure. Once the minimal structural element, presumably recognizable as a barb, existed, a variety of phenotypes followed rapidly. A tubercular growth center of appropriate size could produce a simple barb-like element, with cortex and medulla. This might be recognized externally as a bristle, but need never existed as a separate morphological unit. Rather, if individual placodes gave rise to multiple barb ridges that fused proximally, a structure resembling natal down would have resulted. Subsequent differentiation is controlled by the follicular symmetry, and the feather shape is regulated by barb length. Barb length is directly related to growth period. As feathers appear to grow at roughly similar, size independent rates, shape is determined by individual barb growth periods. The simple fusion of individual proto-barbs would produce a morphology identifiable as natal down. Although this might be the simplest feather structure, others could emerge quickly, perhaps simultaneously, a consequence of the same redundant processing. Once the machinery existed, broad phenotypic plasticity was possible. I constructed a feather phylogram based on these conditions, the fossil record, and ontogeny. I organized the subsequent changes in morphology by perceived complexity. The changes are simply individual responses to similar processes that might be time (when in ontogeny) and space (where on body) dependent.

Also there were filoplumes:

Feathers are equipped with a variety of sensors which are able to detect both position and movements. There are hair-like feathers (filoplumes) associated with most feathers which play a special role as sensory "hairs". Interestingly the information of these sensors is transmitted directly to the cerebellum of the brain which is very important for the control of locomotion.

There are two basic types of feather: vaned feathers which cover the exterior of the body, and down feathers which are underneath the vaned feathers. The pennaceous feathers are vaned feathers. Also called contour feathers, pennaceous feathers arise from tracts and cover the whole body.A third rarer type of feather, the filoplume, is hairlike and (if present in a bird) grows along the fluffy down feathers. In some passerines, filoplumes arise exposed beyond the contour feathers on the neck.[1]

Filoplumes are always situated beside other feathers. They are simple, hairlike structures that grow in circles around the base of contour or down feathers. They usually stand up like hairs, and are made up of a thin rachis with a few short barbs of barbules at the tip. Filoplumes are generally smaller than semiplumes and are on half to three fourths of the length of the covering contour feathers.
The origins of filoplumes is currently under debate. Some ornithologists disagree with the theory that filoplumes are degenerate contour feathers and believe instead that they are sensitive structures that assist in the nerve endings in the follicle. It is therefore quite possible the filoplumes play a key role in keeping contours in place during preening, display, and flight.
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]