Monday, January 27, 2014

Pycnofibres to Feathers

The evidence indicates that pterosaur pycnofibres were Stage II feathers.

Background - How a Feather Develops
Early stages in the development of a feather:

Figure 9. 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).

Figure 10. 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.
Bird Feathers
The [rhamphorhynchoid] “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 [a rhamphorhynchid] 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 homologues. 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.
The wing membranes are thought to have been stiffened by internal fibers, called aktinofibrils (Martill and Unwin, 1989; Wellnhofer, 1987, 1991). The distal end of a wing membrane is preserved in Pterorhychus which shows clear aktinofibrils that are aligned in parallel rows. However, at right angles to the aktinofibrils are minuscule pinnate fibers which though imperfectly preserved, resemble the larger integumentary structures from the body. These tiny tufts on the wings are set close together in rows and the diamond or V-shaped pattern caused from their general outlines are distinctly visible throughout. These tufts extend across the entire width of the membrane. They are also preserved more as three dimensional structures, whereas the aktinofibrils are preserved two dimensionally as stains within the matrix. Several of the tufts show distinct filaments that emanate from a round base, like a calamus. Therefore, the evidence suggests that the external surface of the pterosaur wing was not naked, but covered by tiny pinnate fibers which would have looked much like a fine layer of velvet.
Ji and Yuan (2002) and Czerkas and Ji (2002) regarded
the fibrous integumentary structures of
pterosaurs as potentially homologous with avian
feathers, implying that feathers are basal to the
clade stemming from the last common ancestor
of pterosaurs and birds, but no evidence from the
fossil record indicates such a distribution.
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 [pycnofibre] 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.
Note that there are some difficulties with the Kellner et al position.
First they think they can override the assessment given by the people who actually have the fossil by looking at a picture.
Second, lacking branching structure is not a problem, since there is no branching in Stage II feathers.
Third their assertion that "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" is based on the dino to bird theory and is not relevant to the pterosaur to bird theory.

And interestingly they even find that:
"The published pictures show that the soft tissue interpreted as protofeathers is of the same nature as the pycnofibres of Jeholopterus."
So in essence they are saying that Jeholopterus (another pterosaur) could also have stage II feathers.
VERY interesting material on page 49 and 51. 


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.
In addition, there is current evidence that favors the hypothesis that the initial function of feathers was related to insulation (Chen et al.1998), but no compelling evidence suggests that coelurosaurians were distinctly different from more primitive non-insulated theropods physiologically or ecologically. One possible piece of evidence suggesting a physiological change is miniaturization at the base of the Coelurosauria. It appears that miniaturization characterizes basal coelurosaurians. If this holds true, the development of substantial feathered coverings is likely to be solicited to insulate the small bodies of basal coelurosaurians.
Over the course of the last two decades, the understanding of the early evolution of feathers in nonavian dinosaurs has been revolutionized. It is now recognized that early feathers had a simple form comparable in general structure to the hairs of mammals. Insight into the prevalence of simple feathers throughout the dinosaur family tree has gradually arisen in tandem with the growing evidence for endothermic dinosaur metabolisms. This has led to the generally accepted opinion that the early feather coats of dinosaurs functioned as thermo insulation. However, thermo insulation is often erroneously stated to be a likely functional explanation for the origin of feathers. The problem with this explanation is that, like mammalian hair, simple feathers could serve as insulation only when present in sufficiently high concentrations. The theory therefore necessitates the origination of feathers en masse. We advocate for a novel origin theory of feathers as bristles. Bristles are facial feathers common among modern birds that function like mammalian tactile whiskers, and are frequently simple and hair-like in form. Bristles serve their role in low concentrations, and therefore offer a feasible first stage in feather evolution.
  • 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.
Sawyer et al. (2003b:27) observed that in turkeys (Meleagris),
beard bristles, which are structurally similar
to the fibrous structures identified as feathers in
coelurosaurs, display “simple branching, are hollow,
distally, and express the feather-type β keratins,”
even though they are not feathers.
Sawyer et al. (2003b:30) argued that
the present study raises the possibility that [the]
“filamentous integumentary appendages” [of
coelurosaurs] may more closely resemble the
bristles of the wild turkey beard, and may not
depict intermediate stages in the evolution of
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:
The beard of the wild turkey
Sinosauropteryx coloured "feathers" debunked

There is no evidence that the true dinosaur (eg. tyrannosaurs, compsognathus) filaments, were anything other than simply bristles. There is no evidence that those bristles have any relationship to feathers in the long-bony-tailed feathered flying creatures such as the basalmost paraves.
Believe it or not, we now know that some ornithischians had feathers as well. Two incredible fossil discoveries prove this. First, there is a well-preserved specimen of the small horned dinosaur Psittacosaurus (an early cousin of Triceratops) with a series of hair-like bristles running down the tail. Second, there is a beautiful specimen of the small, fast-running Tianyulong (a heterodontosaurid ornithischian) with similar bristles covering the neck, back and tail.
These bristles aren't exactly the same as the feathers of living birds. In fact, they look quite different. They are more like the quills of a porcupine: long, perhaps hollow, structures that stand up straight, forming something that would have looked like a Mohawk.
They did not have vanes, or barbs, or barbules, or the other components of the characteristic ‘quill pen’ feathers of living birds.
They were not used for flight, but were more likely used for display: to intimidate rivals, impress mates, or differentiate one species from another.
But although these bristles are different from the feathers of living birds, scientists are confident that they are essentially the same type of structure. In other words, they are comprised of the same material and are controlled by the same basic genes. In more technical terminology, they are 'homologous' to feathers.
The bristle-like structures of ornithischians are probably primitive versions of feathers. The earliest dinosaurs probably evolved simple feathers like this for display or to regulate body temperature, and later they were modified into more elaborate structures that were useful for an entirely new purpose: flight.

For reference:

Figure 13. Hypothesized stages I–III of feather evolution. Stage I of this model assumes an unbranched, hollow filament, which developed from a cylindrical invagination of the epidermis around a papilla. In stage II, a tuft was formed by fusion of several filaments at their bases. Stage III represents the formation of a central rachis and development of serially fused barbs (III A) — to which, at a slightly later stage (III B), secondary barbs (barbules) were added. The two other stages, IV (bipinnate feathers with elaborate barbules and a closed vane) and V (the asymmetrical flight feathers of modern flying birds), are not shown (From: Sues 2001).
This developmental model provides functionally neutral criteria to evaluate the homology between
avian feathers and other fossil integumental structures.
The model predicts that feathers with single
unbranched keratin structures (stage I) or many
unbranched keratin filaments (stage II) preceded
the origin of the branched or pennaceous feather.
From my direct observations of the two specimens
of Sinosauropteryx (Chen et al., ’98), the integumentary
structures appear to consist of unbranched
filaments about 20 mm long.
Reports of
the filamentous structures of Beipiaosaurus [a
therizinosaur] indicate that they are 50–70 mm long and possibly
branched. It is uncertain whether the reported
branches in both species are bifurcations of single
structures or the merely the appearance of branching
created by closely adjacent, separate unbranched
filaments within the specimens. However,
the length and position of these structures in
Beipiaosaurus demonstrate convincingly that these
were not internal integumental structures.
All described feathers in nonavian theropods are composite structures formed by multiple filaments. They closely resemble relatively advanced stages predicted by developmental models of the origin of feathers, but not the earliest stage. Here, we report a feather type in two specimens of the basal therizinosaurBeipiaosaurus, in which each individual feather is represented by a single broad filament. This morphotype is congruent with the stage I morphology predicted by developmental models, and all major predicted morphotypes have now been documented in the fossil record. This congruence between the full range of paleontological and developmental data strongly supports the hypothesis that feathers evolved and initially diversified in nonavian theropods before the origin of birds and the evolution of flight.
Chen et al., (1998) described Sinosauropteryx as a compsognathid dinosaur. The structures are essentially filaments and have “no structures showing the fundamental morphological features of modern bird feathers, but they could be previously unidentified protofeather which are not as complex as either down feathers or even the hair-like feathers of secondarily flightless birds.” (Chen, et al., 1998). The structures are clearly epidermal in origin, unbranched, probably tubular, and may cover most of the body.

Colored porcupine bristles:

Monday, January 20, 2014

The development of wing feathers

There are fibres on the pterosaur wing that are close (proximal) to the arm called pycnofibres. (These pycnofibres also cover the body of the pterosaur).


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 pycnofibers 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.[35]Pterosaur pycnofibers were structured similarly to theropod proto-feathers.[18] Pycnofibers were flexible, short filaments, "only 5-7mm in some specimens" and rather simple, "apparently lacking any internal detail aside from a central canal".[35] 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,[35] at least on the parts of the pterosaur covered in pycnofibers. The coat thickness, and surface area covered, definitely varied by pterosaur species.
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]

Tuesday, January 14, 2014

Mandibular Fenestra

Here is an accumulation of info about mandibular fenestra. Since this character varies within the various groups we cannot establish ancestry based on it.
Right, so back to the [mandibular] fenestra itself, what’s going on? Given that the evolution of pterosaurs is essentially one of ever lighter constructions and better flight capabilities, one would expect a hole to be kept as long as a possible. Getting rid of any excess bone, no matter how small will make a bit of a difference to the mass, and lowering it is always good so one would expect the fenestra not just to be retained in pterosaurs, but in fact to get bigger, not disappear.
The obvious answer to this is that pterosaurs actually reduced their jaws as a whole making the bones relatively low and thin. Sticking a hole in a very thin set of bony plates might make them incredibly weak, and so if you close up that fenestra you can reduce the weight of the jaw overall and keep the jaw relatively strong, than keeping a normal jaw and putting a hole in it. So it makes sense for pterosaurs to close it up, but in that case how? There is absolutely no evidence of it anywhere.
In 2003 pterosaur supremo Peter Wellnhofer described an isolated jaw of the basal (ish) pterosaur Eudimorphodon from the Late Triassic of Austria that had, yes, wait for…wait a bit longer…a mandibular fenestra.
This [mandibular fenestraat least suggests that this really is a hang over from the ancestral archosaurian condition and that it was then lost several times in various pterosaur clades, though probably quite quickly given how rare it seems to be.
All taxa recovered as basal avialans by our analysis, such as the scansoriopterygids, Sapeornis and Jeholornis, resemble oviraptorosaurs and to a lesser degree therizinosaurs4 but differ from deinonychosaurs including archaeopterygids in having such cranial and dental characteristics as a dorsoventrally high premaxilla that is significantly larger than the maxilla, a dorsally positioned external naris, a dorsoventrally tall antorbital fossa, a jugal with a relatively vertical postorbital process and a long quadratojugal process, a quadrate with a large pterygoid ramus, a relatively long parietal, an anteriorly downturned and strongly dorsally convex mandible, a large external mandibular fenestra, and enlarged anterior teeth. Some of these features are optimized by our analysis as synapomorphies of a clade containing the Oviraptorosauria, the Therizinosauroidea, the Avialae and the Deinonychosauria, but are lost in the last group.
367. External mandibular fenestra, size: small (0) or large (1).
It [Archaeopteryx] does not appear to have had a mandibular fenestra
Elsewhere within Theropoda, mandibular fenestrae are absent in compsognathids but are otherwise ubiquitous in non-avian theropods and only absent in certain avian lineages [9–11]
Pterosauria, a successful clade of extinct flying vertebrates, possesses a radical body plan that offers few clues about their origin and closest relatives. Whereas most researchers hypothesize an origin within Archosauria as the sister-group to Dinosauromorpha, others favor a position among non-archosauriform archosauromorphs. Here we present evidence that supports a placement within Archosauriformes: the presence of an external mandibular fenestra in two basal pterosaur taxa, Dimorphodon macronyx and a specimen referred to Eudimorphodon cf. ranzii (= ‘Seefeld Eudimorphodon’; BSP 1994 I 51). Furthermore, the arrangement of the mandibular bones surrounding the mandibular fenestra and the presence of a posterior process of the dentary that laterally overlaps the angular in the mandible of Dimorphodon and BSP 1994 I 51 are identical to those of Erythrosuchus, Euparkeria, and Archosauria.
When mapped on a cladogram, presence or absence of an external mandibular fenestra in basal pterosaurs possibly indicates that the feature is primitive for Pterosauria but later lost. The presence of an external mandibular fenestra, along with morphological evidence elsewhere in the body of pterosaurs (serrated teeth, antorbital fossa present, fourth trochanter on the femur present), supports a placement of Pterosauria within Archosauriformes and is consistent with a position within Archosauria.

Pterosaurs have been cited as lacking a lateral (or external) mandibular fenestra (Bennett, 1996). A lateral mandibular fenestra is clearly absent in the holotype of Eudimorphodon (Wild 1978). However, a mandibular fenestra is clearly present in a specimen referred to Eudimorphodon sp. (BPS 1994 I 51; Wild, 1993) and Dimorphodon (BMNH R1034) (S.J.N., personal obs.). 

Unlike most archosaurs, which have several openings in the skull in front of the eyes, in pterodactyloid pterosaurs the antorbital opening and the nasal opening was merged into a single large opening, called the nasoantorbital fenestra. This likely evolved as a weight-saving feature to lighten the skull for flight.
Darwinopterus, like its closest relatives, is characterized by its unique combination of basal and derived pterosaurian features. While it had a long tail and other features characteristic of the 'rhamphorhynchoids', it also had distinct pterodactyloid features, such as long vertebrae in the neck and a single skull opening in front of the eyes, thenasoantorbital fenestra (in most 'rhamphorhynchoids', the antorbital fenestra and the nasal opening are separate).[5]

In most 'rhamphorhynchoids', the antorbital fenestra and the nasal opening are separate. 
In the Monofenestra pterosaurs the nasal opening was merged into a single large opening, called the nasoantorbital fenestra.
The Monofenestrata are an unranked group of pterosaurs that includes the family Wukongopteridae and the suborder Pterodactyloidea.[1]
The clade Monofenestrata was in 2009/2010 defined as the group consisting of Pterodactylus and all species sharing with Pterodactylus the synapomorphy, shared derived trait, of an external nostril confluent with the antorbital fenestra, the major skull opening on the side of the snout.
An antorbital fenestra (plural: fenestrae) is an opening in the skull that is in front of the eye sockets. This skull character is largely associated with archosaurs, first appearing during the Triassic Period. Among extant archosaurs, birds still possess antorbital fenestrae, whereas crocodylians have lost them.
In theropod dinosaurs, the antorbital fenestra is the largest opening in the skull. Systematically, the presence of the antorbital fenestra is considered a synapomorphy that unites tetanuran theropods as a clade