New Siberian ornithischian and the (over) feathering of dinosaurs…again.

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Artist's impression of the fleshed out Kulinda specimen. Image by Andrey Atuchin
Artist’s impression of the fleshed out Kulinda specimen. Image by Andrey Atuchin

Well, as is often the case, this post is a bit late to the party, despite starting early. Unless you have been living under a rock (or don’t care that much about dinosaurs), you have probably heard about the discovery of a small ornithischian from Siberia, Russia that apparently sports feathers as well as scales on its body. It’s a crazy half-and-half animal that has given many the green light for making all dinosaurs feathery.

As is often the case with these studies I am writing to urge caution against taking things too far, if just so there is some voice of dissent out there in an internet fully of trigger-happy feather reconstructions.

Let’s start from the beginning.

This story has been cooking for quite some time. It all started in early 2013 during the abstract submission process for the Society of Vertebrate Paleontology meeting later that year. Pascal Godefroit and colleagues submitted an abstract on the fauna from a new fossil locality in Siberia, Russia known as the Kulinda valley. In the abstract (and title) Godefroit announced the discovery of a new neoornithischian that was alleged to preserve scales along the tail and legs, along with branched pennaceous (i.e., true) feathers on the body. Despite the SVP meeting being eight months away the buzz around this new taxon was already spreading like wildfire across the dinosaur paleo community. Many paleo-artists used this new taxon as further justification for feathering all dinosaurs.

The kicker, however, was that this new species did not see the light of day in 2013. During the SVP meeting, on the day of his talk, Godefroit had to cancel due to a leg injury he had sustained a few days earlier. Up until now there had been no details (not even a blurry picture) to indicate that this “feathery” ornithischian was real. There was further strangeness about this new locale. A few months prior to the abstract announcement news reports were coming out of Russia talking about a ‘Dinosaur Pompeii.’ These reports all referred to the Kulinda valley locality and its amazing preserved fauna, but they also talked about how this locality had been prospected in for the past two years. Yet despite all that time, not a single fossil had been described from there. News reports talked about the amazing preservation of scales and feathers in dinosaurs and other fauna. Thus it seems strange that such a high-impact discovery such as the Kulinda valley would take this long to have anything published. Having the talk about these fossils canceled at the last minute at SVP only further added suspicion to these finds. Our first look at the fossils of the Kulinda Valley (short of blurry news reports) finally came in early 2014 when Vladimir Alifanov wrote a brief communication that detailed the geological setting of the region. It is worth noting that even this short communication took two years to get published (it was originally accepted back in 2012). That is a remarkably long delay for any journal, and one that only further raised suspicions about what all was going on with these Russian fossils (more on this below).

The Kulinda valley is located in the Chernyshevskii district near the city of Chita in Siberia, Russia. According to Alifanov (2014) the strata in the Kulinda valley has been associated with the Ukureisk Formation. The exact age of this deposit is contentious and has ranged from Middle Jurassic to Early Cretaceous (Alifanov 2014). The current, middle ground, assessment of the Ukureisk Formation being Late Jurassic in age is based on the insect assemblage within the formation. As it currently stands the age of these rocks is in flux.  The paper does discuss the fauna of the valley, but does not go into much detail on anything.  The only figure to show some of the fossils is figure 2. This figure shows the jaw of an ornithischian (largely as a poorly preserved impression), the caudal vertebrae of a “theropod” with associated scales (apparently, though the quality of the photos does not allow for much discernment) and lastly a shot of the alleged bristles on an ornithischian. In the paper Alifanov refers to these structures as “bristle-like skin derivatives”. The figure only shows the “bristles”. No skeletal association can be discerned. This was done on purpose, apparently to tease at the find more than anything else. As I mentioned earlier, the photos are extremely poor quality (approximately 538 x 401 pixels, and in black and white), so there is not much that can be ascertained from them.

However now, one year after the SVP abstract, we have the release of not one, but three papers on this “feathery” creature, as well as three different names for it.

Saveliev, S.V., Alifanov, V.R. 2014. A New Type of Skin Derivatives in Ornithischian Dinosaurs from the Late Jurassic of Transbaikalia (Russia). Doklady Biol. Sci. Vol. 456:182–184.

Alifanov, V.R., Saveliev, S.V. 2014. Two New Ornithischian Dinosaurs (Hypsilophodontia, Ornithopoda) from the Late Jurassic of Russia. Paleontological Journal (Russian Edition). Vol. 4: 72–82.

Godefroit, P., Sinitsa, S.M., Dhouailly, D., Bolotsky, Y.L., Sizov, A.V., McNamara, M.E., Benton, M.J., Spagna, P. 2014. A Jurassic Ornithischian Dinosaur from Siberia with both Feathers and Scales. Science. Vol. 345(6195):451–455.

What’s my name again?

Faux NMMNHS bulletin
Remember this mess?

Why three papers? Well it turns out that this Kulinda valley ornithischian was a hot-ticket item. Astute readers no doubt noticed that the first two papers have a completely different authorship from the third paper. To explain the reason behind it I’ll turn to a quote from Pascal Godefroit in a Facebook post (turned DML post) from a few weeks back:

These are based on specimens that Alifanov stole in Chita, and that are illegally housed in PIN in Moscow, but belonging in fact to the Institute of Natural Resources, Ecology and Cryology (Chita).

So it would appear that we have another Aetogate on our hands here. Alifanov and Sergei Saveliev seem to have intentionally claim jumped Godefroit et al. with regards to this specimen. Further confusing matters is the fact that Alifanov and Saveliev described two different ornithischian taxa where Godefroit et al. only saw one. So this new ornithischian is either Kulindadromeus zabaikalicus, Kulindapteryx ukureicaDaurosaurus olovus, or some combination thereof. Following the standard rules of taxonomic nomenclature, the first published work out the gate gets priority. This means that the new ornithischian would technically be K. ukureica and D. olovus. However, if the analysis is bad (i.e., the material is not diagnostic) then it is possible that the names could be sunk as nomina dubia. This could free up K. zabaikalicus for use, but the fact that it has come out weeks after the description by Alifanov and Saveliev means that it might get sunk as a junior synonym of the first two names and thus could get sunk with them both. This has the potential to be a huge taxonomic nightmare and will likely require a formal petition to the International Coalition for Zoological Nomenclature (ICZN) to fix.

Well that, or everyone will just choose the name they prefer and just ignore the others, basically working it out via a de facto consensus. Either way these specimens are now viewed as tainted, which could greatly affect their research potential (just look at how much has been done with the allegedly filamented Psittacosaurus, which was also obtained via illegal means).

For the purpose of this blog post I am going to refer to these specimens as the Kulinda valley ornithischian.

 

Bristles, feathers and scales, oh my!

Though the taxonomic validity (biological bookkeeping) is likely to remain contentious for some time, the actual structures on this animal can be discussed much more easily. Our first real information on these structures came from Alifanov and Saveliev 2014. Here, in between discussing the taxonomic affinities of the animals in question, the authors set about describing the integument. Since this came from a journal that was published in Russian, the following translation by Dave Černý (posted here) may not be 100% accurate to the original text. Still it is a hell of a lot better than what Google translate provides, and the gist can be fully grasped.

[NOTE: An English version of Alifanov and Saveliev has since been published. Comparing the quoted material below with the English translation reveals little differences. The only major difference was the changing of ‘scutes’ into ‘plates’. As such I have left Dave’s transcription below and added the English-language version of Alifanov and Saveliev to the references section.]

Three different interpretations of the integument distribution in the Kulinda ornithischian. Skeletals adapted from figure 4 of Alifanov and Saveliev 2014 (top two) and figure 1 of Godefroit et al. 2014 (bottom).
Three different interpretations of the integument distribution in the Kulinda ornithischian. Skeletals adapted from figure 4 of Alifanov and Saveliev 2014 (top two) and figure 1 of Godefroit et al. 2014 (bottom). Click to enlarge.

From Alifanov and Saveliev 2014 (translated. bold type mine):

The impressions of integument in PIN 5435/57 are located close to the humerus and are concentrated in front of it (mostly at its proximal end) and behind it, where they are represented by [skin] derivatives of two types. One of them takes the form of oval scutes or scales, the other one [consists of] bristle-like structures. In this specimen (Plate XI, Fig. 4), around the posterior margin of the humerus, the “bristles” lie atop the scutes. However, some of the “bristles” appear to be extensions of the scutes. If so, the “bristles” can be either the result of scale splitting or the consequence of their differential growth. Judging by the arrangement of the areas [of bristles] in front of and behind the humerus, the described type of integument evenly covered the surface of the forelimb, and perhaps of the whole body. Interestingly, with regard to the length of the bristles, this fossil differs from the one that is described below.

In PIN 5435/56, the existence of which has played a role in the choice of the name for Kulindapteryx[Kulinda wing]ukureica gen. et sp. nov., long bristle-like structures are present next to the bones of the forelimb (the humerus is preserved on the main slab and the radius on the counterslab), forming an extensive halo in the matrix similar to wing impressions of fossil birds.

The preservation of the bones of the last specimen makes even an approximate systematic placement impossible. However, considering that two length variants of bristle-like structures on the same bones correspond to two species of hypsilophodontids, it is not ruled out that in Kulinda, different species of hypsilophodontids had “bristles” of different length. If so, it would be in agreement with the pattern of predominance of Daurosaurus olovus gen. et sp. nov. remains in the locality, which we have established, and judging from the distribution of specimens with impressions of bristles of different length, it is possible to tentatively assume that it was the latter species that had the short-bristled type of scales. In that case, it remains to infer the presence of the long-bristled type of integumental appendages for Kulindapteryx ukureica gen. et sp. nov.

The authors appear to allude to knowledge of many more specimens from the Kulinda valley. As mentioned above, their decision to separate these two skeletons into two different genera is questionable, as is their assignment of these taxa to Hypsilophodontidae (apparently the diagnostic characters for anything short of Neornithischia, just aren’t preserved). It’s also worth noting that the authors refer to slabs and counterslabs. This tells us that we are looking at flat, “pancake” fossils similar to the types of fossils that pervade Liaoning, China.

However the most interesting point of this entire description comes from the association of the scales with the bristles. As I have mentioned previously on this site (extensively), our knowledge of feather evolutionary development strongly suggests that feathers and scales cannot coexist. At the very least it appears to be extremely difficult to do so. The likely re-evolution of scales in birds (Dhouailly 2009) further suggests that the evolution of feathers was a punctuated event that was likely caused by changes in the developmental mechanisms that form scales. So the presence of bristles that “lie atop the scutes [plates]” strongly suggests that what we are looking at in these ornithischians are not protofeathers but some entirely different type of integument. Unfortunately the authors images of these specimens are just about as piss poor as the previous paper (Alifanov 2014), making it extremely difficult to determine what these structures look like (though plate XI-4 does have some promise). The authors do provide a skeletal drawing of the specimens indicating that the bristly structures covered the entire body (contra Godefroit et al. 2014. However, look at how much was preserved vs. interpretation [see above image]). The exact structure of these bristles is further elaborated on in Saveliev and Alifanov 2014.

Integumentary remains of ornithischian dinosaurs are usually represented by bristle-like outgrowths, which are arranged on the matrix surfaces either chaotically or in bunches or regular groups of varying density. Some samples show the basal portion of the “bristles” in the form of a small plate with a rounded proximal end. One plate can give rise to several outgrowths of various lengths. We propose to call these integumentary structures “bristle-like scales.” No such structures have previously been found in association with ornithopod or ornithischian remains….

…. Samples with integumentary impressions most frequently have scale with three or four “bristles.” The next most common are scales with five bristles, in which the central “bristle” is usually longer than the four lateral ones. The six, seven, and eight “bristle” scales are less common… In some samples, long “bristles” are observed as a dense entangled pattern. — Saveliev and Alifanov 2014

The authors provide a series of pictures to illustrate their description of the bristle-like scales. Unfortunately there are no pictures of the structures on the associated specimens (likely due to the illicit nature of their acquisition). Nonetheless the anatomical description of the bristle formation is extremely interesting and is suggestive of a new scale-type. Unlike feathers, these structures actually appear to form by a “fraying” and differential growth of the distal end of the scale. That this “fraying” is so varied may explain why the original Godefroit et al. abstract referred to these as “compound feather-like structures“.

Saveliev and Alifanov go further in their description, talking about the pigmentation associated with these structures and what that may mean for feather development.  In particular:

Usually, the scales are pigmented similarly and relatively uniformly along the entire length. Portions of preserved dermal fields were formed only from compactly arranged dark and short-bristle scales. Dark colored “bristles” occur in isolation or in bunches of varying appearances and size. The uniform dark color is characteristic of scales possessing five or fewer “bristles.” Less commonly found are weakly segmented “bristles” connected with the dark-colored basal ends of the scales. Initial parts of the bristle-like structures in such scales are also dark-colored (Fig. 1). A two color pattern is observed mainly in six-to-eight-bristle scales. If the pigment border is taken to be a marker separating the introdermal and extrodermal zones of scales, it appears that some scales and the bases of the bristles are submerged. Thus, bunches of “bristles” extending from the skin could be connected to each other at their bases inside the derma. It is possible that a similar structure could occur on the dorsal end of the tail of the bipedal horned dinosaur Psittacosaurus, judging from a skeleton with skin impressions from the Lower Cretaceous of China.

It’s an interesting interpretations, but there isn’t really much reason to suppose this darker pigmentation should represent the epidermal outline. If so that would make these scales dermal structures more akin to the scales of fish and amphibians. These structures are strange enough on their own without having to make them any stranger. This is not the first time that Saveliev and Alifanov have made questionable interpretations of data. A similarly strange interpretation of ornithopod neuroanatomy was made by these authors two years ago wherein they interpreted fossae in the endocast of Amurosaurus riabinini as being bulbs for the vomeronasal organ (Saveliev et al. 2012) despite evidence that strongly supports loss of this structure in Archosauria (Senter 2002). I suspect that part of the reason for the authors argument for a dermal structure to these scales comes from the part later in the paper where they attempt to homologize these structures with the filaments seen in advanced coelurosaurs. However, it is done in a very slipshod manner, as evidenced by a total lack of citations in regards to the evolutionary development of feathers. The paper itself is extremely light on citations anyway (six total), further suggesting that these authors were attempting to beat Goldefroit et al. to the punch.  So no, I don’t buy their case for dermal scales with epidermal bristles coming off them.

Now Godefroit et al. have, by far, the most in-depth study on these specimens (even if most of it resides in the supplemental section). The Kulinda specimen description is based on six different skulls along with hundreds of disarticulated skeletons. The species is known from two monospecific bonebeds. That they were unearthed by paleontologists and not bought off a seedy black market, tells me that we are dealing with the real deal and not some potential forgery. Godefroit et al. argue that the preserved bristles are feathers. Not just filaments, but full-on feathers. Such an interpretation seems rather bold given that their description of the bristles is in near complete agreement with that of Saveliev and Alifanov. The one notable difference is that Godefroit et al. are less willing to call the plate-like structures that the filaments are coming off of, scales.

Kulindadromeus also shows compound, nonshafted integumentary structures along the humerus and femur… These occur as groups of six or seven filaments that converge proximally and arise from the central regions of a basal plate….Whether the basal plates represent modified scales or calamus-like structures remains unclear and requires further investigation.

Interpretations of these compound filamentous structures. Images adapted from plate XI-4 of Alifanov and Saveliev 2014 (top left), figure 1 of Saveliev and Alifanov 2014 (top right), and figure S9-B, C of Godefroit et al. 2014.
Interpretations of these compound filamentous structures. Images adapted from plate XI-4 of Alifanov and Saveliev 2014 (top left, red outline of forelimb bones for ease of contrast), figure 1 of Saveliev and Alifanov 2014 (top right), and figure S9-B, C of Godefroit et al. 2014.

The authors also discuss a third filamentous structure observed on the Kulinda ornithischian. This was a series of ribbon-like structures located near the proximal tibia. They are longer than the monofilaments and the compound filaments. They are also thicker, resembling leaves, almost (Godefroit et al. 2014 figure 3H). Interestingly, the only other integumentary impression like this are the pseudofeathers of the archosauromorph Longisquama insignis. However, unlike L. insignis, these structures laid close to the bone surface, and thus, may not even be integumentary, but some type of subdermal structure.

Half and half?

Along with these unique filamentous structures is their strange distribution. Monofilaments are found along the head, neck and thorax. The femur and humerus house the strange compound structures. The forearm, leg (tibia and fibula) and tail, meanwhile, contain scales. The scales range from tuberculate scales reminiscent of the scales seen in hadrosaurs (Godefroit et al. argue that they look more like bird scales, but as hexagonal structures I just don’t see the resemblance) to slightly overlapping scales on the tail that look similar to the belly scutes of crocodylians. Keels on the dorsal scales of the tail, along with their different colouration, makes them seem like the dorsal scutes of some turtles. So we have a critter that seems to have a filamentous core with scaly extremities. The compound structures look like they may have been used for display, but their location and orientation make it a bit difficult to tell for certain. Interestingly, as these compound sections approach the distal humerus they appear to grade into the scales of the forearm (Godefroit et al. 2014 figure 4A). One of the author’s misgivings about calling these “basal plates” scales was their rather spread out nature. They neither overlap nor abut each other. However, as these compound structures approach the forearm this splaying starts disappearing and these “basal plates” end up looking very similar to the scales on the forearm. That said, once one reaches the humeroulnar joint its not really possible to distinguish individual scales anymore.

Some gecko lineages such as this bronze gecko (Ailuronyx tachyscopaeus) are capable of "wiggling out of their skin" when attacked by a predator. Was the Kulinda ornithischian doing something similar? Photo by Henrik Bringsøe
Some gecko lineages such as this bronze gecko (Ailuronyx tachyscopaeus) are capable of “wiggling out of their skin” when attacked by a predator. Was the Kulinda ornithischian doing something similar? Photo by Henrik Bringsøe.

As far as I know such a strange arrangement of integument is unheard of in the modern world, which makes it hard to determine what the point of such strange structures was.  The typical go to answer of ‘insulation’ doesn’t really make much sense. Yes, the animals were rather small at their (presumed) adult size, and thus would benefit from some kind of insulation better than larger dinosaurs, but then so was the scaly Juravenator starki, as were the babies of all known scaly dinosaurs. Looking at the life reconstructions of the animal one can see a definite mammal-centric vibe to the reconstructions, with tucked in forelimbs and a thin tail. However, as previous anatomical studies (Allen et al. 2009, Persons and Currie 2011) have indicated, dinosaurs were ‘rear-wheel drive’ animals (Hotton 1994) that received most of their leg retracting power from the large caudofemoralis muscles located on the tail. This would have given the Kulinda ornithischian a larger, thicker tail. One would suspect that, if the primary function of these structures was body-heat maintenance, then at least the proximal part of that tail would have been covered in fuzz. Yet scales seem to take over immediately caudal to the hips. Another problem comes from the inferred paleoenvironment for the Kulinda valley. It was believed to have been a swamp at the time. That’s hardly a place where an animal has to worry about keeping warm. The rather diffuse coverings of filaments would also suggest that body-heat maintenance may not have been the primary function of these structures. Were they anti-predator defenses? Perhaps, but it would seem strange that the extremities were not also covered in filaments too, as these are more likely to meet the business end of a predator’s mouth. Then again, having a fuzzy core could reduce the damage inflicted from getting a direct hit by a predator. Perhaps these structures were used in a similar vein to that of some gecko species in which the skin sloughs off very easily, allowing for a quick escape. Of course all of these are just speculations based on no evidence. Without detailed information of the ultrastructure of these filaments there really isn’t much that can be said about their function right now.

What the Kulinda ornithischian means for Dinosauria

Last year it only took an abstract to get many in the feathered-dinosaur movement (the self-described ‘Feather Nazis’) overly excited and insistent on covering every dinosaur species with a thick layer of plumage (the so called ‘enfluffening‘). Now that the beast is actually out what are its implications for the rest of Dinosauria?

If these filaments were homologous and thus ancestral to Dinosauria. Blue circles indicate how often scales would have to re-evolve. Click to enlarge.

If filaments evolved convergently in Dinosauria. Red dots indicate the amount of times filaments would have to evolve. Click to enlarge.

First let’s start with where the Kulinda specimens show up in the family tree of Dinosauria.

As is often the case, the answer is not that clear cut. Alifanov and Saveliev argued for placement within Hypsilophodontidae. However they provided no phylogenetic analysis to back this up. Godefroit et al. did better with their parsimony analysis. Their results suggested that the Kulinda specimens were basal neornithischians most closely related to Cerapoda (hadrosaurs and ceratopsians). However, the authors pointed out that their most parsimonious trees still had very little support for their topology. In fact Bremer support and bootstrap values were so low that the authors didn’t even report them for the node that the Kulinda specimen was in (Bootstrap proportions lower than 50 and Bremer decay values lower than 2 are not indicated — Godefroit et al. 2014 supplement). Although the authors nested these specimens deeper in the phylogenetic tree of Ornithischians than Alifanov and Savaliev did, the statistical support for this position was so low that we really can’t say for certain where these critters belong.

What that means is that this critter is going to bounce around for awhile until a better description of this and other ornithischians is put out. Judging from the shape of its skull (especially the large palpebrals) it is tempting to stick it either in Hypsilophodontidae or Heterdontosauridae, near Tianyulong confuciusi. The skulls are a bit different in their dentition, though the enlarged dentary canine of T. confuciusi is not seen in the Kulinda specimen, that portion of the skull is also not preserved. Judging from the description, it looks like the Kulinda specimen shares many traits in common with Heterodontosaurus and Hypsilophodon, but also plenty of things that are different. This paper illustrates just how little we know about ornithischian relationships in comparison to theropods. Still, if I were to predict placement, I would not be surprised if the Kulinda specimen wound up grouping closely with Tianyulong confuciusi, either as a heterodontosaurid, hypsilophodontid, or as something exclusive of the two.

 

On to the $64,000 question: Does the Kulinda specimen favour a “feathers on everything” approach to Dinosauria? Looking at the above two images we can see that the addition of the Kulinda specimens doesn’t really change the distribution of filaments within dinosaurs. Most dinosaurs are still scaly and it is still most parsimonious to assume that these structures evolved separately in ornithischians and advanced coelurosaurs.

Unfortunately neither group of authors took this position and instead opted for pushing “feathers” back to the base of Dinosauria, if not Ornithodira. Both groups argue for either homology of these filaments with feathers, or for just calling them feathers outright.

…bristle-bearing scales should be considered an important stage of skin evolution in dinosaurs, showing the transition from a simple scale to a birdlike feather….The above interpretation makes it possible for Ornithischia to be included in the concept of “Feathered dinosaurs.” — Saveliev and Alifanov 2014

The presence of both simple and compound filamentous structures in Kulindadromeus…supports the hypothesis that the integumentary structures in Ornithischia, already described in Psittacosaurus and Tianyulong, could be homologous to the“protofeathers” in non-avian theropods. In any case, it indicates that those protofeather-like structures were probably widespread in Dinosauria, possibly even in the earliest members of the clade. — Godefroit et al. 2014

Both groups appear to have ignored the extensive evolutionary developmental studies that have been performed on feather formation. We now have a pretty good idea of how feathers formed. In no case do feathers form from the distal portions of completed scales, which is what the Kulinda specimens seem to be showing.  At the very least, they don’t form from a “basal plate.” Feathers form during the formation of the embryonic epidermis, in particular the periderm and subperiderm. At this stage scales and feathers are the same thing (and don’t look like much). Changes in developmental timing, determined by a host of biochemical factors such as bone morphogenetic protein (BMP) and sonic hedgehog (SHH)  determine whether a feather will form or if a scale will form and then slough off the embryonic periderm (Sawyer et al. 2003, Alibardi et al. 2006). Dermal-epidermal recombination studies, in which the epidermis of one integument forming region is grafted to the dermis of another, has succeeded in achieving  “feathery scales” (Rawles 1963). However these should not be looked at as evidence that structures could, or did exist in the past, as they involved heavy tissue recombination. The purpose of these studies was to determine which portion of the skin (dermis or epidermis) was responsible for inducing which type of integument. Similar studies (Kato 1969, Dhouailly 1973) have succeeded in having mammalian hair grow on the dermis of chickens or feathers grow from the ectoderm of the extraembryonic fluids (chorion). Studies such as these reveal the mechanisms behind integument formation; they don’t recover lost phenotypes.

It is worth noting that one of the authors on the Godefroit et al. paper was Danielle Dhouailly, an evo-devo researcher who has done extensive work on the origin and formation of feathers. Unfortunately it seems as if Dhouailly’s contribution to the paper was mostly as a consultant for feather formation in birds rather than as an analyst of the Kulinda specimen’s structures. Thus the hope that this would be the first ornithischian to have its integument vetted have been partially dashed. I write ‘partially’ because the supplementary material does provide a couple of tests for alternate origins of these structures. The authors looked at the alternative interpretations for these structures as collagenous rot or coincidental plant material. They dismissed both, and provided good reasons for their rejections. For that I give the authors credit, and I accept their interpretation that these structures were part of the individuals.

The anatomy of a feather. Image from:
The anatomy of a feather. Image from the Arizona State University School of Life Sciences

However I differ pretty strongly with their repeated use of ‘feather’ in the paper and the supplement. Feathers are hierarchically branched structures arising from the epidermis (Prum 1999, Chuong et al. 2003). They are composed of a matrix of intracellular keratin and are anatomically composed of a follicle, calamus (base), rachis (central shaft), barbs (branches off the rachis) and barbules (branches off the barbs). That is a feather. To date pennaraptorans are the only animals known to exhibit feathers. The structures on Sinosauropteryx prima, Beipiaosaurus inexpectus, Dilong paradoxus, and Yutyrannus huali are not feathers. These are filamentous structures (epithelial appendages [Chuong et al. 2003]) that may be ancestral to feathers. They are commonly referred to as protofeathers (interestingly Godefroit et al. put protofeathers in quotes, but don’t do the same for feathers). The alleged structures on that one Psittacosaurus individual, as well as the structures on Tianyulong confuciusi, and the pycnofibres on pterosaurs are basically simple shafts, like hairs or arthropod setae. All of these structures match Prum’s (1999) predicted stage 1 protofeather, highlighting the degree of convergence that basic filaments have.

The simple filaments found on the Kulinda specimens similarly fall in the “stage 1 protofeather” / basic filament category. The more complex structures also found on the specimens don’t fit Prum’s model, as they are coming off these basal plates/scutes and they apparently lack rachides.

…except for our monofilaments (which correspond well to Type 1 in Xu et al. [2010. Note this is Prum’s stage 1 feather]), we could not assign with confidence the other two feather morphotypes in Kulindadromeus to categories described by Prum et al. [1999]. or Xu et al. [2010] — Godefroit et al. 2014 Supplementary information.

 

So I find it quite strange and disheartening that Godefroit et al.—despite being fairly objective in their supplementary material—go completely gung-ho in calling these structures feathers. Instead of talking about a really neat and new integumentary structure for dinosaurs, or at least pulling a Xing Xu and saying: “they could be protofeathers, or they could not “, we get:

…diverse epidermal appendages, including grouped filaments that we interpret as avianlike feathers.

This is very reminiscent of the initial description fo the carcharodontosaur Concavenator corvatus (Ortega et al. 2010) in which the authors found raised bumps along the ulna that they interpreted solely as quill knobs. No alternate explanation or detailed comparison with the quill knobs of birds were given. Now, four years later, there are many who believe that these bumps agree better with intermuscular septa than with quill knobs (Foth et al. 2014). Nonetheless, it’s not hard to find C. corvatus still grouped in with examples of “feathered dinosaurs”.

The potential fuzziness of archosaurs

Examples of non-feathery filamentous (or near so) integument in diapsids. The adhesive setae of geckos (left), the dorsal spines of iguanas (center) and the "beard" of turkeys. Gecko image by Danielle Whittaker. Iguana image by: Christian Ziegler. Turkey "beard" image by: Arlene Koziol
Examples of non-feathery filamentous (or near so) integument in diapsids. The adhesive setae of geckos (left), the dorsal spines of iguanas (center) and the “beard” of turkeys. Gecko image by Danielle Whittaker. Iguana image by: Christian Ziegler. Turkey “beard” image by: Arlene Koziol.

Pushing feathers back to the base of Dinosauria or Ornithischia seems to be the trend for many in the dinosaur paleontological community these days. However, as discussed above, this requires that many criteria be met in order for this statement to be true. Not the least of which is that we need evidence that the structures seen in all these filamented dinosaurs are actually homologous. Following Patterson (1982), this means that these structures need to pass the three tests of homology:

  1. Similarity — is the anatomy the same (shape, location to other structures, development)?
  2. Congruence — is it monophyletic?
  3. Conjunction — is a structure found to the exclusion of its alleged homologue?

These tests are meant to be done in succession. So similarity (primary homology) would be tested first followed by congruence (secondary homology) and conjunction (tertiary homology). To date there has been no test of primary homology on any filamented dinosaur specimen, save perhaps Sinosauropteryx prima and Caudipteryx zhoui.  In regards to the Kulinda ornithischian, a cursory look at the description indicates that only the monofilaments share any similarity with the structures seen in advanced coelurosaurs and Tianyulong confuciusi. They also match mammalian hair and insect setae, at least on a gross level, so that doesn’t tell us very much. Evidence of a follicular structure would go a long way to showing homology, but that requires an analysis of the ultrastructure, which has yet to happen. So on the outset the first test for homology (primary homology) isn’t looking good. Theoretically one need not test the other two if the first test fails, but if we were to generously assume primary homology of these structures, we can still test for congruence. That is exactly what Paul Barrett did last year at SVP (Barrett 2013). He compiled a list of all known dinosaur integumentary structures. He then used both a parsimony approach and a maximum likelihood approach to assess the ancestral character state for Dinosauria. Barrett’s analysis indicated that there is little support for a deep nesting of feathers within Dinosauria. This analysis came out a few months later in a news release in the journal Nature. Though a full-on paper would have been preferred this is, nonetheless, the only test for secondary homology of feathers within Dinosauria, and it was yet another test that feathers failed. As it currently stands there is still no support for homologizing the filaments in ornithischians with the filaments in advanced coelurosaurs, or the filaments in pterosaurs. To quote Barrett:

“I’d go so far as to say that all dinosaurs had some sort of genetic trait that made it easy for their skin to sprout filaments, quills and even feathers”

Many folks seem to have trouble swallowing the concept of filaments arising multiple times during archosaur evolution. It is important to keep in mind that we are talking about 185 million years, or approximately 3 times the span of time from dinosaur extinction to the rise of humans. That is a long time for evolution to tinker around. Roger Sawyer and his colleagues were the first to suggest that archosaur integument had an inherent capacity to form multiple epidermal appendages, due to their discovery of unique embryonic epidermal layers in developing birds and alligators (Sawyer and Knapp 2003, Sawyer et al. 2005). So it’s not like Barrett’s proposal was unique. We have extant examples of simple filaments arising on at least three different occasions in extant diapsids (see the image above), so there is already precedent for convergent evolution of filaments within Diapsida. In many cases we are just talking about the evolution of simple filaments. Only pennaraptorans seem to have elaborated beyond simple filaments, and that’s including the Kulinda specimens, which may have weird structures but they are still fairly simple compared to protofeathers and actual feathers.

For comparison keep in mind that Squamata has evolved viviparity a conservative 100 times (Shine 2005)! In terms of complicated developmental processes, going from an external egg to an internally supported baby (including the evolution of a placenta) is way more difficult than sprouting a long, thin filament.

So in the end the Kulinda specimen offers us new insight into the diversity of epidermal derivatives found in dinosaurs, but based on our current knowledge it doesn’t actually do anything to “fluff up” the dinosaur family tree anymore than it already is.

~ Jura

References

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