Paleo Irony: Rhetoric vs. Reality on Birds (+ Pterosaurs, while we’re at it)

A new paper
by Smith et al. (2015) cements the relationship of birds with mairaptoran theropod dinosaurs (a nesting confirmed by the large reptile tree.) It was inspired by recent papers attempting to distance birds from theropod dinosaurs by Alan Feduccia and the late Stephen Czerkas (links below).

From the Smith et al. abstract: “Birds are maniraptoran theropod dinosaurs. The evidence supporting the systematic position of Avialae as a derived clade within Dinosauria is  voluminous and derived from multiple independent lines of evidence. In contrast, a paucity of selectively chosen data weakly support, at best, alternative proposals regarding the origin of birds and feathers. Opponents of the theory that birds are dinosaurs have frequently based their criticisms on unorthodox interpretations of paleontological data and misrepresentation of phylogenetic systematic methods. Moreover, arguments against the nested position of Avialae in Dinosauria have often conflated the logically distinct questions of avian origins, the evolution of flight, and the phylogenetic distribution of feathers. Motivated by a Perspectives article with numerous factual inaccuracies that recently appeared in The Auk, we provide a review of the full complement of facts pertaining to the avian origins debate and address the misplaced criticisms raised in that opinion paper.”

All you have to do is substitute
‘pterosaurs’ for ‘birds’ in the abstract and the rest follows in perfect irony:

Pterosaurs are fenestrasaur tritosaur lepidosaurs. The evidence supporting the systematic position of Pterosauria as a derived clade within Fenestrasauria is  voluminous and derived from multiple independent lines of evidence (fenestrasaurs are not necessary to nest pterosaurs within tritosaur lepidosaurs). In contrast, a paucity of selectively chosen data weakly support, at best, alternative proposals regarding the origin of pterosaurs as archosaurs. Opponents of the theory that pterosaurs are fenestrasaurs have frequently based their cladograms on taxon exclusion and misrepresentation of scoring data. Moreover, arguments against the nested position of Pterosauria in Fenestrasauria/Tritosauria/Lepidosauria have often conflated the logically distinct questions of pterosaur origins, the evolution of flight, and the phylogenetic distribution of patagial and other membranes. Motivated by a Sues and Nesbitt (2013) paper based on a Nesbitt (2011) cladogram with numerous scoring inaccuracies and taxon exclusion that has been a traditional fault, I provide a review of the full complement of facts pertaining to the pterosaur origins debate and address the misplaced criticisms raised in a Hone and Benton (2007, 2008) paper.

See ReptileEvolution.com and various topics within PterosaurHeresies.Wordpress.com for text and figures.

See here and here for Nesbitt 2011 issues and here for Hone and Benton issues.

And while you’re at it
you can look up alternative nestings for Vancleavea, Casea, Mesosaurus, turtles, synapsids, tiny pterosaurs, Eudibamus, Cartorhynchus, Gephyrostegus, etc. etc.

Isn’t it ironic
that the paleontologists who support an archosaur relationship won’t even look at a lepidosaur relationship? And they reject papers that do present a lepidosaur relationship because such a nesting is heterodox (= different). AND they continue to promote the hypothesis that pterosaurs evolved “without obvious antecedent” with purported sisters that don’t look anything like pterosaurs.

We need
a generally accepted large scale umbrella study of the Reptilia (= Amniota) in order to proceed with smaller more focused studies with greater confidence and to repair old issues. In fact, such a study should also quiet the opposition from Dr. Feduccia on the bird/theropod issue.

References
Smith NA, Chiappe LM, Clarke JA, Edwards SV, Nesbitt SJ, Norell MA, Stidham TA, Turner A, van Tuinen M,  Vinther J and Xu X 2015. Rhetoric vs. reality: A commentary on “Bird Origins Anew” by A. Feduccia. The Auk 132(2): 467-480

doi: http://dx.doi.org/10.1642/AUK-14-203.1
http://www.bioone.org/doi/abs/10.1642/AUK-14-203.1

Eurazhdarcho and LIPB R 2.395: two new azhdarchid pterosaurs

Two European azhdarchids
have become known recently. Eurazhdarcho langendorfensis EME VP 312/2 (Vremir et al. 2013, Fig. 2) and the unnamed LIPB R 2.395 (Vremir et al. 2015. Fig. 1). Eurazhdarcho is known from a distal mc4, a proximal m4.1 and a proximal mt3 (not a distal mc3 as originally labeled, see below), plus cervicals 3 and 4. LIPB R 2.395 is known from a cervical 4 only.

What little is known indicate that both are similar in size and proportions to Zhejiangopterus. And they are just as gracile.

Figure 1. LPB-(FGGUB)-R.2395 cervical 4 with other cervicals imagined.

Figure 1. LPB-(FGGUB)-R.2395 cervical 4 with other cervicals imagined.

The re-identification
of distal metacarpal 3 in Eurazhdarcho (Figs. 2, 3) as metatarsal 2, 3 or 4 is based on the shape of the bone in question. It is expanded asymmetrically proximally and flattened as preserved in situ in Eurazhdarcho (Figs 2, 3) and Quetzalcoatlus (Fig. 4). By contrast distal metacarpal 3 in all pterosaurs has a convex articular surface to accommodate an unrestricted metacarpophalangeal 3 joint permitting extreme extension for implanting posteriorly while walking.

Figure 2. Eurazhdarcho with mc3 reidentified as mt3.

Figure 2. Eurazhdarcho with distal mc3 (in red and in figure 3) re-identified here as proximal portion of metatarsal 2, 3 or 4.

The in-situ placement
of the bone in question (Fig. 2) on the fossil near metacarpal 4 cannot be valid evidence because the cervicals are also extremely displaced. These bones became a jumbled mess long after the body had disintegrated and these few scattered elements were fossilized.

Figure 3. Close up of bone labeled distal mc3. This looks more like proximal mt3.

Figure 3. Close up of bone labeled distal mc3 in Eurazhdarcho. This looks more like a proximal metatarsal in Quetzalcoatlus in figure 4. There is no spherical articulation surface here that would indicated a distal metacarpus. The pink area is a restoration that could represent a much longer distal metatarsal.

The metatarsus of Quetzalcoatlus (Fig 4)
provides comparable data for the Eurazhdarcho bone in question. Metatarsal 4 is shown because it shows better on the lateral edge of the foot. Metatarsal 3 lies beneath it. Both appear to be a good match.

Figure 3. Metatarsal 3 in Quetzalcoatlus looks like the same bone in Eurazhdarcho labeled as a distal metacarpal 3.

Figure 4. Metatarsal 3 in Quetzalcoatlus looks like the same bone in Eurazhdarcho labeled as a distal metacarpal 3. Click to enlarge.

Good to see
mid-sized azhdarchids in eastern Europe to go with the giant Hatzegopteryx, also known from scraps.

I sincerely hope
one of the authors of both papers, Darren Naish, is not too upset by this reinterpretation. We’ve heard from him before. I confess: I used DGS. Never saw the actual fossil. And I don’t have a PhD. Did I make a mistake? Let me know and a change will be made.

References
Vremir MTS, Kellner AWA, Naish D, Dyke G 2013. Laurent  V, ed. A New Azhdarchid Pterosaur from the Late Cretaceous of the Transylvanian Basin, Romania: Implications for Azhdarchid Diversity and Distribution. PLoS ONE 8: e54268.
Vremir MTS, Witton M, Naish D, Dyke G, Brusatte SL, Norell M and Totoianu R 2015. A medium-sized robust-necked azhdarchid pterosaur (Pterodactyloidea: Azhdarchidae) from the Maastrichtian of Pui (Haţeg Basin, Transylvania, Romania). American Museum Novitaes 3827 16 pp.

 

Much appreciated support ‘out there’ for ReptileEvolution.com

I found
a blog that repeated and supported Darren Naish’s diatribe, “Why the world has to ignore ReptileEvolution.com.” That was answered in a multipart reply here, here and in links therein back in 2012.

The name of that blogpost is:“the-best-scientific-smackdown-about-evolution-youll-read-this-week. from io9.com. If I read things correctly, the blog is hosted by Annalee Newitz under the topic Science Scandel, Newitz reports, “Since that time, he [David Peters] has become a bane of the paleontology community by insisting that he’s invented a new kind of technological analysis for fossils. And using this analysis — which he calls Digital Graphic Segregation — he believes he’s proven that pterosaurs are far more distant from dinosaurs in the reptile family tree than previously believed.”

The bane? Is that true?
As loyal readers know, DGS is a technique I applied a name to, but did not invent. Paleontologists, like Michel Laurin (1996), had been tracing photographs of fossils long before I came on the scene. And, as loyal readers (and all pterosaurologists) know pterosaurs don’t really fit will with dinosaurs. Just look at the fingers.

The Newitz blogpost goes on repeating Naish’s logic and images. What I found interesting were some of the blog’s comments. Most ganged on, disliked my web code or worried about SEO and Google robots. A few others took the opposite tack and urged caution before continuing the attack and those are re-printed below:

  1. KipHansen wrote: Nothing wrong about proposing an alternate hypothesis, certainly in a field as based on opinion as Reptile Evolution. I was expecting Naish to blow Peter’s out of the water with carefully researched DNA evidence or something equally scientifically strong – instead we get “I don’t see what you see.” — which, in all honesty, adds up to zero – zip – nada – and nothing. Certainly Naish can come up with *something* more concrete? In science, “I don’t agree with you and I am, after all, an Expert” doesn’t cut much ice. Peter’s may be full of it but Naish has done nothing to convince me of the superiority of his position.
  2. KipHansen wrote: “Is not Peters just proposing shifting some of these things around about? I can’t quite see what is so exasperating about some single person suggesting a different arrangement of something that we are unlikely to be sure about for some time yet. Just because paleontologists have finally agreed, at least for the time being, about reptile evolution doesn’t mean that we have finally ‘found the truth’. The current consensus is just your collective best guess based on available data and techniques and seems to be supported, for the most part, by what we know so far. This consensus will be shattered when someone makes a new remarkable find, or develops a new technique or method of investigation and is brave enough to publish an alternate view. Meanwhile, is there nothing whatever to the DGS techniques in the viewing of fossils, irrespective his interpretations? Is this a interesting new digital technique that could add something to our ability to understand rock encased fossils? Has anyone asked Peters to clearly mark his interpretation as an “alternative hypothesis” to a linked exposition of the consensus view?”

  3. KipHansen wrote: Annalee Newitz: You fail to mention that Mr. Peters, who you characterize as an ‘amateur paleontologist”, is the lead author on a half a dozen or so peer-reviewed papers in respectable paleontology journals. And not just in the 1980’s and 90’s. What’s up with that? Are you sure this isn’t just one of those silly academic wars where some outlier publishes papers in the journals but the entrenched consensus refuses to deal with them, instead resorts to ad hominem attacks via gullible journalists?”

  4. David Marjanovic wrote: “On a few things, he [David Peters] may turn out to be right. One of his first papers (yes, published and peer-reviewed) was on the origin of pterosaurs: he thinks they’re not close relatives of the dinosaurs (the consensus view), but close relatives of (to say it in a neutral way) lizard-shaped animals like Cosesaurus and Langobardisaurus. Peters is the first to have tested this idea by including enough species in a phylogenetic analysis; “the establishment” has never done this, because it’s too much work (it would be at least one complete PhD thesis). Unfortunately, Peters hasn’t put enough work in to this either: his analysis lacks several characters that support the consensus.”

  5. Alanborky wrote: “As an artist/visual type he [David Peters] sees and extracts vastly more visual data from whatever he’s looking at than a none artist (eg most people see a blue sky but artists see literally millions of shades and tones of blue as well as myriads of other colours derived from objects peripheral to their eyes bleeding into those blues subtly influencing how those blues differ in appearance as the eyes shift their focus around the sky) which’s probably why Goethe spotted the intermaxillary bone before none artists did.”

  6. jazzraptor wrote: “How has Peters “muffled” his opposition? Promoting ones own ideas is very different than censoring other people’s ideas. Disagreements about details of evolution are typical and ever-present in the field — not one bit unusual. Isn’t Peters entitled to his opinion? Obviously the guy has put a ton more hours than you have into his studies. And it’s not fallacious to ask for a better explanation for evidence than the one put forward. (Of course his request for competing hypothesis doesn’t mean that he’s right. But there’s nothing wrong with the argument. Ever hear of Occam’s Razor?) Your article looks way too much like a hatchet job. Science is tentative and provisional after all; how will you feel if Peters eventually gains consensus? I’ll answer for you: like an idiot.”

I also wrote a reply to the Newitz blog post. It follows:

Hi Annalee,  David Peters here. Sorry to be late to the party. In 2012 I replied to Darren Naish’s blogpost in a seven-part series that ended here: https://pterosaurheresies.wordpress.com/2012/07/06/reptileevolution-com-and-tetrapod-zoology-part-7/  You’ll find links to the first six posts within. A few quick notes here will clear up some issues.

1. The latest cladogram at http://www.reptileevolution.com/reptile-tree.htm includes 504 taxa and they nest in near complete resolution. All sister taxa resemble one another (you can see the reconstructions throughout the website), a great clue that that cladogram reflects actual evolutionary lines of descent. Add to that 59 therapsids and their kin plus 219 pterosaurs and their kin and you have the largest phylogenetic analysis ever attempted for reptiles. (That, I think, is the extraordinary evidence requested by Carl Sagan and one of your readers.)

1a. More characters would be great, as D. Marjanovic requests, but they are not necessary. Fewer characters will recover the same tree. 228 characters is enough to provide complete resolution as proven at reptileevolution.com. Almost all characters can be correlated, like vertebral counts and limb lengths. Correlated characters are hard to avoid.

2. With so many taxa, you can trace the lineage of pterosaurs, or any included genus, back to Ichthyostega or to any node in-between. You can delete large branches or individual taxa from this tree and it will recover the same topology. The fact that this tree nests mammals (synapsids) in a different place than some DNA studies do is a problem that has not been resolved yet. You probably know that many DNA studies do not agree with one another. You may not know that embryological studies support a closer relationship between mammals and archosaurs than with turtles and lizards, which matches my cladogram.

3. Current and traditional cladograms (i.e. Nesbitt 2011) nest pterosaurs with parasuchia and proterochampsia, two croc-like clades that everyone realizes are bad matches for pterosaurs. Pterosaurs nest where they do in Nesbitt 2011 because he excluded the taxa that nest around pterosaurs at reptileevolution.com. Some workers ignore Nesbitt 2011 and nest pterosaurs with dinosaurs, all the while realizing that there is no way the vestigial lateral fingers of even the most basal dinosaurs and their ancestors could ever evolve to become the long wing-fingers of pterosaurs. The same goes for the lateral digits of the foot.

4. The sternal complex of pterosaurs, as the name implies, is a fusion of the interclavicle, the clavicles and the sternum. My work with DGS shows how that happens in Cosesaurus and Longisquama, non-volant pterosaur sisters. Dinosaurs are not a more parsimonious match.

5. The fact that Darren Naish does not see both prepubes of Cosesaurus (in your illustration above) does not mean that everyone agrees with Naish. I encourage you and your readers to see for yourself at www.reptileevolution.com/cosesaurus.htm and let me know the consensus. Those prepubes are 2mm long in life, so they are tiny, but well formed. Naish reported he saw the stems in the photo. No sister taxa have such stems on their pelves. Those stems are the prepubes, even if Naish wants to deny it.

6. In Science we don’t ‘trust’ –anything– because in Science we can prove everything for ourselves. Many of the taxa I present are the reconstructions of others. Yet other taxa have never been reconstructed, so I’ve done the work with as much detail as can be gleaned from the best available data. You don’t have to trust those reconstructions –or– my color tracings. You are invited and encouraged to repeat the experiment, make your own observations and either refute or support any part or all of what I have presented. It’s simply a presentation. Rarely it’s an alternative. My best contribution to paleontology is simply adding more taxa to the cladogram so that more nesting opportunities are provided, minimizing the effects of bias, tradition and paradigm.

7. Digital Graphic Segregation (DGS) is a name I proposed for a technique that has been used by paleontologists for several years prior to my first attempt at it. Laurin (1996) used it in tracing Utegenia and I dare say anyone tracing fish bones and scales is going to trace a photo rather than get lost in the chaos of those repeating structures without some sort of mechanical aid. I use DGS to color every other reptile rib another color, again, to avoid confusion in a smashed roadkill. Then, I can lift those colors and move them around (usually slightly) to reconstruct the ribcage with the precision of the original.

8. I realize that D. Naish carries a lot of weight with the paleo-blog community. Unfortunately Naish published some of my work that has been in my trash bin for several years. In Science you can admit you made a mistake and you can propose a new reconstruction or cladogram to reflect the latest data. I have made tens of thousands of scoring errors in my cladogram, as I’ve reported at www. pterosaurheresies.wordpress.com. That also means I’ve made tens of thousands of corrections to past errors. With all of those corrections the tree topology has changed a little here and there, but overall, not so much. With 228 traits and 504 taxa the matrix can handle nearly 115,000 scores.

9. Finally, unless you have other unanswered questions, it’s true I have not seen for myself the vast majority of the fossils shown at reptileevolution.com. However I’ve taken three trips to Europe, one to China and several others to USA museums to visit specimens and see them in person. Longisquama and Sharovipteryx both came to St. Louis several years ago, so I was able to study them both. I spent several days with Cosesaurus in Barcelona. Some of the rumors to the contrary have gotten out of hand.

Let me know if YOU have any issues that need clarification. I am here for you.

And I’ll give you the same challenge I gave Darren Naish. If what I’ve done is so off the mark, then the results cannot possibly make sense. The challenge is, please send me two taxa that should not nest together, but they do at reptileevolution.com. If you do find two mismatches, please let me know so I can make yet another correction. If you cannot find two mismatches, I hope you’ll let me and others know that maybe what I’ve done has some value.

PS. I am not a professional web designer. I was an agency art director who wrote and illustrated some books in the 1980s and 1990s, then published, with peer review, a half dozen papers, some with co-authors. D. Marjanovic is correct that I have submitted several other manuscripts for peer review. They were rejected, not sent back to correct errors. Often referees note that what I’m proposing in those manuscripts cuts across traditional paradigms.

Thank you one and all.
The Internet is full of ideas and images. Decide for yourself which have value and which make the most sense. Feel free to follow the links above to see the original Annalee Newitz post and the replies that followed.

References
Laurin M 1996. A reappraisal of Utegenia, a Permo-Carboniferous seymouriamorph (Tetrapoda: Batrachosauria) from Kazakhstan. Journal of Vertebrate Paleontology 16(3):374-383.

The origin of feathers and hair (part 3: feathers)

Yesterday, in part 2, we looked at the origin of mammal hair. The day before, in part 1, we looked at scales and skin. Today, in part 3, we’ll look at the origin of dinosaur scales and feathers with a concentration on their lumbar zones, as you’ll see.

Figure 1. The origin of dinosaurs to scale. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Trialestes, Herrerasaurus, Tawa and Eoraptor.

Figure 1a. The origin of dinosaurs to scale. Gray arrows show more derived taxa. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Trialestes, Herrerasaurus, Tawa and Eoraptor. We don’t know if these taxa were scaly or naked, but basal taxa did have a line of dorsal scutes over the dorsal vertebrae, which is shorter in obligate bipeds.

Figure 1. Scales on the back of Scleromochlus, a basal bipedal croc and thus a distant sister to basal bipedal dinosaurs.

Figure 1. Scales on the back of Scleromochlus, a basal bipedal croc close to the base of all archosaurs and thus a distant sister to basal bipedal dinosaurs. No primordial feathers or scutes here.Was the rest of it naked? We don’t know…

First: phylogeny
Pseudhesperosuchus (Fig. 1a) is the last taxon in the lineage of Euparkeria to Herrerasaurus to retain dorsal scutes, the only dermal structures known for those fossils. ‘No scales’ might mean no scales were preserved. It could also mean the skin was naked. The latter is the scenario based on phylogenetic bracketing between pelycosaurs and chickens (get pdf of dermal tree here). But scales arise often within the Reptilia and a new origin cannot be discounted as it occurs in several marine clades, aetosaurs and Revueltosaurus.

No poposaurs have scutes. No basal dinosaurs have scutes — but Herrerasaurus had spine tables (perhaps vestiges of dorsal scutes fused to dorsal verts?).

When last we left dinosaurs,
they were just evolving from sisters to Gracilisuchus, Lewisuchus, Saltoposuchus, Pseudhesperosuchus, the PVL 4597 specimen (Lecuona and Desojo 2011) and Trialestes (in phylogenetic order Fig. 1a). All were bipeds or near bipeds. They ranged in size from something over a meter down to a half meter, so none were small or tiny, as in basal fenestrasaurs or basal mammals.

However, like basal fenestrasaurs, these croc and dino precursors elevated the forelimbs off the substrate, so they were free to do something else with them. Bipedal fenestrasaurs started flapping their forelimbs for several reasons, none related to flying…at first. Basal dinosaurs were just the opposite because dinosaur coracoids became more disc-like and less strut-like compared to their croc-like precursors (Fig. 1a).

With that said, let’s get back to skin, scales and feathers
At present the only clue to dermal appearance near the origin of dinosaurs is with Scleromochlus, a tiny bipedal croc close to Gracilisuchus (Fig. 1a). Scleromochlus has transverse bands of tiny scales (not large scutes) across its back (Figs. 1b, 2). Note this is exactly where feather primordials appear in embryo chicks (Fig. 3). Was the rest of Scleromochlus naked like a bird? Or scaled like…like I said, we have no examples of scales in fossil taxa near this node.

Were dorsal scales used to help stiffen the Scleromochlus lumbar area, like a girdle? That’s where the maximum stress would be felt on the long lever arm of the presacral area with a fulcrum at the acetabulum and sacral series.  A little support in the lower back would have been useful for these basal bipeds with long lumbar zones. But that’s not quite the situation in Herrerasaurus (Fig. 1a), which had a shorter torso and a bigger pelvis.

Scleromochlus, a basal crocodylomorph

Figure 2. Scleromochlus, a basal crocodylomorph not far from basal dinos, with tiny bands of scales. Gracilisuchus (not to scale) is in the upper right corner.

Now let’s put proto-dinosaurs into their environment 
Proto-dinosaur taxa were not denizens of the leaf litter. They were sprinting over it. And IF going bipedal suddenly makes you want to be glamorous and colorful, like a fenestrasaur, then dinosaurs might have gone down that same route starting with primordial feather bumps (Fig. 3) — IF ontogeny and embryology recapitulate phylogeny. Those primordials do make a pretty pattern, don’t they?

Figure 2. Primordial feathers on the back of a 10-day-old chick embryo.

Figure 3. Primordial feathers on the back of a 10-day-old chick embryo. From Dhouailly 2009., who reports: “In the chick embryo, the future feather first appears on the back as a round primordial. Then a weave of primordials develops across the back.” Note these primordial appear first on the back, as in Scleromochlus (Fig. 1).

Or maybe not…
Persons and Currie (2015) report 
It is now recognized that early feathers had a simple form comparable in general structure to the hairs of mammals. This has led to the generally accepted opinion that the early feather coats of dinosaurs functioned as thermo insulation. Like mammalian hair, simple feathers could serve as insulation only when present in sufficiently high concentrations. 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.”

They go on… “It is not difficult to imagine the first simple feather, or sparse arrangement of simple feathers, appearing on the face of a dinosaur, or more basal archosaurs, and providing an immediate slight selective benefit in the form of increased tactile sensitivity. Evolutionary pressures could then gradually favor more and longer bristles for the same function. Concentrations of bristles around the eyes and other key facial regions would begin to offer hygienic benefits as dust shields, and, once a high enough concentration of bristles was reached, they would begin to provide a small degree of insulation. As facial feathers, bristles would have been optimally positioned to insulate the relatively intense heat that is generally emitted from an animal’s head. In the final step, a high concentration of simple facial feathers with the primary function of thermal insulation would develop and eventually spread to encompass the rest of the body.”

Essentially this is the same as the whisker (vibrissae) hypothesis
for mammals. The problem is: dinosaurs did not go through a burrowing phase, or even a nocturnal leaf litter phase where tactile input would have been more important. No, they were primarily visual, aural and olfactory hunters.

Persons and Currie also mistakenly report
that pterosaurs were dinosaur relatives when they report, “Outside the Dinosauria, but on an adjacent branch of the archosaur family tree, are the hair-like pycnofibres found pervasively throughout pterosaurs.” This is an outdated paradigm as shown in the large reptile tree. So they’re not off to a good start here. To make matters worse for the Persons and Currie hypothesis, Dhouailly 2009 reports: “In the chick embryo, the future feather first appears on the back as a round primordial. Then a weave of primordials develops across the back.” (See fig. 3). So these primordia do not appear first on the face or neck, as Persons and Currie postulate — again IF ontogeny and embryology recapitulate phylogeny.

The bird/theropod connection
has been reinforced several dozen times with wonderful transitional examples from China and Germany, so there’s no need to hash through that again. The question has become: how far back do feathers go in dinosaurs now that we know ornithischians, like Kulidadromaeus (Fig. 6), likewise had protofeathers? So far, no one has found anything resembling feathers on sauropods and they probably never will…

Figure 2. In situ anterior causals of Eoraptor. A tracing (left) appears to indicate fibers (f not cracks, chisel marks or plant debris).

Figure 4. In situ anterior causals of Eoraptor. A tracing (left) appears to indicate fibers (f not cracks, chisel marks or plant debris).Click to enlarge.

But wait…
there may be some fibers arising from around the spines in Eoraptor (Fig. 2), which nests between sauropods and ornithischians. If basal dinosaurs had proto-feathers and ornithichians had proto-feathers, then intervening taxa, like Eoraptor, should also have had proto-feathers. In Eoraptor these lines were not described, and perhaps for good reason. Perhaps they are the flotsam and jetsam that sometimes attend fossils still in the matrix. Perhaps someday they will be looked at under a microscope with an eye to determine what they are.

Scales originated several times within the Reptilia
and feathers do not arise from scales as shown below (Fig. 5).

Figure x. From Dhouailly 2009, the various pathways to scales, hair and feathers, first in traditional phylogenies, and below according to the large reptile tree.

Figure 5. From Dhouailly 2009, the various pathways to scales, hair and feathers, above in traditional phylogenies, and below according to the large reptile tree. Click to enlarge. Note that mammals and archosaurs share a dermal condensation. Remember this could be analogous rather than homologous considering the phylogenetic distance.

However, some scales arose from feathers
Dhouailly (2009) proposed that “overlapping scales in some birds may be secondarily derived from feathers. Owl feet are covered with feathers, not scales.” This puts a whole new light on the scaly feet of birds — and beyond, perhaps, in dinosaurs. Workers have shown that feathers are not elaborate scales. But Dhouailly’s work (also see references therein) indicates that the only scales on birds (discounting the ventral pedal pads) are the foot scales and they were derived from feathers.

Many samples of dinosaur skin 
consist of granulated scales, not overlapping scales. The question is, are these former proto-feather primordia, too? Or just scales? Scales could be new structures in dinosaurs or evolved primordial. As carnivorous bipeds, basal birds were closer to the bauplan of basal dinosaurs than were the other large herbivorous dinosaur clades. And under their feathers, birds are naked.

Dhouailly 2009 reports: “Birds may have been entirely covered by feathers, except for the plantar face of their feet, of which the feather formation program is blocked at its initiation step by genetic limb regulation. The early morphogenesis of avian and mammalian integument implicates the formation of a dense dermis, followed by that of placodes overlying dermal condensations, in contrast to squamate skin.”

The origin of feathers
If feather primordials appeared on basal dinosaurs in the same pattern and shape they do in chick embryos (Fig. 3) then decoration for secondary sexual selection appears to be reason for the origin of dinosaur proto-feather primordial starting on the back. Evidently those patterned bumps were attractive but would only have made a visual impression at close range. As evolution progressed, evidently primordials became less interesting as crests and gigantism became the fashion — both in theropods and phytodinosaurs. Perhaps those more obvious secondary sexual traits were easier to see at a distance. So basal dino primordials could have become scales in later giants. They became feathers in smaller theropods and more obvious feathers as primordials elongated posterior to the now flapping forelimbs. Does that make sense?

(Godefroit et al. 2014) conclude that “protofeather-like structures were probably widespread in Dinosauria, possibly even in the earliest members of the clade.” That appears to be supported by phylogenetic bracketing.

Unfortunately Godefroit et al. go too far afield
when they report, “the ability to form simple monofilaments and more complex compound structures is potentially nested within the archosauromorph clade, as exemplified by Longisquama, pterosaurs, ornithischians, and theropods (including birds). As noted earlier, Longisquama and pterosaurs developed their monofilaments independently according to the large reptile tree.

 Figure 1. Kulindadromeus, a sister to Heterodontosaurus with proto-feathers. Images from and traced from Godefroit et al. 2014. Since theropods and heterodontosaurs both had something like feathers, if they were the same kind of feathers, their last common ancestor had feathers. That last common ancestor was a herrerasaur or its proximal predecessor. Note the Godefroit et al. skull does not match their description but has a standard maxilla ascending process. See color overlays for correct ed interpretation.


Figure 6. Kulindadromeus, a sister to Heterodontosaurus with proto-feathers. Images from and traced from Godefroit et al. 2014. Since theropods and heterodontosaurs both had something like feathers, if they were the same kind of feathers, their last common ancestor had feathers. That last common ancestor was a herrerasaur or its proximal predecessor. Note the Godefroit et al. skull does not match their description but has a standard maxilla ascending process. See color examples for correct ed interpretation. Click to enlarge.

Kulindadromeus
Godefroit et al 2014 described three types of scales and three types of feather-like structures on the heterodontosaur, Kulindadromeus (Fig. 6).

  1. Small (<3.5 mm long) imbricated and hexagonal scales, resembling the scutella in modern birds are associated with the distal parts of the tibiae
  2. Smaller (<1 mm) rounded and non overlapping scales occur around the manus, tarsus (metatarsus, and pes resembling the reticula along the plantar face of the pes in modern birds
  3. The tail is covered by at least five longitudinal rows of slightly arched scales. The largest scales (~20 mm long and 10 mm wide) occur along the proximal part. Each scale forms a triangular anterior spur that covers the preceding one, so that adjacent elements are interconnected by a clip-like system. Proximally, at the level of the base of the tail the scales become progressively smaller and more rounded and do not overlap.
  4. Monofilaments are widely distributed around the thorax, on the back, and around the head.
  5. Compound, non-shafted integumentary structures are 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.
  6. On the proximal tibia clusters of six or seven ribbon-shaped elements appear more or less bundled together proximally, close to the bone surface. Thin internal parallel filaments are within each ribbon-shaped element.

Godefroit et al. report, “In Kulindadromeus the distal hindlimb is extensively covered by scales and devoid of featherlike structures. This condition might thus be primitive in  dinosaurs… [but] paleontological and genetic evidence suggests that the pedal scales of ornithuromorph birds are secondarily derived from feathers” as earlier described by Dhouailly (2009). And if so, are all dinosaur scales secondarily derived from primordials?That’s the big question at this point. 

Naked skin
was primitive for reptiles. Until evidence indicates otherwise, scales may have appeared independently in turtles, lepidosaurs, crocs, birds and non-bird dinosaurs. Currently there is no phylogenetic connection, and thus no homology between scale appearances in these several clades. That could be the fault of the fossil record. Or it could be that certain clades remained naked, as already demonstrated for pelycosaurs, therapsids, enaliosaurs and birds. Feathers arise from naked skin in chick embryos. Everyone know that. Even so, it’s still a potential paradigm buster when it comes to thinking about basal dinosaurs and their scales or lack thereof.

Scales come and go.
Scales may be less widely distributed in the reptile tree than mot of us thought before. Some scales become scutes, but none become feathers. And in meter-long basal dinos feathers probably originated in the middle of the back as primordials for decoration, not as face bristles.

Like you,
I’m learning as I go (just finished this the day it was published) and looking forward to the next discoveries and hypotheses that come out on this subject. If I’ve missed anything, please send me the data and corrections will be made.

References
Bennett AF and Ruben JA 1986. The metabolic thermoregulartory status of therapsids. In The Ecology and Biology of Mammal-like reptiles (Hottom, Roth and Roth eds) 207-218. Smithsonian Institution Press, Washington DC
Chudinov PK 1970. Skin covering of therapsids [in Russian] In: Data on the evolution of terrestrial vertebrates (Flerov ed.) pp.45-50 Moscow: Nauka.
Dhouailly D 2009. A new scenario for the evolutionary origin of hair, feather, and avian scales. Journal of Anatomy 214:587-606.
Godefroit P et al. 2014. A Jurassic ornithischian dinosaur from Siberia with both feathers and scales. Science 345:451-455.
Lecuona A and Desojo, JB 2011. Hind limb osteology of Gracilisuchus stipanicicorum(Archosauria: Pseudosuchia). Earth and Environmental Science Transactions of the Royal Society of Edinburgh 102 (2): 105–128.
Persons WC4 and Currie PF 2015. Bristles before down: A new perspective on the functional origin of feathers.Evolution (advance online publication)DOI: 10.1111/evo.12634

The origin of feathers and hair (part 2: hair)

Yesterday we looked at reptile skin and scales, alpha and beta-keratins and examined the fossil record of scales, naked skin and pterosaur extra dermal membranes. Today we’ll take on mammal hair.

Pre-mammals
Mammals, like Megazostrodon, evolved in the Jurassic from synapsid reptiles, like Archaeothyris, that first appeared in the Late Pennsylvanian.

Dhouailly 2009 reports: “The synapsid lineage, which separated from the amniote taxa in the Pennsylvanian about 310 million years ago, may have evolved a glandular rather than a scaled integument, with a thin alpha-keratinized layer adorned with alpha-keratinized bumps. Those bumps may have even presented some cysteine-rich alpha-keratins, precursors of the hair-type keratins. In addition, the first synapsids may have developed both a lipid barrier outside the epidermis, similar to current amphibians living in xeric habitats, and some lipid complex with the alpha-keratins of the stratum corneum as in current mammals as a means to strengthen the barrier against water loss of the integument.”

So reptilian scales were never part of the mammal legacy — just naked glandular skin.

Mammals
A dense coat of fur is found in all basal extant mammals, even those that lay eggs. Thus the origin of hair is to be found in the common ancestor of all living mammals, perhaps among therapsid-grade synapsids (Thrinaxodon Chiniquodon), or, more conservatively, perhaps right at the origin of early Jurassic mammals.

Dhouailly 2009 reports: “No intermediate form has ever been found between scales and hairs, resulting in only a few proposals of how mammalian hairs may have evolved from scales. These proposals were based on the development of sensory bristles in the hinge scale region of reptiles.”  Unfortunately basal reptiles and therapsids did not have scales (see below).

The traditional cynodont whisker hypothsis
Foramina (tiny holes) on the faces of basal gorgonopsians, therocephalians and cynodonts have been interpreted as providing passages for nerves and blood vessels supplying movable skin (subcutaneous muscles) and sensory vibrissae (whiskers). This would represent the first appearance of hair only to be followed by more and more hair spreading around the body. This essentially duplicates the new hypothesis on feather origin by Persons and Currie (2015, see that discussion tomorrow).

Unfortunately for this hypothesis,
the basal lizard, Tupinambis has similar rostral foramina, yet it lacks sensory vibrissae (Bennett and Ruben 1986).

An alternate mammal hair genesis hypothesis
Given that pelycosaurs and Estemmenosuchus were naked and had no hair, the origin of mammal-type hair must have occurred closer to mammals. On their way to evolving into mammals, taxa like Pachygenelus and Megazostrodon became progressively smaller in a rather common process known as phylogenetic miniaturization (the opposite of Cope’s Rule).

Due to their increased surface/volume ratio, smaller animals find it more difficult to internally thermoregulate because their insides are closer to their outsides. Having insulating fur when tiny would be helpful. That’s the traditional hypothesis for mammal hair genesis in tiny taxa, like Megazostrodon. Unfortunately the insulation hypothesis gives no reason for the first appearance of tiny sprigs of precursor hair, not yet plentiful enough to trap air (for insulation). Nor does it take into account that the smallest of all basal mammals, their newborns, are hairless.

Dhouailly 2009 reports: “Hairs [may have] evolved from sebaceous glands, with the hairshaft serving as a wick to draw the product of the gland to the skin surface, strengthening the barrier against water loss.”

Figure 2. An automobile driver can sense the presence of the curb on approach when a curb feeler is in place. This saves wear and tear on tires, just like individual hairs would touch the inside of burrows before the skin comes into contact.

Figure 2. An automobile driver can sense the presence of a curb on approach when a “curb feeler” is in place. This saves wear and tear on tires. Similarly individual hairs would touch the inside of burrows before the skin comes into contact.

The curb-feeler hypothesis
As others have noted, individual hairs provide tactile feedback. Those are especially useful to nocturnal and burrowing animals.

Naked mole rats provide a good analogy. Like therapsids, naked mole rats burrow, adjust their internal temperature to ambient temperatures, AND they have only a few whisker-like hairs that crisscross the body to form a sensitive array that helps them navigate in the dark. We know that certain small cynodonts were  also burrowers. That’s where we find them. We don’t know if they had whisker-like hairs that crisscrossed their body. Only the bones are preserved.

In this way,
individual hairs would have been like curb-feelers (Fig. 2), small wires that make a noise whenever a 1950s era automobile approaches a curb. Thus provided, basal mammals could have avoided multiple abrasions while running through their tunnels using their own curb feelers.

Nevertheless,
if that’s how hair started, once provided with the ability to grow hair, simply growing more hair would have provided incremental opportunities to spend more and more time outside of the burrow. Hair insulated mammals not only from ambient temperature, but from the environment at large, including the approach of winged insects like flies and mosquitoes. Note that those insects that finally developed the ability to burrow past the hair barrier, fleas, lost their wings in order to do so.

Navigation skills
learned in dark tunnels could be readily transferred to leaf litter in the open air at night (all the while avoiding the predatory gaze of hungry Jurassic dinosaurs).

Opossum tail showing rectangular eupelycosaurian scales

Figure 2. Opossum tail showing false scales. A couple of ‘curb feelers’ appear on the proximal tail.

The “scaly tail” of mammals,
like the opossum (Fig. 2), is actually, a criss-cross series of epidermal folds interspersed with hairs, not homologous with the scale of any other animal (Dhouailly 2009).

Figure 3. Naked mouse babies surround the furry mother mouse.

Figure 3. Naked mouse babies surround the furry mother mouse. The babies may be recapitulating evolution as they are naked and unable to maintain their own body temperature without a little help from mom.

The surprising origin of mammary glands
Dhouailly 2009 reports: “The mammary gland apparently derives from an ancestral sweat or sebaceous gland that was associated with hair follicles, an association which is retained in living monotremes, and transiently in living marsupials. The original function of the mammary gland precursor may not have been feeding the young, but as a means to provide moisture to the eggs.”

Tomorrow: dinosaur feathers.

References
Bennett AF and Ruben JA 1986. The metabolic thermoregulartory status of therapsids. In The Ecology and Biology of Mammal-like reptiles (Hottom, Roth and Roth eds) 207-218. Smithsonian Institution Press, Washington DC
Chudinov PK 1970. Skin covering of therapsids [in Russian] In: Data on the evolution of terrestrial vertebrates (Flerov ed.) pp.45-50 Moscow: Nauka.
Dhouailly D 2009. A new scenario for the evolutionary origin of hair, feather, and avian scales. Journal of Anatomy 214:587-606.
Persons WC4 and Currie PF 2015. Bristles before down: A new perspective on the functional origin of feathers.Evolution (advance online publication) DOI: 10.1111/evo.12634

 

The origin of feathers and hair (part 1: skin and scales)

Three clades
developed extra dermal hair-like structures: mammals, dinosaurs (reaching an acme in birds) and pterosaurs. Traditional thinking holds that reptile scales evolved early, along with the origin of the amniotic membrane. Both of these were viewed as adaptations to a non-aquatic, (i.e. ‘dry’) environment. Unfortunately there’s very little evidence for scales in the earliest reptiles (see below). They appear to have lived in a moist coal forest leaf litter environment throughout the Carboniferous.

Basal amniotes
Dhouailly 2009 reports: “The common ancestor of amniotes may have presented both a glandular and a ‘granulated integument’, i.e. an epidermis adorned with a variety of alpha-keratinized bumps, and thus may have presented similarities with the integument of common day terrestrial amphibians. Whereas the glandular quality of the integument was retained and diversified in the mammalian lineage, it was almost completely lost in the sauropsid lineage (non-mammalian amniotes). When the amniote ancestors started to live exclusively on land in the late Carboniferous, they derived from a group of basal
amphibiotic tetrapods, and it is plausible that they evolved a skin barrier similar to that of modern toads to prevent desiccation”

Two dermal proteins
are key to discussions on reptile skin: alpa-keratins and beta-keratins.

Alpha-keratins
Dhouailly 2009 reports: “In all living vertebrates, at least from trout to human, specific types of alpha-keratins characterize the epidermis and corneal epithelium showing a strong homology in the different lineages.In all amniotes, the last supra-basal layers of the epidermis are cornified, meaning they are formed of dead cells filled entirely with alpha-keratin filaments coated with specific amorphous proteins and lipids, providing a barrier to water loss.”

Beta-keratins
Dhouailly 2009 reports: “Only the sauropsids (birds and reptiles) possess an additional capacity for beta-keratin synthesis, an entirely different type of intermediate filament, which appears to result from a phylogenetic innovation that occurred after that of the alpha-keratins.”

Perhaps a correction here: In the large reptile tree there is no clade “Sauropsida.” Rather synapsids are more derived than the basal reptiles that ultimately evolved into the other amniotes. So, if beta-keratins had a single origin, mammals and perhaps their closest ancestors lost the capacity to produce beta-keratins. Phylogenetic bracketing indicates this could have happened at any node between Protorothyris and Megazostrodon.

Scales
When did scales arise? And are lizard scales homologous with those of turtles, crocs, birds, pangolins and opossum tails? Unfortunately fossils of skin and scales are rare.

Carroll and Baird 1972
traced long interwoven ventral ‘scales’ for the basal lepidsosauromorph, Cephalerpeton,  similar to those found in basal amniotes like Gephyrostregus watsoni. Carroll and Baird also report, “The skin impressions along the forelimb [of Cephalerpepton] have a slightly pebbly texture—rougher than the limb bones but smoother than the broken surface of the matrix. There is no evidence of discrete scales. An indication of epidermal scales would be expected in this type of preservation, if they were present in the animal.epidermal scales can only be recorded as impressions and this type of preservation is rare and apparently not reported in other Paleozoic reptiles.”

As you’ll recall, reptiles divide at the start into two lineages, the Lepidosauromorpha and the Archosauromorpha.

Lepidosauromorphs 
The most primitive appearance of dermal tissue in the lepidosaurorph line occurs with the scutes of pareiasaurs, Sclerosaurus and basal turtles. These include a bony base. At some point turtles developed scales that covered the face and limbs, but when is not known. My guess is as far back as Stephanospondylus because it was a large and tasty herbivore.

Otherwise nothing on scales appears until  Xianglong, a gliding basal lepidosaurifom (not a squamate). Li et al. 2007 report, “The entire body including the skull is covered with small granular scales, which show little size variation.” Perhaps noteworthy, this is the node at which some short-legged, ground-dwelling flattened owenettids evolved to became large-limbed and arboreal, exposed to the dry air above the damp leaf litter.

Perhaps more misunderstood, those wing spars are actually ossified dermal extensions, as in a sister taxon, Coelurosauravus, not extended ribs, as we carefully considered earlier here and here.

Figure 1. Xianglong, a basal lepidosauriform with dermal extensions, not ribs, with which it used to glide.

Figure 1. Xianglong, a basal lepidosauriform with dermal extensions, not ribs, with which it used to glide.

Then there’s Sphenodon, an extant basal lepidosaur with a variety of large and small scales, some were overlapping and others were not. Basalmost sphenodontids, like Pleurosaurus, were trending toward an aquatic niche. Sphenodon is a burrowing and foraging reptile. the best clue to basal sphenodontid squamation comes from a tritosaur sister, Tijubina (see below).

Of course, all living lizards (squamates) have scales.
and they shed their skin in whole or in patches during ontogeny.

The tritosaur lepidosaurs are a special case,
The basal tritosaur, Tijubina, preserves rhomboid scales on the neck, large rhomboid scales on the trunk and annulated ones on the ventral side of the entire caudal region. Not far removed from Sphenodon with regard to squamation.

By contrast, a more derived tritosaur, Huehuecuetzpalli preserves tiny disassociated calcified granular scales over its dorsal neural arches. A more derived tritosaur, Macrocnemus (Renesto and Avanzini 2002), had a scale covering in the sacral and proximal caudal region.

Now things get more than interesting…
The scales of Cosesaurus (Ellenberger and DeVillalta 1974, Fig. 2) were about the size of the matrix particles in its mold, so they have not been described. However, Cosesaurus had extra dermal tissues in the form of a gular sac, a dorsal frill, fibers streaming from the posterior arm, uropatagia trailing the hind limbs and long hairs emanating from the tail. A larger sister, Kyrgyzsaurus had scales and similar extra dermal ornaments. Sharovipteryx shares these traits and accentuates the uropatagia. Longisquama shares these also but accentuates the dorsal plumes. The latter two taxa also have pycnofibers (hairs) at least surrounding the cervical series. Their sisters, the pterosaurs, accentuate the trailing arm fibers, which become fiber-embedded foldable wings. Pterosaur ‘hair’ reaches its acme in Jeholopterus, which may have used its ‘hair ball’ as a barrier to insects likewise attracted bloody patches of dinosaur skin. In certain basal pterosaurs the tail hairs coalesce to become tail vanes.

Figure 1. Click to enlarge. The origin and evolution of Longisquama's "feathers" - actually just an elaboration of the same dorsal frill found in Sphenodon, Iguana and Basiliscus. Here the origin can be found in the basal tritosaur squamate, Huehuecuetzpalli and becomes more elaborate in Cosesaurus and Longisquama.

Figure 2. Click to enlarge. The origin and evolution of Longisquama’s “feathers” – actually just an elaboration of the same dorsal frill found in Sphenodon, Iguana and Basiliscus. Here the origin can be found in the basal tritosaur squamate, Huehuecuetzpalli and becomes more elaborate in Cosesaurus and Longisquama.

It is clear in fenestrasaurs that extra dermal membranes were secondary sexual traits, decorations that enhanced their chances for mating. Hairs ultimately became barriers or acted as insulation. Arm fibers ultimately became wings.

Archosauromorphs
Like the basal lepidosauromorph, Cephalerpeton, basal archosauromorphs like Eldeceeon  had ossified belly scales in V-shaped patterns, but not coalesced to form gastralia.

According to Carroll and Baird (1972) in Brouffia, “many ventral scales are present in the blocks. They are quite broad, rather than being narrowly wheat-shaped, as has been considered typical in early reptiles. A faint impression of dorsal scales is evident also, but these are too insubstantial to illustrate.”

Pelycosaurs lacked scales. They were naked. So were basal therapsids as far as the fossil record goes. Estemmenosuchus (Chudinov 1970), an herbivorous therapsid, preserves no scales, hair or hair follicles. However, the preserved skin was well supplied with glands.

Since all living basal mammals (Fig. 3) are richly endowed with fur, that trait probably extends to the first tiny egg-laying mammals, denizens of the leaf litter. In tiny animals, so in contact with the substrate, the leaf litter and water, hair appears to have developed not only to insulate its little warm-blooded body, but also to act as a barrier to all dermal contact with the environment. Insects, like fleas, had to lose their wings to burrow past the hair to get to the skin.

Figure 2. This is Amphitherium a basal mammal.

Figure 3. This is Amphitherium a basal mammal.

In basal diapsids, the sisters of basal synapsids no dermal material has been found.

Plesiosaurs and ichthyosaurs were naked, so pachylpleurosaurs, thalattosaurs and mesosaurs were likely naked as well. A rare exceptions, the thalattosaur Vancleavea, was covered with large bony scales. Hupehsuchids had short bony plates over the neural spine tips.

For protorosaurs or proterosuchids no dermal scales have been reported.  Dorsal armor developed as large plates in the likely piscivore Doswellia, and to a less degree in Champsosaurus, Diandongosuchus, and then again to a greater degree in parasuchids, proterochampsids and chanaresuchids.

For euarchosauriformes a line of dorsal scutes also appeared on the dorsal midline of Euparkeria and many descendant taxa (except finbacks and poposaurs). The herbivorous Aeotosaurs,  Revueltosaurus and Simosuchus independently expanded their armor in similar ways. So did the carnivorous extant alligators and crocodiles and their ancestors. However basal bipedal and near-bipedal croc taxa, like Gracilisuchus do not preserve scales, other than their dorsal scutes. These may have enhanced the strength of the backbone. Otherwise, basal bipedal crocs were likely not heavily scaled, and neither were the oceanic swimmers, like Metriorhynchus.

That brings us to dinosaurs.
Kaplan (2013) reports “the overwhelming majority had scales or armor.” We’ll cover dinosaur scales and dinosaur feathers in more detail in part 3: feathers.

References
Kaplan M 2013. Feathers were the exemption rather than the rule for dinosaurs. Nature News. doi:10.1038/nature.2013.14379
Renesto S and Avanzini M 2002. Skin remains in a juvenile Macrocnemus bassanii Nopsca (Reptilia, Prolacertiformes) from the Middle Triassic of Northern Italy. Jahrbuch Geologie und Paläontologie, Abhandlung 224(1):31-48.
Carroll RL and Baird D 1972. Carboniferous Stem-Reptiles of the Family Romeriidae. Bulletin of the Museum of Comparative Zoology 143(5):321-363. online pdf
Bennett AF and Ruben JA 1986. The metabolic thermoregulatory status of therapsids. In The Ecology and Biology of Mammal-like reptiles (Hottom, Roth and Roth eds) 207-218. Smithsonian Institution Press, Washington DC
Chudinov PK 1970. Skin covering of therapsids [in Russian] In: Data on the evolution of terrestrial vertebrates (Flerov ed.) pp.45-50 Moscow: Nauka.
Dhouailly D 2009. A new scenario for the evolutionary origin of hair, feather, and avian scales. Journal of Anatomy 214:587-606.
Lecuona A and Desojo, JB 2011. Hind limb osteology of Gracilisuchus stipanicicorum(Archosauria: Pseudosuchia). Earth and Environmental Science Transactions of the Royal Society of Edinburgh 102 (2): 105–128.
Persons WC4 and Currie PF 2015. Bristles before down: A new perspective on the functional origin of feathers.Evolution (advance online publication)
DOI: 10.1111/evo.12634
http://onlinelibrary.wiley.com/doi/10.1111/evo.12634/abstract

* too bad I did not know this when I painted Estemmenosuchus with scales for the cover of a book.

A new solution to the Pisanosaurus pelvis problem

Everything
about the basal ornithischian, Pisanosaurus, (Casamiquela 1967), indicates it is a basal ornithischian — except the published pelvis (Fig. 1, lower left hand corner), which preserves only the circum-acetabular portions of the ilium, pubis and ischium. And these published elements give every indication that they were preserved in their in vivo positions.

Figure 1. Pisanosaurus with new hypotheses on pelvis morphology after shifting in situ bones to in vivo positions.

Figure 1. Pisanosaurus with new hypotheses on pelvis morphology after shifting in situ bones to in vivo positions.

Unfortunately
that produces a rather sauropod-like pelvis when restored (Fig. 1, in the full body outline). That’s great for a basal ornithischian that had not yet developed the retroverted pubis. But the large reptile tree indicates there are more basal taxa, like Jeholosaurus (Fig. 3), that have a completely retroverted pubis.

But what if
there were some post-mortem taphonomic shifting in Pisanosaurus? It happens occasionally. Earlier we looked at the pterosaur Sordes and the problems taphonomic shifting has given paleontologists who assumed a minimum of disturbance in the fossil.

If only
the pubis in Pisanosaurus was taphonomically rotated from its in vivo position… then when re-rotated back into position (Fig. 1) the pelvis can be restored to appear very much like that of sister taxa, like Haya (Fig. 1, lower right), with the ischium now the pubis and the pubis now the ischium.

Figure 2. Pelvis elements of Jeholosaurus, a basal ornithischian, in situ and restored to in vivo positions. Note how gracile the pubis is. It is also lacking a prepubic process.

Figure 2. Pelvis elements of Jeholosaurus, a basal ornithischian, in situ and restored to in vivo positions. Note how gracile the pubis is. A boken bone (in yellow) may indicate a pubis prepubic process. Click to enlarge. Photo from Han et al. 2012.

Otherwise, the most primitive ornithischian pelvis we know
belongs to Jeholosaurus (Fig. 2) from the early Cretaceous, a sister to Daemonosaurus from the late Triassic. The pubis and ischium are quite gracile here. Perhaps that is a clue as to how and why the pubis rotated posteriorly in basal Ornithischia. Panphagia (Fig. 3) is an outgroup taxon with a similar short and gracile pubis and ischium, but apparently not yet rotated. Compare to Eoraptor a sister to Panphagia with larger ventral pelvic elements.

Figure 1. Panphagia with a closeup of the skull. This is a proximal outgroup taxon to the Ornithischia.

Figure 1. Panphagia with a closeup of the skull. This is a proximal outgroup taxon to the Ornithischia.

I think the Pisanosaurus solution is worth considering
since it solves a problem rather elegantly. If there are contra indicators, I am not aware of any. Please advise.

References
Bonaparte JF 1976. Pisanosaurus mertii Casamiquela and the origin of the Ornithischia. Journal of Palaeontology 50(5):808-820.
Brusatte SL , Benton MJ , Desojo JB and Langer MC 2010. The higher-level phylogeny of Archosauria (Tetrapoda: Diapsida), Journal of Systematic Palaeontology, 8:1, 3-47.
Casamiquela RM 1967. Un nuevo dinosaurio ornitisquio triásico (Pisanosaurus mertii; Ornithopoda) de la Formación Ischigualasto, Argentina. Ameghiniana 4 (2): 47–64.
Han, F-L, Barrettn PM, Butler RJ and  Xu X 2012. Postcranial anatomy of Jeholosaurus shangyuanensis (Dinosauria, Ornithischia) from the Lower Cretaceous Yixian Formation of China.”. Journal of Vertebrate Paleontology 32(6):1370–1395.
Irmis RB, Nesbitt SJ, Padian K, Smith ND, Turner AH, Woody D and Downs A 200a. A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs. Science 317 (5836): 358–361. doi:10.1126/science.1143325. PMID 17641198.
Irmis RB, Parker WG, Nesbitt SJ and Liu J 2007b. Early ornithischian dinosaurs: the Triassic record. Historical Biology 19:3-22.
Makovicky PJ, Kilbourne BM, Sadleir and Norell MA 2011. A new basal ornithopod (Dinosauria, Ornithischia) from the Late Cretaceous of Mongolia. Journal of Vertebrate Paleontology 31 (3): 626–640.
Nesbitt SJ, Irmis RB, Parker WG, Smith ND, Turner AH and Rowe T 2009. Hindlimb osteology and distribution of basal dinosauromorphs from the Late Triassic of North America. Journal of Vertebrate Paleontology 29 (2): 498–516. doi:10.1671/039.029.0218
Sereno P 1991. Lesothosaurus, “Fabrosaurids,” and the early evolution of Ornithischia. Journal of Vertebrate Paleontology 11:168-197.
Xu X, Wang and You 2000. A primitive ornithopod from the Early Cretaceous Yixian Formation of Liaoning. Vertebrata PalAsiatica 38(4:)318-325.
wiki/Pisanosaurus

 

The Sues et al. 2011 matrix has flaws, but there is good news, too…

Earlier posts on Daemonosaurus reported that Sues et al. 2011  nested sauropods outside of theropods and ornithischians outside of those two. That tree topology is often repeated. It has become the paradigm. The Sues et al. analysis was built upon the the Nesbitt (2011) analysis, which was looked at earlier here and here.

Over the past four days
I rebuilt the Sues et al (2011) supplementary material matrix into a computer-friendly .nex file (MacClade) and recovered the same tree as Sues et al.

Then I dived in
and examined every pertinent character score. Unfortunately I found over 200 errors. Some were not scored correctly. Others should have been scored but were left blank. Just a few others should not have been scored because, to my understanding, those parts were not preserved.

I also deleted
the pterosaur and Lagerpeton clades because, according to the large reptile tree, they both nest outside of the clade that includes Euparkeria, the listed dinosaurs and all the intervening taxa.

When the Sues et al. matrix was corrected,
a single tree was recovered that almost matched the large reptile tree in topology (Fig. 1). A single exception at the base of the Dinosauria: Marasuchus shifted to a proximal outgroup node. This is likely due to the exclusion by Sues et al. of several bipedal basal crocodylomorph ancestors of dinosaurs, as recovered by the large reptile tree. Only one bipedal crocodylomorph was included, Dromicosuchus, but it is the most derived of the bunch. Fiurthermore, the theropod sisters of Marasuhcus (Procompsognathus and Segisaurus) were also excluded from the Sues et al. dataset.

Sues et al. 2011 tree topology modified to the re-scoring. Click to enlarge.

Sues et al. 2011 tree topology modified to the re-scoring. Note that sauropodomorpha and ornithischia now nest as sisters to Tawa and the Theropoda, all derived from herrerasaurids with crocs as the proximal outgroup to the Dinosauria. WhileAetosaurus and Arizonasaurus do not look alike, they nest together here, even without the presence of Ticinosuchus, a stem aetosaur, and other clade taxa excluded by Sues et al.

This is good news
With the matching tree topologies now we have two large datasets that produced very similar tree topologies for the Dinosauria using two different character lists, one with 228 traits and the other employing 319. Very few traits are common to both. That’s boosts confidence that the tree topologies mirror actual evolutionary events.

How was it then, that so many erroneous scores were made in Sues et al.?
As a human being myself, I understand that bias is part of every decision. If a particular score started to veer from the accepted paradigm, then perhaps the scored should be questioned. That’s why we need each other. That’s why writers need editors. That’s why artists need art critics. A different perspective might not be correct. Then again, it might be. Every matrix that is published is done for two reasons: to demonstrate validity and to invite criticism so the next matrix can be improved. This is Science at its best, working under the paradigm that humans are behind every datapoint.

Anyone interested in having both .nex files (the Sues dataset and the revised Sues et al dataset) can have them both sent via email on request. Please let me know if I should ZIP your files to a PC or Mac format. If you find any bad scores, please report them.

Sues, Nesbitt and Mortimer
have all been sent the rescored file and I look forward to their comments.

References
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.
Sues H-D, Nesbitt SJ, Berman DS and Henrici AC 2011. A late-surviving basal theropod dinosaur from the latest Triassic of North America. Proceedings of the Royal Society Bpublished online

Effigia palate and occiput

Updated March 13, 2015 with a new palate figure based on the photo, not the original drawing in Effigia and Shuvosaurus was modified in turn.

We looked at the poposaur Effigia earlier here and here. Having never attempted a reconstruction of the palate I do so here.

effigia588

Figure 1. Effigia. is an odd derived poposaur with tiny hands and no teeth. In competition with dinosaurs, poplars did not fare as well. The dentary and predentary have been modified here from prior attempts to more closely match the mandible of Shuvosaurus (Fig. 3).

Effigia okeeffeae (Nesbitt and Norell 2006, Nesbitt 2007) Carnian, Late Triassic, ~210 mya, ~ 2 m in length, was originally considered an early theropod dinosaur by Colbert, who collected the specimen in the late 1940s but never removed it from its jacket. A recent reassessment by Nesbitt and Norell (2006) and Nesbitt (2007) nested Effigia among the poposauridis. It is an odd bipedal poposaur and perhaps the most derived member of a clade composed almost entirely of odd derived members. The reconstruction of the skull has been controversial. Perhaps only a direct tracing and shifting of the elements can solve this puzzle. All the pieces in the disarticulated fossil will come together precisely if they are correctly reassembled.

The palate 
It is possible that the palatine (Fig. 2). was misidentified originally as the right ectopterygoid. If so, then the palate resembles that of known sister taxa, like Shuvosaurus (Fig. 3)..

Figure 2. Effigia palate in situ (left) and reconstructed by reassembling colored elements (at right).

Figure 2. Effigia palate in situ (left) and reconstructed by reassembling colored elements (at right). Click to enlarge.

Due to the long premaxilla
and the short maxilla the Effigia palate shifts most of the palatal elements into a smaller space. Even so all maintain their original and typical connections to the other skull elements.

Figure 3. Shuvosaurus, a sister to Effigia, has a similar palate in this reconstruction, but it was not reconstructed like this originally.

Figure 3. Shuvosaurus, a sister to Effigia, has a similar palate in this reconstruction, but it was not reconstructed like this originally.

You really can’t talk about
the palate of Effigia without comparing it to its sister, Shuvosaurus (Fig. 3). Here the main triangular part of the pterygoid must be imagined, but the quadrate processes are present and quite robust. The palatines frame the internal nares posterior to the palatal processes of the maxilla and premaxilla.

effigia-occiput588

Figure 4, the occiput of Effigia colorized here to segregate elements. That’s the central supraoccipital in pink flanked by two opisthotics in lavender, all displace dorsally. Originally they were framed by the squamosals in gold. Quadrates in red and basisphenoid in purple.

Effigia occiput
The above image (Fig. 4, Nesbitt 2007) is a CT scan of the Effigia occiput colorized to aid identification of the elements. The occiput is so inclined it is almost continuous with the palate. Originally the supraoccipital + opisthotics were identified as the two parietals with no median element recognized. Neither the supraocipital or the opisthotic were identified otherwise.

Effigia References
Nesbitt SJ and Norell MA 2006. Extreme convergence in the body plans of an early suchian (Archosauria) and ornithomimid dinosaurs (Theropoda). Proceedings of the Royal Society B 273:1045–1048. online
Nesbitt S 2007. The anatomy of Effigia okeeffeae (Archosauria, Suchia), theropod-like convergence, and the distribution of related taxa. Bulletin of the American Museum of Natural History, 302: 84 pp. online pdf
AMNH Effigia webpage
wiki/Effigia

Shuvosaurus References
Alcober O, Parrish JM. 1997. A new poposaurid from the upper Triassic of Argentina. Journal of Vertebrate Paleontology 17:548–556
Brusatte SL, Benton MJ, Desojo JB and Langer MC 2010. The higher-level phylogeny of Archosauria (Tetrapoda: Diapsida), Journal of Systematic Palaeontology, 8:1, 3-47.
Chatterjee S 1991. An unusual toothless archosaur from the Triassic of Texas: the world’s oldest ostrich dinosaur? Abstract, Journal of Vertebrate Paleontology, 8(3): 11A.
Chatterjee S 1993. Shuvosaurus, a new theropod: an unusual theropod dinosaur from the Triassic of Texas. National Geographic Research and Exploration 9 (3): 274–285.
Rauhut OWM 1997. On the cranial anatomy of Shuvosaurus inexpectatus (Dinosauria: Theropoda). In: Sachs, S., Rauhut, O. W. M. & Weigert, A. (eds) 1. Treffen der deutschsprachigen Palaeoherpetologen, Düsseldorf, 21.-23.02.1997; Extended Abstracts. Terra Nostra 7/97, pp. 17-21.
Long R and Murry P 1995. Late Triassic (Carnian-Norian) Tetrapods from the Southwestern United States. New Mexico Museum of Natural History and Science Bulletin 4, Pp. 153-163.

wiki/Shuvosaurus

 

Marasuchus skull restored

Updated March 13 with text and figure corrections and overlooked references.

Very few skull bones are known for Marasuchus, the tiny theropod-like dinosaur or proto-dinosaur. Here’s a shot at a restoration of the skull (Fig. 1).

Figure 1. Marasuchus skull restored. My what big teeth you have! Based on the maxilla and occiput, this appears to be a long, low skull. Looks like a little basal theropod, like Tawa. Line drawing from Theropod Database in which M. Mortimer moved the 'quadrate' to the postorbital, based on Bonaparte 1975.

Figure 1. Marasuchus skull restored. My what big teeth you have! Based on the maxilla and occiput, this appears to be a long, low skull. Looks like a little basal theropod, like Tawa. Line drawing from Theropod Database in which M. Mortimer moved the ‘quadrate’ to the postorbital, based on Bonaparte 1975.

Marasuchus would make a pretty good little basal theropod/basal dinosaur EXCEPT,

  1. each cervical is too short
  2. no cervicals have epipophyses
  3. the pubis is too short
  4. and it has no boot
  5. the ischium is too deep and V-shaped along its entire length.
  6. the femur lacks some grooves and bumps found in sister taxa
  7. the proximal tibia has a lateral bump does not reach the posterior rim
  8. distal tarsal 4 is not flat
  9. the astragalus has a larger facet for a larger fibula

Marasuchus is also smaller than basal dinosaur/theropod sisters (Fig. 2) and, considering this list, one wonders if some of these traits are due to neotony, the juvenilization of traits when a taxon experiences generational miniaturization.

Figure 1. To scale compared to Marasuchus, Agnosphitys cromhallensis (Fraser et al. 2002) is known from a selection of uncrushed bones, all of which resemble those from Marasuchus, but slightly larger with a relatively longer rostrum and shorter arms. These two represent a separate and distinct lineage of theropods.  Click to enlarge.

Figure 2. To scale compared to Marasuchus, Agnosphitys cromhallensis (Fraser et al. 2002) is known from a selection of uncrushed bones, all of which resemble those from Marasuchus, but slightly larger with shorter arms. These two represent a separate and distinct lineage of theropods.  Click to enlarge.

If not as a basal theropod close to the odd theropods, Procompsognathus and Segisaurus, then where else could Marasuchus more parsimoniously nest? Most of the above traits can be found individually far from bipedal dino-types, but the suite cannot be found elsewhere. I think we have to rely on maximum parsimony here.

Your thoughts?

References
Bonaparte JF 1975. Nuevos materiales de Lagosuchus talampayensis Romer (Thecodontia – Pseudosuchia) y su significado en el origen de los Saurischia, Chañarense Inferior, Triasico Medio de Argentina [New materials of Lagosuchus talampayensis Romer (Thecodontia – Pseudosuchia) and its significance on the origin of the Saurischia, Lower Chañares, Middle Triassic of Argentina]. Acta Geológica Lilloana 13:5-90.
Romer AS 1971. The Chanares (Argentina) Triassic reptile fauna X. Two new but incompletely known long-limbed pseudosuchians: Brevoria 378: 1-10.
Romer AS 1972. The Chanares (Argentina) Triassic reptile fauna. XV. Further remains of the thecodonts Lagerpeton and Lagosuchus: Breviora 394: 1-7.
Sereno PC and Arcucci AB 1994. Dinosaurian precursors from the Middle Triassic of Argentina: Marasuchus lilloensis gen. nov. Journal of Vertebrate Paleontology, 14: 53-73

Theropod Database

wiki/Marasuchus