Aurornis (pre-bird) skull, traced using DGS

Aurornis xui (Godefroit et al. 2013, Late Jurassic, 50cm in length, 160 or 125mya) is one of the few outgroup taxa known for Archaeopteryx and the birds. (Balaur is another in the large reptile tree).

Auronis is a small, gracile dromaeosaur
without a large elevated pedal digit 2. The skull is complete, but slightly disarticulated (Fig. 1). A little DGS colorizes the bones. These can then be reassembled to form a skull in lateral view.

Fig. 1 Aurornis skull in situ, various elements segregated from the in situ fossil and reassembled into a complete and articulated skull. Only the easy bones are colorized here, leaving others uncolored. No doubt there are some errors here. I had only a medium resolution image and my knowledge of dinosaur skulls is still at the freshman stage. The hole in the surangular is an artifact. The little lavender ovals are displaced sclerotic bones.

Fig. 1 Aurornis skull in situ, various elements segregated from the in situ fossil and reassembled into a complete and articulated skull. Only the easy bones are colorized here, leaving others uncolored. No doubt there are some errors here. I had only a medium resolution image and my knowledge of dinosaur skulls is still at the freshman stage. The hole in the surangular is an artifact. The little lavender ovals are displaced sclerotic bones.

Like many other small theropods,
Aurornis was feathered, agile and fast, a descendant of basal dromaeosaurids, like Halplocheirus. In palatal view, the internal nares are located on the anterior palatines and the anterior palate is narrow but solid. The premaxilla is still relatively short and toothed. The pterygoids are narrow and have lost their primitive triangular shape. As a result of taphonomy, tracings for the anterior dentary teeth are distinct from one another. The wider, more typical, pointed teeth are the correct morphology.

Figure 2. Aurornis in several views alongside Archaeoperyx to scale.

Figure 2. Aurornis in several views alongside Archaeoperyx to scale.

On a side note:
Pappochelys (‘grandfather turtle’) has been getting a lot of press, none critical. Take a fresh look at all the PR here.

On another side note:
Chilesaurus, which the large reptile tree nested as the long sought and current most basal member of the Ornithischia, and we looked at earlier here, was given a good look over at the TheropodDatabase blog here.  Evidently others also think the original Chilesaurus report has issues.

References
Godefroit P, Cau A, Hu D-Y, Escuillié, Wu, W-H and Dyke G 201. A Jurassic avialan dinosaur from China resolves the early phylogenetic history of birds. Nature 498 (7454): 359–362.

wiki/Aurornis

 

The Origin and Evolution of Bird Wings

Earlier we looked at
the evolution of the wing in pterosaurs and in bats. Today we’ll look at the evolution of wings in birds. Other than falsifying/modifying the ‘phase shift’ hypothesis (Wagner and Gauthier 1999), there’s nothing heretical about what you’re going to see and read here. Everyone agrees on the taxon list, phylogenic order and bone identification.

Figure 1. The ancestry of birds illustrated by Haplocheirus, Velociraptor, Aurornis, Archaeopteryx and Gallus.

Figure 1. The ancestry of birds illustrated by Haplocheirus, Velociraptor, Aurornis, Archaeopteryx and Gallus to scale. Click to enlarge. Thanks to Scott Hartman for his Velociraptor, manus flesh outline oddly omitted.

The origin of feathers and wings
in birds has been well documented in hundreds of publications. Here (Figs. 1, 2) all those accounts have been simplified into just two graphics and a little text.

Figure 2. A selection of pre-bird and bird hands/wings including Haplocheirus, Limusaurus, Velociraptor, Archaeopteryx, Anser, Passer and two versions of the Hoatzin , Opisthocomus, adult and juvenile.

Figure 2. A selection of pre-bird and bird hands/wings including Haplocheirus, Limusaurus, Velociraptor, Archaeopteryx, Anser, Passer and two versions of the Hoatzin , Opisthocomus, adult and juvenile. Click to enlarge. Not to scale. Note the medial digit of the outlier, Limusaurus, which is a product of neotony, retained from embryonic tissue recapitulating the seven-finger manus of basal tetrapods (figure 3). Note the return of digit 0 fused to the anterior rim of Anser, Passer and the adult Opisthocomus.

Haplocheirus
had grasping hands and trenchant unguals. The fingers were relatively short. Digit 1 was the most robust. Unlike the more basal theropods, Tawa and Herrerasaurus (Fig. 4, 5), manual digits 4 and 5 were absent in Haplocheirus and kin. Digit 3 was also reduced compared to those basal theropods.

Limusaurus
is very much an outlier, not a transitional taxon, different than other related taxa due to its vestigial size and embryonic development. As noted earlier, the Limusaurus manus retains a vestigial embryonic bud of digit ‘0’ which appears in basalmost tetrapods and many embryos, but not otherwise — unless you accept the hypothesis that the anterior process of metacarpal 1 in many extant birds (Fig. 2) is the return of this digit.

Velociraptor
was smaller overall and had longer fingers and longer metacarpals. Note metacarpal 3 is now subequal to metacarpal 2, but metacarpal 1 remains the most robust. One gets the impression that the fingers in Velociraptor had to be stiffer when they supported feathers. At some point they lost or were losing their ability to flex. At the same time the wrist better able to fold the manus in the plane of the forearm, as birds do.

Aurornis
was smaller overall and also had longer more gracile fingers. There is no bow to metacarpal 3 in Aurornis. This manus can be called a wing here.

Archaeopteryx
was overall smaller, but otherwise quite similar to Aurornis. This manus/wing of Archaeopteryx bore large primary feathers.

Anser
is an extant goose. Metacarpal 1 develops an anterior process where digit ‘0’ appeared on Limusaurus. Metacarpal 3 was bowed. The unguals are much smaller. The proximal metacarpals are fused.

Passer
is an extant sparrow. The phalanges are fused to one another.

Opisthocomus
is the extant hoatzin, which goes through a metamorphosis during growth. Juveniles have claws and adults absorb those while fusing the fingers together.

Wagner and Gauthier (1999)
noted the primitive phalangeal formula for tetrapods goes back to Tulerpeton, (Fig. 3) which they considered, “a synapomorphy that arose in the late Devonian, before the origin of Tetrapoda.” Now paleontologists consider Tulerpeton a tetrapod. The phalangeal formula, of course, has roots in Acanthostega, which has three extra digits, one medially and two laterally. Note: it is the reappearance of the medial digit, digit ‘0’, that is key to the present controversy. Note that Tulerpeton has lost one medial and one lateral digit.

Figure 3. Manus of a bird embryo, and two basal tetrapods, Acanthostega and Tulerpeton, the latter with digits 1-3 colorized like the birds in figure 2. Note the extra medial digit in Acanthostega.

Figure 3. Manus of a bird embryo, and two basal tetrapods, Acanthostega and Tulerpeton, the latter with digits 1-3 colorized like the birds in figure 2. Note the extra medial digit in Acanthostega. This is key to the present controversy. The metapterygial axis runs through the longset finger in basal tetrapods.

Embryology
Wagner and Gauthier (1999) report, “There has long been a dissenting view from the hypothesis that the bird hand is composed of digits DI, DII, and DIII. This position is held chiefly by embryologists who argue that the remaining fingers actually represent DII, DIII, and DIV because the DI and DV were thought to have been lost. Morse (19) observed that, when digital reduction occurs in mammals and lizards, the first digit (DI) is invariably the first to be lost in ontogeny, followed by the fifth (DV), and that a modified version of this pattern applies to the foot of birds as well. Thus, the proposition that ultimately became known as Morse’s Law holds that the three functional fingers remaining in adult birds must be DII, DIII, and DIV.”

That hypothesis assumes that the metapterygial axis continued to produce digit 4. The other option is this:  Evidently there WAS a phase shift, shifting the metapterygial axis from 4 in basal archosaurs to 3 in basal theropods and birds. This is a possibility that was not considered in prior studies. And it makes sense because theropods lose manual digits 3 and 4.

Sometimes paleontology does not occur out in the field,
or in the lab, but between the ears, as a new way of thinking becomes the solution to a vexing problem. (Note: no DGS was involved in this heretical appraisal.)

Figure 3. The source of the phase shift hypothesis, assuming the homology of manual digit 4 as the first digit to appear on the manus of Alligator (above) and Struthio (below).

Figure 3. The source of the phase shift hypothesis, assuming the homology of manual digit 4 as the first digit to appear on the manus of Alligator (above) and Struthio (the Ostrich, below). Clic to enlarge. It is easy to see how the mistake was made. Evidently there WAS a phase shift, shifting the metapterygial axis from 4 in basal archosaurs to 3 in basal theropods and birds. This is a possibility that was not considered in prior studies.

Which manual digit is the longest in in basal theropods?
Distinct from most other theropods, manual digit 3 is the longest in Herrerasaurus (Fig. 4) and Tawa (Fig. 5). So, digit 3 is where the new metapterygial axis is located on theropods and birds. Digits 4 and 5 are tiny and tinier vestiges, completely lost in later theropods and birds. It doesn’t make sense that the metapterygial axis should produce a vestige – or no digit at all! Rather, it is the metapterygial axis that has shifted one digit medially. That’s the new heretical phase shift promoted here.

A new nose for Herrerasaurus

Figure 4. Herrerasaurus. The manus has three functional fingers. The two lateral fingers are vestiges.

 

Figure x. The basal theropod, Tawa, with its long manual digit 3. This is where the metapterygial axis has shifted.

Figure 5. The basal theropod, Tawa, with its long manual digit 3. This is where the metapterygial axis has shifted.

Wagner and Gauthier (1999)
also point to the example of the Kiwi manus, some of which have only one finger and two metacarpals. One of these examples had one less phalanx than the other. IMHO you should use fully functioning examples, real wings and real hands, not tiny useless vestiges that are taking various fast tracks toward reduction and disappearance. Wagner and Gauthier also placed the phase shift between Torvosaurus and Allosaurus on their cladogram. That’s an odd place to put a major transition: between two giants. I put the new phase shift at the very base of the Dinosauria, just prior to Herrerasaurus and the basal phytodinosaur, Eoraptor, which also has vestigial lateral fingers.

Wagner and Gauthier (1999) also report,
“We are not aware of any other case in which such a conflict between a developmental and a functional constraint in digit reduction existed.” That’s true. And there is no such conflict in birds if one accepts the novel hypothesis that the metapterygial axis shifted medially as the lateral digits became useless vestiges.

The deeper you get into evolution, the more it all comes together…

References
Müller GB and Alberch P 1990. Journal of Morphology 203, 151–164.
Wagner GP and Gauthier JA 1999. 1,2,3 = 2,3,4: A solution to the problem of the homology of the digits in the avian hand. Proceedings of the National Academy of Science 96:5111-5116.

The genesis of feathers tied to the genesis of bipedalism in dinosaurs

Earlier we looked at the origin of feathers and the evolution of epidermal structures in dinosaurs, noting that embryo birds first develop primal buds (primordia) in the middle of their otherwise naked back. As we learned earlier, feathers are not elaborate scales, but develop from naked skin. We see this every time we pluck a chicken. We also learned that leg scales on birds are derived from feathers. Remember those 4-winged Mesozoic birds?

Today some further thoughts on the genesis of feathers.

Figure 1. Sinosauropteryx in lateral view on a primitive conifer.

Figure 1. Sinosauropteryx in lateral view on a primitive conifer. Despite the complete preservation of several specimens attributed to Sinosauropteryx, very few reconstructions (Fig. 1) have been made of it. Clinging to trees ultimately led to clinging to dinosaurs in dromaeosaurids. Like Limusaurus, Sinsauropteryx is off the main line of bird evolution.

Feathers are rarely preserved on dinosaur fossils.
One of the most primitive dinosaurs to preserve (admittedly very primitive) feathers is Sinosauropteryx (Figs. 1-3; Ji and Ji 1996) from the late Jurassic (with origins earlier in the Jurassic). It has short filamentous feathers running down its spine and around its throat and apparently nowhere else. This ‘mohawk haircut’- pattern could be due to the process of fossilization. Perhaps only those feathers on the parasagittal plane got preserved. However, from available evidence if the feathers were not restricted to the back, they did not stray very far from the spine at this stage. You don’t see feathers around the belly or legs in Sinosauropteryx (Fig. 2).

Figure 2. Sinosauropteryx fossil.

Figure 2. Sinosauropteryx fossil. As everyone knows, those are primitive feathers lining the spinal column and below the throat. Analysis indicates this is not the most primitive feathered theropod. Note the on/off appearance of the tail feathers indicating a decorative device: stripes!

 

Adding Sinosauropteryx to the large reptile tree
nests it with Limusaurus and both were basal to the much larger Sinocalliopteryx, which also had primitive feathers (Fig. 3). So Sinosauropteryx is not the most basal dinosaur with feathers or proto-feathers (contra Ji and Ji 1996). Unfortunately, more primitive theropods do not preserve feathers or scales. Scales do appear on later, larger dinosaurs of all sorts, not so much on the smaller, earlier dinos. Based on birds we can’t assume that small, early dinos had scales (contra Barrett et al. 2015). Rather, based on the appearance of primordia and feather-like structures on a wide variety of dinosaurs, feather primordia appears to precede scales, and perhaps many of these primordia ultimately became scales on larger dinos.

Figure 2. Sinocalliopteryx along with Limusaurus, Aurornis and Archaeopteryx to scale.

Figure 3. Sinocalliopteryx along with Limusaurus, Aurornis and Archaeopteryx to scale. Similar to Sinopteryx, but includes leg feathers here. Sinopteryx and Limusaurus are off the main line of bird evolution, which includes Haploceheirus and dromaeosaurs. Note the depth of the pelvis here compared to Scleromochlus (fig. 5).

 

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

Figure 4. Scales on the back of Scleromochlus forming a lumbar girdle for support during bipedal excursions. This taxon nests as a basal bipedal croc and thus a distant sister to basal bipedal dinosaurs.

The genesis of feather primordia appears to be correlated to bipedal locomotion and a long torso. Before a feather was a feather, or even a quill, it was something else more primitive.

When one looks
at the pattern of dorsal scalation in Scleromochlus (Figs. 4, 5), a basal archosaur, one gets the impression that it was wearing a kind of lumbar girdle to support the long lower back. Indeed, as a newbie biped, Scleromochlus would have used such support near the fulcrum of the large leverage arm created by its stance, its long dorsal region and short ilium. Nothing appears to be sticking out above the dermal layer here. All of the scales (or whatever they were) appear to in lines, like a weave.

Unlike ancestral rauisuchians and the more closely related and larger Erpetosuchus and Gracilisuchus, there were no dorsal parasagittal scutes on Scleromochlus. It was a small animal that lost these structures as it evolved to depend on speed, not armor, to defend itself from predators.

 

Scleromochlus, a basal crocodylomorph

Figure 5. Scleromochlus, a basal crocodylomorph and an early biped in the archosaur line. Scleromochlus reinforced its long lower back with a dermal lumbar support or girdle. This is same area on a chicken embryo that first develops feathers. Compare torso length here to figure 3.

Primordia evolved into feathers only on the short torso basal dinos
Pre-dinosaurs are distinct from pre-crocs in many ways, but pre-dinos all have a shorter torso and a deeper pelvis (Fig. 3) reducing the leverage arm and the need for a reinforcing lumbar girdle. After the pelvis deepened and the torso shortened in early dinosaurs, the individual primordia of that old girdle were free to evolve into something else, in this case, something decorative.

Sinosauropteryx, with its dorsal line of feathery filaments extending from head to tail is one such example. When more feathers began to wrap around the body, that added insulation as a use. When wing feathers lengthened, the forelimbs began to flap to bring attention to those decorations. Later, wing feathers were co-opted for thrust and lift to enable flight.

But the genesis of feathers
still appears to be in the middle of the back, where primordia first appear on embryo chicks, replaying the old lumbar girdle innovation of Scleromochlus. The ornithischians, Tianyulong and Psittacosaurus had elongated primordia along their backs and tails indicating that this trait probably goes back to Herrerasaurus and Trialestes, no doubt in a smaller, more primitive state. With that small field of primordial  scales on the lower back of an otherwise naked Scleromochlus (Fig. 5), the genesis of extradermal structures appears to extend to basal archosaurs.

Figure 6. Feathers, scales and scutes in the Archosauria.

Figure 6. Feathers, scales and scutes in the Archosauria.

If anyone can provide evidence for scales or any other dermal preservation in any Triassic or Early Jurassic dinosaur, please let us know of them.

If anyone has other thoughts on the origin of feathers, please share them. If the above scenario does not make sense, please tell us your thoughts.

References
Barrett PM, Evans DC, Campione NE 2015. Evolution of dinosaur epidermal structures. Biol. Lett. 11: 20150229. online
Ji Q and Ji S-A 1996. On the Discovery of the earliest fossil bird in China (Sinosauropteryx gen. nov.) and the origin of birds. Chinese Geology 233:30-33.

One key fact overturns a bizarre interpretation steadily gaining steam

Figure 1. Jim Clark putting his best interpretive spin on the weird vestigial hand of Limusaurus. Click to play.

Figure 1. Jim Clark putting his best interpretive spin on the weird vestigial hand of Limusaurus. Click to play.

I ran across this YouTube video featuring Dr. Jim Clark talking about his then new ceratosaur dinosaur, Limusaurus, which we looked at earlier here. Clark addresses the importance of the hand of Limusaurus, which he claims with admirable confidence that this was a ‘transitional’ theropod that demonstrates how digit 1 was lost, digit 2 took on the appearance of digit 1, digit 3 took on the appearance of digit 2 and so on. That’s called a ‘phase shift’ as one digit takes on the identify of the one next to it and it is gaining wide acceptance, despite its bizarre premise.

That same hypothesis
is echoed here online at the Varagas Lab and it is becoming the standard paradigm on theropod hands. As an example, the recent paper on Haplocheirus labeled the three manual digits 2, 3 and 4.

This all started
with a report on chicken embryo hands by Thulborn and Hamely (1984), Thulburn (1993) and Burke and Feduccia (1997). Before then everyone labeled the three digits of theropod hands, 1, 2 and 3, which was eminently  logical. Shortly after the Burke and Feduccia study workers struggled against the new hypothesis, but recently (following the publication of Limusaurus) have rallied to support this hypothesis in papers appearing online here and here and here.

Let’s remind ourselves
Alan Feduccia has a vested interest in separating birds from dinosaurs.

This isn’t the first time Occam’s razor was ignored.
We’ve already seen several very odd paradigms arise in paleontology. A forelimb launch for giant pterosaurs is one such boondoggle. The extra bone in the wing of Yi qi is another. The nesting of Vancleavea and pterosaurs with archosauriformes are yet other examples. There are dozens of others. The theropod finger ‘phase shift’ is one more false paradigm that keeps spreading and needs to be stopped.

As discussed earlier, chicken embryos develop an extra medial finger as embryos. This finger bud ultimately disappears by the time of hatching. It is a relic from our basal tetrapod ancestry, from a time when our ancestors had six or more fingers. This has nothing to do with the normal count of five fingers in all post-Devonian tetrapods. We all develop through an embryonic stage when our hands are webbed mittens. In only one adult animal that we know of, Limusaurus, did this extra medial finger appear in an adult — and only because the hand of Limusaurus is a tiny vestige that stopped developing normally. Essentially it’s an embryo hand that retained the medial bud.

This one key fact
has been overlooked by other workers who have flocked to the ‘phase shift’ hypothesis. Which is the simpler explanation: 1) all the fingers suddenly appear like their neighbor finger, changing phalanx counts, or 2) an embryonic bud appears then disappears before hatching.

There is always a simple explanation
for every seemingly magical event or paleontological problem. The six-fingered ancestry of chickens is a key fact overlooked by modern theropod paleontologists who apparently are content to just count the fingers. Sometimes it’s not what you see that counts, but what experience you bring to what you see that trumps logic-busting arguments.

In theropods, what you see is what you get.
Fingers 1, 2 and 3 are indeed fingers 1, 2 and 3. In embryos you may see another medial digit, but it’s not homologous with the medial digit in any other tetrapod, except Limusaurus, as noted above. There is no phase shift of theropod fingers.

References
Burke AC and Feduccia A 1997. Developmental patterns and the identification of homologies in the avian hand. Science 278: 666–668.
Thulborn RA and Hamley TL 1984. ON the hand of Archaeopteryx. Nature 311:218.
Thulborn RA 1993. A tale of three fingers: Ichnological evidence revealing the homologies of manual digits in theropod dinosaurs. New Mexico Museum of of Natural History and Science Bulletion 3:461-463.

Some thoughts on Shuvuuia, Mononykus and Sharovipteryx

Modified June 1, 20-15 with new data on Mononykus (Perle et al. 1994). Thanks to M. Mortimer for the reference.

Figure 1. Shuvuuia and Mononykus to scale in various poses. The odd digit 1 forelimb claws appear to be retained for clasping medial cylinders, like tree trunks. The forelimb is very strong. Perhaps these taxa rest vertically and run horizontally. Click to enlarge.

Figure 1. Shuvuuia and Mononykus to scale in various poses. The odd digit 1 forelimb claws appear to be retained for clasping medial cylinders, like tree trunks. The forelimb is very strong. Perhaps these taxa rest vertically and run horizontally. Click to enlarge.

Mononykus and Shuvuuia
(Fig. 1) are two odd bird/dinosaurs from the Late Cretaceous of Mongolia. Their forelimbs are reduced to a single digit (#1) with digits 2 and 3 vestiges in Shuvuuia GI 100/975 and other specimens (Chiappe, Norell and Clark 1998) or absent in Mononykus  IGM N107/6 (Perle et al. 1993), the larger and more derived of the two.

The question is what are those odd forelimbs used for?
They can’t be traditional vestiges because the olecranon process (elbow) is hyper-developed. The forelimbs look to be very strong. The radius and ulna are essentially fused (but not quite) proximally. The digit 1 ungual is a grappling hook.

In modern birds,
extending the elbow unfolds the tucked wing. In Mononykus and kin the hand (wing) can never be tucked or even rotated. Everything appears to be locked in place except the elbow and shoulder.

Senter (2005)
suggested the odd forelimbs of Mononykus were used to rip open termite mounds. Unfortunately for this hypothesis these dinosaurs would have to belly up to each mound they ripped open, making them vulnerable to a counterattack by termites under their feathers. Current anteaters are lumbering creatures with long snouts that keep them well away from termite defenders. Mononykids were built for bipedal speed. Anteating is not a good match no matter how it is considered.

Whatever those forelimbs were used for,
they were not used full time.

Anything those birds touched with their tiny forelimbs
they would have to belly up to. So let’s consider the safest substrate available, a tree trunk. Neither of these mononykids has a perching foot for tree branches. If these birds spent half their lives resting/sleeping, then why not do it within the relative safety of elevation above the ground, clinging to a tree trunk (Fig. 1)? The sternum on these creatures was sturdy, larger than in Archaeopteryx, ideally built for strong adduction (clinging). If Mononykus was too-large for tree clinging, then the forelimbs could have been used as props for maintaining balance while resting horizontally. After all, nest building and egg-laying were requirements.

Sisters had big claws and some were clingers
Mononykids descend from basal alvarezsaurids, like Haplocheirus (Early Late Jurassic, Choinere et al. 2010), a theropod dinosaur nesting between ornithomimosaurs and more bird-like dinosaurs like Archaeopteryx, oviraptosaurs and therizinosaurs. So it is within their phylogenetic bracket, and well within their abilities for mononykids to cling to trees and other suitable substrates.

The Sharovipteryx analogy
Another unrelated, but speedy biped with tiny forelimbs is Sharovipteryx (Fig. 2, Late Triassic), a fenestrasaur also capable of clinging to tree trunks, especially in preparation for a glide. Longisquama had a similar morphology.

Figure 1. Sharovipteryx in various perching attitudes.

Figure 2 Sharovipteryx in various perching attitudes. Similar in overall build to mononykids, Sharovipteryx was unrelated but developed several traits by convergence, including, perhaps, the ability to belly up to a tree trunk to spend the night clinging to it.

The odd forelimbs of mononykids
evolved from the prey-catching forelimbs of basal alvarezsauroids, like Hapolcheirus, to enable mononykids to rest vertically on tree trunks in the present hypothesis. I haven’t read all the literature. Has this idea been put forth earlier? Any other ideas out there?

References
Chiappe LM, Norell MA and Clark JM 1998. The skull of a relative of the stem-group bird Mononykus. Nature, 392(6673): 275-278.
Chiappe LM, Norrell MA and Clark JM 2002. The Cretaceous, Short-Armed Alvarezsauridae: Mononykus and its Kin pp. 87-120 in Chiappe LM and Witmer LM eds, Mesozoic birds: Above the Heads of Dinosaurs. University of California Press. 536 pp.
Choiniere JN, Xu X, Clark JM, Forster CA, Guo Y and Han F 2010. A basal alvarezsauroid theropod from the Early Late Jurassic of Xinjiang, China. Science 327 (5965): 571–574.
Perle A, Norell MA, Chiappe LM and Clark JM 1993. Flightless bird from the Cretaceous of Mongolia. Nature 362:623-626.
Perle A, Chiappe LM, Rinchen B, Clark JM and Norell 1994. Skeletal Morphology of Mononykus olecranus (Theropoda: Avialae) from the Late Cretaceous of Mongolia. American Museum Novitates 3105:1-29.
Senter P 2005. Function in the stunted forelimbs of Mononykus olecranus (Theropoda), a dinosaurian anteater. Paleobiology 31(3):373–381.
Suzuki S, Chiappe L, Dyke G, Watabe M, Barsbold R and Tsogtbaatar K 2002. A new specimen of Shuvuuia deserti Chiappe et al., 1998, from the Mongolian Late Cretaceous with a discussion of the relationships of alvarezsaurids to other theropod dinosaurs. Contributions in Science (Los Angeles), 494: 1-18.

Archaeornithura: a basal modern bird from 130 mya

Figure 1. Archaeornithura meemannae DGS tracing over aligned plate and counter plate (left). Tracing without fossil at right. Lateral view of post cervical skeleton (with black body outline).

Figure 1. Archaeornithura meemannae DGS tracing over aligned plate and counter plate (left). Tracing without fossil at right. Lateral view of post cervical skeleton (with black body outline). Click to enlarge. Different from a chicken or sparrow: 1. smaller sternum, 2. more gracile ventral pelvis, 3. longer tail and 4. unfused manus bones. The broad and robust sacrum is similar to modern birds.

A recent paper by Wang et al. (2015) brings us the earliest bird of modern aspect, one from the modern Ornithomorpha clade (all living birds), Archaeornitura (Fig. 1). It lived 130 mya in the Early Cretaceous. Two specimens were found. Both had rich feather preservation with primary wing feathers long enough for flight.

Primitive, yet modern
The sternum is small. The ventral pelvis is gracile. The sacrum is large and robust, but not fused together and not fused to the ilium. At least one specimen appears to have retained a long set of tail bones. The coracoids were long and firmly attached to a large sternum, though not nearly as large as in modern flying birds. The fingers were reduced, but unfused. The skull was not well preserved in either specimen. About nine not-very-long cervicals were present. Not much, if any, of a pubic boot in Archaeornithura, but all sister tested sister taxa have one.

Compare the skeleton
of Archaeornithura (Fig. 1) to that of Gallus the chicken (Fig. 2). The chicken, like most modern birds, has a larger, deeper sternum, a larger deeper ventral pelvis, fused fingers and more cervicals.

Figure 1. Gallus the chicken is representative of modern birds. Note the large size of the sternum and ventral pelvis, the fused manual bones, the extended cervical series and the reduced tail

Figure 1. Gallus the chicken is representative of modern birds. Note the large size of the sternum and ventral pelvis, the fused manual bones, the extended cervical series and the reduced tail

So, in pterosaurs and their predecessors 
the pectoral and pelvic girdles came first, the wings developed later. In birds, the wings came first, the pectoral and pelvic girdles took a while to develop.

References
Wang M et al. (7 other authors) 2015. The oldest record of ornithuromorpha from the early cretaceous of China. 6:6987 DOI: 10.1038/ncomms7987

No styliform element on Yi qi. That’s just a displaced radius and ulna.

Modified May 3, 2015 with the new identification of the curved ‘styliform element’, as the ulna, not the radius. 

Error alert
Apparently all the fuss and PR over the new batwing dino/bird Yi qi  is based on an error of bone identification. Both antebrachia on the specimen were splintered during crushing. The splinters were misidentified as slender radii. The purported ‘styliform elements’ (Xu et al. 2015) that gave Yi qi such an odd appearance are actually a displaced right radius and left ulna. The pictures below tell the story (Figs. 1-3).

Figure 1. Identification errors (in red) on the original Yi qi diagram from Xu et al. 2015.

Figure 1. Identification errors (in red) on the original Yi qi diagram from Xu et al. 2015.

The digits
were also mislabeled following the pattern in Limusaurus, which we touched on earlier.

The long scapula identified by Xu et al.
appears instead to be a pair of opposing elongate coracoids. Long coracoids make Yi qi a flapper, not a glider, weak though it may have been.

Figure 2. The Yi qi fossil plate and counter plates. Counterplates above and flipped to match plate.

Figure 2. The Yi qi fossil plate and counter plates. Counterplates above and flipped to match plate. Click to enlarge.

Only a few elements
appear on the counter plate (Fig. 2) that are not present on the plate. Putting them together in Photoshop and painting the bones using the methodology of DGS helped sort out the data (Fig. 3).

Figure 3. Closeup of the former 'styliform element' here identified as a radius in Yi qi.

Figure 3. Closeup of the former ‘styliform element’ here identified as a radius in Yi qi. Click to enlarge. Bone splinters led to earlier misidentification.

Reports say
the Xu et al. team struggled for several months to come to grips with this large, never-before-seen bone, the so-called ‘styliform element’. Evidently the left ulna splinters looked enough like a radius that they discounted the possibility that the odd bone was indeed the radius, likewise splintered. Note the odd orientation of the left manus (Fig. 3) in which the lateral digits are medial. The observed membrane may have been the propatagium. Or it could have simply trailed the wing like other bird membranes do. Remember, birds have no scales, as we learned earlier. Birds have naked skin with some feathers later transforming to scales on their legs with few exceptions (like owls).

Figure 4. Yi qi tracing of the in situ specimen using DGS method and bones rearranged, also using the DGS method, to form a standing and flying Yi qi specimen. Note the lack of a styliform element, here identified as a displaced radius and ulna.

Figure 4. Yi qi tracing of the in situ specimen using DGS method and bones rearranged, also using the DGS method, to form a standing and flying Yi qi specimen. Note the lack of a styliform element, here identified as a displaced radius and ulna.

Reconstructions (Fig 4) are also part of the DGS process, making sure that all bones fit together and also match those of closely related taxa (Fig. 5). Odd autapomorphies, like a styliform element, are immediately suspect, but odd autapomorphies do occasionally occur.,, apparently not this time.

Figure 4. Right ulna of Yi (former 'styliform element') compared to right ulna of Epidendrosaurus.

Figure 4. Right ulna of Yi (former ‘styliform element’) compared to right ulna of Epidendrosaurus. Click to enlarge.

DGS has gotten a bad rap.
This is just another example where, without seeing the fossil, a contribution to identification and understanding can be made. Maybe now would be a good time to take down some of those anti-DGS websites and blogposts out there.

References
Padian K. 2015. Paleontology: Dinosaur up in the air. Nature (2015) doi:10.1038/nature14392
Xu X, Zheng X-T, Sullivan C, Wang X-L, Xing l, Wang Y, Zhang X-M, O’Connor JK, Zhang F-C and Pan Y-H 2015.
 A bizarre Jurassic maniraptoran theropod with preserved evidence of membranous wings.Nature (advance online publication)
doi:10.1038/nature14423