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

 

Yi Qi (‘strange wing’) new bat-like dinosaur/bird

It’s May 2, 2015 and I’m going to let this blogpost stand unaltered, but please see May 2 for notes that the so-called styliform process is really just a displaced radius.

The big news today is the announcement of a new Chinese dinosaur/bird, Yi Qi, with a long wrist bone that extended into soft membranes trailing the forelimb, likely to extend them like a bat wing (Fig. 1).

Two possible reconstructions were offered (Fig. 1). I offer below a new reconstruction that does not have the forelimbs overextended at the elbow and shoulders.

Figure 1. Above: the two Yi Qi reconstructions offered by Xu et al. Below: a little bend at the elbows, as in bats, birds and pterosaurs, probably replicates the wing a little bit better.

Figure 1. Above: the two Yi Qi reconstructions offered by Xu et al. Below: a little bend at the elbows, as in bats, birds and pterosaurs, probably replicates the wing a little bit better and adds strength. Also the feet are tucked under, as in birds. Click to enlarge.

From the Xu et al. abstract:
“Most surprisingly, Yi has a long rod-like bone extending from each wrist, and patches of membranous tissue preserved between the rod-like bones and the manual digits. Analogous features are unknown in any dinosaur but occur in various flying and gliding tetrapods, suggesting the intriguing possibility that Yi had membranous aerodynamic surfaces totally different from the archetypal feathered wings of birds and their closest relatives.” 

References
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

Problem: the Scansoriopteryx pelvis and humerus

I’m guessing that most paleontologists agree
that Scansoriopteryx (Fig. 1) is a strange little theropod dinosaur in the lineage close to birds. After all, it has feathers! And it has very theropod-like bones.

Figure 1. Scansioropteryx compared to Aurornis, Archaeopteryx and Columba, the pigeon. Note the shapes of the pelvis and the humerus.

Figure 1. Scansioropteryx compared to Aurornis, Archaeopteryx and Columba, the pigeon. Note the shapes of the pelvis and the humerus. Not sure if the Aurornis humerus (green) is right side up or upside down.  Below it are the humeri of Scansioropteryx, Archaeopteryx and Columba, the pigeon. Click to enlarge.

However, there is disagreement on the nesting of Scansioropteryx
Czerkas and Feduccia (2014) wrote: “Unlike theropod dinosaurs, invariably exhibiting a completely perforated and open acetabulum, Scansoriopteryx has a partially closed acetabulum, and no sign of a supra-acetabular shelf or an antitrochanter. Along with the mostly enclosed acetabulum indicated by the surface texture of the bone within the hip socket, the proximally oriented head of the femur is functionally concordant with a closed or partially closed acetabulum and with sprawling hind limbs.”

Figure 2. Pelvis of Scansioropteryx with DGS layering. Apparently the left isichium was slightly displaced, covering the acetabulum. When right and left elements are compared, the acetabulum appears to be open as in other theropod dinosaurs. Note the left pubis was flipped on its long axis durring taphonomy. The femur appears to have an theropod-like head and neck (ignore the overlapping matrix that gives it a notch).

Figure 2. Pelvis of Scansioropteryx with DGS layering. Apparently the left isichium was slightly displaced, covering the acetabulum. When right and left elements are compared, the acetabulum appears to be open as in other theropod dinosaurs. Note the left pubis was flipped on its long axis durring taphonomy. The femur appears to have an theropod-like head and neck (ignore the overlapping matrix that gives it a notch).

The crushed pelvis
of Scansioropteryx (Fig. 2) may have been misinterpreted. From what I can tell the left ischium had shifted over the acetabulum and other pertinent post-acetabulum areas, obscuring the open acetabulum (which is plainly visible on the right side). This hypothesis assumes that both ischia were the same length as their posterior tips must meet.

Apparently the left femur
has a more developed head when crushed in an appropriate plane. The right femur had somewhat of a head, but it was crushed in an inappropriate plane.

Figure x. Femur and humerus of a juvenile Scansioropteryx. The femoral head is there, just not very well developed. The humerus lacks a deltopectoral crest extending a quarter of the way down the humerus, but a sister taxon, Aurornis, also lacks this crest.

Figure 3. Femur and humerus of a juvenile Scansioropteryx. The femoral head is there, just not very well developed. The humerus lacks a deltopectoral crest extending a quarter of the way down the humerus, but a sister taxon, Aurornis (Fig. 4), also lacks this crest. Those traits do not prevent these taxa from being theropod dinosaurs.

The deltopectoral crest
on most dinosaurs, including Archaeopteryx (Fig. 1), is prominent and extends down a quarter of the humerus. We don’t see this in Scansioropteryx (Fig. 3). But then again, we don’t see this in Aurornis (Fig. 4) either. That doesn’t delete them from the theropod clade because every other aspect of their anatomy says: theropod!

Figure 3. Aurornis humerus. Note the near complete lack of a deltopectoral crest.

Figure 4 Aurornis humerus. Note the near complete lack of a deltopectoral crest. And certainly not a quarter of the way down the humerus.

If lacking a long deltopectoral crest removes a bird from theropod ancestry then Struthio the ostrich (Fig. 5) is not a theropod either. I’m not seeing much of a deltopectoral crest on Compsognathus or Juravenator either. Did Czerkas and Feduccia set up a straw dog? A red herring?

Maybe that crest is a clue
toward flight/flightlessness in birds (other than the obvious clue of relative wing size!). Applied to Aurornis and Scansioropteryx, neither was flighted. Applied to most theropods and I’ll ask you to rely on relative forelimb size and overall size (Fig. 5). After all, T-rex has a large and appropriately placed deltopectoral crest.

Figure 5. Ostrich humerus with a short deltopectoral crest (from Pop and Penea 2007).

Figure 5. Ostrich humerus with a short deltopectoral crest (from Pop and Penea 2007).

They key to nesting taxa in a cladogram is to:
produce a cladogram. Unfortunately Czerkas and Feduccia did not do this. So if Scansioropteryx was not a theropod, what was it? They don’t tell us.

Here’s what they do tell us: “Scansoriopterygids are not members of either Saurischia or the derived clade of carnivorous Theropoda, which birds have been largely thought to be derived from, based on phylogenetic analyses. Characteristics such as the structure of the deltopectoral crest of the humerus indicate affinities that have been attributed to Dinosauriformes, but it could be further argued that the lack of the offset articular head of the femur suggests an ancestry that predates Dinosauromorphs well into Ornithodira or Avemetatarsalia, if not further into more basal Archosauria.”

You can’t say what Scansoriopterygids are not!
You have to say what they are! And be specific! (On the same note, don’t be like so many modern workers who tell you pterosaurs are archosaurs, but can’t give you a good sister taxon or ten, like the large reptile tree can!)

And you can’t
just pick out a few traits and think you have a solution. You have to examine a large suite of traits (preferably 150+) from every aspect of the taxon. You don’t want to pull a Larry Martin like these guys did with Dimorphodon.

Sometimes paleontologists forget the key to nesting taxa.
Then they’re in deep with their critics. Sometimes they toss out key taxa. Sometimes paleontologists dismiss as impossible what a large cladogram recovers. None of this is acceptable — most of the time — to most paleontologists.  :  )

References
Czerkas SA and Feduccia A 2014. Jurassic archosaur is a non-dinosaurian bird. Journal of Ornithology 155(4):841-851.
Pop C and Pentea M 2007. The osteological features of the skeleton in ostrich (Struthio camelus). Lucrari stiinifice medicine veterinary 15:561-568 Timisoara (online here).

 

Bird skull evolution

Earlier I attempted a color tracing of the skull of the common chicken (Gallus gallus), and I got some flak for it, but, unfortunately, no corrective illustrations.

Figure 1. Chicken skull from around 1905.

Figure 1. Chicken skull from around 1906. Note this illustration has only a smidgen of a maxilla above the anterior jugal. Sadly only a few bones and openings are identified here.

So I went to Digimorph.org and also found several online illustrations of bird skulls (Fig. 1; anatomical studies are quite rare and typically very old) to try to figure out where I went wrong.

Here (Fig. 2) are the results. The skulls of Archaeopteryx (courtesy of Greg Paul), an Early Cretaceous enathiornithine  (Sanz et al. 1997), Struthio (the ostrich), Anser (the goose) and Gallus (the chicken) are compared (Fig. 1, click to enlarge).

Figure 2. Bird skulls compared. Here are Archaeopteryx, Struthio (ostrich), Gallus (chicken) , Anser (goose) and an unnamed Early Cretaceous enantiornithine nestling as large as Archaeopteryx (Sanz et al. 1997). Archaeopteryx by Greg Paul used with permission. Click to enlarge.

Figure 2. Bird skulls compared. Here are Archaeopteryx, Struthio (ostrich), Gallus (chicken) , Anser (goose) and an unnamed Early Cretaceous enantiornithine nestling as large as Archaeopteryx (Sanz et al. 1997). Archaeopteryx by Greg Paul used with permission. Click to enlarge.

The similarities and variations among the bird skulls are interesting. I have avoided birds for too long (probably the reason for earlier errors). Let’s discuss them in brief.

Similarities
You’ll notice first off that the skulls of Archaeopteryx, Struthio and the LP specimen are quite similar overall. By comparison, the more derived Anser and Gallus skulls are less similar.

Figure 3. The Struthio toothless rostrum has regularly spaced pockets where teeth once appeared in its ancestry.

Figure 3. The Struthio toothless rostrum in palatal view has regularly spaced pockets where teeth once appeared in its ancestry. Now these provide nutrients to the ever-growing beak. Click to enlarge.

Tooth disappearance
Archaeopteryx and the LP specimen both had teeth, but extant birds do not. The last clues left by the teeth can still be seen in the primitive bird, Struthio (Fig. 3), which has living tissues, lips and gums and a beak in place of teeth. Those are not tooth roots, but nutrient foramina.

Upper temporal fenestrae disappearance
Archaeopteryx and the LP specimen have an upper temporal fenestrae bordered laterally by the postorbital and squamosal. In extant birds, the situation is not so clear. The postorbital is reduced to a vestige and the squamosal is incorporated into the brain case. That leaves the quadrate (jaw joint bone) less connected to the skull.

Lacrimal reduction
Archaeopteryx and the LP specimen have a lacrimal (stem-like bone between the antorbital fenestra and orbit) but it becomes a vestige in extant birds, still connected to the prefrontal above it.

Premaxilla/maxilla variation
Archaeopteryx and the LP specimen have a typical premaxilla tipping the snout. The maxilla extends halfway beneath the naris. In Struthio and Gallus the premaxilla extends further posteriorly, crowding out the maxilla. In Anser the premaxilla extends further posteriorly, and the maxilla is distinctly robust, both traits strengthening the rostrum.

Ectopterygoid disappearance
In most tetrapods and most dinos the ectoptergoid (a palate bone) arises from the lateral flange of the pterygoid and contacts the cheek bones, typically the maxilla, sometimes the maxilla and jugal. In Archaeopteryx it contacts only the jugal, and then just barely. In a late Cretaceous flightless bird, Hesperornithis, the ectopterygoid is a vestige not in contact with the cheek. Ultimately the ectopterygoid is not present in the extant Struthio, Gallus or Anser. So evidently the ectopterygoid doesn’t fuse to the pterygoid and become part of it. Rather the ectopterygoid becomes a vestige and disappears.

Loss of maxilla ascending process
Archaeopteryx and the LP specimen have a typical maxilla with an ascending process arising to meet the nasal and lacrimal. But note it is much more gracile in the LP specimen. In extant birds the ascending process is not visible in lateral view, either replaced or covered by the descending process of the nasal.

Shorter quadrate
Archaeopteryx has a tall quadrate. The others have a short quadrate, The others also have a larger cranium, housing a larger brain. That also lowers the ventral squamosal.

If I made any errors this time,
don’t be shy about providing illustrated corrections. I’ve only studied comparative birds skulls for one day so far. I’m sure there’s more to learn.

BTW
The animated Longisquama post had about twice as many hits as on a typical day. Thank you for your interest.

References
Sanz et al. 1997. A Nestling Bird from the Lower Cretaceous of Spain: Implications for Avian Skull and Neck Evolution. Science 276:1543-1546.

Digimorph.org

 

Chicken skull colorized

Updated February 05, 2015 with a revised illustration of the chicken skull following further study. See comparisons on the blog post dated 02/05/2015.

Figure 1. Chicken skull (Gallus gallus) with fused and semi-fused skull bones colorized. Postorbital = orange. Squamosal = tan. Lacrimal = brown. Prefrontal = purple. Quadrate = red.

Figure 1. Chicken skull (Gallus gallus) with fused and semi-fused skull bones colorized. Postorbital = orange. Squamosal = tan. Lacrimal = brown. Prefrontal = purple. Quadrate = red.

The chicken (Gallus gallus) was recently added to the large reptile tree. Like most birds several skull bones fuse in adults. Other bones are greatly reduced, losing their old theropod dinosaur appearance. The antorbital fenestra is confluent with the orbit. The  ascending process of the jugal is unossified. Like mammals, birds have a greatly enlarged brain and cranium and that coincides with a reduced quadrate.

This is an example of how DGS (digital graphic segregation) can help illustrate a very common taxon. Earlier mistakes were examples of naiveté as I have avoided studying bird skulls until just recently.

 

 

Bird stem evolved faster than other theropods

Figure 1. The evolution of birds as a consequence of miniaturization. Artist: Davide-Bonnadonna

Figure 1. The evolution of birds as a consequence of miniaturization. Artist: Davide-Bonnadonna. I think the last taxon on the right has been enlarged somewhat for clarity. See Figure 2. 

A new paper by Lee et al. (2014)
reported on their phylogenetic analysis of theropods employing 1549 characters. They found two drivers underlying the dinosaur-bird transition: 1) sustained miniaturization; and 2) the evolution of skeletal adaptations 4x faster than other dinosaurs.

They found that miniaturization facilitated the evolution of morphological novelties associated with small size: reorientation of the body mass; 2) increased aerial ability; and 3) paedomorphic skulls with enlarged eyes and brains along with a reduced snout and smaller teeth without serrations.

I heartily endorse this work.
It supports a paradigm that miniaturization that produces new clades. Cope’s Rule generally does not. We see similar miniaturization at the genesis of reptiles, amphibians, therapsids, mammals, dinosaurs, crocodylomorphs (together the archosaurs), pterosaurs, diapsids and several clades within each of these, like bats and pterodactyloid-grade pterosaurs. We knew for a long time that sustained miniaturization also produced birds. So that’s not news. It just has never been so well laid out before.

Figure 2. Sinocalliopteryx along with Aurornis and Archaeopteryx to scale. This illustration produced over a year ago, tells the same tale as the new Lee et al. paper, but without the great supporting details.

Figure 2. Sinocalliopteryx along with Aurornis and Archaeopteryx to scale. This illustration produced over a year ago, tells the same tale as the new Lee et al. paper, but without the great supporting details.

Lee et al. conclude: 
“Because size reduction, feather elaboration, paedomorphism, and other anatomical novelties permitted by small size all evolved in concert along the bird stem, identifying the primary driver of this sustained trend is probably impossible. It is likely that all traits influenced and provided the context for the evolution of others.” 

Actually not so impossible.
The authors make no mention of the fact that smaller taxa generally mature more quickly, breed more often and die sooner. In other words, generational turnover happens more quickly in smaller taxa, as everyone know. The rate of evolution over time is accelerated by the rate of reproduction over time (all other things being equal). That’s the primary driver. 

In the family tree of amniotes,
you see this all the time, not just in bird origins. Good to see this get the press it deserves.

References
Lee MSY, Cau A, Naish D and Dyke GJ 2014. Sustained miniaturization and anatomical innovation in the dinosaurian ancestors of birds.