The first flightless birds

Yesterday we looked at several early birds (Fig. 1). Earlier we considered the phylogenetic nesting of Balaur (Fig. 2; Csiki Z et al. 2010), which some workers (Cau et al. 2015) considered an early flightless bird.

Figure 7. Bird cladogram with the latest additions. Here the referred specimen of Yanornis nests with enantiornithes while Archaeovolans nests within the Scansoriopterygidae, not with Yanornis.

Figure 7. Bird cladogram with the latest additions. Here the referred specimen of Yanornis nests with enantiornithes while Archaeovolans nests within the Scansoriopterygidae, not with Yanornis.

When determining
the first flightless birds, one must first decide which taxon represents the first or basal bird. In the large reptile tree (subset Fig. 1) the last common ancestor of Enantiornithes and Euornithes is Archaeopteryx siemensi, represented by the Berlin and the Thermopolis specimens. Thus they represent, in this cladogram, the first or basal birds. Both the Enantiornithes and Euornithes produced specimens with a locked down coracoid and expanded sternum, anchors for powerful flight muscles attached to long feathered forelimbs.

Thus the purported first flightless bird,
Balaur, nests outside the bird clade (Fig. 1) established by the large reptile tree.

Figure 1. Balaur compared to various dromaeosaurids and to Sapeornis, both to scale and enlarged for detail. Cau, Brougham and Naish wondered if Balaur was the first neoflightless bird, a sort of dodo of the Cretaceous.

Figure 1. Balaur compared to various dromaeosaurids and to Sapeornis, both to scale and enlarged for detail. Cau, Brougham and Naish wondered if Balaur was the first neoflightless bird, a sort of dodo of the Cretaceous.

Instead
the Scansoriopterygidae produced the first taxa in the Eurornithes with more of a dinosaur/theropod look, with Mei (Early Cretaceous) having the smallest forelimbs relative to the rest of the body in that clade. No doubt it was flightless — and with shorter coracoids and a tiny sternum, reduced its flapping. By contrast, its current sister, Archaeovolans (Fig. 3), retained a robust pectoral girdle and long forelimbs.

Figure 9. Sister taxa at the base of the scansoriopterygidae include Jeholornis, Mei and Archaeovolans, here shown to scale.

Figure 2. Sister taxa at the base of the scansoriopterygidae include Jeholornis, Mei and Archaeovolans, here shown to scale.

As everyone knows,
flightless birds have arisen several times since the Early Cretaceous with Hesperornis and Struthio as examples in the large reptile tree. In evolution everything is gradual and often enough, reversible. And behavior is best determined at the extremes of morphology. More generalized taxa probably had more generalized behavior.

In Dinosaurs of the Air
author Greg Paul Paul “argues provocatively for the idea that the ancestor-descendant relationship between the dinosaurs and birds can on occasion be reversed, and that many dinosaurs were secondarily flightless descendants of creatures we would regard as birds.” According to the large reptile tree, dromaeosaurids and basal troodontids were not birds. But birds are derived troodontids. And troodontids arise from basal dromaeosaurids.

Along these same lines Kavanau 2010 reported
“Varricchio et al. propose that troodontids and oviraptorids were pre-avian and that paternal egg care preceded the origin of birds. On the contrary, unmentioned by them is that abundant paleontological evidence has led several workers to conclude that troodontids and oviraptorids were secondary flightless birds. This evidence ranges from bird-like bodies and bone designs, adapted for climbing, perching, gliding, and ultimately flight, to relatively large, highly developed brains, poor sense of smell, and their feeding habits.” Not so, according to the large reptile tree. But, to their point, bird-like theropods have arisen about 8 times by convergence, as we looked at earlier here.

References
Cau A, Brougham T and Naish D. 2015. The Phylogenetic Affinities of the Bizarre Late Cretaceous Romanian Theropod Balaur bondoc (Dinosauria, Maniraptora): Dromaeosaurid or Flightless Bird? PeerJ. 3: E1032. DOI: dx.doi.org/10.7717/peerj.1032
Csiki Z, Vremir M, Brusatte SL, Norell MA 2010. An aberrant island-dwelling theropod dinosaur from the Late Cretaceous of Romania. Proceedings of the National Academy of Sciences of the United States of America 107 (35): 15357–15361.
Kavanau JL 2010. Secondarily flightless birds or Cretaceous non-avian theropods? Med Hypotheses 74(2):275-6.
Paul G 2002. Dinosaurs of the Air: The Evolution and Loss of Flight in Dinosaurs and Birds. Johns Hopkins University Press, Baltimore, 472 pp.

wiki/Balaur_bondoc

newslink on secondarily flightless bird Epidexoptryx.

Hesperornis walking GIF

Figure 1. Hesperornis compared to a king penguin, Atenodytes. Hesperornis has larger feet and a longer tibia. Since penguins swim with their forelimbs, they have large pectoral muscle anchors. That is not the case with Hesperornis.

Figure 1. Hesperornis compared to a king penguin, Atenodytes. The patella is blue. Hesperornis has larger feet and a longer tibia. Since penguins swim with their forelimbs, they have large pectoral muscle anchors. That is not the case with Hesperornis. Click to enlarge. Marsh 1872 thought Hesperornis could stand upright. I do too. That makes only two of us.

Hesperornis regalis
(Figs. 1,2, Late Cretaceous, Campanian, Marsh 1872, 1.8m long) was a toothed, flightless marine bird with vestigial wings and asymmetrical feet. Although not related to living loons, Hesperornis is often compared to loons, which have no teeth and retain the ability to fly. Both swim with powerful hind limbs. Hesperornis can also be compared to another flightless bird clade, the penguins, with the proviso that penguins swim with powerful forelimbs and their skeletons (Fig. 1) reflect this.

Figure 2. Click to enlarge. Hesperornis walking GIF movie. In this hypothetical scenario Hesperornis walks bipedally.

Figure 2. Click to enlarge. Hesperornis walking GIF movie. In this hypothetical scenario Hesperornis walks bipedally. Like penguins and ducks, Hesperornis does not flex its toes while walking. Nor does it take very big steps.

Wikipedia reports,
“In terms of limb length, shape of the hip bones, and position of the hip socket, Hesperornis is particularly similar to the common loon (Gavia immer), probably exhibiting a very similar manner of locomotion on land and in water. Like loons, Hesperornis were probably excellent foot-propelled divers, but ungainly on land. Like loons, the legs were probably encased inside the body wall up to the ankle, causing the feet to jut out to the sides near the tail. This would have prevented them from bringing the legs underneath the body to stand, or under the center of gravity to walk (Reynaud 2006). Instead, they likely moved on land by pushing themselves along on their bellies, like modern [loons].”

It was not difficult
to animate a bipedal Hesperornis (Fig. 2). It appears fully capable of doing so penguin-style. But the comparison to loons is indeed compelling.

Loons are ungainly
on the beach. See a YouTube video here. Yes, it does look wounded, unable to walk like a normal bird. It would probably fly if it was in a hurry. Hesperornis shares many traits by convergence with loons, but, if anything, loon hind limbs are more extreme in their proportions, including a proportionately larger projecting patella (Figs. 3, 4).

Just added after publication: The axis of the acetabulum is further foreword in Hesperornis, at the 51% mark on the torso (measured from the posterior pelvis) versus the 43% mark on the loon. That big butt makes Hesperornis less top heavy.

Figure 3. Loon skeleton with femur (yellow) and tibia/patella (green) highlighted. In this mount the center of gravity is in front of the toes, which makes this an untenable mount, unless the loon is floating on water.

Figure 3. Loon skeleton with femur (yellow) and tibia/patella (green) highlighted. In this mount the center of gravity is in front of the toes, which makes this an untenable mount, unless the loon is floating on water.

The loon femur is a little shorter and the patella is a little larger
(Figs. 3, 4) than on Hesperornis (Figs. 1,2). It’s up to our imaginations whether or not that would enable a more penguin-like locomotion in Hesperornis. Note that penguins do have a patella (knee bone) but it does not extend above the femur as it does in Hesperornis and loons.

Figure 4. Loon femur and tibia/patella. These proportions are more extreme than those found in Hesperornis.

Figure 4. Loon femur and tibia/patella. These proportions are more extreme than those found in Hesperornis. Note the right angle femoral head, as in most birds, but then look at the skeleton (Fig. 3) in which the femora are held laterally, unlike more birds and dinosaurs.

Nat Geo
and Andy Farke report on a bone growth and possible migration study (Wilson and Chin 2014) of Hesperornis here.

According to Marsh:
“The clavicles are separate, but meet on the median line, as in some very young existing birds.The coracoids are short, and much expanded where they join the sternum. The latter has no distinct manubrium, and is entirely without a keel. The wings were represented by the humerus only, which is long and slender, and without any trace of articulation at its distal end.”  

Various authors
believe the humerus would have been hidden beneath the skin and appressed to the ribs. As is typical for Kansas fossils, Hesperornis specimens are typically crushed flat. In the large reptile tree Hesperornis nests with its volant contemporary, Ichthyornis.

References
Marsh OC 1872. Discovery of a remarkable fossil bird. American Journal of Science, Series 3, 3(13): 56-57.
Marsh OC 1872. Preliminary description of Hesperornis regalis, with notices of four other new species of Cretaceous birds. American Journal of Science 3(17):360-365.
Marsh, OC 1880. Odontornithes, a Monograph on the Extinct Toothed Birds of North America. Government Printing Office, Washington DC.
Reynaud F 2006. Hind limb and pelvis proportions of Hesperornis regalis: A comparison with extant diving birds. Journal of Vertebrate Paleontology 26 (3): 115A. doi:10.1080/02724634.2006.10010069.
Wilson L. and Chin K 2014. Comparative osteohistology of Hesperornis with reference to pygoscelid penguins: the effects of climate and behaviour on avian bone microstructure. Royal Society Open Science. 1: 140245. doi: 10.1098/rsos.140245

OceansofKansas/Hesperornis

wiki/Hesperornis

Sometimes it takes the paleo crowd an ‘epoch’ to accept new data

A few short bios here demonstrate 
that paleontology often takes a lonnnggg time to accept data, break with paradigm and adopt new hypotheses. Judge for yourself whether this is due to data, peer pressure, public opinion, inertia, fear, pride, being too busy or what have you.

Thomas Henry Huxley
In the 1860s TH Huxley proposed a relationship between birds and dinosaurs. According to Wikipedia: “Huxley had little formal schooling and was virtually self-taught. He became perhaps the finest comparative anatomist of the latter 19th century. After comparing Archaeopteryx with Compsognathus, he concluded that birds evolved from small carnivorous dinosaurs, a theory widely accepted today.” But not back then.

“Darwin’s ideas and Huxley’s controversies gave rise to many cartoons and satires (cartoon attacks continue in the present day). It was the debate about man’s place in nature that roused such widespread comment: cartoons are so numerous as to be almost impossible to count.”

“Although Huxley was opposed by the very influential Owen, his conclusions were accepted by many biologists, including Baron Franz Nopcsa (that’s good to know!)while others, notably Harry Seeley, argued that the similarities were due to convergent evolution. After the work of Heilmann, the absence of clavicles in dinosaurs became the orthodox view despite the discovery of clavicles in the primitive theropod Segisaurus in 1936. The next report of clavicles in a dinosaur was in a Russian article in 1983.” Even so, that paradigm was not broken for another 17 years. See below.

John Ostrom
According to Wikipedia, “Ostron, revolutionized modern understanding of dinosaurs in the 1960s. His 1964 discovery of Deinonychus is considered one of the most important fossil finds in history. The first of Ostrom’s broad-based reviews of the osteology and phylogeny of the primitive bird Archaeopteryx appeared in 1976.” That’s his legacy. However, his life, as he lived it, was apparently something different and something we can all empathize with.

According to the Hartford Courant (2000), “In 1973, Ostrom broke from the scientific mainstream by reviving a Victorian-era hypothesis (see above) that his colleagues considered far-fetched: Birds, he said, evolved from dinosaurs. And he spent the rest of his career trying to prove it.” With the announcement of the first dinosaurs with feathers from China, Ostrom (then age 73) was in no mood to celebrate. He is quoted as saying, ““I’ve been saying the same damn thing since 1973, `I said, `Look at Archaeopteryx!'” Ostrom was the first scientist to collect physical evidence for the theory. Ostrom provoked a debate that raged for decades. “At first they said, `Oh John, you’re crazy,”’ Ostrom said in 1999.

Robert Bakker
Wikipedia reports, “One alternate hypothesis challenging Seeley’s classification (the dichotomy of Saurischia/Ornithisichia) was proposed by Robert T. Bakker in his 1986 book The Dinosaur Heresies. Bakker’s classification separated the theropods into their own group and placed the two groups of herbivorous dinosaurs (the sauropodomorphs and ornithischians) together in a separate group he named the Phytodinosauria (“plant dinosaurs”). The Phytodinosauria hypothesis was based partly on the supposed link between ornithischians and prosauropods, and the idea that the former had evolved directly from the later, possibly by way of an enigmatic family that seemed to possess characters of both groups, the segnosaurs. However, it was later found that segnosaurs were actually an unusual type of herbivorous theropod saurischian closely related to birds, and the Phytodinosauria hypothesis fell out of favor.” Yes, the segnosaurs are indeed derived theropods, but the Phytodinosauria is recovered in the large reptile tree. Click here for a supporting opinion (not supported by a cladogram).

There are several hundred daily readers of this blog
Many read it because they hate it. Others because they find something interesting enough here to keep coming back. Still others drop in to see what’s up only when something big or controversial comes around.

Only every so often
does the world of paleontology comes around to agree with conclusions first found here. The ‘Eoraptor as a phytodinosaur’ hypothesis comes to mind as an example.

On the other hand,
I’ve noticed if I have anything to do with a hypothesis (pterosaur origins, reptile origins, dinosaur origins, etc.), others completely avoid the taxa, avoid the hypothesis and to top it off, Hone and Benton (2009) went so far as to attribute my published work to another worker after earlier (Hone and Benton 2007) making the correct attribution. It can be crazy out there. Not sure why…

Perhaps there is a reason for this conservatism
As readers have seen here on many, many occasions, a long list of paleontologists have come up with incorrect hypotheses, especially in the realm of systematics. As has been demonstrated, much of this is due to relying on old matrices, inappropriate taxon exclusion and inclusion, problems minimized with a large gamut study like the large reptile tree. But that is something that most paleontologists are currently loathe to accept or even test. Then again…

Conspicuous by its absence, Cartorhynchus was excluded from Ji et al. 2016.
Earlier we looked at a new ichthyosaur cladogram by Ji et al. 2016. Yesterday it crossed my mind that the cladogram did not include the Early Triassic Cartorhynchus, which Motani et al. 2014 considered a strange “basal ichthyosauriform.” Earlier here and here we nested Cartorhynchus as a basal sauropterygian/ pachypleurosaur. Montani, Ji and Rieppel were coauthors on both studies. So that team was aware of Cartorhynchus and two years had passed since publication. So, what happened? I can only wonder if the large reptile tree had some influence.

References
Ji C, Jiang D-Y, Motani R, Rieppel O, Hao W-C and Sun Z-Y 2016. Phylogeny of the Ichthyopterygia incorporating recent discoveries from South China. Journal of Vertebrate Paleontology 36(1):e1025956. doi: http://dx.doi.org/10.1080/02724634.2015.1025956
Motani R, Jiang D-Y, Chen G-B, Tintori A, Rieppel O, Ji C and Huang D 2014. A basal ichthyosauriform with a short snout from the Lower Triassic of China. Nature doi:10.1038/nature13866

wiki/Cartorhynchus

 

Is this the missing skull of the basal bird, Archaeornithura?

Updated March 16, 2016 with new images. The beak, if present, is ephemeral, questionable. Only two scores changed.

The spectacular plate and counter plate
of the basal ornithouromorph bird, Archaeornithura (Figs. 1-3, Early Cretaceous, Wang et al. 2015) appear to present every aspect of this specimen in full detail, but only the back of the skull (the occipital plate) appears to be readily preserved on the split surfaces.

Figure 2. That little patch by the shoulder could be the beak, eye and cranium of Archaeornithura.

Figure 2. That little patch by the shoulder could be the beak, eye and cranium of Archaeornithura.

Where is the rest of the skull? 
It might be here (Fig. 2). At least part of it, the beak tip, scleral ring and cranial bones (frontal and parietal) give the impression of being there. I can’t be sure working from photos alone, but when you put the parts on a reconstruction of the rest of the body (Fig. 3), the parts fit both morphologically and phylogenetically.

Figure 3. Reconstruction of the basal ornithuromorph bird, Archaeornithura with skull added. Feathers and ribs omitted. The length of the tail is hard to determine.

Figure 3. Reconstruction of the basal ornithuromorph bird, Archaeornithura with skull added. Feathers and ribs omitted. The length of the tail is hard to determine.

Despite the rather short arms, 
the long wing feathers (Fig. 1) made the wings large enough for flapping flight. The robust and long coracoids attest to the ability to flap with great vigor. The sternum is not flat, but more deeply keeled than in more primitive birds. The large pelvis anchors strong leg muscles. The fragile pubes framed larger air sacs. Despite robust sacral vertebrae that broadened the hips, the tail was reduced and without a robust parson’s nose-type pygostyle, which developed by convergence in other birds clades and in more derived ornithuromorphs. The perching toe was not so well developed and all pedal unguals were rather small, similar to those of wading pterosaurs like Ctenochasma.

Hedging paragraph:
I don’t think there is no way to tell how long the beak of Archaeornithura was given the present data. Currently I have the beak tip not very separated from the occiput giving it a rather short skull. Alternatively the length of the skull might be measured from the in situ beak tip to the in situ occiput. Then this bird would have had a longer rostrum, more like that of its beach combing analog among pterosaurs, Ctenochasma. Perhaps other specimens will help fill in the data gap here.

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

wiiki/Archaeornithura

 

Finding the foot of Yi qi

The fossil scanoriopterygid bird,
Yi qi (Xu et al. 2015) is infamous for purporting to have a long extra bone (the so-called ‘styliform element’) somehow anchored to the wrist (see below) that many experts, including Dr. Kevin Padian (2015, see below), regarded as acting like a bat finger to stretch and support a bat-like wing membrane (not feathers). No sister taxa, all of them scansoriopterygid birds, have even a hint of such a bone. Here at pterosaurheresies alone that bone was determined to be a displaced radius on one wing and a displaced ulna on the other. Without these displaced bones, the forearms do not have their radius or ulna counterpart, which is standard equipment in all tetrapods with limbs. Not sure why this went unnoticed by the experts.

On a side note,
the foot was not reconstructed because the bones were very faint and intermixed with tail bones (Fig. 1). Dr. Padian reported that nothing below the waist was known. That is incorrect. He must have been shown only one plate or counter plate.

With the recent reconstruction of a sister taxon,
Omnivoropteryx, which has an odd (autapomorphic) long pedal digit 4, a second attempt was made to trace and reconstruct the foot of Yi qi (Fig. 1). If the tracing is correct, then the reconstruction of the Yi pes greatly resembles that of it sister, Omnivoropteryx, as one would expect. However, digits 3 and 4 are similar in length. In some other scansoriopterygids, digit 4 is shorter to much shorter.

This tracing
is just about at the limit of DGS capabilities without a higher resolution dataset. Fortunately a sister taxon provides a blueprint to model this foot against. And yes, the caudal vertebrae are confusing as they mix in with the pedal elements. And yes, some of the bones are only represented by faint impressions distally and proximally with the rest filled in using a-z bracketing.

Figure 1. The foot (pes) of the scansoriopterygid bird, Yi qi, both in situ and reconstructed. The amber bones are causals.

Figure 1. The foot (pes) of the scansoriopterygid bird, Yi qi, both in situ and reconstructed. The amber bones are causals.

Back to the ‘styliform element’
Dr. Padian (2015) reports, “Their (Xu et. al) find opens two cans of worms: about interpreting unique structures in fossils and about what it means to fly. The styliform element, which may be a hypertrophied wrist bone or a neomorphic calcified structure, is longer than any of the animal’s fingers and is curved at both ends. It is probably not a true finger. How the structure is attached to the wrist is not clear, because its proximal end seems quite  squared off; this means that we also do not know if or how it could move.  What could this element be except a support for some kind of aerofoil? The authors infer this on the basis of its position and the presence of membranous tissue in the wrist area.”

Note that 
Dr. Padian does not consider the possibility that the ‘styliform element’ is either a displaced radius or ulna, despite matching lengths and morphologies. This lack of recognition is rare, but not unknown. For instance, in 2000 I did not recognize the stem of the displaced prepubis in Cosesaurus.

Fliapping
Padian also notes: “Furthermore, in flapping animals the outboard skeletal elements (wrist, hand and so on) are primarily responsible for thrust, the essential component of powered flight, but these are not particularly long in Yi qi. So, at present we can shelve the possibility that this dinosaur flapped.” This appears to be an oversight statement. Not only does Yi qi have an elongate hand, the point is: it doesn’t matter how large or feathered a forelimb is. Even flightless birds, including most baby birds, flap. However tetrapods that flap for locomotion all have locked down and elongate coracoids. Perhaps Padian meant ‘flying.” If so, he is likely correct. Scansoripterygids have been discovered with tail feathers, but not bird-like wing feathers. This may have been the first clade of flightless birds. As we learned yesterday, the dromaeosaurid, Balaur was not a basal flightless bird. If you want to see what basal flightless birds actually look like, check out the scansoriopterygids.

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

Ornitholestes nests with Microraptor now

Earlier we looked at a new nesting for four-winged Microraptor in the Tyrannosaurus clade. Here a close relative (Figs. 1-2) supports that nesting (Fig. 2) and calls into question the currently accepted shrinking bird ancestor hypothesis (Fig. 3).

Ornitholestes hermanni 
(Ostrom 1903, 1917, 2m, incomplete skeleton, Late Jurassic, 154 mya) According to Wikipedia, “All published cladistic analyses have shown Ornitholestes to be a coelurosaur as defined by Gauthier.” A coelurosaur? That’s pretty general. As the arbiter of all that is known and accepted, can Wiki be more specific? Is Ornitholestes such an enigma? In the large reptile tree (subset in Fig. 4)  Ornitholestes nests between Compsognathus and Microraptor, close to Tianyuraptor in the lineage of Tyrannosaurus. The skeleton shown here was restored based on the AMNH restoration (Fig. 1), which may not be accurate with regard to the number of cervicals and dorsals (see below).

Figure 1. Ornitholestes, as originally mounted by the American Museum and revised together with Microraptor to scale. Click to enlarge.

Figure 1. Ornitholestes, as originally mounted by the American Museum and revised together with Microraptor to scale. Click to enlarge.

Ornithologist
Percy Lowe hypothesized in 1944 that Ornitholestes might have borne feathers. Now, as a close relative of Microraptor and Tianyuraptor, Ornitholestes probably had long wing and leg feathers.

Note the resemblance
of the skull of Microraptor to that of Ornitholestes (Fig. 3) and the very similar body proportions, distinct chiefly in size (Fig.1).

Figure 5. The skull of another Microraptor, QM V1002. The two nest together in the large reptile tree.

Figure 2. The skull of Microraptor, QM V1002. Note the resemblance to Ornitholestes.

Earlier phylogenetic studies
Wikipedia reports, “All published cladistic analyses have shown Ornitholestes to be a coelurosaur as defined by Gauthier. Some analysis have shown support for the hypothesis that it is the most primitive member of the group Maniraptora, though more thorough analyses have suggested it is more primitive than the Maniraptoriformes, and possibly a close relative of the “compsognathid” Juravenator starki.” That is not a very precise nesting. Here Ornitholestes supports the earlier hypothesis that Microraptor was not in the main lineage of birds, nor of dromaeosaurs, but this clade represents a pseudo-bird lineage that did not produce extant relatives. The pectoral girdle is not known for Ornitholestes, so we don’t know if it had long coracoids and a furcula suitable for flapping.

Behavior
Osborn (1903) originally considered Ornitholestes a bird catcher and “doubtless related as a family to Struthiomimus.” That behavior is unlikely (see below,) but the relationship is true in the large reptile tree as Struthiomimus nests with Compsognathus both proximal basal sisters to Ornitholestes.

Distinct from all tested sister taxa,
Ornitholestes
had a tibia not longer than the femur, a trait that usually occurs in much larger theropods, like T-rex, but also occurs in the unrelated Sinosauropteryx.

Repairing errors
Osborn (1917) thought the referred manus specimen (AMNH 587) was not adapted to seizing or holding a struggling live prey, as he originally imagined. Pertinent to an earlier discussion, Osborn 1917 noted several inaccuracies in Osborn 1903. This was not considered just cause for other paleontologist of that – or any era – to question everything Osborn produced from then on. He corrected a mistake and everyone accepted that as what Science does.

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

Figure3. The evolution of birds as a consequence of miniaturization. Artist: Davide-Bonnadonna

The Shrinking Bird Ancestor Hypothesis
Earlier we looked at a paper on bird origins (Lee et al. 2014) that found a gradual size reduction in the theropod lineage that produced birds. Unfortunately, with the new cladogram, it is no longer reasonable to accept a Large > Medium > Small sequence. Rather it is more reasonable to follow a Medium > Mediium > Small  hypothesis OR a Small > Small  > Small hypothesis  of bird origins (Fig. 4). In other words, the lineage that ultimately produced birds may have stayed small and occasionally branched off medium and large-sized clade members.

Figure 2. Here, in this subset of the large reptile tree, Ornitholestes nests at the base of the Microraptor clade, close to the base of the Tyrannosaurus clade. Depending on how you look at it, either medium-size dinosaurs produced large and small dinosaurs, or small dinosaurs produced medium and large dinosaurs. In pterosaurs small always produced medium and large.

Figure 4. Here, in this subset of the large reptile tree, Ornitholestes nests at the base of the Microraptor clade, close to the base of the Tyrannosaurus clade. Every 5 seconds the graphic will change, 3 frames. Depending on how you look at it, either medium-size dinosaurs produced large and small dinosaurs, or small dinosaurs produced medium and large dinosaurs. In pterosaurs small always produced medium and large.

Of course, a more complete fossil record
could solve this problem. But at present we should not loose sight of the fact that basalmost dinosaurs, like Barberenasuchus and Eodromaeus, were small, not medium or large (depending on your definition and cut-off, of course). With Tyrannosaurus in the mix, Struthio the ostrich becomes a medium-sized theropod, even though it is a large bird. The presence of small dinosaurs, like Compsognathus, at several basal nodes in the large reptile tree allow the possibility that theropod evolution happened at a small scale that occasionally produced medium and large-sized clade members. These did not directly contribute to the lineage of stem birds. Earlier we looked at the several bird-mimic clades that sprang from the basic bird lineage.

References
Lee MSY, Cau A, Naish D and Dyke GJ 2014. Sustained miniaturization and anatomical innovation in the dinosaurian ancestors of birds.
Osborn HF 1903. 
Ornitholestes hermanni, a New Compsognathoid
Dinosaur from the Upper Jurassic. Bulletin of the AMNH 19:(12):459-464.
Osborn HF 1917. Skeletal adaptations of Ornitholestes, Struthiomimus, Tyrannosaurus. Bulletin of the AMNH 35 (43) pdf
Xing L, Persons WS, Bell PR, Xu X, Zhang J-P, Miyashita T, Wang F-P and Currie P 2013. Piscivery iin the feathered dinosaur Microraptor. Evolution 67(8):2441-2445.
Xu X, Zhou Z, Wang X, Kuang X, Zhang F and Du X 2003. Four-winged dinosaurs from China. Nature, 421: 335–340.

wiki/Microraptor
wiki/Ornitholestes

Chiappeavis – what is it?

There’s a wonderful new
Early Cretaceous bird out there, Chiappeavis (Figs 1, 2), named for a famous bird paleontologist, Luis Chiappe. The question is, what clade does it belong to?

Figure 1. Chiappeavis nests as an ornithurine bird in the large reptile tree, rather than as an enantiornithine. Click to enlarge. Image from O'Connor et al. 2015. 

Figure 1. Chiappeavis nests as an ornithurine bird in the large reptile tree, rather than as an enantiornithine. Click to enlarge. Image from O’Connor et al. 2015.

From the O’Connor et al. 2016 abstract: The most basal avians Archaeopteryx and Jeholornis have elongate reptilian tails. However, all other birds (Pygostylia) have an abbreviated tail that ends in a fused element called the pygostyle. In extant birds, this is typically associated with a fleshy structure called the rectricial bulb that secures the tail feathers (rectrices). The bulbi rectricium muscle controls the spread of the rectrices during flight. This ability to manipulate tail shape greatly increases flight function. The Jehol avifauna preserves the earliest known pygostylians and a diversity of rectrices. However, no fossil directly elucidates this important skeletal transition. Differences in plumage and pygostyle morphology between clades of Early Cretaceous birds led to the hypothesis that rectricial bulbs co-evolved with the plough-shaped pygostyle of the Ornithuromorpha. A newly discovered pengornithid, Chiappeavis magnapremaxillo gen. et sp. nov., preserves strong evidence that enantiornithines possessed aerodynamic rectricial fans. The consistent co-occurrence of short pygostyle morphology with clear aerodynamic tail fans in the Ornithuromorpha, the Sapeornithiformes, and now the Pengornithidae strongly supports inferences that these features co-evolved with the rectricial bulbs as a “rectricial complex.” Most parsimoniously, rectricial bulbs are plesiomorphic to Pygostylia and were lost in confuciusornithiforms and some enantiornithines, although morphological differences suggest three independent origins.”

Figure 2. Chiappeavis reconstructed. Is this specimen just another Pengornis? The large reptile tree does not nest them together.

Figure 2. Chiappeavis reconstructed. Is this specimen just another Pengornis? The large reptile tree does not nest them together. The wing size alone is enough to distinguish this taxon from Pelagornis. 

Elsewhere on the Internet, at
Theropoddatabase.blogspot.com, M. Mortimer presents arguments that Chiappeavis is just another Pengornis (Figs. 3, 4).

Figure 3. Pengornis reconstructed not from tracing, but from cutting out the bones and putting them back together. Color tracing is used only for the skull elements. This holotype specimen does not have the same morphology or proportions that Chiappeavis has and it nests within the Enantiornithes.

Figure 3. Pengornis reconstructed not from tracing, but from cutting out the bones and putting them back together. Color tracing is used only for the skull elements. This holotype specimen does not have the same morphology or proportions that Chiappeavis has and it nests within the Enantiornithes with Sulcavis.

Okay, this is going to ruffle a few feathers…
In the large reptile tree Chiappeavis nests firmly between the clade of Wellnhoferia (aka: the Solnhofen specimen of Archeopteryx + Confuciusornis and Archaeornithura, the now former basalmost ancestor of extant birds. I’m using different traits, but they seem to work. Unlike other studies we know of, there are no scores for absent traits, all derived taxa demonstrate a gradual accumulation of derived traits, and the tree remains completely resolved.

Figure 4. Pengornis in situ with tracing from O'Connor et al. identifying bones.

Figure 4. Pengornis in situ with tracing from O’Connor et al. identifying bones.

>If<  I’ve made enough mistakes
to shift Chiappeavis over to the enantiornithes, please let me know, but everything seems to check out from head to toe.

And yes,
I realize the shape of the scapula/coracoid articulation, the lateral shape of the coracoids, and the stem at the base of the clavicle are all obvious enantiornithine traits. Unfortunately, none of these traits are included in the large reptile tree. However, traits along the lines of a lack of a maxillary fossa, and the elongation of the premaxillary ascending process are included.

So two questions have been provisionally answered here.
Chiappeavis does not share enough traits with Pengornis to be considered conspecific in the large reptile tree. And, Chiappeavis does not share enough traits with enantiornithine birds to be nested with them. Rather Chiappeavis appears to be the new basalmost member of the Ornithurae, for which fan tails are standard equipment. And look at the size of those wings!!!

Perhaps the confusion might stem from
other studies that do not include the various specimens of Archaeopteryx as taxonomic units. Several are distinct and nests basal to one of several derived clades. Reconstructions also seem to help.

References
O’Connor JK, Wang X-L, Zheng X-T, Hu H, Zhang  X-M and  Zhou Z 2016.
An Enantiornithine with a Fan-Shaped Tail, and the Evolution of the Rectricial Complex in Early Birds.Current Biology (advance online publication) DOI: http://dx.doi.org/10.1016/j.cub.2015.11.036