The skull of Sapeornis: not so weird after all…

Sapeornis chaoyangensis 
(Zhou and Zhang 2002, Fig. 1) is known from many specimens including the holotype (IVPP V12698, postcrania only). When two skulls were discovered (Zhou and Zhang 2003) others reconstructed Sapeornis with a high anterior rostrum at odds with putative sister taxa. Here we review the skull of the holotype and find that it is not so odd as others have thought (Google “Sapeornis”). Instead, the newly reconstructed skull is more like Zhou and Zhang 2003 originally reconstructed it, with a low, bird-like rostrum.

Figure 1. The skull of the IVPP V13276 specimen of Sapeornis traced and reconstructed using DGS methods. This is not such an odd skull after all.

Figure 1. The skull of the IVPP V13276 specimen of Sapeornis traced and reconstructed using DGS methods. This is not such an odd skull after all. The mandible is from the 13275 specimen.

Those teeth are distinctive
They are shaped like short cones on slender roots. And if the maxilla has teeth, they are tiny.

Once again 
I encourage workers to start tracing bones in color, especially in crushed and broken fossils. Colors help the eye segregate one bone from another much better than a line drawing can both for identification, reconstruction and presentation.

Figure 1. Subset of the large reptile tree focusing on birds, not including bird-like taxa in more basal clades. Not the nesting of Jeholornis within the clade of Solnhofen birds, too often lumped under a single taxon, Archaeopteryx.

Figure 2. Subset of the large reptile tree focusing on birds, not including bird-like taxa in more basal clades. Sapeornis nests at the base of the Ornithurae, which includes extant birds.

Oddly, and distinct from sister taxa
the coracoids of Sapeornis are short and the sternum is absent (Fig. 3). Those big wings and short legs suggest we have a flying bird here, but the short coracoids and lack of a sternum argue against flapping.

Figure 3. Original reconstruction of Sapeornis with a repaired foot together with coracoids and clavicles from the two referred specimens.

Figure 3. Original reconstruction of Sapeornis with a repaired foot (putting digit 1 nest to digit 2) together with coracoids and clavicles from the two referred specimens. Note the coracoid convex articulation with the concave scapula, an enantiornithine trait by convergence here.

Zhou and Zhang 2003 reported,
“The skeleton of Sapeornis has several unique features, such as a distinctively elongated fenestra on the proximal end of the humerus, a robust furcula with a distinctive hypocleidum, and an elongated forelimb.”

Evolution goes its own way
and in this case, apparently, the coracoids and sternal area reverted to an ancestral state that was not successful beyond this taxon. We can guess that Sapeornis had a distinct niche and/or behavior regimen that did not select for flapping, despite the big wings. It’s proximal sister, Chiappeavis, had a sternum and elongate coracoids together with big forelimbs (Fig. 3). Despite the strong differences these two share more traits than any competing candidates.

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

Figure 3. Chiappeavis reconstructed. Is this specimen just another Pengornis? The large reptile tree does not nest them together.

The perforated humerus
is also found in the Solnhofen specimen of Archaeopteryx and its sister Confuciusornis. Chiappeavis may also have this trait. Hard to tell.

References
Zhou Z-H and Zhang F-C 2002. Largest bird from the Early Cretaceous and its implications for the earliest avian ecological diversification. Naturwissenschaften, 89: 34–38.
Zhou Z-H and Zhang F-C 2003. Anatomy of the primitive bird Sapeornis chaoyangensis from the Early Cretaceous of Liaoning, China. Canadian Journal of Earth Science 40:731-747.

Jeholornis nests within current Archaeopteryx specimens

That Jeholornis nests
as the Chinese Archaeopteryx comes as no surprise. Jeholornis was always considered a close relative of Archaeopteryx. The key difference here (Fig. 1) in this subset of the large reptile tree is that earlier we nested several specimens of Archaeopteryx at the bases of all the later major bird clades (Fig. 1). That’s an unorthodox hypothesis seeking acceptance and widespread practice.

Figure 1. Subset of the large reptile tree focusing on birds, not including bird-like taxa in more basal clades. Not the nesting of Jeholornis within the clade of Solnhofen birds, too often lumped under a single taxon, Archaeopteryx.

Figure 1. Subset of the large reptile tree focusing on birds, not including bird-like taxa in more basal clades. Not the nesting of Jeholornis within the clade of Solnhofen birds, too often lumped under a single taxon, Archaeopteryx.

Now we can nest Jeholornis
with between certain specimens of Archaeopteryx and not others.

  1. Archaeopteryx siemensii (Thermopolis specimen) – basalmost Aves
  2. Archaeopteryx siemensii  (Berlin specimen)- basal Enantiornithes
  3. Archaeopteryx lithographica  (London specimen- holotype)- basal Enantiornithes
  4. Archaeopteryx bavarica  – basal Scansioropterygidae
  5. Jeholornis prima – basalmost Ornithurae
  6. Archaeopteryx [Jurapteryx] recurva (Eichstaett specimen) basal Ornithurae (including extant birds)
  7. Archaeopteryx [Welllnhoferia] grandis (Solhnhofen specimen) – Confuciusornithiformes (within Ornithurae)

The nesting of Jeholornis within the clade of basal Solnhofen birds solves many problems.

Jeholornis is the only long-tailed avian genus from China.
Zhou and Zhang 2002 report, “This bird is distinctively different from other known birds of the Early Cretaceous period in retaining a long skeletal tail with unexpected elongated prezygopophyses and chevrons, resembling that of dromaeosaurids, providing a further link between birds and non-avian theropods.”

O’Connor et al. 2011 report, “The Early Cretaceous long bony-tailed bird Jeholornis prima displays characters both more basal than Archaeopteryx and more derived, exemplifying the mosaic distribution of advanced avian features that characterises early avian evolution and obfuscates attempts to understand early bird relationships.”

Confusion over the nesting
of Jeholornis has probably resulted from taxon exclusion. Virtually all prior studies included only one Archaeopteryx as a taxon. Which one? I don’t know. More taxa of Solnhofen birds need to be added.

Contra Zhou and Zhang 2002
in the large reptile tree, birds are not derived from dromaeosaurids, but from increasingly bird-like troodontids like Sinornithoides, Aurornis, Anchiornis, Eosinosauropteryx, and Xiaotingia.

Figure 2. The holotype of Jeholornis skull traced and reconstructed using DGS methods. Here maxillary teeth and the premaxilla were identified. Colorizing helps identify bones more easily than simple black outlines.

Figure 2. The holotype of Jeholornis skull traced and reconstructed using DGS methods. Here maxillary teeth and the premaxilla were identified. Colorizing helps identify bones more easily than simple black outlines. If you see any errors, pleas call them to my attention. The postorbital is reconstructed with a process entering the orbit. This is an unrestored break, not a real process.

Maxillary teeth
Zhou and Zhang 2002 report, “The maxilla is reduced and does not bear any teeth.” Using Photoshop and the DGS method, I was able to find left maxillary teeth in the holotype of Jeholornis (Fig. 2). The right maxillary teeth may be scattered or buried. The premaxilla (with teeth) was found to be jammed up against the other rostral bones.

Flapping
Zhou and Zhang 2002 report, “The  derived features of the pectoral girdle of Jeholornis such as a strut-like coracoid and the well-developed carpal trochlea of the carpometacarpus, suggest the capability of powerful flight.”  I agree.

Also note
Sapeornis nests within the Ornithurae grade with this list of taxa as other Sapeornithiformes are not currently listed. We’ll look at the skull tomorrow.

Jeholornis is not the first archaeopteryx-like bird from China.
We also have the Liaoning embryo, which nests with the holotype of Archaeopteryx, the London specimen (Fig. 1). Basically, only the relatively large skull, large orbit and small, gracile cervicals of the embryo, distinguish the two taxa, but then those are juvenile traits in birds that change allometrically during ontogeny.

The Jehol Group
(according to O’Connor et al. 2011) “consists of three formations, namely the Dabeigou, Yixian and Jiufotang (Zhou 2006), which record primarily lake and volcanic deposits that are approximately 131 to 120 Ma old (He et al. 2004, 2006; Yang et al. 2007; Zhu et al. 2007). The youngest formation of the Jehol Group, the Jiufotang Formation, preserves the most diverse Mesozoic avifauna known in the world, with long-tailed birds most closely related to Archaeopteryx living alongside the earliest ornithurines (Zhou 2006).”

Lumping or splitting
Some paleontologists lump all Archaeopteryx specimens together. Phylogenetic analysis (Fig. 1) indicates they should be split apart. That needs to start happening in bird studies. I’m happy to support it and promote it.

In similar fashion
earlier I disagreed with those who lump all Rhamphorhynchus specimens together. Phylogenetic analysis is able to split them apart and even find a juvenile of a giant. This juvenile is the size of smaller adult species, hence the confusion.

For those still insisting that the large reptile tree needs more ‘key’ characters
let me remind you that the currently employed list of non-theropod, non-bird specific character traits is doing a better job of lumping and splitting 645 taxa with the current list of 228 traits, (151 parsimony informative traits in theropods), even while testing close matches, like Jeholornis, to current taxa like the several Archaeopteryx specimens. We have a saying here in the USA: “If it ain’t broke, don’t fix it.”

References
O’Connor JK, Sun C-K, Xu X, Wang X-L and Zhou Z-H 2011. A new species of Jeholornis with complete caudal integument. Historical Biology iFirst article, 2011, 1–13.
Zhou Z-H and Zhang F-C 2002. A long-tailed, seed-eating bird from
the Early Cretaceous of China. Nature 418:405-409.

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

When true birds, pre-birds and pseudo-birds first started flapping

Figure 1. Xiaotingia with new pectoral interpretation. See figure 3 for new tracing.

Figure 1. Xiaotingia with new pectoral interpretation. See figure 3 for new tracing. Based on the height of the coracoids, comparable to the height of the furcula, Xiaotingia was an early flapper. Based on the shorter tail length those taller coracoids represent yet another convergence with true birds. 

According to the cladogram
of the large reptile tree the proximal outgroup to Archaeopteryx and the flapping birds includes Eosinopteryx (Godefroit et al. 2013, Middle-Late Jurassic, Tiaojishan Formation, YFGP-T5197, 30 cm, 12 in long) and Xiaotingia (Figs. 1-4; Xu et al. 2011, STM 27-2).  This nesting has not changed despite the addition of several very bird-like theropod taxa recently (some listed below) to the large reptile tree.

Although they both had large wing feathers,
only Xiaotingia had tall coracoids. Coracoids were narrow, but short in Eosinopteryx. Tall coracoids are morphological signs that an extinct taxon was flapping.

Figure 2. Eosinopteryx with new pectoral interpretation. See figure 4 for in situ tracings.

Figure 2. Eosinopteryx with new pectoral interpretation. See figure 4 for in situ tracings. This taxon had smaller coracoids than in Xiaotingia. Based on tail length, this is the plesiomorphic condition.

Tall coracoids first appear
in the true bird lineage with the basalmost Archaeopteryx, the Thermopolis specimen (Fig. 5).

Figure 3. GIF animation of Xiaotingia pectorals showing new interpretations for the coracoid and sternum. Reconstruction in figure 1.

Figure 3. GIF animation of Xiaotingia pectorals showing new interpretations for the coracoid and sternum. Reconstruction in figure 1. The fuzzy yellow and gray drawing is the original published interpretation.  Outlying areas are low rez surrounding higher resolution central area. The difficult to see left coracoid is in green, crushed and scattered. The ventral rim of the right coracoid might be peeking beneath the vertebrae, angled toward the sternum. 

By convergence
and along with Xiaotingia, tall-ish coracoids also appear in the unrelated pseudo bird-like taxa Microraptor + Sinornithosaurus and Velociraptor + Balaur. Evidently they were flapping too.

Figure 4. GIF animation for new interpretation of Eosinopteryx pectoral region. The coracoids appear to be half as long but just as tall as previously interpreted. This is a reduction, as in Cosesaurus, rather than an elongation.

Figure 4. GIF animation for new interpretation of Eosinopteryx pectoral region. The coracoids appear to be half as long but just as tall as previously interpreted. This is a reduction, as in Cosesaurus, rather than an elongation. Reconstructed in figure 2. There were two clavicles hidden in their. The dark green areas may be dermal in origin. 

The Thermopolis specimen
of Archaeopteryx (Fig. 5) has the shortest and smallest coracoids of the Solnhofen birds. Note the basal troodontid (Fig. 7) proportions of the small skull and long tail, distinct from the larger skulls and shorter tails in the clade that includes Xiaotingia and Eosinopteryx.

Figure 1. The six tested Solnhofen birds currently named Archaeopteryx, Jurapteryx and Wellnhoferia.

Figure 1. The six tested Solnhofen birds currently named Archaeopteryx, Jurapteryx and Wellnhoferia.

By contrast and convergence,
and based on the reduction of their coracoids to struts, prevolant pterosaur ancestors, like Cosesaurus (Fig. 6), were flapping millions of generations before this clade had anything resembling wings,

Figure 1. Cosesaurus flapping - fast. There should be a difference in the two speeds. If not, apologies. Also, there should be some bounce in the tail and neck, but that would involve more effort and physics.

Figure 6. Click to enlarge and animate. Cosesaurus flapping – fast. There should be a difference in the two speeds. If not, apologies. Also, there should be some bounce in the tail and neck, but that would involve more effort and physics.

Many workers nest
microraptors and velociraptors closer to birds. At least part of that nesting includes the presence of feathers and tall narrow coracoids, ideal for flapping. Unfortunately these alternate nestings cannot be confirmed by the large reptile tree that nest small troodontids, like Xiaotiingia and Eosinopteryx, basal to birds. At least one prior analysis was riddled with errors. I have not examined others yet.

Figure 1. Sinornithoides youngi figure modified from Russell and Dong 1993.

Figure 7. Sinornithoides youngi figure modified from Russell and Dong 1993. Compare these proportions to the basal Archaeopteryx specimens with their small skulls, short torsos and long tails. 

This is where software comes in handy,
finding most parsimonious trees based on a long list of traits despite convergence in a few traits and making every attempt to keep paradigm and tradition out of every computation. These taxa were reexamined and discovered because the the coracoids did not match while so many other characters do match and nest them together. The coracoids still do not match on sisters Xiaotingia and Eosinopteryx, but several errors were repaired.

References
Godefroit P, Demuynck H, Dyke G, Hu D, Escuillié FO and Claeys P. 2013. Reduced plumage and flight ability of a new Jurassic paravian theropod from China. Nature Communications 4: 1394. doi:10.1038/ncomms2389
Xu X, You H, Du K and HanF-L 2011. An Archaeopteryx-like theropod from China and the origin of Avialae. Nature 475 (7357): 465–470.

 

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

The troodontid Sinornithoides: finally a taxon nesting that almost matches tradition

Lately
we’ve been having trouble nesting taxa where they have traditionally nested. Earlier we looked at some reasons why that might be so.

Figure 1. Sinornithoides youngi figure modified from Russell and Dong 1993.

Figure 1. Sinornithoides youngi figure modified from Russell and Dong 1993. The skull is tucked under the tail and matrix supporting the gastralia, so it is probably complete, just not exposed. The ‘killer’ toe claw is not so large n this specimen. 

Today
I’m pleased to announce the nesting of Sauronithoides youngi (Russell and Dong 1993, Early Cretaceous, Aptian/Albian, IVPP V9612), about where it nests in other cladograms, between the dromaeosaurids and the pre-birds + birds.

One little problem
In the large reptile tree, however, the order has been shifted around compared to the cladogram of Turner, Makovicky and Norell (2012) in which Anchiornis, Xiaotingia, Jinfengopteryx and Mei nest as basal troodontids, rather that pre-birds and birds, while Sauronithoides nests in a derived node with Troodon. Their cladogram, like the large reptile tree, nests the above named pre-birds closer to birds. The major difference is the separation of dromaeosauridae from the quite similar overall Sauronithoides by a long list of intervening transitional taxa. That can happen in cladistic analysis. Parsimony rules, of course.

Note the further separation
of Velociraptor from Archaeopteryx. If valid, the retroverted pubis developed by convergence in both clades. Intervening and basal taxa have a ventral pubis without a pubic foot. We looked at bird and pre-bird convergence earlier here.

Figure 2. Sinornithoides cladogram. This taxon nests at the base of the pre-birds and birds, derived from the same ancestors as Velociraptor and Balaur.

Figure 2. Sinornithoides cladogram. This taxon nests at the base of the pre-birds and birds, derived from the same ancestors as Velociraptor and Balaur. We’re not getting a clade of troodontids, but a grade of pre-birds here. 

Sinornithoides youngi
 
is one of the most complete troodontid theropod dinosaurs. It was preserved in a bird-like resting posture. In the large reptile tree (632 taxa, Fig. 2) it nests derived from Tanycolagreus and the Velociraptor clade and basal to the pre-birds and birds. Distinct from the predecessor taxa, the rostrum and nares were low, the forelimbs were shorter, the pubis lacked a foot, the pelvis was smaller. Sinornithoides was one of the earlier bird-like dinos to come out of China. It, too, was fossilized in a resting posture with both tail and neck wrapped around its presumably warm-blooded body.

Everything here, of course, is provisional
as are all scientific hypotheses. That the present cladogram (Fig. 2) makes sense in terms of sister taxa appearing similar and of roughly the same size and that predecessors to derived taxa demonstrate a gradually accumulating set of traits I think bodes well for it.

References
Russell D and Dong Z 1993. A nearly complete skeleton of a new troodontid dinosaur from the Early Cretaceous of the Ordos Basin, Inner Mongolia, People’s Republic of China. Canadian Journal of Earth Sciences, 30: 2163-2173.

wiki/Sinornithoides

Mei long: not bird-like, but a real basal flightless bird!

Mei long (IVPP V12733, Xu and Norell 2004, Early Cretaceous, 130 mya, Figs. 1-3) is famous for its 3D preservation in a curled up sleeping posture. Originally considered a young juvenile, bird-like troodontid, Mei long instead nests in the large reptile tree between the Munich specimen of Archaeopteryx BSp 1999 I 50 and Scansoriopteryx along with other scansoriopterygid basal birds. A second specimen, DNHM D2154 (Gao et al. 2012), was also preserved in a sleeping posture.

Troodontidae
Wikipedia reports, “There are multiple possibilities of the genera included in Troodontidae as well as how they are related.” Adding to this problem, in the large reptile tree several taxa sometimes included in the Troodontidae instead nest sequentially basal to birds (Archaeopteryx), not in a single offshoot clade.

Figure 1. Two Mei long specimens, one in vivo, one in situ.  Click to enlarge.

Figure 1. Two Mei long specimens, one in vivo, one in situ.  Click to enlarge.

From Xu and Norell (2004):
“Mei long is distinguishable from all other troodontids on the basis of extremely large nares extending posteriorly over one half of the maxillary tooth row*; closely packed middle maxillary teeth; maxillary tooth row extending posteriorly to the level of the preorbital bar”; a robust, sub-‘U’-shaped furcula*; presence of a lateral process on distal tarsal IV; and the most proximal end of the pubic shaft is significantly compressed anteroposteriorly* and extends laterally just ventral to the articulation with the ilium*.” 

*These happen to be traits found in sister taxa, the Munich Archaeopteryx and/or Scansoriopteryx.

Figure 2. Mei long compared to the BSP 1999 I 50, Munich specimen of Archaeopteryx and Scansoriopteryx to scale. Click to enlarge.

Figure 2. Mei long compared to the BSP 1999 I 50, Munich specimen of Archaeopteryx and Scansoriopteryx to scale. Click to enlarge.

Scansoriopterygids
One branch of basal birds, the scansoriopterygids (Fig. 3), famous for their long third finger, now includes a new sister, Mei long. 

Figure 3.  GIF animation - the skull of Mei long IVPP specimen in situ and reconstructed.

Figure 3.  GIF animation – the skull of Mei long IVPP specimen in situ and reconstructed.

Juvenile?
The orbit is comparatively large in Mei long and several cranial and vertebral features are unfused. Gao et al. 2012 report, “Although the skeleton exhibits several juvenile-like features including free cervical ribs, unfused frontals and nasals, and a short snouted skull, other attributes, full fusion of all neurocentral synostoses and the sacrum, and dense exteriors to cortical bone, suggest a small, mature individual. Microscopic examination of tibia and fibula histology confirms maturity and suggests an individual greater than two years old with slowed growth. Despite being one of the smallest dinosaurs, Mei long exhibits multi-year growth and cortical bone consisting largely of fibro-lamellar tissue marked by lines of arrested growth as in much larger and more basal theropods.”

Distinct from its new sister taxa
Mei has shorter forelimbs and longer hind limbs. It is also a little larger even if not fully grown. Pedal digit 3 is much longer. The sacrum is much wider. The facial bones are much more gracile. The jugal may not have had an ascending process. Some of these are indeed juvenile traits that may have been retained into adulthood. Such fragility may have contributed to its general lack of fusion (less bone, lighter weight, but not for flying despite being (no doubt, but not preserved) fully feathered. Metatarsal 3 appears to be pinched between 2 and 4. Pedal 2.1 is less than half the length of p2.2 and pedal ungual 2 is quite long, but not tightly curved.

Shifting
Mei to any node prior to Archaeopteryx currently and provisionally adds at least 12 steps.

References
Xu X and Norell MA 2004. A new troodontid dinosaur from China with avian-like sleeping posture. Nature 431:838-841.
Gao C, Morschhauser EM, Varricchio DJ, Liu J, Zhao B 2012. Farke AA ed. “A Second Soundly Sleeping Dragon: New Anatomical Details of the Chinese Troodontid Mei long with Implications for Phylogeny and Taphonomy”. PLoS ONE 7 (9): e45203. doi:10.1371/journal.pone.0045203. PMC 3459897. PMID 23028847.

wiki/Mei_(dinosaur)