Specimen STM 15-15 of Sapeornis under the laser and DGS

Serrano et al. 2020
used Tom Kaye‘s laser-stimulated fluorescence (LSF) device to reveal more feathers on the STM 15-15 specimen of Sapeornis more clearly than in visible light (Fig. 1). All the glue between the reassembled stones also shows up much more clearly. In this specimen the bones are easier to see in visible light. Under LSF everything organic glows: feathers, bones, guts.

Figure 1. Sapeornis specimen STM-1515, in situ, under laser, under DGS.

Figure 1. Sapeornis specimen STM 15-15, in situ, under laser and under DGS. Ventral view. Here bones are easier to see in visible light, feathers under laser.

From the abstract
“Unseen and difficult-to-see soft tissues of fossil birds revealed by laser-stimulated fluorescence (LSF) shed light on their functional morphology. Here we study a well-preserved specimen of the early pygostylian Sapeornis chaoyangensis under LSF and use the newly observed soft-tissue data to refine previous modeling of its aerial performance and to test its proposed thermal soaring capabilities.”

Figure 2. Sapeornis skull specimen STM 1515

Figure 2. Sapeornis skull specimen STM 15-15

From the discussion
“Our study is the first to use the preserved body outline of a fossil bird—as revealed under LSF—to refine its flight modeling.”

Figure 3. Sapeornis skull, specimen STM 1515.

Figure 3. Sapeornis skull reconsructed —  specimen STM 15-15.

An overlay of colors in Photoshop
(Figs. 1, 2 = digital graphic segregation, DGS) also helps each bone stand out from the matrix. Moreover, the color tracings are used to build a reconstruction (Figs. 3, 4) from which it is easier to compare features, point-by-point with other Sapeornis specimens (Fig. 4).

In this way, character scores are backed up
with visual data for referees and readers to quickly judge whether the contours of every bone are valid or not without laboriously examining every score and every centimeter of every in situ specimen. Given the world-wide dispersal of fossils and occasional permission restrictions, DGS tracings just make things easier.

An earlier specimen of Sapeornis
(IVPP V13276; Fig. 4), from a previous post, is grossly similar and larger than STM 15-15. Subtle differences (e.g. toe length, coracoid shape, sternae presence, maxillary tooth presence, etc.) separate the two individuals, perhaps splitting them specifically. Even so, the two humeri are nearly identical in size and shape, despite the overall size differences.

Figure 4. Sapeornis specimen STM 15-15 reconstructed from DGS tracing, figure 1 compared to a more robust specimen with larger feet but an identical humerus.

Figure 4. Sapeornis specimen STM 15-15 reconstructed from DGS tracing, figure 1 compared to a more robust IVPP V13276 specimen with larger feet but an identical humerus.

Sapeornis chaoyangensis (Zhou and Zhang 2002. 2003; Early Cretaceous; IVPP V13276) is a basal ornithurine bird, the clade that gave rise to modern birds. Sapeornis nests in the same clade as Archaeopteryx recurva, the Eichstätt specimen, in the large reptile tree (LRT, 1729+ taxa). The short tail was tipped with a pygostyle and a fan of feathers. The coracoids were oddly wide and relatively short.


References
Serrano FJ, Pittman M, Kaye TG, Wang X, Zheng X and Chiappe LM 2020.
Laser-stimulated fluorescence refines flight modeling of the Early Crettaceous bird Sapeornis. Chapter 13 in Pittman M and Xu X eds. Pennaraptoran theropod dinosaurs. Past progress and new Frontiers. Bulletin of the American Museum of Natural History 440; 353pp. 58 figures, 46 tables.

What happened to the postfrontal and postorbital in birds?

Fauth and Rauhut 2020 bring us
“A short overview of the evolution of the skull of birds.”

From the first paragraph (Google translated from German)
“There are a number of advantages to being able to fly, be it the possibility of rapid geographical expansion, the settlement of trees, the escape from predators or the development of new feed sources, including prey capture. However, it cannot be regarded as the sole factor for the success of birds.”

Thereafter
the authors discuss and show (Fig. 1) skull traits, but make a traditional mistake based on a lack of attention to detail. Foth and Rauhut provide only one figure (Fig. 1), in which the postorbital is identified (in orange) only in Allosaurus (B) Archaeopteryx (C) and the enanthiornine, Shenqiornis (D). The postorbital is deemed absent in the extant Crax (A) and the extinct Ichthyornis (E) despite its presence in their diagram.

Figure 1. Theropod and bird skulls from Foth and Rauhut 2020. Postorbital is highlighted in orange, but not the same vestigial postorbital is not highlighted in bird skulls.

Figure 1. Theropod and bird skulls from Foth and Rauhut 2020. Postorbital is highlighted in orange, but not the same vestigial postorbital is not highlighted in bird skulls. Note: ‘Archaeopteryx’ is a wastebasket taxon with variation among the 13 known specimens.

Unfortunately
Foth and Rauhut took the easy way out by using previously provided oversimplified diagrams that lack the data needed to create a valid figure. They also followed paleontological tradition, which, at times like this, fail to provide valid data in the details.

Here are the missing details
in an actual Crax skull (Fig. 2) colorized using DGS methods. It shows a descending postfrontal (orange) and a vestigial postorbital (yelllow splint, but see caption for one more option). The postfrontal is largely fused to the frontal, but that does not negate its presence. No unfused frontal descends beyond mid depth in any vertebrate skull. We should label and score with reason, not with invalid traditions.

Figure 1. Crax tuberosa skull in three views.

Figure 2. Crax tuberosa skull in three views. Note the splint-like post0rbital (yellow). Alternate hypothesis: the splint is the postorbital process of the jugal (cyan, separate ossification from the base below the quadratojugal (olive). That would make the lumpy orange postfrontal the postfrontal + fused postorbital. Time to look at some embryos to see what is happening here: another great PhD dissertation.

The Eichstätt specimen of Archaeopteryx (= Jurapteryx)
shows the separation of the postfrontal (orange) from the frontal and the postorbital (in yellow) disarticulated and shifted slightly posteriorly in situ. This is the specimen basal to extant birds.

Figure 3. The Eichstätt specimen, Jurapteryx recurva, nests with the living ostrich, Struthio, presently in the LRT.

Figure 3. The Eichstätt specimen, Jurapteryx recurva, nests with the living ostrich, Struthio, presently in the LRT.

The tiny Early Cretaceous theropod, Scipionyx
(Fig. 4), demonstrates the separation of the frontal (blue), postfrontal (yellow-green) and postorbital (orange) in non-avian theropods. These elements tend to fuse with size. Phylogenetic miniaturization (= neotony) tends to separate the original elements. When dealing with shrinking taxa, like birds, try to keep this in mind.

Figure 1. Scipionyx skull and overall. The tail and feet are restored.

Figure 4. Scipionyx skull and overall. The tail and feet are restored.

The enantiornithine, Shenqiornis,
will be considered in greater detail In future blogposts.


References
Foth C and OWM Rauhut 2020. Eine kurze Betrachtung der Evolution des Vogelschädels [A short overview on the evolution of the skull of birds]. Jahresbericht 2019 und Mitteilungen 48. ISSN 0942-5845 ISBN 978-3-89937-253-3

Oculudentavis: not a tiny bird or dinosaur. It’s a tiny cosesaur lepidosaur.

Figure 1. Oculudentavis in amber much enlarged. See figure 2 for actual size.

Figure 1. Oculudentavis in amber much enlarged from Xing et al. 2020. See figure 2 for actual size.

I never thought the tiny Middle Triassic pterosaur ancestor, Cosesaurus
(Fig. 2, 4) would ever be joined by an Early Cretaceous sister taxon that was even smaller. Yesterday the impossible happened when the editors of Nature published a description of tiny Oculudentavis (Xing et al. 2020; Figs. 1, 2; Early Cretaceous, 99 mya; 1.4cm skull), which the authors mistakenly considered a basal bird with teeth and the smallest Mesozoic dinosaur.

Figure 2. CT scans of Oculudentavis from Xing et al. 2020 and colored here, plus a comparison of Cosesaurus to scale.

Figure 2. CT scans of Oculudentavis from Xing et al. 2020 and colored here, plus a comparison of Cosesaurus to scale.

Taxon exclusion
Unfortunately the authors did not test Oculudentavis with Cosesaurus, a fenestrasaur, tritosaur lepidosaur… a taxon far from dinosaurs. When Oculudentavis was added to the large reptile tree (LRT) as the 1656th taxon, the tree length was 20291.

As a test
I forced Oculudentavis over to the London specimen of Archaeopteryx, which Xing et al. recovered as a sister, and the LRT bumped up to 20324, a mere 33 steps more despite the huge phylogenetic distance.

I’ve said it before,
convergence is rampant in the tetrapod family tree.

To that point, it should be remembered,
the original describers of Cosesaurus (Ellenberger and de Villalta 1974) mistakenly considered it a Middle Triassic stem bird.

In contrast,
Peters (2000) recovered Cosesaurus and kin with pterosaurs using four previously published phylogenetic analyses. Later, with more taxa, Peters (2007) recovered pterosaurs and kin with the lepidosaur Huehuecuetzpalli (Fig. 3). In addition, ResearchGate.net holds an unpublished manuscript and figures redescribing Cosesaurus and kin much more accurately. The pterosaur referees did not want that manuscript published, having ignored the earlier ones for so long.

Figure 3. Oculudentavis added to the LRT.

Figure 3. Oculudentavis added to the LRT with previously untested  tritosaur lepidosaurs.

Ironically
Xing et al. noted in tiny Oculudentavis lepidosaur-like sclerotic (eyeball) bones and acrodont to pleurodont teeth extending below the orbit, as in modern lizards. Even with these clues, they did not add lepidosaurs to their analysis. They assumed from the start they had a tiny dinosaur-bird (with lepidosaur traits).

Figure 2. Cosesaurus running and flapping - slow.

Figure 4. Cosesaurus running and flapping. If you want to know what the Oculudentaivis post-crania looks like, this is the closest known sister taxon, slightly smaller than full scale.

Distinct from Cosesaurus,
(Fig. 2) the palate of Oculudentavis is solid below the rostrum. The antorbital fenestra is reduced. Damage to the skull displaced one ectopterygoid to the mid palate and broke the jugal. The post-crania remains unknown, but Cosesaurus (Fig. 4) is the most similar taxon.

From the Xing et al. 2020 abstract:
“Here we describe an exceptionally well-preserved and diminutive bird-like skull that documents a new species, which we name Oculudentavis khaungraae gen. et sp. nov. The find appears to represent the smallest known dinosaur of the Mesozoic era, rivalling the bee hummingbird (Mellisuga helenae)—the smallest living bird—in size. The O. khaungraae specimen preserves features that hint at miniaturization constraints, including a unique pattern of cranial fusion and an autapomorphic ocular morphology9 that resembles the eyes of lizards. The conically arranged scleral ossicles define a small pupil, indicative of diurnal activity. The size and morphology of this species suggest a previously unknown bauplan, and a previously undetected ecology.”

The authors saw lepidosaur traits not found in basal birds/tiny dinosaurs.
Rather than seeking and testing more parsimonious sister taxa elsewhere, the authors chose to follow their initial bias and described their find as an odd sort of tiny bird.

In a similar fashion
just a few days ago Hone et al. 2020 did much the same as they mistakenly described a large pteryodactylid, Luchibang, as a small istiodactylid, following their initial bias.

The LRT provides a wide gamut of 1656 taxa 
to test your next new taxon. Don’t make the same mistake as the above authors by assuming your odd little something is something it isn’t.


References
Ellenberger P and de Villalta JF 1974. Sur la presence d’un ancêtre probable des oiseaux dans le Muschelkalk supérieure de Catalogne (Espagne). Note preliminaire. Acta Geologica Hispanica 9, 162-168.
Peters D 2000. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2007.The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Xing L, O’Connor JK,; Schmitz L, Chiappe LM, McKellar RC, Yi Q and Li G 2020. 
Hummingbird-sized dinosaur from the Cretaceous period of Myanmar. Nature. 579 (7798): 245–249.

Thanks to Dr. O’Connor for sending a PDF of the Nature paper. 

wiki/Oculudentavis
www.researchgate.net

The pterosaur tongue bone… and others, too

I did not give the pterosaur tongue much thought
until Li, Zhou and Clarke 2018 discussed it. They report, “Pterosaurs show convergent evolution of traits linked to tongue protrusion and mobility in birds (narrow midline element [achieved through fusion] and elongate, paired and rostrally positioned ceratobranchials).”

Figure 1. Scaphognathus (holotype) with hyoid traced in magenta.

Figure 1. Scaphognathus (holotype) with hyoid traced in magenta.

“We find pterosaurs similarly show lightly-built single pairs of ceratobranchial elements.

“Here, we bring together evidence from preserved hyoid elements from dinosaurs and outgroup archosaurs, including pterosaurs, with enhanced contrast x-ray computed tomography data from extant taxa.” (That means crocs and birds. Pterosaurs are not outgroup archosaurs, but fenestrasaur tritosaur lepidosaurs. Only taxon exclusion and academic suppression prevents this from being widely accepted.)

“The absence of direct and cranially-extensive support from bony elements make crocodilian tongue incapable of significant independent motion. Relative to outgroup lepidosaurs and other tetrapods the bony structure in crocodilians and surveyed basal archosaurs is uniformly simple and small with a single pair of ceratobranchials and no well-mineralized midline element or fusion.” 

“Elongation of hyobranchial elements co-occurs with increased ossification of a midline element (i.e., in paravians) and ceratobranchial fusion on the midline (i.e. pterosaurs). It is also well mineralized in some primarily quadrupedal, herbivorous ornithischians dinosaurs (e.g., ankylosaurids and hadrosauroids.) Within testudines, increase ossification of the midline element is seen in terrestrial taxa with an increase role for intraoral manipulation of food by the tongue.” Quoted verbatim. Ornithischia hyoids from Pinacosaurus are shown in figure 7.

Ludodactylus.

Figure 2. Click to enlarge. Ludodactylus, with rare pterosaur hyoid.

Li, Zhou and Clarke conclude
“In lepidosaurs, which show remarkable diversity in hyoid shape, there remains a primary respiratory function for the hyoid elements. The hyobranchial elements (multiple sets of ceratobranchials) show a primarily dorsoventral movement that is deployed during buccal pumping. The hyoid structure shows strong muscular links to the pectoral girdle that are lost in archosaurs and any tongue protrusion is via attached fleshy extensions rather than bony components. Perhaps not true in fenestrasaurs, which have a bird-like hyoid. See below.

“In Archosauria, the evolution of novel respiratory mechanisms apparently drove a simplification of the tongue that was retained in most taxa. Only with the evolution of flight (birds and pterosaurs) and in select quadrupedal herbivores was tongue structure elaborated.” By convergence, one must assume. Otherwise, what is the common thread?

Li, Zhou and Clarke did not realize
pterosaurs are lepidosaurs, not archosaurs. Anyone can test this by adding more relevant taxa to any relevant cladogram.

Figure 4. Sphenodon hyoids in two views.

Figure 3. Sphenodon hyoids in two views from Jones et al. 2009

Phylogenetic bracketing
using Sphenodon (Schwenk 1986) and Iguana (both with a fleshy tongue and posteriorly branching hyoids) should give tritosaur pterosaurs a fleshy tongue, too… except pterosaurs are highly derived and volant tritosaurs. Only the juvenile Huehuecuetzpalli, otherwise identical to the adult except in size, preserves hyoids. These are only visible posterior to the jaw. “According to their position, the anterior element was identified as the first ceratobranchial and the posterior element as the epihyal. The latter one, however, may be the hyoid cornu.” (Reynoso 1998). Tanystropheus and Macrocnemus have simple slender hyoids that approach one another anteriorly.

Figure 3. Longisquama in situ with hyoids identified.

Figure 4. Longisquama in situ with straight lateral and Y-shaped central hyoids identified.

Overlooked by Li, Zhou and Clarke,
a flightless lepidosaur and pterosaur outgroup taxon, Longisquama (Fig. 4) shares the pterosaur hyoid morphology. Sharovipteryx (Fig. 5) and Kyrgyzsaurus may as well. However in the lateral two taxa the lateral hyoids are so large they appear to have been able to spread laterally and so produce a cobra-like fleshy strake from otherwise loose neck skin and so introduce another aerodynamic membrane. Skull material prevents seeing a central hyoid if present.

Figure 4. Sharovipteryx in situ with hyoids identified. Note the expansive neck skin. Much has been said about the wasp-like insect in the left orbit, but Sharov was an insect collector first and there are many other insects, particularly beetles, all over the matrix.

Figure 5. Sharovipteryx in situ with hyoids identified. Note the expansive neck skin. Much has been said about the wasp-like insect in the left orbit, but Sharov was an insect collector first and there are many other insects, particularly beetles, all over the matrix.

Very few pterosaurs preserve hyoids.
The few that do have bird-like, y-shaped central hyoids (Figs. 1, 2) and sometimes straight lateral hyoids (Fig. 4), as Li, Zhou and Clarke correctly reported.

Yet another bunch of overlooked lepidosauriforms,

  1. Megalancosaurus has a Y-shaped central hyoid, unknown in other drepanosaurs.
  2. Stem chameleon (Early Cretaceous from amber) has a large central element split anteriorly
  3. Chlamydosaurus and kin use the hyoid elements for stretching the dermal skin, whether neck, like the Triassic Sharovipteryx (see above) or throat, as in the anole, Polychrus.
  4. Earliest reptile hyoids I have found: Diplovertebron (Fig. 6, a basal archosauromorph (in the LRT) from the Westphalian, but with its genesis in the Viséan.
Figure 3. Reconstruction of G. watsoni as a distinctly different genus, nesting with Eldeceeon rather than G. bohemicus.

Figure 6. Reconstruction of Diplovertebron (= Gephyrostegus watsoni) showing paired hyoids, the earliest I have seen on a reptile (Westphalian, Late Carboniferous, 300 mya)

Conclusions:
Hyoids vary greatly in size and shape in tetrapods. The basal/typical tetrapod tongue is boneless, fleshy and anchored by hyoids (see Sphenodon (Schwenk 1986), Caiman, Homo or Iguana). A few tongues are modified with an internal Y-shaped element for prey apprehension or reduced mobility, as in Melanerpes and Trioceros. This is found in various lepidosaurs (including pterosaurs) and birds by convergence. Mammals that use their tongues for prey/nectar apprehension do not have hyoids inside the tongue.

Figure 7. A selection of hyoids from Hill et al. 2015 with a focus on the ornithischian, Pinacosaurus.

Figure 7. A selection of hyoids from Hill et al. 2015 with a focus on the ornithischian, Pinacosaurus.

References
Hill RV, D’ Emic MD, Bever GS and Norell MA 2015. A complex hyobranchial apparatus in a Cretaceous dinosaur and the antiquity of avian paraglossalia. Zoological Journal of the Linnean Society 175: 892–909.
Jones et al. 2009. The head and neck muscles associated with feeding in Sphenodon (Reptilia: Lepidosauria: Rhynchocephalia). Palaeontologia Electronica 12(2).
Li Z, Zhou Z and Clarke JA 2018. Convergent evolution of a mobile bony tongue in flghted dinosaurs and pterosaurs. PLoS ONE 13(6):e0198078. https://doi.org/10.1371/journal.
Reynoso V-H 1998. Huehuecuetzpalli mixtecus gen. et sp. nov: a basal squamate (Reptilia) from the Early Cretaceous of Tepexi de Rodríguez, Central México. Philosophical Transactions of the Royal Society, London B 353:477-500.
Schwenk K 1986. Morphology of the tongue in the tuatara, Sphenodon punctatus (Reptilia: Lepidosauria), with comments on function and phylogeny. J Morphol. 1986; 188: 129–156. pone.0198078

Zhongjianosaurus: a tiny dromaeosaurid? No.

Wikipedia reports,
“Zhongjianosaurus yang (Xu and Qin 2017, Yixian Fm. ~60 cm in ln length; ) is a genus of dromaeosaurid belonging to the Microraptoria.”

Unfortunately
the large reptile tree (LRT) nested Zhongjianosaurus with the scansoriopterygid bird, Mei long (Fig. 1). Neither does Microraptor nest with dromaeosaurids. It nests closer to Ornitholestes. Increasing the taxon list will resolve this issue for other workers as it did here.

Figure 1. Zhongjianosaurus compared to Mei long, a scansoriopterygid bird.

Figure 1. Zhongjianosaurus compared to Mei long, a scansoriopterygid bird. Both have relatively short forelimbs vs. long hind limbs among other traits.

Xu and Qin report,
The distal carpal is represented by the compound ‘semilunate’ carpal, formed by the addition of distal carpal 4 on its ventrolateral corner, and this morphology also is present in the troodontid Mei long (Xu et al., 2014a).”

Well, 
Mei long is indeed a troodontid, but so are all birds. Better to label it a scansoriopterygid bird to avoid confusion.

When you read the PDF, bear in mind
that the authors do not label the manual digits 1–3, but 2–4 as they pay homage to Limusaurus with what I call digit 0.

Perhaps if the pelvis or skull was preserved
in Zhongjianosaurus it would nest elsewhere. At present shifting Zhongjianosaurus to Microraptor adds 6 steps. Shifting Zhongjianosaurus to Velociraptor adds 9 steps. With the given data set and character list, this is how it all shakes out at present. And, you have to admit, it’s a pretty good match!

References
Xu X; Qin Z-C 2017. A new tiny dromaeosaurid dinosaur from the Lower Cretaceous Jehol Group of western Liaoning and niche differentiation among the Jehol dromaeosaurids” (PDF). Vertebrata PalAsiatica. In press.

wiki/Zhongjianosaurus

The geologically oldest Archaeopteryx (#12)

Updated November 10, 2016 with higher resolution images of the specimen. The new data moved the taxon over by one node. 

Not published yet in any academic journal,
but making the news in the popular press in Germany to promote a dinosaur museum (links below) is the geologically oldest Archaeopteryx specimen (no museum number, privately owned?). Found by a private collector in 2010, the specimen has been declared a Cultural Monument of National Significance. It is 153 million years old, several hundred thousand years older than the prior oldest Archaeopteryx. It is currently on  display at a new museum, Dinosaurier-Freiluftmuseum Altmühltal in Germany, about 10 kilometers from where the fossil was found.

Figure 1. The new oldest Archaeopteryx in situ with color tracings of bones.

Figure 1. The new oldest Archaeopteryx in situ with color tracings of bones. The ilium has been displaced to the posterior gastralia, or is absent. I cannot tell with this resolution.

Figure 1b. Archaeopteryx 12 in higher resolution.

Figure 1b. Archaeopteryx 12 in higher resolution.

So is it also the most primitive Archaeopteryx?
No. But it nests as the most primitive scansioropterygid bird. As we learned earlier, the Solnhofen birds formerly all considered members of the genus Archaeopteryx (some of been subsequently recognized by certain authors as distinct genera) include a variety of sizes, shapes and morphologies (Fig. 3) that lump and separate them on the large reptile tree. The present specimen has been tested, but will not be added to the LRT until it has a museum number or has been academically published (both seem unlikely given the private status). Given the additional publicity the specimen is now in the LRT.

The fossil is wonderfully complete and articulated
and brings the total number of Solnhofen birds to an even dozen.

This just in
Ben Creisler reports, “The fossil specimen was originally found in 2010 in fragmented condition and took great effort to prepare and piece together as it now appears.”

Figure 2. Reconstruction of the geologically oldest Archaeopteryx, now nesting at the base of the Scansoriopterygidae.   Note the large premaxillary teeth and short snout on a relatively small skull.

Figure 2. Reconstruction of the geologically oldest Archaeopteryx, now nesting at the base of the Scansoriopterygidae. Note the large premaxillary teeth and short snout on a relatively small skull.

Compared to other Archaeopteryx specimens
you can see the new one is among the smallest (Fig. 3) and has a distinct anatomy.

Figure 2. Several Archaeopteryx specimens. The geologically oldest one, (at bottom) is among the smallest and most derived, indicating an earlier radiation than the Solnhofen formation.

Figure 2. Several Archaeopteryx specimens. The geologically oldest one, (at bottom) is among the smallest and most derived, indicating an earlier radiation than the Solnhofen formation.

References
Spektakulaerer-Fund-kommt-in-Ausstellung-article
originalskelett-eines-archaeopteryx-zu-sehen.html
auf-zum-archaeopteryx

Website

Omnivoropteryx reconstructed and nested

A recent addition
Omnivoropteryx sinousaorum (Czerkas & Ji 2002, Fig. 1) now nests in the large reptile tree as a sister to Epidexipteryx (Fig. 4), a derived scansoropterygid bird.

Figure 1. Omnivoropteryx reconstructed from an X-ray photograph.

Figure 1. Omnivoropteryx reconstructed from X-ray photographs (Figs. 2, 3) Some workers think this bird looks like an oviraptorid. I think it looks like an anurognathid.

From the Wikipedia article
“Omnivoropteryx
 (meaning “omnivorous wing”) is a genus of primitive flying bird from the early Cretaceous Upper Jiufotang Formation of China.

Figure 2. The Omnivoropteryx skull X-ray with DGS color tracings. These were used to reconstruct the skull in lateral view.

Figure 2. The Omnivoropteryx skull X-ray with DGS color tracings. These were used to reconstruct the skull in lateral view.

“The authors
who described Omnivoropteryx, Stephen Czerkas and Qiang Ji, stated that their specimen closely resembles Sapeornis (Fig. 5), but the pubis was longer and, since no skull was known for Sapeornis, they did not consider the two names synonyms. The later discovery of Sapeornis skulls shows that they were indeed similar to Omnivoropteryx. This may make Omnivoropteryx a junior synonym of Sapeornis, and the name may be abandoned.”

Now that you can see
the two taxa together, do you agree that they are conspecific? BTW, they nest in separate clades in the large reptile tree.

Figure 4. Omnivoropteryx shares the plate with parts of another bird.

Figure 3. Omnivoropteryx shares the plate with parts of another bird.

Omnivoropteryx was preserved
with parts of another bird (Fig. The only data I have found comes from an X-ray.

Figure 3. Epidexipteryx, another scansoriopterygid with a bird-like pelvis.

Figure 4. Epidexipteryx, another scansoriopterygid with a bird-like pelvis. The toes are not known.

Epidexipteryx (Fig. 4) is a sister
to Omnivoropteryx. Both share a long third finger. Omnivoropteryx also has a long fourth toe. Unfortunately sister taxa do not preserve the toes. This clade produced some anurognathid mimics.

Figure 4. Sapeornis does not nest as a sister to Omnivoropteryx.

Figure 5. Sapeornis does not nest as a sister to Omnivoropteryx.

Sapeornis
is basal to living birds. The scansoriopterygid clade, of course, became extinct.

References
Czerkas SA and Ji Q 2002. A preliminary report on an omnivorous volant bird from northeast China.” In: Czerkas, SJ (editor): Feathered Dinosaurs and the origin of flight. The Dinosaur Museum Journal 1:127-135.

wiki/Omnivoropteryx

 

 

What makes a bird a bird? Everyone knows, it’s not feathers any more…)

The line between birds and theropod dinosaurs
has become increasingly fuzzy now that so many non-birds have feathers and other former bird-only traits.

This is a good sign
that evolutionary theory embraces: small changes and a gradual accumulation of traits in derived taxa.

Ultimately
it may come down to a single defining trait (like mammary glands in mammals, or alternatively a squamosal/dentary jaw joint when soft tissue is missing) when you have lots of taxa near the base of a new major clade. So what is that trait? Or what are those traits as recovered by the large reptile tree?

The basal bird and its proximal outgroup
At present the last common ancestor of all extant birds, scansoriopterygids and enantiornithes in the large reptile tree. is the Thermopolis specimen of Archaeopteryx (Fig. 1). The original authors (Mayr et al. 2007; Rauhut 2013) did not employ a phylogenetic analysis, so perhaps did not realize what they had.

For now
the pre-bird theropod, Eosinopteryx (Fig.1) nests just basal to the basal bird theropod, Archaeopteryx. You might find it interesting to see which traits differentiate the latter from the former in the large reptile tree. This list, short as it is, is by no means complete. It simply reflects the general characters used for all reptiles in the large reptile tree.

Figure 1. Eosinopteryx, a pre-bird, compared to Archaeopteryx, a basal bird to scale. Click to enlarge.

Figure 1. Eosinopteryx, a pre-bird, compared to Archaeopteryx, a basal bird to scale. Click to enlarge.

Archaeopteryx (Thermopolis) novelties vs. Eosinopteryx

  1. Frontal/parietal suture straight and > than frontal/nasal suture
  2. Metacarpals 2-3 subequal
  3. Pubis and ischium oriented posteriorly (convergent with some deinonychosaurs)
  4. Pedal 4 subequal to metatarsal 4  (convergent with some deinonychosaurs)
  5. Pedal 2.1 not > p2.2
  6. Metatarsal 5 shorter than pedal digit 5 (all vestigial, of course)
Figure 2. The coracoid of the Thermopolis specimen is not as elongate as in the more derived taxa. It is just barely not a disc. Thus, this basal taxon was not quite the flapper as the other Solnhofen birds.

Figure 2. The coracoid of the Thermopolis specimen is not as elongate as in the more derived taxa. It is just barely not a disc. Thus, this basal taxon was not quite the flapper as the other Solnhofen birds.

Unfortunately
none of these traits are unique to the bird clade.

I thought, perhaps
that an elongate and locked down coracoid (the key to the origin of flapping) would prove to be present in all basal birds. Such a coracoid is indeed present in other specimens of Solnhofen birds, but not in the Thermopolis specimen (Fig. 2), the basalmost example. 

So what we are seeing
in these six Solnhofen birds are discrete steps in the evolution of the flapping behavior, necessary for creating thrust and ultimately flight, as in many living birds. Just as in Late Jurassic pterosaurs, the island/lagoon environment of Solnhofen was as powerful an agent as the Galapagos islands at splitting basal birds into various clades.

From the Mayr et al. abstract on the Thermopolis specimen:
“We describe the tenth skeletal specimen of the Upper Jurassic Archaeopterygidae. The almost complete and well-preserved skeleton is assigned to  Archaeopteryx siemensii
 Dames, 1897 and provides significant new information on the osteology of the Archaeopterygidae. As is evident from the new specimen, the palatine of Archaeopteryx
 was tetra-radiate as in non-avian theropods, and not triradiate as in other avians. Also with respect to the position of the ectopterygoid, the data obtained from the new specimen lead to a revision of a previous reconstruction of the palate of Archaeopteryx. The morphology of the coracoid and that of the proximal tarsals is, for the first time, clearly visible in the new specimen. The new specimen demonstrates the presence of a hyperextendible second toe in Archaeopteryx*.  This feature is otherwise known only from the basal avian Rahonavis and deinonychosaurs (Dromaeosauridae and Troodontidae), and its presence in Archaeopteryx provides additional evidence for a close relationship between deinonychosaurs and avians**. The new specimen also shows that the first toe of Archaeopteryx was not fully reversed but spread medially, supporting previous  assumptions that Archaeopteryx was only facultatively arboreal*. Finally,we comment on the taxonomic composition of the Archaeopterygidae and conclude that Archaeopteryx bavarica Wellnhofer, 1993 is likely to be a junior synonym of  A. siemensii****, and Wellnhoferia grandis Elzanowski, 2001 a junior synonym of  A. lithographica***** von Meyer, 1861.”

* Actually not as prominent as in deinonychosaurs. Such a toe works just as well at climbing tree trunks as climbing dinosaur flanks.

**This may be a convergence as the two clades are separated by taxa without a hyper extensible pedal 2.

*** Perhaps facultatively able to perch, but arboreality would have been a precursor behavior.

**** These two are sisters in the large reptile tree.

***** These two are not sisters.

Other traits in the Theromopolis specimen 
visible in Figure 1 not present in the large reptile tree include the following:

  1. Smaller antorbital fenestra
  2. Longer attenuate tail
  3. Slightly narrower coracoids
  4. Slightly larger forelimb
  5. Bowed gap between ulna and radius
  6. More gracile pubis, posteriorly oriented
Figure 3. Archaeopteryx Thermopolis pedal digit 2 (in pink). Pedal 2.2 was capable of hyperextension (see figure 4).

Figure 3. Archaeopteryx Thermopolis pedal digit 2 (in pink). Pedal 2.2 was capable of hyperextension (see figure 4).

Mayr et al. looked at pedal digit 2
and noticed it was capable of hyperextension (Fig. 3). They likened it to pedal digit 2 in deinonychosaurs (Fig. 4) which is famous for its ability to elevate the ‘killer claw’.

Figure 4. Deinonychus with elevated pedal digit 2 demonstrating hyperextension.

Figure 4. Deinonychus with elevated pedal digit 2 demonstrating hyperextension.

The large reptile tree
does not nest birds with deinonychosaurs. Rather Xiaotingia and Eosinopteryx nest between these clades. And Xiaotingia also has a similar pedal 2.1 (Fig. 5).

Figure 5. Pedal digit 2 in Xiaotiniga shows the ability to hyperextend pedal 2.2.

Figure 5. Pedal digit 2 in Xiaotiniga also shows the ability to hyperextend pedal 2.2.

On a final note:
Mayr et al. (2007) report four premaxillary teeth in the Thermopolis specimen. I think they might have missed counting the anteriormost premaxillary tooth (Fig. 6) bringing the total to five.

Figure 6. Archaeopteryx, Thermopolis specimen, premaxilla with five teeth, not four, identified here.

Figure 6. Archaeopteryx, Thermopolis specimen, premaxilla with five teeth, not four, identified here.

References
Rauhut OWM 2013. New observations on the skull of Archaeopteryx. Paläontologische Zeitschrift 88(2)211-221.
Mayr G, Pohl, B, Hartmann S and Peters DS 2007. The tenth skeletal specimen of Archaeopteryx. Zoological Journal of the Linnean Society 149:97-116.

Reconstructing Cathayornis using DGS methodology

Updated October 23, 2015 with modifications to the ectopterygoids from data beneath the mandibles.. 

Cathayornis yandica (Zhou et al. 1992, Figs. 1-3, IVPP V9769) was an Early Cretaceous enantiornithine bird known from a virtually complete skeleton on plate and counter plate. It is crushed flat.

The best published tracings
of this specimen are shown here (Fig. 1). I wonder if you’ll agree there is too much left to the imagination in both of these professional tracings. The easy parts are correctly labeled, but I sense confusion in the more difficult details. Some of these were labeled originally with a “?”.

Figure 1. Above, Tracing of Cathayornis from Zhou and Zhang 1992. Below tracing of Cathayornis skull by O'Connor and Dyke 2010 traced using camera lucida. Some element labels are guesses. A few are mistakes.

Figure 1. Previous best efforts at tracing Cathayornis. Above, Tracing of Cathayornis from Zhou et al.  1992. Below tracing of Cathayornis skull by O’Connor and Dyke 2010 traced using camera lucida. Some element labels are guesses (See “?”). A few are mistakes.

Try DGS just once to see if it works for you.
Applying color overlays to digital images of Cathayornis (Fig. 2, 3) recovers more bones more accurately than prior efforts (Fig. 1). And these can be used in reconstructions (Fig. 3). Note the postorbital and squamosal both drifted over the right frontal. That was a surprise. Yes, a tiny postfrontal is present, not fused to the frontal. Broken bones can be identified and repaired. Even the palatal bones can be identified.

Figure 2. Cathayornis skull animated GIF. Each frame lasts 5 seconds. Here virtually all skull elements are identified and applied to the reconstruction in three views (below). Compare the results of this technique to figure 1. Note how the upper and lower jaws match curves.

Figure 2. Cathayornis skull animated GIF. Each frame lasts 5 seconds. Here virtually all skull elements are identified and applied to the reconstruction in three views (below). Compare the results of this technique to figure 1. Note how the upper and lower jaws match curves.

There is no guarantee you’re going to get things right the first time.
I don’t get things right the first time. I make changes as the interpretation runs its course. All DGS does is to remove some of the confusion inherent in the roadkill by segregating one bone after another until most – or all – of the bones are accounted for and fit the reconstruction while matching the patterns of sister taxa.

The postcrania
of Cathaysaurus is traced here (Fig. 3) and used to create a reconstruction in several views. The furcula can be traced here. Originally it was overlooked and misidentified.

Figure 3. Cathayornis tracing and reconstruction from tracing. Boxed area are ventral and rib elements originally segregated on a distinct layer and offset here for clarity. Note the green furcula, overlooked originally.

Figure 3. Cathayornis tracing and reconstruction from tracing. Boxed area are ventral and rib elements originally segregated on a distinct layer and offset here for clarity. Note the green furcula, overlooked originally. Those green bones on either side of the sternum are considered part of the sternum in traditional works. Perhaps they are, but the visible one appears to overlay the sternum, rather than be a part of it.

It may just be a matter of applied effort
When you discover something in paleontology, all you have to do is unveil it. The discovery is the big deal. Not much effort is required, but it is always appreciated. Later workers can add details with appropriate levels of support and criticism. If I had access to the specimen or a higher resolution image, perhaps the level of accuracy would increase further.

Now I’ll ask of the bird people 
what I ask of the pterosaur people. Try to build a reconstruction. It helps when you realize there are parts missing and then you can apply more effort to look for that part in the specimen itself.

If I have made any mistakes here, please bring them to my attention. I’m no bird expert, but I’m learning as I go. Here is a new image of enantiornithine birds to scale (Fig. 4) including Sulcavis, which we looked at recently.

Figure 4. Enanthiornithine birds to scale. Click to enlarge.

Figure 4. Enanthiornithine birds to scale. Click to enlarge.

References
O’Connor J-K and Dyke G 2010. A Reassessment of Sinornis santensis and
Cathayornis yandica (Aves: Enantiornithes). Records of the Australian Museum 62: 7-20.
Zhou Z.-H, Fan F-J and Zhang J 1992.
Preliminary report on a Mesozoic bird from Liaoning, China. Chinese Science Bulletin 37: 1365-1368.

Sulcavis – an enantiornithes bird without a sternum

Figure 1. Pre-bird and bird sternae. Note the replacement of the sternum with gastralia in Sulcavis.

Figure 1. Click to enlarge. Pre-bird and bird sternae. Note the replacement of the sternum with gastralia in Sulcavis.

Ever since the advent
of the dual sternae in Velociraptor and kin, and of the single sternum in Archaeopteryx (Fig. 1), most birds had/have an ossified sternum. One exception is the enantiornithine bird, Sulcavis (Fig. 1-4).

Sulcavis geeorum (O’Connor et al. 2013, Early CretaceousBMNH Ph-000805) is a robin-sized enantiornithes with a relatively small skull and, remarkably, no sternum. Teeth with grooved enamel radiating from the tips gave it its name (sulcus = groove). That was seen as the most distinctive feature. A sternum replaced by gastralia was not considered an issue (see below).

Soft tissue
Although the specimen includes some soft tissue, O’Connor et al. report one pubis missing and another present only proximally. The ischium was reported missing. My examination identifies areas were both pubes (green) and ischia (magenta) used to be (Fig. 2).

Figure 1. Sulcavis in situ with GIF animation original tracing from O'Connor et al. in black and white. Colors identify elements originally reported as missing. Pubis (green), ischium (magenta), ilium (cyan).

Figure 2. Sulcavis in situ with GIF animation original tracing from O’Connor et al. in black and white. Colors identify elements originally reported as missing. Pubis (green), ischium (magenta), ilium (cyan). Reconstruction in figure 2. A proximal ischium was mislabeled a sacral rib.

Enantiornithes are like basal birds
except for the following traditional traits listed by O’Connor et al. 2013 :

  1. Pygostyle proximally forked and distally constructed with ventrolateral processes
  2. Furcula Y-shaped and dorsolaterally excavated
  3. Coracoid with convex lateral margin
  4. Proximal humerus rises dorsally and ventrally to centrally on the concave head
  5. Metacarpal 3 longer than mc2
  6. Distal tarsals fused to metatarsals, but metatarsals unfused distally
Figure 2. Sulcavis reconstruction. PILs on foot. Note the lack of a sternum.

Figure 3. Sulcavis reconstruction. PILs on foot. Note the lack of a sternum. The pedal ungual length and curvature indicate an arboreal lifestyle.

Unfortunately, none of theses traits are listed as characters in the large reptile tree, yet Sulcavis nests with Cathayornis sharing the following traits distinct from other birds:

  1. Skull not shorter than cervicals
  2. Posterior quadrate straight
  3. More than 4 premaxillary teeth
  4. Posterior mandible deeper anteriorly
  5. Retroarticular descends
  6. Metatarsals 2-3 aligned with 1
  7. Pedal 2.2 > p2.1

More pertinent taxa would reduce this list.

Figure 3. Sulcavis skull as originally interpreted (above) and traced using the DGS method (middle) to create a reconstruction (below).

Figure 4. Sulcavis skull as originally interpreted (above) and traced using the DGS method (middle) to create a reconstruction (below). Note, several bones here were not originally identified. It looks possible that a substantial mandibular fenestra might have been present.

Due to the contrived problem
of digit identification in birds and bird-like theropods described and falsified here, O’Connor et al. describe the three manual digits as the

  1. alular digit
  2. major digit
  3. minor digit

Such renaming of digits 1-3 is totally unnecessary.

Re: The sternum
O’Connor et al. report, “No direct information regarding the morphology of the sternum is preserved.” That’s because there is no sternum in this taxon (Figs, 1, 2). The gastralia run right up to the coracoids. So, does this taxon appear to demonstrate how the sternum in enatiornithine birds is formed? Yes, by enlarging and fusing the gastralia, not as a new single, complete bone.

Sternae also appear in dromaeosaurs and oviraptors by convergence. Twin sternae in these taxa do not appear to be homologous with the single sternum of birds. A single sternum originates as a small bone, wider than long followed by a long set of gastralia extending to the pubis, distinct from large twin sternae.

References
O’Connor JK, Zhang Y, Chiappe LM, Meng Q, Quanguo L, Di L 2013. A new enantiornithine from the Yixian Formation with the first recognized avian enamel specialization. Journal of Vertebrate Paleontology 33(1):1-12.