Liaoningvenator: Bird-like troodontid? Or troodontid-like bird?

Shen et al. 2017 describe
a new troodontid, Liaoningvenator curriei (DNHM D3012; Dalian Natural History Museum; Figs. 1-2; Early Cretaceous), they nest Liaoningvenator outside of the Aves (birds).

Figure 1. Liaoningvenator has a long neck and short torso. It nests as a secondarily flightless bird in the LRT, rather than as a troodontid.

Figure 1. Liaoningvenator has a long neck and short torso. It nests as a secondarily flightless bird in the LRT, rather than as a troodontid.

From the abstract:
“A new troodontid, Liaoningvenator curriei gen. et sp. nov., is described based on a complete skeleton from the Early Cretaceous Yixian Formation of Beipiao City, Liaoning Province. It bears the following characteristics of Troodontidae: numerous and more closely appressed maxillary and dentary teeth; the teeth markedly constricted between the roots and crowns; the nutrient foramina in groove on the external surface of dentary; distal caudal vertebrae having a sulcus on the dorsal midline rather than a neural spine. Unlike other troodontids, Liaoningvenator exhibits a sub-triangular ischial boot in lateral view and slender ischial obturator process; transition point in caudal vertebrae starts from the seventh caudal vertebra. A phylogenetic analysis recovers Liaoningvenator and Eosinopteryx as sister taxa that belong to the same clade.”

Figure 2. Troodontid-like birds and bird-like troodontids shown together to scale.

Figure 2. Troodontid-like birds and bird-like troodontids shown together to scale. Note the robust hind limbs  in the secondarily flightless birds, Jianianhualong and Liaoningvenator.

By contrast,
the large reptile tree (LRT, 1011 taxa) nests Liaoningvenator with Jianianhualong as a large flightless basal sapeornithid bird—and all birds nest within the Troodontidae. Size-wise Liaoningvenator is midway between the smaller Archaeopteryx recurva (Fig. 2) and the larger Jianianhualong. So this might be a transitional taxon between the two.

Unrelated
Eosinopteryx (Fig. 2) continues to nest outside of Aves (birds). Distinct from Eosinopteryx, Liaoningvenator has a much shorter torso and much longer neck, as in other birds. Like Jianianhualong metarsal 4 is longer than 3 in Liaoningvenator, among many other traits (see below). Shen et al. did not mention Jianianhualong, probably because the two taxa were published within a few weeks of each other. You might remember earlier Xu et al. 2017 also nested Jianianhualong with the non-avian troodontids. Shen et al. included Sapeornis in their phylogenetic analysis. Not sure why they nested apart in the LRT.

A reconstruction of the Liaoningvenator skull
(Fig. 2) has a large openings and gracile bones. What Shen et al. identified as a maxillary foramen is identified here as the base of the naris. The in situ tail curls anteriorly and several caudal vertebrae are visible over the torso.

From the Shen et al. diagnosis:
“A new troodontid dinosaur bears the following unique combination of characters including autapomorphies indicated with an asterisk and new characters indicated with a double asterisk: prominent slender triradiate postorbital*; deltopectoral crest distinctly extended to the half of the humeral shaft*; no posterior process on the dorsodistal end of ischium**; slender obturator process of ischium**; manual phalanx I-1 longer than metacarpal II**, the length ratio of phalanx I-1 to metacarpal II about 1.49**; the width of metatarsus distally distinctly decrease**; transition point in caudal series starts from the seventh caudal vertebra**.

Troodontid or not?
The large flightless basal birds share a long list of traits in common with troodontids and a few that show they are distinct. Here is a list of the differences between bird-like troodontids, like Sinornithoides and Anchiornis, and the troodontid-like sapeornithid birds, like Jianianhualong and Liaoningvenator.

Liaoningvenator bird traits not shared with non-avian troodontids:

  1. Ventral aspect of premaxilla > 1/3 preorbit length
  2. Ascending process of premaxilla extends beyond naris and contacts frontals (nasal separated)
  3. Lacrimal deeper than maxilla
  4. Major axis of naris 30-90º
  5. Posterolateral premaxilla absent (also in Xiaotingia and Eosinopteryx)
  6. Nasals not longer than frontals (also in Xiaotingia and Eosinopteryx)
  7. Antorbital fenestra without fossa
  8. Manual mc2 and 3 do not align with joints on digit 1
  9. Metatarsal 5 not shorter than pedal digit 5

Shifting
Liaoningvenator and Jianianhualong to Sinornithoides adds 14 steps.

Paul 2002
considered the possibility of secondarily flightless (neoflightless) birds, unfortunately without the benefit of a phylogenetic analysis. Paul wrote: “Reversal normally associated with loss of flight is observed in ornithomimids, therizinosaurs and dromaeosaurs.” The LRT found possibly volant bird-like taxa associated with therizinosaurus (Rahonavis), Ornitholestes (microraptorids) and troodontids (birds), but not ornithomimids (related to Compsognathus) and dromaeosaurs (related to Shuvuuia).

Paul wrote:
“The less sharply flexed, broad coracoids of flightless birds recapitulate the dino-avepod condition. The loss of any sternal keel and shortening of the arms area also normal reversals for flightless birds. The semilunate carpal block and arm folding mechanism…are sometimes lost in flightless birds.”

References
Paul G 2002. Dinosaurs of the Air. Johns Hopkins Press
Shen C-Z, Zhao B, Gao C-L, Lü J-C and Kundrat 2017. A New Troodontid Dinosaur (Liaoningvenator curriei gen. et sp. nov.) from the Early Cretaceous Yixian Formation in Western Liaoning Province. Acta Geoscientica Sinica 38(3):359-371.
Xu X, Currie P, Pittman M, Xing L, Meng QW-J, Lü J-C, Hu D and Yu C-Y 2017. Mosaic evolution in an asymmetrically feathered troodontid dinosaur with transitional features. Nature Communications DOI: 10.1038/ncomms14972.

Let’s take out all Solnhofen birds except Archaeopteryx from the LRT

Figure 1. Theropod subset of the LRT focusing on birds and bird mimics. Only one Archaeopteryx, the holotype, nests here with Enantiornithes.

Figure 1. Theropod subset of the LRT focusing on birds and bird mimics. Only one Archaeopteryx, the holotype, nests here with Enantiornithes.

Traditional cladograms include
only one Solnhofen bird, typically labeled Archaeopteryx. Whether they use the holotype specimen or not, I don’t know. Earlier the large reptile tree (LRT, subsets Figs. 1, 2) added several Solnhofen birds, many workers continue to call Archaeopteryx, while others have given new generic names. A recent paper by Wang and O’Connor 2017 on pygostyles brought this subject back to the table. They recovered four different sorts of pygostyles, but did not recognize four convergent origins for the pygostyles due to (I thought at the time) lacking more than one Archaeopteryx specimen. It’s time to test that assertion.

As reconstructions show
the variety of Solnhofen birds has been largely, but not completely overlooked. In any case the variety is certainly apparent and a revision of the genus Archaeopteryx is long overdue given the interest in every new specimen.

So, what happens to the LRT when only one Archaeopteryx (the holotype) is employed?

< See figure 1.
There is no change in the tree topology, other than the loss of six Solnhofen bird taxa (Fig. 2). The holotype Archaeopteryx continues to nest within Enantiornithes, an extinct bird clade.

Taxon deletion is a good test

Figure 2. Subset of the LRT with seven Solnhofen birds included.

Figure 2. Subset of the LRT with seven Solnhofen birds included. Note their basal positions in the several basal bird clades. This chart, by implication, demonstrates that the first birds preceded the Solnhofen Formation.

Having seven Solnhofen birds
in a cladogram illuminates the origin of birds, the origin of enantiornitine birds, the origin of scansoriopterygid birds and the origin of ornithuromorph birds all from Late Jurassic Solnhofen taxa, something we haven’t had until this point. This is what Wang and O’Connor 2017 lacked and so their report on pygostyles was unnecessarily incomplete.

I encourage all bird workers
to include as many Solnhofen birds as possible in their phylogenetic analyses, and for at least one of them (hopefully more) to revise their taxonomy to include more genera. That would make a great PhD thesis.

References
Wang W and O’Connor JK 2017. Morphological coevolution of the pygostyle and tail feathers in Early Cretaceous birds. Vertebrata PalAsiatica 2017:10: 55:3: 1-26.

Jurassic birds took off from the ground – SVP abstracts 2016

Everyone knows:
Ground up hypothesis – 

implies and includes flapping, always has. Birds flap, always have, at least since the elongation and locking down of the coracoid in ancestral troodontids.

Trees down hypothesis –
has always implied gliding. Gliders don’t flap, never have.

But
baby birds dropping out of trees always flap. It’s what they do. But that fact is often ignored in bird origin videos.

And, as everyone knows by now…
young birds with pre-violant wings flap them like crazy when climbing bipedally — even vertical tree trunks… also something several animated bird origin videos ignore, perhaps because of one glaring opposite extant example: the young wet hoatzin that struggles to climb with all four limbs.

With that preamble…Habib et al. 2016 provide us
a hypothesis on the origin of bird flight that appears to ignore trees and experimental work with pre-volant birds and goes straight to take-off from flat ground. Is that okay?

From the abstract:
“Many small non-avian theropods possessed well-developed feathered forelimbs, but questions remain of when powered flight evolved and whether it occured more than once within Maniraptora. Here, using a first principles modeling approach, we explore these questions and attempt to determine in which taxa takeoff and powered flight was possible. Takeoff is here defined as a combination of both the hindlimb driving the ballistic launch phase, and the wing-based propulsion (climb out). [1]

“Microraptor, Rahonavis, [2] and all avian specimens generated sufficient velocity during leaping or running for takeoff. We re-ran our analysis factoring in life history changes that can alter the flight capability in extant avians, such as egg retention and molting, to examine how these would influence take off capacity. Of the two, molting shows the most significant effects.

“When these results are coupled with work detailing the lack of arboreal features among non-avian maniraptorans and early birds, they support the hypothesis that birds achieved flight without a gliding intermediary step, something perhaps unique among volant tetrapod clades.” [3] [4] [5]

Figure 2. Cosesaurus running and flapping - slow.

Figure 1. Cosesaurus running and flapping – slow.

Notes

  1. Interesting that Habib et al. ignore the presence of trees, which are key to Dial’s hypothesis (updated in Heers et al. 2016)  and opts to go straight from ground to air. That kind of ignores key work, doesn’t it? You might recall that Dr. Habib became famous as the author of the infamous but popular forelimb quad launch hypothesis for pterosaurs.
  2.  Microraptor and Rahonavis are NOT in the lineage of birds in the LRT, but both show how widespread long feathered wings were in Theropoda. The former has elongate coracoids by convergence. The latter does not preserve coracoids, fingers or feathers, but does have the long forearm that might imply bird-like proportions for missing bones… or not.
  3. Apparently Habib et al. assume that pterosaurs and bats originated as gliders when present largely ignored evidence indicates exactly the opposite. Cosesaurus (Fig. 1) was a pterosaur precursor with elongate coracoids, unable to fly, but able to flap. Bats rarely glide, so it is unlikely that they did so primitively. Lacking coracoids, bats employ elongate clavicles to anchor flight muscles.
  4. Okay, so remember the preamble (above) about gliding and trees. When Habib et al. bring up ‘a gliding intermediary step‘, they are implying the presence of trees (high places) in competing and validated-by-experiment hypotheses for the origin of bird flight  — which they are ignoring. They also ignore the fact that baby birds don’t glide when they fall out of trees. They flap like their lives depend upon it. I find those omissions odd, but its not the first time pertinent work has been ignored in paleontology.
  5. In the LRT Xiaotingia (Fig. 2) is the most primitive bird-like troodontid to have elongate coracoids and so may have been the first flapper in the lineage.
Figure 1. Xiaotingia with new pectoral interpretation. See figure 3 for new tracing.

Figure 2. Xiaotingia with new pectoral interpretation.

References
Habib M, Dececchi A, Dufaault D and Larsson HC 2016. Up, up and away: terrestrial launching in theropods. Abstract from the 2016 meeting of the Society of Vertebrate Paleontology.
Heers AM, Baier DB, Jackson BE & Dial  KP 2016. 
Flapping before Flight: High Resolution, Three-Dimensional Skeletal Kinematics of Wings and Legs during Avian Development. PLoS ONE 11(4): e0153446. doi:10.1371/journal.pone.0153446
http: // journals.plos.org/plosone/article?id=10.1371/journal.pone.0153446

YouTube video showing birds running up tree trunks while flapping with nonviolent wings

ScienceNews online promo.

Paravian phylogeny revisited – SVP abstracts 2016

Pei et al. 2016
reveal the origin of birds in a new phylogenetic analysis. Some aspects confirm earlier recoveries in the large reptile tree (LRT) made about a year ago. Not sure about other aspects given the brevity of the abstract and lack of cladogram imagery.

From the Pei et al. 2016 abstract
“Paraves are theropod dinosaurs comprising of living and fossil birds and their closest fossil relatives, the dromaeosaurid and troodontid dinosaurs. Traditionally, birds have been recovered as the sister group to Deinonychosauria, the clade made up of the two
subclades Dromaeosauridae and Troodontidae. However, spectacular Late Jurassic paravian fossils discovered from northeastern China – including Anchiornis and Xiaotingiapreserve anatomy that seemingly challenges the status quo. (1) To resolve this debate we performed an up-to-date phylogenetic analysis for paravians using the latest Theropod Working Group (TWiG) coelurosaur data matrix which we supplemented with new data from recently described Mesozoic paravians from Asia and North America (e.g., Zhenyuanlong and Acheroraptor). This includes data from the unnamed dromaeosaurid IVPP V22530 and Luanchuanraptor, which are included in a phylogenetic analysis for the first time. We also incorporate new data from iconic paravians such as Archaeopteryx and Velociraptor based on firsthand study. (2) The analysis adopted the maximum parsimony criterion and was performed in the phylogenetic software TNT. Our preliminary results support the monophyly of each of the traditionally recognized paravian clades. (3) The Late Jurassic paravians from northeastern China (e.g., Anchiornis and Xiaotingia) are recovered as avialans rather than deinonychosaurians, at a position more basal than Archaeopteryx and other derived avialans (4). The traditional sister group status of Troodontidae and Dromaeosauridae is reaffirmed (5) and is supported by a laterally exposed splenial and a characteristic raptorial pedal digit II. Recently reported Early Cretaceous dromaeosaurids from northern and northeastern China, including Zhenyuanlong, Changyuraptor and IVPP V22530, are closely related to other microraptorines as expected. (6) Luanchuanraptor, a dromaeosaurid from the Late Cretaceous of central China is recovered as a more advanced eudromaeosaurian. By tracing character evolution on the current tree topology we report on the latest insights into the adaptive radiation amongst early paravians, including the origin of flight and changes in body size and diet. (7)

Notes

  1. In the LRT Xiaotinigia and Anchiornis have nested as derived troodontids, basal to birds since their insertion into the LRT more than 3 years ago. So that’s confirmation that troodontids are basal to Archaeopteryx and other birds with Xiaotinigia and Anchiornis as proximal outgroup taxa.
  2. But did they include five or more Archaeopteryx specimens, as in the LRT? They don’t say so…
  3. In the LRT there is a clade that includes Velociraptor, but the Troodontidae does not produce a clade that does not include birds. Rather birds are derived troodontids in a monophyletic clade.
  4. If avialans are usually defined as all theropod dinosaurs more closely related to modern birds (Aves) than to deinonychosaurs, all troodontids are avialans in the LRT. Since Troodontidae was named by Gilmore in 1924, the term Avialae (Gauthier 1986) is a junior synonym.
  5. Troodontidae and Dromaeosauridae are also sisters in the LRT.
  6. This confirms the topology recovered in the LRT from about a year ago. Microraptorines, like Microraptor and basal tyrannosauroids like Zhenyuanlong are not related to troodontids or birds, but to tyrannosaurs and compsognathids.
  7. I’d like to see their tree whenever it is published to compare the two.
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 1. Bird cladogram from several months ago. Here Avialae is a junior synonym for Troodontidae.

References
Pei R, Pittman M, Norell M and Xu X 2016. A review of par avian phylogeny with new data. Abstract from the 2016 meeting of the Society of Vertebrate Paleontology.

The first Jurassic feather – SVP abstract 2016

Pittman et al. 2016
describe a new way of looking at fossils, with laser stimulated fluorescence. I can’t show you what attendees saw at SVP as it is awaiting publication, but other examples can be seen here online. This image from Tom Kaye (Fig. 1) was bumped by me with Photoshop to increase contrast and perhaps reveal a wee bit more detail.

Figure 1. Archaeopteryx feather from T. Kaye. Second image is Photoshop contrast bump created here.

Figure 1. Archaeopteryx feather from T. Kaye. Second image is Photoshop contrast bump created here. Pittman et al. laser stimulated fluorescence imagery was shown at SVP and is awaiting publication. 

From the Pittman et al. 2016 abstract
“The single feather initial holotype of Archaeopteryx lithographica is one of the world’s most iconic fossils, but contains a 150 year old mystery. The specimen’s 1862 description by Hermann von Meyer shows that the calamus is 15 mm long and 1 mm wide. However, the calamus is no longer visible on the fossil, and there is no record of when or how it disappeared. The specimen is a rare example of a lone Archaeopteryx feather, giving access to its entire morphology, as opposed to only parts of it in the overlapping feathers of articulated specimens. This makes it an important addition to the anatomical record of Archaeopteryx and basal birds more generally. After 150 years, laser stimulated fluorescence has recovered the calamus as a chemical signature in the matrix and reveals preparation marks where the original surface details have been obliterated. The feather has recently been imaged by others under UV light as well as with X-rays at the Stanford Linear Accelerator Center, with no reports of the existence of the calamus. This demonstrates the capability of laser stimulated fluorescence to visualize important data outside the range of current methodologies. The feather has at different times, been cited as a primary, secondary and covert, and has even been suggested to belong to another taxon. With the new calamus data in hand, the morphology of the feather was examined within the framework of modern feather anatomy. The percentage of calamus length to overall feather length, when plotted against a histogram of 30 phylogenetically and ecologically diverse modern birds, comes out in the middle of the range, placing it in the flight feather regime. The most recent identification of the feather as a primary dorsal covert can be discounted because the rachis is in line with the calamus rather than curving upwind of the calamus centre line. The curvature of the rachis is also too pronounced to function as a primary or tail feather. If the feather is scaled as a secondary in the wing of Archaeopteryx, only five feathers fit the reconstruction along the ulna, rather than the 9-13 that have been estimated for this taxon and the 7-14 that are found in modern birds. These inferences suggest that the isolated feather is fundamentally inconsistent with those of Archaeopteryx and is instead a secondary of another early bird taxon or potentially even a feather of a non-avialan pennaraptoran theropod.”

Kaye’s work with fossil imaging
has revealed many interesting and otherwise invisible traits. Let’s call this one more ‘feather in his cap.’

References
Pittman M, Kaye TG, Schwarz D, Pei R and Xu X 2016. 150 year old Archaeopteryx mystery solved. Abstract from the 2016 meeting of the Society of Vertebrate Paleontology.

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0125923

2015 SVPCA abstract supports troodontid-bird clade

Nice to get confirmation
for a subset of the large reptile tree in a SVPCA poster (Brougham 2015).

From the Brougham results:
“The modified matrix strongly supports a Troodontidae + Avialae clade rather than a monophyletic Deinonychosauria, a topology remarkably convergent on that seen in modified Godefroit phylogeny, in which Aurornis, Eosinopteryx and the Tiaojishan paravians form a sister clade to Anchiornis and more derived avialans, the two of which in turn form a sister clade to Troodontidae.”

Figure 1. Basal theropod subset of the large reptile tree showing troodontids basal to birds and separate from dromaeosaurs.

Figure 1. Basal theropod subset of the large reptile tree showing troodontids (light red) basal to birds (red) and separate from dromaeosaurs (white).

References
Brougham T 2015. Multi-matrix analysis of new Chinese feathered dinosaurs supports troodontid-bird clade. researchgate.net/publication/280728942

Flapping before flight

This is a long overdue and very welcome paper
Many paleontologists of the past thought flight appeared after gliding. This is the so-called trees down theory seen in this PBS video on Microraptor. Others thought the flight stroke appeared while clutching bugs in the air. This is the so-called ground up theory. Through experimentation Ken Dial found out that baby birds armed with only protowings flapped them vigorously to help them climb trees, no matter the angle of incline. Now the kinematics of this wing/leg cooperation are presented in Heers et al. 2016, students of Ken Dial.

Key thoughts from the abstract:
“Juvenile birds, like the first winged dinosaurs, lack many hallmarks of advanced flight capacity. Instead of large wings they have small “protowings”, and instead of robust, interlocking forelimb skeletons their limbs are more gracile and their joints less constrained. Such traits are often thought to preclude extinct theropods from powered flight, yet young birds with similarly rudimentary anatomies flap-run up slopes and even briefly fly, thereby challenging longstanding ideas on skeletal and feather function in the theropod-avian lineage.
For the first time, we use X-ray Reconstruction of Moving Morphology to visualize skeletal movement in developing birds. Our findings reveal that developing chukars (Alectoris chukar) with rudimentary flight apparatuses acquire an “avian” flight stroke early in ontogeny, initially by using their wings and legs cooperatively and, as they acquire flight capacity, counteracting ontogenetic increases in aerodynamic output with greater skeletal channelization.Juvenile birds thereby demonstrate that the initial function of developing wings is to enhance leg performance, and that aerodynamically active, flapping wings might better be viewed as adaptations or exaptations for enhancing leg performance.”
Figure 2. Cosesaurus running and flapping - slow.

Figure 1. Cosesaurus running and flapping – slow.

The same theory
can be applied to the development of wings in fenestrasaurs (Fig. 1) evolving into pterosaurs (Fig 2), as shown several years ago, but does not play a part in the development of flapping wings in bats, which do not walk upright and bipedally.
Quetzalcoatlus running like a lizard prior to takeoff.

Figure 2 Quetzalcoatlus running like a lizard prior to takeoff. Click to animate.

It should be obvious
that competing take-off theories for pterosaurs (Fig. 3) do not take into account this theory on the origin of flapping. Just one more reason not to support the forelimb wing launch hypothesis that has become so popular with ptero-artists recently.

Unsuccessul Pteranodon wing launch based on Habib (2008).

Figure 3. Unsuccessul Pteranodon wing launch based on Habib (2008) in which the initial propulsion was not enough to permit wing unfolding and the first downstroke.

Remember,
getting into the air is difficult if you’ve never done it before. Using both your arms AND your legs to get up speed is a good idea that has worked in the past and in present day laboratories.

References
Heers AM, Baier DB, Jackson BE & Dial  KP 2016. 
Flapping before Flight: High Resolution, Three-Dimensional Skeletal Kinematics of Wings and Legs during Avian Development. PLoS ONE 11(4): e0153446. doi:10.1371/journal.pone.0153446
http: // journals.plos.org/plosone/article?id=10.1371/journal.pone.0153446