Study says: toothless beak + grainivory in basalmost Paleocene birds

Larson , Brown and Evans 2016 conclude:
“To explain this sudden extinction of toothed maniraptorans and the survival of Neornithes, we propose that diet may have been an extinction filter and suggest that granivory associated with an edentulous beak was a key ecological trait in the survival of some lineages.” … like birds (Euornithes).

A few days ago we looked at the most likely candidate at present to nest at the base of all extant birds, and it wasn’t a little seed-eater. Unfortunately, the Larson et al. study was done without a phylogenetic analysis based on morphology. So they don’t know what the basalmost Euornithine was or looked like. Rather they looked at tooth shapes in derived theropods… and threw a Hail Mary pass.

The authors report,
“To date, only one Maastrichtian bird has been assigned to a crown group clade based on a phylogenetic analysis [1], suggesting that crown group birds were less common than contemporary non-neornithine birds in the Cretaceous. There are also no Late Cretaceous neornithines or advanced ornithuromorphs with known cranial remains.”

Seed eaters
as basalmost Euornithine birds appears unlikely given that basalmost Euornithine birds resemble cranes and ratites. Moreover, the crown group Maastrichtian bird isn’t part of the crown group according to the LRT.

References
Larson DW, Brown CM and Evans DC 2016. Dental Disparity and Ecological Stability in Bird-like Dinosaurs prior to the End-Cretaceous Mass Extinction. Current Biology 26(10):1325–1333.

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Vegavis: Late Cretaceous, but not a member of the Euornithes

Clarke et al. 2005 brought us
Vegavis iaai (MLP 93-I-3-1, MACN-PV 19.748; Late Cretaceous. 68 mya; Figs. 1, 2), a disarticulated partial fossil from Antarctica, which they considered a duck relative and the first definite member of the Euornithes (extant birds and kin) that lived before the K-T boundary.

Unfortunately
I was not able to confirm this. The large reptile tree (LRT, 1064 tax, subset fig. 5) nests Vegavis as the proximal outgroup to Yanornis and the Ornithurae.

It appears that mistakes were made
by Clarke et al. which affected their matrix scores. If I made mistakes, I’d be happy to change them when better data comes along.

Figure 1. Vegavis in situ from Clarke et al. 2005. Colors added and used to create the reconstruction in figure 2. What they thought was the other humerus is instead a tibia still linked to the femur. What they thought was a long sacrum is instead the inside of the other humerus.

Figure 1. Vegavis in situ from Clarke et al. 2005. Colors added and used to create the reconstruction in figure 2. What they thought was the other humerus is instead a tibia still linked to the femur. What they thought was a long sacrum is instead the inside of the other humerus The original scale bars did not permit a good match between plate and counter plate.

From the Clarke et al. abstract:
“Long-standing controversy surrounds the question of whether living bird lineages emerged after non-avian dinosaur extinction at the Cretaceous/Tertiary (K/T) boundary or whether these lineages coexisted with other dinosaurs and passed through this mass extinction event.” 

“Here we identify a rare, partial skeleton from the Maastrichtian of Antarctica as the first Cretaceous fossil definitively placed within the extant bird radiation. Several phylogenetic analyses supported by independent histological data indicate that a new species, Vegavis iaai, is a part of Anseriformes (waterfowl) and is most closely related to Anatidae, which includes true ducks. A minimum of five divergences within Aves before the K/T bound- ary are inferred from the placement of Vegavis; at least duck, chicken and ratite bird relatives were coextant with non-avian dinosaurs.”

 

Figure 2. Vegavis had a relatively short scapula and small deltopectoral crest on a long humerus with a shorter antebrachium. The gracile elongated proportions are crane-like. The torso may have been shorter, reducing the gap between the pelvis and scapula. The original sacrum (yellow) is identical to the distal humerus in outline. Note the metatarsal elements are not fused.

Figure 2. Vegavis had a relatively short scapula and small deltopectoral crest on a long humerus with a shorter antebrachium. The gracile elongated proportions are crane-like. The torso may have been shorter, reducing the gap between the pelvis and scapula. The original sacrum (yellow) is identical to the distal humerus in outline. Note the metatarsal elements are not fused. Gray bones are restored.

Figure x. Reconstruction of Vegavis at published size (print 300 dpi reduced to web 72 dpi).

Figure 2.5. Reconstruction of Vegavis at published size (print 300 dpi reduced to web 72 dpi).

Only a tiny reconstruction
(Fig. 2.5) was provided by Clarke et al., so a larger one is provided here (Fig. 2) and it seems to be more crane- or ratite-like than duck-like, although the Eocene duck, Presbyornis (Fig. 3) does have a stork-like morphology.

Clarke et al. conclude:
Vegavis has different proportions from Presbyornis that are closer to other extant basal anseriform species [geese, screamers). Thus, there is further support that the wader proportions and the ecology used to diagnose Presbyorntihidae are derived for that particular anseriform lineage and not ancestral avian characteristics.” Not sure why they arrived at this conclusion because Vegavis appears to have  long-legged, stork- and ratite-like proportions (Fig. 2). This is a gracile bird.

Figure 2. Presbyornis (Eocene) and Anas (extant), a basal and modern duck.

Figure 3. Presbyornis (Eocene) and Anas (extant), a basal and modern duck.

Clarke et al. nest Vegavis

and ducks with chickens, like Gallus, among basalmost Neognaths, derived from sisters to paleognath tinamous like Pseudocrypturus.

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

Figure 4. Reconstruction of the basal ornithuromorph bird, Archaeornithura with skull added. Feathers and ribs omitted. The length of the tail is hard to determine.

By contrast,
the LRT nests ducks higher on the tree (Fig. 5), closer to long-legged predatory birds. Here Vegavis nests with other pre-Ornithurae Cretaceous birds, like Archaeornithura (Fig. 4), most of which have teeth, unfused metatarsals and gastralia. I found gastralia on the published photo of Vegavis. Unfused metatarsals were originally illustrated. The purported fused sacrum (yellow in figs 1, 2) is the same shape as a distal humerus. It appears to be a split humerus, internal view (Fig. 6). The other split ‘humerus’ appears to be a tibia still articulating with the distal femur. Unfused sacral vertebrae are identified above. Pedal digit 5 is not absent. No scattered cervicals are longer than tall. The ischium is shorter than the pubis, which has a small pubic foot.

Apparently 
all birds with shorter limbs evolved them by neotony. Ratite, flamingo and stork juveniles have shorter legs.

Figure 5. Subset of the LRT with the addition of Vegavis as a proximal outgroup to Yanornis and the Ornithurae.

Figure 5. Subset of the LRT with the addition of Vegavis as a proximal outgroup to Yanornis and the Ornithurae.

I’m interested only
in getting things right. If you can provide better resolution images that support the original identifications, I will make changes to the data presented here. At present Vegavis is the result of a gradual accumulation of traits. It is transitional from birds with unfused sacrals and metatarsals to those with fused sacrals and metatarsals and no pedal digit 5 among several other traits.

Figure 6. Here's the purported sacrum of Vegavis with color added. This looks more like a crushed bird humerus. Higher resolution would be helpful.

Figure 6. Here’s the purported sacrum of Vegavis with color added. This matches the one good humerus. I don’t see the hallmarks of a typical fused sacrum here Note the longitudinal lines that should be transverse if this was indeed a sacrum. Of the fused sacra I have seen, fusion extends to the ilia, which are not fused to the sacrum here. Is this the dorsal view? Lateral view? Ventral view of the purported sacrum? Other unfused sacrals are identified closer to the pelvis. Higher resolution would have been helpful, but the authors did not provide it for this key identification.

If you want to see what a related bird sacrum should look like
click here for several samples.

References
Clarke, JA, Tambussi CP, Noriega JI, Erickson GM and Ketcham RA 2005. Definitive fossil evidence for the extant avian radiation in the Cretaceous. Nature 433, 305–308.

 

digimorph.org/specimens/Vegavis_iaai/
wiki/Vegavis

Serikornis: Pre-bird or flightless bird?

Several authors have wondered over the years
how we might be able to tell (or nest) a flightless post-Archaeopteryx  bird from a flightless pre-Archaeopteryx troodontid. Earlier we nested a very large flightless sapeornithid bird, Jianianhualong, distinct from its original nesting as a troodontid. So it can be done.

Figure 1. Serikornis and Jurapteryx (Archaeopteryx) recurva to scale. These two nest as sisters in the LRT.

Figure 1. Serikornis and Jurapteryx (Archaeopteryx) recurva to scale. These two nest as sisters in the LRT. The larger Serikornis was non-volent.

Lefèvre et al. 2017 bring us
a new Late Jurassic ground-dwelling theropod from China, Serikornis sungei (Figs. 1–3; PMOL-AB00200; 50 cm in length) that they nested with the derived troodontid, Eosinopteryx. They reported, “The plumage of this new specimen brings new information on the structure and function of the feathers in basal paravians and consequently on the early evolution of flight.”

By contrast
in the large reptile tree (LRT, 1050 taxa) Serikornis nests strongly with the Eichstätt specimen of Archaeopteryx, aka Jurapteryx recurva. That Solnhofen bird has large wing and tail feathers. The latest Jurassic, earliest Cretaceous formations from which Serikornis came are chronologically appropriate to this relationship. Apparently taxon exclusion by the Lefèvre team is the cause of the disparate nestings.

Figure 2. Serikornis in situ, with original drawing, skull under DGS and reconstructed.  As you can see, the metatarsus was feathery, not scaly, and the wing feathers were reduced. The teeth were longer, curved and sharper.  DGS did a pretty good job with the skull.

Figure 2. Serikornis in situ, with original drawing, skull under DGS and reconstructed.  As you can see, the metatarsus was feathery, not scaly, and the wing feathers were reduced. The teeth were longer, curved and sharper.  DGS did a pretty good job with the skull.

As earlier authors have noted
the most likely time for an early volant bird to go back to flightlessness is when they are still not very good at flight. And that seems to be the case here. Serikornis probably got too big to fly. And its teeth were larger, opposite the general trend for volant birds. And so its flight feathers, like those of any number of extant and extinct flightless birds, became less able to perform aerial duties.

What about that short coracoid?
It is not long and strap-shaped, a common shape in flapping tetrapods. The coracoids in the Eichstätt specimen are lost in a crack so coracoids could not be scored for that Solnhofen bird. That short coracoid of Serikornis must have been a reversal, an atavism. That happens. It’s only one trait out of 228.

Maybe a sternum was overlooked.
The two putative coracoids (Fig. 3) do not have the same outline. So I wonder if one of them was a sternum? Certainly part of the large furculum is buried.

Figure 3. Serikornis pectoral girdle. Here one of the putative coracoids is rei-dentified as a sternum rotated from its in vivo position.

Figure 3. Serikornis pectoral girdle. Here one of the putative coracoids is rei-dentified as a sternum rotated from its in vivo position. A tiny portion of the bottom coracoid peeks out (in indigo).

At first I scored Serikornis
by copying the row for Eosinopteryx then renaming it. Soon distinct scores started appearing. The list became long. PAUP nested Serikornis apart from Eosinopteryx, among the very early birds and with Jurapteryx recurva, close to the base of the clade that includes all extant birds.

An abbreviated list of birdy traits in Serikornis include:

  1. orbit in the posterior half of the skull
  2. ascending process of premaxilla extends to frontals
  3. tail longer than presacral spine
  4. that long gracile pubis
  5. fibula poorly ossified to absent at mid length
  6. metatarsal 5 lacking phalanges

So the claim to fame for this taxon
should have been yet another one of the earliest flightless birds –- not a transitional troodontid documenting the advent of flight feathers. These flight feathers were on their way out, not on their way in.

References
Lefèvre U, Cau A, Cincotta A, Hu D-Y, Chinsamy A, Escuillié F and Godefroit P 2017. A new Jurassic theropod from China documents a transitional step in the macrostructure of feathers. Sci Nat 104:74. DOI 10.1007/s00114-017-1496-y

to soon yet for a Wikipedia article

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.