The origin of hummingbirds

Hummingbirds are the tiniest of living birds.
They are famous for hovering with wings beating so rapidly they essentially blur from view. Today hummingbirds live only in the New World.

Prum et al. 2015
based on DNA, nested hummingbirds with swifts and these nested with the nocturnal nightjars. That is the traditional nesting.

In the LRT 2015
based on morphology, hummingbirds nest with the extinct Eocypselus (Fig. 4, 50 mya) and the sea gull, Chroicocephalus (Figs. 1, 3; extant). Mayr 2004 reported on an Old World hummingbird, Eurotrochilus inexpectatus (Fig. 4; 30 mya), from the early Oligocene.

Elsewhere on the cladogram,
swifts nest with owls in the large reptile tree (LRT, 1129 taxa).

Figure 1. A sea gull hovering. Many birds can do this for short periods, but sea gulls are phylogenetic sisters to hummingbirds, so this is where it all began for hummers.

Figure 1. A sea gull hovering. Many birds can do this for short periods, but sea gulls are phylogenetic sisters to hummingbirds, so this is where it all began for hummers.

To be fair,
swifts also hover. And here is a sample of that on YouTube. https://www.youtube.com/watch?v=9u8YuBGQWb0
It should be noted that swifts do not feed while hovering. They speed through the air snatching insects in flight. On the other hand, gulls do hover, and here is another image of that (Fig. 2). Gulls appear to hover only in a breeze, which is often present at shorelines. Thus gulls represent the awkward origin of hummingbird hovering, which improved with faster wingbeats. a deeper sternum and a smaller size.

Figure 2. The smallest gull, Hydrocoloeus_minutus, hovering while feeding.

Figure 2. The smallest gull, Hydrocoloeus_minutus, hovering while feeding.

Fossils tell us
that hummingbird-sized specimens, like Eocypselus (Figs. 3, 4), lived 50 mya and probably originated much earlier. One-sixth the size of the small gull, Hydrocoloeus (Figs. 2, 3), Eocypselus had a relatively short, small beak and shorter legs, though still longer than the wings.

Figure 2. Chroicocephalus, the smaller Hydrocoloeus, the much smaller Eocypselus and the ruby-throated hummingbird, Archilochus to scale.

Figure 3. Chroicocephalus, the smaller Hydrocoloeus (the smallest living gull), the much smaller Eocypselus and the ruby-throated hummingbird, Archilochus to scale.

Of course, small size is key to hummingbird evolution.
At this point, I’m not aware of any gulls smaller than Hydrocoloeus, whether extant or in the fossil record. I would like to see a skeleton of Hydrocoloeus to see if it had a larger sternum relative to the 1.25x larger Chroicocephalus. I also wonder if it has a faster wingbeat when hovering based on its smaller size.

Figure 3. Eocypselus from 50 mya, Eurotrochilus, from 30 mya and Archilochus, the extant ruby-throated hummingbird to scale.

Figure 4. Eocypselus from 50 mya, Eurotrochilus, from 30 mya and Archilochus, the extant ruby-throated hummingbird to scale.

The fossil Eutrochilus
(Fig. 4, Mayr 2004) bridges the time gap between Eocypselus and extant hummingbirds and would appear to be a complete and fully realized hummingbird itself, living some 30 mya, while originating much earlier. Eocypselus (Fig. was not much different in size or morphology.

Old World vs. New World
So, based on Eutrochilus, hummingbirds used to be in Europe. Now they are restricted to the New World. Why? There is a long list of hummingbird eaters online here. Something killed European hummingbirds in the Old World… maybe microbes?

Vultures had a similar split.
Today we have New World vultures (like Coragyps, derived from petrels) and Old World vultures (like Torgos, derived from falcons) in the LRT. The odd exception to this hemispherical split is the dodo, Raphus, and its kin, all New World flightless vultures isolated on islands in the Old World. Then there’s a report of an Old World vulture in Miocene Nebraska (Zhang et al. 2012). Really, what’s to stop them? And what killed Old World vultures in the New World? So again, there’s another mystery in need of a good explanation.

References
Mayr G 2004. Old World fossil record of modern-type hummingbirds. Science 304:861–864,
Ksepka DT, Clarke JA, Nesbitt SJ, Kulp FB and Grande L. 2013. Fossil evidence of wing shape in a stem relative of swifts and hummingbirds (Aves, Pan-Apodiformes). Proceedings of the Royal Society B: Biological Sciences 280 (1761): 20130580. doi:10.1098/rspb.2013.0580. Supplementary materials here.
McGuire JA et al. (7 coauthors) 2014. Molecular Phylogenetics and the Diversification of Hummingbirds. Current Biology, 2014; DOI: 10.1016/j.cub.2014.03.016
Zhang Z, Feduccia A and James HF 2012. A Late Miocene Accipitrid (Aves: Accipitriformes) from Nebraska and Its Implications for the Divergence of Old World Vultures. PLoS ONE7(11): e48842. https://doi.org/10.1371/journal.pone.0048842

https://wordpress.com/post/pterosaurheresies.wordpress.com/10805
https://www.livescience.com/44593-first-hummingbird-evolutionary-tree.html

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Extant bird phylogeny: basal divisions

Using the same 231 characters from
the large reptile tree (LRT, 1085 taxa) the subset of extant birds and their allies also came out fully resolved (Fig. 1).

Figure 1. 5-frame GIF of a subset of the LRT focused on extant birds and their closest relatives. Though incomplete, patterns are emerging.

Figure 1. 5-frame GIF of a subset of the LRT focused on extant birds and their closest relatives. Though incomplete, patterns are emerging. Please note: Aepyornis now nests with Struthio. 

Prum et al. 2015 used DNA
to determine the phylogeny of Neoaves (nearly all living bird species). They reported this “remains the greatest unresolved challenge in dinosaur systematics”, but that was before the recent alignment of Ornithischia and Theropoda by Baron et al. 2017.

I have to admit
as usual, before I started adding more extant birds to the LRT, I knew nothing about them. Their generic names were new to me. You might remember the LRT started with just a chicken (Gallus) and an ostrich (Struthio). Now there are 42 birds with 143 outgroup taxa.

Birds are tough.
Often they fuse skull bones. That may be why other workers find protrusions and bumps to base their traits on. Some of the best data for many taxa come from decades old drawings and photos from skull sellers. I made many mistakes along the way, now minimized. The cladogram was my mentor here, telling me with autapomorphies where to look for mistakes.

Matching all prior workers,
tinamous and ratites were recovered as basalmost taxa. In the Prum et al. DNA study, chickens, crakes, screamers and ducks branch off first. In the LRT, which includes extinct taxa, the predators and toothed birds split off first. Distinct from the Prum et al. study, in the LRT long-legged walking birds are basal to many clades. Even the basalmost toothed bird, Yanornis, from the Early Cretaceous, is a long-legged walking bird, also capable of flying. And yes, this puts the origin of the clade of extant birds back to just after the Jurassic. Jurapteryx, from the Late Jurassic, is not far off.

Herons come next,
followed by all other birds with the corn crake (Crex) the hammerkop (Scopus) and the limp kin (Aramus) at the base. Adding taxa allows me to amend an earlier nesting of the elephant bird (Aepyornis) with ducks. Now Struthio and Aepyornis nest together.

In the Prum et al. study
swifts + hummingbirds split off after chickens + ducks.

By contrast,
in the LRT swifts (Eocypselus) and hummingbirds (Archilochus) nest between terns (Thalasseus) and kingfishers (Megaceryle). Nearby, high-energy dippers (Cinclus) nest with other wing swimming birds: murres (Uria) and penguins (Aptenodytes). Cinclus is traditionally considered a passerine, but the sparrow, Passer, does not nest with it in the LRT. Passer nests between chickens and parrots (Ara), all seed eaters.

In the Prum et al. study
seed-eating passerines arise from carnivorous falcons and seriema (Cariama). That does not seem right on the face of it. In the LRT passerines arise from omnivores, like Chauna.

Neotony
juvenile traits found in adult specimens, evidently produced all of our short-legged birds and produced smaller adult birds, found at derived nodes. Juveniles of flamingos and other long-legged taxa have short legs. Of course, some small birds also had large and giant descendants, all at derived nodes.

As in many studies that conflict with the LRT
the lack of appropriate fossil outgroup taxa seems to set their cladograms in other directions. That can happen. DNA studies can never solve this problem.

Apologies for earlier mistakes due to
naive misidentifications and taxon exclusion. Those will be repaired.

Nullius in verba

References
Baron MG, Norman DB, Barrett PM 2017. A new hypothesis of dinosaur relationships and early dinosaur evolution. Nature  543:501–506.
Prum RO et al. (6 coauthors) 2015.
A comprehensive phylogeny of birds (Aves) using targeted next-generation DNA sequencing.

Splitting up the Palaeognathae

Distinct from earlier DNA and morphological studies
members of the Euornithes (extant birds and their closest kin) are undergoing tree topology shifts when they enter the large reptile tree (LRT, 1076 taxa). We’ve seen this before with other reptile and mammal clades.

Today we’ll be talking about
the base of the Euornithes, the ratites and tinamous (= Palaeognathae).

Ratites have no keel on their sternum.
But that keel fails to appear on several flightless birds in several clades. Wikipedia reports, “Flightlessness is a trait that evolved independently multiple times in different ratite lineages. The systematics involved [in the ratites] have been in flux.”

Wikipedia reports,
“There are three extinct groups [of Palaeognathae], the Lithornithiformes (Lithornis + Pseudocrypturus.), the Dinornithiformes (moas) and the Aepyornithiformes (elephant birds), that are undisputed members of Palaeognathae.” 

Disputing those traditional assignments,
in the LRT (Fig. 1):

  1. the moa, DInornis, nests with parrots
  2. the elephant bird, Aepyornis, nests with the ostrich, Struthio.

When I added
the kiwi
Apteryx Fig. 2) and elephant bird (Aepyornis (Fig. 3) to the LRT a monophyletic clade(?) Ratites + tinamous (= Palaeognathae; pink taxa in Fig. 1) was not recovered. The remaining ratites are not a clade, but a grade of basal birds with tinamous, like Rhynchotus, nesting basal to and the proximal outgroup to the clade Neognathae.

And yes, the Solnhofen bird
Jurapteryx recurva (= Eichstätt specimen of Archaeopteryx) is the basalmost member (= last common ancestor) of the Euornithes. That means, someday we’ll be finding palaeognathid ostrich, cassowary and tinamou ancestors in the Early and Late Cretaceous. That has not happened yet (to my knowledge).

Currently filling this Cretaceous gap
are the toothed birds Yanornis, Apsaravis, Ichthyornis and HesperornisThey now nest within the Euornithes (the clade of extant birds). Evidently teeth redeveloped in this clade as they did in Pelagornis, the giant albatross-like bird with bony teeth. Earlier we looked at the reappearance of digit ‘0’ in screamers, so old genes can and do reassert themselves in birds.

Without this clade of toothed Cretaceous birds
there would have been, a long Cretaceous gap in the fossil record of Euornithes. I’m sure this gap will be filled someday with toothless birds. When it is filled phylogenetic bracketing indicates they’re going to look like dippers, like Cinclus, and screamers, like Chauna. As mentioned earlier, this gap is currently not filled, nor even hinted at (Fig. 1).

Figure 2. Jurapteryx, Pseudocrypturus, Apteryx and Proapteryx to scale.

Figure 2. Jurapteryx, Pseudocrypturus, Apteryx and Proapteryx to scale. Now we know why the gastralia disappeared in this clade!

When you put both Pseudocrypturus and Apteryx together
to scale (Fig. 2) the several reasons (traits) why they nest together become more obvious. This is contra recent DNA studies that nest elephant birds with kiwis (Mitchell et al. 2014). That study represents one more incidence of the loss of validity with DNA over large phylogenetic distances along with the typical problem of taxon exclusion that the LRT attempts to minimize.

Archaeopteryx (Jurapteryx) recurva 
(JM2257; the Eichstätt specimen; Howgate 1985) is one of the smaller Solnhofen birds. Here it nests as the last common ancestor of all extant birds. A gap spanning the entire Cretaceous separates this taxon from extant taxa and their kin. As in other bird lines, the loss of tail length, the fusion of the pygostyle and the fusion of manus elements are convergent.

Pseudocrypturus cercanaxius 
(Houde 1988; Early Eocene) was originally considered a northern hemisphere ancestor to ratites (like the ostrich, Struthio). That is true, but Pseudocrypturus is also close to the ancestry of all extant birds. Today primitive flightless birds are chiefly restricted to the southern hemisphere. It could be that early birds did start in the South and had migrated to the North during the Paleocene (66-56 mya) or earlier. Perhaps something very much like it was one of the few survivors of the K-T extinction event.

It’s notable that Pseudocrypturus has long legs. Early ducks, like Presbyornis, and basal raptors, like Sagittarius, also had long legs. Evidence is building that this is the primitive condition for the clade of living birds arising from the K-T extinction event.

Apteryx 
(Shaw 1813) The extant flightless kiwi has an elongate naris that extends to the tip of its beak. Maybe two teeth are there. Here it nests with Pseudocrypturus, but flightless traits linking it toward Struthio are by convergence. In the pre-cladistic era, Calder (1978, 1984) considered the kiwi a phylogenetic dwarf derived from the larger moa, but that was invalidated by Worthy et al. 2013 and the LRT.

Note that
Proapteryx (Worthy et al. 2013; Miocene), known from a partial femur and coracoid, falls within the size range of Jurapteryx (Late Jurassic). Proapteryx likely was volant.

References
Calder WA 1978. The kiwi. Scientific American 239(1):132–142.
Calder WA 1984. Size, function and life history. 448 pp. Cambridge (Harvard U Press).
Houde PW 1986. Ostrich ancestors found in the northern hemisphere suggest new hypothesis of ratite origins. Nature 324:563–565.
Houde PW 1988. Paleognathus birds from the early Tertiary of the northern hemisphere. Publications of the Nuttall Ornithological Club 22. 147 pp.
Howgate ME 1985. Problems of the osteology of Archaeopteryx: is the Eichstätt specimen a distinct genus?. In Hecht, Ostrom, Viohl, and Wellnhofer (eds.), The Beginnings of Birds: Proceedings of the International Archaeopteryx Conference, Eichstätt 1984. Freunde des Jura-Museums Eichstätt, Eichstätt 105-112.
Mitchell KJ (seven coauthors) 2014. Ancient DNA reveals elephant birds and kiwi are sister taxa and clarifies ratite bird evolution. Science. 344 (6186): 898–900.
Shaw 1813. Naturalist’s Miscellany 19:
Worthy TH et al. 2013. Miocene fossils show that kiwi (Apteryx, Apterygidae) are probably not phyletic dwarves. Paleornithological Research 2013, Proceedings of the 8th International Meeting of the Society of Avian Paleontology and Evolution.

wiki/Jurapteryx
wiki/Pseudocrypturus
wiki/Apteryx, Kiwi
wiki/Proapteryx
wiki/Dipper
wiki/Proapteryx

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.

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.