Baminornis, new short-tailed bird from Late Jurassic of China

[Ben Creisler]

Ben Creisler

bcre...@gmail.com

A new paper:

========
Baminornis zhenghensis gen. et sp. nov.

Runsheng Chen, Min Wang, Liping Dong, Guowu Zhou, Xing Xu, Ke Deng, Liming Xu, Chi Zhang, Linchang Wang, Honggang Du, Ganmin Lin, Min Lin & Zhonghe Zhou (2025)
Earliest short-tailed bird from the Late Jurassic of China
Nature 638(8050): 441–448
doi: https://doi.org/10.1038/s41586-024-08410-z
https://www.nature.com/articles/s41586-024-08410-z


Recent macroevolutionary studies predict a diversification of early birds during the Jurassic period, but the unquestionable Jurassic bird fossil record is limited to Archaeopteryx, which has also been referred to deinonychosaurian dinosaurs by some analyses. Although they have feathered wings, the known Jurassic birds are more similar to non-avialan theropods in having the ancestral long reptilian tail. This is in stark contrast to most Cretaceous and crownward taxa, which have a short tail that terminates in a compound bone called the pygostyle. Here we report on the oldest short-tailed avialan, Baminornis zhenghensis gen. et sp. nov., from the recently discovered Late Jurassic Zhenghe Fauna, which fills a noticeable spatio-temporal gap in the earliest branching avialan fossil record. B. zhenghensis exhibits a unique combination of derived ornithothoracine-like pectoral and pelvic girdles and plesiomorphic non-avialan maniraptoran hand, demonstrating mosaic evolution along stem avialan line. An avialan furcula collected from the same locality is referrable to ornithuromorphs on the basis of our morphometric and phylogenetic analyses. These newly discovered fossils demonstrate the early appearance of highly derived bird features, and together with an anchiornithine fossil from the same locality, they suggest an earlier origin of birds and a radiation of early birds in the Jurassic.

====

News:

https://phys.org/news/2025-02-china-jurassic-fossil-discovery-bird.html

https://www.nature.com/articles/d41586-024-04212-5

https://novataxa.blogspot.com/2025/02/baminornis.html

https://www.newscientist.com/article/2468073-quail-sized-feathered-dinosaur-may-be-the-earliest-known-bird/

[Mickey Mortimer]

A basal Jurassic bird with a big pygostyle like that would be big news, but *surprise* it's a synsacrum!

https://theropoddatabase.blogspot.com/2025/02/no-pygostyle-for-baminornis.html

Mickey Mortimer

[Tim Williams]

Chen &c suggest that the separate scapula and coracoid of _Baminornis_ might indicate flight abilities superior to basal avialans that had fused scapulocoracoids.   A separate scapula-coracoid is important for powered flight in modern birds.  But did it matter as much to basal avialans, which likely had a deltoideus-driven upstroke, and a very different flight style to modern birds?  (Pterosaurs had fused scapulocoracoids, and they flew just fine.)

Mickey Mortimer <therizino...@gmail.com> wrote:

> A basal Jurassic bird with a big pygostyle like that would be big news, but *surprise* it's a synsacrum!

The authors make much ado about the definition of clade Pygostylia, because the presence of a pygostyle in _Baminornis_ means it's the most basal avialan to have a pygostyle.  Thus, Chen &c wonder if the pygostyle evolved independently in _Baminornis_, or if the pygostyle was lost in the more crownward _Jeholornis_.  But this isn't new.  Some previous phylogenies have recovered long-tailed _Jeholornis_ as more crownward than pygostyle-bearing _Confuciusornis_ - and occasionally even more crownward than _Sapeornis_, which also has a pygostyle (though its morphology is quite distinct, and more similar to that of basal ornithuromorphs).  So the possibility of convergent evolution of a pygostyle in avialans has come up before.   

Irrespective of whether _Baminornis_ has a pygostyle or not, it just highlights the problem of apomorphy-based definitions in general.  It's probably best to stick to a node-based definition of Pygostylia (as proposed by Chiappe, 2001, and followed by most authors), which has _Confuciusornis_ as a specifier.    

I like the hypothesis of Gatesy (2001), that fusion of the distalmost caudals was originally just a byproduct of tail reduction, and the resulting pygostyle (or pygostyle-like structure) was later recruited in ornithuromorphs for an advanced aerodynamic function.

[Scott Hartman]

Synsacrum was my first thought too, glad I'm not the only one!

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[Mike Habib]

On Feb 13, 2025, at 11:35 PM, Tim Williams <tij...@gmail.com> wrote:

Chen &c suggest that the separate scapula and coracoid of _Baminornis_ might indicate flight abilities superior to basal avialans that had fused scapulocoracoids.   A separate scapula-coracoid is important for powered flight in modern birds.  But did it matter as much to basal avialans, which likely had a deltoideus-driven upstroke, and a very different flight style to modern birds?  (Pterosaurs had fused scapulocoracoids, and they flew just fine.)

Short version: no, it probably doesn’t matter much. There’s no real indication that the separation, in and of itself, is important. What matters for neornithines is the central displacement of the sternum, which is critical to pec minor (aka supracoracoideus) expansion. They achieve this through a separated, elongated coracoid. But if you’re not raising the wing with pec minor then there is no clear reason that the fusion-or-not of the scapula and coracoid should matter much.

Cheers,

—Mike

Mickey Mortimer <therizino...@gmail.com> wrote:

> A basal Jurassic bird with a big pygostyle like that would be big news, but *surprise* it's a synsacrum!

The authors make much ado about the definition of clade Pygostylia, because the presence of a pygostyle in _Baminornis_ means it's the most basal avialan to have a pygostyle.  Thus, Chen &c wonder if the pygostyle evolved independently in _Baminornis_, or if the pygostyle was lost in the more crownward _Jeholornis_.  But this isn't new.  Some previous phylogenies have recovered long-tailed _Jeholornis_ as more crownward than pygostyle-bearing _Confuciusornis_ - and occasionally even more crownward than _Sapeornis_, which also has a pygostyle (though its morphology is quite distinct, and more similar to that of basal ornithuromorphs).  So the possibility of convergent evolution of a pygostyle in avialans has come up before.   

Irrespective of whether _Baminornis_ has a pygostyle or not, it just highlights the problem of apomorphy-based definitions in general.  It's probably best to stick to a node-based definition of Pygostylia (as proposed by Chiappe, 2001, and followed by most authors), which has _Confuciusornis_ as a specifier.    

I like the hypothesis of Gatesy (2001), that fusion of the distalmost caudals was originally just a byproduct of tail reduction, and the resulting pygostyle (or pygostyle-like structure) was later recruited in ornithuromorphs for an advanced aerodynamic function.

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[Jura]

On Monday, February 17, 2025 at 1:52:59 PM UTC-6 Mike Habib wrote:

Short version: no, it probably doesn’t matter much. There’s no real indication that the separation, in and of itself, is important. What matters for neornithines is the central displacement of the sternum, which is critical to pec minor (aka supracoracoideus) expansion. They achieve this through a separated, elongated coracoid. But if you’re not raising the wing with pec minor then there is no clear reason that the fusion-or-not of the scapula and coracoid should matter much.

Cheers,

—Mike

======================================================

I thought that supracoracoideus was homologous to the supra and infraspinatus complex (e.g., Jenkins and Goslow 1983; Goslow et al. 1989)? Pectoralis minor, has been proposed to be the major pectoralis muscle of birds (pectoralis superficialis), with only the deep portion (profundus) sharing homology with pectoralis major (e.g, Howell 1937).

Jason

Refs

Howell, A.B., 1937. Morphogenesis of the shoulder architecture: Aves. The Auk, 54(3), pp.364-375.

Goslow Jr, G.E., Dial, K.P. and Jenkins Jr, F.A., 1989. The avian shoulder: an experimental approach. American Zoologist, 29(1), pp.287-301.

Jenkins Jr, F.A. and Goslow Jr, G.E., 1983. The functional anatomy of the shoulder of the savannah monitor lizard (Varanus exanthematicus). Journal of Morphology, 175(2), pp.195-216.

[Mike Habib]

Good catch - the literature from the 60’s I had in mind in my post tended to refer to the supracoracoideus as an avian “pec minor”, but it’s probably not homologous to the pec minor of other vertebrates. That was sloppy of me. The mechanical point remains, however.

Cheers,

—Mike

Michael B. Habib, MS PhD
Director of Data Visualization
Adjunct Associate Professor of Medicine
UCLA Cardiac Arrhythmia Center
Division of Cardiology
Vatche and Tamar Manoukian Medical Building
100 Medical Plaza, Suite 660
Los Angeles, CA 90095
MBH...@mednet.ucla.edu

Research Associate, Dinosaur Institute
Los Angeles County Museum of Natural History
900 W Exposition Blvd. Los Angeles, 90007

biology...@gmail.com
+1 (443) 280-0181

On Feb 17, 2025, at 1:07 PM, Jura <arch...@gmail.com> wrote:



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[Tim Williams]

Mike Habib <biology...@gmail.com> wrote:

> Short version: no, it probably doesn’t matter much. There’s no real indication that the separation, in and of itself, is important. What matters for neornithines is the central displacement of the sternum, which is critical to pec minor 

> (aka supracoracoideus) expansion. They achieve this through a separated, elongated coracoid. But if you’re not raising the wing with pec minor then there is no clear reason that the fusion-or-not of the scapula and coracoid should 

> matter much.

In addition to your point regarding the fusion-or-not of the scapula and coracoid, even if they are separate elements the two might not be mobile relative to each other.  In certain basal avialans (and probably _Rahonavis_), the coracoid and scapula are not fused, but they articulate in such a way that doesn't allow much if any movement.  So a separate but immobile scapula-coracoid is functionally equivalent to a fused scapulocoracoid.

I don't mean to single out Chen &c, but there is a tendency to view the putative flight abilities of Mesozoic theropods through the lens of what flight-related characters are present in modern birds.  As well as being separate from the scapula, the coracoid of _Baminornis_ is described as "strut-like".  But although the coracoid body is elongated, especially compared to the plesiomorphic quadrangular/trapezoidal-shaped coracoid (e.g., in _Archaeopteryx_), it's proportionately shorter than it is in ornithuromorphs (as Chen &c note), and it's arguable whether it's actually "strut-like".  The elongation of the coracoid body into a true "strut-like" shape is associated with the coracoid's function in resisting and transmitting compressive forces during flapping flight.  At least, that's how I understand it.  In modern birds, the compressive forces directed through the "strut-like" coracoid are transmitted from the wings to the ossified sternum, which is not found in _Baminornis_.  The elongation of the coracoid body was the first step in this process, but it's a long way from the complex bracing system seen in ornithuromorphs.

[Mickey Mortimer]

A few more comments on Baminornis now that I've scored it in the Lori matrix-

The ilium as seen in Figure 2f differs from the drawing in Figure 1b in having a large triangular ventral flange on the preacetabular process, and a pubic peduncle that isn't a narrow triangle but instead has a long and slightly concave articular surface that ends anteriorly above the first 'p' in 'ppi' of Figure 2f.

Similarly, although it is labeled as a left ilium, the edges of the femur seem to go behind the pubic peduncle which would make sense for a right ilium in medial view and a right femur, as maniraptoran femora always have anteroposteriorly broader trochanteric crests than femoral heads. And that would also make the anterodorsally trending crack over the ventral flange make sense as the cuppedicus fossa.

Then the supposed right tibia would actually be the left tibia, in anterior view given the narrower proximal edge compared to the other tibia and the fibular crest on the lower right edge.

The coracoids have a semicircular notch just distal to the head on the medial edge, contra the line drawing, which I would attribute to taphonomy if not for the fact it's in the same place on each coracoid.

Surprisingly, in the Lori matrix Baminornis emerges sister to the Archaeopteryx lithographica type, with archaeopterygids still containing anchiornithines and being basal deinonychosaurs. It makes sense temporally, since well supported avialans are Hauterivian or later while all of these Jurassic paravians are archaeopterygids or scansoriopterygids. The strut-like coracoid, lack of ischial dorsal processes and narrow interclavicular angle are all more similar to derived birds than to archaeopterygids of course, but notably these are also all unlike Jeholornis or Sapeornis, so would also be convergences in Chen et al.'s or Cau's trees where Baminornis is just stemward of Jeholornis. It takes 5 steps to place in Avialae (when archaeopterygids aren't), where it is just stemward of Zhongjianornis, which is in turn stemward of Sapeornis and jeholornithids. Interestingly, the Archaeopteryx type also has a medial coracoid notch (Petronievics and Woodward, 1917- Fig. 1a; lower coracoid notch of de Beer, 1954), although that isn't a character in my matrix.

Mickey Mortimer

[Tim Williams]

Mickey Mortimer <therizino...@gmail.com> wrote:

> Surprisingly, in the Lori matrix Baminornis emerges sister to the Archaeopteryx lithographica type, with archaeopterygids still containing anchiornithines and being basal deinonychosaurs.

Not sure I follow.  Are you saying you recovered _Archaeopteryx_ species as paraphyletic (at least w.r.t. _Baminornis_)?

> where it [_Baminornis_] is just stemward of Zhongjianornis, which is in turn stemward of Sapeornis and jeholornithids. 

So _ Zhongjianornis_ goes back to being one of the most primitive known avialans (as per the original decription by Zhou et al. 2010), rather than being an ornithuromorph related to _Chaoyangia_ (as per O'Connor and Zhou 2012)?

[Mickey Mortimer]

"Are you saying you recovered _Archaeopteryx_ species as paraphyletic (at least w.r.t. _Baminornis_)?"

I scored all Archaeopteryx specimens separately, and they form a clade that includes Baminornis and Alcmonavis. There was an abstract this or last year that used CT scanning on Archaeopteryx and found its forelimb had some characters supposedly only found in Alcmonavis, so that would fit. The Lori matrix doesn't include characters supposed to diagnose Archaeopteryx, of course, which might end up excluding Baminornis.

"So _ Zhongjianornis_ goes back to being one of the most primitive known avialans (as per the original decription by Zhou et al. 2010), rather than being an ornithuromorph related to _Chaoyangia_ (as per O'Connor and Zhou 2012)?"

It's that way in Hartman et al.'s (2019) initial results too (Fig. S2), though at that time it was crownward of Sapeornis and Zhongornis. I haven't added Cratonavis or the new skull data for Jeholornis though, which could easily affect this part of the tree.

Mickey Mortimer

[Tim Williams]

Although a pre-proof, AFAIK the description of the euornithine _Kunpengornis_  by Huang &c is the first publication to identify the "pygostyle" of _Baminornis_ as possibly being a synsacrum.  As such, it features a mention of Mickey Mortimer's blog:
 
"We included the recently
named _Baminornis_ (Chen et al., 2025) in the taxon sample. Yet, the purported presence of a
pygostyle in the latter taxon is ambiguous, since the fused vertebrae interpreted as the distal
end of the tail by Chen et al., 2025, could alternatively be partial remnants of the sacral series
(e.g., the "pygostyle" in figure 2a of Chen et al., 2025, closely recalls the shape and
morphology of the lateral side of the avialan synsacrum shown in figure 2c of O'Connor and
Foster, 2010. See also Mortimer, 2025, https://theropoddatabase.blogspot.com/2025/02/no-
pygostyle-for-baminornis.html)."

The phylogenetic analysis recovers _Baminornis_ as a very early-diverging avialan, and sister taxon to a "Jeholornithiformes + Pygostylia" clade (which has been previously called Euavialae):

"A noteworthy result of the
analysis is the placement of _Baminornis_ in all shortest trees found as sister-taxon of
"Jeholornithiformes + Pygostylia", a placement also obtained by the independently-developed
data set used by Chen et al. (2025). Since in our analysis _Baminornis_ was conservatively
coded as "unknown" about the states of the pygostyle characters, this result suggests that the
affinities of that taxon among early-diverging avialans are not significantly biased by the
interpretation of the "fused vertebrae" as a pygostyle vs a sacral series"

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