Which theropods were capable of flapping flight?

Both Pei et al. 2020 and Pittman and Xu et al. 2020 looked into
the origin of flight in birds and bird mimics. They calculated maximum and minimum estimates of wing loading and specific lift. These results confirm powered flight potential in early birds and its rarity among the ancestors of closest avialan relatives.

wing loading  (= the total weight of an aircraft divided by the area of its wing).

specific lift (not defined, even when googled, but Pei et al. report, “In powered flyers, specific lift is critical to weight support and generation of thrust (thrust is primarily a component of lift in vertebrate flapping flyers”) If you find that confusing, so do I. Thrust and lift are typically considered separately, not as a component of each other.

In both papers there was no mention
of elongate, locked-down coracoids. When you find such coracoids, that’s how we know pterosaur ancestors, like Cosesaurus (Fig. 1), started flapping. Here the former disc-like sliding coracoids are reduced by posterior erosion to slender immobile still curved stems. The scapula is likewise a narrow immobile strap, as in flapping birds.

Figure 1. Cosesaurus flapping - fast. There should be a difference in the two speeds. If not, apologies. Also, there should be some bounce in the tail and neck, but that would involve more effort and physics.

Figure 1. Click to enlarge and animate. Cosesaurus flapping – fast. There should be a difference in the two speeds. If not, apologies. Also, there should be some bounce in the tail and neck, but that would involve more effort and physics.

All extant birds have elongate coracoids.
All extant birds can flap. All have flying ancestors, even those that no longer fly. So when do birds begin to have locked down coracoids and strap-like scapulae in the large reptile tree (LRT, 1738+ taxa)? Let’s look, clade by clade.

All Solnhofen ‘birds’ have elongate coracoids and strap-like scapulae.

Prior to that Xiaotingia and kin have the same.

Prior to that Daliansaurus does not preserve a pectoral girdle, but descendant taxa have elongate coracoids and strap-like scapulae. Call that x1 for flapping.

Prior to that Jinfengopteryx and kin have elongate coracoids and strap-like scapulae. Call that x2.

Prior to that Bambiraptor and Haplocheirus have a short disc-like coracoid, but Velociraptor and Balaur have elongate pectoral elements. Call that x3.

Prior to that Ornitholestes had a short, round coracoid, but Changyuraptor and descendants like Microraptor and Sinornithosaurus had elongate pectoral elements. Call that x4.

Prior to that all theropods in the LRT have a short, round coracoid that slid along the left and right sternae. So, they were not flapping according to this hypothesis.

Highlights of Pei et al. 2020:
One: Support Deinonychosauria as sister taxon to birds and Anchiornithinae as early birds

Supported by the LRT

Two: Powered flight potential evolved ≥3 times: once in birds and twice in dromaeosaurids

Supported by the LRT

Three: Many ancestors of bird relatives neared thresholds of powered flight potential

Supported by the LRT

Four: Broad experimentation with wing-assisted locomotion before theropod flight evolved

Supported by the LRT

Figure 2. Subset of the LRT focusing on Pennaraptora 2014 = Tyrannoraptora 1999. Here Khaan and Velociraptor substitute for Oviraptor and Deinonychus.

Figure 2. Subset of the LRT focusing on Pennaraptora 2014 = Tyrannoraptora 1999. Here Khaan and Velociraptor substitute for Oviraptor and Deinonychus.

The authors note:
Scansoriopterygians (Figs. 3, 4) are included in the phylogenetic analysis, but are excluded from the flight parameters because Yi’s wing (Fig. 3) is skin-based rather than feather-based like the other winged taxa in this dataset, while Epidexipteryx (Fig. 4) does not possess pennaceous feathers.”

Both are incorrect. We looked at the Yi and Ambopteryx issues here. Both are descendants of Solnhofen bird . So they had feathers, not bat-like skin membranes.

Figure 4. Yi qi tracing of the in situ specimen using DGS method and bones rearranged, also using the DGS method, to form a standing and flying Yi qi specimen. Note the lack of a styliform element, here identified as a displaced radius and ulna.

Figure 4. Yi qi tracing of the in situ specimen using DGS method and bones rearranged, also using the DGS method, to form a standing and flying Yi qi specimen. Note the lack of a styliform element, here identified as a displaced radius and ulna.

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

Figure 3. Epidexipteryx, another scansoriopterygid bird.

The authors note:
“For Rahonavis (Fig. 4), given only the radius and ulna are known, we reconstructed its wing with similar intralimb proportions to Microraptor where the ulna is 37% of the forelimb length.”

This is guessing, inappropriate for science. In the LRT, Rahonavis (Fig. 4) and Microraptor are not related. We don’t have a hand/manus or a coracoid for Rahonavis. In the LRT Rahonavis is a small therizinosaur, close to Jianchangosaurus, not related to taxa with a long, locked-down coracoid.

Figure 2. Rahonavis nests in the LRT as a tiny derived therizinosaur based on the few bones currently known.

Figure 4. Rahonavis nests in the LRT as a tiny derived therizinosaur based on the few bones currently known. The unknown coracoid is restored as a disc here.

From the Pei et al. Summary:
“Uncertainties in the phylogeny of birds (Avialae) and their closest relatives have impeded deeper understanding of early theropod flight. To help address this, we produced an updated evolutionary hypothesis through an automated analysis of the Theropod Working Group (TWiG) coelurosaurian phylogenetic data matrix. Our larger, more resolved, and better-evaluated TWiG-based hypothesis supports the grouping of dromaeosaurids + troodontids (Deinonychosauria) as the sister taxon to birds (Paraves) and the recovery of Anchiornithinae as the earliest diverging birds.”

With exceptions, Pei et al. confirm the origin of flapping topology
found in the large reptile tree (LRT, 1738+ taxa, subset Fig. 1), except in the LRT large ‘troodontids’ nest with dromaeosaurids. Small ‘troodontids’ nest with Anchiornis basal to birds. Some near birds (see list above) developed, by convergence, the elongate locked-down coracoids seen in Solhnhofen birds and their descendants.

There are two ways to get slender locked-down coracoids in vertebrates,
by erosion of the disc to a remaining stem (as in pterosaur ancestors) or by elongation of the entire disc to produce a stem (as in birds and crocs).

Lacking coracoids, bats 
have elongated and locked down clavicles for symmetrical forelimb flapping. Bats are inverted bipeds.

Wing loading issue
Since birds/theropods depend on feathers for wing chord and span it would seem necessary to use only those theropods in which feathers were well known and to show in graphic form the extent of those wing feathers. I don’s see that in this study.

The rapidity of flapping
permits some certain taxa (ducks, hummingbirds, etc.) to have relatively short and small wings while flying. Gliding is not a primitive trait in birds, pterosaurs or bats.

More from the Pei et al. summary:
“Although the phylogeny will continue developing, our current results provide a pertinent opportunity to evaluate what we know about early theropod flight. With our results and available data for vaned feathered pennaraptorans, we estimate the potential for powered flight among early birds and their closest relatives. We did this by using an ancestral state reconstruction analysis calculating maximum and minimum estimates of two proxies of powered flight potential—wing loading and specific lift. These results confirm powered flight potential in early birds but its rarity among the ancestors of the closest avialan relatives (select unenlagiine and microraptorine dromaeosaurids). For the first time, we find a broad range of these ancestors neared the wing loading and specific lift thresholds indicative of powered flight potential. This suggests there was greater experimentation with wing-assisted locomotion before theropod flight evolved than previously appreciated. This study adds invaluable support for multiple origins of powered flight potential in theropods (≥3 times), which we now know was from ancestors already nearing associated thresholds, and provides a framework for its further study.”

Figue 1. A new reconstruction of the basal bipedal croc, Pseudhesperosuchus based on fossil tracings. Some original drawings pepper this image. Note the interclavicle, missing in dinosaurs and the very small ilium, only wide enough for two sacrals. The posterior dorsals are deeper than the anterior ones.

Figue 5. A new reconstruction of the basal bipedal croc, Pseudhesperosuchus based on fossil tracings. Some original drawings pepper this image. Note the interclavicle, missing in dinosaurs and the very small ilium, only wide enough for two sacrals. The coracoids are elongate and immobile, but does that mean this taxon flapped. Maybe.

Not going to leave this topic without discussing 
the elongate coracoids in bipedal crocodylomorphs and their living, quadrupedal, non-flapping descendants, which retain long coracoids (Fig. 6) and mobile pectoral girdles. Experiments by Baier et al. 2018 documented the rotation of the elongate coracoids was less than expected, but the unossified sternum itself rotated left and right. They wrote, “To our knowledge, this is the first evidence of sternal movement relative to the vertebral column (presumably via rib joints) contributing to stride length in tetrapods.” 

All crocodylomorphs lack clavicles, 
and this likely contributes to pectoral girdle mobility. The basalmost archosaur, PVL 4597 does not preserve any element of the pectoral girdle or forelimb, so it does not shed light on the loss or retention of the clavicles. Among more distantly related proximal outgroup taxa, only Poposaurus and Lotosaurus appear to retain clavicles. Appearances vary in more primitive rauisuchids and erythrosuchids. Euparkeria has clavicles.

So, were basal crocodylomorphs flapping in the Triassic?
Pseudhesperosuchus (Fig. 5) would have been flapping without membranes, elongate fingers and feathers. But look at the clearance between the dangling forelimbs and sprinting hind limbs (Fig. 5). Perhaps Pseudhesperosuchus evolved elongate pectoral elements to lift the forelimbs laterally and keep them elevated while running, giving the narrow-gauge hind limbs room to extend anteriorly during the running cycle. Animators: take note!

Also worthwhile noting,
this is also when the proximal carpals became elongated, a crocodylomorph hallmark. As a biped, Pseudhesperosuchus had less use for its forelimbs. They could have evolved to become something else. Based on the elongation of the proximal carpals, the small size of the manus and the rather long forelimbs, the best guess I’ve seen is that the forelimbs occasionally acted much like those of similar forelimbs on much larger hadrosaurs (duckbill dinosaurs), providing more stability with a quadrupedal pose, without giving up its bipedal abilities. More aquatic short-legged, quadrupedal crocs evolved later. Long coracoids and long proximal carpals were retained in extant crocs from earlier Triassic ancestors.

Exceptions and reversals.
A few small basal bipedal crocodylomorphs, like Scleromochlus and Litargosuchus, re-evolved disc-like coracoids.

Figure 6. At the lower right hand corner is a pectoral girdle typical of crocs.

Figure 6. At the lower right hand corner is a pectoral girdle typical of crocs.

Flapping requires an immobile pectoral girdle
in order that both limbs move symmetrically, the opposite of basal tetrapods with mobile pectoral girdles. Flapping is the first step toward flying in pterosaur and bird ancestors.


References
Baier DB, Garrity BM, Moritz S and Carney RM 2018. Alligator mississippiensis sternal and shoulder girdle mobility increase stride length during high walks. Journal of Experimental Biology 2018 221: jeb186791 doi: 10.1242/jeb.186791
Kruyt JW, et al. 2014. Hummingbird wing efficacy depends on aspect ratio and compares with helicopter rotors. Royal Society Interface. nterface. 2014;11(99):20140585. doi:10.1098/rsif.2014.0585
Pei R et al. 2020.
Potential for Powered Flight Neared by Most Close Avialan Relatives, but Few Crossed Its Thresholds. Current Biology online here.
Pittman M, O’Connor J, Field DJ, Turner AH, Ma W, Makovicky P and Xu X 2020. Pennaraptoran Systematics. Chapter 1 from Pittman M and Xu X eds. 2020. Pennaraptoran theropod dinosaurs. Past progress and new Frontiers. Bulletin of the American Museum of Natural History 440; 353pp. 58 figures, 46 tables.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4233735/#idm140660310181296title

“Pulling a Larry Martin” with basal bird pectorals and hands

This is a cautionary tale
The following blog reminds all workers to score the entire specimen if possible, and to score as many more-or-less-complete specimens as possible. Why?

It is of vital importance to use as much data as possible
when scoring each taxon in a phylogenetic analysis to remove any trace of attraction by convergence that happens when just using bits and pieces of cherry-picked taxa.

From Pittman et al. 2020,
“Generally during early avian evolution, the furcula, coracoid, and sternum become more craniocaudally elongate, while the manual digits become reduced and fusion between the metacarpals increases.” 

Not true. In a valid phylogenetic context (Figs. 1–3), like the wide gamut large reptile tree (LRT, 1729+ taxa; subsets Figs. 2, 3), some taxa developed birdy traits quickly while others dawdled or reversed. In this way some bones demonstrated convergence with other less related clades. With this in mind, start with a valid unbiased topology, then let the taxa tell their own story. Avoid the temptation of an easy diagram. Do the necessary work.

Figure 1. Avian furcula aviation from Pittman et al. 2020 and repaired based on LRT results. Let your software decide based on the whole specimen. Convergence is rampant as you can see here.

Figure 1. Avian furcula aviation from Pittman et al. 2020 and repaired based on LRT results. Let your software decide based on the whole specimen. Convergence is rampant as you can see here.

Due to taxon exclusion
Pittman et al. mixed up the order of the pectoral girdles + hands of basal birds (Fig. 1), hoping to tell the story they wanted to tell: gradual evolution. Not only did they skip about a dozen pertinent taxa, they got the order wrong by eyeballing a few traits on cherry-picked taxa.

With more taxa, as in the LRT,
(Figs. 2, 3) the girdles and limbs are phylogenetically re-ordered here (Fig. 1, layer 2 with colors). If Pittman et al. wanted to show gradual evolution, they needed to first establish a valid tree topology by adding more taxa. Instead, by cherry-picking certain traits to show gradual evolution, Pittman et al. were “Pulling a Larry Martin“, putting individual traits on cherry-picked taxa ahead of an entire suite of traits and a wide gamut of taxa.

Figure 2. Subset of the LRT focusing on Pennaraptora 2014 = Tyrannoraptora 1999. Here Khaan and Velociraptor substitute for Oviraptor and Deinonychus.

Figure 2. Subset of the LRT focusing on Pennaraptora 2014 = Tyrannoraptora 1999 = Coelurosauria 1914. Here Khaan and Velociraptor substitute for Oviraptor and Deinonychus.

Figure 2. Subset of the LRT focusing on bird origins. Crown birds and toothed birds are highlighted.

Figure 3. Subset of the LRT focusing on bird origins. Crown birds and toothed birds are highlighted. Figure 2 is slightly more up-to-date, but includes fewer extant birds.

When the phylogenetic order is corrected
based on unbiased results recovered by the LRT (subsets Figs. 2, 3), what seemed to Pittman et al. a gradual transitional series is here revealed to be an example or two of convergence. Note the similarly elongate coracoids on the enantiornithine Parabohaiornis and the unrelated ornithurine, Yanornis (Fig. 1`), derived from an Early Cretaceous sister to a living taxon, Megapodius.

Time after time paleontologists cherry-pick taxa.
That has to stop. Add more taxa and let the software decide the tree topology. Similarly, don’t rely on parts alone (Fig. 1) to illustrate hypotheses, unless they represent taxa already nesting together based on all of their parts and a wide gamut of taxa. Body parts, like hands and girdles, can converge, as they do here.

Figure 3. Mammal tooth evolution alongside odontocete tooth evolution, reversing the earlier addition of cusps.

Figure 4. Mammal tooth evolution alongside odontocete tooth evolution, reversing the earlier addition of cusps.

On a similar note, basal mammal workers
have put too much reliance on tooth traits. Unfortunately, sometimes that’s all they have. If so, what should they do? They should build a tree topology based on complete or more nearly complete specimens. THEN fit it in those tooth and mandible taxa once the tree topology is established in a broader sense, as in the LRT. Earlier (Fig. 4) you saw how odontocete and archaeocete traits brilliantly document a step-by-step reversal to a simple cone shape, like those of basal pelycosaurs. The addition, subtraction and modification of tooth cusps in mammals occurred much more widely than shown by this one example.


References
Pittman M, O’Connor J, Field DJ, Turner AH, Ma W, Makovicky P and Xu X 2020.
Pennaraptoran Systematics. Chapter 1 from Pittman M and Xu X eds. 2020. Pennaraptoran theropod dinosaurs. Past progress and new Frontiers. Bulletin of the American Museum of Natural History 440; 353pp. 58 figures, 46 tables.

https://pterosaurheresies.wordpress.com/2020/08/23/pennaraptora-avoid-this-junior-synonym/

‘Pennaraptora’ — avoid this junior synonym

A new volume published by the AMNH
(eds. Pittman and Xu 2020), is all about the the putative clade, ‘Pennaraptora’ (Fig. 1). According to the preface, “Pennaraptora comprises birds themselves as well as the pennaceous feathered dromaeosaurids, troodontids, scansoriopterygids, and oviraptorosaurians.”

Here
in the large reptile tree (LRT, 1727+ taxa; subset Fig. 2) scansoriopterygids are birds, not oviraptorosaurian sisters. Oviraptorosaurians are terminal taxa in a larger clade that includes therizinosaurs and the CNJ79 specimen of Compsognathus and that clade is the sister clade of the Compsognathus holotype, struthiomimids and tyrannosaurids (Fig. 2). The last common ancestor of all these clades in the LRT is Aorun zhaoi (Choiniere et al. 2013; IVPP V15709, Late Jurassic 161mya).

So this multipart study on ‘Pennaraptorans’ is off to several bad starts. Neither ‘Aorun‘, nor ‘Tyrannoraptora’ (see below) are mentioned in the text. Several taxa have been omitted from this clade, including the last common ancestor.

Only two generic taxa and “their last common ancestor (LCA)”
should be enough to define a clade. Look what bad things can happen when you use four suprageneric taxa (Fig. 1). Don’t let in generic taxa that do not belong and omit generic taxa that do belong. Even so, and surprisingly, all taxa employed here are clade members. Unfortunately the clades and a few taxa are a little mixed up due to taxon exclusion.

Figure 1. Cladogram of the Pennaraptora from Pittman and Xu eds. 2020. Color overlays added to show clades in the LRT (Fig. 2).

Figure 1. Cladogram of the Pennaraptora from Pittman and Xu eds. 2020. Color overlays added to show clades in the LRT (Fig. 2).

Foth et al. defined Pennaraptora in 2014.
“Pennaraptora is a clade defined as the most recent common ancestor of Oviraptor philoceratops, Deinonychus antirrhopus, and Passer domesticus (the house sparrow), and all descendants thereof,”  Again, this definition only needs the first two taxa. Passer nests within “all descendants thereof”. Even so, this is a definition we can work with (Fig. 2).

Figure 2. Subset of the LRT focusing on Pennaraptora 2014 = Tyrannoraptora 1999. Here Khaan and Velociraptor substitute for Oviraptor and Deinonychus.

Figure 2. Subset of the LRT focusing on Pennaraptora 2014 = Tyrannoraptora 1999. Here Khaan and Velociraptor substitute for Oviraptor and Deinonychus.

In the LRT ‘Pennaraptora’
is almost a junior synonym of Compsognathidae (Cope 1871; Fig. 2) because two specimens of Compsognathus are basalmost taxa. However, Aorun is the last common ancestor taxon. It was originally considered the oldest known coelurosaurian theropod and a juvenile.

Figure 3. Aorun compared to several other theropods to scale.

Figure 3. Aorun compared to several other theropods to scale.

Figure 4. Aorun skull in situ and slightly restored. This is the basalmost tyrannoraptor.

Figure 4. Aorun skull in situ and slightly restored. This is the basalmost tyrannoraptor in the LRT.

According to Wikipedia, Aorun is now considered a member of
the Tyrannoraptora (Sereno 1999) defined as, “Tyrannosaurus, Passer their last common ancestor [Aorun] and all of its descendants.” So Pennaraptora (2014) is a junior synonym of Tyrannoraptora (1999). The two define the same clade in the LRT and share a last common ancestor.

Coelurosauria (von Huene 1914 is defined as theropods closer to birds than to carnosaurs. In the LRT Tyrannoraptora is also a junior synonym for Coelurosauria.


References
Bidar AL, Demay L and Thomel G 1972b. Compsognathus corallestris,
une nouvelle espèce de dinosaurien théropode du Portlandien de Canjuers (Sud-Est de la France). Annales du Muséum d’Histoire Naturelle de Nice 1:9-40.
Choiniere JN, Clark JM, Forster CM, Norella MA, Eberth DA, Erickson GM, Chu H and Xu X 2013. A juvenile specimen of a new coelurosaur (Dinosauria: Theropoda) from the Middle–Late Jurassic Shishugou Formation of Xinjiang, People’s Republic of China. Journal of Systematic Palaeontology. online. doi:10.1080/14772019.2013.781067
Cope ED 1871. On the homologies of some of the cranial bones of the Reptilia, and on the systematic arrangement of the class. Proceedings of the American Association for the Advancement of Science 19:194-247
Foth C, Tischlinger H and Rauhut OWM 2014. New specimen of Archaeopteryx provides insights into the evolution of pennaceous feathers. Nature. 511 (7507): 79–82.
Huene F v 1914. Über de Zweistämmigkeit der Dinosaurier, mit Beiträgen zer Kenntnis einiger Schädel. Sep.-Abd. Neuen Jahrb. für Mineralogie Beil.-Bd.37:577–589. Pls. vii-xii.
Ostrom JH 1978. The osteology of Compsognathus longipes. Zitteliana 4: 73–118.
Peyer K 2006. A reconsideration of Compsognathus from the upper Tithonian of Canjuers, southeastern France, Journal of Vertebrate Paleontology, 26:4, 879-896.
Pittman M and Xu X eds. 2020.
Pennaraptoran theropod dinosaurs. Past progress and new Frontiers. Bulletin of the American Museum of Natural History 440; 353pp. 58 figures, 46 tables.
Wagner JA 1859. Über einige im lithographischen Schiefer neu aufgefundene Schildkröten und Saurier. Gelehrte Anzeigen der Bayerischen Akademie der Wissenschaften 49: 553.

wiki/Compsognathus
wiki/Tyrannoraptora
wiki/Aorun
wiki/Pennaraptora

New YouTube video: The Rise of Birds by Jingmai O’Connor

YouTube.com brings us a 95-minute presentation
on the history of the discovery of Mesozoic birds by Dr. Jingmai O’Connor

O’Connor notes historic difficulty in defining birds
starting with Huxley (1868) who said Archaeopteryx was a bird and a theropod dinosaur, but that hypothesis fell out of favor.

Then, DeBeer (1954) ‘Pulled a Larry Martin‘ by listing traits restricted to birds that turned out to be more widely distributed in dinosaurs that were described after 1954.

Then, Ostrom (1969a, b) described Deinonychus as an Archaeopteryx relative, but one that lived later, in the Early Cretaceous, so that was considered temporal discontinuity in the pre-software days of phylogenetic analysis.

Finally, the deluge of Chinese bird fossils is what tipped the paleo-community toward Huxley’s and Ostrom’s correct hypotheses, according to O’Conner. And sadly, belatedly, she’s correct.

O’Connor supports the hypothesis that birds are living troodontids,
but she mistakenly includes the scansoriopterygid bird, Mei long, and pre-bird anchiornithids. These are not troodontids in the LRT (Fig. 2) as we learned just a few days ago here. Moreover, O’Connor mistakenlynests all 13 Solnhofen birds into Archaeopteryx, thereby missing out on the variation that was present on those Late Jurassic islands.

O’Connor looked at members of the Scansoriopterygidae
and noted cladistic analysis puts them most closely related to birds.

In the LRT scansoriopterygids ARE birds, some experiencing reversals.

Unfortunately, 
O’Connor brought up and bought into the Yi qi and Ambopteryx rmembrane wing hypothesis. That misidentified entirely new bone (not found in any preceding tetrapod) is just a displaced forearm bone (Fig. 1), an ulna in the case of Ambopteryx, which lacks a matching novel elongate wrist bone on the articulated right wing where the ulna is EXACTLY as long and wide as the left disarticulated ulna (= se or styliform element). The left radius was split lengthwise during crushing causing it to be misidentified as two extremely thin ante brachial bones, which is just silly and untenable.

Figure 1. Photos and black tracing from Wang et al. 2019. Colors added here. There is no styliform bone on either wing. That is a displaced ulna... again.

Figure 1. Photos and black tracing of Ambopteryx from Wang et al. 2019. Colors added here. There is no styliform bone on either wing. That is a displaced ulna… again. The elements on the left are identical to the elements on the right. Claims that the left radius and ulna are extremely slender and extremely parallel don’t recognize a taphonomically crushed radius.

By the way,
misinterpreting a broken bone is not pseudoscience. It’s a simple mistake.

According to O’Connor,
pre-wings developed for sexual selection. As proto-wings the forelimbs had incipient flying abilities (thrust + lift). That’s is widely agreed upon, even here. She cites Ken Dial’s studies on pre-volant birds flapping while climbing near-vertical tree trunks.

O’Connor believes there were 3 to 5 separate origins of flight

  1. Microraptor
  2. Yi qi and Ambopteryx 
  3. Birds
  4. Rahonavis
  5. and one other due to be described in an upcoming paper.
Figure 2. Subset of the LRT focusing on bird origins. Crown birds and toothed birds are highlighted.

Figure 2. Subset of the LRT focusing on bird origins. Crown birds and toothed birds are highlighted.

A more comprehensive, wider-gamut phylogenetic analysis
would help Dr. O’Connor. She would not need to ‘Pull a Larry Martin‘ by seeking a single ovary in fossils (some fossorial snakes also lose one ovary) and a crop (pre-stomach with stones might also be found in plesiosaurs) as the only remaining traits she found unique to birds not otherwise found in dinosaurs. Traits don’t matter. Where a taxon or clade nests is all that matters. The last common ancestor (LCA) of all birds is also a bird, by definition.

If you want to list the traits of that LCA taxon,
you may, but you should note where convergence appears in unrelated taxa (i.e. just take a look at the distribution of toothed taxa in Fig. 2).


References
de Beer GR 1954. Archaeopteryx lithographica: a study based upon the British Museum specimen. Trustees of the British Museum, London.
Huxley TH 1868. On the animals which are most nearly intermediate between birds and reptiles. Geol. Mag. 5: 357–65.; Annals & Magazine of Nat Hist 2, 66–75; Scientific Memoirs 3, 3–13.
Ostrom JH 1969a. A new theropod dinosaur from the Lower Cretaceous of Montana. Postilla. 128: 1–17.
Ostrom JH 1969b. Osteology of Deinonychus antirrhopus, an unusual theropod from the Lower Cretaceous of Montana. Peabody Museum of Natural History Bulletin. 30: 1–165.
Ostrom JH 1976. Archaeopteryx and the origin of birds. Biological Journal of the Linnean Society 8 (2): 91–182.

The clade Troodontidae: Who’s in and who’s out?

Summary for those in a hurry:
Compared to traditional taxon lists (Figs. 3, 4), the LRT taxon list for the Troondontidae is greatly reduced (Fig. 2). That means many traditional troodontids nest elsewhere.

We start today with a new taxon.
Zanabazar junior (Norell et al. 2009, originally Sauronithoides junior Barsbold 1975; IGM 100/1; est. 2.3m long, 27cm skull length; Fig. 1), is a late-surviving (Late Cretaceous) basal troodontid in the large reptile tree (LRT, 1274+ taxa; subset Fig. 2). The specimen includes a nearly complete skull and braincase, part of the pelvis, some tail vertebrae, and parts of the right hindlimb. The teeth are relatively small.

Figure 1. Skull of Zanazabar from Digimorph.org and used with permission. Bones are colored here.

Figure 1. Skull of Zanabazar from Digimorph.org and used with permission. Bones are colored here.

Figure 2. Subset of the LRT focusing on theropods leading to birds, including the two newest additions, Bambiraptor and Zanabazar.

Figure 2. Subset of the LRT focusing on theropods leading to birds, including the Troodontidae and the two newest additions, Bambiraptor and Zanabazar.

Prior to the LRT
authors nested Zanabazar as a highly derived troodontid (Figs. 3, 4).

Figure 2. Current cladograms of the Troodontidae currently found in Wikipedia pages.

Figure 3. Current cladograms of the Troodontidae currently found in Wikipedia pages.

Those other authors
also nested LRT pre-bird anchiornithids (Sinovenator, Almas, Daliansaurus, Sinusonasus, Jinfengopteryx) and one scansoriopterygid bird (Mei) in the Troodontidae (Fig. 4). Prior authors include several taxa known from scrappy data that will not be tested in the LRT. These include Talos, Byronosaurus, Troodon, IGM 100/44, Linhevenator, and Philovenator.

Figure 2. Wikipedia cladogram from Shen et al. 2017. Overlay limits LRT Troodontidae to the taxa in the white box.

Figure 4. Wikipedia cladogram from Shen et al. 2017. Overlay limits LRT Troodontidae to the taxa in the white box. Others are in the bird lineage.

On the other hand,
the LRT (Fig. 2) includes troodontid taxa not included or nested elsewhere (e.g. Rhamphocephalus, Haplocheirus, Shuvuuia, Halszkaraptor). Readers will note that several of these taxa are alvarezsaurids that now nest within the Troodontidae in the LRT. This is a novel hypothesis of interrelationships. If there is another prior citation, please let me know so that can be promoted.

According to Wikipedia
“During most of the 20th century, troodontid fossils were few and incomplete and they have therefore been allied, at various times, with many dinosaurian lineages.” By contrast, most taxa included in the LRT are largely complete.

Wikipedia continues:
“More recent fossil discoveries of complete and articulated specimens (including specimens which preserve feathers, eggs, embryos, and complete juveniles), have helped to increase understanding about this group.” None of these sorts of taxa currently in the Troodontidae in the LRT (Fig. 2).

The first question is:
What is the definition of Troodontidae?

Looking for a definition online @ yourdictionary.com
“Any member of a family (Troodontidae) of small, bird-like theropod dinosaurs with large brains, large eyes, and a retractable claw on the second toe of each hind foot, similar to a farmer’s sickle, used for slashing at prey.”

This is a trait-based definition, subject to convergence. We call this “Pulling a Larry Martin.” Only a phylogenetic nesting in a wide gamut cladogram can determine what is and what is not a troodontid and that starts with a definition of the clade.

According to Wikipedia (Troodon) 
“the entire genus is based only on a single tooth.” and this tooth has been considered to belong to a wide variety of Reptilia. “Phil Currie, reviewing the pertinent specimens in 1987, showed that supposed differences in tooth and jaw structure among troodontids and saurornithoidids were based on age and position of the tooth in the jaw, rather than a difference in species.”

So, there’s a definite problem
in defining both Troodon and the Troodontidae. Even so, the theropoddatabase.com has compiled a few that may prove useful.

  1. Troodontidae = Troodon formosus (Gilmore 1924)
  2. Troodontidae = Troodon formosus, Saurornithoides mongoliensis, Borogovia gracilicrus, Sinornithoides youngi but not Ornithomimus velox, Oviraptor philoceratops) (Varricchio 1997)
  3. Troodontoidea Troodon + Saurornithoides (Livezey and Zusi 2007)

What these definitions have in common
are the more completely known taxa, Sinornithoides, Sauronithoides and Zanabazar. Let’s make these, plus their last common ancestor. our working definition. Let’s assume, until proven wrong, that Troodon is similar in most respects. Given these parameters many taxa leave the clade Troodontidae and nest within the bird-line of anchiornithids or within birds (Fig. 2).

FIgure 5. Gobivenator is the most completely known troodontid. It nests with Zanabazar in the LRT.

FIgure 5. Gobivenator is the most completely known troodontid. It nests with Zanabazar in the LRT.

Figure 6. Gobivenator skull, colors added here.

Figure 6. Gobivenator skull, colors added here.

Gobivenator, the most completely known troodontid,
(Fig. 5, 6) was added to the LRT just an hour ago, nesting alongside Zanabazar with very few scoring differences. So, Gobivenator was not forgotten.

Figure 2. Mei long compared to the BSP 1999 I 50, Munich specimen of Archaeopteryx and Scansoriopteryx to scale. Click to enlarge.

Figure 7. Mei long is a scansoriopterygid bird in the LRT. Yes it has small hands and could not fly, but the rest of its traits nest Mei within the bird clade.

Mei
(Fig. 7) nests not with troodontids in the LRT, but with the bird clade scansoriopterygids, between the private #12 Archaeopteryx specimen and Yi qi. Yes, it has small hands and could not fly (like Struthio the ostrich). Moving Mei to the troodontids adds 23 steps. Reversals do happen. A few traits compete against a larger suite. Let your software determine where a taxon nests and make sure you include enough taxa to let convergence happen.

Wikipedia – Mei long reports:
“It is most closely related to the troodontid Sinovenator, which places it near the base of the troodontid family.” In the LRT, Sinovenator (Fig. 8) is not in the Troodontidae, but nests in proximal bird outgroup clades. Moving Mei long to Sinovenator adds 19 steps to the LRT. Taxon exclusion has so far kept Mei long apart from other scansoriopteryids everywhere but here.

Figure 8. Sinovenator nests with anchiornithid birds in the LRT.

Figure 8. Sinovenator nests with anchiornithid birds in the LRT.Likewise,
Sinovenator nests not with troodontids in the LRT, but with the pre-bird anchiornithids, between Almas (Fig. 9) and the BMNHC PH804 specimen of Anchiornis.

The LRT documents a fast track for the origin of birds
from the last common ancestor of Bambiraptor + Zanabazar that leads to the following series of taxa: Anchiornis, Daliansaurus (Fig. 9), Almas, the Daiting specimen of Archaeopteryx, Xiaotingia and the Thermopolis specimen of Archaeopteryx, the last known common ancestor of all birds in the LRT.

Figure 1. Daliansaurus and the origin of birds through Almas and Xiaotingia.

Figure 9. Daliansaurus and the origin of birds through Almas and Xiaotingia.

Daliansaurus liaoningensis 
(Shen et al. 2017; Early Cretaceous, Barremian, 128 mya; 1 m long) nests in the LRT as a basal anchiornithid, not a troodontid.

Almas ukhaa
(Pei et al. 2017; Campanian, Late Cretaceous, IGM 100/1323) nests in the LRT as a basal anchiornithid, not a troodontid.

Several lineages approached and experimented with the bird grade
(e.g. Rahonavis, Microraptor, the Daiting specimen of Archaeopteryx), but only one lineage starting with the Thermopolis specimen of Archaeopteryx created robustly volant and extant birds.

In the LRT,
the reduced clade memberships of Troodontids indicate they are a splinter group,
closer to Bambiraptor + Velociraptor. That combined clade (Fig. 2) is a splinter group to the smaller compsognathids and anchiornithids lineage that led more directly to birds (Fig. 9).


References
Barsbold R 1974. Saurornithoididae, a new family of small theropod dinosaurs from Central Asia and North America. Palaeontologica Polonica. 30: 5−22.
Norell MA et al. 2009. A review of the Mongolian Cretaceous dinosaur Saurornithoides (Troodontidae, Theropoda). American Museum Novitates (3654): 1−63.

wiki/Zanabazar_junior
wiki/Gobivenator
wiki/Troodontidae
wiki/Alvarezsauridae
wiki/Daliansaurus
wiki/Almas_ukhaa

From Berkeley: 3 more evograms updated

Yesterday we updated an online evogram
produced by the University of California – Berkeley under the tutelage of Professor Emeritus Kevin Padian. Today a few remaining evograms get similar updates.

Figure 1. Evogram from the Berkeley website focusing on bird origins.

Figure 1. Evogram from the Berkeley website focusing on bird origins.

The Berkeley evogram on bird origins
(Fig. 1) closely matches that of the large reptile tree (LRT, 1710+ taxa). Only two corrections include: Eoraptor is a basal phytodinosaur, not a theropod. The caption on tyrannosauroids is, “Reduction of III“, but the illustration does not show a reduction of digit 3.

Figure 2. Evogram from the Berkeley website focusing on mammal origins.

Figure 2. Evogram from the Berkeley website focusing on mammal origins.

The Berkeley evogram on mammal origins
(Fig. 2) mistakenly puts Yanaconodon close to eutherians. By contrast the LRT nests Yanaconodon in a pre-mammal clade. There is no need to add the highly derived Dimetrodon to a pre-mammal cladogram. It left no descendants. Haptodus is a more primitive, more plesiomorphic choice here. We are its descendants. Likewise, the platypus (Ornithorhynchus) is also highly derived. Better to put a basal prototherian, like Sinodelphys or Megazostrodon, in its place. We are their descendants. Duckbilled platypusses are not plesiomorphic nor ancestral to any other mammal.

Figure 3. Evogram from the Berkeley website focusing on tetrapod origins.

Figure 3. Evogram from the Berkeley website focusing on tetrapod origins. This is similar to an evogram found in Padian 2013.

The Berkeley evogram on tetrapod origins
(Fig. 3) includes Eusthenopteron, which left no descendants in the LRT. Flatter Cabonnichthys is a better ancestor. Flattened Tiktaalik and Panderichthys switch places here. The latter has four proto-fingers. Ichthyostega and Acanthostega have supernumerary digits and leave no descendants in the LRT. Here flatter basal tetrapods, like Greererpeton, have a skull, body, limbs and fingers more like those of Panderichthys. Dendrerpeton has a shorter torso and longer limbs. Even more so does Gephyrostegus. The loss of lumbar ribs makes room for more and larger amniotic eggs. Contrary to its original description, Tulerpeton does not have supernumerary digits. Gephyrostegus is a more completely known representative reptilomorph. Rather than make the huge morphological jump to Homo, represented here (Fig. 3) by Darwin himself, another living reptile, Iguana, enters the evogram with fewer changes to distinguish it from Gephyrostegus. Smaller steps mark the gradual progress of evolution. Big jumps, like adding Darwin (even as a joke), throw the whole concept into a tizzy. A similar evogram was published in Padian 2013, a paper ironically entitled, “Correcting some common misrepresentations of evolution in textbooks and the media.”

By minimizing taxon exclusion
the LRT does not make the mistakes shown above (Figs. 1-3) in the Berkeley evograms. Due to its large taxon list, the LRT more clearly documents the gradual accumulation of traits that characterizes every evolving vertebrate, and it does so while testing all competing candidates.

Let Kevin Padian at Berkeley know:
It’s time to update those online evograms!

This just in
An email from Anna Thanukos at the UC Museum of Paleontology, “Hi David,  Thanks for your interest in our site.  I wanted to let you know that the material on the page of interest has recently been reviewed by a curator at the Smithsonian and will be updated in a website revamp we are currently developing. Best regards, Anna Thanukos, UC Museum of Paleontology.”


References
Padian K 2013.  Correcting some common misrepresentations of evolution in textbooks and the media.  Evolution Education and Outreach 6: 1-13.

https://evolution.berkeley.edu/evolibrary/article/evograms_02

https://evolution.berkeley.edu/evolibrary/article/evograms_03

https://evolution.berkeley.edu/evolibrary/article/evograms_04

https://evolution.berkeley.edu/evolibrary/article/evograms_05

https://evolution.berkeley.edu/evolibrary/article/evograms_06

https://evolution.berkeley.edu/evolibrary/article/evograms_07

 

Rahonavis returns! (still without resolution due to taxon exclusion)

Forster et al. 2020
bring us up to date on Rahonavis (Fig. 1), a tiny theropod with long forelimbs that has been traditionally hard to nest. Forster et al. adds Rahonavis to two previously published analyses of bird-like theropods …still without resolution (due to taxon exclusion).

Figure 2. Rahonavis nests in the LRT as a tiny derived therizinosaur based on the few bones currently known.

Figure 1. Rahonavis nests in the LRT as a tiny derived therizinosaur based on the few bones currently known.

From the abstract:
“Recent phylogenetic analyses place Rahonavis either within the non-avialan Unenlagi- inae, an early-diverging clade within Dromaeosauridae, or at the base of Avialae. Rahonavis is one of the best represented and preserved Gondwanan paravians, and remains a pivotal taxon for understanding the evolution and biogeography of paravians.”

So the most recent analyses by Forster et al.
have not nested Rahonavis with confidence. In one study (based on the phylogenetic analyses of Lefèvre et al. 2017) Rahonavis nests between Archaeopteryx and Balaur. In the other study (based on Brusatte et al. 2014) Rahonavis nests at the base of three troodontids, Buitreraptor, Austroraptor and Unenlagia. In that study Balaur nests with Velociraptor and kin and all are derived from a sister to Mahakala.

So Rahonavis is not the only theropod
to shift places between the two published studies.

By contrast
the large reptile tree (LRT, 1698+ taxa; subset Fig. 3) nests Rahonavis outside the taxon lists employed by Forster 2020. In the LRT Rahonavis nests with Jianchangosaurus, Falcarius, and Beiapiosaurus, three therizinosaurs not tested by Forster et al. We looked at this still heretical nesting of Rahonavis a few years earlier here. Prior to the addition of therizinosaurs (and a thousand other taxa), Rahonavis nested with Velociraptor in the LRT. So back then, with fewer taxa, the LRT also suffered from taxon exclusion.

Following Forster et al. 2020,
to move Rahonavis to the Berlin specimen of Archaeopteryx adds 18 steps. To move Rahonavis to Buitreraptor adds 14 steps in the LRT. Those smnall numbers are based on the relatively few bones, all post-cranial, preserved by Rahonavis.

Figure 1. Jianchangosaurus nests at the base of the Maniraptora in Cau 2018, but with therizinosaurs in the LRT.

Figure 2. Jianchangosaurus nests at the base of the Maniraptora in Cau 2018, but with therizinosaurs in the LRT. Note the large pedal ungual 2, as in Rahonavis.

Therizinosaurus
are typically larger than Rahonavis, and feathered. Thus phylogenetic bracketing indicates Rahonavis was likely feathered, too.

Rahonavis (orignally Rahona ostromi – Forster et al. 1998, Late Cretaceous, 70mya, UA 8656, 70 cm) was originally considered a bird-like theropod. The partial skeleton is much smaller than sister taxa among the Therizionsauria. The pubis was ventrally oriented and the radius + ulna were very long. The tail was comparatively short with few vertebrae.

Figure 3. Subset of the LRT focusing on theropods and basal birds. Colors added for large (greater than a meter), medium (about a meter), and small (less than a meter) in length. Compare to figure 2 from Rezende et al. Note the depth of small taxa, some of which give rise to large taxa.

Figure 3. Subset of the LRT focusing on theropods and basal birds. Colors added for large (greater than a meter), medium (about a meter), and small (less than a meter) in length.

By minimizing taxon exclusion,
the LRT manages to nest all included taxa with high confidence and high Bootstrap numbers. As demonstrated over and over again, it doesn’t matter how many characters you use (at least 200 multi-state characters). You just have to barely nest taxa with complete resolution. You can only do this by adding taxa. That minimizes taxon exclusion, the biggest single problem in paleontology right now, whether workers know it or not.

Solve your problems by adding taxa.
It works here all the time. It will work for you, too.


References
Forster CA, Sampson SD, Chiappe LM, Krause DW 1998. The Theropod Ancestry of Birds: New Evidence from the Late Cretaceous of Madagascar. Science 279 (5358): 1915–1919.
Forster CA, O’Connor PM, Chiappe LM and Turner AH 2020. The osteology of the Late Cretaceous paravian Rahonavis ostromi from Madagascar. Palaeontologia Electronica, 23(2):a31. https://palaeo-electronica.org/content/pdfs/793.pdf

wiki/Rahonavis

How primitive are megapodes?

Earlier the large reptile tree (LRT, 1663+ taxa) nested megapodes (like Megapodius) at a more primitive node than any other living bird, except the kiwi (Apteryx) and ratites, like (like Struthio). You might remember, a toothed bird clade restricted to the Early and Late Cretaceous was derived from toothless Crypturus (Fig. 1) in the LRT.

Figure 1. Megapodius is the extant bird nesting at the base of all neognathae (all living birds except ratites).

Figure 1. Megapodius is the extant bird nesting at the base of all neognathae (all living birds except ratites). And it looks like a basal bird, not too this… not too that.

With that in mind
and hoping to understand the reemergence of previously lost teeth in Early Cretaceous birds, I checked out Clark 1960, who reported on megapode embryology.

To set the stage, Clark wrote,
Young birds are exceedingly precocious, being able to fly on the day of hatching and feeding actively only a few days after hatching.” He then referenced Portmann (1938, 1951, 1955) who listed several reptile-like characters of megapodes:

  1. no egg tooth (megapodes hatch by kicking their way out of the shell. The ‘egg tooth’ of chickens temporarily appears on the top of the beak, not the rim);
  2. lack of down feathers in embryos or nestlings;
  3. lack of parental care;
  4. primitive method of incubation (by solar heat, fermentation, vulcanism);
  5. long incubation period (8 weeks for Leipoa);
  6. large number of eggs laid;
  7. slow growth to adult size (especially for Alectura);
  8. primitive structure of the brain;
  9. eggs usually not turned and yet hatch relatively successfully;

Clark added to Portmann’s #9
a general lack of movement of the embryo until just before hatching. This may be related to the use of fermentation as a heat source for incubation. Clark notes,
the presence of aerobic bacteria should presumably greatly deplete the available oxygen supply.” Moving embryos might have suffocated for lack of oxygen. Clark also noted: relatively large yolks, as in reptiles.

I never found a tooth thread
connecting Late Jurassic teeth in stem birds to the reemergence of teeth in Early Cretaceous crown birds (Fig. 2) following Apteryx, ratites and megapodes. Even so, every other trait indicated a transition. The above authors further support the extreme primitive nature of megapodes. Ratites no longer bury their eggs. Kiwis dig burrows.

Figure 1. Click to enlarge. Toothed birds of the Cretaceous to scale.

Figure 1. Click to enlarge. Toothed birds of the Cretaceous to scale.

In the post-cladistic era
Dekker and Brom 1992 wrote, “Among megapodes, four different incubation-strategies may be distinguished:

  1. mound-building,
  2. burrow-nesting between decaying roots of trees,
  3. burrow-nesting at volcanically heated soils, and
  4. burrow-nesting at sun-exposed beaches.”

Dekker and Brom employed a cladogram
originally published by Cracraft and Mindell (1989), which mistakenly nested megapodes with galliforms (chickens and kin) due to taxon exclusion. Dekker and Brom wrote, We conclude that similarities shared with reptiles and kiwis are due to convergence.” That traditional nesting is not confirmed by the LRT due to taxon exclusion. Burying and burrowing are primitive, but give no clue as to how Early Cretaceous birds redeveloped small teeth at first, large teeth later. Neither does megapode embryology. Perhaps that’s why this novel hypothesis of interrelationships has never appeared elsewhere. 


References
Clark GA Jr. 1960. Notes on the embryology and evolution of the megapodes (Aves: Galliformes). Postilla 45:1–7.
Cracraft J and Mindell DP 1989. The early history of modern birds: a comparison of molecular and morphological evidence.— In: B. Fernholm, K. Bremer & H . Jörnvall, eds. The Hierarchy of Life: Molecules and Morphology in Phylogenetic Analysis: 389-403. Amsterdam, New York, Oxford.
Dekker RWRJ and Brom TG 1992. Megapode phylogeny and the interpretation of the incubation strategies. xxx 19–31.  Zoologische Verhandelingen  278(2): 19–31.
Portmann A 1938.
Beitrage zur Kenntnis der postembryonalen Entwick- lung der Vogel. Rev. Suisse Zool., 45: 273-348.
Portmann A 1951. Ontogenesetypus und Cerebralisation in der Evolution der Vogel und Sauger. Rev. Suisse Zool., 58: 427-434.
Portmann A 1955. Die postembryonale Entwicklung der Vogel als Evolu- tionsproblem. Acta XI Congr. Int. Orn., 1954. Pp. 138-151.

Cretaceous toothed birds evolved from toothless megapodes in the LRT

Today’s heretical dive
into the origin of Cretaceous toothed birds (Fig. 1) brings new insight to a clade that has been traditionally misrepresented as a stem clade, often represented by just two highly derived toothed taxa, Ichthyornis and Hesperornis (Fig. 1). In the large reptile tree (LRT, 1659+ taxa; subset Fig. 3) Cretaceous toothed birds arise from extant toothless Megapodius (Figs. 1, 2; Gaimard 1823). How is this possible?

Toothy jaws from toothless jaws? 
That seems to break some rules. And if the LRT (Fig. 3) is valid, that makes toothed Cretaceous birds crown bird taxa.

Figure 1. Click to enlarge. Toothed birds of the Cretaceous to scale.

Figure 1. Click to enlarge. Toothed birds of the Cretaceous to scale. They are derived from toothless taxa.

Earlier Field et al. 2020
claimed to discover the ‘oldest crown bird‘ fossil when they described Asteriornis (66 mya), a screamer (genus: Chauna) relative. Unfortunately, due to taxon exclusion, Field et al. 2020 did not consider the ostrich sister, Patagopteryx (80 mya), nor did they understand that Juehuaornis (Wang et al. 2015; Early Cretaceous, Aptian, 122mya; Figs. 1, 4) was also a crown bird taxon, the oldest crown bird, derived from Megapodius, the extant mound builder.

One look
(Fig. 1) at the similarity of Megapodius to basal Cretaceous toothed and toothless birds, like Juehuaornis (Figs. 1, 4), makes the relationship obvious. The LRT recovered that relationship based on hundreds of traits and minimized convergence by testing relationships among 1659 taxa.

So, where did those Cretaceous teeth come from?
Megapodius and Juehuaornis both lack teeth. Basalmost toothed taxa had tiny teeth (Fig. 1) Derived toothed taxa had larger teeth. Try to let that sink in. Teeth re-appeared in these Cretaceous birds.

How is that possible? Consider this:
Juehuaornis is smaller than Megapodius. The sternum and keel of Juehuaornis are smaller than in Megapodius. Why is this important? As we learned earlier, at the genesis of many major and minor clades phylogenetic miniaturization (the Lilliput Effect) is present. That’s how gulls become hummingbirds and rauisuchians become dinosaurs. When adults are smaller they mature more quickly and they retain juvenile traits into adulthood. They also develop new traits, in this case, perhaps ontogeny recapitulated phylogeny.

The tooth genes got turned on again,
at first in a minor way… later in a major way.

Figure 2. Click to enlarge. Origin of birds from Archaeopteryx to Megapodius.

Figure 2. Click to enlarge. Origin of birds from Archaeopteryx to Megapodius. Pseudocrypturus is the sister taxon to the kiwi (Apteryx, Fig. 3), the most basal crown birds, but Juehuaornis is known from much older fossils despite being more derived than Megapodius.

How close were Cretaceous toothless taxa,
like Juehuaornis, to toothed Jurassic ancestors, like Archaeopteryx? Depends on how you look at it.

Chronologically
Juehuaornis is from the Aptian, Early Cretaceous, 122 mya. Archaeopteryx is from the Tithonian, Late Jurassic, 150 myaA transitional taxon, Archaeornithura (Fig. 2) is from the Hauterivian, Early Cretaceous, 131 mya, splitting the time difference. Archaeornithura had teeth and lacked a pygostyle, but had a shorter tail than the most derived Archaeopteryx (Fig. 2).

Morphologically
toothless Juehuaornis follows toothless Megapodius (Figs. 1, 3) and is separated from toothy Archaeornithura by at least three taxa (Figs 2, 3). The question I ask is: did the Cretaceous sisters to these toothless taxa have teeth subsequently lost in later generations over the past 140 million years? Or were teeth lost in  Early Cretaceous transitional taxa (represented by late-survivors (Fig. 2)) only to be regained in the toothy extinct clade (Fig. 3)? For now, let’s leave all options open, but toothlessness followed by toothy jaws is the only option currently supported by phylogenetic evidence (Fig. 3).

Figure 2. Subset of the LRT focusing on bird origins. Crown birds and toothed birds are highlighted.

Figure 3. Subset of the LRT focusing on bird origins. Crown birds and toothed birds are highlighted.

This is what happens when you let the cladogram tell you what happened,
rather than gerrymandering the taxa inclusion list and scores to get the results your professors and colleagues will approve and permit publication.

Figure 2. Juehuaornis reconstructed. Note the scale bars. This is a tiny bird.

Figure 4. Juehuaornis reconstructed. Note the scale bars. This is a tiny bird and the oldest known crown bird.

I should have reported
that Juehuaornis (122 mya) was the oldest known crown bird earlier. I just had to see the toothed birds in phylogenetic order (Fig. 1), making sure they made sense after seeing them listed in the cladogram (Fig. 3).

Add taxa
and your cladograms will be better than most. Create reconstructions to scale and see if your cladograms make sense. When it’s right, it all works out with a gradual accumulation of traits between every node, echoing evolutionary events from deep time. Let me know if this novel hypothesis of interrelationships was published previously anywhere so that citation can be promoted.


References
Gaimard JP 1823. Mémoire sur un nouveau genre de Gallinacés, establi sous le nom de Mégapode. Bulletin General et Universel des Annonces et de Nouvelles Scientifiques 2: 450-451.
Wang R-F, Wang Y and Hu Dong-yu 2015. Discovery of a new ornithuromorph genus, Juehuaornis gen. nov. from Lower Cretaceous of western Liaoning, China. Global Geology 34(1):7-11.

wiki/Megapodius
wiki/Megapode

Asteriornis: Oldest crown bird fossil yet discovered? No.

Taxon exclusion
is the problem here. Still, it’s a wonderful and rare 3D bird fossil.

Writing in Nature, Field et al. 2020
bring us a new latest Cretaceous bird, Asteriornis (Fig. 1).The authors report, “The fossil represents one of the only well-supported crown birds from the Mesozoic era, and is the first Mesozoic crown bird with well-represented cranial remains.The fossil is between 66.8 and 66.7 million years old—making it the oldest unambiguous crown bird fossil yet discovered.”

Figure 1. Asteriornis skull from Field et al. 2020 colors removed and reapplied and restored here.

Figure 1. Asteriornis skull from Field et al. 2020 colors removed and reapplied and restored here.

The authors note,
“The general appearance of the premaxillary beak resembles that of extant Galliformes, particularly in its gently down-curved tip and delicate construction, with no ossified joints among the rostral components.”

Figure 2. Chauna skull. This sister to Asteriornis in the LRT shares most traits and informs the restoration.

Figure 2. Chauna skull. This sister to Asteriornis in the LRT shares most traits and informs the restoration.

Among crown birds, (Neornithes)
Asteriornis is old (66 mya), but the hen-sized ostrich sister, Patagopteryx, is older (80 mya), more primitive and was descried earlier (Alvarenga and Bonaparte 1992). Later Chiappe (1996, 2002, 2015) nested Patagopteryx between Enantiornithes and Hesperonis. Patagopteryx was not tested by Field et al. Instead the authors report, “The Mesozoic record of well-supported crown birds is restricted to a single latest Maastrichtian taxon, Vegavis iaai.” In the large reptile tree (LRT, 1657+ taxa; subset Fig. 4), gracile, long-legged Vegavis lies just outside the clade of Crown birds.

Figure 1. The two-toed ostrich (Struthio) nests with the four-toed Patagopteryx, when all relatives have only three toes.

Figure 3. The two-toed ostrich (Struthio) nests with the four-toed Patagopteryx, when all relatives have only three toes.

Field et al. nested Asteriornis 
uncertainly either closer to geese (Anseriformes) or closer to chickens (Galliformes), or at the base of the traditional, but invalid clade, ‘Galloanserae’. The authors report, “The specimen exhibits a previously unseen combination of features that are diagnostic of Galliformes and Anseriformes, which together form the crown clade Galloanserae—one of the most deeply diverging clades of crown birds and the sister group to the hyperdiverse extant clade Neoaves.”

Figure 3. Subset of the LRT focusing on birds. Note the separation of the duck clade from the chicken clade.

Figure 4. Subset of the LRT focusing on birds. Note the separation of the duck clade from the chicken clade and neither is basal to all other non-ratite birds. Given that both Patagopteryx and Asterornis are Cretaceous, just imagine all the intervening bird fossils still be discovered in that strata.

By contrast,
chickens and ducks are not related to one another in LRT (subset, Fig. 4). Chickens are related to grouse, peacocks, sparrows, hoatzins, parrots and other ground-dwelling seed eaters. Ducks and geese arise from long-legged Presybyornis and other long-legged shorebirds. In the LRT, Asteriornis is closer to Chauna, the screamer, and Fulica, the coot, and Heliornis, the sungrebe, all closer to chickens and sparrows than to ducks and geese. The invalid clade Galloanseriformes typically includes Chauna and Fulica. Heliornis is a grebe-mimic (with similar expanded toe paddles) and a duck-mimic (with a similar swimming mode). That may be at the root of this confusion over convergence.

Field et al. have too few taxa
in their taxon list. Only one Archaeopteryx is shown in their cladogram, but it was not tested in their analysis where Hesperornithes and Ichthyornis are outgroup taxa. By contrast, in the LRT, both of these toothy taxa are members of the crown group, nesting between toothless ratites and all other toothless birds. Neither the chicken clade nor the duck clade are basal clades in the LRT.

Figure 1. Anhima adult and chick compared to Pterocles adults

Figure 5. Anhima adult and chick compared to Pterocles adults

Dr. Kevin Padian (2020) wrote a companion article
explaining the importance of Asteriornis and its relationship to crown birds and stem birds for a broader audience. Padian reports, “Ancient birds are outside the crown group because they lack the structural and physiological features characteristic of living birds. Sometime during the latest Cretaceous, a stem-group lineage of birds evolved that had much higher growth rates than these more basal lineages, and that generally matured within a year or even sooner. These became the crown-group birds.”

Given Dr. Padian’s definitions
several Cretaceous birds, including toothed forms (Fig. 4), qualify as crown group birds because they phylogenetically appear in the LRT after the basalmost extant bird, the kiwi (Apteryx). It only takes one primitive, but extant taxon to define a crown clade.

Dr. Padian also reviews the disagreement
between molecular evidence and the new palaeontological evidence offered by Asteriornis. He reports, “The evidence for Asteriornis reported by Field and colleagues implies that crown-group birds first evolved when the Cretaceous period was nearly over.” That’s not true for many reasons, all based on taxon exclusion.

Asteriornis is unique among known taxa
in exhibiting caudally pointed nasals that overlie the frontals and meet at the midline, and a slightly rounded, unhooked tip of the premaxilla. That first trait marks Asteriornis as a derived and terminal taxon, leaving no ancestors, as shown in the LRT, distinct from the tree topology produced by Field et al. Oddly, the tip of the premaxilla is slightly hooked on one side, not hooked on the other (Fig.1).


References
Alvarenga and Bonaparte 1992. A new flightless land bird from the Cretaceous of Patagonia; pp. 51–64 in K. E. Campbell (ed.), Papers in Avian Paleontology, Honoring Pierce Brodkorb. Natural History Museum of Los Angeles County, Science Series 36.
Chiappe LM 1996a. Late Cretaceous birds of southern South America: anatomy and systematics of Enantiornithes and Patagopteryx deferrariisi; pp. 203–244 in G. Arratia (ed.), Contributions of Southern South America to Vertebrate Paleontology, Münchner Geowissenschaftliche Abhandlungen Volume 30.
Chiappe LM 1996. 
Early avian evolution in the southern hemisphere: Fossil record of birds in the Mesozoic of Gondwana. Memoirs of the Queensland Museum 39:533–556.
Chiappe LM 2002. Osteology of the flightless Patagopteryx deferrariisi from the late Cretaceous of Patagonia (Argentina) pp.281–316 in Mesozoic Birds, Above the Heads of Dinosaurs, Chapter: 13, Editors: Chiappe LM and Witmer LM, University of California Press.
Field DJ, Benito J, Chen A, Jagt JWM and Ksepka DT 2020. Late Cretaceous neornithine from Europe illuminates the origins of crown birds. Nature 579:397–401.
Padian K 2020. Poultry through time. Nature online

Taxon list used by Field et al. 2020.
Ichthyornis_dispar
Tinamus_robustus
Vegavis_iaai
Chauna_torquata
Anhima_cornuta
Wilaru_tedfordi
Presbyornis_pervetus
Conflicto_antarcticus
Anatalavis_oxfordi
Anseranas_semipalmata
Dendrocygna_eytoni
Cereopsis_novaehollandiae
Anser_caerulescens
Tadorna_tadornoides
Leipoa_ocellata
Megapodius_reinwardt
Megapodius_eremita
Alectura_lathami
Macrocephalon_maleo
Gallus_gallus
Phasianus_colchicus
Coturnix_pectoralis
Acryllium_vulturinum
Crax_rubra
Ortalis_vetula
Dromaius_novaehollandiae
Dinornis_robustus
Struthio_camelus
Lithornis_promiscuus
Lithornis_plebius
Paracathartes_howardae
Burhinus_grallarius
Porphyrio_melanotus
Antigone_rubicunda
Cariama_cristata
Asteriornis_maastrichtensis
Gallinuloides_wyomingensis
Pelagornis_chilensis
Protodontopteryx_ruthae