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

Two primitive extant bats enter the LRT

Yesterday we looked at the smallest of the fruit bats (mega bats). Earlier we looked at several micro bats.

Here, at nearly the same size,
Notopteris (Figs. 1, 2( nests in the large reptile tree (LRT, 1671+ taxa, subset Fig. 5) as the most primitive extant megabat due to its long tail and a few other primitive traits.

Figure 1. Notopteris in vivo. Note the microbat proportions and relatively long tail. The wing membrane begins along a dorsal margin, not laterally as in other bats.

Figure 1. Notopteris in vivo. Note the microbat proportions and relatively long tail. The wing membrane begins along a dorsal margin, not laterally as in other bats.

Notopteris macdonaldi (Gray 1859) is the long-tailed fruit bat or Fijian blossom bat. This is the most primitive megabat in the LRT and the only one that retains a long tail. It roosts in large cave colonies only on South Pacific islands. Note the mid-dorsal attachment of the proximal wing membranes, rather than a more lateral attachment. This is a derived trait not shared with other bats.

Figure 2. Notopteris skull and mandible.

Figure 2. Notopteris skull and mandible. Note the primitive skull and derived simple cusp teeth.

The most primitive extant microbat
in the LRT (Figs. 3, 4) is the newly added Rhinopoma, the lesser mouse-tailed bat (Fig. 3). It is similar, to Notopteris (Figs. 1, 2), but with a shorter rostrum and retains primitive multiple cusps on its teeth. Both are cave dwellers.

Figure 3. Rhinopoma is the most primitive extant micro bat in the LRT. Note the long tail, long legs and small feet, all Chriacus-like and Onychonycteris-like primitive traits.

Figure 3. Rhinopoma is the most primitive extant micro bat in the LRT. Note the long tail, long legs and small feet, all Chriacus-like and Onychonycteris-like primitive traits. Note the lateral insertion of the wing membrane on the torso, distinct from Notopteris (Fig. 1).

Rhinopoma hardwickei (Gray 1831) is the extant lesser mouse-tailed bat, an insectivore found from North Africa to India. The tail is 3/4 free and no calcar is present on the heel. The legs are long and the feet are small.

Figure 4. Rhinopoma skull from Digimorph.org and used with permission.

Figure 4. Rhinopoma skull from Digimorph.org and used with permission. Note the prominent ear bones (yellow) in this echolocating microbat.

Simmons et al. 1984 looked at echolocation in Rhinopoma.
They concluded, “Except for duration these signals are relatively inflexible and suggestive of a primitive kind of echolocation in which only one dimension is changed to achieve qualities which most other species of bats obtain by changing a variety of signal dimensions simultaneously.”

Nelson and Hamilton Smith 1982 looked at echolocation in Notopteris.
They concluded, “Some field experiments… showed these flying foxes were unable to avoid obstacles in complete darkness or when blindfolded, but were able to do so in very dim light. No audible or ultrasonic sounds that could be used in echolocation were detected during their flight.”

Holland et al. 2004 looked at echolocation in the megabat Rousettus.
They reported, “Rousettus aegyptiacus Geoffroy 1810 is a member of the only genus of Megachiropteran bats to use vocal echolocation, but the structure of its brief, click-like signal is poorly described.Rousettus aegyptiacus Geoffroy 1810 is a member of the only genus of Megachiropteran bats to use vocal echolocation, but the structure of its brief, click-like signal is poorly described. However, the low energy content of the signals and short duration should make returning echoes difficult to detect. The performance of R. aegyptiacus in obstacle avoidance experiments using echolocation therefore remains something of a conundrum.”

Simmons and Geisler 1998 looked at echolocation in Icaronycteris.
They reported, “We propose that flight evolved before echolocation, and that the first bats used vision for orientation in their arboreal/aerial environment. The evolution of flight was followed by the origin of low-duty-cycle laryngeal echolocation in early members of the microchiropteran lineage. This system was most likely simple at first, permitting orientation and obstacle detection but not detection or tracking of airborne prey.”

Veselka et al. 2010 concluded that Onychonycteris finneyi may have been capable of echolocation. in reply, Simmons et al. 2010 argued that Onychonycteris finneyi was probably not an echolocating bat.

Echolocation seems to have been convergently acquired
in microbats and Rousettus.

Figure 1. Subset of the LRT focusing on the resurrected clade Volitantia, including dermopterans, pangolins, bats and their extinct kin.

Figure 5. Subset of the LRT focusing on the resurrected clade Volitantia, including dermopterans, pangolins, bats and their extinct kin.

Basal bats in the LRT have more plesiomorphic traits overall,
like small ears, simple nose, long legs, long tail and small feet, all Chriacus-like (Fig. 6) traits. This is what we should expect when any cladogram models micro-evolutionary changes.

Figure 2. Chriacus and Onychonycteris nest as a sister to the undiscovered bat ancestor and a basal bat. Miniaturization was part of the transition. So was enlargement of the manus. It is still a mystery why the transitional form decided to start flapping.

Figure 6. Chriacus and Onychonycteris nest as a sister to the undiscovered bat ancestor and a basal bat. Miniaturization was part of the transition. So was enlargement of the manus. It is still a mystery why the transitional form decided to start flapping.

We looked at the origin of bats from Chriacus-like ancestors
earlier here, here and at earlier links therein. These posts are –by far– the most popular posts at this PterosaurHeresies.

To summarize one of those posts
hanging pre-bats simply listened for the sounds of prey in leaf litter below, then pounced from above. Parachuting with flapping evolved into helicoptering then that evolved into flight to return to the branch the bat fell from. Larger hands and extradermal membranes would have increasingly aided entrapment at the moment of impact. Even larger hands and extradermal membranes would have increasingly helped helicoptering while falling. Smaller size and weight (Fig. 6) was co-opted to aid these behaviors. Echolocation seems to have evolved in bats seeking aerial prey and co-opted to live in caves in complete darkness.


References
Gray JE 1831. Description of some new genera and species of bats. The Zoological Miscellany, 1: 37-38.
Gray GR 1859.
 The annals and magazine of Natural History, Zoology, Botany and Geology 3. Series IV: 4859.
Holland RA, Waters DA and Rayner JMV 2004. Echolocation signal structure in the megachiropteran bat Rousettus aegyptiacus Geoffroy 1810. Journal of Experimental Biology 207:4361–4369.
Nelson JE and Hamilton-Smith E 1982. Some observations on Notopteris macdonaldi (Chiroptera: Pteropodidae) in Australian Mammal Society 5: 247–252.
Simmons JA, Kick SA and Lawrence BD 1984. Echolocation and hearing in the mouse-tailed bat, Rhinopoma hardwickei: acoustic evolution of echolocation in bats. Journal of Comparative Physiology A 154: 347–356.
Simmons NB and Geisler JH 1998. Phylogenetic relationships of Icaronycteris, Archaeonycteris, Hassianycteris, and Palaeochiropteryx to extant bat lineages, with comments on the evolution of echolocation. Bulletin of the American Museum of Natural History 235.
Simmons NB, Seymour KL, Habersetzer J and Gunnell GF 2010. Inferring echolation in ancient bats. Nature 466: E8.
Veselka et al. (8 co-authors) 2010. A bony connection signals larygenal echolocation in bats.Nature 463: 939–942.

wiki/Notopteris

wiki/Rhinopoma

When Pteranodon gets big, so do its wing bones, so it can keep flying

Earlier we looked at 
how the best known two dozen Pteranodon specimens can be readily split into about two dozen species. No two are alike and all can be lumped and split in a pterosaur cladogram. Contra traditional studies, no gender differences are apparent.

Size
As certain Pteranodon specimens grew larger and larger (Fig. 1) the arm bones, especially the antebrachium and metacarpal 4, became increasingly robust. This must have been a structural modification for keeping the largest specimens flying. Perhaps this is so because the weight increases more or less by the cube of the length… and the skulls + crests are getting larger, too.

Figure 1. Four Pteranodon specimens of increasing size. More robust arm bones are found in larger specimens. There is no reduction of distal wing elements.

Figure 1. Four Pteranodon specimens of increasing size. More robust arm bones are found in larger specimens. There is no reduction of distal wing elements in this volant genus.

Importantly,
the distal wing phalanges do not become vestiges in volant pterosaurs (Fig. 1) whether in the genus Pteranodon or the very large ornithocheirids.

Figure 1. Quetzalcoatlus specimens to scale.

Figure 2. Quetzalcoatlus specimens to scale with a former 6-foot-tall president. Note the slender antebrachium (radius + ulna) and vestigial distal wing phalanges.

This is distinct from
mid-sized to giant azhdarchids, which have vestigial distal wing phalanges (Fig. 2). This pattern of wing reduction follows the same pattern seen in much smaller flightless pre-azhdarchid like Jme-Sos 2428, the flightless anurognathid PIN 2585/4 and flightless nyctosaurs, like Alcione.

There is a clade of pterosaur paleontologists and artists
who are enamored with the idea of giant flying azhdarchids. They say the math is on their side, but they’re not looking at what small pterosaurs do when they become flightless (see above). Given the present data, the flightlessness of six-foot-tall azhdarchids enabled the next magnitude in size increase, just as the near flightlessness of larger tinamous, secretary birds and parrots enabled the next magnitude of size increase to create giant flightless ostriches, terror birds and Gastornis.

FIgure 2. A basal pteranodotid, the most complete Pteranodon, the largest Pteranodon skull matched to the largest Pteranodon post-crania compared to the stork Ciconia and the most complete and the largest Quetzalcoatlus

FIgure 2. A basal pteranodotid, the most complete Pteranodon, the largest Pteranodon skull matched to the largest Pteranodon post-crania compared to the stork Ciconia and the most complete and the largest Quetzalcoatlus

The largest flying birds,
like Pelagornis, have proportions similar to those seen in the largest flying ornithocheirids and pteranodontids. The largest flying azhdarchid-like, long-legged wading birds, the storks, cranes and shoebills, never get much taller than a human. All larger birds are flightless. All larger azhdarchids are also flightless, based on their reduced wingtips and narrow ante brachia, but still use their wings for thrust (Fig. 3).

Quetzalcoatlus running like a lizard prior to takeoff.

Figure 10. Quetzalcoatlus running like a lizard prior to takeoff. There was no longer any need for aerodynamic balance as a flightless sprinter, so the  neck were free to achieve giraffe-like proportions and size with a giant skull tipping the balance even further.


References

New ground effect study supports origin of bat flight hypothesis proposed here

A new paper by Johansson, Jakobsen and Hendenstram 2018
introduces the benefit of ground effect (the surface acts as an aerodynamic mirror, interrupting the downwash, resulting in increased pressure underneath the wing and suppression of wingtip vortex development) in the origin of bat flight.

This is something every student pilot learns.
Ground effect is basic aerodynamics whether applied to bats, airplanes or flying fish.

Figure 1. The false vampire bat hovering before attacking a mouse in dry fallen leaves, listening to locate is prey.

Figure 1. The false vampire bat hovering before attacking a mouse in dry fallen leaves, listening to locate is prey.

Even so, it is measured here for bats for the first time.
You might remember, an earlier hypothesis first published here proposed an origin of bat flight associated with dropping out of trees while frantically flapping to break the fall in order to attack insects heard in the leaf litter (Fig. 1). The benefit of such unprofessional flapping increases as the ground gets closer and closer. In bats this frantic flapping while parachuting evolved to hovering before ground contact (with the help of ground effect). And this evolved to powered flight in bat-fashion, distinct from bird and pterosaur flight origins.

Highlights of the Johansson, Jakobsen and Hendenstram 2018 paper:

  1. Aerodynamic power is 29% lower when bats fly close to rather than far from ground
  2. Measured savings are twice the savings expected from models
  3. Wing motion is varied with distance to ground, which may modulate ground effect
  4. The results challenge our understanding of how animals use ground effect

References:
Johansson LC, Jakobsen L and Hendenstram A 2018. Flight in ground effect dramatically reduces aerodynamic costs in bats. Current Biology. DOI: https://doi.org/10.1016/j.cub.2018.09.011
https://www.cell.com/current-biology/fulltext/S0960-9822(18)31206-5

“Kinematics of wings from Caudipteryx to modern birds”: Talori et al. 2018

A new paper without peer-review by Talori, Zhao and O’Connor 2018
seeks to “better quantify the parameters that drove the evolution of flight from non-volant winged dinosaurs to modern birds.”

Unfortunately
they employ Caudipteryx, an oviraptorosaur. They correctly state,
Currently it is nearly universally accepted that Aves belongs to the derived clade of theropod dinosaurs, the Maniraptora.” They incorrectly state, “The oviraptorosaur Caudipteryx is a member of this clade and the basal-most  maniraptoran with pennaceous feathers.” In the large reptile tree (LRT, 1269 taxa) oviraptorosaurs nest with therizinosaurus, and more distantly ornithomimosaurs. This clade is separated from bird ancestor troodontids by the Ornitholestes/Microraptor clade.

Figure 1. More taxa, updated tree, new clade names.

Figure 1. Caudipterys is in the peach-colored clade, far from the lineage of birds.

The Talori team
mathematically modeled Caudipteryx with three hypothetical wing sizes, but failed to provide evidence that the Caudipteryx wing was capable of flapping. In all flapping tetrapods the elongation of the coracoid  (or in bats of the clavicle) signals the onset of flapping… and Caudipteryx does not have an elongate coracoid. Rather, it remains a disc.

So, no matter the math, or the accuracy of the mechanical model,
the phylogeny is not valid and the assumption of flapping is inappropriate. It would have been better if they had chosen a troodontid and several Solnhofen birds to test.

Tossing those issues aside,
the Talori team did an excellent job of setting their mechanical model (which could be a troodontid) in a wind tunnel, extracting data from three different wing shapes and presenting their findings. Feathers would have been more flexible than their mold manufactured wings, but the effort is laudable.

References
Zhao J-S, Talori YS, O’Connor J-M 2018. Kinematics of wings from Caudipteryx to modern birds. [not peer-reviewed] bioRXiv
https://www.biorxiv.org/content/early/2018/08/16/393686

http://reptileevolution.com/reptile-tree.htm

Axial rotation: fingers in pterosaurs, toes in birds

A somewhat recent paper by Botelho et al. 2015
looked at the embryological changes that axially rotate metatarsal 1 to produce a backward-pointing, opposable, perching pedal digit 1 (= hallux).

Hallux rotation phylogenetically
Botelho reports: Mesozoic birds closer than Archaeopteryx to modern birds include early short-tailed forms such as the Confuciusornithidae and the toothed Enantiornithes. They present a Mt1 in which the proximal portion is visibly non-twisted, while the distal end is offset (“bent”) producing a unique “j-shaped” morphology. This morphology is arguably an evolutionary intermediate between the straight Mt1 of dinosaurs and the twisted Mt1 of modern birds, and conceivably allowed greater retroversion of Mt1 than Archaeopteryx.”

“D1 in the avian embryo is initially not retroverted9, and therefore becomes opposable during ontogeny, but no embryological descriptions address the shape of Mt1, and no information is available on the mechanisms of retroversion.”

Figure 1. Pes of the most primitive Archaeopteryx, the Thermopolis specimen.

Figure 1. Pes of the most primitive Solnhofen bird, the Thermopolis specimen. This digit 1 never left the substrate.

In Tyrannosaurus,
(Fig. 2) the entire metatarsal 1 with pedal digit 1 is rotated just aft of medial by convergence. It’s not axially rotated. It’s just attached to the palmar side of the pes. This pedal digit 1 was elevated above the substrate.

Figure 2. The semi-retroverted pedal digit 1 of Tyrannosaurus rex in two views.

Figure 2. The semi-retroverted pedal digit 1 of Tyrannosaurus rex in two views. This digit 1 was elevated above the substrate.

In some birds
like the woodpecker, Melanerpes, and the unrelated roadrunner, Geococcyx, pedal digit 4 is also retroverted. Sorry, I digress.

Further digression
The axial rotation of pedal digit 1 in birds is convergent with the axial rotation of metacarpal 4 in Longisquama (Fig. 3) and pterosaurs. In both taxa the manus was elevated off the substrate and permitted to develop in new ways. Manual digit 4 never leaves an impression in pterosaur manus tracks… because it is folded, like a bird wing, against metacarpal 4. In Longisquama such extreme flexion is not yet possible.

Figure 1. Longisquama left and right manus traced using DGS then reconstructed (below). This is a very large hand for a fenestrasaur and manual digit 4 is oversized, as in pterosaurs.

Figure 3. Longisquama left and right manus traced using DGS then reconstructed (below). This is a very large hand for a fenestrasaur and manual digit 4 is oversized and the metacarpal is axially rotated, as in pterosaurs. Manual digit 5 is useless, but not yet a vestige. A pteroid is present, as in Cosesaurus. The coracoid is elongate as in birds. The sternum, interclavicle and clavicle are assembled into a single bone, the sternal complex, as in pterosaurs.

Note the lack of space between
the radius and ulna in Longisquama. This is what also happens in pterosaurs. It prevents the wrist from pronating or supinating, as in birds and bats… which means, the forelimb is flapping, not pressing against the substrate, nor grasping prey. That means all those images of Longsiquama on all fours are bogus. Now you know.

So now we come full circle
While the toes of birds axially rotate and the wing metacarpal of pterosaurs axially rotates, the forearms of birds, pterosaurs and Longisquama do not axially rotate. No one wants their wing to twist.

References
Botelho JF, Smith-Paredes D, Soto-Acuña S, Mpodozis J, Palma V and Vargas AO 2015. Skeletal plasticity in response to embryonic muscular activity underlies the development and evolution of the perching digit of birds. Article in http://www.Nature.com/Scientific Reports · May 2015 DOI: 10.1038/srep09840

Azhdarchid pterosaur flight issues

Pterosaurs,
as fenestrasaur tritosaur lepidosaurs matured isometrically. That’s a widely overlooked fact, even by pterosaur workers. Hatchlings had adult proportions with small eyes and long rostra — if their 8x larger parents had small eyes and long rostra. Hatchlings also had adult-proportioned wings. So presumably they were able to fly shortly after hatching (and drying out a bit) — if their parents were able to fly. But not all adult pterosaurs were able to fly…

Figure 1. GIF animation, 4 frames, showing three pterosaurs specimens in 3 sizes (see scale bars) with short, medium and long wings, drawn to the same torso length. The question is: did Quetzalcoatlus fly?

Figure 1. GIF animation, 4 frames, showing three pterosaurs specimens in 3 sizes (see scale bars) with short, medium and long wings, drawn to the same torso length. The question is: did Quetzalcoatlus fly?

Flightless pterosaurs
Earlier we looked at two related pterosaurs, the no. 57 specimen (Sos 2482) and the no. 42 specimen in the Wellnhofer 1970 catalog (Fig. 1). Both are adults. Both are in the azhdarchid lineage that arose from a tiny pterodactyloid-grade dorygnathid, the no. 1 specimen (TM 10341) in the Wellnhofer 1970 catalog and ultimately gave rise to the giant pterosaur, Quetzalcoatlus (also in Fig. 1). A magnitude or more greater in size and with wings only half as long as the flying no. 42 specimen,

Quetzalcoatlus is widely considered a flying pterosaur.
Can that be verified? Other clades of large (larger than a pelican) pterosaurs all have elongate wings, ideal for soaring. Azhdarchids, apparently deep shoreline waders, did not. The distal two long phalanges (sans the ungual) were shorter in azhdarchids, but the wing was not otherwise reduced, as in the flightless pterosaur, no. 57 (Fig. 1). Witton and Naish 2008 provide a history of workers pondering this question. Unfortunately they provided a bat-wing membrane attached to the ankles or shins with anteriorly oriented pteroids, ignoring key references for pterosaur wing shape (Peters 2002, 2009 and references therein) while ignoring fossilized evidence of pterosaur wing tissue, as others have done.

As anything gets larger,
either ontogenetically or phylogenetically, they generally put on weight at the cube of their length. Air-filled pterosaurs were not as solid, so that ratio was undoubtedly lower.  Even so longer, larger wings on larger pterosaurs makes sense, as in living large birds that fly and are also air-filled.

But that is countered by the isometric growth of individual pterosaurs as they mature to adulthood. Whatever works for hatchlings and tiny pterosaurs, is working just as well for giant adults. Could that mean that all ontogenetic stages of Quetzalcoatlus could fly? Or none of them? Or only half-sized juveniles at about ten percent of the adult weight? With flight, it’s always a balancing act: thrust, lift, drag, weight.

Wings can still provide great thrust
for terrestrial excursions even if they cannot get a big pterosaur off the ground (Fig. 2). So that’s a possibility under consideration, too. After all, why not use all the thrust available?

Quetzalcoatlus running like a lizard prior to takeoff.

Figure 10. Quetzalcoatlus running like a lizard prior to takeoff.

To prevent an extant flying bird, like a cockatiel, from flying, or flying well,
it’s surprising how little of the tips of the feathers need to be clipped. Link here. Basically its the difference between no. 42 and Quetzalcoatlus above (Fig. 1). With this in mind, I cannot join those who say giant Quetzalcoatlus could fly or fly between continents, until supporting evidence comes alone. Rather, giant azhdarchids become hippo analogs in this respect: they were probably constant deep waders (Fig. 3) capable of charging or running from danger. Storks, which azhdarchids otherwise resemble, tend to fly away because they have long, not truncated wings and can do so.

Figure 3. In my opinion this saddle-bill stork wading in water appears to be the bird closest to azhdarchid morphology and, for that matter, niche.

Figure 3. In my opinion this saddle-bill stork wading in water appears to be the bird closest to azhdarchid morphology and, for that matter, niche. It can fly from danger on elongate wings. Not so sure that Q could do the same. 

References
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing—with a twist. Historical Biology 15:277-301.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330.
Wellnhofer P 1970. 
Die Pterodactyloidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Abhandlungen der Bayerischen Akademie der Wissenschaften, N.F., Munich 141: 1-133.
Witton M and Naish D 2008.  A Reappraisal of Azhdarchid Pterosaur Functional Morphology and Paleoecology. https://doi.org/10.1371/journal.pone.0002271. online here.

Flapping before flight

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

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

Figure 1. Cosesaurus running and flapping – slow.

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

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

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

Unsuccessul Pteranodon wing launch based on Habib (2008).

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

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

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

When true birds, pre-birds and pseudo-birds first started flapping

Figure 1. Xiaotingia with new pectoral interpretation. See figure 3 for new tracing.

Figure 1. Xiaotingia with new pectoral interpretation. See figure 3 for new tracing. Based on the height of the coracoids, comparable to the height of the furcula, Xiaotingia was an early flapper. Based on the shorter tail length those taller coracoids represent yet another convergence with true birds. 

According to the cladogram
of the large reptile tree the proximal outgroup to Archaeopteryx and the flapping birds includes Eosinopteryx (Godefroit et al. 2013, Middle-Late Jurassic, Tiaojishan Formation, YFGP-T5197, 30 cm, 12 in long) and Xiaotingia (Figs. 1-4; Xu et al. 2011, STM 27-2).  This nesting has not changed despite the addition of several very bird-like theropod taxa recently (some listed below) to the large reptile tree.

Although they both had large wing feathers,
only Xiaotingia had tall coracoids. Coracoids were narrow, but short in Eosinopteryx. Tall coracoids are morphological signs that an extinct taxon was flapping.

Figure 2. Eosinopteryx with new pectoral interpretation. See figure 4 for in situ tracings.

Figure 2. Eosinopteryx with new pectoral interpretation. See figure 4 for in situ tracings. This taxon had smaller coracoids than in Xiaotingia. Based on tail length, this is the plesiomorphic condition.

Tall coracoids first appear
in the true bird lineage with the basalmost Archaeopteryx, the Thermopolis specimen (Fig. 5).

Figure 3. GIF animation of Xiaotingia pectorals showing new interpretations for the coracoid and sternum. Reconstruction in figure 1.

Figure 3. GIF animation of Xiaotingia pectorals showing new interpretations for the coracoid and sternum. Reconstruction in figure 1. The fuzzy yellow and gray drawing is the original published interpretation.  Outlying areas are low rez surrounding higher resolution central area. The difficult to see left coracoid is in green, crushed and scattered. The ventral rim of the right coracoid might be peeking beneath the vertebrae, angled toward the sternum. 

By convergence
and along with Xiaotingia, tall-ish coracoids also appear in the unrelated pseudo bird-like taxa Microraptor + Sinornithosaurus and Velociraptor + Balaur. Evidently they were flapping too.

Figure 4. GIF animation for new interpretation of Eosinopteryx pectoral region. The coracoids appear to be half as long but just as tall as previously interpreted. This is a reduction, as in Cosesaurus, rather than an elongation.

Figure 4. GIF animation for new interpretation of Eosinopteryx pectoral region. The coracoids appear to be half as long but just as tall as previously interpreted. This is a reduction, as in Cosesaurus, rather than an elongation. Reconstructed in figure 2. There were two clavicles hidden in their. The dark green areas may be dermal in origin. 

The Thermopolis specimen
of Archaeopteryx (Fig. 5) has the shortest and smallest coracoids of the Solnhofen birds. Note the basal troodontid (Fig. 7) proportions of the small skull and long tail, distinct from the larger skulls and shorter tails in the clade that includes Xiaotingia and Eosinopteryx.

Figure 1. The six tested Solnhofen birds currently named Archaeopteryx, Jurapteryx and Wellnhoferia.

Figure 1. The six tested Solnhofen birds currently named Archaeopteryx, Jurapteryx and Wellnhoferia.

By contrast and convergence,
and based on the reduction of their coracoids to struts, prevolant pterosaur ancestors, like Cosesaurus (Fig. 6), were flapping millions of generations before this clade had anything resembling wings,

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 6. 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.

Many workers nest
microraptors and velociraptors closer to birds. At least part of that nesting includes the presence of feathers and tall narrow coracoids, ideal for flapping. Unfortunately these alternate nestings cannot be confirmed by the large reptile tree that nest small troodontids, like Xiaotiingia and Eosinopteryx, basal to birds. At least one prior analysis was riddled with errors. I have not examined others yet.

Figure 1. Sinornithoides youngi figure modified from Russell and Dong 1993.

Figure 7. Sinornithoides youngi figure modified from Russell and Dong 1993. Compare these proportions to the basal Archaeopteryx specimens with their small skulls, short torsos and long tails. 

This is where software comes in handy,
finding most parsimonious trees based on a long list of traits despite convergence in a few traits and making every attempt to keep paradigm and tradition out of every computation. These taxa were reexamined and discovered because the the coracoids did not match while so many other characters do match and nest them together. The coracoids still do not match on sisters Xiaotingia and Eosinopteryx, but several errors were repaired.

References
Godefroit P, Demuynck H, Dyke G, Hu D, Escuillié FO and Claeys P. 2013. Reduced plumage and flight ability of a new Jurassic paravian theropod from China. Nature Communications 4: 1394. doi:10.1038/ncomms2389
Xu X, You H, Du K and HanF-L 2011. An Archaeopteryx-like theropod from China and the origin of Avialae. Nature 475 (7357): 465–470.

 

The Origin and Evolution of Bats Part 2

Earlier we looked at basal bats and their closest outgroups. That entry from several years ago has proven to be a weekly and annual favorite among blog posts here at the pterosaur heresies. Part 3 on this subject was posted here. See Part 4 here. It solves many of the problems attending the origin of bats.

 

Today we’ll do the same with newly arranged graphics (Figs. 1,2) principally matching the non-bat, Ptilocercus, to the basal bats, Onychonycteris and Icaronycteris (Fig. 1). I’m surprised I never did this before because the results are illuminating.

Figure 1. Ptilcercus (above) and Icaronycteris (below), sister taxa in the origin of bats.

Figure 1. Ptilcercus (above) and Icaronycteris (below), sister taxa in the origin of bats. Click to enlarge. Despite the similarities of these two, the differences in dent ion and the size of the manus kept scholars from comparing these two taxa directly with one another. Ptilocercus is also close to the flying lemur, which is why its dentition is more like the flying lemur.

In figure 1 the similarities are striking:

  1. skull, torso, pelvis and tail have similar shapes
  2. ribs are flat in both
  3. radius is longer than the humerus in both.
  4. ulna is reduced distally, to no more than one third the width of the radius (as in bats).
  5. carpus rotates posterolaterally in both
  6. the ability to spread the digits so widely that digits 1 and 5 oppose one another by 180º
  7. first manual digit is somewhat thumb-like, able to grasp objects.
  8. tibia longer than femur in both
  9. ankles are more flexible in both. The astragalus and calcaneum move away from stacked one upon the other to more of a  side-by-side configuration.
  10. Pedal digits 2 – 5 are equal in length and their metatarsals follow suit. The pedal unguals also deepen

Now let’s examine the differences. In the bat:

  1. cervicals are more gracile
  2. clavicle is longer and the scapula is larger (for large pectoral flight muscles)
  3. lumbar region is longer
  4. tail is shorter
  5. entire forelimb is longer, especially the hand
  6. hand is webbed
  7. The tibial malleolus (lateral distal process), which restricts ankle rotation in most mammals is not present in bats
  8. tarsals of bats are smaller, the penultimate phalanges are longer and the unguals are larger. Better to hang inverted.
  9. medial digit of the foot loses its ability to oppose the other pedal digits
  10. Onychonycteris develops a new bone arising from the ankle which helps frame the uropatagium.
  11. some bats use echolocation for prey capture
Figure 2. Selected details of Ptilocercus and Onychnycteris.

Figure 2. Selected details of Ptilocercus and Onychnycteris. The spreading of the metacarpals is a synapomrophy.

Remember
Ptilocercus has different teeth because it is more closely related to Cynocephalus, the flying lemur (Fig. 3), which is also not too distant from bats. Despite the appearance of extradermal membranes in dermopterans, it appears that those were obtained convergently in bats.

Figure 3. Cynocephalus, the flying lemur, shares many traits with Ptilocercus and basal bats.

Figure 3. Cynocephalus, the flying lemur, shares many traits with Ptilocercus and basal bats. Note the distally reduced ulna.

Take another look at the bat family tree (Fig. 4).
Ptilocercus
is not another tree shrew, like Tupaia. Ptilocercus is a miniature civet. Tupaia is in the lineage of rabbits. DNA evidence (Tsagkogeorga et al. 2013) supports this tree topology with bats arising from carnivores, like civets.

Figure 2. Bat evolution and origins from the Carnivora/Viverridae. They are sisters to the Pen-tailed tree shrew and colugos among living taxa. Protictis is an extinct outgroup taxon from the Paleocene.

Figure 4. Bat evolution and origins from the Carnivora/Viverridae. They are sisters to the Pen-tailed tree shrew and colugos among living taxa. Protictis is an extinct outgroup taxon from the Paleocene.

The origin of flight
and flapping in bats continues to be a vexing problem. An earlier hypothesis based on current behavior remains unsatisfying.

Interesting YouTube video
on bat cooling in the tropics here. Yes they flap gently to generate a self-directed breeze, but they also lick themselves for evaporative cooling.

Interesting YouTube video on bat flight here.

More tomorrow.

References
Jepsen GL, MacPhee RDE 1966. Early Eocene bat from Wyoming. Science 154 (3754): 1333–1339. doi:10.1126/science.154.3754.1333. PMID 17770307.
Le Gros-Clark WE 1926. On the Anatomy of the Pen-tailed Tree-Shrew (Ptilocercus lowii.) Proceedings of the Zoological Society of London 96: 1179-1309.
DOI – 10.1111/j.1096-3642.1926.tb02241.x
Simmon NB, Seymour KL, Habersetzer J, Gunnell GF 2008. Primitive Early Eocene bat from Wyoming and the evolution of flight and echolocation. Nature 451 (7180): 818–21. doi:10.1038/nature06549. PMID 18270539.
Tsagkogeorga G, Parker J, Stupka E, Cotton JA, Rossiter SJ 2013. Phylogenomic analyses elucidate the evolutionary relationships of bats (Chiroptera). Current Biology 23 (22): 2262–2267.

wiki/Icaronycteris
wiki/Onychonycteris
wiki/Ptilocercus