Mid-sized Changyuraptor nests between big Ornitholestes and small Microraptor in the LRT

Han et al. 2014 brought us a new feathered theropod,
Changyuraptor yangi (Aptian, Early Cretaceous, HG B016). In the large reptile tree (LRT, 1720+ taxa) Changyuraptor nests between a bigger Ornitholestes and a smaller Microraptor… in that order (from big to medium to small).

By contrast
Han et al. nested Changyuraptor in unresolved nodes with Microraptor and others (see below), all close to dromaeosaurids and several nodes apart from Ornitholestes.

Figure 1. Changyuraptor reconstructed.

Figure 1. Changyuraptor reconstructed.

Changyuraptor is not so much a giant microraptorine
as a small ornitholestid. At least that’s the phylogenetic order.

Stem-like locked-down coracoids (= narrower, not taller) are traits that indicate flapping in Changyuraptor. Maybe it was a little too big to fly. That would have to wait for Microraptor and Sinornithosaurus. Even so, that extra thrust might have added speed to running. The display function would have given it a good bluff or a seductive show.

Figure 1. Changyuraptor to scale with Ornitholestes, Scriurumimus and Microraptor.

Figure 2. Changyuraptor to scale with Ornitholestes, Scriurumimus and Microraptor.

From the abstract:
“Microraptorines are a group of predatory dromaeosaurid theropod dinosaurs with aerodynamic capacity.”

By contrast the LRT nests microraptorines as bird mimics, closer to Ornitholestes than to dromaeosaurids and troodontids. Elongate coracoids were overlooked by Han et al. So this clade was flapping long flight feathers symmetrically, as birds, pterosaurs and bats do, not just carrying them around for show.

“These close relatives of birds are essential for testing hypotheses explaining the origin and early evolution of avian flight.”

By contrast, in the LRT microraptors are phylogenetically bird mimics, unrelated to the avian lineage.

“Here we describe a new ‘four-winged’ microraptorine, Changyuraptor yangi, from the Early Cretaceous Jehol Biota of China. With tail feathers that are nearly 30 cm long, roughly 30% the length of the skeleton, the new fossil possesses the longest known feathers for any non-avian dinosaur. Furthermore, it is the largest theropod with long, pennaceous feathers attached to the lower hind limbs (that is, ‘hindwings’).”

In the LRT Changyuraptor is transitional both in size and morphology between Ornitholestes and microraptorines. Earlier, without Changyuraptor, Ornitholestes and microraptorines nested together in the LRT.

“The lengthy feathered tail of the new fossil provides insight into the flight performance of microraptorines and how they may have maintained aerial competency at larger body sizes. We demonstrate how the low-aspect-ratio tail of the new fossil would have acted as a pitch control structure reducing descent speed and thus playing a key role in landing.”

On this topic, the coracoids of Changyuraptor and microraptorines are relatively small (smaller than in the chicken, Gallus) and Changyuraptor is relatively large. Plus Han et al. also overlooked the large sternum on Changyuraptor, but it lacks a ventral keel (distinct from Gallus). These traits indicate relatively small pectoral muscles, just barely suitable for weak flapping, but inadequate for flight on this mid-sized theropod. So Changyuraptor would have been a runner, not a flyer. Thus the feathered tail would not have needed pitch control if it stayed on ‘the runway.’ Perhaps, along with raised feathered elbows, raised tail feathers might have served as secondary sexual traits or bluffs designed to increased apparent size to marauding predators.

Diagnosis. A microraptorine dromaeosaurid theropod characterized by having the unique combination of traits: furcula more robust than that of Sinornithosaurus millenii and much larger than that of Tianyuraptor ostromi;

The LRT nests Tianyuraptor basal to tyrannosaurids along with Zhenyuanlong. Clavicles are separate and small elements in Ornitholestes, so the larger clavicles in Changyuraptor support the elongate coracoids.

“forelimb proportionally much longer when compared with hindlimb than in other microraptorines;

Figure 2. Changyuraptor limbs to scale.

Figure 3. Changyuraptor limbs to scale. Distinct from sister taxa, this taxon has a long forelimb.

True. Both Ornitholestes and Microraptor have relatively shorter fore limbs relative to the hind limbs.

“humerus much longer (>20% longer) than ulna as opposed to Microraptor zhaoianus, in which these bones are more comparable in length;”

The humerus of Changyuraptor is not >1.2x the ulna (Fig. 3), but the humerus of Ornitholestes (Fig. 4) is in that ratio range.

“metacarpal I proportionally shorter than in Sinornithosaurus millenii (1/4–1/5 versus 1/3);”

Metacarpal 1 is also shorter in Ornitholestes (Figs. 4, 5).

FIgure 6. Ornitholestes nests as a sister to Sciurumimus, between Compsognathus and Microraptor.

Figure 4. Ornitholestes nests as a sister to Sciurumimus, between Compsognathus and Microraptor.

Large, procumbent teeth
on a short skull can be seen even in ventral view on Changyuraptor.

Figure 3. Ornitholestes with a short metacarpal 1.

Figure 5. Ornitholestes with a short metacarpal 1.

“well-developed semi-lunate carpal covering all of proximal ends of metacarpals I and II as opposed to the small semi-lunate carpal that covers about half of the base of metacarpals I and II in most other microraptorines;”

Not illustrated in Ornitholestes.

“manual ungual phalanx of digit II is the largest, followed by that of digits I andt III, as opposed to Graciliraptor lujiatunensis in which the ungual of manual digit I is very small, and Sinornithosaurus millenii and Microraptor zhaoianus in which the unguals of manual digits I and II are comparable in size;”

See Ornitholestes (Figs. 4, 5) for available comparisons.

“ischium shorter than in Microraptor zhaoianus;

Ischium length is difficult to assess due to overlying elements.

“midshaft of metatarsal IV significantly broader than that of metatarsal III or metatarsal II, as opposed to G. lujiatunensis in which metatarsal IV is the narrowest;”

Comparables are difficult to assess in Ornitholestes due to lost metatarsals.

“mid-caudals roughly twice the length of dorsals as in Sinornithosaurus millenii as opposed to long caudal vertebrae in Microraptor zhaoianus;”

In Changyuraptor the midcaudals are 1.5x the dorsals length, and Sinornithosaurus is comparable. Note that Ornitholestes has a similarly hyper elongate tail.

“fewer caudal vertebrae (22 vertebrae) than Microraptor zhaoianus (25–26 vertebrae) and Tianyuraptor ostromi (28 vertebrae);”

Ornitholestes has many more than 20 caudal vertebrae.

“rectories significantly longer than in other microraptorines.”

Rectories not preserved in Ornitholestes.

This clade of microraptorine bird mimics evolved
by phylogenetic miniaturization. The coracoids became elongate (= narrower, not taller) and locked down for minimal flapping, much less than in extant fowl.

Han G, Chiapped LM, Ji S-A, Habib M, Turner AH, Chinsamy A, Liu X and Han L 2014. A new raptorial dinosaur with exceptionally long feathering provides insights into dromaeosaurid flight performance. Nature Communications DOI: 10.1038/ncomms5382



Microraptor leg feathers and the evolution of bird flight

A recent abstract by Habib et al. 2012 hypothesized that “Microraptoran dinosaurs may have experienced intrinsic difficulties with pitch control because they retained a trunk of typical dromaeosaurid proportions, as opposed to the shortened trunk of ornithurine birds. 

Microraptor with feather impressions.

Figure 1. Microraptor with feather impressions.

“Specimens of Microraptor gui show that a fan of feathers existed near the terminus of the tail. This would be sufficient to correct for small deviations of the center of gravity from the center of lift. The tail could not have provided significant control in yaw or roll, but the forewings and hindwings would have been well suited to providing those control functions.

Microraptor standing

Figure 2. Microraptor standing. Here you have wings, a horizontal stabilizer on the tail and vertical stabilizers on the hind legs. With such small wings and inexperience as a pilot, you need all the control surfaces you can get!

“We suggest that a new and more compelling general model for the evolution of flight in paravians and early birds is emerging. Early in the evolution of theropod flight, major flight control functions were relatively evenly distributed between the forewings and the auxiliary control surfaces – namely, the hindwings and tail. This allowed the comparatively robust hindlimbs and tail of paravians to carry much of the mechanical loading associated with tight maneuvers, launching, and landing.  In more derived members of the avian line, most control function shifted to the forewings, though primary launch power continued to be provided by the hindlimbs. This model explains how animals such as Microraptor could fly in cluttered environments with small pectoral muscle fractions and gracile forelimbs.”

I did not see the presentation by Habib et al. 2012. Funny that the abstract title (see below) focuses on the tail, when the hind limb feathers are what everyone is chatting about. Their presentation made some news here at Findognews.blogspot.com. The opening paragraph states, “A rethink of four-winged dinosaurs suggests that the much-debated hind wings stayed tucked under the body until deployed in the air for tight turns to dodge branches or chase prey.” I suppose this was the gist of the talk.

ScientificAmerican.com included this statement by Habib, “A combination of pitch control by the tail, roll generation by the ‘hindwings’ and multi-purpose control by the main wings would have madeMicroraptor a highly maneuverable animal.” Seems more than reasonable.

The blogspot went on with history of the hind leg feathers, “The first reconstruction showed the small dinosaur gliding in the air with all four limbs extended outward. A later proposal lowered the hind-limb feathers for a Wright-Brothers biplane of wings. Both arrangements have drawn criticism. In a simpler solution, the dinosaur could have kept its hind limbs under its body much of the time until needed for banking in a turn.”

Early illustration of Microraptor sprawling like a flying lizard,

Figure 3. Early illustration of Microraptor sprawling like a flying lizard, not a flying dinosaur.

Yes, that first sprawling Microraptor illustration (Fig. 3) had everyone aching, as it essentially popped those dinosaurian right angle femora out of their sockets.

Kevin Padian commented about the abstract in the blogspot, “Powered flight and gliding downward have developed in quite different evolutionary branches.” Maneuverability is certainly important to both, but he does not see gliding as an evolutionary baby step on a path toward powered flight.”

Dr. Padian jumped on the gliding half of the hypothesis because he observed that the presentations focused on the effect of the hindlimb on a gliding animal. From the Scientific American blogspot, “He questioned why the team’s model would focus on gliding parameters when the forelimb shape was consistent with flapping, not gliding, and the hindlimb would have generated so much drag.” 

Not sure about hind feather drag. Cylinders create lots of drag. Bare legs are cylinders. Feathered legs turn those cylinders into tear drop shapes, which minimize drag while providing large surfaces that can be turned into the line of flight in order to increase drag, redirect the airstream and maneuver, the way airplanes do. That’s why wheels on airplanes are often given “pants.” That’s why vertical stabilizers are shaped like they are.

The coracoids of Microraptor were shaped and immobilized in the manner or birds and fenestrasaurs (including pterosaurs), which are ideal for for flapping. Maybe not great flapping, but you got start somewhere.

Longisquama in lateral view

Figure 4. Longisquama in lateral view, dorsal view and closeup of the skull. Like Microraptor, Longisquama glided/flew with similarly-sized wings both fore and aft, and here with a much longer torso, ideal for leaping. Note the stem-like coracoids, a sure sign of a flapper.

The distribution of flight control systems across all four limbs (and tail) find an interesting parallel in Longisquama (Fig. 4), a sister to the Pterosauria, in which the forelimb wings and hind wing uroptagia formed four wings. Here again, the forelimbs could have provided thrust while in the air. In the air the hind limbs could have acted like vertical stabilizers, or, when extended laterally, could have provided lift, but not flapping.

While the key reason for developing hind leg flight surfaces might have been for maneuverability, the most important moment in that maneuverability would have been a two-point landing following a positive pitch flare, bringing the airspeed down to zero while still maintaining control. I think Habib et al. (2012) are right on the money. There are analogous reptiles demonstrating the same sort of evolution (Longisquama) and it all makes sense in every way. If they didn’t talk enough about flapping, that’s a minor point.

And those extra feathers ain’t a bad secondary sexual character either.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

Habib M, Hall J, Hone DW and Chiappe LM 2012. Aerodynamics of the tail in Microraptor and the evolution of theropod flight control. Journal of Vertebrate Paleontology Abstracts, p. 105.