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.

Flapping?
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.


References
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

wiki/Changyurapator

 

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