Zhenyuanlong: Dromaeosaur? No. Tyrannosaur with wings? Yes.

Lü and Brusatte 2015
described a short-armed, winged Early Cretaceous Liaoning theropod, Zhenyuanlong suni (Fig. 1, JPM-0008 Jinzhou Paleontological Museum), as a dromaeosaur. Their published phylogenetic analysis included only dromaeosaurs but their text indicates a large inclusion set.

Figure 1. Zhenyuanlong in situ with colors applied to bones and feathers. These colors are transferred to create the reconstruction in figure 3.

Figure 1. Zhenyuanlong in situ with colors applied to bones and feathers. These colors are transferred to create the reconstruction in figure 3. The pelvic elements are reconstructed at right. The manus and pes are reconstructed at left.  Scale bars are 10cm.

From the Lü and Brusatte text
“We included Zhenyuanlong in the phylogenetic dataset of Han et al., based on the earlier analysis of Turner et al, which is one of the latest versions of the Theropod Working Group dataset. This analysis includes 116 taxa (two outgroups, 114 ingroup coelurosaurs) scored for 474 active phenotypic characters. Following Han et al., characters 6, 50, and 52 in the full dataset were excluded, 50 multistates were treated as ordered, and Unenlagia was included as a single genus-level OTU. The analysis was conducted in TNT v1.142 with Allosaurus as the outgroup.”

I reconstructed this theropod,
from published photographs (Figs. 1, 2) using (DGS digital graphic segregation), added it to the large reptile tree and found that it nested between tiny Compsognathus and gigantic Tyrannosaurus rex. Of course, Zhenyuanlong had the opportunity to nest with several dromaeosaurs, but it did not do so.

Figure 2. Skull of Zhenyuanlong in situ, as originally traced, colorized with skull, palate and mandible segregated.

Figure 2. Skull of Zhenyuanlong in situ, as originally traced, colorized with skull, palate and mandible segregated. Original quadrate may be a quadratojugal.

When you look at the reconstruction,
(Fig. 3) the similarity to T. rex becomes immediately apparent… except for those long feathered wings, of course.

I’ll run through several of the traits that link
Zhenyuanlong to Tyrannosaurus to the exclusion of dromaeosaurs here. It’s a pretty long list. Even so, if you see any traits that should not be listed, let me know and why.

  1. skull not < cervical series length
  2. skull not < half the presacral length
  3. premaxilla oriented up
  4. lacrimal not deeper than maxilla
  5. naris dorsolateral
  6. naris at snout tip, not displaced dorsally
  7. orbit length < postorbital skull
  8. orbit not > antorbital fenestra
  9. orbit no > lateral temporal fenestra
  10. orbit taller than wide
  11. frontal with posterior processes
  12. posterior parietal inverted ‘B’ shape
  13. jugal posterior process not < anterior
  14. parietal strongly constricted
  15. quadratojugal right angle
  16. majority of quadrate covered by qj and sq
  17. postorbital extends to minimum parietal rim
  18. maxillary teeth at least 2x longer than wide
  19. mandible tip rises
  20. angular not a third of mandible depth
  21. retroarticular process expands dorsally and ventrally
  22. cervicals taller than long
  23. cervicals decrease cranially
  24. mid cervical length < mid dorsal
  25. caudal transverse processes present beyond the 8th caudal
  26. humerus/femur ratio < 0.55
  27. metacarpals 2 & 3 do not align with manual one joints
  28. pubis angles ventrally – not posteriorly
  29. 4th trochanter of femur sharp
  30. metatarsals 2 & 3 align with p1.1
Figure 3. Zhenyuanlong reconstructed in lateral view. Something behind the pelvis could be the remains of an egg, but needs further study. Both sets of wing feathers are superimposed here. Click to enlarge.

Figure 3. Zhenyuanlong reconstructed in lateral view. Something behind the pelvis could be the remains of an egg, but needs further study. Both sets of wing feathers are superimposed here. Click to enlarge. Note the pubis is not oriented posteriorly. Note the longer legs of Zhenyuanlong compared to tested dromaeosaurs.

Shifting
Zhenyuanlong to the dromaeosaurs adds a minimum of 127 steps to the large reptile tree. There is one clade of theropods that nests between the current tyrannosaur and dromaeosaur clades.

Figure 3. Cladogram subset of the large reptile tree showing the strong nesting of Zhenyuanlong as the current sister to Tyrannosaurus. Obviously many more theropod taxa are missing here. They have not been tested yet.

Figure 4. Cladogram subset of the large reptile tree showing the strong nesting of Zhenyuanlong as the current sister to Tyrannosaurus. Obviously many more theropod taxa are missing here. They have not been tested yet.

Note
I have not tested as many theropods as there are in several theropod cladograms.

The possible faults with the Lü and Brusatte study were

  1. a lack of reconstructions to work with, rather than just a score sheet that others had created and they trusted. Reconstructions test identifications by making sure the puzzle pieces actually fit, both morphologically and cladisitically.
  2. I think they were fooled by the apparent posterior orientation of the pubis in situ when in vivo it was not oriented posteriorly
  3. I’m guessing that the traits they used could be used on in situ fossils without making reconstructions. The traits I use require reconstructions.

With this nesting
the origin of long pennaceous wing feathers is evidently more primitive than earlier considered, developed twice. And perhaps this is why T. rex had such tiny arms. They were former wings, not grasping appendages.

References
Lü J and Brusatte SL 2015. A large, short-armed, winged dromaeosaurid (Dinosauria: Theropoda) from the Early Cretaceous of China and its implications for feather evolution. Scientific Reports 5, 11775; doi: 10.1038/srep11775.

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