Another look at Yutyrannus

(Before It's News)

Figure 1. Comparing the skulls of Eutyrannus (center) to Allosaurus (above) and Tyrannosaurus (below). Which one appears to share more traits with Yutyrannus? See text for details. The pink portion of the nasal appears to be a lateral crest, as in Allosaurus.

So, the theropod community
is not happy with the large reptile tree nesting of Yutyrannus with Allosaurus (Figs. 1, 2) and the nesting of Microraptor with Compsognathus (see tomorrow).

I don’t blame them.
A larger matrix with more taxa and more characters specific to theropods (Cau et al. 2015) nests these provisional sisters elsewhere — Microraptor with Velociraptor and Yutyrannus with Tyrannosaurus. Shifting Microraptor next to Velociraptor in the large reptile tree adds 30 steps. Shifting Yutyrannus to T-rex adds 25.

The large theropods
under consideration (Fig. 1) all have a robust skull and share a common ancestor, a sister to Coelophysis in the Late Triassic. Each of the three candidates has prominent lacrimal horns (more prominent in A and Y), an elevated naris (larger in A and Y) and a deep angled jugal (PO process more gracile in A and Y). The nasals also produce lateral crests in A and Y, but crushed into the parasagittal plane in Y.

Note
I have replaced the old skull of Yutyrannus based on the original published drawing with a DGS tracing (Fig. 1) that appears to be more accurate as it replaces certain broken pieces to their invivo positions. The changes did not affect the earlier tree topology.

Yutyrannus/Allosaurus traits
Here following traits scored Yutyrannus with Allosaurus opposed to T-rex.

1. A and Y share a horizontal premaxilla ventral rim. In T it rises anteriorly.
2. A and Y share a vertical quadratojugal that interlocks with the squamosal. The quadratojugal of T is hourglass-shaped.
3. A and Y share a shallow angled posterior dentary. The posterior dentary of T is almost vertical.
4. A and Y share a ventral naris composed of equal parts premaxilla and nasal. In T the premaxilla extends the majority of the rim.
5. In A and Y the skull is less than half the length of the presacral column. In T the skull is not less than this length.
6. In A and Y the nasal is widest at mid length. Not so in T.
7. In A and Y the lacrimal was deeper than the maxilla. Not so in T.
8. In A and Y the frontals lack posterior processes. Not so in T.
9. In A and Y the coronoid process is absent. It is low in T.
10. In A and Y cervical centra are longer than tall. Not so in T.
11. In A and Y the cervicals do not decrease cranially. Not so in T.
12. In A and Y the sacrals are not fused to the ilia. Fused in T.
13. In A and Yh the second caudal transverse processes are not > centrum width. > in T.
14. In A and Y a mineralized sternum is absent. Present in T.
15. In A and Y mc2-3 align with m1.1 They do not align with that joint in T.
16. In A and Y the ilium anterior process is not > the acetabulum length. It is > in T.

Figure 2. Yutyrannus (middle) compared to Allosaurus (above) and Tyrannosaurus (below). Not to scale. Which one appears to share more traits with Yutyrannus?

Also note
the large three-fingered hand in Y (relatively larger than in A, the lack of a pinched metatarsal 2 in Y and a long narrow H-shaped palatine in A and Y, not in T.

Of course 
there is also a list of traits that link Allosaurus with T-rex to the exclusion of Yutyrannus. That’s par for any phylogenetic analysis.

References
Madsen JH Jr. 1993 [1976]. Allosaurus fragilis: A Revised Osteology. Utah Geological Survey Bulletin 109 (2nd ed.). Salt Lake City: Utah Geological Survey.
Marsh OC 1877. Notice of new dinosaurian reptiles from the Jurassic formation. American Journal of Science and Arts 14: 514–516.
Osborn HF 1905. Tyrannosaurus and other Cretaceous carnivorous dinosaurs. Bulletin of the AMNH (New York City: American Museum of Natural History) 21 (14): 259–265′
Xu X, Wang K, Zhang K, Ma Q, Xing L, Sullivan C, Hu D, Cheng S, Wang S et al. 2012. A gigantic feathered dinosaur from the Lower Cretaceous of China. Nature 484 (7392): 92–95. doi:10.1038/nature10906.  PDF here.

wiki/Yutyrannus
wiki/Allosaurus
wiki/Tyrannosaurus

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