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Xiongguanlong: not a tyrannosauroid

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I hate to keep doing this…
I know it pisses off theropod-o-philes.

A few years ago
Li, et al. 2010 described a new theropod dinosaur, Xiongguanlong, as “a longirostrine tyrannosauroid from the Early Cretaceous of China” which they nested between Eotyrannus + Dilong and Tyrannosaurus + other Late Cretaceous tyrannosaurs.

Figure 1. Xiongguanlong does not nest with tyrannosaurs, but with other long rostrum theropods, including Denocheirus and Sinocalliopteryx.

the large reptile tree nests Xiongguanlong along with other longistrine theropods, like Deinocheirus (Fig. 2), Sinocalliopteryx and the spinosaurs. I have not yet encountered any valid longirostrine tyrannosauroids. Dilong and Guanlong also nest close to these long-rostrum theropods. They were removed from the tyrannosauroids earlier here and here. Eotyrannus was likewise removed from the tyranosauroids here, and nested with Tanycologreus close to the base of the dromaeosaur/troodontid + bird split.

Figure 2. Deinocheirus skull. This long rostrum theropod nests close to Xiongguanlong and shares many traits with it.

I keep hoping one of these taxa
are going to shift the tree topology back toward the traditional thinking, but each new taxon just drops into place, adding their leaf to the tree.

Figure 3. Theropod cladogram with the addition of Xiongguanlong nesting with Deinocheirus and Sinocalliopteryx, not tyrannosaurs.

Li et al. report
“Xiongguanlong marks the earliest phylogenetic and temporal appearance of several tyrannosaurid hallmarks such as a sharp parietal sagittal crest, a quadratojugal with a dramatically flaring dorsal process and a flexed caudal edge, premaxillary teeth bearing a median lingual ridge, and a flaring axial neural spine surmounted by distinct processes at its corners.”

“Remarkably, Xiongguanlong has dorsally smooth nasals. Unlike the conical tooth crowns of taxa such as Tyrannosaurus, Xiongguanlong has mediolaterally compressed tooth crowns. The cervical vertebrae display only a single pair of pneumatic foramina, and the dorsal centra are not pneumatic in contrast to Albertosaurus and more derived tyrannosaurids. Xiongguanlong is remarkable in having a shallow and narrow snout forming more than two thirds of skull length…most tyrannosaur ids have short deep snouts mechanically optimized for powerful biting.”

No blame here. 
Li et al could have extended their comparative search to Sinocalliopteryx, which was published in 2007, but the skull of Deinocheirus was not published until 2014, so they are not to blame for missing such possibilities. These things happen.

Li D, Norell MA, Gao K-Q, Smith ND and Makovicky PJ 2010. A longirostrine tyrannosauroid from the Early Cretaceous of China. Proceedings of the Royal Society B 277:183-190.


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