Deinocheirus: not an ornithomimosaur

Following a long list of blog posts
that reported an inability here (Fig. 3), in the large reptile tree, to nest various theropods in their traditional nodes, today Deinocheirus (Fig. 1) nests not with ornithomimosaurs, like Struthiomimus, but at the base of the spinosaur clade. Here Deinocheirus nests between Sinocalliopteryx and Dilong + Guanlong, none of which have elongate dorsal spines and all of which have long teeth.

Figure 1. The skull of Deinocheirus. Note the new interpretation of the anteriorly flaring nasals. Note how the mandible does not completely close cranially when the anterior tips touch. I wonder if this was a sieving organ lined with baleen-like structures. That hypothesis goes with the very deep mandible and the equal lengths of both upper and lower jaws.

Figure 1. The skull of Deinocheirus. Note the new interpretation of the anteriorly flaring nasals. Note how the mandible does not completely close cranially when the anterior tips touch. I wonder if this was a sieving organ lined with baleen-like structures. That hypothesis goes with the very deep mandible and the equal lengths of both upper and lower jaws.

Previous studies
assumed that Deinocheirus was an ornithomimosaur, because it had very similar manus and forelimb proportions. When the skull was discovered, it was likewise toothless. The large reptile tree finds that those traits were convergent with ornithomimosaurs.

Figure 2. Deinocheirus specimens and a composite illustration.

Figure 2. Deinocheirus specimens and a composite illustration.

Deinocheirus mirificus (Osmólska & Roniewicz, 1970, Latest Cretaceous, 70 mya 11m) was originally and later considered a giant and basal ornithomimosaur. The large reptile tree (see below) nests Deinocheirus between Guanlong and Sinocalliopteryx in the spinosaur clade.

Figure 4. Sinocalliopteryx currently nests as a provisional sister to Deinocheirus, awaiting the discovery of transitional sister taxa.

Figure 4. Sinocalliopteryx currently nests as a provisional sister to Deinocheirus, awaiting the discovery of transitional sister taxa.

Like ornithomimosaurs, Deinocheirus was toothless and had long slender arms with a metacarpus of subequal metacarpals. Like spinosaurs, Deinocheirus had long dorsal neural spines. Like SinocalliopteryxDeinocheirus had an elongate rostrum, a tall orbit and nasals that flared laterally at the nares.

Figure 2. Here, in this subset of the large reptile tree, Ornitholestes nests at the base of the Microraptor clade, close to the base of the Tyrannosaurus clade.

Figure 2. Here, in this subset of the large reptile tree, Ornitholestes nests at the base of the Microraptor clade, close to the base of the Tyrannosaurus clade.

I’m sure theropod workers
can’t be happy that the detailed nestings of their cladograms are not verified here. Tradition may have misguided them, perhaps in this case. Using the matrices of prior workers without testing them for typos and scoring errors may be another problem.

Pure speculatiion
I wonder if the very elongate teeth of Sinocalliiopteryx somehow evolved into water straining structures in Deinocheirus. Only a transitional taxon with more, longer, thinner teeth or similar structures are ever found. It will also likely have a deeper mandible. Both taxa may have fed in water. A third taxon, Spinosaurus, is also considered a piscivore.

References
Ibrahim N et al. 2014. Semiaquatic adaptations in a giant predatory dinosaur. Science 345 (6204): 1613–6.
Ji S, Ji Q, Lu J and Yuan C 2007. A new giant compsognathid dinosaur with long filamentous integuments from Lower Cretaceous of Northeastern China. Acta Geologica Sinica, 81(1): 8-15.
Lee YN, Barsbold R, Currie PJ, Kobayashi Y, Lee HJ, Godefroit P, Escuillié F and Chinzorig T 2014. Resolving the long-standing enigmas of a giant ornithomimosaur Deinocheirus mirificus. Nature 515 (7526): 257–260.
Osmólska H and Roniewicz E 1970. Deinocheiridae, a new family of theropod dinosaurs. Palaeontologica Polonica. 21:5-19.
Sereno PC, et al. 1998. A long-snouted predatory dinosaur from Africa and the evolution of spinosaurids. Science 282 (5392): 1298–1302.

wiki/Sinocalliopteryx
wiki/Suchomimus
wiki/Deinocheirus

 

 

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