Majungasaurus: four stubby fingers and a unicorn-like bump on its head

The latest theropod cladogram
by Cau et al. (2015) nested the Late Cretaceous abelisaur giant, Majungasaurus (Krause et al. 2009) with the small toothless Limusaurus and the toothy Masiakasaurus (not yet tested). By contrast the large reptile tree (subset Fig. 1, 625 taxa) nested Limusaurus with the oviraptor Khaan and nested Majungasaurus with Yutyrannus and Allosaurus.  Let’s see why…

Figure 1. Subset of the large reptile tree, the Theropoda. As more taxa are added, resolution increases. Here Limusaurus nests with Khaan. Majungasaurus nests with Eutyrannus, both distinct from Cau et al. 2015.

Figure 1. Subset of the large reptile tree, the Theropoda. As more taxa are added, resolution increases. Here Limusaurus nests with Khaan. Majungasaurus nests with Eutyrannus, both distinct from Cau et al. 2015.

I wonder if 
Limusaurus nested with Majungasaurus in the Cau et al. 2015 study because both have four fingers. They both do have four fingers, but they are not the same four fingers, as explained here. Otherwise, the two theropods seem to share few traits in common, including their great divergence in size (Fig. 2). If anyone has a high rez image of the Yutyrannus manus in situ, I’m wondering if we’ll find a metatarsal 4 there? Allosaurus doesn’t have one.

Figure 2. Yutyrannus compared to Majungasaurus and Limusaurus to scale. Note the frontal bump shared by Yutyrannus and Majungasaurus. This trait is not used in the large reptile tree. Distinctly different in many aspects, Yutyrannus and Majungasaurus nevertheless nest together with this taxon list. No doubt additional taxa will someday separate them. Limusaurus is distinctly different in most aspects, throwing doubt on that node of the Cau et al. 2015 study.

Figure 2. Yutyrannus compared to Majungasaurus and Limusaurus to scale. Note the frontal bump shared by Yutyrannus and Majungasaurus. This trait is not used in the large reptile tree. Distinctly different in many aspects, Yutyrannus and Majungasaurus nevertheless nest together with this taxon list. No doubt additional taxa will someday separate them. Limusaurus is distinctly different in most aspects, throwing doubt on that node of the Cau et al. 2015 study.

Limusaurus is not a good match
for the much larger Majungasaurus both at first glance and after analysis. Limusaurus is a better match for the oviraptorid, Khaan (Fig. 3). Even so, several transitional taxa are not shown or tested here.

Figure 3. Limusaurus and Khaan compared. Khan is a better match for Limusaurus than Cau et al. 2015 recovered.

Figure 3. Limusaurus and Khaan compared to scale. Khan is a better match for Limusaurus than Cau et al. 2015 recovered.

Theropod fans
like the Cau et all (2015) tree. They support it, too. The large reptile tree echoes the Cau et al cladogram overall, but has not recovered a similar topology at several nodes. The additional taxa add further weight to the nesting of Yutyrannus apart from Tyrannosaurus. Once again I’ll suggest that making in vivo reconstructions really helps avoid phylogenetic problems.

The little bump on the head
Majungasaurus has a little hollow bump on its frontals (Fig. 2), termed the cornual process. Since Majungasaurus nested so strongly with Yutyrannus the small hollow bump on the skull of Yutyrannus appears to be convergent. It’s a small untested trait, but I think it’s curious that among all the differences in these two taxa, that trait is shared.

And all of these taxa had feathers
or probably had feathers due to phylogenetic bracketing.

Birds, Proto Birds and Bird-like Microraptors
The way the cladogram (Fig. 1) is coming together, it appears that the posteriorly-directed pubis of birds is convergent, not homologous, with the same sort of pubis in Velociraptor, Moreover, the clade that includes Microraptor, despite its bird-like appearance and size, is not closely related to extant birds and their extinct kin. Even so, feathered legs on the pre-bird, Anchiornis, indicates that extradermal trait either had a wider range or a convergent appearance.

References
Balanoff AM and Norell MA 2012. Osteology of Khaan mckennai (Oviraptorosauria: Theropoda) Bulletin of the American Museum of Natural History 372:1-77.
Cau et al. 2015. The phylogenetic affinities of the bizarre Late Cretaceous Romanian theropod Balaur bondoc (Dinosauria, Maniraptora): dromaeosaurid or flightless bird? PeerJ 3:e1032; DOI 10.7717/peerj.1032
Krause DW, Sampson SD, Carrano MT, O’Connor, PM 2007.
 Overview of the history of discovery, taxonomy, phylogeny, and biogeography of Majungasaurus crenatissimus (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar. In Sampson SD & Krause DW (eds.). Majungasaurus crenatissimus (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar. Society of Vertebrate Paleontology Memoir 8. pp. 1–20.
Xu X, Clark JM. Mo J, Choiniere J, Forster CA, Erickson GM, Hone DWE, Sullivan C, Eberth DA, Nesbitt S, Zhao Q, Hernandez R, Jia C-K, Han F-L. and Guo Y 2009. A Jurassic ceratosaur from China helps clarify avian digital homologies. Nature, 459(18): 940–944.
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/Khaan
wiki/Majungasaurus
wiki/Limusaurus
wiki/Yutyrannus

 

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