Masiakasaurus: a large compsognathid, not a ceratosaur/abelisaur

This new taxon examination began with
a recent paper by Delcourt 2018 on ceratosaur palaeobiology that included Masiakasaurus (famous for its strong procumbent dentition, Fig. 1). When I looked at the restored skull in Delcourt 2018, figure 2, alongside other abelisaur/ceratosaur skulls, I was struck by the thought, first voiced by Ernie on Sesame Street, “One of these things is not like the other.” Other funny examples are here.

Figure 1. Masiakasaurus drawings from Carrano, Loewen and Sertic 2011) with photos from same.

Figure 1. Masiakasaurus drawings from Carrano, Loewen and Sertic 2011) with photos from same.

Delcourt 2018 reported,
“Ceratosaur theropods ruled the Southern Hemisphere until the end of the Late Cretaceous. However, their origin was earlier, during the Early Jurassic, a fact which allowed the group to reach great morphological diversity.” Perhaps there is just a little too much diversity in Delcourt’s taxon list. See below.

Masiakasaurus knopfleri (Sampson, Carrano and Forster 2001; Carrano, Loewen and Sertic 2011) was originally considered a ‘bizarre predatory dinosaur’ related to abelisaurids like Majungasarus. Here, in the large reptile tree (LRT, 1240 taxa) Masiakasaurus is related to Tianyuraptor, which also has procumbent teeth and a long torso. Essentially Masiakasaurus is a larger compsognathid leading to giant tyrannosaurs, not far from larger ornithomimosaurs (Fig. 4).

Figure 2. Tianyuraptor skull in situ and reconstructed.

Figure 2. Tianyuraptor skull in situ and reconstructed.

Other taxa with a descending anterior dentary with teeth
include Tianyuraptor (Fig. 2) and the large Compsognathus (CNJ79, Fig. 3) both of which share a long list of traits with Masiakasaurus. All of these taxa have really long cervical ribs.

Figure 1. The large (from Peyer 2006) and small Compsognathus specimens to scale. Several different traits nest these next to one another, but at the bases of two sister clades. Note the differences in the forelimb and skull reconstructions here. There may be an external mandibular fenestra. Hard to tell with the medial view and shifting bones.

Figure 3. The large (from Peyer 2006) and small Compsognathus specimens to scale. Several different traits nest these next to one another, but at the bases of two sister clades. Note the differences in the forelimb and skull reconstructions here. There may be an external mandibular fenestra. Hard to tell with the medial view and shifting bones.

Figure 4. Subset to the LRT focusing on Masiakasaurus and kin.

Figure 4. Subset to the LRT focusing on Masiakasaurus and kin.

Taxon exclusion plagues the Delcourt paper. Neither Tianyuraptor nor Compsognathus are mentioned in the text. Nor could I find the taxon Masiakasaurus mentioned with these two.

Inappropriate taxon inclusion. Like Tianyuraptor, Limusaurus also should not have been included as a ceratosaur. The LRT nests Limusaurus with oviraptorids.

When Masiakasaurus was first described
by Sampson et al. 2001, the authors reported, “[Masiakasaurus] is unique in being the only known theropod with a highly procumbent and distinctly heterodont lower dentition. Such a derived dental morphology is otherwise unknown among dinosaurs.” Actually, and this was easy to overlook, the large Compsognathus (Fig. 3) was known since Bidar et al., 1972, but it is more conservative in this feature. Tianyuraptor was reported several years later, in 2010 and the anterior dentary is broken and flipped in situ (Fig. 2). Fukuivenator is known from bits and pieces.

Addendum from Mickey Mortimer:
“Etrigansauria [from the Delcourt paper] is just a junior synonym of Neoceratosauria, which is basically ignored by Delcourt.  The phylogenetic taxonomy in this paper is horrible, ignoring Phylocode Article 11.7, ignoring earlier and better definitions than those of Wilson et al. (2003), redefining Ceratosauroidea as if it were Abelisauroidea, proposing definitions that only work in the topology being used, and citing incorrect definitions for Elaphrosaurinae, Noasaurinae and Furileusauria.  More details on my blog-“

http://theropoddatabase.blogspot.com/2018/06/etrigansauria-unnecessary-demon.html

References
Bidar AL, Demay L and Thomel G 1972b. Compsognathus corallestris,
une nouvelle espèce de dinosaurien théropode du Portlandien de Canjuers (Sud-Est de la France). Annales du Muséum d’Histoire Naturelle de Nice 1:9-40.
Carrano MT, Loewen MA and Sertic JJW 2011. 
New materials of Masiakasaurus knopfleriSampson, Carrano, and Forster, 2001, and implications for the morphology of the Noasauridae (Theropoda: Ceratosauria). Smithsonian Contributions to Paleobiology. 95: 53pp.
Delcourt R 2018. Ceratosaur palaeobiology: new insights on evolution and ecology of the southern rulers. Nature.com/scientificreports 8:9730 | DOI:10.1038/s41598-018-28154-x
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.
Sampson SD, Carrano MT and Forster CA 2001. A bizarre predatory dinosaur from the Late Cretaceous of Madagascar. Nature. 409 (6819):504–506. doi:10.1038/35054046.
|Zheng X-T; Xu X; You H-L; Zhao, Qi; Dong Z 2010. A short-armed dromaeosaurid from the Jehol Group of China with implications for early dromaeosaurid evolution. Proceedings of the Royal Society B 277 (1679): 211–217.

wiki/Tianyuraptor
wiki/Masiakasaurus
wiki/Fukuivenator

 

5 thoughts on “Masiakasaurus: a large compsognathid, not a ceratosaur/abelisaur

  1. Delcourt’s tree is based on the phylogenetic analysis of Wang et al. (2016; the Limusaurus juvenile teeth paper), which did include Compsognathus and several tyrannosauroids and dromaeosaurids. So it’s not taxon exclusion, it’s your tiny character list and misinterpretation of theropod anatomy (among numerous issues, what you show as a light blue left dentary in Tianyuraptor is actually the left maxillal the anterior dentary and its teeth are hidden so we don’t know if they were procumbant). Masiakasaurus and Limusaurus emerged as ceratosaurs in my analysis using 700 maniraptoromorph characters, not even with the help of ceratosaur characters.

  2. Masiakasaurus is with Elaphrosaurus, Noasaurus and Velocisaurus, while Limusaurus is with Deltadromeus and Gualicho. But it’s not a great tree, since I don’t include characters suggested to resolve ceratosaurs, just like you don’t. And no, Tianyuraptor has a ton of characters shared with other dromaeosaurids lacking in Masiakasaurus- elongate distal caudal prezygapophyses, short and triangular postacetabular process, anteroposteriorly long pubic peduncle of ilium, short ischium with tapered distal end and prominent triangular obturator process, etc.. Just like Masiakasaurus has a ton of characters shared with other ceratosaurs, which you don’t include.

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