Stenopelix reconstructed and nested

Figure 1. Stenopelix in situ with several bones colorized then transferred to figure 2.

Figure 1. Stenopelix in situ with several bones colorized then transferred to figure 2. The ischia appear to be wide, as in birds, but that is due to crushing. In vivo they curved ventrally.

Stenopelix valdensis
(Meyer 1857; Early Cretaceous, Barremian, 125 mya; Germany; Fig. 1) is a small ornithischian dinosaur based on a single partial skeleton preserved in part and counterpart in dorsal view. Stenopelix has been difficult to classify for about 150 years because it lacks a skull. Various authors listed in Wikpedia have weighed in on the nesting of this enigma.

  1. Early pachycephalosaur (Maryanska and Osmólska 1974)
  2. Early ceratopian (Sues and Galton 1982)
  3. Pachycephalosauria (Sereno 2000)
  4. Marginocephalia (Butler and Sullivan 2009)
  5. Ceratopsia and a sister to Yinlong (Butler et al. 2011)
Figure 1. Stenopelix reconstructed in lateral and dorsal views to scale with Psittacosaurus. The curved ischium and short tail with short chevrons allies Stenopelix with ceratopsians.

Figure 2. Stenopelix reconstructed in lateral and dorsal views to scale with Psittacosaurus. The curved ischium and short tail with short chevrons allies Stenopelix with ceratopsians.

When Stenopelix was added
to the large reptile tree, it nested between (Yinlong + Psittacosaurus) and the ceratopsians. Note that the psittacosaurs have a long slender publs and straight ischium. Ceratopsians have a reduced pubis and dorsoposteriorly convex ischium, traits shared with Stenopelix. The tail is relatively short with small chevrons, as in ceratopsians. Otherwise this specimen is similar to several ornithischians.

Figure 3. The Phytodinosauria with the addition of Stenopelix basal to the Ceratopsidae.

Figure 3. The Phytodinosauria with the addition of Stenopelix basal to the Ceratopsidae.

The curved ischium and reduced pubis
of ankylosaurs and pachycephalosaurs are convergent with ceratopsian pelves. There is no indication of the ilium turning laterally in Stenopelix, as in ceratopsians. The pedal elements are long as in psittacosaurs. The tibia is shorter than the femur, as in ceratopsians.

A short note on turtle origins:
I wondered if taking out all the extinct turtles from the large reptile tree would change the topology. It did not.

The large reptile tree is now 9 taxa short of 700.
If you want me to add any of your favorites, from the Carboniferous to the present, please offer your suggestion.

References
Butler RJ and Sullivan RM 2009. The phylogenetic position of Stenopelix valdensis from the Lower Cretaceous of Germany and the early fossil record of Pachycephalosauria. Acta Palaeontologica Polonica 54(1):21-34.
Butler RJ, Jin L-Y, Chen J, Godefroit P 2011. The postcranial osteology and phylogenetic position of the small ornithischian dinosaur Changchunsaurus parvus from the Quantou Formation (Cretaceous: Aptian–Cenomanian) of Jilin Province, north-eastern China. Palaeontology 54 (3): 667–683. doi:10.1111/j.1475-4983.2011.01046.x.
Meyer H von 1857. Beiträge zur näheren Kenntis fossiler Reptilien. Neues Jahrbuch für Mineralogie, Geologie und Paläontologie 1857:532–543
Maryańska T and Osmólska H 1974. Pachycephalosauria, a new suborder of ornithischian dinosaurs. Palaeontologia Polonica 30:45-102.
Schmidt H 1969. Stenopelix valdensis H. v. Meyer, der kleine Dinosaurier des norddeutschen Wealden. Palaeontologische Zeitschrift 43(3/4):194-198.
Sereno PC 2000. The fossil record, systematics and evolution of pachy−
cephalosaurs and ceraptosians from Asia. In: M.J. Benton, M.A. Shiskin, D.M. Unwin, and E.N. Kurochkin (eds.), The Age of Dinosaurs in Russia and Mongolia, 480–516. Cambridge University Press, Cambridge.
Sues H-D and Galton PM 1982. The systematic position of Stenopelix valdensis Reptilia: Ornithischia) from the Wealden of north-western Germany. Palaeontographica Abteilung A 178(4-6): 183-190.

wiki/Stenopelix

 

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