Inside Psittacosaurus

Figure 1. Psittacosaurus wood and wire model by yours truly, several years back.

Figure 1. Psittacosaurus wood and wire model by yours truly, several years back, now sitting on a kitchen shelf with other hand made and ITC plastic dino models.

Psittacosaurus is a bipedal/quadrupedal ceratopsid sister to Yinlong, recently added to the large reptile tree (now at 689 taxa). Scoring involved a good look at the skull. Note a recent interpretation (You et al. 2008) deletes the vomer, palatine and ectopterygoid (Fig. 2).

Figure 2. Psittacosaurus major skull from You et al. colorized here withe the addition of the vomer, palatine and ectopterygoid. The great height of the rostrum permits a great height to the internal nares and lingual side of the maxilla. Note, the postfrontals, that are fused to the postorbitals in many sister taxa, do not appear to be completely fused together here. 

Figure 2. Psittacosaurus major skull from You et al. colorized here withe the addition of the vomer, palatine and ectopterygoid. The great height of the rostrum permits a great height to the internal nares and lingual side of the maxilla. Note, the postfrontals, that are fused to the postorbitals in many sister taxa, do not appear to be completely fused together here.

The ceratopsian palate
rises, with essentially vertical maxillary walls lining the central choanae. This obviates the need for the vomers, palatine and ectopterygoid, which become incorporated with the maxilla. Evidently You et al. thought they were gone. I see vestiges here, at least on one side, and note them above.

The ceratopsian ancestral taxon
is currently Hexinlusaurus, a gracile, long-necked, small headed ornithischian close to Dryosaurus. Unfortunately, the premaxilla and naris are missing in the Hexinlusaurus holotype.

The post-crania of Hexinlusaurus reveals it to be a small-skull taxon with long running legs.

Figure 3. The post-crania of Hexinlusaurus reveals it to be a small-skull taxon with long running legs. Currently this taxon is the outgroup to the Ceratopsia, but no pachycephalosaurs are currently included. 

References
Osborn HF 1923. Two Lower Cretaceous dinosaurs from Mongolia. American Museum Novitates 95: 1–10.
Xu X, Forster CA, Clark J M and Mo J 2006. A basal ceratopsian with transitional features from the Late Jurassic of northwestern China. Proceedings of the Royal Society B: Biological Sciences. First Cite Early Online Publishing. online pdf
You H−L, Tanou K and Dodson P 2008. New data on cranial anatomy of the ceratopsian dinosaur Psittacosaurus major. Acta Palaeontologica Polonica 53 (2): 183–196.

wiki/Yinlong 

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3 thoughts on “Inside Psittacosaurus

  1. Again, just as with Yinlong, there is no postfrontal. Just an optical illusion caused cracks and complex bone shapes.

    • It’s not if it’s an illusion, you’re just adding noise. And you didn’t even trace the same representative area in Lateral view as Dorsal view.

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