Hexinlusaurus – A Small Heterodontosaur

This is a revision of an earlier blog on the same taxon.

A Basal Ornithischian of Uncertain Affinities
Hexinlusaurus multidens ZDM T6001 (He and Cai 1983, Barrett, Butler and Knoll 2005) middle Jurassic, was originally considered a basal ornithischian of uncertain affinities. Unfortunately the predentary area (anterior mandible) was not preserved, but the pelvis was standard for ornithischians with a completely retroverted pubis. A palpebral bone (“eyebrow” bone) was also present, as in other ornithischians.

Nesting in the Large Reptile Study
This blog originally found Hexinlusaurus to be  nested between the Sauropodomorpha and the Ornithischia, apparently linking these two clades of the Phytodinosauria. However, I noted then that with that pelvis morphology, Hexinlusaurus was 100% ornithischian.

Here, with further study, Hexinlusaurus nests with Heterodontosaurus (Fig. 1). The missing anterior likely included some fangs. The Middle Jurassic age of Hexinlusaurus compares to the Early Jurassic age of Heterodontosaurus.

Hexinlusaurus compared to its closest relative, Heterodontosaurus.

Hexinlusaurus compared to its closest relative, Heterodontosaurus. Is the size related to ontogeny or phylogeny? I don’t know.

A Single Autapomorphy
Barrett, Butler and Knoll (2005) described Hexinlusaurus with a single autapomorphy, a laterally concave postorbital. It appears that Heterodontosaurus has a similar postorbital depression.

Generally I Avoid the Dinosauria
There are very few dinosaurs in the present study, only basal taxa. The family tree of the Dinosauria is relatively uncontroversial and is better covered in detail elsewhere (and references therein).

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Barrett PM, Butler RJ and Knoll F 2005. Small-bodied ornithischian dinosaurs from the Middle Jurassic of Sichuan, China. Journal of Vertebrate Paleontology 25:823-834.
He X-L and Cai K-J 1983.
A new species of Yandusaurus (hypsilophodont dinosaur) from the Middle Jurassic of Dashanpu, Zigong, Sichuan. Journal of Chengdu College of Geology, Supplement 1:5-14.

wiki/Hexinlusaurus

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