Emausaurus added to the large reptile tree

Emausaurus (Haubold 1990, early Jurassic), the primitive thyreophoran ornithischian dinosaur (Fig. 1), was recently added to the taxon list and it nested with Scelidosaurus at the base of the Ornithischia without upsetting the rest of the large reptile family tree.

Figure 1. Emausaurus skull. This taxon nests with the armored basal ornithischian Scelidosaurus.

Figure 1. Emausaurus skull. This taxon nests with the armored basal ornithischian Scelidosaurus.

Emausaurus is interesting because the palpebral bones, common to all ornithischians, virtually contacted the postorbital/postfrontal creating a roof over the eyeball, leaving a virtual fenestra in the posterior remainder of the orbit. Later taxa incorporate the palpebral(s) into the skull itself.

Since Emausaurus nests with Scelidosaurus in the large reptile tree, it is difficult to say at this point which is the more primitive of the two. Additional taxa will be needed for that. It is interesting to note the longest teeth in the dentary of Emausaurus are the anterior ones, where fangs once appeared in the phylogenetic ancestor, Daemonosaurus.

The Archosauria as of today with several new taxa added since last posted.

Figure 2. The Archosauria as of today with several new taxa added since last posted. The addition of Emausaurus does not change the topology of the large reptile family tree. 

The Genasauria
Traditionally the most primitive ornithischians are Pisanosaurus and Heterodontosaurus. Both are considered sisters to all other ornithischians, collectively known as the Genasauria, a clade that traditionally splits into Thyreophora (Lesothosaurus and armored dinos) and Neornithischia (Stormbergia, Agilisaurus, Hexinlusaurus and Cerapoda (duckbills, ceratopsians and pachycelphalosaurs).

No outgroup is known yet for the Ornithischia in traditional trees.

The large reptile tree does not dive deeply into the Dinosauria, but basal forms divide into different divisions with a base on a sister to Daemonosaurus. Unfortunately, this taxon is omitted or ignored in all prior ornithischian studies. In the large reptile tree, the armored dinosaurs (Scelidosaurus and Emausaurus) split off first. Pisanosaurus is a poposaur, so is not as directly related to ornithischians as traditional paleontologists suppose.

I hope other workers will add the taxa listed above to their trees to see if this experiment can be duplicated. M. Mortimer did something similar, but oddly the theropods nested as derived rather than basal in that tree, basically upside-down from the present topology.

Similarly, Lesothosaurus, which is basal in several other trees, nests as derived in this tree, all due to the influence of new outgroups.

References
Haubold H 1990. Ein neuer Dinosaurier (Ornithischia, Thyreophora) aus dem Unteren Jura des nördlichen Mitteleuropa. Revue de Paleobiologie 9(1):149-177. [In German]

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.