Youngina, Youngoides and the Younginiformes

There are several skulls and fewer post-crania attributed to Youngina and Youngoides, originally by R. Broom (1914), but CE Gow (1975) and others (see below) also made contributions.

The big question is: are the skulls crushed into a variety of shapes? Or do the variety of shapes reflect important morphologies that separate the various specimens into various clades? If you have any Youngina/Youngoides skull photos, please send them!!

The other question is: do some specimens harbor an antorbital fenestra?

Here’s why I wonder:

Youngina BPI 375. Is this a nascent antorbital fenestra?

Figure 1. Youngina BPI 375. Is this a nascent antorbital fenestra?

And Here’s Another One:

Youngina AMNH 5561. Is this a nascent antorbital fenestra?

Figure 2. Youngina AMNH 5561. Is this a nascent antorbital fenestra?

At the Base of the Archosauriformes
These two Youngina specimens nest at the base of the Archosauriformes in the midst of several other younginiforms. Do those little skull breaks/indentations represent antorbital fenestra? Good question. The answer is, it really doesn’t matter in phylogenetic analysis because predecessors in the protorosauria do not have an antorbital fenestra and successors in the archosauriformes do. Not all Youngina had or have to have an antorbital fenestra. These things tend to come and go, especially when they first appear.

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
Broom R 1914. A new thecodont reptile. Proceedings of the Zoological Society of London, 1914:1072-1077.
Gardner NM, Holliday CM and O’Keefe FR 2010. The braincase of Youngina capensis(Reptilia, Diapsida): New insights from high-resolution CT scanning of the holotype. Paleonotologica Electronica 13(3):online PDF
Gow CE 1975. The morphology and relationships of Youngina capensis Broom and Prolacerta broomi Parrington. Palaeontologia Africana, 18:89-131.
Olsen EC 1936. Notes on the skull of Youngina capensis Broom. Journal of Geology, 44 (4): 523-533.
Reisz RR, Modesto SP and Scot DMT 2011. A new Early Permian reptile and its significance in early diapsid evolution. Proceedings of the Royal Society, London B
doi:10.1098/rspb.2011.0439

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