Diandongosuchus – another giant younginid

Earlier we looked at Diandongosuchus, which was originally considered a poposaurid (Li et al. 2012). The large reptile tree (now needs to be updated) nested Diandongosuchus at the base of the parasuchians and proterochampsids (including the biped, Lagerpeton). It’s easy to see the resemblance.

Today we’ll revise the skull of a tiny Youngina, BPI 2871, which is the basal taxon in this lineage (more primitive than Diandongosuchus). Seems the rostrum of the BPI specimen was probably crushed dorsoventrally, resulting in a false concave rostral profile. The posterior skull is missing, but it can be restored closer to Diandongosuchus now that the phylogenetic analysis shows the close relationship.

Figure 1. The large reptile tree nests these two taxa as sisters despite their size difference. With greater size came the development of an antorbital fenestra, independent of the one developing in other Younginids leading toward archosauriformes beginning with Proterosuchus.

Figure 1. The large reptile tree nests these two taxa as sisters despite their size difference. With greater size came the development of an antorbital fenestra, independent of the one developing in other Younginids leading toward archosauriformes beginning with Proterosuchus.

Evolution works in baby steps.
That’s why maximum parsimony (fewest morphological changes) is still the best route for finding ancestors and descendants and for filling in missing parts by the method of phylogenetic bracketing. Diandongosuchus also gives us clues as to the post-crania of the BPI 2871 specimen of Youngina, with reservations regarding the great size difference.

I’d like to see the BPI 2871 specimen, but the last I heard (several years ago) it was ‘on loan’ and had not been returned.

Some workers, Gow (1975), among them, consider the BPI 2871 specimen congeneric with other Youngina and Younginoides specimens, with all apparent changes in morphology due to crushing. While that is likely true to a certain extent, there are differences that can be scored in phylogenetic analysis to reveal their differences and relationships. And you can always take out the crushing to check out prior hypotheses.

Earlier we looked at Garjainia as another giant younginid.

References
Gow CE 1975. The morphology and relationships of Youngina capensis Broom andProlacerta broomi Parrington. Palaeontologia Africana, 18:89-131.
Li C, Wu X-C, Zhao L-J, Sato T and Wang LT 2012. A new archosaur (Diapsida, Archosauriformes) from the marine Triassic of China, Journal of Vertebrate Paleontology, 32:5, 1064-1081.

wiki/Diandongosuchus
wiki/Youngina

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