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Re: where have all the ornithischians gone?/Cart before horse



David Peters wrote:

Yes. Marasuchus sister to Herrarasaurus within Saurischia.

> I'm curious not just about what's attracting _Silesaurus_ to _Pisanosaurus_, > but what's pulling _Silesaurus_ *away* from the basal dinosauromorphs.

Name a taxon that would be a better sister taxa. I'll plug it in.

As others have mentioned, perhaps the problem lies in an insufficient number of characters, rather than in the choice (or number) of taxa.


The rest of Lotosaurus, other than the tarsus. Remember, croc normal tarsus shows up three times: in basal Rauisuchids (with Euparkeria showing as a precursor), in Crocodiliformes (not basal bipedal crocs), and in lotosaurs.

If you're implying that the CN joint arose three separate times, I'm not sure I'm on board with this. Here's what Chris Brochu has to say:


"Most analyses agree that Parasuchia (phytosaurs), Aetosauria, and the various ?rauisuchian? lineages are close relatives of Crocodylomorpha (Gauthier, 1986; Benton and Clark, 1989; Sereno and Arcucci, 1990; Sereno, 1991a; Parrish, 1993; Juul, 1994; Gower and Wilkinson, 1996; Fig. 2 ). All of these animals (pseudosuchians) have a so-called ?crocodile-normal? ankle, with a rotary ankle joint in which the proximal tarsals (astragalus and calcaneum) move against each other with a peg-and-socket articulation. In these taxa, the peg is on the astragalus and the socket on the calcaneum. Whether the ?crocodile-reversed? archosaurs (ornithosuchids, where the peg is on the calcaneum and socket on the astragalus) are related to crocodylians (Sereno, 1991a; Parrish, 1993) or closer to dinosauromorphs with plesiomorphic mesotarsal articulations (Gauthier, 1986; Juul, 1994) is a matter of controversy, but the difference is one or two nodes. Cruickshank (1979), Sereno (1991a), Parrish (1986, 1993), Gower (1996), and Dyke (1998) provide valuable reviews of archosaur ankle morphology and phylogenetic relevance."

Reference

Brochu, C.A. (2001). PROGRESS AND FUTURE DIRECTIONS IN ARCHOSAUR PHYLOGENETICS. Journal of Paleontology 75: 1185?1201.

Cheers

Tim