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Re: Saltopus... a silesaurid?



David Marjanovic <david.marjanovic@gmx.at> wrote:

> So... just to make sure... the idea that *Lewisuchus* is actually a
> crurotarsan is history?

Simple answer: Yes.  Technical answer: It's complicated.

_Lewisuchus_ is recovered by all recent phylogenetic analyses as a
dinosauriform.  It is highly possible that it and _Pseudolagosuchus_
are one and the same - at the moment, sufficient overlapping material
is lacking that would establish this for sure.

However... Nesbitt's recent analysis (2011) showed that the
"crocodile-normal / crurotarsan" condition is actually primitive for
archosaurs, with his analysis placing phytosaurs outside the
Archosauria (sensu stricto).  In his words, the classic 'crocodile
normal ankle' is rendered plesiomorphic for Phytosauria + Archosauria
(= Crurotarsi).  So all archosaurs would be crurotarsans, including
those on both the crocodile- and bird-lines.

Crurotarsi was originally intended to include only those archosaurs on
the crocodile-line (as opposed to the bird-line), and all definitions
have pretty much stuck to this intent.  Nesbitt's definition of
Crurotarsi is "The least inclusive clade containing _Rutiodon
carolinensis_ and _Crocodylus niloticus_".  But having phytosaurs
(including _Rutiodon_) as stem-archosaurs complicates things.  This
means that Crurotarsi now includes all of Archosauria.  Interestingly,
Nesbitt avoids labeling the Phytosauria+Archosauria clade (Crurotarsi)
in his tree.

Applying Sereno and Arcucci's (1990) original definition of Crurotarsi
("Ornithosuchidae, Parasuchia, Aetosauria, Rauisuchia,
Crocodylomorpha, and all extinct descendants that are most closely
related to these taxa.") would probably see Crurotarsi disappear
altogether with Nesbitt's topology, because "all extinct descendents"
would appear to preclude birds from being included inside Crurotarsi.

See... told you it was complicated.   ;-)


> Are non-archosauromorphs included in the matrix?


Nope.  Would it have made a difference?



Cheers

Tim