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re: kellner's ankle abstract



Tim recently brought up this abstract as an example of recent papers
promoting an archosaurian/ornithodiran origin for pterosaurs. My
comments are peppered throughout (sorry,  I should have done this
earlier when it was fresh).


Kellner, A.W. (2004). The ankle structure of two pterodactyloid
pterosaurs from the Santana Formation (Lower Cretaceous), Brazil.
Bulletin AMNH 285: 25-35.

>ABSTRACT: The extremely well-preserved tarsus of the tapejarid
_Tapejara_ sp. and the anhanguerid _Anhanguera piscator_ (Pterosauria,
Pterodactyloidea) are described and regarded as representative of the
ankle structure of Pterosauria. The pterosaur ankle joint (PAJ) shows
the following features: astragalus mediolaterally elongated forming a
hemicylinder;

DP:  Not really very elongated in basal pterosaurs like Peteinosaurus.
Elongation would then be a derived character within the Pterosauria.

>proximal part of the astragalocalcaneal contact characterized by a
ridge bordered on each side by a depression on the astragalus that has a
perfect counterpart in the calcaneum, and distal part that is
concavo-convex, with the concavity present in the astragalus;

DP: No such ridge in Silesaurus, Herrarasaurus or Marasuchus, all basal
"ornithodires." Here the contact lies in a valley. In Lagerpeton there
seems to be a ridge, part of a astragalar ascending process, but
pterosaurs don?t have this. So there?s a problem. And maybe Lagerpeton
is not an ornithodire (not with those metatarsals and toes!)

>calcaneum extremely reduced not reaching the posterior portion of the
tarsus;

DP: Well, first of all, I thought the calcaneum was (part of) the
tarsus. Putting that aside, if the calcaneum doesn?t reach the posterior
of the astragalus, then this may be true of Cretaceous taxa. (Haven?t
seen the specimen). But it is not true of basal pterosaurs. Regardless,
also not true of Silesaurus, Herrarasaurus or Marasuchus, all basal
"ornithodires". Here the calcaneum is typically as deep as the
astragalus.

>absence of an astragalar posterior groove,

DP: a posterior groove has never been seen on any protorosaur

>[absence of a] perforating foramen,

DP: disappears following Macrocnemus.

>[absence of a] calcaneal tuber,

DP: protorosaurs don?t have this.

>[absence of] an astragalar ascending process;

DP: protorosaurs don?t have this

>proximal tarsals fusing very early in ontogeny, forming a tibiotarsus.

DP: Many basal pterosaurs don?t share this. Kellner?s specimens are
relatively big too. Big pterosaurs fuse stuff more often.

>The main movement between the crus and foot in the PAJ occurs between
the proximal and distal tarsals as in the advanced mesotarsal-reversed
joint (AM-R).

DP: As in Cosesaurus, Langobardisaurus and more derived taxa.

>The main differences from the latter are the lack of an ascending
process and the extreme reduction of the calcaneum that make the PAJ
unique.

DP: Not unique. Lots of protorosaurs have this. And it appears that a
number of bipedal crocs do too.

>The absence of an astragalar groove and the reduction of the calcaneum
reinforce the hypothesis that pterosaurs are basal ornithodirans and
closely related to the Dinosauromorpha.

DP: If you assume an Archosaurian ancestry, which is not the case...

>As has been demonstrated by this and other studies, the ankle structure
(a complex of characters) is phylogenetically informative and, in light
of characters from other parts of the animal's body, can contribute to a
better understanding of archosaur relationships.

DP: Once again, Kellner knew of the protorosaur paper. He refereed it.
Puzzling why he chose to put on blinders here. Like others, apparently
Kellner is clinging to what he?s been taught and what he teaches to
others. Still, this is only one mistake. Kellner?s body of work has many
stars. Mistakes are allowed. BTW: Anytime someone has reason to believe
that pterosaurs are archosaurs, send me the evidence. If it?s valid,
I?ll hand carry a six-pack of your favorite beverage to you anywhere in
the world.

David Peters
St. Louis