Re: The Phylogenetics of Nycotosaurs

["Chris Bennett" <cbennett@bridgeport.edu>]

----- Original Message -----
From: "Chris" <Chris_Collinson@monarch.net>
To: "dinosaur list" <dinosaur@usc.edu>
Sent: Friday, August 15, 2003 12:19 PM
Subject: The Phylogenetics of Nycotosaurs


> Chris Bennett wrote:
> >but of course nyctosaurs are not at all closely related to the clade
> >(Istiodactylus (Ornithocheiridae + Pteranodontidae)) despite what Dave
> >thinks.
>
> Ok, what would be the alterntive to the clade Ornithocheiroidea
> (Istiodactylus (Ornithocheiridae
> (Pteranodontidae+Nyctosaurus)))
>

Dave Unwin and I have rather different views on the relationships of the
large pterodactyloids.  First of all there is essentially semantic bickering
as to what the clade of large pterodactyloids sharing the warped
deltopectoral crest should be called.  I originally followed Padian and
referred to it as the Pteranodontidae, but more recently Kellner elevated it
to the Pteranodontoidea and I have accepted that change.  Unwin wishes to
refer to the clade as the Ornithocheiroidea, and the question of priority
has not been settled.

More significantly, we differ on our interpretations of the relationships of
the azhdarchids, tapejarids, dsungaripterids, and pteranodontoids to the
Jurassic taxa such as Pterodactylus, Germanodactylus, etc.  Some years ago,
I published a cladogram that suggested that the azhdarchids,
dsungaripterids, and pteranodontoids formed a clade Dsungaripteroidea
sharing the advanced pectoral girdle with the scapula articulating with a
notarium.  Kellner soundly criticized my cladogram, but for all that the
cladogram in his dissertation also supported a clade Dsungaripteroidea
sharing an advanced pectoral girdle.  Unwin's cladograms have not included
my pectoral girdle characters and suggest that various Jurassic taxa lacking
advanced pectoral girdles are more closely related to particular large
pterodactyloid clades than the large pterodactyloid clades are to each other
(e.g., Germanodactylus related to dsungaripterids, etc.), and according to
this view the advanced pectoral girdle would have been evolved convergently
in 2 or 3 different lineages.  I have argued that the advanced pectoral
girdle complex is too bizarre to have been arrived at convergently in 2
pterosaur clades even though it occurs in two forms (Dino Frey's high- and
low-deckers).  In the last few years, I have been busy with morphological
work and consequently cannot whip out a cladogram to counter Unwin's, so if
you think any cladogram is better than someone with a logical argument but
no cladogram, then you want to adopt Unwin's view.

As for Nyctosaurus, it has long been linked to Pteranodon because both have
slender edentulous jaws and come from the Niobrara--Miller even suggested
that Nyctosaurus (which he thought was crestless) was ancestral to the
crested Pteranodon and demoted it to a subgenus of Pteranodon.  In
Nyctosaurus the scapula does not articulate with the notarium, so if you try
to embed it next to Pteranodon deep within the "Ornithocheiroidea" as Unwin
did (viz:  "Istiodactylus (Ornithocheiridae
(Pteranodontidae+Nyctosaurus)))") you have to hypothesize that the advanced
pectoral girdle complex was devolved.  Maybe that is easy to do if you can
evolve it over and over again in multiple lineages.  Worse yet, the humerus
of Nyctosaurus does not exhibit the warped deltopectoral crest of the
"Ornithocheiroidea", but instead has an interesting modification of the
primitive pterodactyloid deltopectoral crest morphology, so that is another
character that has to be devolved.  Excuse me while I go listen to "Whip
It".

Chris


S. Christopher Bennett, Ph.D.
Assistant Professor of Basic Sciences
College of Chiropractic
University of Bridgeport
Bridgeport, CT  06601