Re: pteros have lift-off

[Augusto Haro <augustoharo@gmail.com>]

Sorry to David Peters by saying above that he said that swan wings at
take-off do not pass vertical. I tried to mean that he said they do
not, or barely do, pass horizontal at downstroke.

David Peters seems to be right to me in that bipedalism represents the
ancestral state for Pterosauria if they are ornithodirans (the
currently more favored hypothesis). Although not based on a through
study, here it goes why I think he is right in this. You have likely
bipedalism for Scleromochlus. In Lagerpeton, forelimbs are unknown.
Marasuchus is currently considered a biped (Sereno and Arcucci, 1994,
in JVP). For dinosaurs, the primitive state seems to be bipedalism, as
shown in basal members such as Herrerasaurus, Saturnalia, Eoraptor,
basal neotheropods, Thecodontosaurus, Heterodontosaurus and
Lesothosaurus. Quadrupedalism seems likely in Silesaurus. Accepting
the tree of Brusatte et al. (2008, Science), you have to admit in the
hypothesis that pterosaur's ancestor was a quadruped that bipedalism
independently appeared in Scleromochlus, Marasuchus, and dinosaurs (3
steps, alternatively you can change the last two changes by
considering Dinosauriformes -less surely Dinosauromorpha- originally
biped and then Silesaurus reverting). In the hypothesis that
pterosaurs have biped ancestry, and are biped themselves, you need
only two steps: bipedalism in Ornithodira, reacquisition of
quadrupedalism in Silesaurus. If Silesaurus ends up being an
ornithischian, as suggested by Ferigolo and Langer (2007, Historical
Biology), I think somewhat similar would be the case.

However, I am not saying all these I call bipedal are obligate bipeds,
some have relatively long (Heterodontosaurus) or robust (Saturnalia)
forelimbs, so reconstructing obligate bipedalism seems a more
difficult task. I think that the basal state of pterosaurs seems to be
bipedalism if they are ornithodirans, and so more parsimonious to
consider them bipeds, but I do not consider the saving of this step
enough to prove bipedalism. Mechanical reasons, such as hindlimb
feebleness, big heads, long forelimb together with not complete
folding of the wing, and thin tails, seem to superate in number this
step-saving argument. To me, Silesaurus seems quadruped because it has
relatively long forelimbs (however, they are too gracile, reminding
hadrosaurs or Iguanodon, so perhaps it was not an obligate quadruped).
By this reason, one can say that quadrupedalism should be even more
suggestive in pterosaurs because of the much longer and stouter
forelimbs.

Cheers

Augusto.