re: pterosaur/bat wing membranes

[David Peters <davidrpeters@earthlink.net>]

2¢ worth ~

Just read two days of arguments on the above header. Someone wondered  
if we could get to the bottom of this. Let's try these for starters:

1. Colugos and bats make great models for gliders and flappers  
respectively. Colugos have small hands and wide proximal membranes.  
Colugo hands provide no thrust and so colugos are relegated to  
gliding. Bats have big hands and they provide thrust. Thus flapping  
actually moves huge quantities of air and bats can land higher than  
their takeoff spot. Lesson learned: you need large distal membranes  
to provide thrust. Otherwise you glide. Pterosaurs had large distal  
membranes that developed from hypertrophy of the (already long in  
basal lepidosauria) fourth finger. Thus pterosaurs were flappers from  
the start. Of course a flapper can become a soarer over time, but  
diametrically opposed aspect ratios should indicate that it's a  
different ball game than gliding colugo-style.

1b. Peters 2002 (Hist. Bio. 15: 277) showed that no pterosaur, even  
Sordes, has a proximally broad wing membrane. Misinterpretation of  
matrix cracks that extend beyond the fingers is the cause of the  
confusion. Lots of membranes show a mid-thigh attachment, fuselage  
fillet style, as Jim mentioned earlier. Many mentioned and shown in  
the paper. Also on pterosaurinfo.com.

1c. Recent pictures of bat embryos (ref. doesn't come to mind at  
present, but every bat textbook has them) shows that big hands with  
widespread metacarpals with no cell death between the fingers appear  
very early in bat development. However, by the time bats are born the  
hands have slowed down to let the the wings and proximal membranes  
catch up, then while nursing the hands assume adult proportions.  
Nature provides as necessary, but it does seem to indicate that the  
unknown ancestors of bats could have had big hands with widespread  
metacarpals. Haven't found big hands yet, but we have found  
widespread metacarpals, a prerequisite, in nonvolant sister taxa.

2. re: Darren's stork-like hypothesis versus prior hypotheses in  
Quetzalcoatlus. I've said this before, it's very likely that both the  
mud-prober hypothesis (based on site fauna) and the stork-like  
hypothesis (based on morphology) are correct. The illustration that  
Darren shows in his blog-site is also correct, except that on  
weekends Q. was uniquely capable of going where no pterosaur before  
was capable: to the deeper parts of the pond. And you can see this  
phylogenetically with ever increasing size, following an initial bump  
in relative neck length, metacarpal length and distal wing shrinkage  
in smaller Q-ish sisters. Poling (hand only) pterosaur ichnites of  
smaller genera show that at least some pterosaurs were doing this.  
Phylogeny also supports this hypothesis in that Quetzalcoatlus, was  
descended from Dorygnathus, which, with its relatively short wingspan  
and a wide-mouth raking dentition, appears to have been a sand/mud- 
sifter, perhaps seeking crustaceans. Q. sp. has a rostrum that is  
wider than tall, resembling the end of a yard stick. Yes it is  
crushed, but it is crushed dorso-ventrally, which is a highly  
unlikely crushing angle for a laterally compressed rostrum.  And that  
transversely straight tip is really the end of the rostrum. There is  
not pointed tip broken off beyond it. Aerodynamics aside, in any  
poling pterosaur, if that wing, perhaps entirely underwater, is not  
stashed away (as in the narrow wing model), it will billow like a  
pelican's throat, which isn't good. And everyone knows that pushing a  
yardstick width-wise through water, as if it was attached to a  
skimmer) is not the most efficient way to 'knife' through the water.  
But it does make a good mud probe.

2a. It must also be remembered that Quetzalcoatlus is not related to  
Azhdarcho, which has similar cervical construction (as does  
Tanystropheus for that matter). Azhdarcho is related to Bakonydraco  
at the base of Pteranodon + Nyctosaurus and not far from tapejarids.  
Like its bretheren, Azhdarcho has a laterally compressed rostral tip.  
Essentially it's a long-necked germanodactylid, as are the others. It  
is very likely (especially considering that list of sister taxa) that  
the Azhdarcho-style azhdarchids were indeed skimming the waters.  See  
pterosaurinfo.com for a family tree and more discussion. So, everyone  
is right, but we just have to be more specific and not assume monophyly.

3. PAL 3830, which Darren mentioned, is a great specimen showing  
legs, arms and some membranes – and nothing else. Cladistic analysis  
places it within the Germanodactylids close to the aforementioned  
Azhdarcho and Bakonydraco. Unfortunately for Darren's model,  
actinofibrils are seen around the ankle of PAL 3830. That should not  
be, according to the Zittel wing, the Vienna specimen, Jeholopterus  
and other more complete specimens. And why would fibers be there? It  
doesn't make sense. That should be the stretchy part, according to  
the dc (deep chord) model. A better explanation: Wing membrane torn  
from its mooring and/or a wing tip just under the ankle with membrane  
at the surface of the matrix seems to be the situation here. an  
unfortunate jumbling of body parts and an erroneous conclusion. Again  
pterosaur info.com has pictures.

David Peters
St. Louis