E & P of Pterosaurs - Notes 3

[david peters <davidrpeters@earthlink.net>]

More notes from a recent reading of Ecology and Paleobiology of Pterosaurs, 
special pub. no. 217 of the Geo. Soc.

Pterosaur Pectoral Myology - S.C. Bennett

DML member Chris Bennett presents the first reconstructions of the pectoral 
musculature of an early pterosaur [Campylognathoides] and a later one 
[Anhanguera] exhibiting a notarial articulation, but with a single unfused 
(=non-notarium) vertebra. Itâ??s good work. Chris argues that no bird-like 
humeral elevator originating from the coracoid -- nor any pulley-like 
arrangement -- is apparent, contradicting earlier hypotheses by Furbinger 
(1900) and Padian (1983), and he is convincing.

Chris also showed a dorsal view of a Pterodactylus antiquus pectoral region, 
but (to my mind) curiously did not bring the medioposterior ends of the 
scapulae closer to or in contact with the dorsal vertebrae. Prior to becoming 
â??notarium-izedâ?? the scapulae in precursors would have to approach and 
contact the spine, and this seems to have occurred as primitively as Sordes, if 
not earlier.

Chris noted that in P. antiquus the scapulae extended as far as the 7-8th 
dorsal, but that may be due to an error in placement of the coracoid. Angle the 
coracoid anteriorly and the scapula will come with it for a proper posterior 
termination as occurs on all other pterodactylids. If that doesnâ??t quite fit, 
then lateral rotation might help.

Chris argues that an advanced pectoral girdle improbably evolved more than 
once, due to its complexity, but the cladogram Iâ??m working on sez otherwise. 
Weâ??ll see as we trace the inbetween steps. Other short scaps can be found in 
P. micronyx (no. 6) and another â??Pterodactylusâ?? (No. 13) leading towards 
the sharp-nosed pterodacs; in Scaphognathids leading toward Cycnorhamphus and 
the ornithocheirids; and finally in microazhdarchids (i.e. SMNS 2428 and AMNH 
1715) leading from dorygnathids to azhdarchids. Thatâ??s three times. And 
almost a fouth considering the similar situation of a proto-notarium and short  
scaps in Diopecephalaus longicollum, a sister taxon to P. antiquus.

Very few muscle imprints are preserved in fossils, but in some pterodactylids 
the trapezius and deltoids appear to make their presence known. The trapezius 
impressions appear to extend to the lateralmost scapula, or about twice the 
distance shown by Bennett, who followed muscle scars exclusively.  

Maybe the next paper on this subject will take on muscle changes due to warping 
of the deltopectoral crest and to any rearrangements and their consequences in 
bottom-decker pteros -- which I now understand and accept!

David Peters
St. Louis