[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Pterosaur pectoral girdle (stupefyingly long)

Regarding the advanced pectoral girdle of pterosaurs.

In response to my earlier comments on the notarium/advanced pectoral girdle 
Bennett sent the following: 

'I'll gladly take your bottle of champagne, however, we may be talking apples 
oranges here.  I have been aware of this for quite some time, but have not 
the time to clarify the situation.  You are talking about the notarium while I 
was talking about the advanced pectoral girdle.  To me a notarium is simply a 
series of coossified anterior dorsal vertebrae, and it is certainly conceivable 
that such a structure could have been evolved convergently in various lineages 
pterosaurs, just as notaria have been eveolved in various birds, and the fossil 
record of small pterosaurs may not be adequate to determine in all cases 
the anterior dorsal vertebrae were fused in fully mature individuals.  For 
example, do we know whether Gnnathosaurus had its anterior dorsal fused into a 
notarium?  No, all we know of its poscranial skeleton is based on immature 
individuals that have been called "Pterodactylus micronyx" in the past.  When I 
talk about the advanced pectoral girdle of large pterodactyloids, I am talking 
about the complex of osteological characters that includes a scapulocoracoid 
the scapula rotated so that it articulates with the supraneural plate of the 
notarium in the region of the 3rd and 4th dorsals, and with anterior dorsal 
fused to the the notarium, AND if you read my contribution to the pterosaur 
symposium volume that complex of osteological characters reflects a whole 
of changes to the pectoral musculature as well.  I have not suggested that the 
mere presence of a notarium is a synapomorphy of a Dsungaripteroidea as the 
is used by Kellner and myself, however, I do think that the complex of 
that I term the advanced pectoral girdle is a synapomorphy of such a clade.  
if you are willing to tie the champagne to the advanced pectoral girdle rather 
than a notarium, then I'll consider it a wager.'

Apples, pears and oranges perhaps, in that I suspect that the situation 
the 'advanced pectoral girdle (APG)' is rather more complex than we currently 

In Tupuxuara, for example, the shape and arrangement of the pectoral girdle is 
the same as that in Tapejara, and in other basal pterodactyloids such as 
Pterodactylus (e.g. BSP 1938 I, Wellnhofer Encyc. p.89), with the scapula 
slanting forward and downward over the rib cage. This can be determined for 
certain in Tupuxuara because of marks on the ribs over which the scapula fits 
perfectly. Now, the posterior end of the scapula of Tupuxuara has a well 
developed facet that articulates with a facet on the supraneural crest of a 
notarium. The facet on the scapula is strongly oblique (NOT perpendicular as in 
ornithocheiroids) to the long axis of the scapula (as you might predict), so 
contact can be achieved. What this all means is that although Tupuxuara is 
supposed to have the APG complex, except for the notarium it is largely 
of structures and orientations seen in many other smaller pterosaurs, including 
the Campylognathoides beautifully illustrated in Bennett's article in the 
pterosaur symposium volume (PSV). 

I suspect that in Quetzalcoatlus and in Dsungaripterus the shoulder girdle also 
adopted a similar, forwardly directed and 'typical' (plesiomorphicish) 
orientation as in Tupuxuara, at least partly because the glenoid faces outward 
when the scapulocoracoid is viewed laterally, so if you orient them with the 
scapula directed laterally the glenoid faces backwards - which is not very 
helpful. But, wait a minute, in ornithocheiroids (sensu Unwin), represented by 
Anhanguera (= Brasileodactylus = Coloborhynchus) the scapula IS directed 
laterally as shown in Bennett's article (PSV) yet the glenoid faces laterally, 
NOT backwards. This is because in ornithocheiroids (sensu Unwin) the 
scapulocoracoid is strongly modified compared to that of other pterosaurs, 
including reorientation of the glenoid and the presence of a scapula that is 
shorter than the coracoid, and with a perpendicular notarial facet distally 
(compare for example figs a and b in Figure 1 of Frey et al. 'Middle and bottom 
decker pterosaurs' in the PSV). All of these enable the scapulocoracoid to be 
swung outwards into a position perpendicular to the spinal column. 

So, to try to summarise, there seems to be a consistent set of characters of 
shoulder girdle in ornithocheiroids that could be referred to as Bennett's 
restricted APG. However, there are grounds for believing that this APG does not 
apply to other pterodactyloids. First, because in other groups the construction 
of the shoulder complex is quite different from that seen in ornithocheiroids. 
Secondly, because important components of the shoulder girdle complex of the 
large, derived members of those groups (e.g. Tupuxuara, Quetzalcoatlus, 
Dsungaripterus) can be found in smaller less derived member of the same groups, 
or in groups (e.g. ctenochasmatoids - sensu Unwin) that are not supposed to 
an APG sensu Bennett. And thirdly, because basal members of groups (sensu 
within the 'Dsungaripteroidea (sensu Bennett and Kellner) lack derived features 
of the APG such as the presence of a notarium. (In fact, I am not aware of a 
single character or character state that unambiguously supports 
(sensu Bennett and Kellner), but as this is going of subject I will stop here). 

Chris was the first person to take up my 'Bottle of champagne' challenge. So, 
bet is on. Ladies and Gentlemen start your data sets please. 

Meanwhile, I shall return to my sofa and get on with my snot gargling.

The Bogey Monster

PS: Whoever it was who emailed me asking what a wussie is - its a wimp.