review of Andres and Ji 2006, Istiodactylus

[David Peters <davidrpeters@earthlink.net>]

In A New Species of Istiodactylus (Pterosauria, Pterodactyloidea)  
from the Lower Creteaceous of Liaoning, China (Andres and Ji 2006)  
(JVP 26: 70-78) the authors describe an new istiodactylid and erect a  
new species.

It joins Nurhachius, Istiodactylus and (overlooked by the authors)  
SMNS 1136 PAL as the fourth istiodactylid taxon. The specimen is  
compressed, somewhat articulated (the wings) and somewhat complete,  
however the various parts are folded upon themselves. No attempt was  
made by the authors to reconstruct the skull or other parts.

The authors refer to the lacrimals as the 'nasolacrimals' while  
overlooking the real nasals on either side of and laminated to the  
ascending process of the premaxilla. They also could not determine  
the line separating the premaxilla and maxilla, and thus could not  
determine the premaxillary tooth count. The line is visible. The  
tooth count is four in total (standard) but here three erupt  
ventrally per ramus with the first set tiny, elevated far above the  
jaw line and lost in the crack that splits the premaxilla into upper  
and lower portions. The authors describe an ectopterygoid, but this  
is a misnomer. The ectopterygoid and palatine fuse early in  
(Triassic) pterosaur phylogeny forming an ectopalatine. The broad  
palate bones often (but not in this study) referred to as the  
'palatines' are medially directed plates of the maxilla. No attempt  
was made to show the portion of the jugal that laminates against the  
maxilla ventral to the antorbital fenestra. No effort was made to  
dilineate the post orbital skull elements. Rather a linear silhouette  
of the bony areas was provided. The elements are all present and  
traceable.

Some skull bones are not fused to one another, suggesting, the  
authors report, that this specimen is subadult, following the  
paradigm set by Bennett (1993). However, other istiodactylids also  
exhibit such patterns. Either all should be considered less than  
adult or this might be considered a phylogenetic, rather than  
ontogenetic, pattern, as the authors suggest at the close of their  
paper. Bennett's list clearly does not refer to all pterosaurs equally.

As mentioned earlier, a crack separates the premaxillary ascending  
process + nasals from the lower rostrum. Cracks typically form at  
zones of weakness. Two nares per ramus can be seen in the Isle of  
Wight specimen. In the Chinese specimen, a broken portion of the  
nasal shows embayment for same. A reconstruction would tell the tale  
here.

The authors say the deltopectoral crest has a warped shape, but that  
could be argued. Crushing seems to have taken out the warp. It  
certainly is no match for the corkscrew warp of the Isle of Wight  
specimen, which was not nearly so compressed during taphonomy.

Nice to see those big non-wing fingers show up.

Otherwise a good description, but one that could have been improved.

1. We need more data on the pedal elements of this clade.
2. We need more precision on the skull elements.
3. We need more comparative reconstructions. They do help.
4. Not sure why (seemingly) every pterosaur known makes mention in  
the discussion portion. Overkill.

David Peters
StL