Quick question:
The tail of Cosesaurus was once considered to be sheathed in a fin, like the
fletching of an arrow. However, the (sadly, now defunct) David Peters site
showed a reconstruction without the fin, which was, I supposed, the new
interpretation of the animal. However, I don't know where this new
interpretation came from---why was the fin discarded?
Since Ellemberger times, something has been noticed around the tail and in
some other spots in Cosesaurus. Indeed, the interpretations of such
structures vary according to the pre-concepts of the observer:
Ellemberger, thinking it was protoavian saw feather like impressions a la
Archaeopteryx, while others assuming it was a pre-pterosaur saw a sheat.
Indeed the mode of preservation of Montral Alcover material (A colleague
of mine worked extensively on the fishes) prevents any reliable
intepretation. More likely of all, they are sedimentary structures. The
"fin" was discarded because it does not exist. A US PhD student (Phil
Senter, I don't remember his affiliation) should have something in
preparation on this critter and he very kindly sent me some photos and a
draft of his impressions. IMHO his notes represent the best interpretation
of Cosesaurus I've read so far. I think he has a paper in preparation on
this. Maybe he can be more precise.