Along with the recent abstract on desert drepanosaurs, an earlier paper (Harris and Downs 2002) reported on a 3D drepanosaur pectoral girdle (Fig. 1).
Harris and Downs (2002) accurately reported on most of the elements here. But they overlooked the big one in the middle. They either overlooked the interclavicle binding all the other pectoral elements together, or else they considered it part of the scapulocoracoid. They also did not notice the right clavicle overlapped the left one.
These color images were created using a very simple version of DGS, digital graphic segregation, which also involves phylogenetic analysis and phylogenetic bracketing.
Drepanosaurs are tritosaur lepidosaurs. Earlier we looked at several other tritosaur pectoral girdles. Tritosaurs do weird things with their interclavicle/sternum.
Here (Fig. we see in ventral view the interclavicle and overlapping clavicles of Jesairosaurus, the mother of all drepanosaurids. Cosesaurus, likewise, has these overlapping clavicles, as does Longisquama and the Pterosauria, as part of their sternal complex.
Hypuronector (Fig. 4 ) is also ancestral to drepanosaurids, nesting between Vallesaurus and Jesairosaurus.
Vallesaurus is represented by a crushed specimen in which the interclavicle appears to be broken at or near the midline during crushing. The clavicles and sterna are likewise split medially.
Dr. Seuss had it right
This clade of tritosaur lepidosaurs (drepanosaurs, tanstropheids, fenestrasaurs, pterosaurs) are indeed a bizarre bunch of the most unusual reptiles known to science.
Harris JD and Downs A 2002. A drepanosaurid pectoral girdle from the Ghost Ranch (Whitaker) Coelophysis quarry (Chinle Group, Rock Point Formation, Rhaetian), New Mexico. Journal of Vertebrate Paleontology 22(1):70-75.