Also, am I correct in assuming that a hypotarsus has
to date only been found to occur in Ornithothoraces,
and that it is an autapomorphy in these?
Only in Lectavis and Ornithuromorpha (unknown in Hongshanornis and
Archaeorhynchus). Zhou and Zhang believe it's present in the probable
enantiornithine Liaoningornis too, but Clarke does not.