I believe unique combinations of characters are just as
useful for supporting validity as completely unique autapomorphies.
I agree. I haven't read the _Amtosaurus_/_Bissektipelta_ paper so I won't
comment on this particular example... but in general I'm curious why a given
species is regarded as a _nomen dubium_ simply because it lacks
autapomorphies. This has been done for the type species for _Lagosuchus_,
for example. _Lagosuchus_ was described by one study as non-diagnostic
because (unlike _Marasuchus_) the type specimen lacked any autapomorphies.
However, it can easily be shown that _Lagosuchus_ is not the same as
_Marasuchus_, or any other "lagosuchian"-grade archosaur. Thus,
_Lagosuchus_ should be retained as a valid genus.
BTW, does any one know of a study that has described autapomorphies in
_Archaeopteryx_? This is undoubtedly a valid genus, and it can be
distinguished from any other known maniraptoran in a heartbeat. But most of
_Archaeopteryx_'s characters are plesiomorphic for the bird clade, and at
the moment I can't bring to mind a single autapomorphy. (Doesn't mean there
aren't any - I just can't think of any.)
Tim
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