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Re: scapulae, sauropods



Nick Longrich wrote-

> The thing about free scapula-coracoid articulations is that the
scapula and coracoid appear to have fused over ontogeny. There is
dromaeosaur material in which the scapula is not fused to the coracoid, and
there is also dromaeosaur material in which it is. Caudipteryx and
Microvenator have free coracoids, those of the Ingenia and an unnamed AMNH
oviraptorid are fused. So what does it mean that Rahonavis and Unenlagia
don't have coracoids fused onto their scapulae? Not necessarily anything.
Incidentally Mononykus does not have a scapula fused to the coracoid. A lot
of characters are like this, you have to look at how they change over the
life of the animal- especially fusion and ossification characters. My guess
is that an adult oviraptorid would have uncinate processes, sternal plates,
a tarsometatarsus, a fourth trochanter, a fused semilunate, and a
scapulacoracoid, but that a hatchling wouldn't have any of these. So we have
to be careful.


When I wrote back Ekaterina about scapulocoracoideal joints, I assumed they
were asking about it being a mobile joint, which is a feature of Rahonavis
anf Pygostylians.  Caudipteryx, Microvenator, etc. don't have fused
scapulacoracoids, but they were joined with cartilage and functioned as a
single unit.  On the other hand, Rahonavis' scapula has a "facet for the
coracoid, indicating a mobile joint as in derived birds, rather than the
plesiomorphic sutural contact of theropods and Archaeopteryx" (Forster, et
al. 1998).
I assumed that Ekaterina was writing about this feature as opposed to the
fusion or lack of fusion between the bones, which as you note, is
ontogenetically variable and therefore not phylogenetically useful.

Mickey Mortimer