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MariusRomanus@aol.com wrote-
> As for the sternal bit..... Right off the bat, many
parts of the sternum is not bone. Only part of it is
> bone. This is almost always true. My understanding is
that it is a well established phenomenon that > the sterna in theropods
ossify late in development, and if they do not have sterna, preserved for
> example, this only means that they were in a
cartilaginous state. What is also known is that the
> sternal ribs of many different species simply do not
ossify.... Ever. This is true for many dinosaurs,
> humans, and most other mammals. Only with old age might
there be the beginnings of ossification.
At least some theropods had sterna that ossified early in
development, as seen by the juvenile Scipionyx specimen. Then there are
ornithomimids, which never ossify their sterna. So there was a lot of
variation in this character. Many maniraptorans seem to have ossified
nearly all of their sternum and most maniraptoriformes ossified their sternal
ribs.
> When it particularly comes to theropods, I bet the articulation between the coracoids and sternum > was cartilage. Just look at the sternum in some theropods. Look at the
way some restorations try to > articulate them. The limbs simply do not line
up right unless you fill in the gaps with cartilage.....
> Upfront bewteen the coracoids, at the anterior margine of the sternum,
the back of the sternum, and > where the gastralia is. Such things are good
indications that the sternums were longer than what
> was actually preserved. Yet, some still try to make them fit without
doing this. I have never
> understood that.
Though there was undoubtedly a small amount of cartilage between the
coracoids and sternum, eumaniraptorans at least had almost direct contact
between the coracoids and ossified sterna. There are paired grooves
anteriorly in these forms' sterna, which articulated with the
coracoids.
Mickey Mortimer |