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Re: An Odd Question on Tyrannosaurs Rephrased



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