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Re: Sauropod spines
> "Spines," particularly dermal scutes, are well known in titanosaurids such as
> _Saltasaurus_ and _Ampelosaurus_. These were probably homologous to the
> spines recently found in other sauropods. Dermal armor is primitive for
> Dinosauria and is well expressed in numerous phytodinosaurian groups,
> including the Ankylosauria and Stegosauria, which are famous for it. It was
> also present in Lesothosauria (primitive ornithischians of uncertain
> relationships) and to some extent in Ornithopoda.
Dermal armour primitive for Dinosauria? I don't think so. The loss of
osteoderms is a character that diagnoses the Ornithodira. It is reversed
in some dinosaur clades: Titanosauridae, Thyreophora and Ceratosaurus.
However there is no evidence that these are retaining the primitive
condition of the ancestral dinosaur. Indeed many basal dinosaurs
(Eoraptor, Herrerasaurus, Prosauropods, Lesothosaurus)
and close dinosaur outgroups (Marasuchus) are known from relatively
complete skeletal remains that don't include any trace of osteoderms.
What primitive ornithischian are you refering to when you say that
armour was present in Lesothosauria? If you are reffering to
Scutellosaurus then this is a thyreophoran, the one and only (to my
knowledge) group of ornithischians to posses armour (either supported by
osteoderms or not).