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re: Tanystropheus egg question.
Even further, the bones found are never found anterior to the pelvis,
unlike epipubics, but epipubics in pterosaurs are virtually ALWAYS either
adacent to or anterior to the pelvis without extreme disarticulation. They
may NOT be haemal arches, but extraneous neomorphic dermal bones, as
Silvio implied (heterotopic ossification), without any correllate in other
fossils, such as chevrons, epipubics, or ribs. It may be, therefore, that
these elements are completely useless phylogenetically.
If I follow your arguments, Jaime, I think the epipubics in pterosaurs are
called prepubes. And true, they have no homologs in other taxa, other than they
appear in Longisquama and Sharovipteryx. They are not homologous with the
epipubic bones in tanys.
The epipubic bones, aka heterotopic bones, in tanystropheids are interesting
because you cannot find chevrons in the vicinity, but following them, yes,
chevrons reappear. The epipubic bones in tanys are separated anteriorly, joined
or fused posteriorly, just like chevrons, aka hemal arches. That's why if
anyone finds chevrons coincident with these enigmas in tanystropheids, please
let me know so we can dismiss this concept. Until then, it holds promise.