Haemal arch

[1] In 1956, Alfred Sherwood Romer hypothesized that the position of the first haemal arch was sexually dimorphic in crocodilians and dinosaurs.

[2] However, subsequent research established that the size and position of the first haemal arch was not sexually dimorphic in crocodilians and found no evidence of significant variation in tyrannosaurid dinosaurs, indicating that haemal arches could not be used to distinguish between sexes after all.

[3] Haemal arches play an important role in the taxonomy of sauropod dinosaurs, as sauropods exhibit a wide range of morphologies of the haemal arches.

[1] In 1878, Othniel Marsh named the sauropod Diplodocus after the distinctive shape of its haemal arches, which were forked to have both an anterior and posterior process.

[4] Though once thought to be a specialized characteristic of Diplodocus and its close relatives, forked chevrons are now known to have been widespread among sauropod dinosaurs, although titanosauriform sauropods returned to the unforked condition.