Spinosaurus Spines

Ernst von Stromer speculated at length on the positioning and relationship of the spines found at Baharija in Egypt. At the time, much work done on the organization of features of the dorsal vertebrae of large vertebrates had not been done, as no exceptionally large terrestrial reptile was known save a few lucky specimens in North America and Poekilopleuron in France. In the end, though, this specimen and the holotype of Poekilopleuron would be destroyed during bombing raids during WWII, and thus all current work done on the exceptional Spinosaurus aegyptiacus holotype is based on von Stromer's original plates.

I have taken a small hand at organizing the material here based on new data on the morphology of the centrum, neural spine, arch, diapophysis, and zygapophyses, which suggest some of the material is not correctly associated (centrum to arch), were out of sequence, or were in the wrong position on either side of the sacrum.

A: This represents von Stromer's original organization, and for the most part I have no conflict with a lot of his conclusions about the smaller vertebrae.

B: This represents my personal views based on centrum face flattening, posterior centrum concavity, orientation of the physeal extensions, positioning and extent of the diapophyseal laminae and parapophyses, and orientation of the neural spines, which appear to radiate into a fan-like structure. I have tried to reject this position, but the tallest spine seems to belong to the tail, as it is the only caudally-oriented spine and the infradiapophyseal lamina are restricted and do not appear to have any connection to other regions of the arch as in the other dorsal vertebrae; this is also rather unique in that most caudal vertebrae of theropods are very simply and typically lack infradiapophyseal lamina of any sort. As it is, it may be the posteriormost dorsal, the spine is certainly not a sacral as it lacks coosified elements of the known sacral elements, but the high angle between it and the most vertical spine in the dorsal column indicate there must have been a HIGH level of reorientation to arrive an this position. The vertebrae is certainly not in reverse, as the prezygapophyses are certainly to the anterior (left) in the image, as confirmed by von Stromer and a translation of the original paper.