Temporal range: Middle Triassic
Butler et al., 2009
Hypselorhachis is a genus of extinct reptile, possibly a ctenosauriscid archosaur related to Ctenosauriscus. It lived during the Triassic Period. It is currently known only from a single vertebra found from the Middle Triassic Manda Beds in Tanzania.
The type species is H. mirabilis, mentioned but never fully described by English paleontologist Alan J. Charig. Hypselorhachis was assigned to the Ctenosauriscidae, a group of sail-backed archosaurs, in 1988. It was formally described by Richard J. Butler and co-workers in 2009.
Hypselorhachis is known from a single anterior dorsal vertebra found from the Lifua Member of the Manda Beds, which is thought to have been deposited during the Anisian stage. The only characteristic that diagnoses the genus is a feature seen in the prezygapophysis. Because of the lack of any other material, comparisons between it and other early archosaurs can only be based on features seen in the vertebrae, making any current phylogenetic classification tentative. Because the neural spine of the holotype is elongate, being over five times the height of the centrum, Hypselorhachis may be a ctenosauriscid. Other ctenosauriscids such as Arizonasaurus and Ctenosauriscus possessed characteristically large sails that were formed from elongate neural spines.
- Carroll, R.L. (1988). Vertebrate Paleontology and Evolution. W.H. Freeman and Company
- Butler, R.J.; Barrett, P.M.; Abel, R.L.; Gower, D.J. (2009). "A Possible Ctenosauriscid Archosaur from the Middle Triassic Manda Beds of Tanzania". Journal of Vertebrate Paleontology 29 (4): 1022–1031. doi:10.1671/039.029.0404.
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