Akidostropheus

Akidostropheus oligos was a small tanystropheid archosauromorph reptile that lived during the late Triassic, about 223-218 million years ago, in what is now Arizona, USA.

Only a few tiny isolated vertebrae have been discovered, so its full size and appearance isn’t known – making any reconstruction rather speculative – but it was probably around 30cm long (~12″). Like other tanystropheids it would have been a long-necked lizard-like animal, and may have had a similar build to the closely-related Tanytrachelos.

But despite the scarcity of material the few known vertebrae are unique among archosauromorphs, bearing elongated spikes with a surface texture that suggests they were covered with keratinous sheaths. The spikes were conical, sharp, and hooked on the neck and upper back, but became more flattened, straighter, and blade-like on the lower back and tail.

These structures were probably defensive in nature, especially considering that there’s direct fossil evidence for predators targeting the long necks of tanystropheids and decaptiating them.

Akidostropheus lived in a tropical floodplain environment around a meandering river system, but without more and better fossils it’s impossible to tell what its ecology was. Tanystropheids were a strange and diverse bunch, with both terrestrial and aquatic lifestyles, bipedal runners, and possibly even bizarre leg-gliders, so this spiky little Triassic weirdo could have been doing almost anything.

References:

• Schubul, Alaska N., Adam D. Marsh, and Ben T. Kligman. “A diverse assemblage of tanystropheid archosauromorphs from the continental interior of Late Triassic Pangea includes a new taxon (Akidostropheus oligos gen. et sp. nov.).” Palaeodiversity 18.1 (2025): 99-125. https://doi.org/10.18476/pale.v18.a5
• Smith, Amy C. “Description of Tanytrachelos ahynis and its implications for the phylogeny of Protorosauria.” PhD thesis, Virginia Polytechnic Institute and State University, Blackburg, VA, USA. 2011. http://hdl.handle.net/10919/37652
• Spiekman, Stephan NF, and Eudald Mujal. “Decapitation in the long-necked Triassic marine reptile Tanystropheus.” Current Biology 33.13 (2023): R708-R709. https://doi.org/10.1016/j.cub.2023.04.027
• Spiekman, Stephan NF, et al. “A redescription of Trachelosaurus fischeri from the Buntsandstein (Middle Triassic) of Bernburg, Germany: the first European Dinocephalosaurus-like marine reptile and its systematic implications for long-necked early archosauromorphs.” Swiss Journal of Palaeontology 143.1 (2024): 10. https://doi.org/10.1186/s13358-024-00309-6
• Wikipedia contributors. “Akidostropheus” Wikipedia, 04 Aug. 2025, https://en.wikipedia.org/wiki/Akidostropheus