Akidostropheus: a tiny tanystropheid with spiked vertebrae
Known from several tiny vertebrae
with unique dorsal spikes, Akidostropheus (Fig 1, Schubul, Marsh and Kligman 2025) was originally considered a tiny tanystropheid, perhaps close to Tanytrachelos (Fig 1), a taxon also described from the Petrified Forest (Late Triassic, Arizona) and from a coeval formation in Virginia. The vertebrae were procoelus, a trait shared with Cosesaurus (Fig 1), Sharovipteryx, Longisquama and pterosaurs.
The authors reported,
“Procoely is seen in the tanystropheids Langobardisaurus pandolfi (Renesto 1994), Tanytrachelos ahynis (Olsen 1979), Ozimek volans (Dzik & Sulej 2016), and the Ghost Ranch tanystropheids (Pritchard et al. 2015).”
Other taxa with procoelus vertebrae include: Trilophosaurus, and the giant crocodile, Stomatosuchus.
Figure 1. Akidostropheus vertebrae compared to other small tanystropheids to scale. Top images with scale bars are 0.9x life size.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/08/cosesaurus.akidostropheus588-1.jpg?w=120″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/08/cosesaurus.akidostropheus588-1.jpg?w=411″ class=”size-full wp-image-93981″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/08/cosesaurus.akidostropheus588-1.jpg” alt=”Figure 1. Akidostropheus vertebrae compared to other small tanystropheids to scale. Top images with scale bars are 0.9x life size.” width=”584″ height=”1454″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/08/cosesaurus.akidostropheus588-1.jpg?w=584&h=1454 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/08/cosesaurus.akidostropheus588-1.jpg?w=60&h=150 60w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/08/cosesaurus.akidostropheus588-1.jpg?w=120&h=300 120w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/08/cosesaurus.akidostropheus588-1.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 1. Akidostropheus vertebrae compared to other small tanystropheids to scale. Top images with scale bars are 0.9x life size.
The problem is
the cervicals are relatively robust in Tanytrachelos and other large and small tanystropheids (Fig 1). The one cervical representing Akidostropheus (Fig 1) is not more robust than the other vertebrae.
Let’s put that detail aside for the moment.
What about those unique spikes?
They are unique! Iguana and Sphenodon have similar structures made of keratin = scale material, not bone. The authors noted, “These striations likely indicate that a keratinous sheath attached to this boney core, a structure that would have projected dorsally beyond the dorsal extent of the bone to an unknown height.”
In Cosesaurus, Mirasaura and Longisquama a tall median dorsal frill is present (Fig 1), which brings us back to the tanystropheid affinity of Akidostropheus. No spike has ever been seen in other tanystropheids, large or small.
Even so, Akidostropheus is a tanystropheid candidate IMHO. More data will help.
Figure 2. Tiny Tanystropheus cervicals from the Petrified Forest, described by Schubel, Marsh and Kligman 2025.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/08/petrifiedforesttanystropheid-cervicals588.jpg?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/08/petrifiedforesttanystropheid-cervicals588.jpg?w=584″ class=”size-full wp-image-93976″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/08/petrifiedforesttanystropheid-cervicals588.jpg” alt=”Figure 2. Tiny Tanystropheus cervicals from the Petrified Forest, described by Schubel, Marsh and Kligman 2025.” width=”584″ height=”199″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/08/petrifiedforesttanystropheid-cervicals588.jpg?w=584&h=199 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/08/petrifiedforesttanystropheid-cervicals588.jpg?w=150&h=51 150w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/08/petrifiedforesttanystropheid-cervicals588.jpg?w=300&h=102 300w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/08/petrifiedforesttanystropheid-cervicals588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 2. Tiny Tanystropheus cervicals from the Petrified Forest, described by Schubel, Marsh and Kligman 2025.
Perhaps even more fascinating
are the tiny Tanystropheus cervicals also described in this paper (Fig 2).
Typically Tanystropheus specimens are much larger (Fig 3).
Figure 3. The large Tanystropheus specimens to scale. On the right the new China specimen has large girdles, larger vertebrae, more robust ribs and shorter toes, among the more visible distinctions. Click to enlarge. Above right is the new M. Witton reconstruction with erect limbs, an overly large scapula, an overly large ilium, lacking an interclavicle and other minor issues.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2015/11/tanystropheus-growth11202.jpg?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2015/11/tanystropheus-growth11202.jpg?w=584″ class=”size-full wp-image-21050″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2015/11/tanystropheus-growth11202.jpg” alt=”Figure 3. The large Tanystropheus specimens to scale. On the right the new China specimen has large girdles, larger vertebrae, more robust ribs and shorter toes, among the more visible distinctions. Click to enlarge. Above right is the new M. Witton reconstruction with erect limbs, an overly large scapula, an overly large ilium, lacking an interclavicle and other minor issues. ” width=”584″ height=”322″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2015/11/tanystropheus-growth11202.jpg?w=584&h=322 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2015/11/tanystropheus-growth11202.jpg?w=150&h=83 150w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2015/11/tanystropheus-growth11202.jpg?w=300&h=166 300w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2015/11/tanystropheus-growth11202.jpg?w=768&h=424 768w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2015/11/tanystropheus-growth11202.jpg?w=1024&h=565 1024w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2015/11/tanystropheus-growth11202.jpg 1120w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 3. The large Tanystropheus specimens to scale. On the right the new China specimen has large girdles, larger vertebrae, more robust ribs and shorter toes, among the more visible distinctions. Click to enlarge. Above right is the new M. Witton reconstruction with erect limbs, an overly large scapula, an overly large ilium, lacking an interclavicle and other minor issues.
A gentle reminder:
Other clade members from Huehuecuetzpalli (Fig 1) to Zhejangopterus and Pterodaustro, hatched with adult proportions. Isometry is a lepidosaur trait not commonly found in archosauromorphs (contra Schubul, Marsh and Kligman 2025). Egg shells would be leathery, not calcareous.
Figure 1. Hypothetical Tanystropheus egg. Below a single cervical fits the 1:6.4 ratio described by Heidenfelder et al. Isometric growth is a trait of this lepidosaur clade.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2023/10/tanystropheus-embryo-cervical588.jpg?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2023/10/tanystropheus-embryo-cervical588.jpg?w=584″ class=”size-full wp-image-81966″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2023/10/tanystropheus-embryo-cervical588.jpg” alt=”Figure 1. Hypothetical Tanystropheus egg. Below a single cervical fits the 1:6.4 ratio described by Heidenfelder et al. Isometric growth is a trait of this lepidosaur clade.” width=”584″ height=”401″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2023/10/tanystropheus-embryo-cervical588.jpg?w=584&h=401 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2023/10/tanystropheus-embryo-cervical588.jpg?w=150&h=103 150w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2023/10/tanystropheus-embryo-cervical588.jpg?w=300&h=206 300w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2023/10/tanystropheus-embryo-cervical588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 1. Hypothetical Tanystropheus egg. Below a single cervical fits the 1:6.4 ratio described by Heidenfelder et al. Isometric growth is a trait of this lepidosaur clade.
Heidenfelder et al 2023 (SVP abstract)
looked at New Mexico tanystropheids from a microvertebrate assemblage. The image above was in that 2023 post.
Thanks to
reader Sean M for sending me the link for this new paper. Fascinating stuff!
References
Schubul AN, Marsh AD and Kligman BT 2025. 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) : 99-125. Stuttgart State Museum of Natural History.
Source: https://pterosaurheresies.wordpress.com/2025/08/03/akidostropheus-a-tiny-tanystropheid-with-spiked-vertebrae/
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