Aenigmaspina and its enigmatic spines

Coming from the same fissure pit
as the basal bipedal crocodylomorph, Terrestrisuchus (Crush 1984, Fig. 2, Late Triassic), comes a new taxon based on a curled up set of cervicals, a scapula and…maybe/probably some other parts…including extraordinarily long forelimb bones (Fig. 1) and distinctive pelvis bits and pieces.

Figure 1. The bits and pieces of Aenigmaspina, reconstructed with an uncurled set of cervicals, plus some possibly associated parts.

Figure 1. The bits and pieces of Aenigmaspina, reconstructed with an uncurled set of cervicals, plus some possibly associated parts.

Patrick et al. 2019
named the bones Aenigmaspina and ran four phylogenetic analyses with prior matrices.

Wikipedia reports,
“Although parts of its skeleton is relatively well known, the affinities of Aenigmaspina to other pseudosuchians are unclear, although it is possibly related to families OrnithosuchidaeErpetosuchidae or Gracilisuchidae.” So, Wikipedia is kind of clueless, based on the paucity of materials.

Figure 2. GIF animation of Terrestrisuchus compared to scale with the bits and pieces of Aenigmaspina...just to get a possible reconstruction in mind.

Figure 2. GIF animation of Terrestrisuchus compared to scale with the bits and pieces of Aenigmaspina…just to get a possible reconstruction in mind.

Patrick et al. 2019 report:
“We report a third archosaur from the Late Triassic cavity-fill sediments of Pant-y-ffynnon Quarry in South Wales, in addition to the basal crocodylomorph Terrestrisuchus [Fig. 2] and the basal sauropodomorph dinosaur Pantydraco. The new taxon, Aenigmaspina pantyffynnonensis, previously referred to informally as ‘Edgar,’ was recovered in 1952 and is preserved as a tight cluster of vertebrae, ribs, and a scapula in a single block, as well as numerous associated, but now isolated, elements, including skull bones, vertebrae, further putative elements of the forelimb, and a partial pelvis. We present a digital model based on computed tomography (CT) scans of the main associated blocks, which shows exquisite detail of an associated series of 12 cervical and anterior dorsal vertebrae, with ribs and a scapula. The well-developed spine tables and eight matching osteoderms confirm that this is a crurotarsan archosaur, but it lacks apomorphies of all major crurotarsan clades. Phylogenetic analysis gives equivocal results, showing weak relationships with Proterochampsidae and Ornithosuchidae; the new taxon might lie close to Erpetosuchidae, based on the ‘Y’-shaped spine tables.

In the large reptile tree (LRT, 1565 taxa) there are too few bones preserved in the holotype to make a firm assessment. Adding the referred material helps, but not enough.  Erpetosuchus nests with other basal bipedal crocodylomorpha close enough to Terrestrisuchus that no other taxa intervene.

Strangely, after all the comparisons to Terrestrisuchus in the text,
in none of the four presented cladograms was Terrestrisuchus listed.

  1. In the first cladogram, based on Ezcurra (2016, with non-archosaurs deleted) Aenigmaspina nested with the much larger ornithosuchid, Riojasuchus.
  2. In the second cladogram, baed on Ezcurra et al. (2017) after strict consensus Aenigmaspina nested with the poorly known proterochampsid Rhadinosuchus, the protorosaur, Jaxtasuchus and the pararchosauriform, Doswellia. This diverse clade is a sister to an even more diverse clade including the pterosaur Dimorphodon + the proterochampsid, Lagerpeton + the basal croc Scleromochlus + Dinosauria.
  3. In the third cladogram based on Ezcurra et al. (2017) after majority rule consensus from 18 trees Aenigmaspina also nested as in #2.
  4. In the fourth cladogram based on Ezcurra e al. (2017) after deletion of three taxa Aenigmaspina nested with Rhadinosuchus, basal to Ornithosuchidae.

We looked at Ezcurra 2016
earlier here. It had 1.8 million+ MPTs. By dropping incomplete taxa that number dropped to 40 MPTs. His taxon list suffered from invalid taxon inclusion and taxon exclusion. Ezcurra did not realize the basal dichotomy splitting Lepidosauromorpha from Archosauromorpha occurred immediately following the advent of the clade Reptilia (=Amniota) in the early Carboniferous (Viséan).

Too few traits are preserved in Aenigmaspina
to enter it into the LRT, but the evidence, at present, seems to nest it within the basal bipedal crocs, close to Terrestrisuchus (Fig. 2) a coeval specimen from the same formation. Aenigmaspina is the same size as Terrestrisuchus and preserved parts are quite similar in all respects. Perhaps Patrick et al. 2019 should have included Terrestrisuchus in their cladograms.


References
Allen D 2003. When Terrestrisuchus gracilis reaches puberty it becomes Saltoposuchus connectens!”. Journal of Vertebrate Paleontology 23 (3): 29A.
Crush PJ 1984. A late upper Triassic sphenosuchid crocodilian from Wales. Palaeontology 27: 131-157.
Ezcurra MD 2016. The phylogenetic relationships of basal archosauromorphs, with an emphasis on the systematics of proterosuchian archosauriforms. PeerJ 4:e1778https://doi.org/10.7717/peerj.1778
Ezcurra MD et al. (9 co-authors) 2017. Deep faunistic changes preceded the rise of dinosaurs in southwestern Pangaea. Nature Ecology and Evolution 1:1477–1483.
Huene F von 1921. Neue Pseudosuchier und Coelurosaurier aus dem Wurttembergischen Keuper: Acta Zoologica, v. 2, p. 329-403.
Patrick EL, Whiteside DI and Benton MJ 2019. A new crurotarsan archosaur from the Late Triassic of South Wales. Journal of Vertebrate Paleontology e1645147 (18 pages) DOI: 10.1080/02724634.2019.1645147

wiki/Terrestrisuchus
wiki/Saltoposuchus

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