Early Triassic Elessaurus: another overlooked Cosesaurus sister!

Cosesaurs (basal fenestrasaurs)
(Figs. 1–3) are popping up everywhere lately!

Current interpretation of Cosesaurus.

Figure 1. MIddle Triassic Cosesaurus. Double its size and it would be close to Early Triassic Elessaurus. See figure 6.

Earlier we looked at a tiny Early Cretaceous cosesaur skull in amber
originally mistaken for a bird/dinosaur: Oculudentavis.

Figure 2. Elessaurus hind limb elements gathered together to scale. Some original scale bars were off by 2x.

Figure 2. Elessaurus hind limb elements gathered together to scale. Some original scale bars were off by 2x.

Today De-Oliveira et al. 2020 bring us
a new Early Triassic cosesaur, Elessaurus gondwanoccidens (UFSM 11471, Figs. 2, 3) known from a hind limb, pelvis, partial sacrum and proximal caudal vertebrae. Cosesaurus was a derived tanystropheid, close to Langobardisaurus, but was not included in the De-Oliveira taxon list.

Figure 1. Elessarus pes compared to Cosesaurus to scale and x2. Note differences between original tracing and DGS tracing.

Figure 3. Elessarus pes compared to Cosesaurus to scale and x2. Note differences between original tracing and DGS tracing. Digit 5 was not lost. It is tucked beneath the metatarsals and was not scored in the LRT.

In the De-Oliveira et al. published cladogram
(Fig. 4) Elessaurus nests basal to the Tanystropheidae (= Macrocnemus, Amotosaurus, Tanystropheus, Tanytrachelos and Langobardisaurus) a clade they derive from Protorosaurus and Trilophosaurus. in one cladogram (Fig. 4), but not in the other (Fig. 5). The authors reported, “In addition, the new specimen presents some features only found in more specialized representatives within Tanystropheidae, such as the presence of a well-developed calcaneal tuber with a rough lateral margin.” 

Figure 3. Published cladogram by De-Oliveira et al. 2020. Note difference with their SuppData cladogram.

Figure 4. Published cladogram by De-Oliveira et al. 2020. Note different nesting than their SuppData cladogram in figure 5.

By contrast, in the De-Olveira et al. SuppData cladogram
Elessaurus nests without resolution within the Rhynchosauria (Fig. 5). Distinct from the first analysis (Fig. 4), this (Fig. 5) included the drepanosaur ancestor, Jesairosaurus, and the derived macrocnemid, Dinocephalosaurus. The authors reported, “In this second analysis, Elessaurus adopts different positions among the MPTs, it is recovered, e.g. within Archosauriformes, as a sister-taxa of Allokotosauria+Archosauriformes and an early rhynchosaur.” This is a red flag indicating major problems in scoring and taxon exclusion.

Figure 3. Cladogram from DeOliveira et al. 2020 with colors added to show distribution and mixing of Lepidosauromorpha and Archosauromorpha clades in the LRT. Many of these purported sister taxa do not look alike! Here Elessaurus nests with rhynchosaurs, not tanystropheids. 

Figure 5. Cladogram from DeOliveira et al. 2020 with colors added to show distribution and mixing of Lepidosauromorpha and Archosauromorpha clades in the LRT. Many of these purported sister taxa do not look alike! Strangely, here Elessaurus nests with rhynchosaurs, not tanystropheids (Fig. 2). The taxon in pink had to be looked up and revised here.

By contrast, 
in the large reptile tree (LRT, 1661+ taxa), Elessaurus nests as a derived tanystropheid, alongside Cosesaurus (Fig. 1). a smaller Middle Triassic taxon omitted from the original study. The authors mistakenly considered tanystropheids to be archosauromorphs, again due to taxon exclusion. Despite the many traits that converged with archosauromorph protorosaurs, tanystropheids are tritosaur lepidosaurs, derived from Huehuecuetzpalli (Fig. 7) and Tijubina. In the LRT, adding taxa does not create chaos. New taxa neatly take their place within the current tree topology. By omitting Cosesaurus, the authors omitted the most similar taxon to Elessaurus and all the added information included herein.

The cladogram by De-Oliveira et al. shuffles lepidosauromorphs
with archosauromorphs without an understanding of their Viséan split. As a result, several purported ‘sisters’ in figure 5 do not look alike, but apparently nested together by default. Based on these ‘odd bedfellows’ I suspect the authors borrowed another worker’s cladogram without checking scores or examining results.

From the abstract:
“The origin and early radiation of Tanystropheidae, however, remains elusive.”

This is false. We know the origin of Tanystropheidae back to Cambrian chordates. Taxon exclusion by the authors prevents them from recovering both distant and proximal sister taxa.

“Here, a new Early Triassic archosauromorph is described and phylogenetically recovered as the sister-taxon of Tanystropheidae.”

By contrast, in the LRT Elessaurus is a derived fenestrasaur close to Cosesaurus, a taxon excluded by the authors. We know cosesaur tracks (= Rotodactylus, Fig. 6) go back to the Early Triassic and some were much larger than Cosesaurus.

Figure 1. Scaling a quadrupedal Cosesaurus to the larger Rotodactylus tracks from Haubold 1983. Quadrant represents center of balance in the closeup foot. Graphic representation of a butt joint is nearby.

Figure 6. Click to enlarge. Scaling a quadrupedal Cosesaurus to the larger Rotodactylus tracks from Haubold 1983. Quadrant represents center of balance in the closeup foot. Graphic representation of a butt joint is nearby.

More from the abstract:
“The new specimen, considered a new genus and species, comprises a complete posterior limb articulated with pelvic elements. It was recovered from the Sanga do Cabral Formation (Sanga do Cabral Supersequence, Lower Triassic of the Parana Basin, Southern Brazil), which has already yielded a typical Early Triassic vertebrate assemblage of temnospondyls, procolophonoids, and scarce archosauromorph remains. This new taxon provides insights on the early diversification of tanystropheids and represents further evidence for a premature wide geographical distribution of this clade. The morphology of the new specimen is consistent with a terrestrial lifestyle, suggesting that this condition was plesiomorphic for Tanystropheidae.”

Likewise, Cosesaurus and related fenestrasaurs in the LRT are terrestrial taxa, distinct from other tanystropheids, all arising from tritosaur lepidosaurs like Tijubina and Huehuecuetzpalli.

Huehuecuetzpalli

Figure 7. The father of all pterosaurs and tanystropheids, Huehuecuetzpalli, a late survivor in the Early Cretaceous from a Late Permian radiation.

Larger quadrupedal cosesaurs, 
like Elessaurus, had two sacrals (Fig. 1). Smaller bipedal cosesaurs (Fig. 1) had four. Both had anterior processes on the ilium, not longer than the acetabulum width, distinct from non-fenestrasaur tanystropheids.

PS
Figure 2 in De-Oliveira has a scale bar problem in their figure 2 (explained here in Fig. 2).


References
De-Oliveira TM, Pinheiro FL, Da-Rosa AAS, Dias-Da-Silva S and Kerber L 2020.
A new archosauromorph from South America provides insights on the early diversification of tanystropheids. PLoS ONE 15(4): e0230890

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