Cosesaurs (basal fenestrasaurs)
(Figs. 1–3) are popping up everywhere lately!
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.
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.”
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.
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.
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.
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.
Figure 2 in De-Oliveira has a scale bar problem in their figure 2 (explained here in Fig. 2).
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