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| Silescelida acristata Garcia, Cerqueira, Battista, Andrade & Müller, 2026 life reconstruction by Matheus Fernandes Gadelha. |
Abstract
Archosauriformes comprise a diverse range of reptiles, including the crown-group Archosauria, which flourished during the Triassic Period. Early-diverging archosauriforms, such as proterosuchids and erythrosuchids, are becoming progressively well-known due to recent studies and consistently resolve at the base of the clade. More crownward, Eucrocopoda includes archosauriform taxa that increasingly approximate the ancestral archosaur body plan. Early-diverging eucrocopodan archosauriforms have a widespread paleogeographic record but remain poorly understood in terms of ingroup relationships. Within this radiation, Euparkeriidae is particularly challenging, because its ingroup composition and monophyly is debated, with some authors supporting a non-monospecific Euparkeriidae, whereas others fail to recover this hypothesis. The eponymous Euparkeria capensis is known from the Early to Middle Triassic of South Africa, whereas other putative euparkeriids are primarily known from the Early to Middle Triassic of China, Germany, Poland, and Russia. Here, we describe a new early-diverging eucrocopodan (Silescelida acristata gen. et sp. nov.) from the Middle Triassic of southern Brazil. Phylogenetic analyses incorporating this taxon suggest a possible placement within Euparkeriidae, though its position shows instability depending on the operational taxonomic units considered, especially among other putative euparkeriids. This discovery not only informs on the temporal and paleogeographic distribution of euparkeriids but also sheds light on the origin and early evolution of eucrocopodans, representing the first record of this archosauriform grade in the Triassic of Brazil. More broadly, the new taxon underscores the significance of South American Triassic deposits within the evolutionary history of archosauriforms.
Archosauromorpha von Huene, 1946 sensu Gauthier, 2020
Archosauriformes Gauthier et al., 1988 sensu Gauthier, 2020
Eucrocopoda Ezcurra, 2016
cf. Euparkeriidae von Huene, 1920 sensu Sookias and Butler, 2013
Silescelida acristata gen. et sp. nov.
Holotype. MCP 4186-PV, a left scapula, a right ilium, and a left femur (Fig. 1C, D). The elements were found in association (attached to each other) and are size-compatible; therefore, they are considered to belong to the same individual.
Type locality, age, and horizon. Posto (or Posto de Gasolina; Fogliarini) site (29°37’38.9”S 53°22’06.5”W), municipality of Dona Francisca, Rio Grande do Sul, Brazil (Fig. 1A, B). Dinodontosaurus AZ of the Pinheiros-Chiniquá Sequence of the Santa Maria Supersequence, Paraná Basin51,52. It is considered Ladinian in age30,35,53,54,55,56,57,58.
Diagnosis. The holotype of Silescelida acristata differs from all other known non-archosaurian archosauriforms in the following combination of traits: scapular blade without an anteroposterior constriction at its base; asymmetrical expansion of the scapular blade at its dorsal portion; straight posterior margin of the scapular blade, forming a right angle with the dorsal margin of the glenoid; elliptical tuber for the m. triceps dorsal to the glenoid; dorsal margin of the dorsal iliac blade straight in dorsal and lateral views; dorsal iliac blade as deep as the acetabulum; notch between the ischiadic peduncle and the ventral apex of the medial acetabular wall; medially expanded femoral head; absence of a longitudinal groove on the proximal surface of the femoral head; posteromedial tuber as the only well-developed tuber on the femoral head; absence of an elevated mound or crest-like structure as the attachment site for the m. caudofemoralis (local autapomorphy); extensor fossa on the anterior surface of the femoral distal end; distal femoral condyles with the same degree of ventral development (not uneven).
Etymology. The generic name combines the Latin siles (“silence”) and the Greek skelēs (“hind leg”), referencing the loss of the proximal femur bearing the specimen’s collection code, which obscured its provenance until its recent rediscovery. The specific epithet derives from the Latin prefix a- (“without”) and cristāta (“crested”), referring to the absence of a crest or flange attachment site for the m. caudofemoralis (= fourth trochanter), a diagnostic feature of the taxon.
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| Silescelida acristata gen. et sp. nov. life reconstruction. Artwork by Matheus Fernandes Gadelha. |
Maurício S. Garcia, Gabriela M. Cerqueira, Francesco Battista, Marco B. de Andrade and Rodrigo T. Müller. 2026. A New eucrocopodan Archosauriform from the Middle Triassic of southern Brazil and the Phylogeny of Euparkeriidae. Scientific Reports. 16: 16585. DOI: doi.org/10.1038/s41598-026-53740-9 [10 June 2026]









































