Stenoscelida

Stenoscelida (meaning "narrow hind leg") is a genus of proterochampsid archosauriforms from the Late Triassic Santa Maria Supersequence (Paraná Basin) of Rio Grande do Sul, Brazil. The genus contains a single species, S. aurantiacus, known from a right hind limb.^[1]

Stenoscelida Temporal range: Late Triassic (late Carnian/early Norian) PreꞒ Ꞓ O S D C P T J K Pg N ↓
Speculative life restoration
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	†Proterochampsia
Genus:	†Stenoscelida Müller, Garcia & Fonseca, 2022
Species:	†S. aurantiacus
Binomial name
†Stenoscelida aurantiacus Müller, Garcia & Fonseca, 2022

Discovery and naming

Stenoscelida type locality in Rio Grande do Sul, Brazil

The holotype specimen, CAPPA/UFSM 0293, was found at the Exaeretodon sub-Assemblage Zone (Hyperodapedon Assemblage Zone) of the Santa Maria Supersequence (lower Candelaria Sequence) in the Paraná Basin. This locality is dated to the late Carnian/early Norian ages of the upper Triassic period, around 228 million years old. It consists of a complete, articulated right hind limb.^[1]

In 2022, Stenoscelida aurantiacus was described as a new genus and species of proterochampsid archosauriforms by Rodrigo T. Müller, Mauricio S. Garcia, and André O. Fonseca based on these remains. The generic name, "Stenoscelida ", is derived from the Greek words "στενός", meaning "narrow", and "σκέλος" meaning "hind leg", in reference to the morphology of the holotype remains. The specific name, "aurantiacus", means "orange" in Latin, in reference to the color of the sediments of the type locality.^[1]

Description

Based on the known fossil remains, Stenoscelida would have been smaller than the related Pseudochampsa and Proterochampsa from Argentina.^[1]

Classification

In their phylogenetic analyses, Müller, Garcia & Fonseca (2022) recovered Stenoscelida as a member of the Proterochampsidae clade within Proterochampsia, in a polytomy with Tropidosuchus, Cerritosaurus, Gualosuchus, and Proterochampsa spp.^[1] In an updated analysis, Müller (2025) recovered greater resolution within Proterochampsia. He recovered Stenosclida immediately outside of the Proterochampsidae, as the sister taxon to this clade. These results are displayed in the cladogram below:^[2]

Avemetatarsalia Pseudosuchia Proterochampsia Doswelliidae Litorosuchus Vancleavea Polymorphodon Jaxtasuchus Doswellia Rugarhynchos Stenoscelida Proterochampsidae Proterochampsinae Sphodrosaurus Retymaijychampsa Proterochampsa nodosa Proterochampsa barrionuevoi Cerritosaurus Tropidosuchus Rhadinosuchinae MCP-4195-PV Gualosuchus Pseudochampsa Chanaresuchus Pinheirochampsa Kuruxuchampsa Rhadinosuchus