 |
| Isodapedon varzealis Schiefelbein, Garcia, Doering & Müller, 2026 Artwork by Caio Fantini. |
Abstract
We describe Isodapedon varzealis gen. et sp. nov., a new hyperodapedontine rhynchosaur from the Carnian deposits of the Candelária Sequence, southern Brazil. Phylogenetic analyses place this taxon outside known South American hyperodapedontines, including Macrocephalosaurus mariensis and ‘Hyperodapedon’ species, and support the restriction of the genus Hyperodapedon to its type species, thereby revealing greater diversity within the group than previously recognized. Isodapedon varzealis gen. et sp. nov. is characterized by symmetrical maxillary tooth bearing areas and distinctive dentary morphology, indicating divergent feeding adaptations relative to known rhynchosaurs. Stratigraphic occurrence in beds correlated with the Exaeretodon sub-zone of the Hyperodapedon Assemblage Zone, and its phylogenetic affinities with early diverging hyperodapedontines from Argentina and Scotland, imply a geographically widespread radiation of conservative morphotypes across southwestern Gondwana. This study highlights the complexity of Late Triassic rhynchosaur evolution and underscores the importance of continued palaeontological investigation in refining the taxonomy, biostratigraphy and palaeoecology of this key herbivorous clade.
Keywords: Rhynchosauria, Late Triassic, Candelária Sequence, Archosauromorpha
Subjects:palaeontology
 |
| Geological context of the Várzea do Agudo site and provenance of CAPPA/UFSM 0371. (A) Geologic map of the central region of Rio Grande do Sul (southern Brazil) showing the surface distribution of stratigraphic units of the Paraná Basin. (B) Field photograph of the Várzea do Agudo site. (C) Stratigraphic column of the Várzea do Agudo site depicting its fossiliferous content distribution. (D) Life reconstruction of CAPPA/UFSM 0371 by Caio Fantini. (E) Tridimensional model of the partial cranium of CAPPA/UFSM 0371 in right lateral view. Abbreviations: cs, coarse-sandstone; Fm, formation; fs, fine-sandstone; g, gravel-sandstone; m, mudstone; ms, medium-sandstone. Silhouettes based on artwork by Caio Fantini and Felipe Elias. |
 |
| Skull and lower jaws of Isodapedon varzealis gen. et sp. nov. (CAPPA/UFSM 0371). (A) photographs, interpretative illustration and three-dimensional model from surface scan of the skull of CAPPA/UFSM 0371 in right lateral view. (B) Photographs, interpretative illustration and three-dimensional model from surface scan of the skull of CAPPA/UFSM 0371 in left lateral view. Abbreviations: a, angular; aoc, anguli oris crest; d, dentary; jug, jugal; max, maxilla; mf, mental foramen; pmx l, left premaxilla; pmx r, right premaxilla; sa, surangular; sp, splenial. Black arrow points anteriorly. |
 |
| Isodapedon varzealis gen. et sp. nov. craniomandibular elements. (A) Left skull in lateral view of Isodapedon varzealis gen. et sp. nov. (CAPPA/UFSM 0371) with emphasis on maxillary dentition area (occlusal view). (B) Left lower jaw in medial view with emphasis on lingual dentition area (oblique occlusal view). Abbreviations: dg, diagonal gaps; lbt, labial teeth; lgt, lingual teeth; ls, longitudinal sulcus; sg, shallow groove; sms, short medial shelf. Black arrow points anteriorly. |
Archosauromorpha
Rhynchosauria
Rhynchosauridae
Hyperodapedontinae
Isodapedon gen. nov.
Type and only species: Isodapedon varzealis sp. nov.
Etymology. The genus name is derived from the Ancient Greek ἴσος (ísos), meaning ‘equal’ or ‘the same’, as a reference to the equally wide tooth-bearing areas of the maxilla.
Isodapedon varzealis sp. nov.
Etymology. The species name refers to the locality of ‘Várzea do Agudo’ in which the specimen was collected.
Diagnosis. The holotype of Isodapedon varzealis is distinguished from all other known rhynchosaurids by the following unique combination of morphological traits (* asterisk denotes autapomorphies): maxilla divided into two tooth-bearing areas by a single longitudinal sulcus; equally wide maxillary lateral and medial tooth-bearing areas; same number (three) of longitudinal rows of teeth in both maxillary lateral and medial tooth-bearing areas; absence of lingual teeth in the medial surface of the maxilla; straight posterior margin of the parietal; sharp sagittal crest extending up to the posterior margin of the parietal; short and rounded ventral process of the squamosal; distinct posterior process in the squamosal; no contact between the lacrimal and palatine; ‘blunt’ and greatly reduced posteroventral process of the dentary; single dorsal blade in the dentary; medial shelf in the medial surface of the posterior portion of the dentary that does not reach half the length of the bone*; medial shelf separated from the dorsal blade of the dentary by a shallow groove; dorsal margin of the posterior portion of the dorsal blade extending markedly further dorsally than the posterior portion of the medial shelf at the level of the posteriormost lingual tooth; and single well-defined row of small, dorsally projected, closely packed lingual teeth in the dentary.
 |
| Artistic representation of a Late Triassic landscape of southern Brazil depicting individuals of Isodapedon varzealis gen. et sp. nov. in the foreground and a proterochampsid in the background. Artwork by Caio Fantini. |
Jeung Hee Schiefelbein; Maurício Silva Garcia; Mariana Doering and Rodrigo Temp Müller. 2026. A New hyperodapedontine rhynchosaur from a Cynodont-dominated Site (Upper Triassic) of southern Brazil. R Soc Open Sci. 13(4); 260176. DOI: doi.org/10.1098/rsos.260176 [15 Apr 2026]
