Fig 1.
Chrono- and biostratigraphy of Triassic units with vertebrate assemblages zones (AZ) from southern Brazil.
Modified from [29, 48, 49]. The ages of the column follow Gradstein et al., [50]. The radiometric dating of 236.1, 231.4 and 225.9 Ma correspond to the first half of the Chañares Formation [51], the base of the Ischigualasto Formation, and the base of Los Colorados Formation [6], respectively. Abbreviations: Ind., Induan; Ole., Olenekian; Se., sequence.
Table 1.
List of cynodonts and specimens.
Specimens for each taxon that was described, used for comparisons and/or for check character-states in data matrix.
Fig 2.
(A) Map showing the Middle to Upper Triassic outcrops (in light red colour) in Candelária and Santa Cruz do Sul municipalities, state of Rio Grande do Sul (RS), southern Brazil (based partially on [80]). The two specimens (MCT-1716-R and MCT-1717-R) of Bonacynodon come from the Pinheiros region, about 12 km south of Candelária city, and the arrow indicates the site where the specimen (UFRGS-PV-1121-T) of Santacruzgnathus was discovered from the Santacruzodon AZ. Catalog cards of MCT-1716-R (holotype) from “Sanga do Janguta” (B) and MCT-1717-R (referred specimen) from “Sanga do Forno” (C) of Bonacynodon schultzi.
Fig 3.
Bonacynodon schultzi, holotype MCT-1716-R.
Partial skull and lower jaws, with the snout and right lower jaw positioned in lateral view. Dark grey indicates broken areas and soft grey indicates matrix.
Fig 4.
Bonacynodon schultzi, holotype MCT-1716-R.
Partial skull and lower jaws, with the secondary palate horizontally positioned, in ventral view. Dark grey indicates broken areas and soft grey indicates matrix.
Fig 5.
Bonacynodon schultzi, holotype MCT-1716-R.
Detail of the basicranial region in ventral view with interpretative line drawing.
Fig 6.
Bonacynodon schultzi, holotype MCT-1716-R.
Detail of the left postdentary bones in medial view with interpretative line drawing.
Fig 7.
Bonacynodon schultzi, holotype MCT-1716-R.
Detail of the right upper dentition in lateral view. Dark grey indicates broken areas and soft grey indicates matrix.
Fig 8.
Bonacynodon schultzi, holotype MCT-1716-R.
Detail of right upper canine in lateral labial view (A). Detail of incisors in anterolateral view (B). Detail of the only lower postcanines of the holotype, two anterior-middle left teeth in labial view (C).
Fig 9.
Bonacynodon schultzi, referred specimen MCT-1717-R.
Partial skull and lower jaws in right laterodorsal view (A) and detail of the right upper canine (B).
Fig 10.
Bonacynodon schultzi, referred specimen MCT-1717-R.
Partial skull and lower jaws in left lateral view. Dark grey indicates broken areas and soft gray indicates matrix.
Fig 11.
Bonacynodon schultzi, referred specimen MCT-1717-R.
Detail of upper canine and postcanine dentition in labial view. Dark grey indicates broken areas and soft grey indicates matrix.
Fig 12.
Skull reconstruction and upper canines morphologies.
(A) Reconstruction of the skull of Bonacynodon schultzi, in lateral view, based on both known specimens and its close relative Probainognathus jenseni [41, 63]. Comparisons of upper canines in labial view. (B) right canine of Bonacynodon (MCT-1716-R), (C) left canine of Bonacynodon (MCT-1717-R), (D) left canine of Probainognathus (PVL 4673), (E) apical half of right canine of Trucidocynodon (UFRGS-PV-1051-T), and (F) right canine of Chiniquodon (PVL 4167). Not to scale.
Fig 13.
Details of the postcanine dentition of Probainognathus jenseni from Chañares Formation, Ischigualasto-Villa Unión Basin, western Argentina.
Upper and lower postcanines (A) and detail of the lingual aspect of the upper postcanines (B) (picture taken in ventrolingual view) of PVL 4673. Right lower jaw in labial view (C) and detail of pc5 and pc6 in labial (D) and lingual (E) views of PVL 4445. Left lower pc1and pc2 in lingual view (F) of PVL 4446.
Fig 14.
Selected postcanines of probainognathians used for comparisons.
A, B, Chiniquodon theotonicus, anterior right upper (A) and posterior left lower (B) postcanines in labial view (PVL 4444). C, D, Trucidocynodon riograndensis, posterior right upper (C) and left lower postcanines in labial view (UFRGS-PV-1051-T). E, F, Prozostrodon brasiliensis, posterior left upper (E) and lower (F) postcanines in labial view (UFRGS-PV-0248-T). G, H, Irajatherium hernandezi, left upper (G, UFRGS-PV-1175-T) and posterior right lower (H, UFRGS-PV-1029-T) in labial view. I, Riograndia guaibensis, left lower postcanines in lingual view (UFRGS-PV-0833T). J, K, Botucaraitherium belarminoi, left upper postcanine in labial view (J) and posterior left postcanine in lingual view (K) (MMACR-PV-003-T). L, Brasilodon quadrangularis, right upper postcanines in labial view (UFRGS-PV-0611T). M, Brasilitherium riograndensis, left lower postcanines in labial view (UFRGS-PV-0603T). The arrows indicate mesial side. Scale bar equals 2 mm.
Fig 15.
Restoration of Bonacynodon schultzi in life by Jorge Blanco.
Fig 16.
Santacruzgnathus abdalai, holotype UFRGS-PV-1121-T.
Partial right lower jaw with complete crown of last postcanine in lateral (A) and medial (B) views. Gray indicates broken areas.
Fig 17.
Santacruzgnathus abdalai, holotype UFRGS-PV-1121-T.
Detail of last lower postcanine in labial (A), lingual (B) and occlusal (C) views. Gray indicates broken areas.
Fig 18.
Strict consensus tree (L = 450, Ci = 47, Ri = 77) of four most parsimonious trees depicting the phylogenetic position of Bonacynodon schultzi. Bremer support is indicated at each node.
Fig 19.
Protheriodon estudianti (Holotype UFRGS-PV-0962-T).
Skull in right lateral (A), left lateral (B), dorsal (C), ventral (D) views. Dark grey indicates most broken areas and soft grey indicates matrix.
Fig 20.
Protheriodon estudianti (Holotype UFRGS-PV-0962-T).
Details of canines and incisors in right lateral (A) and anteroventral (B) views, middle left upper postcanine (C) and left posterior lower postcanines (D) in labial view. Dark grey indicates broken areas and soft grey indicates matrix. Arrow indicates mesial direction.