Table 1.
List of specimens used for comparisons.
Table 2.
Angles and indices of non-mammaliaform cynodonts.
TH, torsion of humeral shaft; ADC, angle of deltopectoral crest; LDC, length ratio of deltopectoral crest (Length of deltopectoral crest / Humeral length * 100); DW, width ratio of distal end (Distal end width / Humeral length). The angle TH was measured between the transversal axes of the proximal end (the axis “Lesser Tuberosity—Medial margin of the humeral head”) and the distal end (the axis “Ectepicondyle-Entepicondyle”), based on the photography of the humerus in proximal view. The angle ADC was measured between the deltopectoral crest and the transversal axis of the proximal end, based on the photography of the humerus in proximal view. The distal end width was measured between the two epicondyles, based on the photography of the humerus in anterior view.
Fig 1.
Localities and stratigraphic level with Brasilodon quadrangularis.
A, location map showing the Linha São Luis and Sesmaria do Pinhal sites, in Rio Grande do Sul state, southern Brazil; B, chrono- and biostratigraphy of Triassic units with vertebrate assemblage zones (AZ); C, compositive phylogenetic position of Brasilodon amongst Probainognathia (based on [6–7, 25]). Clade names: 1, Cynodontia; 2, Epicynodontia; 3, Cynognathia; 4, Gomphodontia; 5, Traversodontidae; 6, Probainognathia; 7, Prozostrodontia; 8, Ictidosauria; 9, Tritheledontidae; 10, Tritylodontidae: 11, Mammaliaformes. The ages (Ma) of the column follow Ogg et al. [78], chrono- and biostratigraphy were modified from Zerfass et al. [75] and Horn et al. [76], the age of Riograndia AZ was taken from Langer et al. [77].
Fig 2.
Vertebra and scapula of Brasilodon quadrangularis (UFRGS-PV-1043-T).
A, photography (1) and drawing (2) of a fragmented vertebra; B, photography of the possible dorsal part of the right scapula, in medial view; C, photography of the ventral part of the right scapula, in lateral view; D, photography of the glenoid, in distal view. Abbreviations: ac, acromion; ang, posterodorsal angle; ant.m, anterior scapular margin; cor, area of contact with the coracoid; gl, scapular glenoid facet; inf, infraspinous (supracoracoideus) fossa; pos, postzygapophysis; post.m, posterior scapular margin; pre, prezygapophysis. Scale bar = 2 mm.
Fig 3.
Photography (1) and drawing (2) of the left humerus of Brasilodon quadrangularis (UFRGS-PV-1043-T).
A, in anterior view; B, in lateral view; C, in posterior view; D, in medial view; E, in proximal view; F, in distal view. Abbreviations: b.gr, bicipital groove; cap, capitulum; d.c, deltopectoral crest; ect, ectepicondyle; ent, entepicondyle; ent.f, entepicondylar foramen; gr.tb, greater tubercle; h, humeral head; int.gr, intercondylar groove; l.tb, lesser tubercle; t.c, teres crest; tub.tm, tuberosity for the origin of the M. teres major; ul.c, ulnar condyle. Scale bar = 3 mm.
Fig 4.
Forearm of Brasilodon quadrangularis.
A, photography (1) and drawing (2) of the left radius (UFRGS-PV-1043-T), in medial view; B, photography (1) and drawing (2) of the right ulna (UFRGS-PV-1043-T), in medial view; C, photography of the right ulna (UFRGS-PV-0765-T), in posterior view; D, same material, in lateral view. Abbreviations: anc, anconeal process; f.rad, facet for the radial head; not, notch for the ulnar condyle; ol, olecranon. Scale bar = 2 mm.
Fig 5.
Photography and drawing of the left acetabulum of Brasilodon quadrangularis (UFRGS-PV-1043-T), in lateral view.
Abbreviations: acet, acetabulum; IL, ilium; IS, ischium; ob, obturator foramen; PU, pubis; pu.t, pubic tuberosity. Scale bar = 2 mm.
Fig 6.
Photography (1) and drawing (2) of the right femur of Brasilodon quadrangularis (UFRGS-PV-1043-T).
A, right femur in anterior view; B, right femur in lateral view; C, right femur in posterior view; D, right femur in medial view; E, right femur in proximal view; F, right femur in distal view. Abbreviations: add, fossa for hip adductor muscles; gr.tr, greater trochanter; h, femoral head; int.c, intertrochanteric crest; int.f, intertrochanteric fossa; lat.co, lateral condyle; l.tr, lesser trochanter; med.co, surface for the medial condyle; pop, popliteal fossa. Scale bar = 3 mm.
Fig 7.
Photography (1) and drawing (2) of the left tibia of Brasilodon quadrangularis (UFRGS-PV-1043-T).
A, in proximal view; B, in posteromedial view. Abbreviations: f.f, facet for the fibula; lat, facet for the lateral femoral condyle; med, facet for the medial femoral condyle; RIB, fragment of rib; TIB, tibia; t.tub, tibial tuberosity. Scale bar = 2 mm.
Fig 8.
Photography (1) and drawing (2) of the calcaneum and astragalus of Brasilodon quadrangularis (UFRGS-PV-1043-T).
A, left calcaneum, in dorsal view; B, left calcaneum, in plantar view; C, left astragalus, in dorsomedial view; D, left astragalus, in lateroplantar view. Abbreviations: f.cub, facet for the cuboid; f.na, facet for the navicular; f.pc, facet for the proximal facet of the calcaneum; f.st, facet for the sustentaculum tali; f.tib, facet for the tibia; MET, metatarsus; pc, proximal facet of the calcaneum for the astragal; psf, peroneal shelf; st, sustentaculum tali; su, sulcus of the astragalus (tarsal sinus); tbc, tuber calcis. Scale bar = 2 mm.
Fig 9.
Photography (1) and drawing (2) of the metapod and phalange of Brasilodon quadrangularis (UFRGS-PV-0765-T).
A, fragment of a metapod; B, intermediate phalange, in dorsal view. Scale bar = 2 mm.
Fig 10.
Main evolutionary patterns of the humeral structures through the probainognathian evolution.
The left humeri are represented in anterior and posterior view. 1, loss of ectepicondylar foramen; 2, hemispherical humeral head; 3, distinct and bony greater tubercle; 4, posteriorly flat trochlea (instead of bulbous ulnar condyle) with deep olecranon fossa; 5, less anteriorly expanded deltopectoral crest with narrow bicipital groove; 6, lesser tubercle smaller than the greater one; 7, posteriorly facing humeral head.. The ectepicondylar foramen is also absent in Boreogomphodon, Trucidocynodon and Probainognathus, but it is not represented in this phylogeny. The ulnar condyle is bulbous posteriorly in multituberculates, but it is not represented in this phylogeny. Abbreviations: b.gr, bicipital groove; cap, capitulum; delt, deltopectoral crest; ect.f, ectepicondylar foramen; gr.tb, greater tubercle; h, humeral head; l.tub, lesser tubercle; ol.f, olecranon fossa; tro, trochlea; ul, ulnar condyle.
Fig 11.
Main evolutionary patterns of the pelvic and femoral structures through the probainognathian evolution.
The right pelvis and femora are respectively represented in lateral and posterior view (with exception of the femur of Irajatherium, which is represented in anterior view*). 1, reduced postacetabular region of the iliac blade; 2, medial projection of the lesser trochanter; 3, distinct greater trochanter; 4, head set-off from the shaft by a short femoral neck; 5, confluent acetabular facets of the three bones composing the acetabulum; 6, hemispherical femoral head; 7, narrow intertrochanteric fossa instead of wide and circular; 8, well-marked intertrochanteric crest; 9, presence of the fovea capitis; 10, narrow distal end of the femur; 11, rim of the acetabulum without dorsal emargination; 12, femoral head strongly projected medially and long femoral neck. The hemispherical femoral head is only present in Tritylodon among Tritylodontidae, but it is not represented in this phylogeny. Abbreviations: ac, acetabulum; f.h, femoral head; gr.tr, greater trochanter; int.cr, intertrochanteric crest; int.f, intertrochanteric fossa; l.tr, lesser trochanter; ob, obturator foramen; post.ac, postacetabular region of the iliac blade; pre.ac, preacetabular region of the iliac blade; p.tb, pubic tuberosity.
Fig 12.
Materials previously cataloged as indeterminate brasilodontids.
A, specimen UFRGS-PV-0600-T; B, specimen UFRGS-PV-1361; C, specimen UFRGS-PV-0922-T; D, specimen UFRGS-PV-1042-T, representing a new morphotype of probainognathian. Abbreviations: ect, ectepicondylar foramen; ent, entepicondylar foramen; int.cr, intertrochanteric crest; UL, ulna. Scale bar = 2 mm.
Fig 13.
Paleoartistic reconstruction of Brasilodon quadrangularis (left) and Riograndia guaibensis (right), two abundant probainognathian cynodonts from the Riograndia AZ of the Candelária Sequence, Santa Maria Supersequence (Brazil), which exhibits different morphologies in skull, dentition and locomotor apparatus.
Made by Jorge Blanco.