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. 2015 Jul 15;2(7):150090.
doi: 10.1098/rsos.150090. eCollection 2015 Jul.

Tiarajudens eccentricus and Anomocephalus africanus, two bizarre anomodonts (Synapsida, Therapsida) with dental occlusion from the Permian of Gondwana

Juan Carlos Cisneros  1 , Fernando Abdala  2 , Tea Jashashvili  2 , Ana de Oliveira Bueno  3 , Paula Dentzien-Dias  4
Affiliations

Tiarajudens eccentricus and Anomocephalus africanus, two bizarre anomodonts (Synapsida, Therapsida) with dental occlusion from the Permian of Gondwana

Juan Carlos Cisneros et al. R Soc Open Sci. .

Abstract

Anomodontia was a highly successful tetrapod clade during the Permian and the Triassic. New morphological information regarding two bizarre basal anomodonts is provided and their palaeoecological significance is explored. The osteology of the recently discovered Tiarajudens eccentricus Cisneros et al. 2011, from the Brazilian Permian, is described in detail. The taxon exhibits unusual postcranial features, including the presence of gastralia. Additional preparation and computed tomography scans of the holotype of Anomocephalus africanus Modesto et al. 1999 discovered in the Karoo Basin of South Africa allow a reappraisal of this genus. Anomocephalus is similar to Tiarajudens with regard to several traits, including a battery of large, transversally expanded, palatal teeth. Molariform teeth are present in the mandible of the African taxon, providing additional insight into the function of the earliest tooth-occlusion mechanism known in therapsids. At least two waves of tooth replacement can be recognized in the palate of Anomocephalus. The outsized, blade-like caniniforms of the herbivorous Tiarajudens allow several non-exclusive ecological interpretations, among which we favour intraspecific display or combat. This behaviour was an alternative to the head-butting practised by the contemporary dinocephalians. Combat specializations that are considered typical of Cenozoic herbivores likely evolved during the Middle Permian, at the time the first communities with diverse, abundant tetrapod herbivores were being assembled.

Keywords: Anomodontia; Permian; Therapsida; agonistic behaviour; dental occlusion; herbivory.

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Figures

Figure 1.
Figure 1.
(a) Anomocephalus africanus (BP-1-5582) from the Middle Permian of South Africa, cranium, right lateral view. (b) Tiarajudens eccentricus (UFRGS PV393P), from the Middle Permian of Brazil, cranium, left lateral view.
Figure 2.
Figure 2.
Skeleton of T. eccentricus. (a) Sandstone blocks containing articulated skeletal material. (b) Schematic drawing showing the identity of the preserved elements. (c) Skeletal reconstruction. as, astragalus; c, caniniform; ca, calcaneum; cl, clavicle; co, coracoid; d, digits; ga, gastralia; h, humerus; m, mandible; mt, metatarsals; ra, radius; sk, skull; ti, tibia; ta, tarsal.
Figure 3.
Figure 3.
Provenance of T. eccentricus. (a) Location of the Tiarajú District in Rio Grande do Sul State, southern Brazil. (b) Sedimentological log of the type locality.
Figure 4.
Figure 4.
Cranium of T. eccentricus, technical drawings. (a) Left medial view. (b) Left lateral view. i–iv, tooth positions; an, angular; ar, articular; c, caniniform; dt, disarticulated teeth; ect, ectopterygoid; j, jugal; l, left; la, lacrimal; lf, left frontal; ln, left nasal; lpm, left premaxilar; lt, lower jaw tooth; mx, maxilla; pc, precaniniform; po, postorbital; pof, postfrontal; prf, prefrontal; pt, pterygoid; q, quadrate; qj, quadratojugal; r, right; rf, right frontal; rn, right nasal; rpm, right premaxilar; sa, surangular; sc, scleral ossicles; sm, septomaxilla; sq, squamosal.
Figure 5.
Figure 5.
Cranium and dentition of T. eccentricus. (a) Cranium, left lateral view. (b) Cranium, parasagittal section (CT scan), right view. (c) Cranium, transversal section (CT scan) at the level of the caniniform, posterior view. (d) Ventral view of the base of the left caniniform (exposed due to a fracture) and a precaniniform, anterior to the left. (e) Incisiform teeth, medial view. (f) Left palatal teeth, occlusal view, anterior to the right. i–iv, tooth positions; dt, disarticulated teeth; l, left; pc, precaniniform; r, right; rt, replacement tooth.
Figure 6.
Figure 6.
Isolated molariforms of T. eccentricus, probably right palatal teeth, including a replacement element. (a,e) ?Distal view. (b) ?Labial view. (c,g) ?Medial view. (d) ?Lingual view. (f) Old tooth, occlusal view. ot, old tooth; rt, replacement tooth.
Figure 7.
Figure 7.
Left pectoral girdle of T. eccentricus. (a, b, d–g) Scapulocoracoid. (a) Lateral view, and (b) medial view, stereo-pairs. (d) Lateral view, (e) medial view, (f) posterior view and (g) anterior view, drawings. Clavicle in (c) medial view, stereo-pair, and (h) medial view, drawing. co, coracoid; gc, glenoid cavity; lf, lateral fossa; mf, medial fossa; sc, scapula.
Figure 8.
Figure 8.
Left humerus of T. eccentricus. (a,b) Stereo-pairs in (a) dorsal and (b) ventral view. (c−f) Drawings in (c) medial, (d) lateral, (e) dorsal and (f) ventral views. dpc, deltopectoral crest; ec, ectepicondyle; ef, entepicondylar foramen; en, entepicondyle; f, fossa; r, ridge; rc, radial condyle; t, trochlea.
Figure 9.
Figure 9.
Left radius of T. eccentricus, stereo-pairs and drawings. (a,b) Posterior view, (e,f) anterior view, (c,d) lateral view and (g) medial view. pc, posterior crest; f, fossa; t, tuberosity.
Figure 10.
Figure 10.
Left ulna of T. eccentricus, stereo-pairs and drawings. (a,b) Lateral view, (c,d) anterior view, (e,f) medial view and (g) posterior view. aem, attachment of extensor muscle; afm, attachment of flexor muscles; c, crest; d, depression; f, fossa; lr, longitudinal ridge.
Figure 11.
Figure 11.
Left manus of T. eccentricus. (a) Photograph and (b) drawing of two digits. (c) Photograph and (d) drawing of a metacarpal and an unidentified bone found disarticulated. mca, metacarpal; ph, phalanx; uph, ungual phalanx; ?, unidentified bone.
Figure 12.
Figure 12.
Left tibia of T. eccentricus, stereo-pairs and drawings. (a,b) Lateral view, (c,d) anterior view, (e,f) medial view and (g) posterior view. cc, cnemial crest; d, depression; s, sulcus; t, tuberosity; uf, unidentified bone fragment.
Figure 13.
Figure 13.
Left foot of T. eccentricus. (a–d) Rock slabs showing foot elements in basal cross section. (a,b) Palmar view, (c,d) dorsal view. (e,f) X-ray images showing digits 1 (dorsal view) and 2 (medial view). (g,h) Three-dimensional renderings of foot reconstructed from X-ray images: (g) palmar and (h) dorsal views. as, astragalus; cal, calcaneum; dt, distal tarsal; mt, metatarsal; ph, phalanx; uph, ungual phalanx; I–V, digit number.
Figure 14.
Figure 14.
Left foot of T. eccentricus. (a) Proximal articular facets of the metatarsals. Metacarpal and phalanges of digit II in (b) dorsal and (c) lateral view. i–v metatarsal number; mt, metatarsal; ph1, first phalanx; ph2, second phalanx; uph, ungual phalanx.
Figure 15.
Figure 15.
Gastralia of (a) T. eccentricus, (b) A. africanus, (c) gorgonopsian from the Pristerognathus Assemblage Zone (SAM-PK-K 10585), (d) basal anomodont Galechirus, (e,f) basal dicynodont Eodicynodon (NMQR 2991).
Figure 16.
Figure 16.
Dentition of A. africanus. (a) Lateral view; (b) medial view; (c) drawing of the cranium; (d) CT scan of the cranium showing replacement teeth (arrows). an, angular; ar, articular; bo, basioccipital; de, dentary; ect, ectopterygoid; j, jugal; la, lacrimal; mx, maxilla; n, nasal; pc, precaniniform; pmx, premaxilla; po, postorbital; pra, prearticular; prf, prefrontal; q, quadrate; qj, quadratojugal; r, replacement tooth; sa, surangular; sc, sclerotic ossicle; T, upper tooth; t, lower tooth.
Figure 17.
Figure 17.
Cladistic analysis. Majority rule consensus from 15 most parsimonious trees (score 251) obtained on TNT [20]. Symmetric resampling support values (from 10 000 replicates, p=33) are provided before each node.
Figure 18.
Figure 18.
Artistic representation of two T. eccentricus individuals on agonistic behaviour in southern Brazil. Illustration by Voltaire Paes Neto.
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