Fig. 1. Mesosaurid parareptile Stereosternum tumidum Cope, 1886 in Tooth microstructure of the Early Permian aquatic predator Stereosternum tumidum

Fig. 1. Mesosaurid parareptile Stereosternum tumidum Cope, 1886 from Passo do São Borja outcrop, Irati Formation, Lower Permian of the Paraná Basin. A. UFRGS-PV-0378-P. Lateral view of the partial left dentary (A 1), before abrasion. The rostral portion is to the left. Enlarged partial view (A 2), highlighting some of the pores of the anterior region of the dentary. B. UFRGS-PV-0378-P. Partial abrasion of specimen (B 1), showing the alternation of empty and tooth-bearing sockets Arrows indicate two consecutive empty sockets that break the alternate pattern. The partially exposed meckelian cavity is also indicated. Detail (B 2), some anchorage trabeculae are indicated. Thin section of the anterior tooth from B2 (B 3), shown in oblique cut. Dashed line indicates the boundary between alveolar bone and dentary bone. Two trabeculae are also pointed. At the base of the tooth, some canalicles are indicated, connecting the pulp cavity with the dentary bone. Enlarged view (B 4) of the alveolar wall indicated in B3. Large white arrows point to the boundary between the alveolar bone and the dentary bone. The space between the alveolar bone and the cementum layer that covers the tooth base is indicated between dashed lines, and was supposedly filled in life with soft periodontal ligament. Abbreviations: ab, alveolar bone; bc, bone cell lacunae; ce, cementum; db, dentary bone; dw, dentine wall; es, empty tooth socket; mc, meckelian channel; pl, inferred location of periodontal ligament; tr, anchorage trabecula.