Overview photographs of long bone thin sections in normal light of Pistosaurus and Plesiosaurus . A-D, diaphyseal sections; A-B, Pistosaurus humeri (A, SIPB R 46, B, SMNS 84825); C, Pistosaurus femur (SIPB R 74); D, Plesiosaurus humerus SIPB R 90). In all images, ventral is at the bottom. The Pistosaurus humeri in A and B have a thick cortex and a very small medullary region unlike the Pistosaurus femur in C, which resembles the nothosaur femur in Figure 4C. The Plesiosaurus femur in D exhibits incipient osteoporosis, typical for pelagically adapted marine tetrapods.