Saurischia

Figure 3. Pneumosteum in saurischian dinosaurs. A-C, a megaraptoran theropod caudal vertebra (MPMA 08-003-94).D-F, a cervical vertebra of the lithostrotian titanosaur Uberabatitan (CPPLIP-1024). G-I, a dorsal vertebra of the saltasaurid titanosaur Ibirania (LPP-PV-0200). Pneumosteum is distinguished from regular lamellar bone due to the presence of an array of tiny asbestiform densely packed fibres (usually shorter than 60 µm; arrowheads).These feature low optical relief and undulose extinction. Silhouettes in A, D and G indicate sampled elements (not to scale; art by Felipe A. Elias). All polarized light. Crossed nicols in A-E and G-I. Parallel nicols in F. Compensator in A-D, G-I, and L. The relative angle to the bone surface is approximately 320° in A-B; 220° in C-D; 105° in E-F; 290° in G; 80° in H-I.Scale bar in A, D = 250 μm; in C, E = 100 μm; in B, F, H, I = 50 μm; in G = 200 μm.