Saurischia

Aureliano, Tito, Ghilardi, Aline M., Fernandes, Marcelo A. & Ricardi-Branco, Fresia S., 2024, Air sac attachments or tendon scars: the distinction between soft tissue traces in archosaur bone, Zoological Journal of the Linnean Society 202 (1), pp. 1-8 : 3-4

Saurischia : Sauropoda: Titanosauria:

Arrudatitan maximus Santucci & Arruda-Campos, 2008 (Silva Junior, Martinelli, Iori, Marinho, Hechenleitner & Langer, 2022).

MPMA 12-0001-97-1024, dorsal vertebra ( Santucci & de Arruda-Campos, 2011; Silva Junior et al., 2022). See Supporting Information, Figs S1–S 3 .

The vertebra is considerably fragmented. Several parts are badly preserved and have collapsed during early burial or diagenesis, probably due to the highly pneumatized nature of the bone. There are some anatomical observations missing in the literature worth mentioning below.

The anterior-most portion of the neural arch is slightly eroded in lateral view and compromised in proximal view (> 50% loss of material). Only the left lateral portion has been preserved. Foramina are absent throughout the preserved volume but the sedimentary matrix still covers most fossae. The diapophysis has collapsed but can be identified. Part of the vertebral centrum is preserved but has been mistakenly identified as the prezygapophysis by Santucci & de Arruda-Campos (2011). The prezygapophysis has been deformed by a smooth proximal twist. The prezygapophysis has a subcircular articulation, sizeable and convex. The parapophysis is dislocated anteriorly towards the centrum and bears a thick and flat articular facet that connects to the latter. It is surrounded by two deep fossae (cpaf and prpadf) and is connected to three laminae (cprl, prpl and acdl). A further two laminae (pcpl and pcdl) connect to the mid-posterior portion of the centrum. The fossae prpadf, cpaf and pocdf are deep, but pacdf is subtle and partially covered by collapsed bone. The neural spine is more abraded than the region between the diapophysis and the centrum. However, traces of collapsed laminae (spdl and sprl) and two fossae (prsdf and spof) can be detected. The dorsal vertebra MPMA 12-0001-97-1024 shows an advanced degree of complexity and leads us to conclude it was placed more posteriorly than originally proposed by Santucci & de Arruda-Campos (2011). The CT scan did not reveal much about the internal structures due to diagenetic artefacts (see Supporting Information, Figs. S1–S 3 ).

Finally, cross-sections of the laminae (pcdl and acdl) and the core section of the prezygapophysis reveal lamellar bone throughout the cortex. There are neither trabeculae nor pneumosteum. There are many traces of Sharpey’s fibres, which are expected in an area of complex morphology with many muscles and tendons ( Fig. 2 ).

Figures

Figure 1. Lamellar bone fibres in an anhanguerid pterosaur ulna (DGEO-CTG-UFPE 7516; A-F) and in a spinosaurine theropod tibia (LPP-PV-0042; G-L). Note that these fibres are only visible at high magnifications (100×; arrowheads). Silhouettes in A and G indicate sampled elements (not to scale; art by Felipe A. Elias). All polarized light. Crossed nicols in A-E and G-L. Parallel nicols in F. Compensator in A-D, G-I and L. The relative angle to the cortical surface is approximately 80° in A, B; 340° in C; 290° in D-F; 120° in G-L.Scale bar in A, H = 250 µm; in B, I = 50 µm; G = 500 µm; in C-F, J-L = 10 µm.

Figure 2. Sharpey’s fibres in a dorsal vertebra of Arrudatitan (MPMA 12-0001-97-1024; A-F) and in a spinosaurine theropod tibia (LPP-PV-0042; G-I). Note that these fibres are visible at low magnifications (5×; arrowheads).G, H show a cross pattern of Sharpey’s fibres. Silhouettes in A and G indicate sampled elements (not to scale; art by Felipe A.Elias). All polarized light. Crossed nicols in A-F. Parallel nicols in. Compensator in G, H. The relative angle to the bone surface is approximately 150° in A-C; 90° in D; 70° in E; 120° in F; 90° in G-I. Scale bar in A = 300 µm; in D, I = 250 µm; in B, C, E, F = 100 µm; in G, H = 500 µm.

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.