Figure 1
(Colour online) Selected bone elements of Araripemys barretoi specimens from Santana Group of the Araripe Basin before sectioning. A, Carapace (UFRPE 5302). B and C, Shell (MPSC R 010). D, Humerus associated with the ulna and radius (MPSC R 010). E, Distal portion of the humerus (MPSC R 010). F, Ulna and radius (MPSC R 010). G, Left pes (MPSC R 010). The dashed lines indicate the histological section planes. Scale bars represent 0.5 cm (e and g); and 1 cm (a, b, c, d and f).
Figure 2
(Colour online) Histological section of costal IV plate of Araripemys barretoi (UFRPE 5302) from Crato Formation, Lower Cretaceous. A, Microanatomical overview of the perpendicular section of the costal IV plate. B, Detail of the composition of the external cortex. C, Detail of the inner region with reduced vascular spaces. D–E, Cortical bone of the costal composed of parallel-fibred bone tissue interrupted by annuli. Images: Normal transmitted light. Abbreviations: Blue arrowhead, Annulus; ECO, External cortex; ICO, Internal cortex; IR, Inner region; LVC, Longitudinal vascular canal; and PFB, Parallel-fibred bone tissue. Scale bars represent 1 mm (a); 200 µm (b and d); and 5 µm (c and e).
Figure 3
(Colour online) Histological section of neural V plate of Araripemys barretoi (UFRPE 5302). A, Microanatomical overview of the perpendicular section of the neural V plate. B, The external cortex is composed of woven bone tissue. C, Detail of the external cortex and inner region of the neural plate. D, Remodelling process occurs at the interior region. Images: Normal transmitted light. Abbreviations: ECO, External cortex; ICO, Internal cortex; LB, Lamellar bone tissue; PFB, Parallel-fibred bone tissue; PO, Primary osteon; SO, Secondary osteon; and WB, Woven bone tissue. Scale bars represent 100 µm (a); and 20 µm (b–d).
Figure 4
(Colour online) Histological section of costal V plate of Araripemys barretoi (MPSC R 010) from Romualdo Formation, Lower Cretaceous. A, Microanatomical overview of the parallel section of the costal V plate. B, Centre of embryonic periosteal collar of the rib at the internal region. C and H, internal cortex composed of parallel-fibred bone tissue. D, Longitudinal vascular canals at the internal cortex. E, Anastomosed vascular canals are predominant at the external cortex. F, Microanatomical overview of the perpendicular section of the costal V plate. G, Growth marks are visible in the internal cortex. Images: Normal transmitted light. Abbreviations: AVC, Anastomosed vascular canal; CEPCR, Centre of embryonic periosteal collar of the rib; ECO, External cortex; ICO, Internal cortex; LVC, Longitudinal vascular canal; PFB, Parallel-fibred bone tissue; and White arrowhead, Line of arrested growth. Scale bars represent 300 µm (a); 100 µm (f) and 20 µm (b–e; g and h).
Figure 5
(Colour online) Histological section of peripheral plate of Araripemys barretoi (MPSC R 010). A, Microanatomical overview of the transverse section of the peripheral plate. B, External cortex with vascular canals opening up to the surface of the bone. C, Limit between the cancellous bone and internal cortex marked by a resorption line. D, Trabeculae forming the cancellous bone layer. E, Longitudinal vascular canals dominate in the external cortex. Images: Normal transmitted light. Abbreviations: AVC, Anastomosed vascular canal; Black arrowhead, Resorption line; CB, Cancellous bone; ECO, External cortex; ICO, Internal cortex; ITS, Inter-trabecular space; LVC, Longitudinal vascular canal; PFB, Parallel-fibred bone tissue; RC, Resorption cavity; and Tr, Trabecula. Scale bars represent 500 µm (a); and 20 µm (b–e).
Figure 6
(Colour online) Histological section of the humeral epiphysis of Araripemys barretoi (MPSC R 010). A, Overall view of an epiphyseal cross-section of the humerus. B, Cancellous bone is dominated by slender bone trabeculae and some secondary osteons. C, Close-up of B showing parallel-fibred cortex interrupted by LAGs. D, Detail of the transition between cortical and cancellous bone demarcated by a thin resorption line. E, Details of the thin lamellar trabeculae of the cancellous bone. Images: Normal transmitted light (a, b, c and e); and Cross-polarised light with lambda waveplate (d). Abbreviations: Black arrowhead, Resorption line; ITS, Inter-trabecular space; LB, Lamellar bone; SO, Secondary osteon; Tr, Trabecula; and White arrowhead, Line of arrested growth. Scale bars represent 1 mm (a); 100 µm (b and e); and 50 µm (c and d).
Figure 7
(Colour online) Histological section of the humeral metaphysis of Araripemys barretoi (MPSC R 010). A, Overall view of a metaphyseal cross-section of the humerus. B, Note the presence of Sharpey’s fibres that extend perpendicularly to the bone margins. C, LAGs interrupting parallel-fibred cortical bone. D, Poor vascularised parallel-fibred bone tissue of the periosteal cortex and highly vascularised inner cortex of primary osteons and primary vascular canals. E, Secondary bone remodelling in the perimedullary region. Images: Normal transmitted light. Abbreviations: ITS, Inter-trabecular space; LVC, Longitudinal vascular canal; PO, Primary osteon; PFB, Parallel-fibred bone tissue; RC, Resorption cavity; Shf, Sharpey’s fibres; SO, Secondary osteon; White arrowhead, Line of arrested growth. Scale bars represent 1 mm (a); 100 µm (b and d); and 50 µm (c and e).
Figure 8
(Colour online) Histological section of the ulna of Araripemys barretoi (MPSC R 010). A, Overall view of the cross-section of the ulna. B and C, Parallel-fibred cortex interrupted by cyclical growth marks. D, Inner cortex remodelled by secondary osteons and resorption cavities. Images: Normal transmitted light. Abbreviations: Blue arrowhead, Annulus; LVC, Longitudinal vascular canal; MC, Medullary cavity; PO, Primary osteon; RC, Resorption cavity; SO, Secondary osteon; and White arrowhead, Line of arrested growth. Scale bars represent 500 µm (a); and 5 µm (b–d).
Figure 9
(Colour online) Histological section of the radius of Araripemys barretoi (MPSC R 010). A, Overall view of the cross-section of the radius. B, Cortical bone interrupted by cyclical growth marks. C, Detail of B showing parallel-fibred primary cortex. D, The inner and middle cortex contains several growth marks. Images: Normal transmitted light. Abbreviations: Blue arrowhead, Annulus; LVC, Longitudinal vascular canal; MC, Medullary cavity; PFB, Parallel-fibred bone tissue; PO, Primary osteon; and White arrowhead, Line of arrested growth. Scale bars represent 500 µm (a); 200 µm (b); and 5 µm (c and d).
Figure 10
(Colour online) Histological section of left metatarsals of Araripemys barretoi (MPSC R 010). A, Overall view of cross-sections of the metatarsals. B, Detail of metatarsal I exhibiting thin cortical bone and trabecular bone filling the medullary region. C, Detail of metatarsal II showing the remodelling process in the perimedullary region. D, Detail of metatarsal III showing compacted coarse cancellous bone tissue in the innermost cortex. E, Detail of metatarsal IV displaying parallel-fibred bone tissue in the cortical region. Images: Normal transmitted light. Abbreviations: Black arrowhead, Resorption line; CCCB, Compacted coarse cancellous bone; ITS, Inter-trabecular space; PFB, Parallel-fibred bone tissue; SO, Secondary osteon; and Tr, Trabecula. Scale bars represent 500 µm (a); and 50 µm (b–d).