Histological details of the humeral cortex of a growth series of the derived titanosaur <i>Alamosaurus sanjuanensis</i> from the Upper Cretaceous Javelina Formation, Texas, USA.

<p>The bones tissues in this growth series of the large titanosaur <i>Alamosaurus</i> are identical to those of large diplodocoid and basal macronarian sauropods. The plane of sectioning is perpendicular to bone long axis, and the direction of bone apposition is towards the top of the images. <b>A</b>) Typical laminar fibrolamellar bone tissue of a young individual (HOS 4; TMM 45600-1; 460 mm long, 31% max. size) in normal light. Note the absence of LAGs but the subtle modulations in vascularization (arrows). <b>B</b>) Same view in polarized light. Note the dominance of the scaffolding of woven bone in the fibrolamellar complex. <b>C</b>) Typical laminar fibrolamellar bone tissue of a young adult individual (HOS 7; TMM 43600-2; 915 mm long, 61% max. size). Note the strictly circumferential arrangement of the vascular canals. <b>D</b>) Same view in polarized light. Note the primary osteons in the scaffolding of woven bone. <b>E</b>) Incipient <u>EFS</u> in the outermost cortex and scattered secondary osteons in laminar fibrolamellar bone of a fully grown individual (HOS 12; TMM uncat.; 1350 mm long, 90% max. size). <b>F</b>) Same view in polarized light. Note the highly birefringent parallel-fibered bone of the EFS and the woven to parallel-fibered scaffolding of the fibrolamellar bone in the deeper cortex, between the secondary osteons. The high amount of parallel-fibered bone in the scaffolding of the fibrolamellar bone is typical in late ontogenetic stages in diplodocoid and basal macronarian dinosaurs <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036907#pone.0036907-Klein1" target="_blank">[6]</a> as well as for <i>Alamosaurus</i> but occurs already in early ontogenetic stages in <i>Ampelosaurus</i>.