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Histovariability in bones of two pterodactyloid pterosaurs from the Santana Formation, Araripe Basin, Brazil: preliminary results

Abstract Thin sections of pterosaur bones have not been extensively studied so far. Until now mainly isolated bones were the subject of this type of analysis. Here we present preliminary results of the histological analysis of two pterodactyloid pterosaurs from the Romualdo and Crato Members of the Santana Formation. The first specimen (Museu Nacional, MN 4809-V) comprises both wings (from humerus to the third phalanx of the fourth digit) and one hindlimb (tibia, fibula and pes). The second (MN 6527-V) consists of a partial skeleton with the incomplete left wing (humerus, radius, ulna, carpals, pteroid, wing metacarpal, two phalanges of the fourth digit) and fragments of one hindlimb (complete tibia and proximal articulation of the femur). Thin sections of the diaphyseal portion of each bone were ground in transverse, longitudinal and oblique orientation and the histological structures were compared. The following features can vary in the first observed specimen (MN 4809-V): presence of primary and secondary tissues in the cortex; absence or presence and position of lines of arrested growth; resorption of primary structures. These variations in different bones of the same individual represent differential growth rates. The second specimen (MN 6527-V) is well vascularized and has fibro-lamellar bone indicative of rapid growth in the thin section of the radius, ulna and first phalanx of the fourth digit. This last feature is very similar to the condition observed in most living birds.