Lepisosteoid-type fish scales in the Barremian-Aptian (Lower Cretaceous) of the Sanfranciscana Basin, Southeastern Brazil

•We describe lepisosteoid scales from the Barremian-Aptian of Sanfransciscana Basin.•The scales are similar to those commonly referred to as Lepidotes in Brazil.•The microanatomy suggests affinities with ginglymodians or aspidorhynchids.•Scale-based identification of early neopterygians must be seen with caution.

Lepisosteoid-type scales are described in detail for the first time from the Barremian-Aptian (Lower Cretaceous) Quiricó Formation of the Sanfranciscana Basin, Southeastern Brazil. The specimens studied herein have been recovered from a new outcrop in northern Minas Gerais state and comprise a few nearly complete posterior scales and hundreds of scale fragments extracted from the sedimentary matrix. The scales are rhombic and preserve both the ganoine and the basal plate. The ganoine layer is thin, pierced by foramina and ornamented by microtubercles, showing the typical arrangement of superimposed sheets. The basal plate is composed by lamellar and woven bone, with flattened and isodiametric osteocytes, canaliculi of Williamson, and Sharpey's fibers. An EDS analysis suggests diagenetic alteration of the basal plate but not the ganoine layer. The morphology of the specimens is similar to that of early neopterygian fishes, including ginglymodians and aspidorhynchids. A less inclusive identification is hampered by the fragmentary condition of the material and the lack of specific diagnostic features in this type of scale. This can be also extended to some isolated scales commonly referred to Lepidotes recovered from several sedimentary basins in the Jurassic-Cretaceous of Brazil. The results add a new record of ganoid scales in the Sanfranciscana Basin, and highlight the importance of more complete specimens rather than isolated scales for a genus-level identification of early neopterygian fishes.

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