Family CHARACIDAE sensu Mirande, 2019 Genus and species indeterminate REFERRED MATERIAL. — MD-FM-19-03, complete isolated right premaxilla (Fig. 1 A-C); and MD-FM-19-04, incomplete left maxilla lacking portion of the alveolar ramus (Fig. 1 D-F). DESCRIPTION Specimens were found disarticulated and isolated, and thus, it is uncertain if they belonged to the same individuals. Premaxilla The premaxilla is subtriangular in contour with a short and narrow ascending process that surpasses half the length of the premaxillary ramus. The ascending process is subtriangular in contour and has a nearly straight anterior margin. The external surface of the ascending process bears a shallow fossa, and the alveolar ramus has four large external fossae and irregularly disposed smaller pits. In lateral view, near the dorsal margin of the premaxilla, a well-defined and delimited groove extends along the bone. This groove runs subparallel to the margin of the premaxilla and extends nearly to the mid-length of the ascending process. The medial surface of the ascending process has a cupshaped articular surface for a ligamentous articulation with the mesethmoid, that differs from the interdigitating articulation exhibited by members of the Agoniatidae, Bryconidae, and Chalceidae (Mirande 2010, 2019). There are several crypts for the formation of replacement teeth. The posterior end of the premaxilla has a concave notch for articulation with the maxilla, and lacks any sign of a posterior pedicle, as occurs in the Alestidae (Zanata & Vari 2005). In occlusal view, there are two main tooth rows, each one having four tooth positions. The positions of the inner row, except for the second tooth, are smaller than those of the outer series. The outer row elements are subequal in size and shape, whereas those of the inner row are dissimilar to each other. There is no evidence of teeth outside the occlusal surface of the premaxilla. Maxilla This is a long element with an acute anterior process. The base of a single, broad tooth is preserved at the ventral margin of the bone. The dorsal and ventral margins gradually diverge along the preserved portion of bone. The dorsal margin shows the anterior attachment site of the ligamentum primordiale as a small projection. The posteriormost portion of the maxilla is not preserved. In medial view, there is a single small dorsal tubule for the passage of blood vessels.

Published as part of Bogan, Sergio, Agnolin, Federico & Mirande, Juan Marcos, 2021, Fossil record of a Characiform in the Monte Hermoso Formation (lower Pliocene), Buenos Aires, Argentina. Palaeobiogeographical implications, pp. 49-55 in Comptes Rendus Palevol 20 (4) on pages 50-51, DOI: 10.5852/cr-palevol2021v20a4, http://zenodo.org/record/4492292