The history, importance and anatomy of the specimen that validated the giant Purussaurus brasiliensis Barbosa-Rodrigues 1892 (Crocodylia: Caimaninae).

The Solimões Formation is a southwest geological unit of the Brazilian Amazon, being well-known for the Cenozoic giant eusuchian fossils. Among the eight species of Crocodylia described for this formation, the alligatoroid Purussaurus brasiliensis is the best known worldwide due to its enormous size. The holotype was described in 1892 by Barbosa-Rodrigues, composed by a right hemimandible. Later, two other species were assigned to the genus, but the loss of the type specimen brought a series of doubts and discussions about genus and species validity. Here, we provide a historical reconstruction of the genus Purussaurus, especially with a new description of the specimen DGM 527-R, which was first described by L. I. Price. We also provide a review of Purussaurus brasiliensis as a valid species, highlighting the importance of the paleontologist Diogenes de Almeida Campos to the preservation, study availability and divulgation of the specimen. From the six mandibular features discussed, at least two are putative synapomorphies for the genus: the false ziphodont teeth and the thinning of the medial surface of the mandible posterior to the fourteen alveoli, while the lateral surface become laterally expanded from ninth alveoli to behind. The review of the other species of the genus was aggravated due to little sampling of photos and low quality of those contributions. Finally, the curatorial efforts initiated by Price and kept for decades by Campos turned possible the revision of DGM 527-R, an important specimen for understanding the paleobiology and evolution of the genus, and, consequently P. brasiliensis. Such importance was recognized here scientifically and by Campos when considered this specimen as the center-piece of the exhibition in honor of the centenary anniversary of Price.

Comparative anatomy of the clasper of the subfamily Potamotrygoninae (Chondrichthyes: Myliobatiformes).

Claspers of stingrays (Myliobatiformes) are poorly documented in comparison to claspers of skates, with our knowledge restricted mainly to external morphological characters and skeletal components included in descriptions of new species; more encompassing morphological comparative analyses are lacking. Concerning potamotrygonins, clasper morphology has been described for a handful of species, but without elucidating their variation and systematic potential. The present article analyzed clasper structures in all genera of the subfamily Potamotrygoninae (Potamotrygon, Paratrygon, Plesiotrygon, and Heliotrygon), which were compared to the clasper of Styracura and some dasyatid genera. Potamotrygon shows some morphometric variation among the species analyzed. Anatomically, we found variation mainly in the dorsal terminal 1 and accessory terminal 1 cartilages, which are considered diagnostic among potamotrygonin genera; external morphological structures did not present significant differences among potamotrygonins.

A new subfamily, Styracurinae, and new genus, Styracura, for Himantura schmardae (Werner, 1904) and Himantura pacifica (Beebe & Tee-Van, 1941) (Chondrichthyes: Myliobatiformes).

A new subfamily (Styracurinae, subfam. nov.) and genus (Styracura, gen. nov.) are erected for Trygon schmardae Werner, 1904 (type species) and Dasyatis pacificus Beebe & Tee-Van, 1941, species placed in Himantura Müller & Henle, 1837 since 1953 but which differ significantly from it and all dasyatid genera in many morphological features. Recent molecular phylogenetic hypotheses based on the entire protein-coding mitochondrial genome have recovered Styracura as the sister group of the Neotropical freshwater stingrays (Potamotrygonidae), agreeing with previous morphological and molecular phylogenies. The Styracurinae, subfam. nov., is therefore placed in the Potamotrygonidae to reflect the current phylogenetic view. Morphological characters of phylogenetic relevance of the dermal denticles, ventral lateral-line canals, hyoid arch, cranial musculature, and pectoral and pelvic girdles are discussed and compared to other stingrays, in particular to dasyatids and potamotrygonins (now ranked as a subfamily). Inferred derived characters of Styracura and potamotrygonins require homoplasy (they are absent from Paratrygon and Heliotrygon), and ventral lateral-line canal patterns and morphology of the scapular process and pelvic girdle generally reveal an affinity to different dasyatid genera, but one most likely based on plesiomorphies or independent evolution; Styracura is considered more closely related to potamotrygonins.