New taxa of giant caimans from the southernmost hyperdiverse wetlands of the South American late Miocene

Here we present a comparative anatomical study of large late Miocene alligatorids of Argentina (Ituzaingó Formation), in which we analyse their taxonomy, morphological disparity, and phylogenetic relationships. ‘<i>Caiman lutescens</i>’ and <i>Caiman gasparinae</i> are two giant Miocene Argentinean caimanines that are assigned to the genus <i>Caiman.</i> ‘<i>Caiman lutescens</i>’ was originally described based on the large size of several isolated cranial and postcranial elements. In this study we consider that the lectotype of ‘<i>C. lutescens</i>’, an articulated left premaxilla and maxilla (MACN-Pv 5416), is morphologically indistinguishable from rostral morphotypes present in other jacarean caimanines, like <i>Caiman latirostris</i> and <i>Caiman wannlangstoni</i>, and therefore ‘<i>C. lutescens</i>’ is here considered a <i>nomen dubium</i> while MACN-Pv 5416 is an indeterminate Jacarea. A partial skull table, MACN-Pv 13551, was originally and historically referred to ‘<i>C. lutescens</i>’, and even wrongly considered its holotype, but it is here redescribed and reinterpreted as the holotype of a new genus and species. Additionally, after the comparative anatomical study of the holotype of <i>C. gasparinae</i> <b>(</b>MLP-Pv 73-IV-15-1), we conclude that it shows a distinctive combination of skull morphological features that allows it to be distinguished from other caimanines, including extant <i>Caiman</i> species. This situation and the results of the phylogenetic analyses lead us to erect a new genus for this species, which results in a new nomenclatorial combination. These new results support the idea that the alligatorid assemblages of the South American late Miocene wetlands were highly diverse at high latitudes (<i>c</i>. 30–35°S), as evidenced by the taxonomic diversity and morphological disparity present in the crocodylian assemblage of the Ituzaingó Formation in Paraná. The close relationship between the two new taxa + <i>Mourasuchus</i> spp. with <i>Purussaurus</i> spp. recovered in the present study reinstates the question of how to define the <i>Caiman</i> genus, as well as when and where it originated. http://zoobank.org/urn:lsid:zoobank.org:pub:6096F826-7CCA-4795-B4CF-5AFF87D6EBCC