Lewisuchus

Another Chañares archosaur was described by Andrea Arcucci in 1987. This archosaur encompassed four specimens stored at the Miguel Lillo Institute (PVL) of the University of Tucuman, the PULR, and the Museo Argentino de Ciencias Naturales (MACN). Arcucci named a new archosaur genus based on these specimens: Pseudolagosuchus major. It was originally considered a close relative of its namesake, the small dinosauriform Lagosuchus. The holotype of Pseudolagosuchus, PVL 4629, included most of a left hindlimb and pelvis as well as a fragmentary ankle, vertebrae, and ribs. Other specimens included PVL 3454 (fragments of the hip and hindlimb), MACN 18954 (vertebrae and portions of the hindlimb and ankle), and PULR 53 (tail vertebrae and bones from the ankle region).[9] A 1996 study on dinosaur origins by Fernando Novas[10] also placed a well-preserved femur and tibia (erroneously labelled UPLR 53) within the genus, and this may also be the case with PVL 3455, an indeterminate partial skeleton with some similarities to Arcucci's original material.[8]

Despite not sharing much overlapping material, some paleontologists have proposed that Pseudolagosuchus major represented the same species of animal as Lewisuchus admixtus. If this is demonstrated to be the case, the name Lewisuchus would have priority over Pseudolagosuchus due to having been named earlier. Arcucci argued towards synonymizing the two as early as 1997. A 2010 study in the Journal Nature by Nesbitt et al. also made a case for their synonymy, as they were approximately the same size, came from the same locality and strata, and both were found to be basal members of the recently named family Silesauridae.[11] Many other studies supported these arguments, sometimes even scoring the two as a single taxon in their phylogenetic analyses.[12] Several hindlimb, hip, and vertebral fossils (PVL 3456, PULR-V 112 and PULR-V 113) have additionally been referred to Lewisuchus based on their similarity to Pseudolagosuchus remains.[8][13] However, Bittencourt et al.'s 2014 redescription of the Lewisuchus holotype refrained from synonymizing the two due to a lack of data, with the only overlapping material being the tibia and a few cervical (neck) vertebrae. No unambiguous characteristics were shared between these scraps, and one tibia referred to Pseudolagosuchus (Novas's 'UPLR 53') seemed to have a curvature different from that of Lewisuchus's holotype.[8]

A new specimen of Lewisuchus discovered in 2013 was described by Martin Ezcurra et al. in 2019, helping to settle the synonymy debate. This new specimen, CRILAR-Pv 552, was a partial skeleton incorporating parts of the skeleton previously only known in either Lewisuchus (such as the skull) or in Pseudolagosuchus (such as the hip and hindlimbs). It also provided details of the premaxilla, inner ear, and lower forelimbs, which were not preserved in any previous remains. The individual bones of CRILAR-Pv 552 were basically identical to their counterparts in Lewisuchus and Pseudolagosuchus specimens, providing irrefutable evidence that Pseudolagosuchus referred to the same species of reptile as Lewisuchus, and establishing Lewisuchus admixtus as the valid name for all fossils previously referenced with either name.[14]