Large archosaurs from the early part of the archosaur radiation are exceedingly rare and with few exceptions, most of these remains consist of fragmentary postcrania. We redescribe the fragmentary skull of Luperosuchus fractus from the early Middle—Late Triassic Chañares Formation of Argentina, assign newly discovered fragments from the original excavation to the same individual, and analyze its phylogenetic affinities. The dorsally convex and mediolaterally compressed anterior portion of the nasal (= ‘Roman-nose’), convex and circular knob on the dorsolateral margin of the postorbital, and a long anterior process of the prefrontal that fails to extend to the anterior end of the frontal are considered autapomorphies of Luperosuchus. The elongated gap between the nasal and maxilla is likely an artifact of preservation and this prompted a critical reevaluation of the supposed openings in the anterior portion of the skull of other suchians. We confirm that Luperosuchus is a loricatan (composed mostly of the taxa classically termed as ‘rauisuchians’) using a well sampled phylogeny and find a close relationship with the other large southwestern Pangean forms, Prestosuchus chiniquensis and Saurosuchus galilei. We also show that the holotype of Luperosuchus is the only known specimen of the taxon and all other previously referred material cannot be assigned with confidence to it.

A large fossil specimen could easily go unnoticed, especially when the specimen osteology is not well known, is usually represented by fragmentary material and has a sparsely ossified skeleton resulting in low preservation potential. This is particularly true for the suspensionfeeding Pachycormiformes, a clade of actinopterygians. This work provides the description of a complete gill raker recovered from the Upper Jurassic (lower Tithonian) levels of the Vaca Muerta Formation at Cerro Lotena, Neuquén Province, southwestern Argentina. The specimen is referred to the suspension-feeding pachycormid, Leedsichthys, based on similarities in size and shape morphology of the gill raker stalk, the shape of the gill raker base and for having similar morphology of the fimbriae (growing tongue-like distally). Although suspension-feeding pachycormids are known mainly from Laurasia, some remains were also recovered from Gondwana. The lower Tithonian Leedsichthys record extends the geographic and stratigraphic range of the suspension-feeding clade and that of the genus Leedsichthys.

Cranial and postcranial remains of a pyrothere from Quebrada Fiera (Mendoza Province, Argentina) are herein described. A comparison with late Oligocene (Deseadan SALMA) taxa allows its identification as Pyrotherium. In morphological cranial characteristics and size, the pyrothere from Mendoza proves close to the Patagonian species, P. romeroi, and larger than P. macfaddeni from Salla (Bolivia). Contrary to the previously assumed exclusiveness of P. macfaddeni in presenting an enamel tubercle between the lobes of some teeth, the specimens from Mendoza and Patagonia share such features. The mandible of the pyrothere of Quebrada Fiera differs from that of P. macfaddeni in its more horizontal symphysis and more procumbent incisors. A number of large postcranial remains are tentatively and for the first time assigned to Pyrotherium romeroi even though the lack of data on this group prevents an accurate determination. Their assignment to other large mammals that are (homalodotheres, leontiniids) or could be (astrapotheres) present in Quebrada Fiera is discarded. Based on a previous pyrothere data matrix consisting of cranial and dental characteristics, a cladistic analysis is herein performed and three new features plus the Quebrada Fiera taxon as a terminal unit are thereafter added. The obtained results are consistent with the taxonomic determination of the studied material and do not differ in terms of the general phylogenetic relationships within Pyrotheriidae.

The octodontoid rodent Acarechimys was abundant during the early Miocene and had the widest temporal and geographic distribution of any extinct caviomorph. Despite this extensive fossil record Acarechimys has not been well characterized. In this work, we systematically revise Acarechimys, describe new early—middle Miocene fossils from Argentina and Bolivia, corroborate its monophyly, and study its evolutionary history. Acarechimys has brachydont molars, retained deciduous premolars, four crests on upper molars, lowers with variably developed mesolophid and metalophulid II, and absence of mental foramen in the mandible. Acarechimys includes: Acarechimys leucotheae (late Oligocene, Chubut, Argentina), A. gracilis and A. constans (early Miocene, Chubut and Santa Cruz, Argentina), and A. minutus and A. minutissimus (early—middle Miocene of Patagonia Argentina, Bolivia, and Colombia). The temporal and geographic distributions suggest that Acarechimys could have evolved in Patagonia, by the early late Oligocene. Its acme was during the late early Miocene in Southern Patagonia. By the middle Miocene, Acarechimys decreased in diversity and was last recorded in high latitudes of South America (Patagonia). In lower latitudes, the oldest record is from the late early Miocene of Chucal, northern Chile, and during the late middle Miocene, the genus is recorded in localities of Colombia, Bolivia, and Peru. The available evidence suggests that Acarechimys was probably not present in lower latitudes (N of ~ 30° S) before the early Miocene. The reasons Acarechimys dispersed northward at this time remain to be elucidated, but the timing coincides with a massive disappearance of other octodontoids from Patagonia.

Nothrotherium maquinense, Ahytherium aureum and Australonyx aquae are ground sloths endemic of the late Pleistocene of the Brazilian Intertropical Region for which, as opposed to other xenarthrans such as megatheriid sloths and glyptodonts, no information regarding pathological conditions is available. Herein, we describe, based on an anatomopathological examination, four types of lesions for N. maquinense (spondyloarthropathy, Schmorl's node, vertebral trauma and unspecific infection) and one lesion for A. aureum (osteochondritis dissecans). No lesions were observed in A. aquae. Although several different diseases have been diagnosed, considering the significant number of specimens (2,232) and individuals (41) analyzed, low prevalence marks them all.