Aetosaurs are a group of quadrupedal, armoured pseudosuchian archosaurs from the Upper Triassic. They are characterized by dorsal and ventral carapaces, and appendicular osteoderms, all of them ornamented. Aetosaurs have been proposed as index fossils largely based on the distinctiveness of some osteoderms. Therefore, it is important to understand the intraspecific variation of these elements in the clade. In the present contribution, we describe three types of ornamentation on the medial area of paramedian osteoderms in the dorsal armour of Aetosauroides scagliai Casamiquela: the “radial pattern” the “anastomosing pattern”; and an “intermediate” or “transitional pattern”, that is an intermediate between “radial” and “anastomosing” patterns. The articulated dorsal armour preserved in specimens PVL 2059 and PVL 2073 possesses osteoderms carrying all three patterns of ornamentation, but they differ by the position of each type of osteoderm on the carapace. Recent studies on histological thin-sections of osteoderms of A. scagliai reveal the absence of osteoderm tissue remodeling, allowing the estimation of age by counting LAGs (lines of arrested growth). PVL 2073 is slightly shorter (∼10% longer centra) but also ontogenetically younger (5 LAGs) than PVL 2059 (10 LAGs; slightly wider osteoderms). Combining this information and comparing it with that of living crocodiles (where male specimens typically are relatively larger than females of the same age), we conclude that the intraspecific variation observed in A. scagliai is compatible with the hypothesis of sexual dimorphism. These results suggest the need to explore the sources of intraspecific variation in aetosaurs.

Here we describe the northernmost South American record of fossil turtles from the late early Miocene to early middle Miocene of the Castilletes Formation, on the Alta Guajira Peninsula, Cocinetas basin, Colombia. Turtles in the lower segment of the Castilletes Formation (c. 16.33 Ma) are pleurodires or side-necked turtles belonging to Chelus colombiana Wood, Chelus sp., and Podocnemididae incertae sedis, and cryptodires or hidden-necked turtles attributed to Chelonoidis sp., all of them characterized by the large size of their shells, 1 meter or more total length. The middle segment of the formation (c. 14 Ma) contains specimens of Podocnemididae incertae sedis and Chelonoidis sp. The turtle fauna from Castilletes share taxa with faunas from La Venta (middle—late Miocene of Colombia), Urumaco, and Western Amazonia (late Miocene from Venezuela, Brazil, and Peru); all of these records indicate a wider geographical distribution for podocnemidids, chelids, and testudinids of tropical South America during the early to middle Miocene. The large size of the fossils described here also confirms that gigantism was characteristic of South American tropical turtles during the early Miocene, a trend that lasted at least from the Paleocene to the Pliocene in different lineages.

Despite being the dominant group of South American mammalian carnivores for much of the Neogene, most post-early Miocene sparassodonts (Metatheria) are poorly known. Here, we describe new specimens of the hathliacynid sparassodont Acyon myctoderos Forasiepi et al. from the middle Miocene locality of Quebrada Honda, Bolivia, including a juvenile specimen that preserves the first known hathliacynid DP3. This specimen is unique among sparassodonts in preserving both upper and lower deciduous premolars and suggests that hathliacynids may have differed from borhyaenoid sparassodonts in having simultaneous eruption of M3 and m4 rather than M4/m4. Another specimen from Quebrada Honda tentatively assigned to A. myctoderos preserves the first known long bones (femur, tibia) of this genus, allowing us to estimate its body mass (13–17.5 kg) based on postcranial data. These new specimens document further morphological and ontogenetic variation within A. myctoderos as well as the Sparassodonta as a whole.

New, exceptionally well preserved skulls of the basal megalonychid ground sloth Eucholoeops ingens Ameghino have been recovered through recent field work in the late early Miocene Santa Cruz Formation of southern Argentina (Patagonia, Santacrucian SALMA). These specimens have permitted detailed description of the anatomy of the basicranium, endocranium, and orbital wall, including descriptions of the morphology and sutural relationships of the bones from this portion of the skull, and their associated cranial foramina. Comparisons are made to other megalonychid and megatherioid sloths, including the extant two-toed sloth Choloepus Illiger (Megalonychidae). As the descriptions are based on multiple specimens of E. ingens, we have been able to examine intraspecific variation in the features described, and have found marked differences among individual specimens in sutural patterns (e.g., the bones that surround the foramen ovale aperture), cranial foramina (e.g., the presence/absence of a postglenoid foramen), and bony morphology (e.g., fusion of the alae of the vomer). The basicranial and orbital morphology of Eucholoeops ingens is shown to possess numerous plesiomorphic aspects, including the presence of a descending lamina of the pterygoid that is hemispherical in outline, and the absence of an alisphenoid/parietal contact, no doubt due to its position as the oldest megalonychid known from relatively complete material. The presence of distinct grooves on the promontorial surface directed toward the fenestra ovalis suggest that Eucholoeops ingens may be the only known xenarthran to have retained a functional stapedial artery Into adulthood.

This is a systematic study of the Spinicaudata fauna of the Cerro de Las Cabras Formation (Middle Triassic), north of Cerro Bayo, in the classical Potrerillos area, Precordillera of Mendoza, Cuyo Basin, Argentina. Two new species are described: Estheriellites zavattieriae sp. nov. and Euestheria menendezi sp. nov.. The diagnosis of the genus and species of Challaolimnadiopsis mendozaensis Shen and Gallego, is emended; and Euestheria martinsnetoi Gallego et al., previously described for the Río Mendoza Formation is now considered as coming from the Cerro de Las Cabras strata. The studied section consists mainly of fine-grained tuffaceous sandstones and interbedded mudstones interpreted as playa lake, ephemeral rivers and/or streams developed in the floodplain. Ephemeral to shallow lacustrine environments are characterized by interbedded siltstones, nodular-mottle and stromatolitic limestones with sub-aerial exposures and incipient soil development in depressed and flood-prone areas under seasonal semi-arid conditions. Spinicaudatans probably inhabited lacustrine shorelines and small ponds in the floodplain where plant remains (arthrophyte) and rare fish scales were also recorded. The profuse presence of pyroclastic deposits along the sequence indicates considerable explosive volcanic activity coeval with sedimentation. Based on previous lithostratigraphical, paleontological and chronological data, the age of the studied deposits was constrained to Middle Triassic (equivalent to Late Anisian—Late Ladinian of marine sequences) and therefore the E. zavattieriae-E. martinsnetoi Faunal Association is considered as a marker for such age range.

This is an exhaustive analysis of the palynomorph assemblages, organic-walled marine phytoplankton and miospores from the Tucunuco Group. This group includes the La Chilca and Los Espejos formations and is exposed in the Central Precordillera of San Juan. Four localities were included in this study, i.e., Río Jáchal, Río de las Chacritas, Cerro La Chilca and Quebrada Ancha. Previous data concerning several fossil groups, such as graptolites, conodonts and brachiopods, suggest a mainly Llandovery—Wenlock? age for the La Chilca Formation and a Wenlock to locally Lochkovian age for the Los Espejos Formation. Marine palynomorphs are predominant in the two formations in all the studied sections. Although terrestrial palynomorphs are the minor component, trilete spores are abundant, diverse and biostatigraphically relevant in the Los Espejos Formation. Correlations using marine palynomorph assemblages and miospore biozones recognized worldwide allow constraining the age of the two stratigraphic units. Based on marine phytoplankton, the middle—upper part of the La Chilca Formation is assigned to the Wenlock. In the Los Espejos Formation, palynomorph assemblages allow the recognition, from the base to the top, of the Wenlock with doubts, the Ludlow, and the Pridolí. The Lochkovian has been documented exclusively in the northern part of the basin. This confirms the presence of the Silurian/Devonian boundary in the upper part of the Los Espejos Formation. A north-south correlation panel of the studied sections is presented.