We collected nine samples from the middle Miocene of Patagonia, in outcrops of the Río Correntoso Formation (Río Zeballos Group) in north Santa Cruz Province, Argentina. Fossil woods have variable preservation and some are poorly preserved. Six samples are silicified, and three are totally carbonized. Two taxonomic units were confidently described, Cupressinoxylon sp., a conifer with Cupressaceae or Podocarpaceae affinity and Nothofagoxylon scalariforme with Nothofagus subgenus Nothofagus affinity of the Nothofagaceae. Other samples are indeterminate angiosperms and conifers. Growth rings of two samples indicate seasonality and galleries with frass and coprolites found in an indeterminate conifer are similar to those made by coleoptera and acari. The assemblage taxonomic composition is similar to other Miocene wood floras of Patagonia with conifers and Nothofagaceae.

Well-preserved fossil microbiotas normally present relatively high taxonomic diversity, especially if the host-rock is distributed over a large area. Estimates of taxonomic diversity, however, require proper consideration of ontogenetic, taphonomic, and ecological influences on morphological variety. Otherwise, diversity may be overestimated. Chert in the Permian Assistência Formation (Irati Subgroup, Paraná Basin, Brazil) contains an abundant, well-preserved fossil microbiota that has been studied from seven localities distributed over about 500 km. Despite the great numbers of microfossils present, morphological analysis revealed a low apparent diversity. There is no evidence of filamentous microorganisms and the chroococcacean Gloeodiniopsis lamellosa is overwhelmingly dominant, accounting for 98.6% of counted individuals. In addition to G. lamellosa, only five taxa are recognized of which four are formally described: the chroococcaceans Cyanosarcinopsis hachiroi gen. et sp. nov. and cf. Coniunctiophycus sp. and two taxa considered incertae sedis: Myxococcoides sp. A (a probable cyanobacterium) and Myxococcoides sp. B (a possible delicate eukaryote). A unique but markedly different colony was designated as unnamed form (open nomenclature). Two hypotheses may explain the enigmatic absence of filaments: (i) environmental stress associated with hypersaline conditions that severely limited diversity or (ii) long-term optimal growth conditions for coccoidal cyanobacterial blooms due to sustained basin-wide eutrophic conditions.

“Larger” foraminifera appear in different lineages through the evolutionary history of the group. Traditionally, the reason why benthic forams of calcareous wall—mainly milliolids and rotallids—reached centimetric dimensions was attributed to the endosymbiotic relationships with algae. The ecological requirements and morphological characteristics of tests are known from experimental studies in extant forms. These requirements and characteristics are fundamental to establish and maintain symbiosis with diverse chlorophytes, rhodophytes, diatoms, dinoflagellates and cyanobacteria groups. Such relationships are neither exclusive or a sine qua non condition for larger taxa. This work aims to explore the published literature regarding this topic in order to sort out how experimental and palaeontological evidences can be of use to infer symbiotic relationships on the fossil record.

Fossil fingers of crabs (Decapoda, Brachyura) coming from mid-Holocene deposits, Cerro de la Gloria, and Destacamento Río Salado members, from northeastern Buenos Aires, Argentina are herein described. These fossil fingers represent the first record of Danielethus crenulatus, and the first record of varunids from the Canal 15 site. The specimens show diagnostic features and confirm the presence of subtidal-intertidal crabs at least from the mid-Holocene marine transgressive and regressive system tracts. This study also suggests that D. crenulatus could have been represented by large populations as in modern environments since food items (mollusks) were abundant during the mid-Holocene. Moreover, varunids, which feed on detritus, might also have had availability of organic matter during the late Quaternary according to previous fossil fauna records from other sites of Buenos Aires Province and Uruguay, because the coastal plains were extensively developed. These crabs constitute important food items for a diverse fauna and modify the substrate allowing the settlement of a varied coastal flora and fauna.

The first conodont fauna recovered from the Portezuelo del Tontal Formation (PTF) in the Sierra del Tontal, San Juan Province, is analysed, providing a precise biostratigraphic control for the scarcely fossiliferous, thick Ordovician siliciclastic sequences of the western Argentine Precordillera. In the studied Cerro Cóndores stratigraphic section, the lower outcropping levels of the PTF are characterised by sandstone beds, with a few having minor calcareous acidic reaction, deposited under medium energy, open-marine, siliciclastic shelf conditions. The recovered assemblage consists of 50 conodont elements, including Ansella jemtlandica, Costiconus costatus, Drepanodus arcuatus, Parapaltodus simplicissimus, Paroistodus originalis, Periodon macrodentatus, Protopanderodus graeai, and Spinodus spinatus as the most conspicuous species. After the biostratigraphic assessment of species of the Paroistodus horridus complex, the PTF conodont asemblage is referred to the Darriwilian (Middle Ordovician) Yangtzeplacognathus crassus Zone, a critical interval in the tectonostratigraphic history of the Precordillera. The collection also contains reworked conodont specimens whose biostratigraphic ranges coexist during the middle-upper Floian Stage (Lower Ordovician). The conodont assemblage from the PTF allows for a precise correlation with the eastern and central domains of the Precordillera, as well as other regions of the world, improving the knowledge on the dynamics of the Ordovician Precordilleran basin and the palaeogeographic distribution of its faunas.

The cotylar fossa is a complex anatomical character in the astragalar medial malleolar facet. It represents a dynamic relationship between the astragalus and the tibia in the upper tarsal joint. The astragalus must accommodate the medial tibial malleolus when the tibia is in an extreme flexion. It is one of the three morphological synapomorphies considered for Afrotheria, although it is also a recurrent trait among different groups of mammals. Here, fossil South American Native Ungulates and extant mammals were surveyed to reevaluate how much this character is spread and how variable it is. Beyond afrotherians, it is observed that it also appears in primates, macropodid marsupials, laurasiatherian archaic ungulates, perissodactyls, pantodonts, and dinoceratans; it is also in some but not all of the extinct endemic ungulates from South America. No function has been suggested before for the presence of a cotylar fossa. The cotylar fossa could be an adaptation to a passive, rest related posture. Extreme flexion of the tibia/fibula over the foot happens when animal sits or lies down. Because of this, the cotylar fossa may not represent a synapomorphy of afrotherians but a homoplastic feature convergently developed several times. The cotylar fossa, as first described, is more characteristic of the order Primates than of any other taxa, including Afrotheria. But, there is more than one kind of cotylar fossa, and this variation could correspond to more than one cause, including phylogenetic constraints.

Beaks are an edentulous dietary modification present in numerous forms in turtles, birds, cephalopods, and some actinopterygian fishes today. Beaks have a rich fossil record and have independently evolved at least nine times over the past 300 million years in early reptiles, dinosaurs and their relatives, and crocodile and mammal relatives. Here, we focus on the earliest evolution of beaks in the reptile fossil record during the Triassic Period (252–201.5 million years ago). We analyze the phylogenetic distribution of Triassic beaks and review their morphologies to create a framework to estimate beak similarity. With this, we describe a unique fossil beak (PVSJ 427) from the Late Triassic Ischigualasto Formation, San Juan, Argentina, and place it in our similarity analysis alongside other vertebrate clades from the Triassic Period, or with Triassic origins. PVSJ 427 is a small iron-rich cast fossil that is triangular with a concave midline shelf, rounded lateral walls, and an anterior point. No clear synapomorphies are present in PVSJ 427, and as such, its phylogenetic position is not inferred herein. Some remnants of bone are recognizable in thin sections of PVSJ 427, indicating that it likely represents a bony beak replaced by minerals. The morphology of PVSJ 427 is most similar to the predentary, an edentulous element restricted to ornithischian dinosaurs, although this specimen is approximately three times larger than the earliest known ornithischian predentaries. Regardless of phylogenetic position, PVSJ 427 reflects an early evolution of a predentary-like beak and indicates that this animal was ecologically convergent with the earliest ornithischian dinosaurs.