Recent field expeditions have led to the discovery of a selachian assemblage from the earliest Miocene (Aquitanian) deposits of the Uitpa Formation in the La Guajira Peninsula, Colombia. This elasmobranch assemblage provides a unique glimpse into the Caribbean biodiversity at the onset of the Neogene. The assemblage consists of 13 taxa, of which some are reported from Miocene deposits for the very first time. There are also new records of taxa the in southern Caribbean region. The taxonomic composition of the selachian assemblage was used to conduct a paleoenvironmental and paleobathymetric analysis of the lower Uitpa Formation. The maximum likelihood estimation of paleobathymetry suggests that the lower part of the Uitpa Formation was probably accumulated at a water depth of 100 to 200 m. This indicates a rapid increase in relative sea level or basin deepening, providing new insights into the possible causes of marine biota changes in the Cocinetas Basin during the Oligocene/Miocene transition.

Paleobiological integration proceeds from descriptive morphology and paleosynecological reconstruction. This integration is achieved through modeling of function, inference of faculties, performance and resource use to hypothesize about fundamental niche. Environmental information is then incorporated to discuss biological roles and realized niche. Herein, paleobiological integration of Santacrucian (early Miocene of Patagonia) sloths is analyzed as a study case. Santacrucian sloths comprise a diversity of approximately 11 genera ranging from 40 kg to 120 kg in body mass and characterized by being morphologically different from any living relatives. In this study, the realized niche of each taxon is reconstructed via integration of three paleoecological attributes: body size, dietary habits and substrate preference. An ecomorphological approach is applied using Principal Components Analysis to explore the correlation between postcranial linear dimensions and substrate preference together with classical functional indices. Integration of these results with previous studies indicates that the mid-sized Hapalops, Pelecyodon, Schismotherium and Analcimorphus (stem Megatherioidea) and Eucholoeops (Megalonychidae) are members of the arboreal folivore paleoguild. In contrast, the mylodonts Analcitherium and Nematherium, marked by their greater size, may have been semiarboreal consumers of leaves, fruits and tubers due to their digging capabilities. Prepotherium (Megatheriidae), the largest and most terrestrial Santacrucian sloth, was also a folivore. Only the latter three genera competed for trophic resources with other coexistent mammalian herbivores. Their body size, strength and claws made Santacrucian sloths subject of predation solely for the largest Santacrucian carnivores, borhyaenoids marsupials and phorusrhacoid birds. Finally, the absence of modern analogues of these heavy-sized arboreal and semiarboreal herbivore diversity is discussed.

Over the last decades, Paleogene outcrops in northwestern Argentina have been yielding abundant information about the evolution of South American mammals during the early Cenozoic. This region was an important area of early diversification for several groups of native ungulates, particularly notoungulates, during the Eocene. Although many specimens were found in association with postcranial elements, most reports describe cranial material. It is well known that these postcranial elements can provide characters for phylogenetic analyses and important clues for paleobiological inferences. This study presents a series of postcranial remains (proximal tarsals) from the Geste Formation exposed in Antofagasta de la Sierra, Catamarca Province, Argentina. Three calcanei and two astragali are herein described, compared to those of extinct ungulates and taxonomically identified. A functional analysis allows inferring the association of these bones to different types of stances. One calcaneus is assigned to Toxodontidae (Notoungulata) and exhibits some plantigrade features. Presenting digitigrade-like morphology, the other two calcanei and an incomplete astragalus are assigned to Interatheriidae (Notoungulata). Another astragalus, characterized by a configuration suggesting a digitigrade posture, is assigned to Didolontidae Ernestokokenia cf. E. yirunhor. The study of the tarsal provides a more integrative view of the Paleogene forms of the region as well.

Catogenus punctatus sp. nov. is the first fossil species described of the family Passandridae (Coleoptera: Cucujoidea) worldwide. The specimen was collected from the Río Pichileufú fossil-bearing strata, Huitrera Formation, Río Negro, Argentina.

Ichnologic and sedimentologic studies of the Lajas Formation (Middle Jurassic) in Sierra de la Vaca Muerta allowed the recognition of two different types of deltaic mouth bars, each of them showing trace fossil suites with different characteristics. Type I deltaic mouth bars consist of fine to coarse sandstones and fine conglomerates completely reworked by fair-weather and storm wave action, revealing a predominance of basinal hydraulic processes (e.g., waves) during bar construction and progradation. Trace fossil assemblages are composed of Ophiomorpha and Haentzschelinia in the foreset beds, and Polykladichnus, Skolithos, and Arenicolites in the topset beds. Type II deltaic mouth bars comprise sandstones that are fine to coarse and massive or present high angle cross-stratification and current ripples migrating in the opposite direction to the inclination of the foresets. These bars are interpreted to have been deposited during intervals of extraordinary fluvial discharge when wave action was restricted to the topset part of the bars. Whereas equilibrium trace fossils occur in the bottomset beds, escape trace fossils and Ophiomorpha are recorded in the distal foreset beds. In the topset beds, Skolithos and Polykladichnus specimens are very abundant. In general, the two types of mouth bars show low diversity, low abundance of trace fossils and a simple tiering structure. Such traits reflect environmental stresses mainly produced by fluctuating hydraulic energy, salinity, sediment input and high mobility of the substrate.

The first fossil macroflora assemblage from the Cerro de Las Cabras Formation at its type locality, in the Potrerillos area, is presented. The area is tectonically altered, which is why there have been several different interpretations about the real thickness and boundaries of the formation. A detailed analysis of the bibliography showed that previous fossil plant taxa referred to the Cerro de Las Cabras Formation belonged to the overlying Potrerillos Formation. However, the recent discovery of a plant-bearing level in stratigraphically constrained sediments of the Cerro de Las Cabras Formation allows the identification of a flora composed of Corystospermales —Dicroidium odontopteroides (Morris) Gothan; D. lancifolium (Morris) Gothan; D. crassum (Menéndez) Petriella; Zuberia zuberi (Szajnocha) Frengüelli; Z. sp. cf. Z. barrealensis Frengüelli—, Peltaspermales —Scytophyllum sp. cf. S. neuburgianum Dobruskina; Pachydermophyllum sp.; Peltaspermum sp.—, putative Gnetales — Gontriglossa sp.—, Osmundales —Cladophlebis mendozaensis (Geinitz) Frengüelli—, Equisetales, and two taxa of uncertain affinities. Although low in diversity, this assemblage is comparable to coeval assemblages in other basins, particularly the floras from the Agua de los Pajaritos, Barreal and Ischichuca formations, reinforcing the Middle Triassic age assigned by the vertebrate, microfloristic and radiometric dating.

Jurassic hot-spring chert deposits in the Deseado Massif, Patagonia, Argentina, have been known for over two decades, but the associated biota has only begun to be documented recently, and thus far only from a small number of localities. Here we report the discovery of a large complex of well-exposed Upper Jurassic epithermal siliceous deposits represented by organic-rich cherts preserved within the geothermal system from La Bajada, Santa Cruz, Argentina. The chert samples analyzed so far contain exceptionally well-preserved, in situ and transported, tri-dimensionally silicified plants, animals and microorganisms. Plants include equisetaleans (Equisetum thermale), ferns and gymnosperms. Among them, well-preserved in situ osmundaceous rhizomes in different developmental stages are the dominant component of the taphoflora. Conifers are represented by wood, seeds, leaves and pollen tentatively assigned to the families Araucariaceae and Cheirolepidiaceae. The assemblage also contains vegetative and reproductive structures of fungi, oomycetes, cyanobacteria, algae, testate amoebas, ciliates and numerous remains of unresolved taxonomic affinity. Microorganisms are preserved isolated in the chert matrix or directly associated with plants and other organic remains in mutualistic, parasitic and saprotrophic engagements. Also present are numerous coprolites and arthropod remains that, along with the named microorganisms, are indicative of trophic relationships in the ecosystem. Altogether, this fossil assemblage suggests that distal paleoenvironments within the geothermal system are preserved at La Bajada. The diversity, abundance, and exceptional preservation of fossils in the La Bajada ecosystem provides a unique window into the geological past that offers a substantial contribution to the reconstruction of middle Mesozoic terrestrial ecosystems.