In this contribution, we describe assemblages of amorphous silica microfossils from a hydromorphic paleosol of the Southern Pampas and discuss their paleoenvironmental relevance through a comparative analysis with assemblages from two modern shallow lakes. The hydromorphic paleosol analyzed, assigned to the Pliocene/Pleistocene boundary by previous studies, is exposed in the coastal cliffs of the southeastern Buenos Aires province, Argentina. The shallow lakes selected as modern analogous environments are located 4.5 kilometers away. The hydromorphic paleosol contained well-preserved silicophytoliths, whereas diatoms, chrysophycean cysts, and spicules of sponges, were found in low abundances and poorly preserved. In the modern shallow lakes, silicophytoliths were also the main component of the assemblages, being diatoms the second most abundant component. Chrysophycean cysts were found in low abundances and represented by fourteen different types of cysts, five of which are mentioned for the first time in Argentina. Spicules of sponges were rarely found, represented only by fragmented megascleres. Considering the relevance of silicophytoliths for this record, we conducted a comparative analysis that allowed us to infer temperate humid paleoclimate during the pedogenesis of the hydromorphic paleosol. This is the first study comparing the silicophytolith assemblages from a hydromorphic paleosol with a local modern analogous environment. Our results highlight the potential use of amorphous silica microfossils as bioindicators in paleosols of the Late Cenozoic pedosedimentary successions of the Southern Pampas, where the homogeneous lithology has been an obstacle for the understanding of the paleoenvironmental evolution of the region.

On the basis of selected osteological markers, Patterson (1936) identified two pathways (here designated A and B) along which the internal carotid artery in notoungulates was said to travel in order to enter the skull and supply the brain. The existence of these pathways, at least as Patterson defined them, has been disputed but no substantive alternatives have been proposed. Using comparative embryological and morphological evidence based on conditions in extant mammals, we find that pathway A (intratympanic) is not supported. Pathway B (enclosed extratympanic) is supportable, but as far as is now known applies only to a small number of notoungulate taxa. On the basis of new evidence, we propose another route, pathway C, briefly mentioned by Scott (1912) but subsequently ignored, that may apply to the majority of notoungulates. In pathway C (unenclosed extratympanic) the internal carotid passed directly into the endocranium via a naturally unossified area of the basicranium, the piriform fenestra, rather than coursing through or alongside the middle ear in a canal. The absence of a separate, bony carotid foramen on the basicranium's ventral surface may explain the hesitancy of previous workers to consider this routing. There is no evidence that the function of the internal carotid artery was supplanted by another vessel (e.g., external carotid artery) in any notoungulate. Conditions in other major clades of South American native ungulates are poorly investigated, but some clearly differed from notoungulates in carotid patterning, pointing to the existence of substantial intertaxon disparities.

This study describes two new species of cheilostome bryozoans associated with gastropod shells from the Monte León Formation (Burdigalian, early Miocene), Argentine Patagonia. Burdwoodipora griffini sp. nov. is the second known species and the first fossil representative of the genus, whose geographic distribution is so far restricted to the Magellan region in the southern Southwest Atlantic. It differs from the type species, B. paguricola, in lacking suboral adventitious avicularia in most autozooids. Odontoporella miocenica sp. nov. is morphologically very close to the type species, the Recent O. adpressa, from which it differs in having smaller zooids with fewer areolae and relatively wider orifices. The stratigraphic range of Odontoporella is here extended from the Pleistocene to the early Miocene. Its geographic distribution includes southern South America, New Zealand, and New Caledonia, suggesting an austral origin of the genus in the Paleogene of former Gondwana. The possible association of these two species with paguroid crabs is discussed.