Bernardino Rivadavia Natural Sciences Museum

Florentino Ameghino described in 1891 the new species Balaena pampaea and the new genus Notiocetus, with the new species N. romerianus and N. platensis. These taxa were based on isolated tympanic bullae coming from different Pleistocene fossiliferous localities of Buenos Aires Province, Argentina. However, since their original description, the specimens were considered lost, and subsequent authors were not able to review the specimens at first hand. Based on the descriptions and illustrations provided by Ameghino for Balaena pampaea and Notiocetus romerianus (N. platensis was very briefly described, but not illustrated), most authors considered them as valid taxa. The finding of the holotype specimens of Balaena pampaea, Notiocetus romerianus, and N. platensis allows to reevaluate the morphology and validity of these taxa. Notiocetus platensis is based on a partial bulla of an indeterminate mysticete. Balaena pampaea and N. romerianus are very similar to each other, and are re-identified as belonging to an indeterminate balaenid. Previously noted differences are most-likely the result of preservational artifacts or intraspecific variations. We also include brief comments on isolated bullae of other Pleistocene and Holocene mysticetes that were studied by Ameghino, but which remained unpublished up to the date. In this contribution we aim to highlight that paleontological collections preserve much more than samples of our planet’s past. Many of the preserved specimens have a value that goes beyond their biological value, since they have a cultural background that is part of the history of our discipline.

The fossil record of freshwater crayfishes (Astacoidea and Parastacoidea) is globally scarce and dominated largely by trace fossils and bio-gastroliths, particularly in Gondwana. In South America, Mesozoic records have been restricted to ichnofossils, with unequivocal body remains known only from the Paleogene. Here we describe isolated mandible cephalic molar fields attributable to Parastacidae from the Maastrichtian Los Alamitos Formation of northern Patagonia, Argentina. These specimens, recovered from historical collections of the Museo Argentino de Ciencias Naturales "Bernardino Rivadavia" and previously misidentified as vertebrate teeth, represent the oldest confirmed parastacid body fossils from South America and the second Cretaceous record of the clade in the Southern Hemisphere. The material consists of five incompletely preserved molariform structures, including one nearly complete cephalic molar field, exhibiting a distinctive combination of features such as a subrectangular outline, prominent lateral cusps, a longitudinal central depression, and a thick enamel-like apatite coating. Comparative analysis indicates that these remains cannot be referred to any extant South American genus and likely represent a distinct, unnamed parastacid lineage, possibly showing closer affinities to Malagasy taxa. The Patagonian record reported here fills a critical temporal gap between Early Cretaceous parastacids from Australia and Paleogene records from South America and Australasia, supporting a widespread Gondwanan distribution of parastacids during the Late Cretaceous and reinforcing hypotheses of early high-latitude diversification followed by subsequent dispersal.

The Rufous-collared Sparrow ( Zonotrichia capensis ) presents a complex system of dialects based on characteristics of the final trill, which usually correlate with vegetation structure. We studied the songs of this species along an Andean pass from the lowlands to the highlands of Mendoza province, in Argentina. We found four dialects along this route: the Potrerillos and Aconcagua dialects characterized by the presence of a very fast trill (buzz) intercalated with the Uspallata and Las Cuevas dialects, which lack the final trill. Despite the differences in altitude along the transect, dialects do not correlate with environmental variables, or altitude per se, pointing to a more complex explanation for the pattern found. The Potrerillos and Uspallata dialects belong to the more broadly distributed dialects of the Southern and Northern Monte Deserts, respectively, and may represent the source traditions that originated the more localized high-elevation dialects. Specifically, individuals from lower-elevation populations that move seasonally to higher elevations could contribute their songs to newly established or small high-elevation populations, such as those in Aconcagua and Las Cuevas. The differences between these dialects and their source dialects could have developed by a combination of founder effects, chance-driven cultural drift and conformist transmission. The presence of individuals in Potrerillos singing songs with and without trills could also stem from altitudinal seasonal movements and the exposure of low-altitude birds to trill-less songs high-elevation from migrating individuals. This Andean transect illustrates the diversity and complexity of factors that shape vocal dialects in oscine passerines.

Cnesterodon pampeanus was recently described as a species distinct from C. decemmaculatus , but its actual distribution remained poorly understood because populations from central and southern Argentina had historically been assigned to the latter species. Here, we reassessed the identity of Cnesterodon populations using an integrative approach combining mitochondrial DNA barcoding (COI) and diagnostic gonopodial morphology. We analyzed 43 newly generated COI sequences from populations spanning Buenos Aires, Mendoza, San Juan, San Luis, Neuquén, Río Negro and Chubut provinces together with previously published data. All newly analyzed specimens were consistently recovered within the C. pampeanus lineage and their identification was corroborated by morphology. Our results substantially expand the known distribution of C. pampeanus , extending its range from northeastern Buenos Aires Province to northern Patagonia and the Andean drainages of the Cuyo region, including the southernmost record of the genus. These findings indicate that a considerable portion of the historical distribution attributed to C. decemmaculatus in Argentina likely corresponds to C. pampeanus , requiring a reassessment of species distributions within the genus. Remarkably, C. pampeanus occurs across multiple hydrographic systems and environmentally contrasting regions, including high-altitude Andean basins and cold Patagonian drainages, suggesting a broader ecological breadth and a more complex biogeographic history than previously recognized. Our study highlights how recent taxonomic revisions can substantially reshape species distribution patterns and provides a framework for future phylogeographic and genomic studies aimed at understanding the evolutionary history of Cnesterodon in southern South America.

The interaction between multiple secondary sexual characters simultaneously expressed by an organism remains poorly understood. In fact, different interpretations of the role of concurrently expressed signals predict that the correlation of their elaboration across species should be positive, negative or absent —all three possibilities have been supported by studies of different avian groups. In this context, we analysed the interaction between plumage and song elaboration in the passerine family Fringillidae (finches). We used a two-scale approach and studied this association both at the family level and in more detail within the genera Crithagra and Spinus . At both scales, we determined colour elaboration (defined by the number of plumage colour patches in each species and their contrast) and established its association with three aspects of vocal elaboration: energy investment (song length and rate of syllable production), song complexity (repertoire index) and vocal performance (vocal deviation). We found an absence of association between colour elaboration and the three evaluated aspects of song elaboration at both scales, which has been the most frequent result in other avian groups. At first glance, this result appears to be partially discordant with previous findings in finches, but considering these studies together this might not necessarily be the case. We also confirmed that finches have complex songs and a remarkable vocal performance compared to other families of passerines. Considered together, our results suggest an independent evolution of colour and the notable vocal elaboration present in finches.