Mariano Verde

Insect Trace Fossil Associations in Paleosols: The Coprinisphaera Ichnofacies

Abstract Analysis of fifty-eight paleosol trace fossil assemblages, ranging from the Triassic to the Recent, allows refinement of continental ichnofacies models and the proposal of a Coprinisphaera ichnofacies. The Coprinisphaera ichnofacies consists of trace fossils of bees, wasps, ants, beetles, termites, and other unassigned insects. Meniscate burrows, mammal caves, and rhizoliths also may be present. This ichnofacies is named after the dung beetle nest Coprinisphaera, the most common component of this archetypal assemblage. In mature paleosols, the Coprinisphaera ichnofacies has moderate to relatively high trace fossil diversity and high abundance. Ethologically, this assemblage is dominated by nesting traces (calichnia) and exhibits a relatively complex tiering pattern, reflecting variable depths of emplacement of hymenopterous, termite, and dung beetle nests. Common components include the bee cells Celliforma, Uruguay, Ellipsoideichnus, Palmiraichnus, and Rosellichnus; the wasp nest Chubutolithes; the ant traces Attaichnus and Parowanichnus, and other beetle traces, such as Monesichnus, Fontanai, and Teisseirei. Termite nests may occur, but are less common components of the Coprinisphaera ichnofacies. The Coprinisphaera ichnofacies fulfills all the requirements to qualify as a Seilacherian or archetypal ichnofacies, namely recurrence in time and space, and distinct paleoenvironmental implications. Proposal of the Coprinisphaera ichnofacies is based on the analysis of twenty-eight cases, ranging from the? Late Cretaceous to the Recent. The Coprinisphaera chnofacies characterizes paleosols developed in paleoecosystems of herbaceous communities. These herbaceous communities range from dry-and-cold to humid-and-warm climates. More detailed paleoclimatological inferences can be obtained by evaluating the relative abundance of the various traces within the assemblage. A dominance of hymenopterous traces would indicate drier conditions, whereas the presence of termite nests would indicate more humid. The Coprinisphaera ichnofacies occurs in paleosols developed in various depositional systems subject to subaerial exposure, such as alluvial plains, desiccated floodplains, crevasse splays, levees, abandoned point bars, and vegetated eolian environments. This and other potential terrestrial ichnofacies are controlled by ecological parameters (e.g., vegetation, climate, and soil) rather than by depositional processes. The association of fossil insect nests indicates the extent of soil development and, consequently, such ichnofossils are one of the best indicators of paleosols. The previously proposed Termitichnus ichnofacies was defined to include all paleosol trace fossil assemblages. However, the available information indicates that terrestrial environments are far more complex. Therefore, it is suggested that the Termitichnus ichnofacies as presently defined be abandoned because it does not reflect the diversity of paleosol settings and fails to provide significant paleoecologic information. Formal definition of a Termitichnus ichnofacies in a more restricted sense, to include assemblages dominated by termite nests in paleosols of closed forest ecosystems, should await documentation of additional studies to prove recurrence. Other fossil insect-nest associations in paleosols (e.g., halictid nests in calcareous soils) do not have enough recurrence in time and space to be considered Seilacherian ichnofacies, but do represent potential ichnofacies. The model proposed in this paper includes the paleoecologically defined Coprinisphaera ichnofacies plus a definite number of associations, each one possessing its own paleoenvironmental implications, which do not show the necessary recurrence to be considered ichnofacies, at present. Climate and vegetation are considered key factors in the shaping of terrestrial ecosystems and should be taken into account for the definition of additional terrestrial ichnofacies.

FIRST BASAL SYNAPSIDS (“PELYCOSAURS”) FROM THE UPPER PERMIAN-?LOWER TRIASSIC OF URUGUAY, SOUTH AMERICA

In their monograph Review of the Pelycosauria, Romer and Price (1940), proposed that the earliest synapsids (“pelycosaurs”) were cosmopolitan, despite the observation that amniotes appeared to be restricted to the paleotropics during the Late Carboniferous and Early Permian (290–282 Ma). Romer and Price (1940) accounted for the scarcity of terrestrial tetrapods, including “pelycosaurs,” in Lower Permian beds elsewhere to the absence of coeval continental deposits beyond North America and Europe. Indeed, most workers recognized a geographical and temporal gap between Permo-Carboniferous “pelycosaurs” and therapsid synapsids. Recent research has confirmed that varanopid and caseid “pelycosaurs” were components of therapsid-dominated Late Permian faunas preserved in Russia and South-Africa (Tatarinov and Eremina, 1975; Reisz, 1986; Reisz et al., 1998; Reisz and Berman, 2001). In this note, we report the first record of basal synapsids for South America (Fig. 1) and discuss its paleogeographic and temporal implications. These remains come from outcrops assigned to the Buena Vista Formation (Goso et al., 2001; Fig. 2), which filled part of the Parana Basin during Late Permian and probably Early Triassic (Bossi and Navarro, 1991). The Parana Basin is one of the major sedimentary basins of Gondwana, covering an area of nearly 1.5 million km2, in Brazil, Argentina, Paraguay and Uruguay (Franca et al., 1995; Zalan et al., 1990). At the beginning of basin development the Devonian marine and brackish conditions prevailed, but subsequently, during the Late Permian, there was a gradual change to continental sedimentation and the deposition of fossil-bearing red beds. Buena Vista Formation is characterized by reddish fine sandstone interbedded with lenticular clay layers and intraformational conglomerates (Fig. 2), (Bossi and Navarro, 1991; Goso et al., 2001). The paleoenvironment is related to the final withdrawal of the sea, and the upper part of this …

Corimbatichnus fernandezi: A cluster of fossil bee cells from the late cretaceous‐early tertiary of Uruguay

Corimbatichnus fernandezi n.igen, n. isp. is a cluster of fossil bee cells from the Uruguayan Late Cretaceous‐early Tertiary Asencio Formation. It is composed of rows of small excavated cells contained in paleosol peds. Cells have inner surfaces somewhat rough and are closed with loose material. Separation among cells is very thin, and the cells are orientated uniformly, showing a great economy of space as in some halictine constructions. Corimbatichnus can be distinguished from Rosellichnus and Uruguay by its convex face, excavated cells and the spatial arrangement of them.

Mammalian Carnivore Coprolites from the Sopas Formation (Upper Pleistocene, Lujanian Stage), Uruguay

Continental tetrapod coprolites from Uruguay are described for the first time. These remains come from the Piedra Pintada locality (Artigas Department), northern Uruguay, where the Sopas Formation crops out (Upper Pleistocene, Lujanian Stage). It was possible to identify several attributes indicative of a coprolitic origin, such as anisopolar shape, extrusion marks, pointed ends, sutures, gas bubbles, and inclusions. These specimens are assigned to carnivorous mammals, probably large felids, based on morphological attributes and inclusions of rodent bones and teeth.

The first predatory drillhole on a fossil chiton plate: an occasional prey item or an erroneous attack?

ABSTRACT Drillholes represent direct evidence of ecological interactions in the fossil record. Most of them have been interpreted as predatory in origin and enable the analysis of behavioral information of both predator and prey. Drillholes have been found in a variety of fossil organisms, but this is the first report of a bored fossil chiton plate. It was found in the La Coronilla deposit, a Late Pleistocene invertebrate assemblage from southeastern Uruguay. The drillhole belongs to the ichnospecies Oichnus simplex and is attributed to a muricid gastropod, which could likely have been the ocenebrinid Urosalpinx haneti, recorded in the fossil assemblage. The drillhole features all traits for a predatory origin. However, the rareness of this particular interaction between chitons and gastropods in the fossil record and in the recent, could signify an event of arbitrary drilling. The reported occurrence here raises the question as to whether this behavior represents an understudied ecological interaction between polyplacophorans and gastropods.

Paleogene laterites bearing the highest insect ichnodiversity in paleosols

Research on laterites deals mostly with geomorphological and geochemical characterization of extant tropical systems, with few examples of sedimentologic and paleosol analyses of mid-latitude detrital records. Extra-tropical, Lower Eocene laterites from Uruguay include Fe-rich indurated horizons (duricrusts) that preserve paleosol features, and nodular beds. Discrete trace fossils are generally absent in laterites, despite that they are formed in tropical ecosystems with high biodiversity. Uruguayan laterites bear abundant, highly diverse, and superbly preserved insect trace fossils. Association, distribution, orientation, and abundance of trace fossils preserved in strongly developed paleosols (Ultisols), are key for reconstructing cyclic depositional and weathering processes governed by hydrology and tectonics. Each cycle lasted ∼420 ka and included iterative stages of fluvial sedimentation in a pericratonic scenario, pedogenesis and insect nesting and pupation in a seasonal tropical savanna, duricrust formation by desiccation and interruption of insect activities, and duricrust disaggregation (nodular beds) when rainfall increased. The proposed cycle can be used as a heuristic tool in the study of laterites.

Marine Isotope Stage 3 (MIS 3) and Continental Beds from Northern Uruguay (Sopas Formation): Paleontology, Chronology, and Climate

The Sopas Formation is a late Pleistocene continental unit that includes trace fossils, woods, fresh-water mollusks, and vertebrates with mammals being the predominant taxa. Likely, relationships with the Last Interglacial Stage or with the Last Interstadial were proposed. The paleontological content of the Sopas Formation is updated, and the climatic and environmental signals provided by the fossil content are evaluated. Radiocarbon AMS dates ranging from 33,560 ± 700 year B.P. (cal 36,089 − 39,426 year) to 39,900 ± 1,100 (cal 42,025 − 45,389 year) and TL/OSL ages from 27,400 ± 3,300 to 71,400 ± 11,000 year (being the 45–28 ka time interval better represented), support a relationship with Marine Isotopic Stage 3 (MIS 3) in most outcrops. In the fossil assemblage are taxa that indicate open habitats, savannahs, and woodlands including gallery forests and perennial rivers; living representatives of taxa related to benign climatic conditions (mostly tropical to temperate climates), some taxa that suggest arid to semiarid environments, migrants, and seasonality indicators. A replacement versus mixed faunal models is discussed in the light of available evidence.

Continental Late Cretaceous gastropod assemblages from Uruguay. Paleoecology, age, and the oldest record of two families and a genus

ABSTRACT Paleoecological studies of continental gastropods give valuable information about the depositional environment of the fossil assemblages. In South America, these assemblages from the Late Cretaceous/Paleocene are scarce and poorly studied. Most works focuses on taxonomy, but a paleoecological approach is still missing. We analyzed the assemblages present in the Queguay limestones from Uruguay. The total fossil content consists in freshwater and terrestrial gastropods, characean gyrogonites, ostracods, Neosauropoda eggshells, vegetable remains, insect nests, and pupal chambers. As the precise age and sedimentary environment of the Queguay limestones have been discussed for almost nine decades, a paleoecological study was conducted in order to answer these questions from this point of view. Diversity (Simpson, Shannon-Wiener, equitability) and similarity (Jaccard and Kulczynski) indices were calculated; the analyses showed a close relationship among all locations, and therefore we conclude that there are not differences in fossil content among the localities. Moreover, the data allows to consider them basically of the same environment and age. The presence of Neosauropoda eggshells in several outcrops indicate unquestionably a Late Cretaceous age, and establish the oldest record worldwide for Pupillidae, Orthalicoidea and Biomphalaria.