José H. Laza

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.

Dung-Beetle Fossil Brood Balls: The Ichnogenera Coprinisphaera Sauer and Quirogaichnus (Coprinisphaeridae)

Coprinisphaera is one of the most common trace fossils in South American paleosols from the Eocene to the Recent. Nevertheless, an ichnotaxonomical review of this ichnogenus has been lacking until now. The revision of hundreds of specimens of Coprinisphaera from numerous formations in Argentina, Uruguay and Ecuador has resulted in the recognition of two ichnogenera. One of them, Coprinisphaera, includes isolated, spherical, subspherical, pear-shaped and bispherical structures grouped in five ichnospecies: C. ecuadoriensis Sauer, C. murguiai (Roselli), C. kraglievichi (Roselli), C. tonni isp. n., and C. kheprii isp. n. The new ichnogenus and ichnospecies, Quirogaichnus coniunctus, consists of Coprinisphaera-like structures clustered in a common excavated chamber. The ichnotaxobases for the taxonomical arrangement of Coprinisphaera are mostly related to the presence and position of a small chamber (interpreted as the original egg chamber) with respect to a large chamber (provision chamber) and emergence hole. The egg chamber may be included in (1) the provision chamber, leaving no remains in the trace fossils and resulting in cylindrical emergence holes; (2) the wall of the provision chamber, without additional structures; and (3) a mamillate to spherical additional structure, external to the provision chamber, resulting in pear-shaped to bispherical trace fossils.

Fossil bee nests, coleopteran pupal chambers and tuffaceous paleosols from the Late Cretaceous Laguna Palacios Formation, Central Patagonia (Argentina)

Abstract The Late Cretaceous Laguna Palacios Formation in Central Patagonia (San Jorge Basin), southern South America, is composed of tuffaceous deposits supplied by periodical volcanic ash falls partly reworked by rivers, on broad plains. Variations in ash-fall rates allowed the formation of stacked, mature paleosols, which are one of the most characteristic features of this formation. The mature paleosols show well-developed horizons, ped structure and bear an intricate network of trace fossils mostly produced by small roots and invertebrates. Two different insect trace fossils could be recognized in this formation: sweat bee nests and coleopteran pupal chambers. Fossil bee nests are composed of inclined tunnels with cells attached to them by means of short necks, a typical construction of bees of the subfamily Halictinae. Similar halictine constructions were reported from the Cretaceous of the USA. Coleopteran pupal chambers are discrete, ovoid structures, having an internal cavity with a smooth surface, and an outer wall of lumpy appearance composed of different layers of soil material. They are commonly constructed by the larvae of different families of Coleoptera. Similar trace fossils were previously reported from the Asencio Formation (Late Cretaceous–Early Tertiary) of Uruguay and from the Djadokhta Formation of Mongolia (Late Cretaceous). These trace fossils constitute some of the only paleontological data from the Laguna Palacios Formation, allowing inferences about its paleoecology, paleoclimatology and paleogeography. Ecological preferences of Halictinae, as well as some features of the nests, suggest a temperate, seasonal climate and an environment dominated by low vegetation for the Laguna Palacios Formation, which is also compatible with sedimentologic and pedogenic evidence. The morphology of the nests, typical of North American halictinae, adds more evidence to the hypothesis of the existence of faunal interchange between North and South America by the Late Cretaceous. The fossil nests constitute some of the oldest evidence of bees in the fossil record, the third known record of bees of Cretaceous age and the first for the Southern Hemisphere. The two traces described are, together with those of Dakota and the Gobi Desert, the only trace fossils from paleosols of Cretaceous age that can be certainly attributed to insects.

Monesichnus ameghinoi roselli: A complex insect trace fossil produced by two distinct trace makers

Monesichnus ameghinoi, described by Roselli in 1987 from the Late Cretaceous‐Early Tertiary Asencio Formation of Uruguay, is here redescribed and interpreted. Tomographic images of 61 specimens reveal that the traces are composed of an exterior wall surrounding a fusiform to ovate cavity containing a meniscate filling. Many specimens also show a gallery system excavated in the fillings. A detailed tomographic study of one specimen shows that the exterior wall is perforated by tunnels that connect the gallery system with the exterior and that the galleries are generally horizontal or oblique. The fusiform structure having meniscate fillings is very similar to brood masses of extant species of Scarabaeinae, whereas, the internal gallery system, probably produced by a second trace maker, resembles the work of common deptoparasites of dung beetle nests. Two other ichno‐genera, Scaphichnium and Eatonichnus, also attributable to cylindrical brood masses of dung beetles, are compared with Monesichnus. The former...

Biotic association and palaeoenvironmental reconstruction of the Loma del Pterodaustro' fossil site (Early Cretaceous, Argentina)

Abstract A sedimentological analysis of the basal section of the Early Cretaceous, lacustrine LagarcitoFormation at “Loma del Pterodaustro” (San Luis, Argentina) and a summary of its biological components are presented. Three sedimentological facies can be recognized in the basal sequence of the Lagarcito Formation. Fossil remains are particularly abundant in laminated claystones of a facies interpreted as deposits formed in offshore areas of the lake. The preservation of delicate structures allows recognition of these deposits as a Konservat Lagerstatte. Up to now, rocks at “Loma del Pterodaustro” have yielded plants, conchostracans, semionotid and pleuropholid fishes, pterodactyloid pterosaurs, and a variety of invertebrate traces. The chronology of the Lagarcito Formation is discussed and it is concluded that this unit is of Albian age. The palaeoenvironment of deposition of the basal sequence of the Lagarcito Formation at “Loma del Pterodaustro” is interpreted as a perennial, shallow lake developed within an alluvial plain, under semiarid climatic conditions.

Cámaras pupales fosiles de coleópteros: el icnogenero Rebuffoichnus Roselli

The ichnogenus Rebuffoichnus was created by Roselli in 1987 to include a single ichnospecies, R. casamiquelai. In this contribution, this ichnotaxon is redescribed and compared with similar trace fossils attributed to coleopterans based on the examination of the holotype using computerized tomography and a large series of specimens collected recently from another locality of different age. Differences among Rebuffoichnus, Monesichnus, Teisseirei, and particularly Fictovichnus, are analyzed based on the type of wall, chamber fillings, and chamber shape.

Trace fossils on penguin bones from the Miocene of Chubut, southern Argentina

Several traces of biological interaction were found on penguin bones from the basal levels (Aquitanian) of the Miocene Gaiman Formation in the lower Chubut valley of the Provincia del Chubut, Argentina. The fossil-bearing beds were deposited in littoral to sublittoral environments within sediments of mostly pyroclastic origin. We interpret many traces to have been produced by predators and/or scavengers while the penguins were still in a breeding area. Many bones show cracking marks due to aerial exposure. The material is disarticulated as is usual in recent breeding areas. Potential predators were coeval terrestrial mammals, most probably marsupial carnivores. After a marine transgression, these bones were buried or exposed on the sea bottom where they could be colonized by algae, sponges, cnidarians, and other benthic organisms. We identified sponge borings in several bones. Other traces are interpreted to have been produced by echinoderms feeding on sponges or algae. No evidence of other invertebrate predators such as muricid or naticid gastropods, or decapods was found. Finally, other traces appear to have been generated by shark and possibly teleostean vertebrates feeding on epibionts. One coracoid is interpreted to have been marked by a shark that is common in the Gaiman Formation, the carcharhiniform Galeocerdo aduncus. From an ethological (Seilacherian) classification, traces on bones from the Gaiman Formation include Domichnia (sponge perforations), Praedichnia (terrestrial marsupials, sharks, teleosteans) and Pasichnia (echinoderms). Remarkably, remains of marine organisms with skeletons made of calcium carbonate are very poorly preserved in the Gaiman Formation. Only large oysters, sparse shell fragments, skeletal moulds, and bioturbation is evident. The fossil assemblage is mainly composed of phosphatic (e.g. teeth, bones, crustacean parts) and siliceous (sponge spicules, diatoms) remains.