Three main geological units were involved in the Early Palaeozoic history of South America: (1) autochthonous intracratonic and pericratonic basins developed around the Gondwana basement (e.g. the Central Andean basin, CAB); (2) volcano-sedimentary basins marginal to Gondwana (e.g. Famatina and Puna volcanic belts); (3) crustal fragments accreted to the Andean margin through the Palaeozoic (e.g. Precordillera terrane). Knowledge of brachiopods, trilobites and bivalves has increased substantially over recent years, leading to the assembly of a more complete dataset. Furongian–Tremadocian trilobites from Famatina, western Puna and the CAB are mostly widespread forms (Olenid Fauna); however, the record of Amzasskiella and Onychopyge suggests a connection with East Gondwana, Siberia and Kazakhstan. At that time, the Central Andean brachiopods and bivalves show links with Iberia, Bohemia and North Africa. Floian trilobites from these regions show a complex array of endemic and peri-Gondwanan forms, indicative of relatively free migration for some taxa around Gondwana. Coeval brachiopods from Famatina and western Puna volcaniclastic rocks are of Celtic type, having some taxa in common with coeval faunas from south Peru, which would support the existence of a long and nearly continuous volcanic arc marginal to the Iapetus Ocean. Cambrian to Middle Ordovician platform carbonate rocks are confined to the Precordillera basin. Trilobites from the Lower and Upper Cambrian limestones of the Precordillera include key genera indicating Laurentian affinities (Arcuolenellus, Madarocephalus, Plethopeltis). Associated rhynchonelliformean brachiopods (e.g. Nisusia, Wimanella) are also typical of low-latitude palaeocontinents. Trilobites from the upper Tremadocian–Floian sequences of the Precordillera match those of the Bathyurid Fauna, whereas associated brachiopods include a high percentage of Laurentian taxa. From the Floian, a biotic exchange with Gondwana and Baltica becomes evident in the Precordilleran trilobite faunas. By Darriwilian times, Precordilleran brachiopods form a well-defined low-latitude realm, but numerous Celtic and Baltic taxa immigrated into the basin. By the Sandbian, affinities of Precordilleran brachiopods shift to West Gondwanan (North Africa, Armorica, Perunica and central Andes), probably reflecting the accretion of the Precordillera (Cuyania) terrane to the proto-Andean margin, although some mixed faunas persist. The low-richness CAB brachiopod, bivalve and trilobite assemblages display stronger ‘Mediterranean’ affinities than those from the Precordillera. In summary, there are abundant palaeontological data supporting the view that the Precordillera is a Laurentian-derived far-travelled microcontinent accreted to Gondwana during the Early Palaeozoic. A new early Middle Ordovician reconstruction of the southern and central proto-Andean margin is based on recently published geological data as well as the new palaeontological evidence summarized in this paper.
The ontogenies of three new species of Telephinidae, Telephina calandria, Telephina chingolo, and Telephina problematica are described from Arenig-Caradoc strata in the Argentine Precordillera, and compared with the larval stages of some other Proetida, including other telephinids.New findings reveal 1) a radical metamorphosis in the ontogenies of these Telephina species late in the meraspid period, not previously described among Trilobita; and 2) distinctive hypostomes of Telephinidae containing long, thin anterolaterally and dorsally splayed anterior wings. Early ontogenies of different species currently assigned to the genus Telephina fall into at least two distinct morphological and life history groups, and hypostomes (if correctly assigned in previous works) vary significantly. The three new species strengthen the hypothesis of a phylogenetic connection between Oopsites and Telephina.Three morphological types of protaspid instars are described for proetide trilobites. Two are anaprotaspides, and the third is a metaprotaspis. They always occur in the same sequence in the ontogeny, but no cases are known of all three types in the same species. These larval types are important for understanding the systematics and life cycles of the Proetida. Benthic/pelagic transitions identify four life history patterns among the the Proetida. The best larval synapomorphy for the Proetida is the distinctive metaprotaspid larval type, which is absent in very few proetides (some Telephinidae), perhaps as a result of heterochronic displacement of this stage into the meraspid period.
The following new Toernquistiidae from Whiterockian (Llanvirn to lower Caradoc) strata of the Precordillera, western Argentina, are described: Chomatopyge canasi new species, Lasarchopyge benedettoi new genus and species, Lasarchopyge correae new genus and species, Lasarchopyge new species A, and Paratoernquistia sanchezae new genus and species. Phylogenetic analysis suggests that the Toernquistiidae Hupé, 1953 (including Chomatopyge, Lasarchopyge, Mesotaphraspis, Paratoernquistia, and Toernquistia) is closely related to but distinct from the Dimeropygidae Hupé, 1953 (including Ischyrotoma, Ischyrophyma and Dimeropyge). It is difficult to find unique synapomorphies that unite toernquistiids and dimeropygids into a monophyletic group that excludes other proetides (e.g., hystricurids), although details of their ontogenies are similar. Several species of Toernquistiidae are known from the Argentine Precordillera (one species previously described), and other species of this family have been described from Australia, Baltica, China, Kazakhstan and Laurentia. Members of the Dimeropygidae are known only from Baltica and Laurentia.
Balseiro, D., Waisfeld, B.G. & Buatois, L.A. 2010: Unusual trilobite biofacies from the Lower Ordovician of the Argentine Cordillera Oriental: new insights into olenid palaeoecology. Lethaia, Vol. 44, pp. 58–75. The study of biofacies has proven to be relevant in the understanding of trilobite palaeoecology, palaeobiogeography and macroevolution. The widespread Olenid biofacies is one of the best known, and is usually interpreted as occuring in dysoxic environments. Tremadocian successions of the Argentinian Cordillera Oriental bear a diverse and long‐studied olenid‐dominated fauna. Based on cluster analysis, five distinct biofacies are defined for the middle Tremadocian (Tr2 stage slice), distributed from shelf (below storm wave base) to lower‐shoreface settings (above fair‐weather wave base). Ordination shows biofacies along two gradients, a bathymetrical one and another related to oxygen content. All of them are dominated both taxonomically and ecologically by olenids. This detailed quantitative palaeoecological study challenges current views suggesting instead that the Olenidae dominated a broad range of environments, from oxygenated shallow‐marine to dysoxic deep‐marine. Comparisons with largely coeval trilobite records from geodynamically and palaeobiogeographically disparate sites suggest that siliciclastic sedimentation appears as the most influential controlling environmental factor upon olenid distribution and dominance. Further comparisons across different climatic belts show that siliciclastic input controlled trilobite diversity gradients, even more than latitude. From an autoecological viewpoint distribution of traditional olenid morphotypes shows no relation to depth or to oxygen content, and at least some members of the group appear to have had the possibility of coping with low oxygen content, rather than being restricted to oxygen‐deficient environments. The analysis performed herein, together with recent research on the group, demonstrate that factors controlling olenid distribution are more complex than previously envisaged. □Biofacies, diversity, Olenidae, palaeoecology, Tremadocian, trilobite.
Community evenness has recently received much attention, either because it is related to ecosystem functioning or because it may affect estimation of diversity. Temporal and environmental trends in diversity and evenness of trilobite communities during the Late Cambrian – Early Ordovician of the Cordillera Oriental (north‐western Argentina) are here analysed. Richness and evenness increase through time in both deep subtidal (between fair‐weather and storm wave base) and offshore (below storm wave base) communities. Two significant patterns are superimposed on this general trend: (1) the magnitude of the increase in evenness is much more pronounced in deep than in shallower settings, and (2) richness and evenness trajectories are decoupled (while a significant rise in evenness is recorded in the middle Tremadocian (Tr2), an increase in richness is delayed until the late Tremadocian (Tr3)). In contrast to expectations, a single family (Olenidae) is dominant in samples associated with this earlier rise in evenness relative to richness. Hence, this trend is explained neither by the number of families present in the communities nor by the familial identity of the most abundant taxon. Large‐scale comparisons of the timing and geographical components of these trends are restricted to the patterns recognized in Laurentian North American studies. Results from the Cordillera Oriental mirror those of Laurentia regarding the rise in both metrics in deep marine settings. Nevertheless, the timing of this increase in richness and evenness is delayed in the Cordillera Oriental, supporting the idea that palaeogeographical regions differed in the nature and timing of ecological changes. Finally, the rise in trilobite alpha‐diversity through the Late Cambrian – Early Ordovician of the Cordillera Oriental supports the idea that trilobite alpha‐diversity did not decline worldwide, suggesting that the relative decline in trilobite alpha‐diversity is most probably caused by the dilution effect.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.