Ascocerid cephalopods from the Hirnantian?–Llandovery stages of the southern Paraná Basin (Paraguay, South America): first record from high paleolatitudes

Abstract

Ascocerid cephalopods are described for the first time from high paleolatitudes of Gondwana. Studied material was collected from the Hirnantian?–Llandovery strata of the Eusebio Ayala and Vargas Peña formations, Paraná Basin, southeastern Paraguay. The specimens are poorly preserved and were questionably assigned to the subfamily Probillingsitinae Flower, 1941, being undetermined at genus and species rank because diagnostic characters are not visible. A particular feature seen in our material is the presence of both parts of the ascocerid conch (the juvenile or cyrtocone and the mature or brevicone) joined together, which is a very rare condition in the known paleontological record. The specimens are interpreted as at a subadult stage of development because fully grown ascocerids would have lost the juvenile shell. A planktonic vertical migrant mode of life with a subvertical attitude is proposed for the juvenile, and a horizontal demersal nektonic mode for the adult form, as has been previously suggested. A subvertical orientation near the bottom is proposed for the subadult stage. We suggest that the immigration of ascocerids to southwestern Gondwana was possible through ocean currents that would carry the planktonic juveniles from low to high latitudes during the end-Ordovician postglacial transgression that flooded the intracratonic basins of the region.

First record of a nonpaleotropical intejocerid cephalopod from Darriwilian (Middle Ordovician) strata of central Spain

“…The absence of critical internal structures in many of these specimens does not allow for a taxonomic identification at genus or species level and many taxa are in need of a revision. Hopefully, the recent reappraisal of early Paleozoic peri-Gondwanan cephalopod faunas from elsewhere (e. g. Kröger et al, 2012;Evans et al, 2013Evans et al, , 2015Bogolepova et al, 2014;Sone, 2014, 2015;Aubrechtová, 2015;Cichowolski et al, 2015Cichowolski et al, , 2018Ghavidel-Syooki et al, 2015;Rolet and Plusquellec, 2016;Aubrechtová and Turek, 2018;Manda and Turek, 2018;Ebbestad et al, 2019;Fang et al, 2019) will stimulate future research on the Iberian cephalopods. specimen MGM-8187O, lateral view.…”

Cryptospores of Iapó formation: The first evidence of early land plants from Late Ordovician in Paraná Basin, Brazil.

“…During the Late Ordovician, the Parana Basin occupied the southern part of the western Gondwana on a wide depositional platform open to the ocean (Assine et al, 1994;Milani et al, 1995;Assine et al, 1998a) in high palaeolatitudes around 60°S (Adôrno et al, 2016;Cichowolski et al, 2018) (Fig. 2).…”

The first record of Hirnantian Ostracoda in South America: implications for the biostratigraphy and paleozoogeography of the Paraná basin

“…The Iapó Formation is composed of diamictites and fine-grained facies with dropstones, deposited during a glacial advance/retreat cycle (Assine et al, 1994, 1998; Alvarenga et al, 1998). The Hirnantian age of the formation (Assine et al, 1994, 1998) is based, among other features, on stratigraphic correlation with other glacial diamictite-bearing units, such as the Nhamundá and Ipú formations in Brazil (Caputo, 1998; Vaz et al, 2007), the Zapla in Argentina, the Cancañiri in Bolivia, and the Eusebio Ayala in Paraguay (Benedetto et al, 2013, 2015; Cishowolski et al, 2019). The fine-grained facies of the Iapó Formation have so far provided fossiliferous occurrences of archeogastropods and brachiopods such as Kosoidea australis Zabini et al, 2019, an inarticulate brachiopod species of the Hirnantian–Llandovery genus Kosoidea Havlíček and Mergl, 1988 (Zabini et al, 2019, 2021) (Fig.…”