The strophomenide brachiopodAhtiellaÖpik in the Ordovician of Gondwana and the early history of the plectambonitoids

Abstract

The Precordilleran species Ahtiella argentina Benedetto and Herrera, 1986 is redescribed and illustrated and Monorthis coloradoensis Benedetto, 1998b from northwestern Argentina is reassigned to the genus Ahtiella Öpik, 1932. Ahtiella famatiniana new species from volcaniclastic rocks of the Famatina range (western Argentina) and Ahtiella tunaensis new species from the Precordillera basin (Cuyania terrane) are proposed. Paleogeographic and stratigraphic evidence strongly suggests that Ahtiella originated in the Andean region of Gondwana to further migrate to Avalonia, Baltica, and Cuyania. Contrary to previous assumptions, the fossil record from the Famatina volcaniclastic succession suggests that the plectambonitoid Ahtiella famatiniana n. sp. evolved from the hesperonomiid orthoid Monorthis transversa Benedetto, 2003 that always occurs in the underlying strata. Phylogenetic analysis of Ahtiella species shows that A. famatiniana n. sp. and the Peruvian A. zarelae Villas in Gutiérrez-Marco and Villas, 2007 are not only the earliest species of the genus but also are morphologically intermediate between Monorthis Bates, 1968 and the later and more derived species of Ahtiella from Baltica and Cuyania. If, as empirical evidence presented here shows, Ahtiella originated from Monorthis through a series of minor transformations, then the impressive morphological gap between orthides and strophomenides was bridged through short-time cladogenesis events, suggesting that it might not have a definite discontinuity between the species level evolution and the origin of higher taxa (macroevolution).UUID: http://zoobank.org/4b8c5442-ea2c-41b2-97f7-4c0a8b0384a2

Phragmolites (Gastropoda) from the Late Ordovician of the Peruvian Altiplano

“…Most records from here represent widespread taxa, and many identifications can be considered uncertain. It is suggested that the Precordillera Basin derived from the Laurentian margin sometime in the Cambrian, amalgamating with Gondwana in the Middle to Late Ordovician (Benedetto et al, 2009; Torsvik and Cocks, 2013; Benedetto, 2018, and references therein), which could explain the general Laurentian signal. An alternative hypothesis suggests a parautochthonous Gondwanan origin with placement in the paleotropical part of Gondwana before rifting and migration along a transform fault to its present position outboard of the Famatina magmatic belt, adjacent to the central Andean Basin (Aceñolaza et al, 2002; Finney, 2007).…”

Lower Tremadocian (Ordovician) lingulate brachiopods from the Central Andean Basin (NW Argentina) and their biogeographical links

“…Four distinct lower Palaeozoic sedimentary domains can be recognized in southern South America (Benedetto 2018, Waisfeld et al 2023: (1) the intracratonic se dimentary cover of the Amazonian Craton in Brazil, 2) the clastic platforms surrounding the Amazonian Craton and the Pampia terrane, through Peru, Bolivia, and Northwestern Argentina, known as the Central Andean Basin (CAB), (3) the early Palaeozoic subduction-related parautochthonous volcanic arcs and associated volcanosedimentary basins marginal to Gondwana continent (e.g. the Famatina Basin), and (4) the crustal fragments accreted to the proto-Andean margin of Gondwana, of which the better known is the Laurentian-derived Cuyania (or Precordillera) terrane.…”