Early Jurassic Trigoniida (Bivalvia) from Argentina

Abstract

AbstractBivalves of the Order Trigoniida were abundant and diverse in the Andean Early Jurassic shallow-marine paleoenvironments. Based on extensive collections with detailed stratigraphic information from 40 localities in central-western Argentina, we describe 20 species (4 new) belonging to 11 genera (3 new) and 5 families (Groeberellidae, Trigoniidae, Prosogyrotrigoniidae, Frenguelliellidae, and Myophorellidae). The abundant material allows the description of ontogenetic development and intraspecific variability, highlighting the likely phylogenetic significance of previously underestimated features. Within Frenguelliellidae, we show that the stratigraphic range ofFrenguelliellaLeanza in the region is restricted to the Sinemurian–Pliensbachian. We proposePoultoniellanew genus for some late Pliensbachian–Toarcian species.JaworskiellaLeanza is limited to its type species, whereas for certain convergent forms we proposeMoerickellanew genus (most likely the oldest Myophorellidae).Pseudovaugonianew genus likely descended fromMoerickellan. gen., rather than from the highly diversePromyophorellaKobayashi and Tamura, and is unrelated toVaugoniaCrickmay.Frenguelliella chubutensis(Feruglio) andPromyophorella basoaltorumnew species are the most frequently occurring species. Some species were probably endemic (e.g.,Promyophorella?sanjuaninanew species), although a few (such asFrenguelliella eopacificanew species andPoultoniella jaworskiinew genus new species) had a wide paleolatitudinal range and occur throughout the Pacific coasts and terranes of the Americas, revealing a significant faunal interchange among marine basins during Hettangian–Pliensbachian times. The well-documented Argentinian Early Jurassic record shows a rapid recovery and radiation of the Trigoniida after the Triassic/Jurassic extinction. Many of the new taxa that evolved in America eventually dispersed worldwide by Toarcian and Middle Jurassic times.UUID:http://zoobank.org/82c0d95e-f147-4736-a417-ebc252911181.