Diversity and biostratigraphy of the late Oligocene-late Miocene sand dollars (Echinoidea: Scutelliformes) of Argentina and Uruguay

Claudia-J Del Río,Sergio Martínez

doi:10.15517/rbt.v69isuppl.1.46324

Abstract

Introduction: Scutelliforms were diverse and widespread in shallow marine environments during Neogene times in South America. Nevertheless, they have almost never been used as biostratigraphic tools. Objective: To provide a refined stratigraphic frame useful for calibrating temporal dimensions of scutelliform diversity from Argentina and Uruguay and its correlation with the molluscan assemblages previously proposed. Methods: A detailed survey of their geographic and stratigraphic provenance was carried out. We revised both the bibliography and collections (institutional and from our own field work). Results: The group is represented by 14 species belonging to six genera, and four assemblages were identified. Numerical dates of the Neogene marine rocks obtained recently allowed their placement in a chronological scheme: “Iheringiella” sp. A is restricted to the late Oligocene, the genera Camachoaster and “Eoscutella” and the species Monophoraster telfordi to the early Miocene, Abertella gualichensis and Abertella miskellyi to the middle Miocene, and Monophoraster duboisi, Amplaster coloniensis and Amplaster ellipticus to the late Miocene. Non-lunulate scutelliforms are not restricted to the late Oligocene as previously supposed. The oldest occurrence of the genus Monophoraster corresponds to the early Miocene, and along with Iheringiella are long-living taxa that embrace the 25.3 Ma-18.1 Ma (Iheringiella patagonensis) and approximately 15 Ma-6.48 Ma (Monophoraster darwini) intervals. The presence of Iheringiella in the early Miocene of northeastern Patagonia is corroborated, reaching there its northernmost distribution. Monophoraster darwini has a temporal range from the late Miocene (where it was previously thought to be restricted) back to the middle Miocene, since this is the species yielded in the well-known and discussed “Monophoraster and Venericor Beds”. Conclusions: The Paleogene-Neogene scutelliforms of Argentina and Uruguay range from the late Oligocene to the late Miocene. There is a good correspondence among the numerical ages, molluscan biozones and scutelliform assemblages.

Highlights

Scutelliforms were diverse and widespread in shallow marine environments during Neogene times in South America
We carried out a bibliographic analysis that retained only those references with adequate descriptions or illustrations concerning South American scutelliforms, and re-examined more than 300 specimens housed in different institutions, including their types when available
Stratigraphic setting of scutelliform beds: The shallow marine late Oligocene-late Miocene sedimentary sequence exposed in Argentina and Uruguay is represented by the San Julián Formation, El Chacay, Estancia 25 de Mayo and Monte León Formations, Chenque Formation, Gaiman, Bajo del Gualicho, Vaca Mahuida Formations, and the “Isla Escondida Beds” and the Puerto Madryn, Río Negro, Paraná and Camacho Formations

Summary

Introduction

Scutelliforms were diverse and widespread in shallow marine environments during Neogene times in South America. They have almost never been used as biostratigraphic tools. A is restricted to the late Oligocene, the genera Camachoaster and “Eoscutella” and the species Monophoraster telfordi to the early Miocene, Abertella gualichensis and Abertella miskellyi to the middle Miocene, and Monophoraster duboisi, Amplaster coloniensis and Amplaster ellipticus to the late Miocene. Monophoraster darwini has a temporal range from the late Miocene (where it was previously thought to be restricted) back to the middle Miocene, since this is the species yielded in the well-known and discussed “Monophoraster and Venericor Beds”. There is a good correspondence among the numerical ages, molluscan biozones and scutelliform assemblages

Objectives

Methods

Results

Conclusion