The oldest known record of a ground sloth (Mammalia, Xenarthra, Folivora) from Hispaniola: evolutionary and paleobiogeographical implications

Lazaro W Viñola-Lopez,Jorge Vélez-Juarbe,Jonathan I Bloch,Juan N Almonte Milan,Elson E Core Suárez

doi:10.1017/jpa.2021.109

Abstract

AbstractSloths were among the most diverse groups of land vertebrates that inhabited the Greater Antilles until their extinction in the middle-late Holocene following the arrival of humans to the islands. Although the fossil record of the group is well known from Quaternary deposits in Cuba, Hispaniola, and Puerto Rico, remains from older units are scarce, limiting our understanding of their evolution and biogeographic history. Here we report the oldest known fossil ground sloth from Hispaniola, represented by an unassociated partial tibia and scapula that are recognized as a single taxon from the late Miocene-early Pliocene of the Dominican Republic. The combination of characters observed on the tibia suggests a close relationship with Megalocnus, otherwise only known from the Pleistocene–Holocene of Cuba. These fossils fill a temporal gap between those previously known from the early Miocene of Cuba and those from Pleistocene–Holocene deposits in the region and provide additional support for a continuous presence of the group in the Greater Antilles since the Oligocene.

Highlights

Extant sloths are represented by only two arboreal genera, Bradypus Linnaeus, 1758, and Choloepus Illiger, 1811, found in the tropical forest of Central and South America
Absent from the Greater Antilles today, the region was inhabited by an impressive diversity of megalocnid sloths (Silva-Taboada et al, 2007)—an endemic clade thought to be sister to all other living and extinct continental members of Folivora, according to recent molecular analyses (Delsuc et al, 2019; Presslee et al, 2019)
These molecular analyses further suggest that the ancestors of megalocnid sloths arrived in the Caribbean by the late Eocene–early Oligocene (Delsuc et al, 2019; Presslee et al, 2019), which is supported by the presence of an unnamed species from the early Oligocene of Puerto Rico (MacPhee and Iturralde-Vinent, 1995)

Summary

Introduction

Extant sloths are represented by only two arboreal genera, Bradypus Linnaeus, 1758, and Choloepus Illiger, 1811, found in the tropical forest of Central and South America. The exposure surface is overlain by a 2.2-m-thick unit composed of clay-rich wackestone facies with abundant vertebrate fossils (e.g., pelomedusoid turtles), large benthic foraminiferans (e.g., soritids), bivalves, and gastropod fragments These marine invertebrate assemblages combined with the abundance of vertebrate fossils, including an undescribed rodent, a gavialoid, and pelomedusoid turtles, suggest an estuarine environment (0–10 m water depth) that was developed during relative sea-level rise and initial transgression after subaerial exposure (Core, 2015). Sr isotope-derived mean ages from marine bivalves (Kuphus incrassatus Gabb, 1873) located stratigraphically below and above the units of interest in this study indicate a late Miocene to early Pliocene age (ca. 7.15–5.57 Ma, Messinian–Zanclean) for the described units (Core, 2015; Ortega-Ariza et al, 2015)

Materials and methods

Discussion and conclusions