Darwin’s ground sloth: taphonomic analysis of the Scelidotherium leptocephalum (Xenarthra, Folivora) holotype

NAHUEL RUIZ, GABRIEL; MONTALVO, CLAUDIA; DÍAZ-MARTÍNEZ, IGNACIO; TOMASSINI, RODRIGO

Madrid

Congreso; 4th Virtual Palaeontological Congress; 2023

Palaeontological Virtual Congress

Charles Darwin made geological and paleontological interpretations in the Bahía Blanca area (Buenos Aires Province, Argentina), during 1832 and 1833. Among the megamammals remains collected in Pleistocene fluvial deposits, from Punta Alta costal cliff, he recovered a nearly complete skeleton that constitutes the holotype of the extinct ground sloth Scelidotherium leptocephalum. Darwin made comments on the preservation state of this specimen and made an attempt to reconstruct its taphonomic history. In this contribution, we summarize the taphonomic features of this specimen without considering sullegic and trephic factors and also highlight Darwin´s facet as taphonomist. The skeleton, belonging to a juvenile individual, includes most of the skeletal elements (excepts appendicular elements and vertebrae, lost during World War II), articulated to each other and mostly complete. Weathering includes slight splitting in scarce elements. Abrasion is absent. Left hemimandible shows marks (e.g., pits, punctures, furrows, and crenulated edges) linked with predators/scavengers’ activity. All these features suggest a relatively short time of subaerial exposition. The presence of invertebrates (e.g., Cirripedia, Polychaeta, and Bryozoa) attached to the remains and traces of Polychaeta affecting their Surface indicate that, after the original burial, the skeleton was re-exposed (probably during Holocene) and affected by processes related to a water-sediment interphase in a marine environment. Some of these features were noted by Darwin in his publications, but others (e.g., tooth marks, invertebrate traces) are described for the first time here. The information obtained suggest a complex taphonomic history, which generates the particular interest to Darwin for this specimen.