Testudinid turtle remains from the Late Miocene palaeo-island of Gargano, Italy, and an overview of Mediterranean insular tortoises

Abstract

The Late Miocene Gargano "Terre Rosse" in southern Italy has yielded a diverse vertebrate fauna that comprises an array of endemic taxa, including forms characterized by extreme sizes and unique morphologies. We here document new testudinid fossil remains from this insular assemblage. The material comprises a mandible, abundant (though mostly fragmentary) shell remains, appendicular elements, and a few vertebrae, originating from different localities within the Gargano assemblage. Based on its femur morphology, we tentatively refer the Gargano form to Solitudo, a late Neogene and Quaternary insular genus, otherwise known from a few Mediterranean islands. Unfortunately, the incomplete preservation of the trochanters hinders observation of the main diagnostic character of Solitudo, however, the similarities in the femoral head and diaphysis allow an open identification of the Gargano material as cf. Solitudo sp. Still, the Gargano tortoise offers new anatomical information on the Mediterranean insular tortoises. An interesting feature of the few preserved plastral elements is the presence of sulci as distinct raised ridges, a character that has been reported in other insular extant and extinct tortoises as well. The preserved hyoplastron has a medially straight and laterally concave humeropectoral sulcus and a wide axillary scute, pointing to some resemblance to geochelonans. Moreover, the morphology of the mandible from Gargano, which has its lingual serration reaching towards the symphyseal area, is also indicative of geochelonan affinities. If our identification is correct, the Gargano form would correspond to the earliest occurrence of Solitudo, denoting that this insular testudinid already radiated during the Late Miocene. A thorough overview of the diversity and taxonomy of insular testudinids from the Mediterranean islands is provided.