Did titanic stingrays wander the Pliocene Mediterranean Sea? Some notes on a giant-sized myliobatoid stinger from the Piacenzian of Italy

Abstract

A fossil caudal spine of a stingray (Elasmobranchii: Batomorphii: Myliobatoidei) is here reported from upper Pliocene (Piacenzian) shallow-marine deposits exposed at the La Serra locality of Tuscany (central Italy). In spite of being incomplete, this specimen displays an amazing maximum preserved anteroposterior length of 420 mm, which to our knowledge makes it the longest stingray stinger ever reported from both the fossil and the Recent records. Tentatively referred to the family Dasyatidae, the herein described fossil appears to be more than twice as long as the longest caudal spines reported from any living myliobatoid species of the Mediterranean Sea. Therefore, it represents a stingray taxon that is no longer featured in the present-day Mediterranean ray assemblage, and as such, it expands our knowledge on the Pliocene biodiversity of the Mediterranean Sea. Given that the living species Bathytoshia brevicaudata (the smooth stingray) and Urogymnus polylepis (the giant freshwater stingray), while displaying the greatest values of total stinger length (up to c. 375 mm in the latter) among extant myliobatoids, are also known as the largest living species of stingrays besides Mobulidae, it seems much reasonable to hypothesise that the caudal spine from La Serra belonged to a very large- sized stingray individual which would have been larger than (or at least comparable in dimensions to) the largest members of the titan-sized B. brevicaudata and U. polylepis .