Skeletal Anatomy, Phylogenetic Relationships, and Paleoecology of the Eocene Urolophid Stingray Arechia Crassicaudata (Blainville, 1818) from Monte Postale (Bolca Lagerstätte, Italy)

In this paper we re-examine the taxonomy and systematic position of the Eocene stingrays from Bolca Lagerstätte which are traditionally assigned to Urolophus crassicaudatus (Blainville). The analysis of their tooth morphology supports an assignment to the Eocene stingray genus Arechia Cappetta, a taxon known from isolated teeth from the Ypresian-Lutetian of northern and western Africa. The teeth of the Bolca specimens differ from the type species A. arambourgi in some characters (i.e., labial face with concave profile just below the crest, convex lower down; lingual face slightly more developed than the labial, with convex profile in its upper part and a concave profile in its mid-lower region) that justify the recognition of a second species within the genus, i.e., A. crassicaudata. This taxon also shows a unique combination of features (e.g., pectoral disc large and rhomboid; tail short, 44–52% of total length; ca. 238 vertebral centra; distal segment of propterygia located between mouth and antorbital cartilage; mesopterygium single, not fused to radials; 100–117 pectoral radials; 15–17 pelvic-fin radials; elongated caudal fin of aplesodic type) that supports its sister-group relationship with the living urolophids Urolophus and Trygonoptera. Arechia was a typical inhabitant of the near coastal and warm habitats that characterize the Monte Postale paleoenvironment.

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