Federico Marini

• Biodiversity Journal, 6 (1): 393-400 - MONOGRAPH

  Paolo Stara, Federico Marini, Giuseppe Carone & Enrico Borghi
  Distribution of two Amphiope L. Agassiz, 1840 (Echinoidea Clypeasteroida) morphotypes in the Western-Proto-Mediterranean Sea
  Proceedings of the 2nd International Congress “Speciation and Taxonomy”, May 16th-18th 2014, Cefalù-Castelbuono (Italy)

  ABSTRACT
  Several species belonging to the genus Amphiope L. Agassiz, 1840 (Echinoidea Astriclypeidae) from the Mediterranean Oligo-Miocene have been synonymised with A. bioculata (Des Moulins, 1835), the type-species of the genus, based on the interpretation given by Philippe (1998) as a taxon characterized by a large amount of morphological variability. A recent study introduced the characters of the internal test structure and the plating patterns as taxonomic tools in this genus. That paper indicated the occurrence of at least five different species in the examined sample from the Oligo-Miocene of Sardinia, thus pointing to a previous overestimation of the variability-range of the type-species and to the need of a review of the largely unresolved taxonomy of Amphiope. According to a recent study, Amphiope is considered as a shallow-water echinoid, inhabiting sandy bottoms with high hydrodynamic energy; so it represents a coastline marker, useful for the study of the paleo-geographic changes occurred in the Proto-Western-Mediterranean during the Miocene. The diffusion and speciation of Amphiope were highly influenced by those changes. In particular, the speciation rate of this genus was likely favored by the occurrence of isolated populations created when islands (e.g.: Baleares, Calabria, Corse, Kabylies, Sardinia) separate from the mainland, above all in the western part of that Basin, because of the opening of the Balearic Basin during the Late Oligocene-Early Miocene and of the Tyrrhenian Sea during the Burdigalian-Tortonian (references in this work). Two main morphotypes of Amphiope sensu Stara & Sanciu (2014), developed in the Western Mediterranean from the late Oligocene to the late Miocene. They are herein called the “bioculata” group, characterized by roundish to broad elliptical lunules with major diameter/minor diameter ratio (SI) < 1.59, and the "nuragica" group, with more or less narrow lunules and SI > 1.6. According to this authors, most Miocene forms with narrow elliptical lunules would derive from A. nuragica (Comaschi Caria, 1955), late Oligocene-early Miocene of Sardinia, the most archaic form so far known of this genus. The forms belonging to the “bioculata” group likely derived from a different common ancestor bearing round to broad ovoidal lunules. “A. bioculata” described by Cottreau (1914), from the Burdigalian (Philippe, 1998) of Saint Cristol (Nissan, Herault, France), is so far the most ancient known form belonging to this group. This work proposes a possible speciation sequence of the “nuragica” group.

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