The phenomenon of Levantine nanism in the Mediterranean Sea has so far been described in invertebrates and fish. We explored the possibility that it would also apply to marine mammals. To that end, we compared total body length (TBL) and skull condylobasal length (CBL) of adult common bottlenose dolphins Tursiops truncatus collected along the Israeli coastline (representing the Levantine subpopulation) to those of specimens collected along the shores of western Mediterranean seas. Significant differences were found between mean (± SD) CBL values of 40 skulls from Israel and a pooled sample of 40 skulls from the Adriatic, Tyrrhenian, Ligurian and Balearic Seas (49.70 ± 1.87 and 52.18 ± 1.47 cm, respectively, p < 0.001). The mean (± SD) TBL of 26 Israeli animals were significantly smaller than those of 28 animals from the Spanish Mediterranean coast and 36 animals from the French Mediterranean coast (272 ± 18.0, 317.3 ± 16.1 and 313.4 ± 14.8 cm, respectively, p < 0.001). The results clearly demonstrate that animals of the Levantine subpopulation are significantly smaller than those residing in the west. A difference of 16% for TBL between populations fits the range of within-species dwarf morphs in cetaceans and, when translated into volume and mass, also fits the definition of Levantine nanism. KEY WORDS: Dwarfism · Craniometry · Mediterranean Sea · Marine mammals Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 438: [241][242][243][244][245][246][247][248][249][250][251] 2011 (Best 1985) and the dwarf killer whale Orcinus orca in the Antarctic (Berzin & Vladimirov 1983, Rice 1998, Pitman et al. 2007). There is no clear geographical-cline basis for this distinction, as the dwarf and the regular morphs are often sympatric.The common bottlenose dolphin (BD) Tursiops truncatus (Montagu, 1821) has a world-wide coastal distribution in tropical and temperate waters, including the Mediterranean Sea, the Black Sea, and the Red Sea (Leatherwood & Reeves 1983, Kurihara & Oda 2006). The species is very polymorphic, being characterized by variable body size, coloration and skull morphology, according to nutritional traits and geographic distribution (Turner & Worthy 2003). The older literature describes specimens from the Northeast Atlantic and the Northwest Pacific BD populations as being much larger than those of the Mediterranean and the Black Sea populations, the latter comprising the smallest specimens (BarabashNikiforov 1940). This was reaffirmed in a recent craniometric study by Viaud-Martinez et al. (2008), who found mean skull condylobasal lengths (CBL) of 452.3 mm (Black Sea), 520.3 mm (Mediterranean, predominantly from the western basin) and 537.4 mm (Atlantic, Gulf of Lion). Additionally, in regions such as the Northwest Atlantic, 2 distinct morphs are described, one coastal and the other deep-sea, based on differences in hemoglobin content, skull morphology, external body measurements and proportions; in general, the deep-sea morph was described as ha...