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Monk Seal Fact Files

Mediterranean Monk Seal

(Monachus monachus)

Biology

Evolution

Historical Biogeography and Phylogenetic Relationships

Mediterranean monk seals are members of a group of mammals that have adapted well to life at sea, the Pinnipedia – seals. Their ancestral origins, as well as the phylogenetic relationships among the three commonly accepted Families of the group (the Otariidae, a.k.a. “eared” seals, the Odobenidae or walruses, and the Phocidae, a.k.a. “true” seals) and their 33 extant species, have generated considerable academic debate over the years (Arnason et al. 1995, Rice 1998, Berta & Adam 2001).

The Mediterranean monk seal and its congeners [Glossary], the Hawaiian monk seal (Monachus schauinslandi), and the Caribbean monk seal (Monachus tropicalis), now extinct (IUCN 2000), are members of the Subfamily Monachinae and are the only pinniped species to inhabit exclusively low-latitude temperate and tropical waters. It has yet to be established how the group came to frequent seas so far apart as the Mediterranean, the Caribbean and the Pacific. Reppening et al. (1980) and Reppening (1980) maintain, that the early monk seals started their evolutionary journey at the eastern seaboard of Northern America and reached Europe with the help of the warm Gulf Stream. According to Hendey (1972) and de Muizon (1982) however, the original ancestor of the monk seals began its journey in Europe, giving birth to the Mediterranean monk seal (Monachus monachus). Following the warm equatorial currents, some animals managed to cross the Atlantic and traveled north to the Caribbean, giving rise to the Caribbean monk seal. Eventually, after crossing to the Pacific, they reached the Hawaiian Islands and evolved into the Hawaiian monk seal. Latter hypothesis is backed up also by results of a recent study based on the analysis of mitochondrial and nuclear DNA (Fyler et al. 2005).

Regardless of origin or phylogenetic relationships, thorough study of the three species and their comparison with the fossils unearthed to date (Tavani 1943, Boettger 1951, Ray 1976, Springhorn 1978, Barnes et al. 1985) demonstrate that monk seals are, in evolutionary terms, a remarkably conservative group. “It seems that having once adapted to their environment they [monk seals] received little, if any, pressure to cause adaptive change” (Hendey 1972) and have therefore retained features that are characteristic of their early ancestors. The Hawaiian monk seal is often referred to as a “living fossil” due to these particular traits (Lavigne 1998, Lavigne & Johnson 2001).