Part III: The Biogeography of the Maltese Islands

The species found in the Maltese Islands give a clear picture of the origin and previous connections to the surrounding lands.

The shelled slug Testacella riedeli is the only terrestrial gastropod showing strong affinities with North African fauna (Giusti et al., 1995), however, this group of fauna is also derived from South European forms, which survived on landmasses fragmenting from South Europe and colliding into North Africa in the Early Miocene. The majority of animals and plants are closely related to Sicilian organisms, with fossils excluding the possibility that these were imported through human agency.

As an archipelago, Malta probably started to become exposed during the Messinian Salinity Crisis in the late Miocene. The virtual absence of macrofossils in some areas of the UCL suggests a supralittoral (or intertidal) landmass (Pedley et al., 1976). Subsequently, the archipelago was probably submerged and exposed several times with fluctuating sea levels and tectonic activity up to the Pleistocene. Pliocene deposits are absent on the Maltese Islands, suggesting aerial erosion.

The earliest suggestions for links with Sicily can be seen in the Quaternary deposits of Ghar Dalam, which contain fauna similar to that in mainland Europe such as species of Ursus, Palaeoloxodon, Cervus, Hippopotamus and other large mammals. Subsequent isolation of Malta can be deduced by the progressive dwarfing of some of these mammals in a process known as insular dwarfism (Zammit-Maempel, 1989) and the reverse process (insular gigantism) in the lizard Lacerta siculimelitensis (Boehme & Zammit-Maempel, 1982).

More information on the origin of the Maltese Islands is evident by looking at the clausiliid snails (Thake, 1985). Lampedusa originated from a Sicilian ancestor and invaded the land presently containing Malta and Lampedusa island in the Late Miocene. This is supprted by the fact that the island of Lampedusa harbours a species similar to the Maltese Lampedusa, namely L. lopadusae. On isolation of the islands during the Pliocene, the Lampedusa sp. in Malta differentiated into L. imitatrix which later also gave rise to L. melitensis.

Subsequently, either the sea-level fell again or the landmass rose so that Malta became connected to Sicily again. The Lampedusa-like ancestor on Sicily had meanwhile evolved into Muticaria macrostoma, which took the opportunity to invade the islands again. Being more competitive than Lampedusa sp., it managed to take over the areas occupied by Lampedusa, which it pushed to a restricted area on the southern coast of Malta. Interestingly, the island of Filfla was probably already detached from the Maltese mainland since Muticaria does not occur there, but a form of L. imitatrix thrives. Muticaria evolved into local forms following subsequent isolation of the Maltese mainland.

Plants are also mostly allied with South Europe forms, for example, Iris sicula and Ophrys oxyrrhyncos are endemic to Malta and Sicily. A relatively weaker North African link is also shown in plants such as Crucianella rupestris and Hypericum aegypticum.

References:

Boehme, W. & Zammit Maempel, G. (1982) Lacerta siculimelitensis sp. n. (Sauria: Lacertidae), a giant lizard from the Late Pleistocene of Malta. Amphibia-Reptilia, 3 (2-3), pp. 257-268.
Giusti, F., Manganelli, G. & Schembri, P. J. (1995). The non-marine molluscs of the Maltese Islands. pp. 1-608, Torino.
Pedley, H. M., House, M. R., & Waugh, B. (1976), The Geology of Malta and Gozo. Proceedings of the Geologists’ Association, 87, pp. 325-341.
Thake, M. A. (1985). The biogeography of the Maltese Islands, illustrated by the Clausiliidae. Journal of Biogeography, 12, pp. 269-287.
Zammit Maempel, G. (1977). An Outline of Maltese Geology. pp. 1-44, Progress Press, Malta.
Zammit Maempel, G. (1989). Ghar Dalam – Cave and Deposits. pp. 1-74, PEG, Malta.