Nightlife in Fgura

Walking through Fgura at 01:30AM, my girlfriend and I noticed a black shadow scurrying along the edge of the road. Too fast for a kitten and too large for a mouse, we soon realized it was a rat.

Of course I tried to stalk it quietly in the hope of obtaining a couple of good photographs, but apparently not quietly enough to prevent it from disappearing almost immediately, leaving me with just this:

I am inclined to think it's the common black rat Rattus rattus, though identification is not easy if only external morphology is taken into account.

Rats!

One of the commonest rodents in Malta, and the islands surrounding it, is the black rat Rattus rattus (L., 1758). It is usually found living together with man in highly artificial habitats all around the world, but has spread to any area where the temperature is warm enough and where food is in plentiful supply. Since this species is an omnivore (eats both vegetable and animal material), it also creates problematic issues when introduced in areas of ecological uniqueness.

In Malta this problem is seen in mostly relation to the unique reptilian fauna - on the islands of Selmunett, predatory actions of Rattus sp. are the main factors involved in the virtual extinction of the lizard Podarcis filfolensis kieselbachi (Fejervary, 1924), while the introduction of rats on General's Rock may result in the same situation with the lizard Podarcis filfolensis generalensis (Gulia, 1914) (cf. Sciberras & Schembri, 2008; Borg & Sultana, 2003).

The following black rat skulls have been found in Holocene deposits in Buskett and Mistra respectively. The other rat found in the Maltese Islands is the brown rat Rattus norvegicus (Berkenhout, 1769) which, despite its common name, can look highly similar to the black rat in form and colouration.

Examination of the skull, however, makes identification easier.

Black rat Rattus rattus (L., 1798) - specimens from Buskett (left) and Mistra (right). Top photo shows dorsal aspect of the skull, while the bottom photo shows the ventral aspect.

The black rat skull (as can be seen above) has a markedly pointed posterior end, whereas the brown rat's is more rounded. This feature is seen marked with a '1' in the drawings below. In addition, the bony ridges above the eyes also display a distinct difference. They are curved in the skull of the black rat while almost straight in the brown rat's. This feature is seen marked with a '2' in the drawings below. Both drawings are taken from the very interesting paper by Yiğit et al. (1998).

Black rat Rattus rattus (L. 1758) skull drawing

Brown rat Rattus norvegicus (Berkenhout, 1769) skull drawing

References:

Borg, J. J. & Sultana, J., 2003. The presence of the black rat Rattus rattus on Fungus Rock (Maltese islands). The Central Mediterranean Naturalist, 4 (1): 105-106.

Sciberras, A. & Schembri, P. J., 2008. Conservation status of St Paul's Island Wall Lizard (Podarcis filfolensis kieselbachi). Herpetological Bullettin, 105: 28-34.

Yiğit, N., Çolak, E., Sözen, M. & Özkurt, Ş., 1998. The taxonomy and karyology of Rattus norvegicus (Berkenhout, 1769) and Rattus rattus (Linnaeus, 1758) (Rodentia: Muridae) in Turkey. Turkish Journal of Zoology, 22: 203-212.

More on Pleistocene rodents

Dorothea Bate (1878-1951) was a British explorer and palaeontologist whose main interests were Mediterranean Pleistocene mammals. The first woman scientist to hold a permanent post at the Natural History Museum in London, she discovered and named a number of new species from Crete, Cyprus, Malta and the Balearic Islands.

Two Pleistocene vole species bearing her authorship are known from deposits in Għar Dalam, Malta. Voles, from the rodent family Cricetidae, are very similar to mice, but have a stouter body and a hairy tail. They are nowadays extinct from the Maltese Islands - Gulia (1858; 1890) and some subsequent authors list the vole Arvicola amphibius (L., 1758) as occurring in Malta, but this statement is not supported in any way, either by more recent authors on mammals (Lanfranco, 1969) or by the present writer's observations.

The fossil species named by Dorothea Bate are Terricola melitensis (Bate, 1920) and Terricola pauli (Bate, 1935), both originally placed in the Pitymys genus before it was known that this actually indigenous to North America (Chaline et al., 1999, Kotsakis, 2004). T. melitensis is closely related to Terricola savii (de Sélys-Longchamps, 1838), shown above, which nowadays lives mainly along the Italian peninsula (Brunet-Lecomte & Chaline, 1992; Chaline et al., 1999; Wilson & Reeder, 2005). T. pauli is a large enigmatic species with less obvious affinities, and indeed with a name not encountered much in the literature. The figure of the holotype from Bate's original description is reproduced below.


References:

Bate, D. M. A., 1920. Note on a new vole and other remains from the Ghar Dalam Cavern, Malta. Geological Magazine, 57: 208-211.

Bate, D. M. A., 1935. Two new mammals from the Pleistocene of Malta, with notes on the associated fauna. Proceedings of the Zoological Society of London, 247-264.

Brunet-Lecomte, P. & Chaline, J., 1992. Morphological convergences versus biochemical divergences in the holarctic ground voles: Terricola and Pitymys (Arvicolidae, Rodentia). Neues Jahrbuch für Geologie und Paläontologie, 12: 721-734.

Chaline, J., Brunet-Lecomte, P., Montuire, S., Viriot, L., & Courant, F., 1999. Anatomy of the arvicoline radiation (Rodentia): palaeogeographical, palaeoecological history and evolutionary data. Annales Zoologici Fennici, 36: 239–267.

Gulia, G., 1858. Repertorio di Storia Naturale. Malta, 68 pp.

Gulia, G., 1890. Elenco dei Mammiferi Maltesi. Il Naturalista Maltese, 1 (1): 2-3.

Kotsakis, T., 2004. The Plio-Pleistocene rodents of the Mediterranean islands: origin and evolution. 18th Senckenberg Conference 2004 in Weimar.

Lanfranco, G., 1969. Maltese mammals (Central Mediterranean). Malta: Progress Press, 36 pp.

Wilson, D. E. & Reeder, D. M. [eds], 2005. Mammal Species of the World - A Taxonomic and Geographic Reference [3rd edition]. Johns Hopkins University Press, 142 pp.

Picture of Terricola savii (de Sélys-Longchamps, 1838) from http://www.cogecstre.com/Vertebrati/images/ArvicolaDiSavi.jpg

The giant Maltese dormice

Insular gigantism is an evolutionary process that leads to individuals in a population becoming progressively larger in size than their ancestors.

This process occurs when a population is isolated - for example, on a part of land which detaches from the mainland, beoming an island - and therefore divorced from its previous ecosystem, with all the biotic and abiotic factors which this entails.

In the new environment, the successful species may become free from a considerable number of predators (which may not have enough resources in the new ecosystem, therefore decreasing or becoming extinct) and also competitors (which may not be so successful in the new ecosystem).

In Malta, during the Pleistocene, this process can be seen to have occurred with several species of reptiles and mammals. The extinct giant lizard Lacerta siculimelitensis Böhme & Zammit-Maempel, 1982, still has congeners of smaller size living around the Mediterranean.

Two very interesting 'giants' from Maltese Pleistocene deposits are Leithia melitensis (Adams, 1863) and Leithia cartei (Adams, 1867). Fossils of these two animals were found from Middle Pleistocene deposits in Mnajdra, Mqabba and Wied Inċita, and a jaw from the National Museum of Natural History is pictured above. The genus is from the rodent family Gliridae (the dormice), which does not exist anymore on the islands of Malta. The size of the former was about twice that of the recent species Eliomys quercinus L., 1766, a specimen of which can be seen below. L. cartei was only slightly smaller than L. melitensis - indeed, differentiation based solely on size may give errors (Petruso, 2004).

There is also another genus of Maltese Pleistocene dormice, which consisted of animals smaller than Leithia but still large by 'modern' standards. This genus, Maltamys, consists of two species - Maltamys wiedincitensis Zammit Maempel & de Bruijn, 1982 and Maltamys gollcheri de Bruijn, 1966.

Zammit Maempel & de Bruijn (1982) are of the opinion that both Maltamys and Leithia are derived from Eliomys, due to similarity in anatomical features. However, more recent publications (Petruso, 2002; Petruso, 2004) state that convergent evolution is more probable, meaning that Maltamys and Leithia are more distantly related than previously thought.

Some material of the mentioned four fossil species has since been found in other Mediterranean countries, but all type material comes from Malta.

In a future post we shall look at an evolutionary pattern which is the diametrical opposite of insular gigantism - insular dwarfism.

References:

Böhme, 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): 257-268.
Bruijn, H. de, 1966. On the Pleistocene Gliridae (Mammalia, Rodentia) from Malta and Mallorca. Proceedings Koninklijke Nederlandse Akademie van Wetenschappen, B 69 (1): 480-496.
Petruso D., 2002. Il contributo dei micromammiferi alla Stratigrafia e Paleogeografia del Quaternario continentale siciliano. Ph. D. thesis, University of Napoli.
Petruso, D., 2004. New data on Pleistocene endemic Sicilian-Maltese dormice (Gliridae, Mammalia). 18th Senckenberg Conference 2004 in Weimar.
Zammit Maempel, G. & Bruijn, H. de, 1982. The Plio/ Pleistocene Gliridae from the Mediterranean Islands reconsidered. Palaeontology, B 85 (1): 113-128.

Picture of Eliomys quercinus L., 1766 from http://upload.wikimedia.org/wikipedia/commons/d/d5/Eliomys_quercinus02.jpg