The Monte Pellegrino faunal complex is likely from the early Pleistocene age and its fauna is endemic, unbalanced, and poorly diversified, mainly composed by small mammals (Figure 4).

During Early Pleistocene, Sicily was made up of two islands, and the volcano Etna had not yet emerged; Calabria also consisted of two small islands separated by narrow sea straits, while the Strait of Messina was wider than today (Figure 4) [6]. Malta was emergent [27].

Different degrees of endemism, mainly consisting of enlargements of size, have been observed in species composing the FC. Asoriculus burgioi, Apodemus maximus and Maltamys sp. have marked endemic features and are dubitatively considered relics of an undocumented previous fauna, dubitatively spread during Messinian [28,29]. Thaler [14] reported also Leithia sp. from Monte Pellegrino. Daams and De Bruijn [30] considered an ancient form of Leithia as the precursor of Leithia and Maltamys species present in Middle and Late Pleistocene of Sicily and Malta. The authors identified the ancestor of Leithia (and Maltamys) in a form of Eliomys sp. probably dispersed during Messinian (late Miocene). Pellegrinia panormensis has very marked endemic features and has been compared to African Ctenodactilids [14]. Hypolagus peregrinus and Mustelercta (=Pannonictis) arzilla show moderate endemism, and are considered affine to European forms, dubitatively related to an Early Pleistocene dispersal [15,31]. There are no fossil records of mammals from the Early Pleistocene of Malta and Calabria [6,27].

The Spinagallo faunal complex is early Middle Pleistocene in age and is strongly impoverished in number of species (Figure 3), as well as unbalanced in ecological composition [2,5].

During early Middle Pleistocene (Figure 5), Sicily was still consisting of two small islands [32]; the Strait of Messina persisted as a sea strait for the entire Quaternary, with some variations in wideness [10,33]. During Middle Pleistocene, a general uplift influenced all of Calabria, which progressively attained its present shape ([6] and references therein). During early Middle Pleistocene, Calabria was a land not easy to cross, characterized by high mountains and few extended plains [6]. Malta was emerged [27].

Palaeoloxodon antiquus, probable ancestor of Palaeoloxodon falconeri [25,34], is recorded in northern Calabria, in the “Mercure A” site [35], attributed to the Middle Galerian. Praemegaceros cf. P. verticornis and Dama cf. D. clactoniana, recorded at “Mercure A” site, did not disperse to Sicily [6]. There are no other records of mammals from Calabria. On Malta, Palaeoloxodon falconeri is associated with Maltamys gollcheri, Maltamys wiedincitensis (dubitative), Crocidura esuae and Lutra euxena. The Maltese otter is the only species not shared in common with Sicily. Moreover, in Sicily, Maltamys wiedincitensis, considered a descendant of M. gollcheri, is present in the younger Maccagnone FC. Zammit Maempel and De Bruijn [36] consider Maltamys gollcheri as a junior synonym of Leithia cartei, while Masini et al. [4] consider Maltamys sp.–wiedincitensis–gollcheri as chronospecies and Leithia cartei as a distinct species. In both cases, endemic dormice (Leithia and Maltamys) seem to be derived by taxa recorded at Monte Pellegrino, it follows, therefore, that their ancestors reached Sicily and Malta before Quaternary. The probable ancestor might have been a form of Eliomys because the genus was present in both continents during Miocene, though this is not enough to indicate African or European origin [37]. Since dormice are susceptible to passive transport on natural rafts and since their phylogeny is uncertain, it is still not clear if their forerunners reached Sicily from Africa or from Italy.

The shrew Crocidura esuae is considered by Kotsakis [38], Esu et al. [39], and Sarà [40] to be the ancestor of Crocidura sicula, a species present in the fossil record since Late Pleistocene (San Teodoro FC) and still living in Sicily, while it is considered to be the descendant of a newcomer that arrived in the Late Pleistocene, according to Masini et al. [4]. The debate is still open, but genetic and morphological data indicate marked differences among Crocidura sicula and species from the Italian peninsula and, alternatively, strong affinities with living afro-tropical forms [41,42]. Studies on DNA provided by Dubey et al. [43] consider Crocidura sicula to be the descendant of the Saharan shrew Crocidura tarfayaensis, with a split between Saharan and Siculo-Maltese clades dated to Messinian. Taxa possibly related to Crocidura esuae have not been recorded in the Monte Pellegrino FC, although a Late Miocene spreading from North Africa cannot be excluded. Therefore, this small mammal fauna has been long persistent on Sicily and its spreading, probably by floating on natural rafts, might have occurred before Quaternary in a quite different paleogeographical setting.

Large mammals reached Sicily by swimming, most likely from peninsular Italy. The forerunners of the dwarf elephant, Palaeoloxodon falconeri, and the endemic otter, Lutra trinacriae, were good swimmers. Living elephants have been observed swimming the seas, mainly in the Indian Ocean, in order to reach islands [44,45]. They can swim for long distances, searching a new habitat, and are able to see islands on the horizon and to smell edible food resources [44]. Otters have good dispersal ability and they can spread to islands as far as 30 km [46]. Therefore, it can be deduced that the ancestors of Palaeoloxodon falconeri and Lutra trinacriae reached Sicily and small islands of Calabria by swimming. Palaeoloxodon falconeri underwent a strong reduction in size, being an adult male high about 120 cm at the scapula, and heavy at about 170 kg [47]. Moreover, the dwarf elephant shows important changes in skull morphology and body proportions [47]. Lutra trinacriae was moderately reduced in size, probably as a consequence of the permanence of its populations on the island [48]. Chiroptera are recorded but still undetermined [2]. Bats, birds, reptiles, and amphibians associated with mammals enable some paleoecological considerations.

Small vertebrates other than mammals that probably arrived by transport on natural rafts are: Amphibians (Bufo cf. B. viridis, Hyla sp., and Discoglossus cf. D. pictus); Reptiles (Chelonia: Emys orbicularis, Testudo hermanni, and a giant form of Geochelone sp.); Squamata: (Coluber cf. viridiflavus, Natrix sp., Lacerta viridis and the giant endemic Lacerta siculomelitensis) [2].

Avifauna was diversified, with 66 species [2,49]. Among birds, 24 migrant species have spent winters in Sicily [49,50]. Fresh waters have been available, as indicated by the presence of Gruiformes and Anseriformes [50]. The presence of sedentary birds such as Piciformes, Colombiformes and Passeriformes indicates permanent availability of fruits, seeds and invertebrates [50]. Some endemites were present: the giant crane, Grus melitensis, the dwarf swan Cygnus equitum, the Strigiformes Tyto mourerchauvireae and Aegolius martes, both giant species, and Athene trinacriae, which had lengthened forelimbs [49]. Tyto mourerchauvireae seem to have evolved from T. balearica, an owl common in the Mediterranean area, and was at the top of the food chain [51]. This species preyed upon the three species of Gliridae, the shrew Crocidura, and several birds [51]. The presence in Sicily of large-sized Gliridae could have favored the evolution of T. mourerchauvireae, which became extinct in the Maccagnone FC, probably for the arrival of Bubo bubo [51].

Guglielmo and Marra [50] proposed a reconstruction of the food chain. During the night, Strigiformes preyed on small vertebrates; in daylight, Colombiformes, Passeriformes, and small vertebrates were preyed upon by Falconiformes. Birds’ eggs and nestlings might have been eaten by reptiles, dormice and, occasionally, by otters. Elephants did not have had predators and intra-guild competitors. Their strong reduction in size could be related to these peculiar paleocological conditions, and perhaps it occurred through anticipation of the sexual maturity and shortening of the gestational period [52]. In the opinion of Palombo [47], the strong reduction in size of Palaeoloxodon falconeri could also be related to the availability of niches typical of medium- and large-sized herbivores. The reduced size allowed the persistence of P. falconeri populations with a number of individuals adequate to avoid extinction. Moreover, a smaller body mass reduced the deep modification of vegetation typically produced by elephants.

The Maccagnone faunal complex is late Middle Pleistocene in age and almost completely renewed with respect to the Spinagallo FC (Figure 3, Figure 6). Among small mammals, Leithia melitensis and Crocidura esuae persist from the previous FC; Maltamys gollcheri evolves in Maltamys wiedincitensis [2,4,5]. Microtus (Terricola) sp. has “subterraneomorph” characteristics, similar to the European Microtus (Terricola) subterraneus and could have spread to Sicily during MIS 6 [53]. The dwarf elephant Palaeoloxodon falconeri became extinct, while Lutra trinacriae persists. Large mammal fauna is renewed and represented by an association impoverished but balanced and diversified, with a moderate endemism.

In the late Middle Pleistocene, the geography of Sicily, Malta and Calabria was attaining its present-day shape, with an extension of inner and coastal plains (Figure 6). The arrival of several new taxa of European origin can be related to favorable conditions of dispersal through the Strait of Messina [2,5,47]. Dispersals might be related to several events that occurred during the stadial oscillations of the sea level in late Middle Pleistocene (MIS 10, MIS 8, and MIS 6 [47]), or to a single event that occurred 0.3 Ma (MIS 8 [4]). A combination of both the tectonic uplift of Calabria and Sicily and low-stand phases of the sea level likely reduced the relative distance between the two coastlines of the Messina Strait (Figure 6). The strait has been crossable by large mammals with different dispersal abilities, ranging from good swimmers (elephant, cervids) to animals with more or less limited swimming ability, such as bovids and carnivores.

The long-term persistence of the small mammal fauna has been attributed to the absence of new competitors, due to a geographical filter active in the Strait of Messina such as a partially emerged sea floor or a swampy lagoon system, crossable only by large mammals [2,4,5]. However, this hypothesis is not easily sustainable, because of the fact that small mammals can follow more dispersal ways than large ones can; they can disperse simply by walking, and also on natural rafts. Furthermore, there is no reason why a partially emerged bridge cannot be crossed by small mammals. And there are no geological data to support the existence of this peculiar land connection. Paleoecology, discussed in the following, can be the key.

The poor quality of the fossil record in the Middle Pleistocene of Calabria allows limited investigations on the dispersal of the precursors of the Maccagnone FC [6]. However, the latest Middle Pleistocene fossil assemblages from Calabria include all the large mammals considered precursors of Middle Pleistocene endemic species of Sicily [6]. Their presence in Calabria, when they spread to Sicily thereby originating the Maccagnone FC, can only be hypothesized. More than one dispersal might have occurred. As a matter of fact, “normal” sized elephants found in Sicily at Contrada Fusco (MIS 5) can be interpreted as newcomers, or at least as strong intraspecific variations [47]. It is not difficult to imagine elephants that swam several times across the Messina Strait. Among mammals of the Maccagnone FC, only elephant and cervids had swimming attitude, while hippopotamus, wild boar and bear had a good attitude to humid/freshwater environments. Other mammals did not swim, and therefore paleogeography might have been favorable to their dispersal.

On the basis of the available geological and paleontological data, Marra [6] hypothesized a partially emerged “stepping stone” way in the Strait of Messina, available during regressive phases. Mammals could have reach the island crossing the “sill,” an area of the Strait of Messina that is currently deep (80–100 m offshore Sicily) and irregular in its western portion, though shallower (60–100 m offshore Calabria) and smoothed in its eastern part [54]. In correspondence to the “sill,” the Strait of Messina is at present 3 km wide. The sea strait had a maximum wideness in Upper Pliocene–Lower Pleistocene; later, it underwent a sensible narrowing, with morphology very similar to present day [10,33]. The invertebrate fossils and extant forms of marine environment indicate the persistence of elevated hydrodynamics in the Strait of Messina, which exclude the emergence of a land bridge for all Quaternary until now [10,33]. The tectono-sedimentary evolution of the “sill” indicates a sensible uplift from the late Middle Pleistocene [10]. The emergence of small areas of the “sill” during sea-lowering phases occurred since late Middle Pleistocene would be consistent with geopaleontological data and could have allowed “stepping stone” dispersals [6]. Also, the possibility of a “pendel route” (sensu Dermitzakis and Sondaar [8]) has to be taken into account, considering that the Strait of Messina was a narrow sea barrier that enabled the transit of mammals with reduced dispersal abilities. Low-stand phases might be responsible of the faunal renewal on Malta. The faunal association recorded in the late Middle Pleistocene of Malta is impoverished with respect to Sicily and includes Leithia cartei, Maltamys wiedincitensis, Lutra euxena, Palaeoloxodon mnaidriensis, Hippopotamus melitensis, and Crocidura esuae [5,27]. Small mammals persist, while the dwarf elephant is replaced by the new species spread from Sicily. The Maltese hippopotamus is considered the descendant of Hippopotamus pentlandi of Sicily [5,27]. Connections between Sicily and Malta were occasional and submitted to a strong filter, and only two species with aquatic attitude (elephant, hippopotamus) reached the island. On the other hand, the small island did not offer to possible newcomers source availability comparable to that of Sicily.

The increasing biodiversity, the moderate endemism of the herbivores, and the presence of non-endemic carnivores (with top predators among them) observed in the Maccagnone FC are indicative of a large island with diversified environments in addition to a paleogeography enabling the dispersion of species with different dispersal abilities [6].

On the island, species evolved endemic features. Large herbivores were moderately modified with respect to the mainland ancestors, showing a slight reduction in size, while carnivores did not evolve endemic features and included top predators [1,2,5]. Medium-sized ruminants (Cervus elaphus siciliae and Dama carburangelensis) reduced their size (intended as linear dimensions of the skeleton) by about 20%–25% with respect to their ancestors (Cervus elaphus and Dama dama cf tiberina); the large ruminant Bos primigenius siciliae reduced its size by about 20% with respect to Bos primigenius [1,2,55,56]. Endemic features observed in non-ruminant herbivores are of different degrees. Hippopotamus pentlandi had not marked endemic features and a reduction of about 10%–15% in linear dimensions with respect to the ancestor H. amphibius [57]. Palaeoloxodon mnaidriensis had marked allometries and a strong reduction in size, about 50%–60% with respect to the ancestor Palaeoloxodon antiquus [25]; some morphological modifications are related to dwarfing processes, but some others might be related to ecological adaptations (i.e., fusion of radius and ulna; [25]). Omnivorous (Sus scrofa and Ursus arctos) and carnivorous (Canis lupus, Crocuta crocuta spelaea, Panthera leo spelaea) large mammals did not modify their size [2,4,5,58].

Small mammal fauna persisted from the Spinagallo FC, with only one new arrival. The reason for this long persistence might be found in paleoecology. Although sustaining the existence of a filtering land bridge, which prevented the spreading of small mammals, Masini et al. [4] did admit that longer survivorship of small mammals might be due to the equilibrium they established with predators, or to their prolificacy and food requirements. Guglielmo and Marra [50] argued that small mammals could have established deep-rooted populations that defeated possible newcomer competition. Moreover, they might have not been affected by the extinction of their primary predator Tyto mourerchauvireae, replaced by Bubo bubo, having similar body size and predatory attitude [49]. The stability of small mammal populations can also be attributable to the absence of possible secondary predators (i.e., small carnivores) that might have perturbed their ecological equilibrium [50]. It is worth noting that endemic Gliridae disappeared when Vulpes vulpes, their possible secondary predator, entered the island and were replaced by species smaller in size (San Teodoro FC). The life of secondary predators did not depend on the survival of their secondary prey, so the red fox might have caused the extinction of endemic Gliridae [50]. Moreover, small mammals can risk overpopulation (especially in conditions of equilibrium with predators), and the evolution of large body size, probably accompanied by lower metabolic rate and greater life duration, might have been a good life strategy [50]. Furthermore, ecological niches available for possible newcomers were stably occupied.

Among small vertebrates, the amphibian Discoglussus cf. pictus and the Reptiles Emys orbicularis, Testudo hermanni and Lacerta siculomelitensis persisted, while the giant turtle Geochelone sp. became extinct [2]. The other amphibians (Bufo cf. viridis, Hyla sp.) and Reptiles (Coluber cf. viridiflavus, Natrix sp., Lacerta viridis) present in the previous fauna have not been recorded. However, molecular data by their living relatives seem to indicate their long persistence in Sicily [50].

The avifauna underwent several changes [49]. The number of migrant birds increased, with taxa preferring fresh waters. Podicipediformes and Pelicaniformes, adapted to marine waters, dispersed to Sicily. Anseriformes were represented by new species and Ciconiformes increased, with some species of swamp environment. Among Caradriformes, Numenius phaeopus, a species adapted to humid environments, was present. Passeriformes sensitively decreased. Guglielmo and Marra [50] argued for a good availability of humid and fresh water environments. It is likely that a good ichthyofauna was present in the freshwaters, sufficient to sustain the rich avifauna. Endemic Strigiformes disappeared, replaced by Bubo bubo. Among Falconiformes, it is worthy of noting the presence of Aquila heliaca, a bird able to prey on animals with a weight up to 10 kg (mainly mammals and birds). The eagle was probably a menace for the cubs of many mammal’s species, while the other Falconiformes preyed upon small vertebrates, such as amphibians, reptiles, birds and dormice [50].

Top predators (Canis lupus, Crocuta crocuta spelaea, and Panthera leo spelaea) fed on populations of herbivores, mainly cervids (Cervus elaphus siciliae and Dama carurangelensis). Bovids, small mammals, and birds have probably been occasional prey, as observed in the behavior of the extant wolves, hyenas, and lions. As scavengers, large predators also fed on dead animals. In conditions of isolation and reduced areas, the slight reduction in size of herbivores might have been a strategy to maintain the number of individuals adequate to avoid extinction. Furthermore, herbivore populations had been numerous enough to feed three species of social predators, which did not evolve endemic features because the size of endemics fell into the variability range of usual prey.

In the opinion of Palombo [47], Hippopotamus pentlandi and Palaeoxodon mnaidriensis, thanks to their reduction in size, occupied ecological niches vacant on the island, that are respectively those of large horses (grazers) and rhinoceroses (mixed-feeders).

Omnivorous mammals (Sus scrofa and Ursus arctos) exploited various food resources, without suffering the effects of isolation.

Large mammal association is indicative of a composite environment, with prairies and open woods, typical of Mediterranean “macchia” (Table 1).

In the San Teodoro Faunal Complex (Figure 3), some large mammals of the previous fauna became extinct (Panthera leo spelaea, Hippopotamus pentlandi, Dama carburangelensis) and the newcomers (Vulpes vulpes, and Equus hydruntinus) did not evolve endemic features [2]. Bison priscus siciliae might be considered as a newcomer with moderate endemic adaptations, according to Petruso et al. [11]. As already discussed, the arrival of Vulpes vulpes might have been decisive for the extinction of the endemic small mammals’ fauna and the entrance of a renewed stock on the island.

Among small mammals, the endemites Leithia melitensis and Maltamys wiedincitensis became extinct, while the new presence of Apodemus sylvaticus (non endemic), Crocidura sicula, and Microtus (Terricola) savii is recorded. As previously mentioned, Crocidura sicula has been considered a descendant of a new immigrant species [4] and of Crocidura esuae ([38,39,40]. Microtus (Terricola) savii is considered a newcomer, likely dispersing during MIS 4–3, and not a descendent of the Microtus (Terricola) “subterraneumorph” of the Maccagnone FC [53], and probably evolved in the endemic Microtus (Terricola) savii nebrodensis, currently present in Sicily [11].

Paleogeography of Sicily and Calabria was similar to nowadays, with some local variations in the coastal lines (Figure 7). The arrival in Sicily of a new stock of small mammals and some large mammals has been related by Bonfiglio et al. [2] to the opening of a land bridge as a consequence of a eustatic low stand, and by Marra [6] to a “stepping stone” dispersal way. Considerations made for the Maccagnone FC are valid also for the San Teodoro FC: if the hypothesis of a “stepping stone” way can be accepted, small mammals could have been easily spread by natural rafts and/or by swimming crossing a partially emerged “sill”.

The fossil record of Calabria is richer than before and comes from different depositional settings, demonstrating important geographical and environmental changes, such as a wider extension of inner and coastal plains [6]. During Late Pleistocene, Calabria was easier to cross than before, and the Strait of Messina was not a strong barrier. As a matter of fact, precursors of the species of the San Teodoro FC have been recorded in Calabria, in assemblages attributable to the early Aurelian and to the late Aurelian [6]. Only few mammals that adapted to prairie or mountain environments were present in Calabria and not in Sicily [6]: Equus ferus, Stephanorhinus kirchbergensis, Capreolus capreolus, Capra ibex, Rupicapra rupicapra, and Meles meles. Homo neanderthalensis was sporadically present in Calabria, but its presence is not recorded in Sicily.

At Malta, dormice persisted and three new species, strongly endemic (Cervus sp., Microtus (Pitimys) melitensis, Crocidura sp.), have been recorded [27]. Unfortunately, these species are poorly studied. It is evident that the filter between Sicily and Malta was strong.

Paleoecology of the large mammal association of Sicily is indicative of Mediterranean “macchia” (Table 1). The arrival of Equus hydruntinus, and possibly of Bison priscus siciliae, is corroborated by vegetation reconstructions based upon pollen from coprolites of Crocuta crocuta spelaea recorded in the San Teodoro cave, indicating pre-Late Glacial conditions [59]. Vegetation was dominated by steppic taxa, but also arboreal taxa, and small percentages of mesophilus taxa were present [59]. During the Last Glacial cycle, more precisely, 32,000 ± 4,000 yr BP in Sicily, a wooded steppe biome, with elements representing a variety of local conditions, was present [59]. A paleobiome of southern Italy shows the predominance of wooded steppes during Upper Pleistocene [60]. The character of the steppe was Mediterranean, indicating relatively cool summers.

Avifauna was less diversified then earlier, with prevailing migrant species and some Passeriformes [2,61]. The disappearance of birds typical of humid environments is coherent with the wooded steppe biome.

The Castello faunal complex is represented by a mammal fauna low diversified, without endemites and with Homo sapiens. These features indicate easier communication between Italy and Sicily: all mammals recorded in Calabria, except for Martes sp., are present in the Castello FC (Figure 8) [6].

According to Barrier [10] and Di Geronimo [33] the Strait of Messina has always had an elevated hydrodynamics, while according to Bonfiglio et al. [2] and Lambeck et al. [62] a land bridge emerged 20,000 yr BP (Figure 8).

The Castello FC has an ecological assessment still unbalanced but closer to modern ones. Presence of mammals of wooded (Cervus elaphus, Sus scrofa) and open (Equus ferus, Equus hydruntinus, Bos primigenius, Lepus europaeus) environments (Table 1) can be related to the dry conditions of Late Glacial. Amphibians and reptiles are absent from the fossil record. Avifauna was diversified, with species typical of wooded and open environments and with a large number of migrant species.