No abstract

An overview of the population histories of three insular realms (Gargano palaeo-archipelago, Sardinia-Maritime Tuscany palaeobioprovince and the Sicilian insular complex) during the Late Miocene and Quaternary are here presented. The complexity of biodiversity changes in the islands is analysed to propose an interpretation of origination and extinction patterns. The study highlighted several important aspects of insular faunas. Evolutionary radiations were found to contribute significantly only to the Gargano faunal diversity, likely because the area was an archipelago at the time.Another interesting result is that large and small mammals do not disperse and become extinct all at the same time on each island. In fact, because of their distinct body sizes, large and small mammals have different dispersal ability and therefore different chances to cross-filtering barriers. But distinct body sizes means also different influence on diversity, resistance to environmental changes and likelihood of extinction. Another important point is that large mammalian carnivores at the top of the trophic net are quite more fragile and susceptible to become extinct than other predators.The study finally shows the clear influence that the intense Middle and Late Pleistocene climate-driven environmental changes had on island communities. The reconstruction of the faunal histories of Sardinia and Sicily shows that without exchanges with the mainland the island system represents a rather stable refuge area not too affected by the changes in the ''physical'' parameters of the environment. In contrast, if the island is frequently connected with the continent, insular faunal assemblages tend to behave as their mainland counterparts. r

The submerged sill in the Strait of Messina, which is located today at a minimum depth of 81 m below sea level (bsl), represents the only land connection between Sicily and mainland Italy (and thus Europe) during the last lowstand when the sea level locally stood at about 126 m bsl. Today, the sea crossing to Sicily, although it is less than 4 km at the narrowest point, faces hazardous sea conditions, made famous by the myth of Scylla and Charybdis. Through a multidisciplinary research project, we document the timing and mode of emergence of this land connection during the last 40 kyr. The integrated analysis takes into consideration morphobathymetric and lithological data, and relative sea-level change (both isostatic and tectonic), resulting in the hypothesis that a continental land bridge lasted for at least 500 years between 21.5 and 20 cal ka BP. The emergence may have occurred over an even longer time span if one allows for seafloor erosion by marine currents that have lowered the seabed since the Last Glacial Maximum (LGM). Modelling of palaeotidal velocities shows that sea crossings when sea level was lower than present would have faced even stronger and more hazardous sea currents than today, supporting the hypothesis that earliest human entry into Sicily most probably took place on foot during the period when the sill emerged as dry land. This hypothesis is compared with an analysis of Pleistocene vertebrate faunas in Sicily and mainland Italy, including a new radiocarbon date on bone collagen of an Equus hydruntinus specimen from Grotta di San Teodoro (23–21 cal ka BP), the dispersal abilities of the various animal species involved, particularly their swimming abilities, and the Palaeolithic archaeological record, all of which support the hypothesis of a relatively late land-based colonization of Sicily by Homo sapiens

In Sicily few studies have been devoted to the climatic-environmental changes of the Pleistocene and Holocene period. Most of the studies on Quaternary vertebrates in Sicily have been focused on the evolutionary-taxonomic aspects of the fauna. Sicily experienced at least four vertebrate dispersal events during Quaternary time, which are of different provenence (African and/or European) and have been controlled by filtering barriers of different intensities. The marked endemism and the extremely low diversity of the fossil assemblages of early and early-mid-Pleistocene time do not allow detailed interpretations. By way at contrast, younger assemblages are more diverse and, although they display some endemic characters, are similar to those of southern peninsular Italy. The late mid-Pleistocene and early Late Pleistocene assemblages (Elephas mnaidriensis faunal complex) are characterized by the occurrence of a red deer (Cervus elaphus siciliae), a dwarf fallow deer-like endemic megalocerine (Megaceroides carburangelensis), auroch (Bos primigenius siciliae), bison (Bison priscus siciliae), elephant (Elephas mnaidriensis), hippopotamus (Hippopotamus pentlandi), boar (Sus scrofa), brown bear (Ursus cf. arctos) and three large social carnivores (Panthera leo, Crocuta crocuta and Canis lupus). Most of these taxa, except for the megalocerine, are characterized by slightly reduced body size compared with the same taxa from mainland Europe. These assemblages are indicative of a climate with temperate, Mediterranean affinity and of landscapes in which forested areas were associated with more open environments. The relatively low abundance of the red deer and the dominance of the megalocerine in several assemblages suggests that a Mediterranean-type forest locally dominated some of the climatic phases. The assemblages of the youngest Late Pleistocene period on Sicily are characterized by a dramatic drop in diversity, with the disappearance of elephant, hippopotamus, bison, the endemic megalocerine, and the largest predators. This would indicate an environmental crisis probably linked to the drier climatic oscillations of late Pleniglacial time, as is suggested also by the spread of the ground vole, which is the dominant small mammal in several assemblages. The Late Glacial period is characterized by the spread of equids (horse and wild ass), which are indicators of open landscapes and of xerophytic steppe-like cover. The beginning of the Holocene period is characterized by the expansion of forested areas and by a more humid climate, as suggested by the abundance of red deer, and by the dispersal of the common dormouse (Glis glis) and water vole (Arvicola sp.).

Vertebrate Pax genes encode a family of transcription factors that play important roles in embryonic patterning and morphogenesis. Two closely related Pax genes, Pax‐1 and Pax‐9, are associated with early axial and limb skeleton development. To investigate the role of these genes in cartilage formation we have examined the expression profiles of Pax‐1 and Pax‐9 in developing chick limb mesenchyme in vivo and in vitro. Both transcripts are detected by reverse transcription polymerase chain reaction and Northern blotting throughout chick limb development, from the early bud stages (Hamburger‐Hamilton 20–23) to fully patterned appendages (stage 30). Whole‐mount in situ hybridization reveals complex, nonoverlapping expression domains of these two genes. Pax‐1 transcripts first appear at the anterior proximal margin of the limb buds, while Pax‐9 is expressed more distally at what will be the junction of the autopod and the zeugopod. In situ hybridization to serial sections of the girdles reveals that in the pectoral region Pax‐1 is expressed proximally in condensed mesenchyme surrounding the junction of the developing scapula, humerus, and coracoid. In the pelvis, Pax‐1 is expressed between the femur and the developing acetabulum and along the ventral edge of the ischium; this transcript was also found in the distal hindlimb along the posterior edge of the fibula. Pax‐9 transcripts were not detected in the pectoral girdle at any stage, and only weakly in the pelvis along the ventral ischial margin. In the distal parts of both wings and legs, however, Pax‐9 is strongly expressed between the anterior embryonic cartilages (e.g., distal radius or tibia) and the anterior ectodermal ridge. The expression of both genes was strongest in undifferentiated cells of precartilage condensations or at the margins of differentiated cartilages, and was absent from cartilage itself. In micromass cultures of chondrifying limb bud mesenchyme expression of Pax‐1 and Pax‐9 is maintained for up to 3 days in vitro, most strongly at the end of the culture period during chondrogenic differentiation. As seen in vivo, transcripts are found in loose mesenchyme cells at the outer margins of developing cartilage nodules, and are absent from differentiated chondrocytes at the nodule center. Taken together, these investigations extend previous studies of Pax‐1 and Pax‐9 expression in embryonic limb development while validating limb bud mesenchyme culture as an accessible experimental system for the study of Pax gene function and regulation. Our in vivo and in vitro observations are discussed with reference to 1) the relationship between somitic and limb expression of these two Pax genes, 2) what regulates this expression in different regions of the embryo, and 3) the putative cellular functions of Pax‐1 and Pax‐9 in embryonic skeletogenesis. Dev Dyn 1999;214:101–115. © 1999 Wiley‐Liss, Inc.