Insular mammalian fauna dynamics and paleogeography:A lesson from the Western Mediterranean islands

Since the time of Darwin(1859)and Wallace(1869),islands have been regarded by scientists as a prime target for scrutinizing the forces that may influence evolution and diversification and important elements in biogeographic studies.This research aims to scrutinize whether and to what extent the composition and structure of past mammal insular faunas and their changes through time may provide sound clues for inferring the paleogeographical evolution of a region.As a case study,I critically analyzed the dynamics shown by the Plio-Pleistocene mammalian fauna of 3 Western Mediterranean insular districts,the Balearic Islands,Sardinia and Sicily,each characterized by its own peculiar paleobiogeographical evolutionary history.The revision of faunas and the critical analysis of the dispersal ability of the ancestors of island settlers have allowed hypothesizing on the time and mode of island colonization.The results obtained confirm that the early isolation of the Balearic Islands from the mainland led to the establishment of an endemic fauna since the pre-Messinian Miocene(?Astaracian European Land Mammal Age,MN7/8),and that Sardinia has definitely been isolated since the Pliocene,although dispersal events led to some faunal turnovers during the Pleistocene.In addition,the results suggest for Sicily a complex,still imperfectly disentangled history of alternate phases of complete separation and sporadic,more or less difficult connections with southern Italy.

A first comparison of bone histomorphometry in extant domestic horses(Equus caballus)and a Pleistocene Indian wild horse(Equus namadicus)

The microstructural features of the tissue of long bones subjected to different biomechanical stresses could be a helpful tool for a better understanding of locomotor behavior in extant and extinct mammals,including equids.However,few researches have attempted to describe the bone tissue of extinct horses.In our study,we analyze and compare the histomorphometric features of the bone tissue in extant modern horses,Equus caballus,and Equus namadicus,a Pleistocene Indian extinct wild horse.The number,position,and size of the osteons and Haversian canals of the bone tissue,classifiable as dense Haversian tissue,were considered for the comparison.The results obtained highlight some differences between the analyzed species,E.caballus having fewer and bigger osteons than E.namadicus.The microstructural differences may depend on the different lifestyles and environmental conditions characterizing the two species.The results obtained suggest that comparing the biomechanical properties of extinct and modern horse species may provide indirect information on their paleoenvironment.

The intriguing giant deer from the Bate cave (Crete): could paleohistological evidence question its taxonomy and nomenclature?

The research describes for the first time a possible case of pituitary gigantism in fossil mammals,precisely in deer.The pathology was detected in 2 long bones(tibia and metatarsus)belonging to an individual of an unusual large size found at the Bate cave(Rethymnon,Northern Crete).It formed the basis of Candiacervus major,the largest among the endemic deer species recorded in the Pleistocene-Early Holocene of Crete.Radiological and histomorphological examinations highlighted a reduction in cortical bone thickness and the presence of wide lacunae inside of the bone tissue.The pathological conditions suggest a pituitary gigantism diagnosis also supported by some morphological evidence,such as the extremely elongated distal part of the metatarsal diaphysis,the proportionally small proximal epiphysis,and some bone gracility.The diagnosis of a case of pituitary gigantism as presumed responsible for the extraordinary elongation of the tibia and the metatarsal bone is intriguing as they are,respectively,the paratype and the holotype of the C.major.The species represents a case of a deviation from the“island rule”in Pleistocene large mammals.The new evidence recommends a taxonomic and nomenclatural revision of this species.The main outcomes of this research are as follows:(i)a case of pituitary gigantism is described for the first time in an extinct mammal;(ii)it is underlined that paleohistology may provide interesting clues for disentangling taxonomic and nomenclatural issues;(iii)one of the very few cases of gigantism in insular mammals is being questioned.

Do methods for predicting paleohabitats apply for mountain and insular fossil bovids?

A variety of methods have been developed to use bovid postcranial elements in the functional morphology approach to paleohabitat prediction.This study represents a first attempt at testing morphometric methods based on astragalus and phalanges on extant mountain-dwelling bovids and insular fossil bovids from Sardinia assigned to the so-called‘Nesogoral group’,already regarded as close to the Caprini tribe.We intended to answer the questions whether a classic four-habitats model could be successfully applied to extant mountain-dwelling bovids,and whether results obtained could support the hypothesis of a radiative evolution for the Sardinian bovids.Results obtained,on the one hand,highlighted some inadequacies of the method if not applied to African bovids;on the other hand,they stressed the difficulties of discriminating habitat preferences of Sardinian taxa only based on biometry of astragalus and phalanges.Nonetheless,statistical habitat predictions suggest the contemporaneous presence in Sardinia of bovids having about the same size,but inhabiting different environments,giving support to the hypothesis that Sardinian representatives of the genus Nesogoral originated from a still unknown ancestor by an adaptive radiation evolutionary process.