In the East African Rift System, Plio-Pleistocene environmental instability triggered major environmental changes, which in turn influenced patterns of mammal diversification, dispersal, and turnover (Bobe and Eck, 2001; O’Regan et al., 2005, 2011b; Hernández-Fernández and Vrba, 2006; Martínez-Navarro, 2010; Patterson et al., 2014), including hominin evolution (Behrensmeyer, 2006; Bailey and King, 2011; Potts, 2013; Antón et al., 2014).

Introduction

Among the extant mammals, primates display a great diversity of postural and locomotor behaviours. In an evolutionary perspective, this variation relates to their adaptive ability to exploit a full range of arboreal and terrestrial substrates (Jouffroy et al., 1990; Hunt et al., 1996). Principal primate locomotor modes include arboreal and terrestrial quadrupedalism, vertical clinging and leaping, saltation, suspensory climbing, brachiation, knuckle and fist-walking quadrupedalism, and bipedalism (Gebo, 1996). These varied locomotor patterns result in specific types of limb use which rely on a number of anatomical and biomechanical musculoskeletal specialisations (Conroy, 1990; Fleagle, 1999).

Following the principle of uniformitarianism, the reconstruction of body postures and modes of locomotion in fossil taxa is primarily based on the comparative analysis of external bone shape, size and proportions with the respective skeletal elements of living forms. Despite its obvious – but inescapable – intrinsic limits (Preuschoft, 1975), correlations between bony morphology and positional/locomotor behaviours ‘are constantly being tested and refined by experimental studies that permit a clearer understanding of the biomechanical and physiological mechanisms of primate evolution’ (Fleagle, 1999: 298).

In the last few years, there has been a growing interest for potential functional analysis and interpretation of fossil trabecular bone patterns, a previously underexploited tool for various aspects of vertebrate paleobiology. As ‘living bones modify their structure at gross, tissue, and molecular levels in response to the force patterns acting on them … the preserved structure of fossil bones may contain direct information on the forces that may have been experienced during life’ (Thomason, 1995: 249).

One of the several aims of evolutionary biology is to recognize the evolutionary branching order of organisms by means of phylogenetic reconstruction methods. In the last 20 years, other fields of evolutionary biology have undergone a dramatic progress. This is especially true for the study of the developmental basis of evolution (Raff & Kaufman, 1983; Raff, 1996), which has stressed the significance of development for evolution and vice versa. However, this new synthesis between developmental and evolutionary biology, prompted by the publication of Gould's (1977) Ontogeny and Phylogeny, has not yet been applied to phylogenetic studies of hominoid evolution. In our opinion, this situation cannot be maintained any longer, because morphological evolution cannot be properly understood without considering the constraining effect of development upon evolution. This raises the question of whether or not current widely used methods of phylogenetic reconstruction (i.e. cladistics), based on the use of extensive datasets instead of a deep understanding of individual characters, are reliable. After reviewing the significance of developmental constraints in evolution, we will argue that the reasons underlying the appearance of characters are absolutely relevant for phylogenetic analysis, and will try to exemplify their significance through the example of Oreopithecus bambolii, an extinct orthograde great ape of the late Miocene (c. 8 Ma) of the Tusco-Sardinian paleobioprovince. It is our contention that cladistic methodology is seriously flawed in several aspects and can give quite erroneous insights of phylogenetic relationships when evolutionary constraints as well as morpho-functional considerations are not taken into account.

The late Neogene (the period between – 14 and – 2.4 Ma) is one of the most interesting phases in understand the present configuration of terrestrial ecosystems. It was during this time that the change took place from the middle Miocene dominant subtropical forests that stretched across southern Europe and western Asia to a more open but still wooded biotope that now prevails in warm–temperate areas. This change in vegetation, which strongly affected the composition of mammalian faunas, seems to be linked to the rapid spread of grasses around 8–10 Ma ago. Moreover, in the late Neogene, climatic shifts and falling temperatures due to the spread of the Antarctic Ice, were followed by the Plio-Pleistocene Arctic glaciations in the Northern Hemisphere. Furthermore, during the late Neogene, important changes at the regional level gave rise to the present configuration of the Old World land masses, and the successive drying of inland seas in the European area facilitated faunal interchange between Europe and Central Asia and Africa. At the same time, other tectonic processes like the Himalayan and the Tibetan uplifts and the opening up of the great eastern African basins and Red Sea, although working in opposite directions, favoured the processes of speciation and isolated evolution.

All these phenomena must have had a strong influence on hominid evolution between 14 and 2 million years ago (Ma). The diversity of hominid species recorded in that period must be considered in relation to the changing environmental conditions and to constrictions imposed by the existence of significant zoogeographical barriers.

Introduction

There is a small number of Miocene localities with land mammals in Italy (Fig. 10.1). Almost all the known Italian Miocene land mammal faunas display endemic characteristics, testifying to a complex paleogeographic history for the ‘central’ Mediterranean during the Late Miocene.

The record of land vertebrates of Early and Middle Miocene age on the Italian mainland is made by a few isolated findings in marine sediments.

A faunule of small mammals was collected in the 1970s near Oschiri (Northeastern Sardinia). The assemblage includes a soricid: Crocidosorex antiquus (Pomel, 1853); two talpids: Geotrypus oschiriensis Rümke 1974, and Nuragha schreuderae Rümke 1974; three glirids: Myomimus sp., Microdryomys aff. koenigswaldi de Bruijn 1966, and Glis major de Bruijn 1974; and three ctenodactylids: Sardomys dawsonae de Bruijn 1974, Sardomys antoniettae de Bruijn 1974 and Pireddamys rayi de Bruijn 1974. In addition some amphibians, reptiles and terrestrial gastropods were found (De Bruijn & Rümke, 1974; Esu & Kotsakis, 1985). The fauna is oligotypic, rather unbalanced and with gigantism in rodents, so bearing characters of insular endemisms. The fauna has European affinities but includes ctenodactylids, representing African immigrants (Jaeger, 1977; Wang, 1994). Although the dating of this fauna was difficult, the age is interpreted as Middle or Late Agenian (MN 1 or MN 2).

Isolated findings in marine sediments, mainly known from old literature, testify to the occurrence of land mammals from the continental areas surrounding the Early and Middle Miocene Tethys in the ‘Mediterranean’ area (Kotsakis et al., 1997). Among these findings, of particular interest is a third lower molar of a small-sized mastodon found near the village of Burgio (Agrigento, Sicily), in Lower Burdigalian coastal calcarenites (Checchia Rispoli, 1814).