Macroevolutionary analysis of Primates with special reference to the genus Homo

The present thesis focusses on fossil Primates, their ecological characterization, morphological evolution and diversification, and an array of new tools to study their anatomical features. The text is divided in three different parts, presenting a collection of either published or submitted manuscripts. The first part regards the morphological adaptation and diversification of Primates. The inaugural paper (“Macroevolutionary trends of brain size in primates”, Melchionna et al., under review) deals with the identification and the analysis of macroevolutionary trends in brain size evolution in Primates. We applied Phylogenetic Ridge Regression (RRphylo) to found possible shifts in morphological rates and their temporal trend. Furthermore, we computed diversification rates (DR). We found a significant increase in encephalization quotient (EQ) rates in the hominins group with an overall increase in EQ values. We found a significant correlation between DR and both EQ rates EQ values. There is also a linear relationship between speciation and extinction rates. Eventually, we found an increase in speciation rates and a reduction in extinction rates with an increase in EQ values. The second paper (“Unexpectedly rapid evolution of mandibular shape in hominins”; Raia et al., 2018) is about the evolution of mandibular shape from ancient primates to the genus Homo. We used the Geometric Mophometrics and the Phylogenetic Ridge Regression to compute evolutionary rates in mandibular morphology. We found that mandible shape evolution in hominins is exceptionally rapid as compared to any other primate clade. In the second part of the thesis I introduce new advances in the field of the Virtual Anthropology. The first is a new protocol to obtain three-dimensional reconstruction of inner and outer surfaces of fossil specimens (“Reproducing the internal and external anatomy of fossil bones: Two new automatic digital tools”; Profico et al., 2018). By using the R software platform, we developed two automatic tools to reproduce the internal and external structures of bony elements. The first method, Computer‐Aided Laser Scanner Emulator (CA‐LSE), provides the reconstruction of the external portions of a 3D mesh by simulating the action of a laser scanner. The second method, Automatic Segmentation Tool for 3D objects (AST‐3D), performs the digital reconstruction of anatomical cavities. Both methods are embedded in the packages “Arothron” (Profico et al., 2018) and "Morpho" (Schlager, 2017). The second protocol presented in this section is about the reconstruction of the original shape of fossil bones damaged and deformed by taphonomical processes (“A new tool for digital alignment in Virtual Anthropology”; Profico et al., 2018). We developed a new, semi-automatic alignment R software, Digital Tool for Alignment (DTA). This tool uses the shape information contained in a reference sample to find the best alignment solution for the disarticulated regions. The third part of the thesis focusses on Homo, and in particularl on the relationship between Homo neanerthalesis and Homo sapiens. The first paper of this section is about the status of the Neanderthal niche fragmentation toward their demise (“Fragmentation of Neanderthals' pre-extinction distribution by climate change”; Melchionna et al., 2018). By using Species Distribution Models, and a habitat fragmentation analysis, we reconstructed the ecological niche of both human species. We found Homo sapiens had greater ecological plasticity over Neanderthals, which probably allowed this species to better react to climatic worsening at 44 and then at 40 ka. However, Neanderthals potential habitat appears to be very reduced and fragmented during the last phase of their occupation. The second paper of this last section regards the role of Homo sapiens in the Late Pleistocene megafauna extinction (“The well-behaved killer: Late Pleistocene humans in Eurasia were significantly associated with living megafauna only”; Carotenuto et al., 2018). Starting from a rich faunal and archaeological database, and by using SDMs, we obtained megafauna and humans occurrence probability maps over the last 40 ka in Eurasia. Then, we divided species in ecological groups (i.e., body size and feeding category combined). We evaluated their geographical overlap to human range and the species suitability in the core area of Homo sapiens. The results indicated that the extinct megafauna was rare within humans' range and Palaeolithic hunters had stronger association to extant rather than extinct herbivorous species.