L'evolució dels canals semicirculars en els primats antropoïdeusimplicacions filogenètiques per als catarrins del miocè

Resumen

Catarrhine primates originated in Africa by the Oligocene. Besides cercopithecoids and hominoids they include several lineages from the Miocene of Africa and Eurasia. Their phylogenetic relationships are controversial due to their incomplete fossil record, abundant homoplasy, and mosaic evolution. The identification of anatomical areas not very prone to homoplasy, such as the inner ear semicircular canals (SCs), is crucial for inferring the phylogeny of extinct catarrhines. The present dissertation explores the utility of SCs for phylogenetic inference among anthropoids, and particularly Miocene catarrhines. Specific aims include: (1) testing the suitability of different three-dimensional geometric morphometric (3DGM) approaches; (2) quantifying the phylogenetic signal embedded in SC morphology and identifying characters amenable to cladistic analysis; and (3) testing competing phylogenetic hypotheses for European Miocene catarrhines (pliopithecoids and hominids). The methods rely on microcomputed tomography scans and landmark-based standard 3DGM, as well as an innovative deformation-based (landmark-free) alternative approach. Shape data were analyzed by means of bivariate (allometric) regressions and multivariate analyses (between-group principal component analysis), coupled with phylogenetically-informed methods (phylomorphospace with ancestral node reconstruction, cladistic indices), metrics of phylogenetic signal (Pagel’s λ and Blomberg’s K), and cluster analysis. The results are provided in three published articles, which are subsequently discussed in relation to the literature and prospects for the future. The first article analyzes patterns of SC shape variation in extant catarrhines and tests its utility for making phylogenetic inferences in extinct hominoids. The remaining two articles test alternative phylogenetic hypotheses in the pliopithecoid Epipliopithecus and the dryopithecines Hispanopithecus and Rudapithecus. The following conclusions are reached: (1) Deformation-based 3DGM adequately captures SC shape variation and eliminates biases of standard 3DGM that depend on the subjective design of the landmarking protocol. (2) SC shape embeds strong phylogenetic signal and discriminates among major anthropoid clades and even extant hominoid genera, thus being potentially useful to test phylogenetic hypotheses for extinct taxa. (3) The reconstruction of ancestral morphotypes enables the definition of several characters of the SCs potentially synapomorphic for crown catarrhines, crown hominoids, and crown hominids. The latter are most distinctive due to their stout volumetric proportions. (4) The SC morphology of the pliopithecoid Epipliopithecus confirms the widely held view that this taxon is most parsimoniously interpreted as a stem catarrhine more derived than propliopithecoids, rather than a hominoid (as suggested by some recent studies). (5) The enigmatic ape Oreopithecus displays a mosaic of primitive and derived SC features suggestive of a stem hominoid status coupled with the independent acquisition of some hominid synapomorphies. (6) The SC morphology of the dryopithecines Hispanopithecus and Rudapithecus confirms they are distinct great ape genera, but does not conclusively favor a stem hominid vs. hominine status, because African apes are largely plesiomorphic as compared with the more derived orangutans. (7) This dissertation is the first study devoted to the SC morphology among anthropoids by means of deformation-based 3DGM. It confirms the potential of SCs for phylogenetic inference in Miocene catarrhines. These methods should be extended to the cochlea and middle ear ossicles to further contribute to cladistic analyses of extant and fossil catarrhines.