The cavity system of the inner ear of mammals is a complex three‐dimensional structure that houses the organs of equilibrium and hearing. Morphological variation of the inner ear across mammals reflects differences in locomotor behaviour and hearing performance, and the good preservation of this structure in many fossil specimens permits analogous inferences. However, it is less well known to what extent the morphology of the bony labyrinth conveys information about the evolutionary history of primate taxa. We studied this question in strepsirrhine primates with the aim to assess the potential and limitations of using the inner ear as a phylogenetic marker. Geometric morphometric analysis showed that the labyrinthine morphology of extant strepsirrhines contains a mixed locomotor, allometric and phylogenetic signal. Discriminant analysis at the family level confirmed that labyrinthine shape is a good taxonomic marker. Our results support the hypothesis that evolutionary change in labyrinthine morphology is adequately described with a random walk model, i.e. random phenotypic dispersal in morphospace. Under this hypothesis, average shapes calculated for each node of the phylogenetic tree give an estimate of inner ear shapes of the respective last common ancestors (LCAs), and this information can be used to infer character state polarity. The labyrinthine morphology of the fossil Adapinae is close to the inferred basal morphology of the strepsirrhines. The inner ear of Daubentonia, one of the most derived extant strepsirrhines, is autapomorphic in many respects, but also presents unique similarities with adapine labyrinths.

Recent fossil discoveries have demonstrated that Africa and Asia were epicentres for the origin and/or early diversification of the major living primate lineages, including both anthropoids (monkeys, apes and humans) and crown strepsirhine primates (lemurs, lorises and galagos). Competing hypotheses favouring either an African or Asian origin for anthropoids rank among the most hotly contested issues in paleoprimatology. The Afrocentric model for anthropoid origins rests heavily on the >45 Myr old fossil Algeripithecus minutus from Algeria, which is widely acknowledged to be one of the oldest known anthropoids. However, the phylogenetic position of Algeripithecus with respect to other primates has been tenuous because of the highly fragmentary fossils that have documented this primate until now. Recently recovered and more nearly complete fossils of Algeripithecus and contemporaneous relatives reveal that they are not anthropoids. New data support the idea that Algeripithecus and its sister genus Azibius are the earliest offshoots of an Afro–Arabian strepsirhine clade that embraces extant toothcombed primates and their fossil relatives. Azibius exhibits anatomical evidence for nocturnality. Algeripithecus has a long, thin and forwardly inclined lower canine alveolus, a feature that is entirely compatible with the long and procumbent lower canine included in the toothcomb of crown strepsirhines. These results strengthen an ancient African origin for crown strepsirhines and, in turn, strongly challenge the role of Africa as the ancestral homeland for anthropoids.

We present a survey of the morphological diversity of the bony labyrinth of the inner ear in Xenarthra, including the fossil ground sloth Megatherium. Using a combination of traditional and geometric morphometrics, correlation analyses, and qualitative observations, we attempt to extract independent and informative phylogenetic characters of the bony labyrinth for the superorder. Geometric morphometric analyses demonstrate a strong imprint of phylogenetic history on the shape of the bony labyrinth of xenarthrans and a weak influence of allometry. Discrete characters mapped on a consensus cladogram for xenarthrans show support for many traditional nodes within the superorder and may also provide critical information for problematic nodes within Cingulata. A relatively large lateral semicircular canal may, for instance, represent a synapomorphy for the molecular clade allying fairy armadillos (Chlamyphorinae) to the Tolypeutinae. Striking convergences were detected when comparing Megatherium, the giant ground sloth, with extant armadillos and Chlamyphorus, the pink fairy armadillo, with the extant three- and two-toed sloths. These findings have the potential to help understand the phylogenetic relationships of fossil xenarthrans. Presentamos un estudio de la diversidad morfológica del laberinto óseo del oído interno de los xenartros, incluyendo el perezoso fósil Megatherium. Utilizamos una combinación de morfométrica tradicional y geométrica, análisis de correlación y observaciones cuantitativas para intentar extraer caracteres filogenéticos independientes e informativos del laberinto óseo para el superorden. Los análisis geométricos morfométricos muestran una fuerte impronta de la historia filogenética de la forma del laberinto óseo de los xenartros y una baja influencia de la alometría. Los caracteres discretos mapeados en un cladograma de consenso para xenartros apoyan varios nodos tradicionales dentro del superorden y podrían también brindar información importante para los nodos problemáticos dentro de los Cingulata. Un canal semicircular lateral relativamente largo podría, por ejemplo, representar una sinapomorfía que apoye el clado molecular que une a los pichiciegos con los Tolypeutinae. Se hallaron notables convergencias al comparar Megatherium con los armadillos actuales, y Chlamyphorus con los perezosos actuales. Estos hallazgos tienen el potencial para ayudar a entender las relaciones filogenéticas de los xenartros fósiles.