The inner ear hides clues on human evolution 26 January 2021

relatives, belong to the hominid family. Hominids, in turn, are divided in two subfamilies: the pongines (the lineage) and the hominines (the lineage of the great African apes and humans). Unraveling kinship relationships between living and extinct species that make up the tree of human evolution is one of the great challenges in paleoanthropology. great apes play a key role in this puzzle and are crucial for reconstructing the ancestral moprhology from which the first bipedal homininis evolved.

A new study directed by the Institut Català de Paleontologia Miquel Crusafont (ICP) sheds futher light on the relations of kinship between two fossil Reconstruction of the life-appearance of great apes, the driopithecines Hispanopithecus Hispanopithecus laietanus housed at the Institut Català laietanus and Rudapithecus hungaricus. Both lived de Paleontologia Miquel Crusafont museum, at during the late Miocene, about 10 million years ago. Sabadell. Credit: Pere Figuerola / ICP Although they coexisted over time, their representatives probably did not inhabit the same areas: while Hispanopithecus lived in present-day Catalonia (remains have been found in the Vallès- A PNAS study led by the Institut Català de Penedès basin and the Pre-Pyrenees), Paleontologia Miquel Crusafont (ICP) analyzed the Rudapithecus inhabited present-day Hungary. kinship between two Miocene great apes Although there is a consensus among the scientific (Hispanopithecus and Rudapithecus) based on the community that two taxa are closely related morphology of their inner ear semicircular canals. hominid species, the debate about their This anatomical structure is informative in phylogenetic relationships with the living members reconstructing phylogenetic relationships between of the great ape/human clade are not settled. Some fossil species. The results are in authors include the driopithecines in the orangutan accordance with the distinction of these taxa at a lineage, while others consider them as ancestral generic level and reinforce their allocation in the hominines or as basal hominids preceding the . Furthermore, the similarities in divergence of both groups. semicircular canal morphology with extant and bonobos suggest that the latter possibly retained the ancestral condition, while appear to have derived the structure independently.

Living hominoids are a group of that includes the small-bodied apes (gibbons and siamangs) and the larger-body great apes (orangutans, , chimpanzees and bonobos), which, along with humans and their extant

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developed geometric morphometric approach performed on three-dimensional models of the semicircular canals obtained from high-resolution computed tomography of the fossil remains. This new technique consists of analyzing the deformation between continuous surfaces and thus quantifying the differences in shape between individuals and species. The results confirm that both Hispanopithecus and Rudapithecus are, indeed, hominids according to their robust canals (a unique character of great apes and humans). Furthermore, the differences found in the morphology of the two dryopithecine species support support their memberships in two different genera, which has been a matter of debate in the past.

The study goes one step further and, in a kind of time travel based on the analysis of living and fossil hominoid species, reconstructs how the semicircular canals of the last common ancestor of hominids would have looked. In this sense, the Three-dimensional model of Rudapithecus inner ear study concludes that the semicircular canals of (orange) embedded in the temporal bone (blue obtained extant chimpanzees and bonobos closely resemble from computed microtomography images. Credit: those of the ancestor, while the markedly different Alessandro Urciuoli / ICP morphology of orangutans would have evolved independently from the ancestral form.

Dryopithecines belong to a fossil hominid group The study, published in the Proceedings of the that inhabited Europe (and perhaps Asia) during National Academy of Sciences (PNAS) and led by the middle and late Miocene. Both Hispanopithecus Alessandro Urciuoli (ICP), addresses the and Rudapithecus were large sized (reaching 35 to relationship between these two species from an 40 kg in males), fed mostly on fruits, and exhibited innovative perspective: by comparing their inner ear many features shared with today's great apes, semicircular canal morphology. The evolutionary including an orthograde body plan (suitable for relationships between fossil and living species are locomotor behaviors performed with an erect trunk) complicated by the mosaic nature of hominid and adaptations in the forelimbs and in the hand for evolution and the presence of anatomical below-branch suspension. characteristics that evolved independently in response to selective pressures related with More information: Alessandro Urciuoli et al. function. However, previous studies conducted by Reassessment of the phylogenetic relationships of ICP researchers have shown that changes in the the late Miocene apes Hispanopithecus and morphology of the bony labyrinth in the inner ear Rudapithecus based on vestibular morphology, could be used a proxy for inferring the phylogenetic Proceedings of the National Academy of Sciences relationships of hominoids. Furthermore, this (2021). DOI: 10.1073/pnas.2015215118 structure (located in the cranium, inside temporal bone ) is fairly common in the fossil record due to its strong mineralization. Provided by Institut Català de Paleontologia The differences in the morphology of these Miquel Crusafont structures were inspected using a recently

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APA citation: The inner ear hides clues on human evolution (2021, January 26) retrieved 25 September 2021 from https://phys.org/news/2021-01-ear-clues-human-evolution.html

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