2023-06-22 14:15:53
The first modern-looking primates, or euprimates, appeared at the beginning of the Eocene, 56 million years ago, in a period of sudden global warming called the “Paleocene-Eocene Thermal Maximum.” This climatic context of high temperatures on a global scale during which tropical forest environments developed even at high latitudes favored the spread of different groups of animals, including the first representatives of the order to which humans belong: primates.
The first euprimates already presented a series of characteristic features that differentiated them from other animals: nails instead of claws, stereoscopic vision, greater cranial capacity, and opposable hallux and thumbs. Different scenarios have been proposed to explain the main causes that led to the acquisition of these adaptations, which include changes in diet, locomotion, or a combination of both factors.
Despite the fact that in the fossil record the remains of postcranial elements (the part of the skeleton that does not include the skull) are scarce, their study has allowed a better understanding of the locomotor behavior of these animals. In particular, the analysis of the tarsus (the back of the foot that connects to the leg bones) is especially interesting. This area of the foot is relatively abundant in the fossil record and is also very informative in terms of locomotor behavior. However, until now most of the studies on this anatomical element were limited to describing and comparing the morphology of these bones, without addressing the analysis from a quantitative and macroevolutionary perspective.
Recently, an international team headed by Oriol Monclús Gonzalo, pre-doctoral researcher in the Paleoprimatology and Paleoanthropology research group of the Catalan Institute of Paleontology Miquel Crusafont (ICP) and doctoral student in the Geology program of the Autonomous University of Barcelona (UAB), has carried out a study focused on analyzing the evolution and diversification of locomotion in the first euprimates through the morphology of the navicular, one of the bones that are part of the tarsus.
Thanks to the use of geometric morphometry, a technique that allows quantifying the shape of anatomical elements and visualizing their morphological variation, it has been possible to demonstrate that there is a significant relationship between the shape of the navicular and the type of locomotion in primates, indicating, for therefore, the potential of the navicular as a predictor of locomotor behavior in future findings.
The study has also reconstructed the main locomotor modes of up to 13 species of extinct euprimates, where the two main groups that inhabited Eurasia, Africa and North America during the Eocene are represented: the adapiforms (related to current lemurs and lorisoids) and the omomyiforms ( related to tarsiers). The results indicate that these modern-looking early primates already exhibited a wide range of locomotor behaviour, although this was more limited than that of extant species.
Recreation of various species of primates from the Paleogene period representing different postures and locomotor behaviors. From left to right and from top to bottom: Dryomomys szalayi, Ignacius clarkforkensis, Cantius ralstoni, Notharctus robustior and Omomys carteri. (Illustration: Roc Olivé / © Institut Català de Paleontologia Miquel Crusafont. With the collaboration of the Spanish Foundation for Science and Technology – Ministry of Economy, Industry and Competitiveness.)
Finally, it has also been found that the rate of morphological evolution of the navicular increased just before the appearance of modern-looking primates, proving the importance of this bone (and the tarsal region in general) during the initial radiation of the navicular. euprimates.
This study corroborates that changes in locomotion played a key role during the early evolution of primates and deepens their knowledge. Future studies with advanced morphometric techniques (such as geometric morphometry) and through comparative phylogenetic methods will be essential to continue investigating relevant paleobiological aspects of the main groups of organisms, and thus help us to obtain a better understanding of how and what causes led to their evolution.
In addition to Monclús-Gonzalo, the research team includes David M. Alba (ICP), Judit Marigó (ICP and UAB), Anaïs Duhamel (University of Lyon in France) and Anne-Claire Fabre (Museum of Natural History of Bern in Swiss).
The study is titled “Early primates already had a diverse locomotor repertoire: Evidence from ankle bone morphology”. And it has been published in the academic journal Journal of Human Evolution. (Source: ICP)
#clues #locomotion #primates