Morphology and environment in some fossil Hominoids and Pedetids (Mammalia)

Abstract

Linking the environment to functional anatomy is not an easy exercise, especially when dealing with fossils, which are often fragmentary and represent animals that are extinct. A holistic approach permits us to fill the gaps in reconstructing the evolutionary patterns in fossil groups. Identifying the environment where animals lived can help to interpret some anatomical structures and, vice versa, the functional morphological pattern can help to refine some fossil environments. Two examples focusing on locomotor behaviours in fossil mammals are considered in this paper: the hominoids and the origins of hominid bipedalism and the springing adaptations in fossil rodents (Pedetidae) in connection with different habitats. In the first case, the limits of the chimpbased models and the necessity to take into account detailed environmental reconstructions will be addressed. The famous 'savannah hypothesis' is no longer tenable because the palaeontological data support a more vegetated environment for the origins of bipedal hominids. Data from the environment will be considered. The earliest putative hominid fossils which preserve skeletal remains of the locomotor apparatus show mixed adaptations to terrestrial bipedalism and arboreal activities. The second example focuses on the variation in springing adaptations in Pedetidae in the Lower Miocene of East Africa and Southern Africa. In the East, the sites where Pedetidae were preserved were mainly forested, whereas in the South the region was more open and drier, with extensive grassy patches. In the first case, pedetids were robust and heavy jumpers, whereas in the South they were smaller, their skeleton more gracile and their springing was lighter. During the desertification of the southern part of Africa, the large pedetid species became extinct, but a smaller species developed. In the case of primates, as in the case of rodents, the skeletal morphology was adapted to its environment.

Knee function through finite element analysis and the role of Miocene hominoids in our understanding of the origin of antipronograde behaviours: the Pierolapithecus catalaunicus patella as a case study

“…The most common example of suspensory primates are orangutans (Sugardjito ), however, other types of suspension are also included in this category: atelids ( Ateles ) tail‐assisted suspension with the participation of their prehensile tail (Youlatos ); and hylobatids brachiation ( Hylobates and Symphalangus ) that incorporates aerial phases during displacement (Fleagle ). Finally, humans are terrestrial bipeds (Senut ), locomoting along a continuous, horizontal or oblique support using only the hind limbs (Hunt ; Fleagle ).…”

Why do mammals hop? Understanding the ecology, biomechanics and evolution of bipedal hopping

“…As the name suggests, these rodents were more robust in body size as well as morphological features related to locomotion. Species in this genus exhibit five rather than four toes, shorter femoral shafts, tibias and calcaneums, and various skeletal features that suggest members of this genus were less agile than extant Pedetes (Senut, 2016). Megapedetes occupying warm, wooded Namibia during the middle Miocene were smaller and relatively more gracile compared with members of this genus living in forests of Kenya (Senut, 2016).…”

“…Extant Pedetidae includes two species, Pedetes capensis from Southern Africa and Pedetes surdaster, which appears in Eastern Africa. The earliest known Pedetidae representatives, known as genus Megapedetes, appeared around 20 million years ago (Senut, 2016). As the name suggests, these rodents were more robust in body size as well as morphological features related to locomotion.…”

“…Species in this genus exhibit five rather than four toes, shorter femoral shafts, tibias and calcaneums, and various skeletal features that suggest members of this genus were less agile than extant Pedetes (Senut, 2016). Megapedetes occupying warm, wooded Namibia during the middle Miocene were smaller and relatively more gracile compared with members of this genus living in forests of Kenya (Senut, 2016). In Australia, species of the hopping mice genus Notomys diverged in locomotor morphology from quadrupedal ancestors well before the recent appearance of true deserts; however, the prevalent misconception that bipedal hopping evolved in arid environments often leads to a confounding timeline (Ford, 2006).…”

“…Given the overwhelming paleoecological evidence, we conclude that mammalian bipedal hoppers likely first appeared in humid, structurally complex forests. At the very least, no evidence suggests bipedal hopping evolved in deserts (Burk and Springer, 2000;Ford, 2006;Meredith et al, 2009;Ortiz et al, 2012;Senut, 2016;Voorhies, 1975;Wu et al, 2014). Jaw, tooth and gut morphology evolved after bipedal hopping to meet the challenges of increasingly arid environments (Alhajeri et al, 2016;Burk et al, 1998;Hume, 1989;Wu et al, 2014).…”