Palaeopropithecus is a recently extinct genus of large sloth lemurs from Madagascar related to living lemur species found there today. Three species are known, Palaeopropithecus ingens, P. maximus, and P. kelyus. Radiocarbon dates indicate that they may have survived until around 1300–1620 CE. Malagasy legends of the tretretretre or tratratratra are thought to refer to P. ingens. Evidence suggests a solely arboreal lifestyle with frequent upside down suspension, hence the name sloth lemur.
Anatomy Palaeopropithecus primarily lived in the trees to stay away from predators as well as to gain valuable resources. To survive properly in the trees, Palaeopropithecus had long and powerful arms and legs, each with significantly long fingers and toes to allow them to hang upside down on branches. These were used to swing from branch to branch to travel across the jungle of Madagascar. These long arms made it much easier to grab hold of various trees and branches, making travel at the arboreal level easier. Laurie Godrey states in "The Extinct Sloth Lemurs of Madagascar", "Thus, these animals exhibit the odd behavioral combination of being both specialized leapers and adept climbers and hangers." The long arms of Palaeopropithecus had hook like extremities on their hands and feet. This benefited Palaeopropithecus by enabling them to hook their bodies onto the foliage to stabilize themselves as they traversed through the trees. Palaeopropithecus on average weighed between 100 pounds (45 kg)-120 pounds (54 kg). This weight is heavier than most modern lemurs and could potentially have caused the species to fall while hanging on branches, forcing the species to make sufficient use of their long arms and legs to survive. Palaeopropithecus eating habits were different from those of modern lemurs. The teeth of Palaeoprophithecus indicate that the animal was folivorous to eat leaves and tougher so they can eat hard foods such as nuts and seeds. This helped them fill out a generalized niche where they had multiple food resources to rely on. The anatomy of their bones were generally curved with a sixty-degree bend on major bones in the legs and arms. These bones were much denser than normal and with the addition of the curved structure of the bones it allowed Palaeopropithecus an easier capability to swing from branch to branch. This "curvature indicates that the sloth lemurs are one of the most suspensory clades of mammals ever to evolve. The curved bones also helped them gain more torque and speed, allowing them to reach branches at great distances. The relatively small body of Palaeopropithecus, while large compared to the modern lemur, had a great degree curve because it was smaller in stature. There is an inverse relationship between the bigger the animal and the smaller the bone degree curve. Biomechanical theory suggests that bone curvature in Palaeopropithecus hand bones is linked to the functional demands of the organism's environment. This is because curved phalanges, such as the phalanges of Palaeopropithecus, are commonly associated with the gripping function needed to survive in an arboreal habitat.
Diet
The Palaeopropithecus species were probably folivorous based on dental morphology, consuming a mixed diet of foliage and fruit to varying degrees. They supplemented their leaf-eating with substantial amounts of seed-predation, much like modern indrids. There is also no molar use wear evidence that Palaeopropithecus relied on terrestrial foods (C4 grasses, tubers, rhizomes). P. ingens faced weaning early on and lost their deciduous teeth early. After a little over a month they learned and were able to forage for solid food much earlier than other lemur species. More than likely P. ingens had to find food for themselves at an early age. The degree to how much of their diet consisted of seeds is somewhat uncertain but because of the pitting of the teeth it is clear they ate seeds. Palaeopropithecus ingens and P. maximus have similar use-wear scars. These were apparently mixed fruit and foliage consumers; neither species appears to have been a hard-object specialist. P. kelyus had smaller teeth than the other two species. Its dental characteristics could be described from the P. kelyus subfossil maxilla fragmentshowing a parastyle and a highly developed mesostyle. While other Palaeopropithecus must have fed on leaves and fruit, the differences in the teeth of Palaeopropithecus kelyus suggest that this animal could chew much more food like nuts and seeds compared with the other two known species. Evidence is accumulating that they may survive on low quality (that is highly fibrous) staple or fallback foods and a life-history "strategy" of low maternal input and slow returns in an unpredictable and periodically stressful environment. Palaeopropithecus was the most suspensory of all known strepsirhines, and so they would feed in suspensory postures. Locomotion on the ground would have been ungainly, and probably quite rare, except to creep across the ground from one feeding tree to the next when presented with gaps in the forest canopy. Their large, hook-like claws were not optimal for walking.
Behavior Palaeopropithecus likely had a very active behavior based on the morphology of the limbs. It engaged in hanging upside down from all four limbs in a sloth-like posture at a high frequency, as indicated by the morphology of the lumbar vertebrae and the high degree of phalangeal curvature. It is regarded as being among the most suspensory clades of mammals ever to evolve.
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