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Megaladapids of Madagascar Cody Raskin ASM 394 Certainly, the more interesting primates of study are those closest in form to the basil primate, the strepsirrhines of Southern Asia and Madagascar. And the oddest of these primates were the extinct primate group Megaladapidae. For reasons which are the subject of much debate, this group of Madagascar primates diverged from the common primate form, into animals that only barely resembled primates. Species include the ‘pig-like’ M. edwardsi, M. madagascariensis, and M. grandidieri. Megaladapis fossils are found in southern and central Madagascar, and living representatives would have ranged in size from 40 to 80 kg. These primates arrived comparatively late in the phylogenetic history, after the other large Lemuriformes (Hadropithecus, Archaeolemur, and Paleopropithecus). They were entirely unique among primates, and no primate before or since has possessed the range of peculiar traits unique to Megaladapids. It has been suggested that Megaladapids were closely related to the extant family Lepilemuridae, which today contains only one living genus (Lepilemurs, also called Sportive Lemurs). And indeed, many have placed Megaladapids into a subfamily (Megaladapinae) of the larger Lepilemuridae family (Vuillaume-Randriamanantena, 1992). Evidence of this relationship is found in the dental remains of fossil Megaladapids. Megaladapids shared with the Lepilemurs the long, narrow molars and large molar crests, and most strikingly of all, the lack of upper incisors (Megaladapids had a dental formula of 0133/2133). These dental features are indicative of a predominately folivorous diet. The lack of upper incisors is consistent with folivorous eating patterns, which include ‘cropping’. However, there is no direct evidence of a pre-maxillary pad for this function. Since it is unlikely the loss of the upper incisors occurred for any other reason, it may be assumed that Megaladapis did indeed have this feature, as each of its extant analogues do. Megaladapids also possessed a large mandibular condyle, which is not entirely unusual for a large folivorous animal, but is unique among strepsirrhines, and shared only by Lepilemurs (Fleagle, 1999). Due to their size, it was necessary for Megaladapids to possess certain functional characteristics that no other Madagascar primates have. One such feature is the fused mandibular symphasis. While this feature is present in all New World and Old World primates, including Apes and Humans, it is not so in the extant primates of Madagascar, which includes the Lemurs and Lepilemurs, nor in the Lorisids and Galagos of Southern Asia or the Tarsiers. This is clearly a derived trait among Megaladapids, which having been absent, would have certainly posed a difficulty for these large primates during mastication. Among the traits that are unique to Megaladapids is the position of the foramen magnum. In all primates, extant or otherwise, the foramen magnum is directly underneath the skull (with the exception of howler monkeys where it is near 45º), and in Megaladapids, it is directly behind the skull. This creates a very ‘un-primate-like’ Furthermore, skull position (below). Megaladapis orbits were not forward facing as in all other primates, but instead faced outward as in other, non-primate herbivores. The comparisons at right of M. edwardsi to a modern gorilla and lemur respectively illustrate these peculiar differences. What is also evident from these remains is that Megaladapis possessed very large teeth for its skull size, which is indicative of a leaf diet, and a very small brain case with enormous sagital and nuchal crests, atop a much elongated snout (the cranial length for M. edwardsi is 277-317 mm, 235-44 mm for M. madagascariensis, and 273-300 mm for M. grandidieri) (Jenkins, Preuschoft, Tattersall, 1995). The nasal region at the end of this long snout is grossly oversized, and this suggests that Megaladapis may have had large, prehensile lips – a feature which is not found in any other primate (Fleagle, 1999). The zygomatic arches as well, are enlarged in this skull. Unique characteristics of the post-cranial remains include the extraordinarily long hands and feet, coupled with short, stubby legs and arms of approximately equal length. Thus, it was likely to practice quadrupedalism when on the ground (humeri and femurs of the edwardsi species are more equal in length, suggesting it was the most quadrupedal of the 3 Megaladapinae species), but would have been more adept at climbing. However, it would not have practiced the same sort of vertical clinging and leaping as other strepsirrhines (Simmons). Many have come to label its peculiar post-cranial form as Koala-like. Indeed, this animal may very well have had the same positional and feeding behavior as that of the Australian Koala. Some of the bones in this image of M. Edwardsi below have been reconstructed, including the mandible, a complete fossil of which has not yet been found. One thing that is evident in this image of M. edwardsi, though, is that the phalanges on the hands and feet are extremely curved. While this animal may have been a quadruped on the ground, it would not have been very well suited for ground travel. And since it has been established that Megaladapis did not leap from tree to tree, trips between trees on the ground would have been especially perilous for this animal due to predation. Perhaps this is the reason for the outward-facing orbits, which would have given it earlier warning of a predatory attack. However, it has been suggested that Megaladapids evolved at a time when Madagascar was relatively devoid of predators, and perhaps the extreme elongation of its snout ‘pushed’ the orbits into an outward-facing position. Megaladapis seems to have become extinct at about the same time as another large pro-simian Paleopropithecus, at a time which coincides with human colonization of Madagascar. It is likely that a combination of environmental changes brought by the arriving humans (foreign, feral species, livestock overpopulation, and deforestation) along with the possibility of having been hunted by humans brought this animal to extinction. As professor Kaye Reed is keen to point out, often when humans arrive, large animals disappear. The presence of many of Megaladapis features alone, such as outwardfacing eyes, neglecting an evolutionary context, is intriguing, since this is a derived trait from the familiar primate condition of forward-facing eyes. The posterior foramen magnum, too, is derived, and these traits that represent a return to the ‘pre-primate’ condition, are reminiscent of types of changes experienced by Mesonichids. While there were other large pro-simians living in Madagascar, none possessed such strange characteristics. Megaladapids were entirely unique in the order of primates, and their particular features nearly exclude them from being labeled primates. Whatever the environmental conditions that drove their evolution into such a strange direction, they definitely illustrate the potential variability inherent in such a generalized order as primates. Sources Fleagle, John G. (1999). Primate Adaptation and Evolution. New York: Academic Press Simmons, Elwyn L. (unk.). Fossil Collection at the DUPC. Internet Resource Jenkins; Preuschoft; Tattersall (1995). Koala Lemurs. Johns Hopkins University Press