Archaeolemur is an extinct genus of subfossil lemurs known from the Holocene epoch of Madagascar. Archaeolemur is one of the most common and well-known of the extinct giant lemurs as hundreds of its bones have been discovered in fossil deposits across the island. It was larger than any extant lemur, with a body mass of approximately , and is commonly reconstructed as the most frugivorous and terrestrial of the fossil Malagasy primates. Colloquially known as a "monkey lemur," Archaeolemur has often been compared with anthropoids, specifically the cercopithecines, due to various morphological convergences. In fact, it was even misidentified as a monkey when remains were first discovered. Following human arrival to Madagascar just over 2000 years ago, many of the island’s megafauna went extinct, including the giant lemurs. Radiocarbon dating indicates that Archaeolemur survived on Madagascar until at least 1040-1290 AD, outliving most other subfossil lemurs.
Taxonomy
The genus Archaeolemur comprises two known species: A. edwardsi and A. majori, with the former being larger and more robust than the latter. The genus belongs to the family Archaeolemuridae, which, aside from Archaeolemur, also includes the extinct species Hadropithecus stenognathus. Archaeolemuridae has historically been considered the sister group of the extinct family of subfossil lemurs, Paleopropithecidae (also known as the "sloth lemurs"), and the extant family, Indriidae, mainly due to similarities in the teeth and skull. This relationship has been contested by morphological analyses that instead grouped Archaeolemuridae more closely with Lemuridae. One such analysis looked at ontogenetic data for Archaeolemur in order to extrapolate phylogenetic affinities and found the genus had more similarities with lemurids than with indriids in terms of growth and development. Despite such challenges, the sequencing of ancient DNA recovered from A. edwardsi, A. majori, and Hadropithecus stenognathus fossil specimens in a 2008 study lended important support to the phylogenetic placement of Archaeolemuridae as a sister group to living Indriidae, refuting Lemuridae as Archaeolemur’s closest relative. The authors of that genetic study placed Archaeolemuridae, Paleopropithecidae, and Indriidae into the superfamily Indrioidea within the infraorder Lemuriformes, although the exact phylogenetic relationships between the three were still unclear. A further genetic study in 2015 refined the phylogeny of Indrioidea, supporting a sister taxa relationship between Archaeolemuridae and the clade containing Paleopropithecidae and Indriidae.
Functional morphology
Archaeolemur has a lower dental formula of 1-1-3-3. Therefore, the tooth comb, a key feature of strepsirrhines, consists of four teeth rather than the characteristic six teeth of most taxa. This dental reduction is also observed in indriids and palaeopropithecids, suggesting this is a potential synapomorphy among these groups. Microwear analysis of the lower incisors shows no evidence that the tooth comb of Archaeolemur was used for grooming. Rather, the lower incisors are thought to have served a dietary function, such as the procurement and processing of food. The upper incisors are large and spatulate, the premolars form a cutting edge, with the anterior lower premolar adopting a caniniform shape, and the molars are bilophodont and low-crowned. This bilophodont molar morphology converges on that of cercopithecine molars. These features have frequently been attributed to a frugivorous diet.
The enamel of Archaeolemur teeth is very thick and highly decussated, which might have played a role in processing hard-objects. Archaeolemur also has a fused mandibular symphysis, an adaptation for resisting chewing stress. A biomechanical analysis of the jaw showed that Archaeolemur was well suited for breaking apart large food items and dental microwear analysis of A. edwardsi and A. majori molars shows pitting that indicates Archaeolemur processed harder foods, supporting a generalist diet. Furthermore, the most similar microwear pattern among modern primates is found in Cebus apella, a hard-object feeder. Stable isotope analysis of A. majori indicates Archaeolemur was a consumer of C3 plants and coprolites associated with Archaeolemur indicate an omnivorous diet that included fruit, seeds, and even small animals. Overall, the evidence suggests Archaeolemur had a generalist diet that mainly consisted of fruit, seeds, and hard-objects.