Given the task definition and input, reply with output. In this task, you're given passages that contain mentions of names of people, places, or things. Some of these mentions refer to the same person, place, or thing. Your job is to write questions that evaluate one's understanding of such references. Good questions are expected to link pronouns (she, her, him, his, their, etc.) or other mentions to people, places, or things to which they may refer. Do not ask questions that can be answered correctly without understanding the paragraph or having multiple answers. Avoid questions that do not link phrases referring to the same entity. For each of your questions, the answer should be one or more phrases in the paragraph, and it should be unambiguous.

Passage: Mesopropithecus is a genus within the sloth lemur family (Palaeopropithecidae), which includes three other genera: Palaeopropithecus, Archaeoindris, and Babakotia. This family in turn belongs to the infraorder Lemuriformes, which includes all the Malagasy lemurs.Mesopropithecus was named in 1905 by Herbert F. Standing using four skulls found at Ampasambazimba. He noted that the animal had characteristics of both Palaeopropithecus and the living sifakas (Propithecus). In 1936, Charles Lamberton defined Neopropithecus globiceps (based on one skull from Tsirave) and N. platyfrons (based on two skulls from Anavoha). He thought that Neopropithecus was a separate, intermediate genus between Mesopropithecus and Propithecus. In 1971, paleoanthropologist Ian Tattersall merged N. platyfrons into N. globiceps and Neopropithecus into Mesopropithecus.Until 1986, Mesopropithecus was only known from cranial (skull) remains from central and southern Madagascar, and because these are similar to teeth and skulls of living indriids, particularly those of Verreaux's sifaka (Propithecus verreauxi), Mesopropithecus was often assigned to the family Indriidae. For example, in 1974, Tattersall and Schwartz labeled Mesopropithecus as a sister group to sifakas. With the discovery of an associated skeleton of M. dolichobrachion near Ankarana in 1986, it became clear that Mesopropithecus shared distinct traits with sloth lemurs. Unlike the indriids, but like the sloth lemurs, they had elongated forelimbs and other adaptations for arboreal suspension (hanging in trees), linking them most closely to family Paleaeopropithecidae. A comparison of these morphological traits between the sloth lemurs and indriids suggest that Mesopropithecus was the first genus to diverge within the sloth lemur family.
What was labeled as a sister group in 1974?